A new study has recently revealed that magnetospheres plays vital role in protecting planets from even small solar eruptions, which can cause significant damages to the planet.
The interplay between the Sun and Earth was crucial for making the planet livable, a balance between a sun that provides energy and a planet that can protect itself from the harshest solar emissions. The sun steadily emits light, energy and a constant flow of particles called the solar wind that bathes the planets as it travels out into space.
Larger eruptions of solar material, called coronal mass ejections, or CMEs, occur too, which can disrupt the atmosphere around a planet. On Earth, some of the impact of these CMEs is deflected by a natural magnetic bubble called the magnetosphere.
But some planets, such as Venus, don't have protective magnetospheres and this can be bad news. On Dec. 19, 2006, the sun ejected a small, slow-moving puff of solar material. Four days later, this sluggish CME was nevertheless powerful enough to rip away dramatic amounts of oxygen out of Venus' atmosphere and send it out into space, where it was lost forever.
Learning just why a small CME had such a strong impact may have profound consequences for understanding what makes a planet hospitable for life.
Scientists divided CMEs into two broad categories: those fast enough to drive a shock wave in front of them as they barrel away from the sun, and those that move more slowly, like a fog rolling in. Fast CMEs have been observed at other planets and are known to affect atmospheric escape, but no one has previously observed what a slow one could do.
Similarly, the effects of the small CME built up over time, ripping off part of Venus's atmosphere and pulling it out into space. This observation doesn't prove that every small CME would have such an effect, but makes it clear that such a thing was possible.
That, in turn, suggested that without a magnetosphere a planet's atmosphere was intensely vulnerable to space weather events from the sun.
Venus was a particularly inhospitable planet: It is 10 times hotter than Earth with an atmosphere so thick that the longest any spacecraft has survived on its surface before being crushed is a little over two hours. Perhaps such vulnerabilities to the sun's storms contributed to this environment.
Regardless, understanding exactly what effect the lack of a magnetosphere has on a planet like Venus could help us understand more about the habitability of other planets we spot outside our solar system.
The researchers examined their data further to see if they could determine what mechanism was driving off the atmosphere. The incoming CME had clearly pushed in the front nose - the bow shock - of the atmosphere around Venus. The scientists also observed waves within the bow shock that were 100 times more powerful than what's normally present.
The team developed three possibilities for the mechanism that drove the oxygen into space. First, even a slow CME increases the pressure of the solar wind, which might have disrupted the normal flow of the atmosphere around the planet from front to back, instead forcing it out into space.
A second possibility was that the magnetic fields traveling with the CME changed the magnetic fields that are normally induced around Venus by the solar wind to a configuration that can cause atmospheric outflow. Or, third, the waves inside Venus' bowshock may have carried off particles as they moved.
The study is published in the Journal of Geophysical Research.
