Venus : Mysteries of the Forgotten Planet

Venus : Mysteries of the forgotten planet

1 Structure of the Atmosphere Greenhouse effect solar solar thermal thermal

Thermosphere: very cold and highly variable Very high surface temperature No day/night and equator/pole contrasts

150 γ γ Atmospheric H2O CO γ γ SO2 HCl composition γ γ COS O2 Main gases: 100 γ CO2 (96,5%), N2 (3.5%)

SO2, COS, H2S – sulfur cycle γ γ γ 2 2 γ CO – photodissociation γ γ γ 50 H2O – greenhouse agent γ γ γ γ γ γ γ γ γ γ 0 γ -7 -6 -5 -4 -3 Lg (N/CO2)

2 Chemical Cycles

Photochemistry

HOx, Clx, SOx, Ox

Thermochemistry

COS, CO, H2SO4, SO3

Surface- atmosphere interactions

Cloud Layer Visibility > 300 m Total opacity 20-40 Particles: 1-10 µm, 100-1000 cm-3 Composition:

H2SO4 + ? (Sn, AlCl3, H3PO4, …) UV

NIR

Aerosol extinction, km-1

3 Atmospheric Troposphere and mesosphere Dynamics Zonal superrotation (>100 m/s) Poleward winds v ~ 10 m/s Cyclostrophic balance Thermosphere (> 120 km): Solar – antisolar circulation

n o tii S ll ta o a o a lla n rr n r o er t r- Z e iis p o su lla r Altitude, km Altitude, Altitude, km Altitude,

Zonal wind velocity, m/s

Wave phenomena Wave trains Planetary waves: “Y” feature Convectiv e cells

Polar dipole

250 K 220 K

4 Venus atmosphere in motion

Pioneer Venus Orbiter

Goal – to reach the surface !

Venera- 13

Venera- 14

5 Venus unveiled… Venera-15-16

Pioneer- Venus

Magellan

Venus Surface Main landforms Lowlands Tesserae Volcanoes Ishtar Impact craters Terra Global resurfacing ~500 My ago Very slow weathering No plate tectonics

Aphrodite Terra

6 Peeping through the cloud curtain

2.3 µm µ Day 1 m

UV m m µ µ µ µ µ µ µ µ 1 2.3

Night

Plasma Environment Non-magnetic planet Direct interaction of the solar wind with the atmosphere Complex structure of the ionosphere Atom and ion escape

7 Summary of the first phase of Venus exploration /1962 – 1990/ Flotilla of more than 20 spacecraft visited the planet Fly-bys, orbiters, descent probes, balloons Groundbased observations

Basic understanding of the conditions on the planet Complete mapping of the surface Power of remote sensing tools Great number of unsolved fundamental problems

Mysteries of Venus

Composition and chemistry of the lower atmosphere Physics and chemistry of the cloud layer Nature and mechanism of the general circulation Details of greenhouse effect Evolution of the atmosphere and the surface Plasma environment and its interaction with the solar wind

8 Uniqueness of Venus

Natural laboratory to study thermochemistry and surface- atmosphere interactions Atmospheric dynamics on a slowly rotating planet Radiative transfer at extreme conditions Surface is one of the youngest in the Solar System Plasma around non-magnetic planet

Key Question

WHY ?

9 2001 – ESA calls for ideas to re-use the Mars Express spacecraft

Minimum modifications to the spacecraft Use of already available payload Launch in 2005

Venus Express

Venus Express mission goal

Global investigation of the Venus’ atmosphere, plasma environment, and some important aspects of geology and surface physics from orbit

10 Venus Express payload

• PFS (V. Formisano) - high resolution IR Fourier spectrometer • SPICAV / SOIR (J.-L. Bertaux, O. Korablev, P. Simon) -UV & IR spectrometer for solar/stellar occultations and nadir observations • VIRTIS (P. Drossart, G. Piccioni) - UV-vis-near IR imaging and high resolution spectrometer • VMC (W.J. Markiewicz) - Venus Monitoring Camera • VeRa (B. Häusler, M.Pätzold) - radio science experiment • ASPERA (S. Barabash) - Analyzer of Space Plasmas and Energetic Atoms • MAG (T. Zhang) - Magnetometer

Temperature structure: PFS thermal IR spectrum SPICAV, PFS, VIRTIS, VeRa

• Thermosphere and ionosphere – Solar & stellar occultation by SPICAV/SOIR (80-150 km) – Radio occultation by VeRa (140-600 km) • Mesosphere VeRa radio occultatio – PFS and VIRTIS (60-100 km) – VeRa (40- 100 km) • Lower troposphere (0 - 8 km) – PFS, VIRTIS, and VMC

11 Lower atmosphere composition: VIRTIS, PFS, SPICAV, VMC

Venus night side by NIMS/ Galileo

Venus night side PFS and VIRTIS -H ---- CO ------H2O ---- -OCS- -SO2-

Composition of the upper atmosphere: SPICAV / SOIR Star occultation SPICAV UV occultation geometry spectra

SOIR IR occultation spectra

12 Cloud layer: VIRTIS, PFS, SPICAV, VMC

Vertical structure UV • Optical properties • Microphysical parameters • Vertical structure • Aerosol composition Upper cloud • Cloud layer formation • Atmospheric dynamics Middle cloud Near IR Lower cloud

Aerosol extinction, km-1

Atmospheric Dynamics Surface VIRTIS spectral mapping 50 km VMC global imaging 70 km PFS thermal wind field Time varying 3-D picture Airglow at 130 km

13 Plasma and escape processes: ASPERA, MAG, SPICAV, VeRa

Plasma around Venus ASPERA and Magnetometer < Global plasma and neutral gas distribution and velocities < Magnetic field measurements < Solar wind - atmosphere interaction < Study of escape processes SPICAV/ SOIR < Neutral atmosphere up to ~ 180 km VeRa < Ionosphere up to ~ 600 km Sun 45Ε 90Ε

Mars

ENA image at Mars

Magellan radar map Surface studies: VeRa, VIRTIS, PFS, SPICAV, VMC Ishtar Terra

• VeRa bistatic sounding Beta Tesserae • Thermal imaging of the surface γ V13 Atla • Correlation with earlier radar Themis Aphrodite Terra investigations • Search for volcanic activity

Lowland plains • Gravity anomalies

Venera-13 panorama

14 Spectral characteristics of the payload

SPICAV-SOIR

10000

SPICAV-IR VIRTIS-H 1000 PFS SPICAV-UV VIRTIS-M

100 VMC

0.1 1 10 100 Wavelength, µm

Fields of view of the instruments at 20,000 km

VMC VIRTIS M H 1Ε

SPICAV IR PFS UV

15 Coverage of the science themes

Structure Composition Dynamics Clouds Plasma & escape Surface

PFS VIRTIS SPICAV VeRa ASPERA VMC MAG

VENUS EXPRESS ORBIT and SCIENCE OPERATIONS

Pericentre obs Solar and stellar occultation Off-Pericentre and apocentre obs Earth occultation Limb obs Bi-static and solar corona sounding

16 Mission scenario Launch: Oct-Nov 2005 by Sojuz-Fregat from Baykonur (Kazakhstan) Arrival to Venus: April 2006 Polar orbit Pericentre latitude 80N Pericentre altitude 250 km Apocentre altitude ~65,000 km Period ~ 24h Mission duration 4 Venus siderial days Complete latitude and local time coverage

The spacecraft Mars Express

Venus Express Astrium - EADS

Solar panels: smaller and different composition Smaller dish of the main antenna Second antenna Modified thermal design

17 Venus Express integration at Alenia Spazio, Turin