VATMOS-SR: A Fast Mission to Return Samples from Venus Atmosphere

Measuring the abundances of noble gases and their isotope ratios in Venus atmosphere is an essential investigation to understand Venus global evolution [1]. We propose a small satellite concept (ESA F-type mission) that would skim through Venus atmosphere below the homopause to collect samples that will be brought back to Earth and analyzed by the most sophisticated instruments in international laboratories. The science objectives are to determine the origin and geological evolution of Venus and to assess its potential habitability in the past. They are critical in the context of exoplanets detection to assess whether a terrestrial exoplanet is more likely to be Earth-like or Venus-like, which has profound astrobiological implications.

This mission concept has been proposed in response to the ESA call for F3 mission. It has matured from previous mission concepts [2]. It has also beneficiated from targeted work on the fractionation of noble gases during high velocity sampling [3]. Finally, a recent study by a CNES team showed that such a mission is feasible within the constraints (launch vehicle, mass, cost, …) of the ESA F3 call.

We show that measurements of key elemental ratios of noble gases and of Kr and Xe isotopes at high precision in ground-based laboratories would allow determining the origin of Venus’ atmosphere but will also put constraints on how much xenon has been escaping during hydrogen escape episodes. Measurements will also be able to put constraints on the time of outgassing of Venus’ interior into the atmosphere via measurements of radiogenic excesses of noble gas isotopes produced by extinct (¹²⁹I) and extant (²³⁸U) radionuclides.

The two main consequences of hyper-velocity sampling are: i) molecules are likely to be dissociated due to the high-enthalpy flight regime; ii) the atmospheric samples will be fractionated due to differential diffusion in the flow path. Numerical simulations [3] show that elemental and isotopic fractionations are mass-dependent and can be accounted for. Importantly, simulation results show that the isotopic ratios of xenon, due to its high mass, are little affected by fractionation. It highlights the complementarity between VATMOS-SR and the NASA DAVINCI mission with the later providing the in-situ density and the former the exquisite resolution on the isotopic ratios that is required to answer the science questions.

The VATMOS-SR mission would launch in July 2034 and would bring back the samples one year later. Samples will be distributed to European and other international partners for measurements to be performed within a couple of years after landing. This sample return mission may be the first return of a planetary sample.

[1] Avice et al. (2022) Space Science Reviews 218, 60. doi:10.1007/s11214-022-00929-9 [2] Sotin, et al. (2019) EPSC-DPS Joint Meeting 2019, EPSC–DPS2019–989. [3] Borner et al. (2025) submitted.