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Proxima b: The Alien World Next Door
- Is Anyone Home?
Edward GuinanDept. Astrophysics & Planetary Science
Villanova University
Biruni Observatory 40th Anniversary Workshop12 October, 2017
Talking Points
i. Planet Hunting: Exoplanets
ii. Living with a Red Dwarf Program
iii. Alpha Cen ABC -nearest Star System
iv. Proxima Cen – the red dwarf star
v. Proxima b Nearest Exoplanet
vi. Can it support Life?
vii. Planned Observations / Missions
Planet Hunting:
Finding Exoplanets
A brief summary
For citizen science projects: www.planethunters.org
“There are infinite
worlds both like and
unlike this world of
ours...We must
believe that in all
worlds there are living
creatures and planets
and other things we
see in this world.”
Epicurius
c. 300 B.C
Thousands of years ago, Greek philosophers speculated…
Early Thoughts on Extrasolar Planets and Life
Credit: Charbonneau
First Planet Detected
51 Pegasi – November 1995Mayer & Queloz / Marcy & Butler
Many Exoplanets (400+) have been detected by the
Spectroscopic Doppler Motion Technique (now can
measure motions as low as 1 m/s (3.6 km/h = 2.3 mph))
Exoplanet Transit Eclipses
Rp/Rs ~ [Depth of Eclipse] 1/2
Transit Eclipse Depths for Jupiter, Neptune and Earth for the Sun
1.2% (Jupiter-Sun)
0.15% (Neptune-Sun)0.01% (Earth-Sun)
Kepler Mission
See: kepler.nasa.gov
Has so far discovered
6000+ Confirmed &
Candidate Exoplanets
The Search for Planets
Outside Our Solar
System
Exoplanet Census May 2017
Exoplanet Census (May-2017) Confirmed exoplanets: 3483+ (Doppler / Transit)490+ Multi-planet Systems [April 2017]
Exoplanet Candidates: 7900+ orbiting 2600+ stars (Mostly from the Kepler Mission) [May 2017]Other unconfirmed (mostly from CoRot)Exoplanets ~186+
Potentially Habitable Exoplanets: 51 (April 2017) Estimated Planets in the Galaxy ~ 50 -100 Billion!Most expected to be hosted by red dwarf starsNomad (Free-floating planets) ~ 25 - 50 Billion
Known planets with life: 1 so far.http://phl.upr.edu/projects/habitable-exoplanets-catalog
dK
dM
dG
Outer HZ Edge
Earth-equiv Pos.
Inner HZ Edge
Inner HZ Edge
Earth-equiv Pos.
Outer HZ Edge
Outer HZ Edge
Earth-equiv Pos.
Inner HZ Edge
2AU
1AU
0.8AU
0.3AU
1AU
0.5AU
0.14AU
0.2AU
0.1AU
* Earth not drawn to scale
dK
dM
dG
Outer HZ Edge
Earth-equiv Pos.
Inner HZ Edge
Inner HZ Edge
Earth-equiv Pos.
Outer HZ Edge
Outer HZ Edge
Earth-equiv Pos.
Inner HZ Edge
2AU
1AU
0.8AU
0.3AU
1AU
0.5AU
0.14AU
0.2AU
0.1AU
* Earth not drawn to scale
Liquid Water Habitable Zones for mid-dM, -dK and -dG star Note
that the HZs of dM-stars are located <0.3 AU from the host star.
[1 AU = 150 million km]
Habitable Zones
www.astronomy.villanov
a.edu/livingwithareddwa
rf/opener.htm
Program supported by grants
from NASA (HST & Chandra) &
NSF/RUI.
Living with a Red Dwarf
The original “Living With a Red Dwarf”
Program logo (not NASA approved)
Physical properties of dM0-8 Stars
compared to the Sun.
Living with a Red DwarfDo Red Dwarfs make “Friendly” Host
Stars for Life-Bearing Planets?
Photometry of stars with ages: Rotation,
star spots, cycles: Age-Rotation Relations.
Study effects of X-UV radiation
(photoionization / photo-dissociation) on
hosted planets’ water and atmospheres
(volatiles). X-UV radiation & winds
can erode (eliminate) planet atmospheres.
As part of the Living with a Red Dwarf Program we have
been collecting data on the properties of nearby stars (within
30 Ly; ~245 dM stars) that factor into their suitability as hosts
of Potentially Habitable Planets. These factors include X-ray+
UV emissions, rotation / starspots, flare rates and ages.
Rotation-Age-Log (Lx) Relations (Ages from
Clusters, MGs, Wide Binaries, Space Motions)
Proxima Cen: Prot = 83.4 +/-1.2 d (from 11-yrs of time-series
Photometry. Age: 5.4+/-0.4 Gyr (age from alpha Cen A)
Alpha Centauri Star System 4.3 LY (~25.4 trillion km)
1.0 LY = 5.9x1012 miles (=5.9 trillion miles)= 9,625 billion km
The alpha Centauri star system – compared to
the Sun (depicted to scale)
Alpha Cen A & B is an eccentric 79.9-yr binary system- Spectroscopic Doppler studies indicate no Planets (upper mass limit of >2.0 Mj). Many theoretical studies indicate that planets are unlikely due to binary star tidal interactions…But …
alpha Cen Bb ex-Exoplanet
Earth-size planet reported in 2012P = 3.236 d A = 0.04 AU
K = 0.51+/- 0.04 m/s
Min. Planet mass (Mp): 1.13 Mearth
T = 1800- 2200 K (~1500 – 1900C)
Dunusque et al. Nature 2012
Too Hot for LIFE even
If it existed. (recent studies do not
Support the existence of this planet)
Proxima Centauri-The Nearest
Star: --- Red Dwarf Distance= 4.25 LY;
Mass = 0.123 Mo, R = 0.14 Ro; T = 3050 K; L = 0.0015 Lsun, HZ = 0.03 - 0.08 AU Anglada-Escude’ et al. (2016) report the an
Earth-size HZ planet.
11.1 mag
Proxima Centauri
Red Dwarf Program Star
since 2005M5.5 V star) Compared to the Sun
and Jupiter
From our study Proxima
is ~5.4+/-0.5 Gyr old and has a
rotational period of 83-d & ~15%
spot covered, high levels of
magnetic activity:
~1 major flare/30 hrs.
Nature Letter doi:10.1038/nature19106
A terrestrial planet candidate in a
temperate orbit
around Proxima CentauriGuillem Anglada-Escude’ et al. 2016
Proxima Centauri bAnnounced Aug. 25, 2016
Period Analysis of spectroscopic radial velocity observations
of Proxima from Anglada-Escude’ et al. 2016. A definite
period of 11.186 days is found arising from reflex motion of
1.4 m/s (~5 kph = ~3 mph) from the planet Proxima b
Keplerian fit Proxima bPeriod (d) 11.186
Doppler amplitude: 1.38 m/s [5 km/hr / 3 mph]
Derived quantitiesOrbital semi-major axis, a: 0.049 AU
Minimum mass, mpsini (M⊕) 1.27 (1.10–1.46)
Equilibrium temperature: 234K (-39 C)
With a Greenhouse effect of 50 C: T = +11 C
(similar to Earths mean temperature of 15 C)
Irradiance compared with Earth 65%
Geometric probability of transit about 1.5%
Transit depth (Earth-like density) about 0.5%
[From Anglada-Escude’ et al. 2016]
Proxima b
HZ~ 0.04-0.09 AU
http: //phl.upr.edu/projects/habitable-exoplanets-catalog
Sept. 2016
Comparison of the Spectral X-Near-IR
Irradiance of Proxima b and Earth
(from Ribas et al. 2016)
X-ray EUV FUV NUV UV- VIS - NIR
Ly-alpha
1216 A
Loss of water from X-
UV Stellar radiation
X-UV Radiation
Dissociates water:
H2O -> 2 H + O
FUV radiation ionize
H -> H+ + e-
Stellar winds drag H+
ions away (if no protective
geomagnetic field) via ion
pick-up mechanisms.
If atmosphere is lost,
later outgassing can lead
to a CO2 rich atmosphere
High-energy spectral irradiance received by Prox b and the Earth. The integrated values are calculated per unit
wavelength. From Ribas et al. (2016)
X-ray EUV~250 x 50-30 X
FUV15-30 X
Proxima b
Earth
High-energy spectral irradiance received by Proxb and the Earth. The values are calculated per unit wavelength. From
Ribas et al. (2016)
From Griessmeier, Guinan et al. 2004, AA, 425, 753.
Effect of the intense solar wind of a young, active solar-type
star on the Magnetosphere of a nearby tidally locked planet
(X-UV/ Wind Flux data from Sun in Time program)
Strong Wind from young starWeaker Winds from an older Sun
To star->
Griessmeier et al. 2004
From Lammer et al. 2008 , Space Sci. Rev –Atmospheric
Escape and Evolution of Terrestrial Planets and Satellites
during
Proxima b: Climate for Synchronous Rotation
Possible Outcomes for Proxima bStar’s properties are well known but initial conditions of planet -such water inventories and geomagnetic fields are not constrained. As shown by Ribas et al. (2016), Prox b has endured very high radiation levels especially when the star was young. This makes outcomes uncertain.
Proxima Cen b: Possible Outcomes1. Low initial water inventories / weak geomagnetic fields: atmosphere /water
Outcome: like Mercury (dry barren planet) or Mars (cold, dry /ice planet) if Water not resupplied.
2. Weak geomagnetic fields; low – moderate initial water inventory. Young M5 V star’s strong X-UV radiation & wind – produce photolysis's H2O–> 2H + O. Two outcomes: a thick (>100 Bar) O2 rich atmosphere or if all H & O lost; later
outgassing of CO2 –> all (or most?) water lost -a Venus-like planet.
3. Abundant initial water (or water resupplied by comets) with a strong protective geomagnetic field: Water remains or is resupplied by comets – could result in a
Water World (like Earth) or Ice world (depending on outgassing).
4. Planet forms further from the host star and migrates inward. This could avoid / diminish the higher luminosity and strong X-UV effects of the young host star.
Water - Ice planet if it has sufficient water / strong geomagnetic fields
Possible Evolutionary Outcomes for Proxima b
Venus -Type Planet
Thick CO2 Atmosphere
Dense Iron Planet
Beyond Proxima Cen b:Investigating the next nearest PotentiallyHabitable Exoplanets: Kapteyn b (13 Ly) &Wolf 1061 c (14 Ly) – Assessing their Suitability for Life
Edward GuinanScott Engle Villanova University
Ignasi RibasI.C.E. Barcelona, Spain
Nearest Potentially Habitable Planets
Property Earth-Sun Proxima b Kapteyn b Wolf 1061 c [1.0 AU] [0.049 AU] [0.17 AU] [0.083 AU]
Mass (ME) 1.00 >1.27 >4.80 >4.25Radius (RE) 1.00 1.1 ~1.7 ~1.6
S/SE 1.00 0.65 0.40 0.60
Teq(K) 255 [288] 227 [277] 213 [263] 223 [273]
<fx> 0.67 c.g.s 163 5.4 ~30 [243 x Earth] [8.1 x Earth] [45 x Earth]
<f Ly-alph> 7.0 130 12 ~50 (FUV) [18.6 x Earth] [1.7 x Earth] [7.1 x Earth]
S/SE = instellation relative to Earth-Sun at 1.0 AU<f> mean irradiances [flux units: c.g.s = ergs/s/cm2]X-ray and Ly-alpha Irradiances on Earth: 0.67 and 7.1 ergs/s/cm2
TRAPPIST-1 Planetary System39 Light years away contains 2 Earth size planetsIn the liquid water habitable zone.
James Webb Space Telescope (JWST)
Expected Launch: Spring 2018
Searching for Evidence of
Atmospheres and Biosignatures
At orbital quadratures Prox b reaches
an angular separation of ~39 mas
from its host star.
Even though the Proxima b is small
and thus faint relative to Prox Cen, in
the near future (<10 yrs.), it may be
possible image the planet and / or
directly determine the chemical
composition of habitable planets.
Water, Oxygen, CH4 that could
indicate possible life.
Green dot Project – Search for
Exo-Aurorae Emission lines of OI 5577A
(See Luger et al. 2016) to study planet
E-ELT 39-m TelescopeWith AO has a chance to secure
spectra of Prox b free from the light
Of its host star
Under construction / first light 2025/26.
Giant Magellan
Telescope (GMT)(Under construction)
New Worlds Mission (NWM):
Hunting for alien lifeExobiology mission
https://exoplanets.nasa.gov/resources/1015
NWM can resolve Prox b from its host
star (~ 0.039” = 39 mas at quadratures)
permitting imaging and spectroscopy.
Star shade Concept: Occult Star: permit
hosted exoplanets to be imaged (being
considered by NASA with WFIRST Mission
~2025)
http://newworlds.colorado.edu/starshade/
China’s New 500-m FAST (Filled Aperture
Radio Telescope) will participate in searching
SETI radio signals (but Proxima is too far
South to observe)
Maybe in several years radio Signals will be detected with the SKA indicating IntelligentLife from a Nearby Exoplanet.
SETI Program (Allen Array)has been searching for over a decade. (no contact yet)
Going to Proxima b:
Interstellar Missions
and TravelMuch more difficult!(Nearest Star- the alpha Centauri
System is 4.3 LY (~40 trillion km away)
[1 LY = 5.85 x 1012 miles]
Starshot Mission to alpha Centauri
Nuclear Fusion Interstellar spaceshipFrom Icarus Interstellar
Fusion Enginesusing heavy Hydrogen
3H =Tritium• 2H + 3H -> 4He + n + energy• 17.6 MeV • Half-life of 12.32 years• Radiation leaks
• Maybe collect Tritium from the Moon
Slyuta
Bussard Ramjet Fusion
0.2c in one year
Mae Jemison ,MD
http://100YSS.org
Captured Asteroid Concept
Welcome to Proxima b
Thank you!
