# Presentation: 446298

## Europe's concept and plans for a Venus Entry Probe Mission

**Europe's concept and plan****s**** ****for ****a Venus Entry Probe Mis****sio****n**

- E. Chassefière(1), K. Aplin (U.K.), C. Ferencz (Hungary), T. Imamura (Japan), O. Korablev (Russia), J. Leitner (Austria), J. Lopez-Moreno (Spain), B. Marty (France), M. Roos Serote (Portugal), D. Titov (Germany), C. Wilson (U.K.), O. Witasse (ESTEC) & the VEP team

- (1) Service d’Aéronomie, Pôle Système Solaire (IPSL), CNRS & Université Pierre et Marie Curie, 4 place Jussieu 75252 Paris Cedex 05, France

- 4th International Planetary Probe Workshop, June 27-30, 2006, Pasadena, California, USA

## Scientific background

## Compared characteristics of terrestrial planets atmospheres

|  | Venus | Earth | Mars |
| --- | --- | --- | --- |
| Surface temperature | 735 K | 288 K | 218 K |
| Black body temperature | 230 K | 255 K | 215 K |
| Greenhouse gases | CO2, H2O, SO2, CO, clouds (H2SO4...)  | H2O, CO2, O3, ... | CO2 |
| Grenhouse effect | 505 K | 33 K | 3 K |

- - Mars : tenuous atmosphere, ≈ no greenhouse.
- - Earth : moderate greenhouse, liquid water, O2 photosynthetic, CO2 in carbonates.
- - Venus : massive atmosphere, strong greenhouse.

## Volatile inventory of terrestrial planets

- CO2 and N2 : Venus resembles Earth, but Mars is depleted by 3 orders of magnitude
- H2O : Venus is much dryer than Earth and Mars.
- 40Ar mixing ratio : Mars is enriched by ≈100, Venus depleted by ≈4 (wrt Earth) .
- 36Ar mixing ratio: Venus is enriched wrt Earth (≈70) and Mars (700)

- Mass fraction wrt planet

## Why is Venus different from Earth?

- Why is there virtually no water on Venus (a few 10 precipitable cm)?
- Runaway (or moist) greenhouse (Rasool and DeBergh, 1970) occurred in primitive intense EUV/ solar wind conditions **(?)**
- Why is there 4 times less argon 40 than in Earth atmosphere?
- Outgassing ceased ≈300 Myr after Venus formation, before most of Ar is formed within the interior (by K radioactive decay) **(?)**
- Why is there 70 times more argon 36 than on Earth?
- Preplanetary grains which have formed Venus have been enriched in volatiles through solar wind implantation **(?)**

## What was the fate of oxygen on Venus?

- Virtually no oxygen in Venus atmosphere. Why?
- Oxygen was removed by oxidation of rocks. Assuming FeO  Fe2O3, required crust production rate of ≈15 km3/yr (≈ Earth rate). *Not consistent with low **40**Ar (weak outgassing > 300 Myr)*.
- Oxygen was lost by impact erosion. *Not consistent with CO**2**/N**2** inventory similar to Earth*.
- _Oxygen was lost by hydrodynamic escape : dynamically and energetically possible_ (Chassefière, 1996).
- _Possible role of sputtering_ (Kulikov et al, 2006).

## How does the Venus climate system work?

- What is the redox state of the low atmosphere, and its variations with surface elevation?
- Is the atmosphere at thermochemical equilibrium with the surface?
- What are stable mineral phases at the surface?
- Is the Venus climate stable at geological time scales?

- From Fegley et al, 1997

## Cosmic Vision themes

## Addressed Cosmic Vision themes (1)

## Main questions in this theme

- Is the present bulk atmosphere of Venus in thermo-dynamical equilibrium with the surface and, if not, what are the processes responsible for a thermo-dynamical disequilibrium?
- Earth-size extra-solar planets can develop a massive a-biotic oxygen atmosphere by means of a runaway greenhouse and escape of hydrogen to space?
- What does the atmospheric dynamics and climate of a slowly rotating Earth-type extra-solar planet, phase-locked to its central star, look like?

## Addressed Cosmic Vision themes (2)

## Main questions in this theme (1)

- Was Venus originally endowed with as much water as Earth and, if so, where did water go?
- Did the massive greenhouse atmosphere have an impact on the geological history of the planet, and therefore its potential to host life, e.g. by modifying the way volatile species are cycled through the mantle, or by changing upper boundary thermal conditions?
- What is the impact of cloud coverage on atmospheric greenhouse and climate, and did clouds play a significant role in the climatic evolution of terrestrial planets?

## Main questions in this theme (2)

- Was Venus suitable to the appearance of life at some time in the past and, if so, when and how did conditions become unfavourable for life?
- How are volatile species cycled through the complex mantle-crust-surface- atmosphere-cloud system, and to which extent do global scale chemical cycles control bulk atmosphere composition?
- Will Earth evolve toward a massive Venus-type greenhouse by future increasing solar radiation conditions and anthropogenic influence?
- How does a dry, one-plate, planet of Earth size drive and lose heat from inner layers to its outer environment?

## Addressed Cosmic Vision themes (3)

## Main questions in this theme

- How does an Earth-sized planet without global magnetic field interact with the solar wind and why and at which rate does it lose its atmosphere?
- Does Venus’ atmosphere, ionosphere and solar wind interaction region present an electromagnetic wave activity, due to various possible phenomena: seismic and/or volcanic activity, atmospheric lightning, solar wind interaction?
- Did solar evolution (radiation/ particle) play an important role in driving terrestrial planetary climate evolution, e.g. powering runaway greenhouse on Venus or massive escape on Mars, and determining the presence or absence of water at their surface?

## Scientific objectives

## Unanswered questions (1)

- 1) The *isotopic composition*, especially that of noble gases, which provides information on the origin and evolution of Venus and its atmosphere.
- 2) The *chemical composition below the clouds and all the way down to the surface* with more detail than is possible using remote sensing, in order to fully characterize the chemical cycles involving clouds, surface and atmospheric gases.
- 3) The *surface composition and mineralogy* at several locations representing the main types of Venus landforms and elevations.
- 4) A *search for seismic activity** and seismology on the surface*, and measurements at multiple locations to sound the interiors.

## Unanswered questions (2)

- 5)* In situ* investigation of the *atmospheric dynamics*, for instance by tracking the drift of floating balloons.
- 6) The *composition and microphysics of the cloud layer* at different altitudes and locations, by direct sampling.
- 7)* Solar wind-atmosphere interaction processes and resulting escape* as a function of solar activity.
- 8)* In situ* determination of the *surface heat flow* of different landforms and structure-elements.
- 9) The *electromagnetic activity* monitoring and mapping of the planet.

## Main science goals (1)

- Investigation of the molecular composition of the lower atmosphere at various locations
- Study of the surface-atmosphere interactions
- Measurements of isotope abundance of heavy noble gases
- Systematic analysis of the surface both on the plains and tesserae
- Study of sub-surface by means of penetrating radar

## Main science goals (2)

- In situ determination of the surface heat flow
- In situ accurate measurements of the temperature profiles below the clouds in order to quantify atmospheric stability, characterization of local turbulence, and wind measurements
- Direct wind measurements in the upper mesosphere
- Accurate measurements of  radiative fluxes inside the atmosphere
- Determination of interior structure

## Mission elements

## Planetary orbiter

- Cf TRS VEP study of ESA’s SCI-A.
- Possible use of aerobraking to save mass and optimize orbit :
- Should be studied by ESA!

## Plasma orbiter

- Venus Ionospheric Science Probe (VISP)
- Royal Institute of Technology (Stockholm, Sweden)
- Sub-satellite (spinning platform)
- Low periapsis, high apoapsis
- Science payload ≈ 9 kg : DC **E**, **B**, waves, thermal plasma, electron spectrometer, ion spectrometer, ENA spectrometer.
- Total mass : 50-60 kg.

## Cloud-altitude balloon

- Cf TRS VEP study of ESA’s SCI-A.
- Super-pressurized balloon 3.6 m diameter
- Deployed at 55-65 km.
- 5 kg instruments + 3 kg microprobes (15 microprobes for dynamics monitoring)

## Microprobes for cloud-altitude balloons

- Studied par Oxford University (United Kingdom).
- 100 g each.
- Radio-link with balloon for Doppler winds.
- Measurements, p, T, v, Vis, IR down to ≈10 km altitude.

## Low-altitude balloon

- Preliminary design of a 10 km altitude balloon for the Lavoisier project (Chassefière et al, 2000).
- Ongoing R & D study for a 35-km altitude balloon at ISAS/ JAXA :
- Water vapor pressurized balloon deployed at 35 km altitude (auto-inflation in the 45-35 km altitude range).
- Solar cells, power ≈ a few watts, has a lifetime of 2 weeks.
- Scientific payload of 1 kg (pressure, temperature, other sensors TBD : radiative flux, ...), and an emitter allowing Doppler tracking by VLBI from Earth (wind).
- Entry vehicle sized on the basis of the Hayabusa re-entry capsule.
- Total mass of the entry vehicle : 35 kg.

## Descent probes

- Recent study by M. Van den Berg (SCI-A/2006/200/VEP/MvdB).
- Heritage of the Huygens probe is limited (different entry and environmental conditions).
- No operational lifetime assumed after landing.
- Scaling on Vega, PV, Jupiter Entry Probe study (NASA).

## Atmosphere sample return system

- Several existing concepts : direct sampling through a pipe (CNES), use of aerogel (SCIM project), both during a very low altitude pass (≈50 km on Mars).
- Alternative concept proposed in answer to the Call for Ideas for the Re-use of the Mars Express Platform (2001).
- Gas collected by cryotrapping during a flyby at ≈130 km altitude
- Doesn’t require fly-by at low altitude, in extreme thermal conditions.
- Total mass (cryocooler+collector+return capsule) < 50 kg.
- Possibility to use the return capsule developed for Hayabusa (ISAS/ JAXA)

## Launcher

- Future low cost M5 launcher (Japan) : 150 kg in Venus transfer orbit.
- Soyuz-Fregat (SF-21b from Kourou) :  1450 kg in VTO.
- HIIA (Japan) : 1500-2000 kg in VTO.
- Ariane V : ≈3000 kg in VTO.
- Other (small) launchers (Russia) : TBD

## Mission scenario

## The step-by-step approach

- Step 1 (2005-2015) : European Venus-Express mission and Japanese Venus Climate mission Orbiter
-  Atmospheric and cloud dynamics
-  (Incomplete) global scale chemistry of the low atmosphere
- Step 2 (2015-2025) : in-situ mission, with the use of atmospheric probes (balloons, descent probes) and atmosphere sample return (in option)
- Venus climate evolution
- New data relative to atmospheric isotopic ratios, chemistry of the coupled surface/ atmosphere system, dynamics of the whole atmospheric system.
- Step 3 (2025-2035) : Long-lived landers for the characterisation of the interior structure and dynamics of Venus

## Elemental scenarios (1)

## Elemental scenarios (2)

## Elemental scenarios (3)

## Preferred scenario (preliminary)

## International cooperation

- Scientific instruments (and sub-system) proposed by US, Japan, Russia, and Europe.
- Cooperation with Japan at mission element level under study (low-altitude balloon, thermal shield for descent probes, atmosphere return capsule, launcher...).
- Possible cooperation with Russia at mission element level to be studied (coordination with Venera D, launcher...).
- Possible cooperation with US at mission element level to be studied.
- Support by CNES for preparing the proposal (space mechanics, mission analysis...).

## Payloads

## Descent probes (1)

## Descent probes (2)

- Payload mass : 15-20 kg
- Consumption : ≈ 100 W
- To be refined and optimized!

## Cloud-altitude balloon

- Payload mass : ≈12 kg
- Consumption : ≈ 100 W
- To be refined and optimized!

## Planetary orbiter

- Payload mass : ≈45 kg
- Consumption : ≈ 150 W
- To be refined and optimized!

## Plasma orbiter (VIPS/ Sweden)