11 Nov 2020

On 13 November, Moa Persson, Institute for Space Physics, IRF, and Umeå University will defend their doctoral dissertation which shows that only a small part of Venus' historical water volume has flowed from Venus to space in the last 4 billion years. It is much smaller than researchers previously thought.

The dissertation is based on analyzes of how the solar wind, a stream of charged particles from the sun, affects Venus' atmosphere and contributes to particles escaping from the atmosphere to space. Moa Persson has analyzed data from the IRF's space instrument ASPERA-4 which was on board the European space agency ESA's space probe Venus Express.

Venus' surface can today be compared to hell because it is extremely dry and has a temperature of 460 degrees, but historically the surface was more hospitable and probably had such a large amount of water that it could create a water depth of up to several hundred meters. The water must have disappeared in some way. My dissertation shows that only a few decimetres of the water have disappeared into space, ”says Moa Persson.

The studies are based on measurements of ions (charged particles) around Venus. On average, two hydrogen ions for each oxygen ion flow out of the atmosphere, indicating a flight of water. The variation in solar wind and solar radiation affects how many ions escape.

Moa Persson's dissertation shows that the amount of hydrogen ions escaping from the atmosphere varies over the solar cycle and decreases from solar minimum to solar maximum. The decrease is due to the fact that a larger part of the hydrogen ions return to Venus. The flight of oxygen ions is mainly affected by variations in the solar wind.

"In my dissertation, I have calculated how much water has escaped from Venus by assuming how the solar wind affects the flight of ions today and how the solar wind has changed over time," says Moa Persson.

The results of the dissertation can be compared with similar studies of ion flight at Mars and Earth. Such comparisons can provide a more comprehensive picture of the solar wind's impact on atmospheres. Earth, with its strong magnetic field, for example, has been shown to have a greater flight of particles from the atmosphere than both Venus and Mars.

" I hope that more studies will be done on the atmospheres of Venus, Earth and Mars and how the solar wind has affected their evolution. It is especially interesting now that we have found signs that there may be life on Venus, ” says Moa Persson.

Skövde-born Moa Persson defends her dissertation "Escape to Space or Return to Venus: Ion Flows measured by Venus Express" ("Escape to space or return to Venus: Ion flows measured by Venus Express") in the IRF's auditorium at the Space Campus in Kiruna on Friday November 13. The opponent is Dr. Dmitry Titov, from ESTEC / ESA in Noordwijk, the Netherlands. 

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Moa Persson from Skövde shows in her doctoral dissertation that surprisingly little water has flowed into space from the planet Venus. She has analyzed data from the IRF's space instrument on board ESA's Venus Express spacecraft.