With new scientific discoveries, recent flybys and future missions planned, are we about to finally unlock the secrets of the hellish planet? Planetary scientist Emily Lakdawalla investigates
Venus is in the hot seat this year: NASA and ESA recently announced three new missions to our nearest planetary neighbour, and another two have just flown past on their way to different destinations. Back in August, ESA’s Solar Orbiter and the ESA-JAXA collaboration, BepiColombo, performed gravity-assist flybys, marking the first time since 1985 that three spacecraft have made in-situ scientific observations at Venus at the same time. (The third JAXA’s Akatsuki, has been in orbit since December 2015.)
Solar Orbiter is, obviously, a mission to study the Sun, not planets, so most of its cameras are useless at Venus. Most of BepiColombo’s sensitive cameras can’t see space during its long cruise to Mercury. But both spacecraft carry large suites of instruments designed to measure the intensity and direction of magnetic fields and other instruments that count the number and energy of charged particles (electrons, ions and larger particles). BepiColombo also carries an accelerometer that measures variations in the force of gravity as the spacecraft flies across a planet, giving clues to the composition of its mysterious interior.
Across the bow
Venus doesn’t have its own magnetic field, but the Sun induces one. As the solar wind streams outwards Venus’s field cuts a bow shock into it, similar to the wake from a speedboat. Both BepiColombo and Solar Orbiter approached Venus from within Venus’s ‘wake’, crossing over the bow shock near the time of closest
approach. Solar Orbiter travelled the path 33 hours before BepiColombo. Having three different spacecraft travelling across large swaths of the magnetic field at the same time in different positions will have produced a rich set of science data and will help ESA plan its future EnVision mission to the planet (due to launch in the 2030s).
The two spacecraft passed by Venus on different sides. The result was an acceleration of Solar Orbiter, speeding it on towards a November flyby of Earth and the beginning of its science mission. BepiColombo lost speed, dropping it closer to the Sun. It was due to meet Mercury in October this year, the first of six flybys before it gets captured on the seventh meeting in December 2025.
Back on Earth, scientists are still publishing new results from ESA’s Venus Express mission, which ended in January 2015, and are studying our neighbour with ground telescopes. In 2020, astronomers announced they’d detected phosphine in Venus’s atmosphere using the ALMA observatory. This could be a sign of life in the clouds, or could have spewed from volcanoes. Researchers at Portugal’s Instituto de Astrofísica e Ciências do Espaço (IA) recently published a new General Circulation Model for Venus, a computer model of the atmosphere that’s the necessary foundation for all predictions of weather and climate. The work focuses on a largely unexplored region of the atmosphere: a layer between the cloudy troposphere and the Sun-heated thermosphere. It explains some previously mysterious data from Venus Express, but more importantly, it generates new, detailed predictions for EnVision to test with observations.
We’re getting better at predicting the motions of Venus’s winds and clouds, but there’s a lot we don’t understand. What drives its winds? What’s happening below the clouds? Are there active volcanoes today? Why is its atmosphere so thick and choked with carbon dioxide? Did Venus once have liquid water and temperate surface conditions? And what can Venus’s conditions today tell us about the future for Earth?
Action, Akatsuki!
Japan’s probe is exploring Venus’s atmosphere and producing valuable images along the way
Akatsuki’s (see inset) infrared camera IR2 could see the warmth emanating from the clear air under Venus’s clouds at night. In this image, Venus’s nightside is at left (the dayside was too bright and has been masked). Brighter areas show where the lowest cloud decks are thick; in darker regions, the camera can ‘see’ more clear air, but not all the way to the surface.
Akatsuki’s Ultraviolet Imager (UVI) sees Venus’s uppermost clouds, made of drops of sulphuric acid. The dark streaks betray the presence of an unknown chemical that scientists call an ‘ultraviolet absorber’.
Perhaps EnVision will identify it. At the altitude of the clouds seen here, Venus’s atmosphere rotates around the planet once every four days.
Peering beneath the clouds
How Venus’s atmosphere compares to Earth’s
Venus’s atmosphere is much taller than Earth’s, and various exploratory spacecraft that have visited the planet have used scientific instruments to peer through the atmosphere to different depths, giving us detailed information about Venus’s sky and thick cloud decks. However, we have much yet to learn. What might future missions reveal about the ground underneath?
Emily Lakdawalla is a planetary scientist, writer and science communicator