April 12 () –
A brief visit by the ESA/JAXA BepiColombo mission to Venus has revealed surprising insights into how gases are removed from the upper layers of the planet's atmosphere.
The detections in a previously unexplored region of Venus' magnetic environment They show that carbon and oxygen are being accelerated to speeds that allow them to escape the planet's gravitational pull. The results have been published in Nature Astronomy.
Lina Hadid, CNRS researcher at the Laboratory for Plasma Physics (LPP) and lead author of the study, said: “This is the first time that positively charged carbon ions have been observed escaping from the atmosphere of Venus. These are heavy ions “So we're still trying to understand the mechanisms at play. “It may be that an electrostatic 'wind' is blowing them away from the planet, or they could be accelerated by centrifugal processes.”
Unlike Earth, Venus does not generate an intrinsic magnetic field in its core. However, a weak comet-shaped 'induced magnetosphere' is created around the planet by the interaction of charged particles emitted by the sun (the solar wind) with electrically charged particles in the upper atmosphere of Venus. Around the magnetosphere is a region called the “magnetic envelope,” where the solar wind slows down and heats up.
On August 10, 2021, BepiColombo passed by Venus to slow down and adjust course toward its final destination, Mercury. The spacecraft swooped down the long tail of Venus' magnetic pod and emerged out the nose of the magnetic regions closest to the sun. During a 90-minute observation period, BepiColombo's instruments measured the number and mass of charged particles they found, capturing information about the chemical and physical processes that drive atmospheric escape on the flank of the magnetic sheath.
Early in its history, Venus had many similarities to Earth, including significant amounts of liquid water. Interactions with the solar wind have removed water, leaving an atmosphere composed primarily of carbon dioxide and smaller amounts of nitrogen and other trace species.
Previous missions, including NASA's Pioneer Venus Orbiter and ESA's Venus Express, have carried out detailed studies of the type and quantity of molecules and charged particles that are lost in space. However, the missions' orbital trajectories left some areas around Venus unexplored and many questions still unanswered.
Data for the study were obtained by BepiColombo's Mass Spectrum Analyzer (MSA) and Mercury Ion Analyzer (MIA) during the spacecraft's second flyby of Venus. The two sensors are part of the Mercury Plasma Particle Experiment (MPPE) instrument suite, carried by Mio, the JAXA-led Mercury Magnetospheric Orbiter.
“Characterizing the loss of heavy ions and understanding the escape mechanisms on Venus is crucial to understanding how the planet's atmosphere has evolved and how it has lost all its water,” he said. it's a statement Dominique Delcourt, LPP researcher and principal investigator of the MSA instrument.
Europlanet's SPIDER space weather modeling tools allowed researchers to track how particles propagated through Venus' magnetic envelope.
“This result shows the unique results that can arise from measurements made during planetary flybys, where the spacecraft can move through regions generally unreachable by orbiting spacecraft“said Nicolas André, from the Institut de Recherche en Astrophysique et Planétagie (IRAP) and leader of the SPIDER service.
A fleet of spacecraft will investigate Venus over the next decade, including ESA's Envision mission, NASA's VERITAS orbiter and DAVINCI probe, and India's Shukrayaan orbiter. Together, these spacecraft will provide a complete picture of Venus' environment, from the magnetic envelope, through the atmosphere to the surface and interior.
“The recent results suggest that atmospheric escape from Venus cannot fully explain the loss of its historical water content. “This study is an important step in uncovering the truth about the historical evolution of the Venusian atmosphere, and upcoming missions will help fill many gaps,” added co-author Moa Persson of the Swedish Institute for Space Physics.
