Venus: Solar storm breaks gas into space

Solar plasma tower has dramatic consequences for our neighboring planet

The atmosphere of Venus is only partially protected from the solar wind - what consequences this has in a solar storm, now reveal data from the spacecraft Venus Express. © NASA / GSFC
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Direct hit: If our neighbor planet Venus is struck by a strong solar storm, it has dramatic consequences, as revealed by the Venus Express spacecraft. The onslaught of energetic particles magnetically charges the entire ionosphere of Venus, giving it a violently flipping magnetic tail. At the same time, vast amounts of ions from deeper gas layers are sucked outwards and torn out into space.

The Earth is well armed against most solar storms because it is surrounded by a stable magnetic field. This acts as a shield against the onslaught of high-energy plasma from space. This is different with the Venus: Our inner neighbor in the solar system has no effective geodynamo and almost no own magnetic field. However: If our neighboring planet were completely unprotected, the extremely fast stream of high-energy particles would have to tear large parts of the Venus atmosphere into space. However, the planet's extremely dense gas envelope shows that this is not the case.

Only the interaction with the solar wind gives Venus a magnetized tail. © Ruslik0 / CC-by-sa 3.0

Spacecraft in a storm

The solution to the riddle is an induced magnetic field a field that arises only through the interaction of the solar wind and the ionosphere of Venus. If the charged solar wind hits the charged particles in the ionosphere of Venus, a kind of magnetic bow wave forms on the day side, on the night side a long pulled out magnetic tail. The pressure of both actors in this system is balanced so that this induced field is normally sufficient as a protective shield.

But what happens when Venus is hit by a solar storm? Qi Xu from the University of Macau and his colleagues have now examined this in more detail. They were helped by a happy coincidence. When, on 5 November 2011, a particularly strong solar storm hit Venus, the ESA Venus Express spacecraft was on the ground. She recorded how the ionosphere, magnetic field, and atmosphere of our neighboring planet responded to this hit. Xu and his team have now evaluated this data.

Magnetic barrier and a striking tail

The result: The strong solar storm had dramatic consequences for the Venus shelters. "The magnetosphere fluctuated dramatically, the bow shock was compressed by the coronal mass ejection and spread, " the researchers report. "The plasma in the magnetic tail of Venus fluttered so fast that Venus Express crossed it five times in just 1.5 minutes." In addition, formed a 250 nanotesla unusually strong magnetic barrier on the day side of the planet. display

This also had consequences for the ionosphere of Venus: This outer atmosphere layer became completely magnetized and expanded. At the same time, their density increased rapidly: "The ionosphere was so excited that its plasma density was three times greater than during calm solar wind periods, " report Xu and his team.

The space probe Venus Express recorded the consequences of the solar storm on 5 November 2011. ESA

Atmosphere escapes into space

The deciding factor, however, is that these dramatic changes will normalize again when the solar storm is over. For the atmosphere of Venus, however, there are lasting consequences, as the scientists found out. Thus, the planet loses an enormous amount of ions during the passage of such a strong solar storm on its daytime side. "Because the Venus ionosphere is so strongly excited and the entire plasma system fluctuates violently, more planetary ions are lost, " explain the researchers.

The strongly fluttering magnetic tail acts in addition like a vacuum cleaner, which sucks the ions out into space. Overall, during such an event, about 30 percent more gas particles could be taken out into space than normal, the researchers said. According to Xu and his team, "Such solar storms substantially intensify Venus's loss of atmosphere." (The Astrophysical Journal, 2019; doi: 10.3847 / 1538-4357 / ab14e1)

Source: AAS Nova

- Nadja Podbregar