A. Stadelmann J. L. Grenfell D.kusmos.phsx.ku.edu/~dimitra/papers/griessmeier_2... · decrib es the mo dels and umerical n to ols e w use: The atmospheric hemistry c mo del is discussed

Astronomy & Astrophysi s manus ript no. griessmeier_2

©ESO 2014

August 7, 2014

Gala ti osmi rays on extrasolar Earth-like planets: II.

Atmospheri impli ations

J.�M. Grieÿmeier

1, 2, F. Tabataba-Vakili

3, A. Stadelmann

4, J. L. Grenfell

3, and D. Atri

5

1

LPC2E - Université d'Orléans / CNRS, Fran e. e-mail: jean-mathias.griessmeier� nrs-orleans.fr

2

Station de Radioastronomie de Nançay, Observatoire de Paris - CNRS/INSU, USR 704 - Univ. Orléans, OSUC, route

de Souesmes, 18330 Nançay, Fran e

3

Te hnis he Universität Berlin, Germany

4

Te hnis he Universität Brauns hweig, Germany

5

Blue Marble Spa e Institute of S ien e, Seattle, WA 98145-1561, USA

Version of August 7, 2014

ABSTRACT

Context. Theoreti al arguments indi ate that lose-in terrestial exoplanets may have weak magneti �elds, espe ially

in the ase of planets more massive than Earth (�super-Earths�). Planetary magneti �elds, however, onstitute one of

the shielding layers whi h prote t the planet against osmi ray parti les. In parti ular, as dis ussed in a ompanion

arti le (Grieÿmeier et al., 2014), a weak magneti �eld results in a high �ux of gala ti osmi rays to the top of the

planetary atmosphere.

Aims. We want to investigate the e�e ts that may result from a high �ux of gala ti osmi rays to an exoplanetary

atmosphere.

Methods. We al ulate how the atmospheri hemistry hanges under the in�uen e of gala ti osmi rays. We evaluate

the reation and destru tion of atmospheri biosignature mole ules. We derive planetary emission and transmission

spe tra to study the in�uen e of gala ti osmi rays on biosignature dete tability. We further al ulate the resulting

surfa e UV �ux, the surfa e parti le �ux, and the asso iated equivalent biologi al dose rates.

Results. We �nd that up to 20% of stratospheri ozone are destroyed by osmi ray protons. The e�e t on the planetary

spe tra, however, is negligible. The redu tion of the planetary ozone layer leads to an in rease the weighted surfa e UV

�ux by two orders of magnitude during a stellar UV �are. We also examine the surfa e parti le �ux: For a planet with

a terrestrial atmosphere, weak magneti shielding an in rease the biologi al radiation dose rate by a fa tor of two.

For a planet with a weaker atmosphere, the planetary magneti �eld has a mu h stronger in�uen e on the biologi al

radiation dose, hanging it by up to two orders of magnitude.

Con lusions. Under most onditions, the potential absen e of magnetospheri shielding against gala ti osmi rays has

a limited e�e t on the planet. For planets with thin atmospheres, however, magneti shielding be omes important and

ontrols the surfa e radiation dose.

Key words. osmi rays � exoplanets � Planets and satellites: magneti �elds � Planets and satellites: atmospheres �

Astrobiology � ozone

1. Introdu tion

The number of known extrasolar planets is steadily grow-

ing, as is the number of known Earth-like and �Super-Earth�

like planets (i.e. planets with a massM ≤ 10M⊕) around M

stars. Beyond the urrently known planets, many more (yet

undete ted) planets are expe ted to exist. Re ent estima-

tions based on the Kepler Input Catalog indi ate that the

o urren e rate of planets with a radius 0.5R⊕ ≤ R ≤ 4R⊕

orbiting an M dwarf in less than 50 days is 0.9+0.04

−0.03 plan-

ets per star, and the number of planets per star in reases

with de reasing planetary mass (Dressing and Charbon-

neau, 2013).

A �rst Earth-sized planet has been re ently dete ted

in the ir umstellar habitable zone of an M star (Quin-

tana et al., 2014). Again, the number of similar planets is

expe ted to be high: Based on the Kepler Input Catalog,

Dressing and Charbonneau (2013) estimate a mean num-

ber of Earth-sized planets in the habitable zone of M dwarfs

of 0.15+0.13−0.06 planets per ool star. Similarly, Bon�ls et al.

(2013) expe t 0.41+0.54

−0.13 planets per M star. The di�eren e

between both numbers is, among other fa tors, due to the

di�erent de�nition of a super-Earth, and the onversion of a

minimum radius to a minimum mass. The results of Dress-

ing and Charbonneau (2013) have been reanalyzed with

modi�ed HZ limits in Kopparapu (2013), who obtained a

frequen y of 0.48+0.12−0.24 and 0.53+0.08

−0.17 terrestrial exoplanets

per M-dwarf habitable zone for the onservative and opti-

misti limit of the HZ boundaries, respe tively. In any ase,

all studies agree qualitatively: Super-Earths in the liquid

water habitable zone of M stars are abundant!

Be ause of their relatively small mass, low luminosity,

long lifetime and large abundan e in the galaxy, M dwarfs

are sometimes suggested as prime targets in sear hes for

terrestrial habitable planets, (see e.g. Tarter et al., 2007;

S alo et al., 2007). For this reason, it is interesting to look

at super-Earths in the habitable zones of M stars. How-

Arti le number, page 1 of 15page.15

A&A proofs: manus ript no. griessmeier_2

ever, are should be taken not to onfound this �liquid wa-

ter habitable zone� (e.g. Kasting et al., 1993; Selsis et al.,

2007) with a zone where all planets will indeed be habit-

able. A number of onditions need to be ful�lled for �true�

habitability (see e.g. Lammer et al., 2009, 2010).

One of these additional onditions probably is the pres-

en e of a planetary magneti �eld. Until re ently, the mag-

neti �eld of extrasolar ro ky planets was not only un-

a essible to observations, but also to theoreti al studies.

This has hanges in the re ent years, with a number of

studies investigating whether and under whi h onditions

a super-Earth an host a signi� ant magneti �eld. While

these studies use very di�erent approa hes, they all ome

to a similar on lusion: Magneti �elds on super-Earths

around M stars are likely to be weak and short-lived in

the best ase, or even non-existant in the worst ase. The

relevan e of su h �elds and their potential dete tability is

dis ussed elsewhere (Grieÿmeier, 2014). Here, we'll look at

one habitablity-related onsequen e of a low planetary mag-

neti �eld, namely the enhan ed �ux of osmi ray parti les

to the planetary atmosphere, with potential impli ations

ranging from hanges in the atmospheri hemistry to an

in rease of the radiation dose on the planetary surfa e.

The e�e ts of gala ti osmi rays (GCRs) on the plan-

etary atmospheri hemistry were al ulated by Grenfell

et al. (2007). They �nd that for an unmagnetized planet,

GCRs an redu e the total ozone olumn by almost 20%,

whi h is not su� ent to strongly in�uen e the biomarker

signature. Thus, they on lude that biomarkers are robust

against GCRs. GCRs do not only alter the planetary atmo-

sphere, but they an also ause a �ux of se ondary parti les

whi h rea h the planetary surfa e. The resulting surfa e

radiation dose was evaluated by Atri et al. (2013). For an

Earth-like atmosphere, they �nd that the absen e of magne-

tospheri shielding an in rease the surfa e biologi al dose

rate by up to a fa tor of ∼ 3. They also indi ate that atmo-

spheri shielding dominates over magnetospheri shielding;

ompared to a thin atmosphere atmosphere (10 times less

dense than on Earth), an Earth-like atmosphere redu es the

dose rate by 2-3 orders of magnitude.

The exa t severity of these e�e ts, however, depends on

the intrinsi planetary magneti �eld strength: For planets

with a strong magneti �eld, most gala ti osmi ray par-

ti les are de�e ted, whereas for weakly magnetized planets,

the majority of the parti les an rea h the planetary atmo-

sphere. In previous work (Grieÿmeier et al., 2005, 2009),

the �ux of gala ti osmi rays to the atmosphere of extra-

solar planets has been evaluated on the basis of a simple

estimate for the planetary magneti moment. However, it

turns out that su h simpli�ed quantitative estimates are not

very reliable. More omplex approa hes, however, yield val-

ues whi h are not only model-dependent, but also depend

on the pre ise planetary parameters. For this reason, we

have re-evaluated the osmi ray �ux in a ompanion arti le

(Grieÿmeier et al., 2014, hereafter �paper I�), taking a more

general approa h. Instead of applying a model for the plane-

tary magneti moment, we showed how magneti prote tion

varies as a fun tion of the planetary magneti dipole mo-

ment, in the range 0.0M⊕ ≤ M ≤ 10.0M⊕ for the mag-

neti moment, and in the range of 16MeV ≤ E ≤ 524GeVfor the parti les energy.

The aim of the urrent study is to use this greatly ex-

panded parameter range and repeat the analysis of earlier

studies (Grenfell et al., 2007; Atri et al., 2013). In addi-

secondary muons

destruction of O3

UV fluxspectrum

strong flux of GCR

Creation of NOx

paper I

Section 4.2

Section 4.1

Section 4.4Section 4.1

Section 4.3

weak magnetic fieldpaper I

Fig. 1. E�e ts of gala ti osmi rays dis ussed in this work

and in the ompanion arti le (paper I).

tion to the new osmi ray �uxes from paper I, the main

di�eren es with respe t to the approa h of previous work

(Grenfell et al., 2007; Atri et al., 2013) are the following:

� The limate- hemistry atmospheri model has been up-

dated, as explained in Se tion 3.1.

� The al ulation of the atmospheri ionization due to

osmi rays has been updated, as summarized in Se tion

3.1 (see Tabataba-Vakili et al., 2014, for details).

� We have added the analysis of planetary transmission

and emission spe tra (Se tion 4.2).

� We have added the analysis of surfa e UV �ux, and

present results for UV-A, UV-B, UV-C, and biologi ally

weighted UV �ux on the planetary surfa e (Se tion 4.3).

This paper is organised as follows (see also Figure 1): In

Se tion 2, we present the planetary parameters used in our

al ulations. Se tion 3 de ribes the models and numeri al

tools we use: The atmospheri hemistry model is dis ussed

in Se tion 3.1 and the atmospheri muon model is presented

in Se tion 3.2. The gala ti osmi ray �uxes are omputed

in a ompanion arti le (Grieÿmeier et al., 2014, �paper I�).

We dis uss the impli ations of these osmi ray �uxes in

Se tion 4: The modi� ation of the atmospheri hemistry

(Se tion 4.1), the dete tability of biosignature mole ules

(Se tion 4.2), the UV �ux at the planetary surfa e (Se -

tion 4.3) and the surfa e radiation dose rate (Se tion 4.4).

Se tion 5 loses with some on luding remarks.

2. The planetary situation

In a ompanion arti le (paper I), we al ulated a large num-

ber of representative ases. This allows us to systemati ally

study the in�uen e of the planetary magneti �eld on the

�ux of GCRs to the planet. In this way, we explore the

range 0.0M⊕ ≤ M ≤ 10.0M⊕ for the magneti moment,

and the range of 16MeV ≤ E ≤ 524GeV for the parti les

energy.

The following parameters are kept �xed: the stellar mass

M⋆ (M⋆ = 0.45M⊙), the stellar radius R⋆ (R⋆ = 0.41R⊙),

and the orbital distan e d (d = 0.153 AU). In addition, we

keep onstant the planetary mass Mp

and the planetary ra-

dius Rp

. The only planetary or stellar parameter we vary in


J.�M. Grieÿmeier et al.: Gala ti osmi rays on extrasolar Earth-like planets: II. Atmospheri impli ations

the present study is the planetary magneti dipole moment

M. The minimum value of the magneti dipole moment

in this study is 0, whi h orresponds to an unmagnetized

planet. The maximum value of the magneti dipole mo-

ment we study is 10 times the present Earth value, whi h

orresponds to an extremly strongly magnetized planet.

3. Models used

In this part, we des ribe the models used throughout this

arti le. The stellar wind model, magneti �eld model, and

osmi ray propagation model are presented in paper I.

The parti le �uxes al ulated in paper I are used as in-

put into a oupled limate� hemistry atmospheri olumn

model. This model uses an air shower approa h to estimate

GCR-indu ed photo hemi al e�e ts and the resulting mod-

i� ation of atmospheri hemistry. This model is des ribed

in Se tion 3.1. The osmi ray �uxes of paper I are also used

as input for the al ulation of the muon surfa e �ux. We

des ribe the atmospheri muon model we use for this pur-

pose in Se tion 3.2. The results obtained with these models

are given in Se tion 4.

3.1. Climate-Chemistry Atmospheri Column Model

To study the rea tion of the atmosphere on the osmi

ray �ux, we use a Coupled Climate-Chemistry Atmospheri

Column Model as de ribed elsewhere (Rauer et al., 2011;

Grenfell et al., 2012, 2013, and referen es therein). Sin e

Grenfell et al. (2007) we in lude a new o�ine binning rou-

tine for the input stellar spe tra and a variable verti al at-

mospheri height in the model (see Rauer et al., 2011). The

ode has two main modules, namely, a radiative- onve tive

limate module and a hemistry module. The atmospheri

ionization by osmi rays is modeled a ording to Grenfell

et al. (2007) and Tabataba-Vakili et al. (2014).

The Climate Module is a global-average stationary, hy-

drostati atmospheri olumn model ranging from the sur-

fa e up to altitudes with a pressure of 6.6 · 10−5bar (for

the Earth this orresponds to a height of ∼70 km). Start-

ing values of omposition, pressure, and temperature are

based on modern Earth. The radiative- onve tive module

is based on the work of Toon et al. (1989) for the short-

wave region, and on the RRTM (Rapid Radiative Transfer

Module, Mlawer et al., 1997) for thermal radiation. This

uses 16 spe tral bands by applying the orrelated k-method

for major absorbers. Its validity range (see Mlawer et al.,

1997) for a given height orresponds to Earth's modern

mean temperature ±30K for pressures between 10−5and

1.05 bar and for a CO2 abundan e from modern up to 100

times modern. The shortwave radiation s heme features 38

spe tral intervals for the main absorbers in luding Rayleigh

s attering for N2, O2, and CO2 with ross-se tions based

on Vardavas and Carver (1984). The s heme uses a on-

stant, geometri al-mean, solar-zenith angle of 60

◦. Moist

adiabati onve tion is parameterised in the troposphere

based on the S hwarzs hild riterium. Tropospheri humid-

ity omes from Earth observations (Manabe and Wether-

ald, 1967). For the referen e ase of the Sun, we employed a

high resolution solar spe trum based on Gueymard (2004)

binned to the broadband intervals employed in the pho-

to hemistry and limate s hemes of the olumn model. For

the M dwarf s enarios, we assume a stellar spe trum similar

to that of AD Leonis (a M4.5 dwarf star). The spe trum is

derived from observations of the IUE satellite and photom-

etry in the visible (Pettersen and Hawley, 1989), using ob-

servations in the near IR (Leggett et al., 1996) and based on

a nextGen stellar model spe trum for wavelengths beyond

2.4 mi rons (Haus hildt et al., 1999). Clouds are not in-

luded dire tly, although they are onsidered in a straight-

forward manner by adjusting surfa e albedo to a hieve a

mean surfa e temperature of Earth (288 K). The module

ran to onvergen e, then the al ulated temperature, pres-

sure, and water abundan es were input into the hemistry

module.

The Chemistry Module has been detailed in Pavlov and

Kasting (2002). Our s heme has 55 spe ies for more than

200 rea tions with hemi al kineti data taken from the

Jet Propulsion Laboratory (JPL) Report (Sander et al.,

2003). We assume a planet with an Earth-like develop-

ment, i.e. N2�O2 dominated atmosphere et . The s heme

reprodu es modern Earth's atmospheri omposition with

a fo us on biosignature mole ules (e.g., O3, N2O) and ma-

jor greenhouse gases su h as CH4. The module al ulates

steady-state output of the standard 1D ontinuity equa-

tions using an impli it Euler s heme. Mixing o urs via

Eddy di�usion oe� ients (K). Constant surfa e biogeni

(CH3Cl, N2O) and sour e gas (CH4, CO) spe ies were em-

ployed based on the modern Earth (see Grenfell et al., 2011,

for more details). Also al ulated are modern-day tropo-

spheri lightning emissions of nitrogen monoxide (NO), vol-

ani sulphur emissions of SO2 and H2S, and a onstant

downward �ux of CO and O at the upper boundary, whi h

represents the photolysis produ ts of CO2. Dry and wet de-

position is in luded for long-lived spe ies via deposition ve-

lo ities (for dry deposition) and Henry's law onstants (for

wet deposition). The hemistry s heme is run until onver-

gen e. Then, its radiative gas abundan es are used as input

for the limate module. This whole pro ess i.e. the ex hange

of data between the hemistry and limate modules, is re-

peated until hemi al abundan es, the atmospheri temper-

ature and the pressure onverge.

Cosmi Ray S heme - We use an air shower approa h

based on Grenfell et al. (2007, 2012) and Tabataba-Vakili

et al. (2014). The top of atmosphere (TOA) time-average

proton �uxes from the magnetospheri osmi ray model

(paper I) are input into the hemistry module where NOx

is produ ed. In the present work our s heme was updated

to produ e 1.25 odd nitrogen atoms per ion pair produ ed

by osmi rays, a ording to Ja kman et al. (1980), based

on al ulations of disso iation bran hing ratios from rel-

ativisti parti le impa t ross se tions. We introdu ed a

parameterization whereby the GCR-indu ed N-produ tion

was split into two hannels, i.e 45% ground-state N and

55% ex ited-state N (see Ja kman et al., 2005, and refer-

en es therein). We also introdu ed an energy-dependen e

to the total N2 ionization ross se tion by ele tron impa t

(Tabataba-Vakili et al., 2014). Additionally, the input pa-

rameters for the Gaisser-Hillas formula were extended up

to 524 GeV to be onsistent with the osmi ray al ula-

tion. Finally the proton attenuation length data (80 g/ m

2)

was repla ed with a depth of �rst intera tion of 5 g/ m

2a -

ording to Alvarez-Muñiz et al. (2002), whi h led to a loser

mat h with observations. For more details of the above up-

dates and their e�e ts see Tabataba-Vakili et al. (2014).

The modi� ation of atmospheri hemistry by gala ti

osmi rays for our on�gurations are des ribed in Se tions

4.1, 4.2 and 4.3.



3.2. Atmospheri Muon Model

Cosmi ray propagation in the atmosphere is a halleng-

ing problem, beyond the s ope of analyti al tools be ause

one has to ompute a variety of hadroni and ele tromag-

neti intera tions o urring in the atmosphere. Therefore,

we use a robust Monte Carlo pa kage, CORSIKA v.6990

(He k et al., 1998, 2012), whi h is widely used to simu-

late air showers for major parti le dete tion experiments

around the globe. The ode makes use of a number of pa k-

ages to model high and low energy hadroni intera tion

pro esses and all ele tromagneti intera tions of harged

parti les. We take the input spe trum al ulated for di�er-

ent magneti �eld ases (the output of paper I) and model

parti le propagation with 20 million primary parti les for

ea h ase. Using su h a large ensemble of parti les is ne -

essary to redu e the numeri al error as mu h as possible.

Hadroni intera tions up to 80 GeV were modeled using

the GHEISHA model and above 80 GeV using the SIBYLL

2.1 high-energy hadroni intera tion model. None of the

thinning options were used so that no parti le information

is lost. The �nal output gives the momentum and types

of parti les hitting the ground from 20 million primaries.

Primaries are in ident at the top of the atmosphere from

random angles with energies falling randomly a ording to

the energy spe trum. The ele tromagneti intera tions en-

han e the atmospheri ionization rate and hange the at-

mospheri hemistry (Atri et al., 2010). For energies of the

primary parti les above 8 GeV, hadroni intera tions pro-

du e parti les (su h as muons and neutrons), some of whi h

rea h the ground and ontribute to the radiation dose (Atri

et al., 2011, 2013).

The muon �ux resulting for our on�gurations is based

on the al ulations of Atri et al. (2013) and is des ribed in

Se tion 4.4.

4. Impli ations

The intera tion of GCR parti les with a planet and its at-

mosphere an lead to a host of interesting e�e t, several

of whi h have been suggested to be potentially relevant for

habitability. The ex ellent review by Dartnell (2011) men-

tions e�e ts as varied as: The modi� ation of the atmo-

spheri hemistry (whi h we will dis uss below), the ex i-

tation and ionization of atomi and mole ular spe ies, the

reation of an ionosphere, ions driving atmospheri hem-

istry and potentially weather and limate dynami s, the

possible in�uen e on atmospheri lightning, the produ tion

of organi mole ules within the atmosphere, the destru -

tion of high-altitude ozone (whi h we will dis uss below),

the possible sterilization of the planetary surfa e (whi h we

will dis uss below), the degradation of biosignatures (whi h

we will dis uss below).

In the following work, we will fo us on the following

e�e ts: Based on the atmospheri model of Se tion 3.1, we

will look at the modi� ation of the atmospheri hemistry

(Se tion 4.1), verify the stability of biosignature mole ules

agains destru tion by osmi rays (Se tion 4.2), and analyse

the enhan ed UV �ux resulting from a weakened ozone layer

(Se tion 4.3). Finally, with the atmospheri muon model of

Se tion 3.2, we study the radiation dose at the planetary

surfa e (Se tion 4.4).

4.1. Modi� ation of atmospheri hemistry

After having traversed the planetary magnetosphere, the

gala ti osmi ray protons rea h the planetary atmosphere.

On the way through the atmosphere, they intera t with

neutral gas parti les, and reate se ondary ele trons via

impa t ionization:

p+ +X → p+ +X+ + e−. (1)

These free ele trons break N2 mole ules, whi h leads to

the formation of NOx:

N2 + e− → 2N + e− (2)

N+O2 → NO+O (3)

Depending on lo al onditions and the dominating

ozone produ tion me hanism, these NO mole ules an ei-

ther destroy ozone (if ozone was reated by a Chapman

me hanism), or may reate more ozone (if ozone is re-

ated by a smog me hanism). While both me hanisms are

in luded in our model, ozone produ tion by a Chapman

me hanism dominates in the ase of a planet around a hro-

mospheri ally a tive M dwarf, espe ially at altitudes above

20 km (Grenfell et al., 2013), so that in our ase NO de-

stroys stratospheri ozone by atalyti y les. We also know

that for planets around hromospheri ally a tive M stars,

this pro ess is dominant over most other pathways of ozone

destru tion, whi h are also in luded in our model (or ozone

loss via CO oxidation, see Grenfell et al., 2013). The ase

of osmi rays and atalyti HOx is investigated in more

detail elsewhere (Tabataba-Vakili et al., 2014). Thus, we

have (Crutzen, 1970):

NO +O3 → NO2 +O2 (4)

NO2 +O → NO+O2 (5)

net: O+O3 → 2O2 (6)

The O atom in Eq. 5 is reated e.g. by photolysis of O2 and

O3 by photons in the Herzberg region of ∼180nm.In this, equation (6) des ribes the net rea tion of the

atalyti y le: Ozone mole ules are disso iated and trans-

formed into mole ular oxygen. The NOx mole ule is regen-

erated, so that a single mole ule of NOx an ontribute to

the destru tion of a large number of ozone mole ules.

In order to quantify the e�ets des ribed by equations

(1) to (6) for extrasolar planets aroung M stars, we use the

oupled limate- hemistry model des ribed in Se tion 3.1.

In the following, we will present the results obtained with

this model, probing planets with magneti moments in the

range 0.0M⊕ ≤ M ≤ 10.0M⊕.

Figure 2 shows how the in�ux of gala ti osmi rays

into the planetary atmosphere hanges the atmospheri

ompositional pro�le. The left panel of the �gure shows

the hange on the NOx volume mixing ratio. In the ase

of a weak magneti �eld, the in reased in�ux of gala ti

osmi rays enhan ed the NOx by up to a fa tor 3.5. This

enhan ement peaks in the lower stratosphere, where the air

shower intera tion is strong (Tabataba-Vakili et al., 2014).

The right panel of Figure 2 shows that the in reased NOx

atalyti ally destroys up to 20% of stratospheri O3. In the

troposphere, however, O3 abundan es in rease by up to 6%

be ause NOx stimulate the smog me hanism.



Figure 3 shows the e�e t of GCRs on CH4 and H2O.

[Lee: Can you please he k the following para-

graph?℄ Both hemi al spe ies de rease in on entration

with de reasing magnetospheri prote tion (i.e. in reasing

GCR �ux). For H2O this de rease is explained through re-

a tion of H2O with ex ited-state oxygen atoms O(

1D):

H2O+O(1D) → 2OH (7)

O(

1D) an be released e.g. via the destru tion of O3. An-

other reason for the de rease in H2O on entration is the

photolysis in the mid to upper stratosphere via

H2O+ hν → OH+ H (8)

due to the de reased O3 shielding. The CH4 on entration

in Figure 3 de reases as a dire t onsequen e of the loss

of H2O. The hemi al equations (7) and (8) both produ e

OH, whi h is seen as the main sink of atmospheri CH4.

[Lee omment!!? (Lee, in your mail you said: �Note

- weaker CH4 e�e t in Grenfell than in this work.

Why?�). What does this mean?℄

Figure 4 shows how the in�ux of gala ti osmi rays

hanges the total atmospheri olumn density for NOx and

O3. One an see that under the in�uen e of gala ti osmi

rays, the NOx olumn varies by up to 15%, while the O3

olumn varies by up to 13%.

If one ompares the 0.15 M⊕ ase of the present study

to the equivalent run 3 of our previous work using an ear-

lier model version (Grenfell et al., 2007), one �nds that the

results are in good agreement, despite the widened proton

energy range and the numerous updates to the routines of

the limate- hemistry atmospheri model (see Se tion 3.1

for details). For example, run 3 of Grenfell et al. (2007)

found an enhan ement of NO produ tion by a fa tor of 3,

a 10% ozone de rease at 30 km altitude, and an ozone ol-

umn value de reasing by 16%, ompared to the ase with-

out GCR (run 2). In our urrent model (0.15 M⊕ ase),

we have an in rease of the NOx volume mixing ratio by a

fa tor of 2.5, 10% ozone de rease at 30 km altitude and an

ozone olumn value de reasing by 10% when ompared to

a ase without osmi rays.

Similarly, for their run 4 ( orresponding to the 0.0 M⊕

ase here), Grenfell et al. (2007) found an enhan ement of

NO produ tion by a fa tor of ∼ 4, a 12-13% ozone de rease

at 30 km altitude, and an ozone olumn value de reasing by

19% when ompared to their run 2. In our urrent model

(0.0 M⊕ ase), we have an in rease of the NOx volume

mixing ratio by a fa tor of 3.5, 12% ozone de rease at 30

km altitude, and an ozone olumn value de reasing by 13%.

Note that the absolute values of ozone olumns for the

ADL s enarios are lower in the present work than in earlier

modelling versions (e.g. Grenfell et al., 2007). This is due

to s aling the total energy input by ADL to one solar

onstant (1366W/m

2) instead of using a stellar spe trum

resulting in 288K. Other re ent model updates are de-

s ribed in Rauer et al. (2011). [Lee: �Note - in Grenfell

et al., the smog e�e t was mu h suppressed. Why?�℄

Similarly to Grenfell et al. (2007), we rea h the on-

lusion that atmospheri biosignature mole ules are not

strongly in�uen ed by gala ti osmi rays for Earth-like

planets in lose orbits around M-stars. The ase is di�er-

ent for solar energeti parti les, whi h an strongly modify

the abundan e of ozone in the planetary atmosphere (Se-

gura et al., 2010; Grenfell et al., 2012). Using the updated

model as above, this ase is re-evaluated in Tabataba-Vakili

et al. (2014).

4.2. Spe tral signature of biosignature mole ules

As a parti ularly useful method to study exoplanets, it has

been suggested to analyse their atmospheri omposition

via the spe tral lines either emitted or absorbed by the

planetary atmosphere. In the ase of Earth-like exoplanets

or super-Earths, it is parti ularly tempting to sear h for

mole ules whi h ould indi ate the pre en e of life on the

planet and whi h annot be explained by inorgani hem-

istry alone, so- alled �biosignature mole ules� (sometimes

also alled �biomarkers�). Several teles opes that have been

proposed (e.g. DARWIN, TPF, SEE-COAST, ECHO) or

are under onstru tion (e.g. JWST, E-ELT) ould possi-

bly dete t spe tral biosignatures on planets around nearby

stars, although this remains very hallenging.

Of ourse, are has to be taken when sele ting and

interpreting biosignature mole ules. Good biosignature

mole ules in lude oxygen (when produ ed in large amounts

by photosynthesis), ozone (mainly produ ed from oxygen)

and nitrous oxide (produ ed almost ex lusively from ba -

teria).

For the study of biosignature mole ules in planetary at-

mospheres, it is important to understand all inorgani ef-

fe ts whi h an modify the abundan es of these mole ules.

For example, Grenfell et al. (2007b) look at the response of

biosignature mole ules hemistry (e.g. ozone on entration

pro�les) on varying planetary and stellar parameters (or-

bital distan e and stellar type: F, G, and K). Rauer et al.

(2011) and Grenfell et al. (2013) study the e�e t of stellar

spe tral type (from M0 to M7, plus the ase of the a tive

M star AD Leonis, whi h is similar to the star used in the

present study) and of planetary mass in the Earth to super-

Earth range, whereas Grenfell et al. (2014) study the e�e t

of varying stellar UV radiation and surfa e biomass emis-

sions.

One has to be sure to rule out ases where inorgani

hemistry an mimi the presen e of life (�false positives�).

The possible signature of abioti ozone on Venus- and Mars-

like planets has been dis ussed by S hindler and Kasting

(2000, and referen es therein). While this is based on pho-

tolysis of e.g. CO2 and H2O and thus is limited in extent, a

sustainable produ tion of abioti ozone whi h ould build

up to a dete table level has been suggested by Domagal-

Goldman and Meadows (2010) for a planet within the hab-

itable zone of AD Leonis with a spe i� atmospheri om-

position. Indeed, other studies on�rm that abioti buildup

of ozone is possible; however, dete table levels are unlikely

if liquid water is abundant, as e.g. rainout would keep

atmospheri O2 and O3 low (Segura et al., 2007). False-

positive dete tion of biosignature mole ules andidates su h

as methane and ozone is dis ussed by Paris et al. (2011).

As inorgani pro esses annot be ruled out, sear hes for

biosignature mole ules should go beyond the sole sear h

for the signature of ozone. It has been suggested that the

simultaneous presen e of O2 and CH4 an be used as an in-

di ation for life (Sagan et al., 1993, and referen es therein).

Similarly, Selsis et al. (2002) suggest a so- alled �triple sig-

nature�, where the ombined dete tion of O3, CO2 and

H2O would indi ate biologi al a tivity. Domagal-Goldman



Fig. 2. Altitude-dependent hange of the volume mixing ratio of NOx and O3 for exoplanets with a magneti moment of M =

0.0, 0.05, 0.1, 0.15, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 6.0 and 10.0M⊕, relative to a ase without osmi rays.

Fig. 3. Altitude-dependent hange of the volume mixing ratio of CH4 and H2O for exoplanets with a magneti moment of

M = 0.0, 0.05, 0.1, 0.15, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 6.0 and 10.0M⊕, relative to a ase without osmi rays.

and Meadows (2010) suggest to simultaneously sear h for

the signature of C2H6. The dete tability of biosignature

mole ules is dis ussed, e.g. by Paris et al. (2011) and Hedelt

et al. (2013). In parti ular, the simulation of emission spe -

tra for urrently planned or proposed exoplanet hara ter-

ization missions has shown that the amount of information

the retrieval pro ess an provide on the atmospheri om-

position may not be su� ient (Paris et al., 2013).

Similar to �false positives�, whi h an lead to erroneous

interpretation of observational data, one also has to deal

with the problem of �false negatives� for life-bearing plan-

ets. The absen e of ozone does not ne essarily mean that

life is absent. Oxygen or ozone may be qui kly onsumed by

hemi al rea tions, preventing it from rea hing dete table

levels (S hindler and Kasting, 2000; Selsis et al., 2002).

Also, non-dete tion an result from masking by a wide CO2

absorption (Selsis et al., 2002; Paris et al., 2011). Here, we

look into an inorgani pro ess (namely gala ti osmi rays)

whi h an destroy the signature of biosignature mole ules.

Similarly to potential false-positives, these e�e ts have to

be taken into a ount in order to orre tly interpret obser-

vational data.

As has been shown in Se tion 4.1 (Figure 4), the ozone

olumn an be modi�ed by up to 13% by the a tion of

gala ti osmi rays in the ase of weak magneti �elds. We

�nd similar values for other biosignature mole ules. In the

following, we will explore the question: Could this in�uen e

the observed spe trum of a planet, either in emission or in

transmission?



Fig. 4. Column density of NOx (left panel)and O3 (right panel) as a fun tion of exoplanetary magneti moment.

Figure 5 explores the in�uen e of gala ti osmi rays

on the mole ular signature in the planetary spe trum for

wavelengths between 2 ≤ λ ≤ 20µm. Figure 5a shows the

planetary emission spe trum, whereas Figure 5b shows the

relative transmission oe� ient. In both �gures, the bla k

line orresponds to the referen e spe trum, i.e. the ase of

a planet around an M dwarf with no gala ti osmi rays

(zero osmi ray ase), whereas the red line orresponds to

the M dwarf s enario with GCR andM = 0.0M⊕ (i.e. max-

imum gala ti osmi ray ase). Note that the bla k line is

mostly overlain by the red line. Both �gures indi ate that

spe tral observations would show be no dete table di�er-

en e between the ases with and without gala ti osmi

rays. The same is true for observations at higher spe tral

resolution (R=10000, not shown).

We thus rea h the on lusion that the in�uen e of GCRs

on atmospheri biosignature mole ules for Earth-like plan-

ets in lose orbits around M-stars is too weak to be de-

te table in the planetary spe tra. The ase is di�erent for

solar energeti parti les, whi h is dis ussed in Tabataba-

Vakili et al. (2014).

4.3. Surfa e UV �ux

Besides hanges in the planetary spe trum, one of the most

obvious impli ations of the loss of stratospheri ozone is

the hange in the surfa e UV radiation, espe ially in the

UV-B range. The atmosphere-penetrating UV radiation is

frequently divided into three di�erent ranges: UV-A (3150

to 4000Å a ording to the standard de�nition), whi h has

the smallest biologi al signi� an e, UV-B (2800 to 3150Å

a ording to the standard de�nition), whi h is biologi ally

damaging and rea hes the ground in signi� ant quantity

and UV-C (1754 to 2800Å in this study), of whi h very

little rea hes the ground for an Earth-like atmosphere. The

biologi al radiation damage reated by UV-A radiation is

5 orders of magnitude weaker than the damage aused by

UV-C radiation (Horne k, 1995; Co kell, 1999; Cuntz et al.,

2010). Even so, UV-A does still show signi� ant mutageni

and ar inogeni e�e ts (S alo et al., 2007). Be ause of very

e� ient atmospheri shielding, the surfa e �ux of UV-C

is usually many orders of magnitude smaller than that of

UV-A or UV-B, even during stellar �ares (Segura et al.,

2010). For this reason, most work (e.g. Grenfell et al., 2012)

on entrate mostly on UV-B radiation (280-315 nm). Will

will pro eed di�erently. Similarly to Segura et al. (2010),

we will study the full UV spe trum from 1754 − 3150 Å,

and present integrated results for the three bands UV-A,

UV-B and UV-C.

One should note that the ways in whi h UV radiation

an be harmful for living ells are omplex and varied (e.g.

S alo et al., 2007). In addition, some spe ies have found

ways to prote t themselves against harmful radiation, either

through repair me hanisms (S alo et al., 2007), prote tive

layers, or through strategies allowing to avoid strong radi-

ation altogether (e.g. Se tion 7 of Heath et al., 1999; S alo

et al., 2007). The in�uen e of a highly �u tuating environ-

ment on life is dis ussed by S alo et al. (2007).

The spe trum of an M star deviates greatly from a

bla kbody emission. Also, one should note that the UV �ux

of di�erent M stars an di�er onsiderably, and is highly

variable in time (Fran e et al., 2013). When analyzing the

�ux of the UV radiation of an M star to the planetary sur-

fa e, we have to distinguish a number of di�erent ases: The

quies ent stellar UV �ux of an non-a tive star, the quies-

ent UV �ux of an hromospheri ally a tive star (su h as

AD Leo or GJ 643C), and the UV �ux during a stellar UV

�are. For the latter ase, we di�erentiate between �long�

and �short� �ares, depending on the �are duration relative

to the atmospheri response times ale. The relevant ases

are:

E) For omparison, we will ompare to the ase of Earth

in the habitable zone of the Sun (i.e. at a distan e of 1

AU).

Q) The quies ent emission of (model) non-a tive stars is

hara terized by UV �uxes many orders of magnitude

smaller than for the Sun over the whole UV range (Se-

gura et al., 2005). Re ent studies indi ate that this

ase may be less representative than previously thought

(Fran e et al., 2013). No noti able e�e t is expe ted in

that ase, and it is not further dis ussed in this work.

CA) Chromospheri ally a tive stars have additional �ux in

the range 100-300 nm, generated by hromospheri and

oronal a tivity. At a �xed distan e, their absolute UV



(a) Planetary emission ontrast spe trum. (b) Relative transmission spe trum.

Fig. 5. Emission ontrast spe trum and relative transmission spe trum with and without GCR for an M-star world orbiting AD

Leonis with strong planetary magnetospheri prote tion (bla k) and no planetary magnetospheri prote tion (red), as would be

observed with a spe tral resolution of R=1000.

�ux still is inferior to that of the Sun (e.g. Bu ino

et al., 2007, Fig. 1). Their normalized UV �ux (i.e. at

a distan e allowing a surfa e temperature or total �ux

similar to that on present Earth) however may ex eed

the solar value (e.g. by a fa tor up to 10 in UV-C, Se-

gura et al., 2005). Re ent studies indi ate that AD Leo

may be more representative for this ase than previ-

ously thought (Fran e et al., 2013). For a planet in the

habitable zone of a hromospheri ally a tive M star, we

use the top of atmosphere (TOA) UV spe trum of AD

Leonis, as des ribed in Se tion 3.1.

LF) During a stellar �are, the UV �ux in reases by typi ally

one order of magnitude (Fran e et al., 2013), and two or-

ders of magnitude or more in some extreme ases (S alo

et al., 2007; Segura et al., 2010, whi h looked at the 1985

�are of AD Leo), with a times ale of 10

2-10

3se onds.

For a planet in the habitable zone of a �aring M star,

we use a the TOA UV spe trum of Segura et al. (2010,

Fig.3, bold blue line, s aled for distan e). The TOA �ux

thus is approximately solar for UV-A, 2.5 times solar for

UV-B, and∼ 10 times solar for UV-C (see Table 1). This

stellar UV �are an either be long (or quasi- ontinuous),

or short. In the ase of a long �are, the �are times ale

is longer than the typi al rea tion time of the planetary

atmosphere and the atmosphere adjusts to the modi�ed

onditions. In this ase, we dire tly al ulate the surfa e

UV �ux from the TOA �ux, using the model of Se tion

3.1. This ase also applies when the planet is subje t to

a quasi- ontinuous su ession of UV �ares, whi h might

well be the ase for planets around a tive M stars (Kho-

da henko et al., 2007; Grenfell et al., 2012).

SF) If, on the other hand, the times ale of the UV �are

(e.g. its duration) is short ompared to the atmospheri

rea tion time, the atmosphere has not yet adjusted to

the in reased UV �ux. In this short �are ase, we use

the atmospheri tranfer fun tion R(λ) (see below) ob-

tained in the ase CA, and multiply it with the TOA UV

�ux of the ase LF (Segura et al., 2010, Fig.3, bold blue

line s aled for distan e) to obtain the surfa e UV �ux.

In our al ulations, most atmospheri ozone is lo ated

below 50 km, where rea tion times ales are long (e.g.

Allen et al., 1984), so that this s enario is appropriate

for an isolated �are.

SCR) Stellar UV �ares are expe ted to be frequently a om-

panied by stellar osmi ray (SCR) parti les, whi h are

not in luded in the above ases LF and SF. The in-

�uen e of su h SCRs (as opposed to the GCRs dis-

ussed in the work) will be brie�y dis ussed below, but

a more detailed analysis of this ase is presented sepa-

rately (Tabataba-Vakili et al., 2014).

In addition to the UV �ux emitted by the planetary host

star, another sour e an ontribute to atmospheri and sur-

fa e UV. Smith et al. (2004) have suggested that stellar

X-rays may be repro essed in the atmosphere, generating

an additional ontribution of UV photons. They found that

up to 10% of the X-ray energy may be redistributed into

the UV range by aurora-like emission in the absen e of

UV-blo king agents (Rayleigh s attering only). In the ase

of the Earth, UV redistribution may tranfer a fra tion of

2 · 10−3of the in ident energy to the planetary surfa e in

the 200-320 nm range. Segura et al. (2010) estimated the

X-ray energy for a strong �are on the M star AD Leo �are

to be 9 W/m

2, so the energy redistributed as UV radiation

at the planetary surfa e should be < 0.018 W/m

2. This is

negligible ompared to the UV �ux of the �are itself ( f.

Table 1).

For the above ases E), CA) and LF), we are inter-

ested in the transmission of UV radiation through the at-

mosphere. For ea h ase, we will investigate the full range

of M = 0 (i.e. no magnetospheri shielding, where the at-

mospheri ozone is most strongly depleted by gala ti os-

mi rays) to 10M⊕ (i.e. strong magnetospheri shielding),

plus the ase without GCR (whi h, for our purposes, orre-

sponds to a planet with an in�nite magneti moment, and

thus a planet with maximum ozone shield).

We pro eed as follows:

� We take the wavelength-resolved stellar UV �ux and,

with the planetary orbital distan e, al ulate the �ux

in ident at the top of atmosphere (TOA) of the M

star planet. From this we al ulate the wavelength-

integrated TOA UV �uxes, IUV-ATOA

, IUV-BTOA

and IUV-CTOA

( olumns 3, 6 and 9 of Table 1).

� With this UV �ux, the numeri al model des ribed in

Se tion 3.1, and using the magneti -�eld dependent

TOA �uxes of GCR parti les from paper I, we al ulate



the wavelength-resolved �ux of UV at the planetary sur-

fa e. From this we al ulate the wavelength-integrated

surfa e UV �uxes, IUV-Asurfa e

, IUV-Bsurfa e

, and IUV-Csurfa e

( olumns

4, 7 and 10 of Table 1). The e�e ts that are onsidered

here are absorption by O3 and Rayleigh s attering by

atmospheri mole ules.

� We al ulate the ratio of UV penetrating through the

planetary atmosphere, averaged over the orresponding

UV band, e.g. RUV-A = IUV-Asurfa e

/IUV-ATOA

, and similarly

for RUV-B

and RUV-C

( olumns 5, 8 and 11 of Table

1). R thus hara terized the average UV shielding by

the atmosphere in a parti ular wavelength band. Note

that the value of R depends on both the TOA GCR

�ux and the TOA UV �ux (the atmosphere behaves as

a non-linear system).

� We multiply the wavelength-resolved UV surfa e spe -

tra with the DNA a tion spe trum of Cuntz et al. (2010,

Figure 1), whi h is based on previously published data

(Horne k, 1995; Co kell, 1999), to al ulate the e�e tive

biologi al UV �ux W at the planetary surfa e ( olumn

12 of Table 1, and Figures 6 and 7). In this, the DNA

a tion spe trum is normalized to 1 at a wavelength of

300 nm.

Our main results are des ribed in the following (see also

Table 1).

Case E (Earth) : In the ase of the Earth, GCR leave

both the UV transmission oe� ients and the UV surfa e

�uxes virtually un hanged. As a onsequen e, the biologi-

ally weighted UV surfa e �ux W is barely a�e ted by the

presen e of GCRs. The surfa e UV-B results (transmission

oe� ient and surfa e �ux) show a good a ordan e with

Grenfell et al. (2012, Table 2, line 1), where RUV-B = 0.13for the GCR ase, and with Grenfell et al. (2013), where

RUV-B = 0.16 for the ase without GCR. These values alsoagree reasonably with Earth observations (Grenfell et al.,

2012, Table 2, line 4). For the biologi ally weighted �ux, we

�nd W = 0.126 W/m

2. Co kell (1999) obtain a lower value

for W , whi h is likely due to their stronger ozone layer.

Case CA ( hromospheri ally a tive star) : In the ase of a

planet in the habitable zone of a hromospheri ally a tive

M star, the transmission ratio for UV-A is RUV-A = 74%,

independent of magneti shielding, and similar to the ase

of the Earth. As shown in Table 1, the osmi -ray indu ed

weakening of the ozone layer des ribed in Se tion 4.1 has

little in�uen e on the atmospheri UV-B transmission ratio

RUV-B

, whi h in reases from 10% to 11% with de reasing

magneti shielding (i.e. in reasing GCR e�e t). Between

perfe t and zero magneti shielding, the UV-B surfa e �ux

in reases by 14 % (for a de rease of the ozone olumn by

13%). This is onsistent with the near-linear relationship

between atmospheri ozone olumn and surfa e UV-B �ux

observed on Earth (e.g. Kerr and M Elroy, 1993). Due to

the low intensity of UV in the spe trum of the M star, the

resulting UV-B surfa e �ux is very small (two order of mag-

nitude less than on present-day Earth). Table 1 also shows

the hange of the surfa e �ux of UV-C. With a variation of

a fa tor of 200, the surfa e �ux of UV-C radiation is indeed

strongly dependent on magnetospheri shielding. However,

even in the most extreme ase (M = 0.0M⊕), the surfa e

�ux does not ex eed 1.0 · 10−17Wm

−2, whi h is negligi-

CA (chromospherically active)

M [M⊕]

wei

gh

ted

UV

surf

ace

flux

[W/m

2 ]

109876543210

0.003

0.002

0.001

0

Fig. 6. Weighted surfa e UV �ux as a fun tion of magneto-

spheri shielding for a hromospheri ally a tive star ( ase CA).

SF (short flare)LF (long flare)E (Earth)

M [M⊕]

wei

gh

ted

UV

surf

ace

flux

[W/m

2 ]

109876543210

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Fig. 7. Weighted surfa e UV �ux as a fun tion of magneto-

spheri shielding. Dashed line: Long �are ( ase LF). Dash-dotted

line: Short �are ( ase SF). Cir le: Earth ( ase E).

bly small, even when the high biologi al response fa tor to

UV-C is taken into a ount. Figure 6 shows how the biolog-

i ally weigthed UV surfa e �ux W hanges as a fun tion of

magneti shielding; between minimum and maximum mag-

neti shielding, W hanges by ∼ 40%, whi h is in between

the variation of UV-B (14 %) and UV-C (a fa tor 200),

but loser to the value of UV-B (a detailed analysis shows

that for our parameters the UV-B �ux at 300 nm has the

strongest ontribution to W ). In any ase, W is onsider-

ably lower than on Earth ( ase E; see olumn 12 of Table

1). Our results are in good agreement with Grenfell et al.

(2013), who �nd RUV-B = 0.11 for AD Leo ( ase without

osmi rays).

Case LF (long stellar UV �are) : As shown in Table 1, the

results are di�erent in the ase of an exoplanet either ex-

posed to a long UV �are or to a quasi- ontinuous su es-

sion of UV �ares ( ase LF ). The UV-A transmission ratio

RUV-A

is similar to that of the ase CA, but the higher TOA

�ux leads to an in reased surfa e UV-A intensity. For both

UV-B and UV-C, the transmission rates are redu ed when

ompared to the ase CA. For UV-B, the redu ed transmis-

sion rate is ompensated by the in reased TOA �ux, so that



the surfa e �ux is higher than for hromospheri ally a tive

ase (about two orders of magnitude) and ex eeds the level

of ase E. For UV-C, the de rease of RUV-C

outweighs the

in rease in TOA �ux, and the surfa e UV-C �ux is redu ed

by several orders of magnitude. Compared to ase CA, the

biologi ally weighted UV surfa e �ux W (whi h is mostly

determined by shortwave UV-B) is in reased by up to two

orders of magnitude. It is omparable to the value for Earth

( ase E, ir le in Figure 7. See also olumn 12 of Table 1).

Another e�e t of long �ares an be seen in Table 1 and

Figure 7: When the magneti moment in reases, i.e. when

the planet is better shielded against GCRs, the surfa e UV

�ux in reases ! This is a onsequen e of the enhan ed stel-

lar UV �ux, whi h leads to extra ozone produ tion in the

altitude region 5-30 km, with a peak at 18 km (Figure 8).

This strongly suggests an in reasing smog me hanism at

low altitudes, whereas above 30 km O3 is still destroyed by

atalyti NOx. With in reasing CR �ux the smog me ha-

nism in the lower atmosphere dominates over the atalyti

destru tion in the upper atmosphere, so that the olumn in-

tegrated ozone ontents in reases, and the surfa e UV �ux

de reases (Figure 7).

Case SF (short stellar UV �are) : For a short stellar �are

(with a times ale of 10

2-10

3se onds), we do not get the

inversed response of ase LF, but - by onstru tion - a be-

haviour identi al to the ase CA, with higher absolute �ux

values. Also, by onstru tion, the averaged UV transmis-

sion rates are similar to the ase CA. As a result of the

higher input �ux, the surfa e �ux of UV-A, UV-B and UV-

C is at least 50 times higher than in the ase CA, see Table

1. The biologi ally weighted UV surfa e �ux W is higher

than in the ase CA by a fa tor 200-300.

The modulation by the magneti �eld is omparable to

the ase CA: Between M = 0 and 1.0M⊕, W de reases by

30%. For higher magneti �elds, W ontinues to de rease,

by up to 10% (Figure 7). As indi ated in Table 1 ( olumn

12) and Figure 7, W is a fa tor of 3-4 higher than on Earth

( ase E) for the duration of the short �are.

Case SCR (stellar osmi rays) : UV �ares are frequently

a ompanied by stellar osmi ray parti les (Segura et al.,

2010), whi h would amplify the ozone destru tion. In that

ase, the strong removal of stratospheri ozone (Grenfell

et al., 2012) an redu e the UV shielding to∼ 50%, and lead

to onsiderably higher UV surfa e �uxes, surpassing those

on the terrestrial surfa e by an order of magnitude. Using

the urrent model, this ase is re-evaluated in a separate

arti le (Tabataba-Vakili et al., 2014).

Dis ussion : The omparison shows that a short �are is

potentially more harmful than a long �are, in whi h the

atmosphere has time to adjust to the high UV �ux and

absorption is in reased at mid-altitudes. One noti es that

the e�e t of GCRs on UV radiation is weaker than the

modi� ation aused by a hange in the stellar spe trum

(e.g. ase E to CA). Loooking at the di�erent wavelength

ranges, one noti es that:

� GCRs leave the UV-A transmission oe� ient and �ux

virtually un hanged.

� For UV-B, GCRs modify the transmission rate and sur-

fa e �ux by less than 20%, and the relative hange is pro-

portional to the hange in ozone olumn, as expe ted.

� The transmission oe� ient for UV-C varies by a fa tor

of up to 200, so that the surfa e �ux of UV-C radiation is

indeed strongly dependent on magnetospheri shielding.

However, even in the most extreme ase (M = 0.0M⊕),

the surfa e �ux remains negligibly small.

� GCRs may hange the biologi ally weigthed UV surfa e

�ux W by up to 40%, whi h again is mu h less than the

di�eren e due to a hange in stellar emission during a

�are. For example, during a short stellar �are ( ase SF),

one �nds values 3-4 times higher than on Earth ( ase E),

or 200-300 times the quies ent level. Su h values an

be onsidered as non- riti al. In parti ular, Deino o us

radiodurans is able to withstand a �ux of > 40 W/m

2

without signi� ant damage, and life on Earth may have

arisen during times when the biologi ally weighted UV

�ux was even higher (> 96 W/m

2, see Co kell, 1999).

We on lude that this level of UV radiation is non-

riti al, but we note that the UV environment on M star

planets is mu h more variable than what we know from

Earth.

4.4. Surfa e biologi al dose rate

Like the Earth, the surfa e of an exoplanet an be shielded

against gala ti osmi rays by two barriers. The �rst bar-

rier is the planetary magnetosphere, whi h de�e ts parti les

provided their energy is low enough (paper I).

However, this does not mean that all parti les that pen-

etrate through the magnetosphere rea h the surfa e. The

atmosphere a ts as a se ond barrier, and prevents low-

energy parti les and their produ ts from rea hing the sur-

fa e (O'Brien et al., 1996). At Earth, the minimum energy a

proton must have to initiate a nu lear intera tion sequen e

dete table at the surfa e is approximately 450 MeV (Shea

and Smart, 2000). Higher energy protons will generate an

atmospheri nu lear as ade or osmi ray shower, with

high energy se ondary parti les su h as neutrons, ele trons,

pions and muons rea hing the planetary surfa e. Again, the

low-energy omponents of the as ade will be absorbed in

the atmosphere, leading to an altitude with maximum par-

ti le �ux, the Pfotzer maximum. In the ase of the Earth,

the Pfotzer maximum is lo ated at an altitude of 15-26 km,

depending on latitude and solar a tivity level (Bazilevskaya

et al., 2008). Below the Pfotzer maximum, the parti le �ux

de reases towards the surfa e. Depending on the altitude of

the Pfotzer maximum, the atmosphere an either de rease

or in rease the surfa e radiation dose. For an planet with

an Earth-like (or denser atmosphere), the absorption e�e t

dominates, and the atmosphere has to be regarded as a se -

ond barrier whi h partially prote ts the surfa e against the

osmi ray �ux.

If parts of the osmi ray shower rea h the planetary sur-

fa e, one ould expe t that biologi al systems on the plan-

etary surfa e an be strongly in�uen ed and even damaged

by this se ondary radiation. This expe tation is ba ked by

experimental eviden e, whi h shows that during Ground

Level Enhan ements (extreme events where large num-

bers of se ondary osmi rays rea h the Earth's surfa e)

DNA lesion on the ellular level in rease onsiderably (Bel-

isheva et al., 2005; Grieÿmeier et al., 2005; Belisheva et al.,



Fig. 8. Column density of NOx (left panel)and O3 (right panel) as a fun tion of exoplanetary magneti moment for the ase of a

long �are (LF).

2006; Dartnell, 2011; Belisheva et al., 2012, and referen es

therein). In the ase of Earth, muons ontribute 75% of the

equivalent dose rate at the surfa e (O'Brien et al., 1996).

In paper I, we have shown that weakly magnetized

super-Earths orbiting M stars an be exposed to mu h

higher osmi ray �uxes at the top of the atmosphere when

ompared to the ase of the Earth. The question naturally

arises: How does this high �ux at the top of the atmosphere

translate into a radiation dose at the planetary surfa e?

The details of this intera tion and the resulting radia-

tion dose on the planetary surfa e depend on the planetary

atmospheri pressure and omposition. Thus, the best way

to answer this question is to numeri ally simulate the in-

tera tions, following the parti les from the top of the atmo-

sphere down to the planetary surfa e. For this, we use the

atmospheri muon model as des ribed in Se tion 3.2. First

results have been presented by Atri et al. (2013); for the

urrent work, more datapoints have been added.

Figure 9 and Table 2 show the total biologi al radia-

tion dose rate as a fun tion of the planetary magneti �eld,

measured in mSv/yr. In Figure 9, the dash-dotted line or-

responds to a planet with an atmospheri depth of 1036

g/ m

2(B1036

, i.e. the biologi al radiation dose rate for an

Earth-like atmosphere with a surfa e pressure of 1033 hPa),

while the dotted line orresponds to a planet with an at-

mospheri depth of 100 g/ m

2(B100

, the biologi al radia-

tion dose rate for a planet with a surfa e pressure of 97.8

hPa). The verti al line denotes Earth's magneti moment

(M = 1.0M⊕), and the ir le indi ated Earth-like ondi-

tions. The horizontal lines are shown to guide the eye. They

indi ate the total biologi al dose rates for the ases M = 0(upper dotted and upper dash-dotted horizontal line) and

M = 1.0M⊕ (lower dotted and lower dash-dotted line).

In the ase of a planet with a an Earth-like atmosphere

of 1033 hPa (dash-dotted line), magnetospheri shielding

redu es the surfa e biologi al dose rate by a fa tor of ap-

proximately 2 between M = 0 and 1M⊕. Obviously,

for stronger magneti �elds (M > 1M⊕), the biologi-

al dose rate further de reases (by another fa tor of 3 for

M [M⊕]

tota

lbio

log

ical

rad

iatio

nd

ose

1010.1

1000

100

10

1

0.1

Fig. 9. Total biologi al dose rate (i.e. the sum of radiation dose

rates by muons, ele trons, and neutrons, in mSv/yr) in the ase

of modi�ed magnetospheri shielding. Dash-dotted line: planet

with an atmospheri depth of 1036 g/ m

2(i.e. an Earth-like

atmosphere with a surfa e pressure of 1033 hPa). Dotted line:

planet with an atmospheri depth of 100 g/ m

2(i.e. a surfa e

pressure of 97.8 hPa. Verti al line (shown as a guide for the

eye): M = 1.0M⊕. Horizontal lines (shown for omparison):

Total biologi al dose rates for the ase M = 0 (upper dotted

and dash-dotted horizontal line) andM = 1.0M⊕ (lower dotted

and dash-dotted line). Cir le: Earth.

M = 10.0M⊕). As the magneti �eld de reases, the �lter

e� ien y of the magnetosphere de reases, and the number

of osmi ray protons rea hing the top of the planetary

atmosphere in reases (paper I). However, the atmosphere

remains as a se ond �lter, and removes most of the biologi-

ally relevant parti les, so that the total biologi al radiation

dose rate of Figure 9 (i.e. the sum of the radiation dose rates

by muons, ele trons, and neutrons) in reases only slowly

with de reasing magneti moment.



M [M⊕℄ B1036

[mSv/yr℄ B100

[mSv/yr℄

0.0 0.65 553

0.1 0.48 527

0.15 0.46 510

0.25 0.44 405

0.5 0.42 257

0.75 0.39 216

1.0 0.34 172

2.0 0.28 53

3.0 0.23 15

6.0 0.19 5.7

10.0 0.1 2.3

Table 2. Total biologi al dose rate B (i.e. the sum of radiation

dose rates by muons, ele trons, and neutrons, in mSv/yr) in the

ase of modi�ed magnetospheri shielding for a planet with an

atmospheri depth of 1036 g/ m

2(B1036

) and for a planet with

an atmospheri depth of 100 g/ m

2(B100

).

For a planet with a weaker atmosphere of 97.8 hPa

(dashed line), magnetospheri shielding is more important,

and redu es the surfa e biologi al dose rate by a fa tor of

approximately 3 between M = 0 and 1M⊕, and another

fa tor of 70 between M = 1 and 10M⊕.

As was already noted by Atri et al. (2013), atmospheri

shielding dominates over magnetospheri shielding. In Ta-

ble 2, this is indeed obvious: At M = 0, the Earth-like

atmosphere (dash-dotted urve in Figure 9) redu es the

surfa e biologi al dose rate by almost three orders of magni-

tude when ompared to the weak atmosphere ase (dotted

urve). For an Earth-like magneti moment (M = 1M⊕),

the di�eren e is still more than two orders of magnitude.

For strongly magnetized planets, the di�eren e is smaller,

but atmospheri shielding still remains stronger than the

magnetospheri shielding.

We on lude that even a weakly magnetized planet an

be prote ted against strong biologi al radiation generated

by GCR, provided that it has a su� iently thi k atmo-

sphere (where, for example, an Earth-like atmosphere an

be onsidered as �su� iently thi k�). For planets with a thin

atmosphere and a strong magnetosphere, however, magne-

tospheri shielding is important.

5. Con lusion

Magneti �elds on most super-Earths around M stars are

likely to be weak and short-lived in the best ase, or even

non-existant in the worst ase. With this in mind, the ques-

tion of planetary magneti shielding against gala ti osmi

rays be omes important (the ase of stellar osmi rays will

be analyzed in a separate arti le, Tabataba-Vakili et al.,

2014). We use the systemati study of GCR �uxes presented

in paper I, where we found that the �ux of gala ti osmi

rays to the planetary atmosphere an be in reased up to

three orders of magnitude in the absen e of a prote ting

magneti �eld. With this input, we found that these ener-

geti parti les an destroy part of the atmospheri ozone

and other biomarker mole ules. However, with less than

20% di�eren e in ozone olumn, this has little impa t on

remote dete tion of biosignature mole ules. GCRs may also

hange the biologi ally weigthed UV surfa e �ux W by up

to 40%. During a stellar �are, W an in rease mu h more,

and rea h values a fa tor of 3-4 higher than on Earth, or

200-300 times the quies ent level. Su h values an be on-

sidered as non- riti al. Also, this e�e t is not strongly de-

pendent on the GCR �ux, but we note that the surfa e UV

�ux on M star planets is mu h more variable than what

we know from Earth. Finally, part of the energeti harged

parti les will rea h the planetary surfa e, where they on-

tribute to a potentially harmful radiation ba kground and

in rease the e�e tive dose rate. This in rease is only a fa tor

of a few for the ase of an Earth-like atmosphere. For plan-

ets with a thin atmosphere and a strong magnetosphere,

however, magnetospheri shielding is important.

Overall, the potential absen e of magneti shielding

against gala ti osmi rays has surprisingly little e�e t on

the planet and other e�e ts are likely to dominate, unless

the planet has a weak atmosphere and a strong magneto-

sphere. The ase is di�erent in the ase of stellar osmi

rays, whi h is analyzed in a ompanion arti le (Tabataba-

Vakili et al., 2014).

A knowledgements. This study was supported by the International

Spa e S ien e Institute (ISSI) and bene�ted from the ISSI Team �Evo-

lution of Exoplanet Atmospheres and their Chara terisation�.

Referen es

Allen, M., Lunine, J. I., Yung, Y. L., 1984. The verti al distribution

of ozone in the mesosphere and lower thermosphere. J. Geophys.

Res. 89 (D3), 4841�4872.

Alvarez-Muñiz, J., Engel, R., Gaisser, T. K., Ortiz, J. A., Stanev, T.,

2002. Hybrid simulations of extensive air showers. Phys. Rev. D 66,

033011.

Atri, D., , Melott, A. L., 2011. Modeling high-energy osmi ray in-

du ed terrestrial muon �ux: A lookup table. Radiat. Phys. Chem.

80, 701�703.

Atri, D., Hariharan, B., Grieÿmeier, J.-M., 2013. Gala ti osmi

ray�indu ed radiation dose on terrestrial exoplanets. Astrobiology

13 (10), 910�919.

Atri, D., Melott, A. L., Thomas, B. C., 2010. Lookup tables to om-

pute high energy osmi ray indu ed atmospheri ionization and

hanges in atmospheri hemistry. J. Cosmol. Astropart. Phys. 5,

8.

Bazilevskaya, G. A., Usoskin, I. G., Flü kiger, E. O., Harrison, R. G.,

Desorgher, L., Bütikofer, R., Krainev, M. B., Makhmutov, V. S.,

Stozhkov, Y. I., Svirzhevskaya, A. K., Svirzhevsky, N. S., Kovaltsov,

G. A., 2008. Cosmi ray indu ed ion produ tion in the atmosphere.

Spa e S i. Rev. 137, 149�173.

Belisheva, N. K., Kuzhevskii, B. M., Vashenyuk, E. V., Zhirov, V. K.,

2005. Correlation between the fusion dynami s of ells growing in

vitro and variations of neutron intensity near the Earth's surfa e.

Doklady Bio hemistry and Biophysi s 402, 254�257.

Belisheva, N. K., Kuzhevskij, B. M., Sigaeva, E. A., Panasyuk, M. I.,

Zhirov, V. K., 2006. Variations in the neutron intensity near the

Earth's surfa e modulate the fun tional state of the blood. Doklady

Bio hemistry and Biophysi s 407, 83�87.

Belisheva, N. K., Lammer, H., Biernat, H. K., Vashenuyk, E. V., 2012.

The e�e t of osmi rays on biologi al systems � an investigation

during GLE events. Astrophys. Spa e S i. Trans. 8, 7�17.

Bon�ls, X., Delfosse, X., Udry, S., Forveille, T., Mayor, M., Perrier,

C., Bou hy, F., Gillon, M., Lovis, C., Pepe, F., Queloz, D., Santos,

N. C., Ségransan, D., Bertaux, J.-L., 2013. The HARPS sear h for

southern extra-solar planets XXXI. The M-dwarf sample. Astron.

Astrophys. 549, A109.

Bu ino, A. P., Lemar hand, G. A., Mauas, P. J. D., 2007. UV hab-

itable zones around M stars. I arus 192, 582�587.

Co kell, C. S., 1999. Carbon bio hemistry and the ultraviolet radiation

environments of F, G, and K main sequen e stars. I arus 141, 399�

407.



Crutzen, P. J., 1970. The in�uen e of nitrogen oxides on the atmo-

spheri ozone ontent. Q. J. R. Meteorol. So . 96, 320�325.

Cuntz, M., Guinan, E. F., Kuru z, R. L., 2010. Biologi al damage due

to photospheri , hromospheri and �are radiation in the environ-

ments of main-sequen e stars. In: Kosovi hev, A. G., Andrei, A. H.,

Rozelot, J.-P. (Eds.), IAU Symp. 264: Solar and Stellar Variability:

Impa t on Earth and Planets. pp. 419�426.

Dartnell, L. R., 2011. Ionizing radiation and life. Astrobiology 11 (6),

551�582.

Domagal-Goldman, S. D., Meadows, V. S., 2010. Abioti buildup of

ozone. In: du Foresto, V. C., Gelino, D. M., Ribas, I. (Eds.), Path-

ways Towards Habitable Planets. Vol. 430 of ASP Conferen e Se-

ries. pp. 152�157.

Dressing, C. D., Charbonneau, D., 2013. The o urren e rate of small

planets around small stars. Astrophys. J. 767, 95.

Fran e, K., Froning, C. S., Linsky, J. L., Roberge, A., Sto ke, J. T.,

Tian, F., Bushinsky, R., Désert, J.-M., Mauas, P., Vieytes, M.,

Walkowi z, L. M., 2013. The ultraviolet radiation environment

around M dwarf exoplanet host stars. Astrophys. J. 763, 149.

Grenfell, J., Gebauer, S., Godolt, M., Pal zynski, K., Rauer, H., Sto k,

J., Paris, P. v., Lehmann, R., Selsis, F., 2013. Potential biosigna-

tures in Super-Earth atmospheres II. Photo hemi al responses. As-

trobiology 13 (5), 415�438.

Grenfell, J. L., Gebauer, S., Paris, P. v., Godolt, M., Hedelt, P., Patzer,

A. B. C., Stra ke, B., Rauer, H., 2011. Sensitivity of biomarkers

to hanges in hemi al emissions in the Earth's Proterozoi atmo-

sphere. I arus 211, 81�88.

Grenfell, J. L., Grieÿmeier, J.-M., Paris, P. v., Patzer, A. B. C., Lam-

mer, H., Stra ke, B., Gebauer, S., S hreier, F., Rauer, H., 2012.

Response of atmospheri biomarkers to NOx-indu ed photo hem-

istry generated by stellar osmi rays for Earth-like planets in the

habitable zone of M dwarf stars. Astrobiology 12 (12), 1109�1122.

Grenfell, J. L., Grieÿmeier, J.-M., Patzer, B., Rauer, H., Segura, A.,

Stadelmann, A., Stra ke, B., Titz, R., Paris, P. v., 2007. Biomarker

response to gala ti osmi ray-indu ed NOx and the methane

greenhouse e�e t in the atmosphere of an Earth-like planet orbiting

an M dwarf star. Astrobiology 7 (1), 208�221.

Grenfell, J. L., S.Gebauer, Paris, P. v., M.Godolt, H.Rauer, 2014.

Sensitivity of biosignatures on Earth-like planets orbiting in the

habitable zone of ool M-dwarf stars to varying stellar UV radiation

and surfa e biomass emissions. Planet. Spa e S i. 98, 66�76.

Grieÿmeier, J.-M., 2014. Exoplanetary magneti �elds. In: Lammer,

H., Khoda henko, M. (Eds.), Chara terizing stellar and exoplane-

tary environments. Springer, in press.

Grieÿmeier, J.-M., Stadelmann, A., Grenfell, J. L., Lammer, H.,

Mots hmann, U., 2009. On the prote tion of extrasolar Earth-like

planets around K/M stars against gala ti osmi rays. I arus 199,

526�535.

Grieÿmeier, J.-M., Stadelmann, A., Mots hmann, U., Belisheva, N. K.,

Lammer, H., Biernat, H. K., 2005. Cosmi ray impa t on extrasolar

Earth-like planets in lose-in habitable zones. Astrobiology 5 (5),

587�603.

Grieÿmeier, J.-M., Tabataba-Vakili, F., Stadelmann, A., Grenfell,

J. L., Atri, D., 2014. Gala ti osmi rays on extrasolar Earth-like

planets: I. Cosmi ray �uxIn preparation.

Gueymard, C. A., 2004. The sun's total and spe tral irradian e for

solar energy appli ations and solar radiation models. Solar Energy

76, 423�453.

Haus hildt, P. H., Allard, F., Baron, E., 1999. The NextGen model

atmosphere grid for 3000≤ Te�

≤ 10,000 K. Astrophys. J. 512,

377�385.

Heath, M. J., Doyle, L. R., Joshi, M. M., Haberle, R. M., 1999. Hab-

itability of planets around red dwarf stars. Origins Life Evol. Bio-

sphere 29, 405�424.

He k, D., Knapp, J., Capdevielle, J. N., S hatz, G., Thouw, T., 1998.

CORSIKA: A Monte Carlo ode to simulate extensive air showers.

S ienti� report (FZKA 6019), Fors hungszentrum Karlsruhe.

He k, D., Peirog, T., Knapp, J., 2012. CORSIKA: An air shower sim-

ulation program. Astrophysi s Sour e Code Library 1202.006.

Hedelt, P., Paris, P. v., Godolt, M., Gebauer, S., Grenfell, J. L., Rauer,

H., S hreier, F., Selsis, F., , Trautmann, T., 2013. Spe tral features

of Earth-like planets and their dete tability at di�erent orbital dis-

tan es around F, G, and K-type stars. Astron. Astrophys. 553, A9.

Horne k, G., 1995. Quanti� ation of the biologi al e�e tiveness of

environmental UV radiation. J. Photo hem. Photobiol. B: Biol. 31,

43�49.

Ja kman, C. H., DeLand, M. T., Labow, G. J., Fleming, E. L.,

Weisenstein, D. K., Ko, M. K. W., Sinnhuber, M., Russell, J. M.,

2005. Neutral atmospheri in�uen es of the solar proton events in

O tober-November 2003. J. Geophys. Res. 110 (A09), A09S27.

Ja kman, C. H., Frederi k, J. E., Stolarski, R. S., 1980. Produ tion of

odd nitrogen in the stratosphere and mesosphere: An inter ompar-

ison of sour e strengths. J. Geophys. Res. 85 (C12), 7495�7505.

Kasting, J. F., Whitmire, D. P., Reynolds, R. T., 1993. Habitable

zones around main sequen e stars. I arus 101, 108�128.

Kerr, J. B., M Elroy, C. T., 1993. Eviden e for large upward trends

of ultraviolet-B radiation linked to ozone depletion. S ien e 262,

1032�1034.

Khoda henko, M. L., Ribas, I., Lammer, H., Grieÿmeier, J.-M., Leit-

ner, M., Selsis, F., Eiroa, C., Hanslmeier, A., Biernat, H. K., Far-

rugia, C. J., Ru ker, H. O., 2007. Coronal Mass Eje tion (CME)

a tivity of low mass M stars as an important fa tor for the habit-

ability of terrestrial exoplanets. I. CME impa t on expe ted mag-

netospheres of Earth-like exoplanets in lose-in habitable zones.

Astrobiology 7 (1), 167�184.

Kopparapu, R. K., 2013. A revised estimate of the o urren e rate

of terrestrial planets in the habitable zones around KEPLER M-

dwarfs. ApJ 767, L8.

Lammer, H., Bredehöft, J. H., Coustenis, A., Khoda henko, M. L.,

Kaltenegger, L., Grasset, O., Prieur, D., Raulin, F., Ehrenfreund,

P., Yamau hi, M., Wahlund, J.-E., Grieÿmeier, J.-M., Stangl, G.,

Co kell, C. S., Kulikov, Y. N., Grenfell, J. L., Rauer, H., 2009. What

makes a planet habitable? Astron. Astrophys. Rev. 17, 181�249.

Lammer, H., Selsis, F., Chasse�ère, E., Breuer, D., Grieÿmeier, J.-

M., Kulikov, Y. N., Erkaev, N. V., Khoda henko, M. L., Bier-

nat, H. K., Leblan , F., Kallio, E., Lundin, R., Westall, F., Bauer,

S. J., Bei hman, C., Dan hi, W., Eiroa, C., Fridlund, M., Gröller,

H., Hanslmeier, A., Hausleitner, W., Henning, T., Herbst, T.,

Kaltenegger, L., Léger, A., Leitzinger, M., Li htenegger, H. I. M.,

Liseau, R., Lunine, J., Mots hmann, U., Odert, P., Pares e, F.,

Parnell, J., Penny, A., Quirrenba h, A., Rauer, H., Röttgering, H.,

S hneider, J., Spohn, T., Stadelmann, A., Stangl, G., Stam, D.,

Tinetti, G., White, G. J., 2010. Geophysi al and atmospheri evo-

lution of habitable planets. Astrobiology 10 (1), 45�68.

Leggett, S. K., Allard, F., Berriman, G., Dahn, C. C., Haus hildt,

P. H., 1996. Infrared spe tra of low-mass stars: Toward a temper-

ature s ale for red dwarfs. Astrophys. J. Suppl. Ser. 104, 117�143.

Manabe, S., Wetherald, R. T., 1967. Thermal equilibrium of the at-

mosphere with a given distribution of relative humidity. J. Atmos.

S i. 24 (3), 241�259.

Mlawer, E. J., Taubman, S. J., Brown, P. D., Ia ono, M. J., Clough,

S. A., 1997. Radiative transfer for inhomogeneous atmospheres:

RRTM, a validated orrelated-k model for the longwave. J. Geo-

phys. Res. 102 (D14), 16663�16682.

O'Brien, K., Friedberg, W., Sauer, H. A., Smart, D. F., 1996. Atmo-

spheri osmi rays and solar energeti parti les at air raft altitude.

Environ. Int. 22, S1�S44.

Paris, P. v., Cabrera, J., Godolt, M., Grenfell, J. L., Hedelt, P., Rauer,

H., S hreier, F., Stra ke, B., 2011. Spe tros opi hara terization

of the atmospheres of potentially habitable planets: GL 581 d as a

model ase study. Astron. Astrophys. 534, A26.

Paris, P. v., Hedelt, P., Selsis, F., S hreier, F., Trautmann, T., 2013.

Chara terization of potentially habitable planets: Retrieval of at-

mospheri and planetary properties from emission spe tra. Astron.

Astrophys. 551, A120.

Pavlov, A. A., Kasting, J. F., 2002. Mass-independent fra tionation of

sulfur isotopes in ar hean sediments: Strong eviden e for an anoxi

ar hean atmosphere. Astrobiology 2 (1), 27�41.

Pettersen, B. R., Hawley, S. L., 1989. A spe tros opi survey of red

dwarf �are stars. Astron. Astrophys. 217, 187�200.

Quintana, E. V., Bar lay, T., Raymond, S. N., Rowe, J. F., Bolmont,

E., Caldwell, D. A., Howell, S. B., Kane, S. R., Huber, D., Crepp,

J. R., Lissauer, J. J., Ciardi, D. R., Coughlin, J. L., Everett, M. E.,

Henze, C. E., Hor h, E., Isaa son, H., Ford, E. B., Adams, F. C.,

Still, M., Hunter, R. C., Quarles, B., Selsis, F., 2014. An Earth-sized

planet in the habitable zone of a ool star. S ien e 344, 277�280.

Rauer, H., Gebauer, S., Paris, P. v., Cabrera, J., Godolt, M., Grenfell,

J. L., Belu, A., Selsis, F., Hedelt, P., S hreier, F., 2011. Potential

biosignatures in super-Earth atmospheres. I. Spe tral appearan e

of super-Earths around M dwarfs. Astron. Astrophys. 529, A8.

Sagan, C., Thomson, W. R., Carlson, R., Gurnett, D., Hord, C., 1993.

A sear h for life on earth from the Galileo spa e raft. Nature 365,

715�721.

Sander, S. P., Friedl, R. R., Golden, D. M., Kurylo, M. J., Huie,

R. E., Orkin, V. L., Moortgat, G. K., Ravishankara, A. R., Kolb,

C. E., Molina, M. J., Finlayson-Pitts, B. J., 2003. Chemi al kineti s

and photo hemi al data for use in atmospheri studies, evaluation

number 14. Te h. rep., JPL Publi ation 02-25.



S alo, J., Kaltenegger, L., Segura, A., Fridlund, M., Ribas, I., Kulikov,

Y. N., Grenfell, J. L., Rauer, H., Odert, P., Leitzinger, M., Selsis, F.,

Khoda henko, M. L., Eiroa, C., Kasting, J., Lammer, H., 2007. M

stars as targets for terrestrial exoplanet sear hes and biosignature

dete tion. Astrobiology 7 (1), 85�166.

S hindler, T. L., Kasting, J. F., 2000. Syntheti spe tra of simulated

terrestrial atmospheres ontaining possible biomarker gases. I arus

145, 262�271.

Segura, A., Kasting, J. F., Meadows, V., Cohen, M., S alo, J., Crisp,

D., Butler, R. A. H., Tinetti, G., 2005. Biosignatures from Earth-

like planets around M dwarfs. Astrobiology 5 (6), 706�725.

Segura, A., Meadows, V., Kasting, J. F., Crisp, D., Cohen, M., 2007.

Abioti formation of O2 and O3 in high-CO2 terrestrial atmo-

spheres. Astron. Astrophys. 472, 665�679.

Segura, A., Walkowi z, L. M., Meadows, V., Kasting, J., Hawley, S.,

2010. The e�e t of a strong stellar �are on the atmospheri hem-

istry of an Earth-like planet orbiting an M dwarf. Astrobiology

10 (7), 751�771.

Selsis, F., Chazelas, B., Bordé, P., Ollivier, M., Bra het, F., De audin,

M., Bou hy, F., Ehrenrei h, D., Grieÿmeier, J.-M., Lammer, H.,

Sotin, C., Grasset, O., Moutou, C., Barge, P., Deleuil, M., Mawet,

D., Despois, D., Kasting, J. F., Léger, A., 2007. Could we identify

hot o ean-planets with CoRoT, Kepler and Doppler velo imetry?

I arus 191, 453�468.

Selsis, F., Despois, D., Parisot, J.-P., 2002. Signature of life on ex-

oplanets: Can Darwin produ e false positive dete tions? Astron.

Astrophys. 388, 985�1003.

Shea, M. A., Smart, D. F., 2000. Cosmi ray impli ations for human

health. Spa e S i. Rev. 93, 187�205.

Smith, D. S., S alo, J., Wheeler, J. C., 2004. Transport of ionizing

radiation in terrestrial-like exoplanet atmospheres. I arus 171, 229�

253.

Tabataba-Vakili, F., Grenfell3, J. L., Grieÿmeier, J.-M., Rauer, H.,

2014. Atmospheri e�e ts of osmi ray indu ed NOx and HOx

produ tion on earth-like exoplanets around M dwarfs. Astron. As-

trophys. ???, ??, , in preparation.

Tarter, J. C., Ba kus, P. R., Man inelli, R. L., Aurnou, J. M., Ba k-

man, D. E., Basri, G. S., Boss, A. P., Clarke, A., Deming, D., Doyle,

L. R., Feigelson, E. D., Freund, F., Grinspoon, D. H., Haberle,

R. M., Hau k, II, S. A., Heath, M. J., Henry, T. J., Hollingsworth,

J. L., Joshi, M. M., Kilston, S., Liu, M. C., Meikle, E., Reid, I. N.,

Roths hild, L. J., S alo, J., Segura, A., Tang, C. M., Tiedje, J. M.,

Turnbull, M. C., Walkowi z, L. M., Weber, A. L., Young, R. E.,

2007. A reappraisal of the habitability of planets around M dwarf

stars. Astrobiology 7 (1), 30�65.

Toon, O. B., M Kay, C. P., A kerman, T. P., Santhanam, K., 1989.

Rapid al ulation of radiative heating rates and photodisso iation

rates in inhomogeneous multiple s attering atmospheres. J. Geo-

phys. Res. 94, 16287�16301.

Vardavas, I. M., Carver, J. H., 1984. Solar and terrestrial parameteri-

zations for radiative- onve tive models. Planet. Spa e S i. 32 (10),

1307�1325.



1 olumn 2 3 4 5 6 7 8 9 10 11 12

ase M IUV-ATOA

IUV-Asurfa e

RUV-A IUV-BTOA

IUV-Bsurfa e

RUV-B IUV-CTOA

IUV-Csurfa e

RUV-C W

[M⊕℄ [W/m

2℄ [W/m

2℄ [W/m

2℄ [W/m

2℄ [W/m

2℄ [W/m

2℄ [W/m

2℄

E 1.0 127 90.41 0.71 18.29 2.264 0.12 7.06 1.27 · 10−211.8 · 10

−220.126

E no GCR 127 90.41 0.71 18.29 2.256 0.12 7.06 1.12 · 10−211.6 · 10

−220.125

CA 0.0 2.01 1.479 0.74 0.202 0.0225 0.11 0.35 1.0 · 10−172.8 · 10

−170.0021

CA 0.1 2.01 1.479 0.74 0.202 0.0221 0.11 0.35 4.4 · 10−181.3 · 10

−170.0021

CA 1.0 2.01 1.477 0.74 0.202 0.0204 0.10 0.35 1.9 · 10−195.3 · 10

−190.0016

CA 10.0 2.01 1.477 0.74 0.202 0.0198 0.10 0.35 5.1 · 10−201.5 · 10

−190.0015

CA no GCR 2.01 1.477 0.74 0.202 0.0197 0.10 0.35 4.8 · 10−201.4 · 10

−190.0015

LF 0.0 112 75.75 0.68 47 3.053 0.065 81 3.3 · 10−244.1 · 10

−260.145

LF 0.1 112 75.75 0.68 47 3.054 0.065 81 3.3 · 10−244.1 · 10

−260.145

LF 1.0 112 75.79 0.68 47 3.084 0.066 81 3.8 · 10−244.8 · 10

−260.148

LF 10.0 112 75.80 0.68 47 3.099 0.066 81 4.1 · 10−245.1 · 10

−260.149

LF no GCR 112 75.81 0.68 47 3.100 0.066 81 4.1 · 10−245.1 · 10

−260.150

SF 0.0 112 76.50 0.68 47 5.10 0.11 81 7.9 · 10−169.8 · 10

−180.55

SF 0.1 112 76.47 0.68 47 5.00 0.11 81 3.5 · 10−164.3 · 10

−180.52

SF 1.0 112 76.37 0.68 47 4.65 0.10 81 1.5 · 10−171.8 · 10

−190.42

SF 10.0 112 76.33 0.68 47 4.52 0.10 81 4.1 · 10−185.0 · 10

−200.39

SF no GCR 112 76.33 0.68 47 4.51 0.10 81 3.8 · 10−184.7 · 10

−200.39

Table 1. UV-A, -B, and -C �ux at top of atmosphere (ITOA

) and the surfa e (Isurfa e

) for di�erent ases. Also shown:

wavelength-range averaged �ux ratio R = Isurfa e

/ITOA

(i.e. atmospheri transmission oe� ient) for the three UV bands, and

biologi ally weighted surfa e UV �ux W (in weighted W/m

2). Cases: E = Earth, CA = hromospheri ally a tive star, LT = long

�are, SF = short �are (see text for details).


Documents

A. Stadelmann J. L. Grenfell D.kusmos.phsx.ku.edu/~dimitra/papers/griessmeier_2... · decrib es the mo dels and umerical n to ols e w use: The atmospheric hemistry c mo del is discussed