The Exploration of Venus

Home , European Venus Explorer, Venera

Moon 1950s 13 Venus 1960s 18 1960s 63 1970s 10 1970s 22 1980s 7 1980s 0 1990s 0 1990s 4 2000s 1 2000s 11 2010s 1 2010s 13

im a g e cre dit: Éder Ivá n

82% Earth mass

95% Earth radius

0 .72 A U

Goldstone (1962) retrograde rotation

Mariner 2 (1962) h igh temperatures in lower atm osp h ere n o resolvable m a g n etic field

96.5% C O 2

high D/H ratio

super- rotating atmosphere

g lobal cloud layer Vega balloons (1985) highly variable atmospheric co nditions H 2SO4 clouds Earth- like co nditions ~50–65 km

Venera 13 and 14 (1982) photos of the surface sedimentary- like rocks

first recording of sound on another planet

740 K, 93 bar basaltic lithology

g round im a g e cre dit: M attia s M alm er

a world without mod ern plate tectonics differentiated interior Magellan (1990 ) near- g lobal image and topographic co verage thicker crust for some high - standing terrain

some volcanic regions co rrespond to upw elling

deeply co mpensated lowlands suggest downw elling

im a g e cre dit: N a tion a l Geog raphic

distribution indistinguishable from random

Magellan (1990 ) no C aloris/SPA/H ellas ~900 identified craters none few er than ~3 km in diameter

Venus Express (2006) detection of transient hotsp ots high emissivity may d enote recent lavas

active volcanism?

temporally variable S O 2

im a g e cre dit: hd-wallpapersdown load.com

evid ence for lateral motion

Magellan (1990 ) w idesp read tectonic deformation more deformation than Mercury, Mars, or the Moon

what did early Venus look like?

Mariner 5 (1967) P ioneer Venus (1978) p ossib le loss of atmospheric w ater

formerly present o ceans?

im a g e cre dit: N ASA/G SFC

highly deformed terrain

stratigraphically oldest material

Venera 8 (1972) elevated radiogenic element abundances

do these planets have a shared history?

if not, why not?

when did their paths diverge?

im a g e cre dit: N ASA/G SFC

co mposition of surface materials

co mposition, evolution structure (and activity) of the atmosphere of the interior

…but also in terms of how it compares with other worlds, b ecause :

Venus w ill help us understand the rules that govern Earth -like worlds

European Venus Explorer (EVE): a balloon mission in the heart of the habitable layer

• Helium superpressure balloon, 53-57 km float altitude. • Follows heritage of French/Soviet Vega balloons (1984)

• Benefit from benign climate: 10 – 50 °C, atmospheric densities like those found at 0 to 5 km altitude on Earth. • Ideal platform for trace gas mass spectrometry (thermally stable)

• Explore clouds of liquid water (albeit mixed with sulphuric acid).

• Use high winds of 200-250 km/h to circumnavigate the planet in 5-8 days.

T. Balint a pathway to surface operations

1. Short-duration (~ 1 hr) Venera-style landers

2. High-temperature ambient-temperature landers

3. Mobile robotics EnVision Venus orbiter

Finallist in ESA’s M5 Space Science mission competition Strong NASA participation (being defined) Currently entering phase A study (2019-2021) Selection expected summer 2021. Launch in 2032 Aerobraking 2033 - 2035 Nominal science mission 2035-2038

Three science themes Activity – How geologically active is Venus today? History – How have Venus’ surface and interior evolved? Climate – How did Venus’ atmosphere become so hostile? EnVision radar: the value of spatial resolution

• Radar has come a long way since the 1980s when Magellan radar was developed. • Magellan radar spatial resolution was 100 m at best. • Modern radar could enable spatial resolution approaching 1 – 5 m. • Modern radar has lower noise, better radiometric resolution,  clearer imagery.

Mars at 150 m/pxl (Viking) 20 m / pxl (MGS) 1 m/pxl (MRO) EnVision : much more than just high-res radar EnVision science payload

VenSpec-U Mapping SO, SO2 and UV absorber at cloud top. 210–240 nm (@ 0·2 nm), 190–380 nm (@ 2 nm), ~10 km spatial resolution VenSpec-H Mapping of near surface atmosphere H2O, HDO at 0–15 km @1·08–1·2 μm, H2O, HDO, OCS, SO2 at 30–40 km @ 2·44–2·47 μm, ~100 km spatial resolution VenSpec-M Mapping mineralogy by surface emission at 6 channels 0·82– 1·2 μm at <50 km resolution VenSAR Surface morphology, 1–30 m, polarimetry, cm changes by DInSAR @ 3·2 GHz, 5 × 38 km radiometry at 1 K precision, SRS Subsurface radar down to 1000 m depth and ~10 m resolution @ 9 MHz Radio Science Two-way mapping, radio occultations, gravity field, k₂ love number base image © C. Hamilton

EnVision warmly invites your participation and support. More information: www.envisionvenus.eu Lead proposer: Richard Ghail (Royal Holloway) Deputy Leads: Colin Wilson (Oxford U) & Thomas Widemann (Paris Obs)