Non-LTE emission from VIRTIS/Venus Express observations

Non-LTE emission from VIRTIS/Venus Express

observationsPierre Drossart1

With Giuseppe Piccioni2,

Gabriella Gilli3, M. Lopez-Valverde3, Raphaël Garcia4 and the

VIRTIS/VEX team

1LESIA, Observatoire de Paris 2IAPS, CNR, Rome; 3IAA, Granada, 4 IRAP, Toulouse

Launch : 9 November 2005Orbit insertion: 11 April 2006

Today :~2364 orbits

9 octobre 2012

Pierre Drossart Москва, ИКИ РАН 3M-S3

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VIRTIS for Venus Express – 7 years after…P. Drossart, G. Piccioni

– in mem. A. Coradini

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Aeronomy of Venus

The upper atmosphere of planets exhibit a large variety of physical processes, essential

to understand the interaction of a planet with its environment, but these regions are difficult to sound, and still relatively poorly

explored!

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O2 average emission (L. Soret and JC. Gérard , Liège)

O2 emission altitude : ~95 km

VIRTIS O2 Herzberg II spectrum obs.

Cf Migliorini et al – O2 emission altitude ~ 95 – 105 kmMean spectrum, obtained by averaging about 8700 spectra, acquired in the period 17-03-2010 – 28-02-2011.Identification of 8 Herzberg II bands. In addition, 3 Chamberlain bands are observed.

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OH and O2 emission on Venus

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7A.V. Shakun, PhD Thesis 2012

OH altitude emission~ 95 km as O2

cf Piccioni et al 2009

NO observations from VIRTISon VenusGarcia-Munoz et al, PNAS, 2009

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NO altitude (from UV/SPICAV) : ~110 km

CO 4.7 µm Vibrational temperatures

Basics on non-LTE models for Venus, Mars and the Earth : 1) CO

CO 4.7 µm levels scheme

FB and FH bands: main bands responsible for the 4.7 µm emission

LTE breakdown for CO(2) occurs at higher pressure then CO(1) in the 3 planets

Gilli et al. 2011

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Results from CO 4.7 m analysis (I)

Mars80-110km

Venus

100 km 150 km

Earth

68 km

• In Mars and Venus, FH lines dominate the emission at 100

km, FB becomes optically thin in the upper layers

• Rotational lines identified according to the spectral resolution of the instruments

• On the Earth the FB is optically thin at all altitudes, due to the smaller abundance of CO.

Formisano et al.2005

Funke et al 2005

Formisano et al. 2005

Funke et al. 2007

Gilli et a. 2011

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Results from CO 4.7m analysis (I)

• Emitted radiance proportional to the amount of emitters in opt. thin condition

• FB, and FH lines saturated in the mesosphere of Venus and Mars (opt. thick condition)

• FH and FB band do not saturate at any altitudes on the Earth

Gilli et al. 2011

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Results from CO 4.7 m analysis (II)(focus on Venus and Mars)

Data-model comparison for the first time at 4.7 m.

Good overall agreement. In Mars the residuals are within the noise level

The knowledge of the actual thermal structure on Venus and Mars is required

100 km

150 km

80-110 km

Gilli et al. 2011

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Results: VIRTIS-H CO

density (I)Difficult to find spatial and diurnal

variation, due to the irregular distribution of the data

Local time variations

No significant variations with Local Time observed in this latitude box

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CO2 4.3 m levels scheme

Basics on non-LTE models for Venus, Mars and the Earth : 2) CO2

• FB band: Transition from 001 level to the ground

• FH, SH bands: arises from higher energy states

CO2 high energy states directly excited during daytime by solar absorption.

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Comparative planetology: atmosphere of the terrestrial planets

1. Limb data from VIRTIS/Vex, PFS/Mex (Formisano et al. 2005) and results from MIPAS/Envisat (Funke et al. 2007) were used.

2. Non-LTE models for Venus (Roldan et al. 2000, López-Valverde et al. 2007), for Mars (Lopez-Puertas and Lopez Valverde 1994) and for the Earth (Lopez-Puertas et al. 2005)

DIFFERENCES

• Venus and Mars thermosphere colder than on the Earth

• O, CO about 10 times more abundant on Venus and Mars

• Stronger cooling in the upper regions of Mars and Venus by the CO2 15-m vibrational excited levels

• CO2 vmr on the Earth is 1000 time smaller

SIMILARITIES

• UV, soft X-rays absorption in the Thermosphere

• IR absorption in the mesosphere

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Basics on non-LTE models for Venus, Mars and the Earth

CO2 4.3 m Vibrational temperatures

• LTE departure at similar pressure levels for Mars and Venus, lower pressure on Earth

• Vibrational temperatures constant at the top of the atmosphere

Lopez-Valverde, Gilli,… PSS, 2011

9 octobre 2012

VIRTIS observations for CO2 non-LTE

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Gilli et al, JG

R 2009

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VIRTIS-M maps VIRTIS-M spectra & profiles

CO2 4.3-m non-LTE measurements

- CO2 emission peak around 110-120 km

- Higher emission at lower SZA

- good S/N up to 160 km

-Change in the overall shape of the band with altitude

-The altitude peak is maximum at the centre of the band (4.32 m)

Gilli et al. JGR, 2009

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R. Garcia, 2011

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Venus as seen by Akatsuki on 6 December 2010 from 600 000 km (UV- 380 nm)

Что дальше на Венере ?

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Non-LTE emission from VIRTIS/Venus Express observations