No one knows for sure what constitutes a “habitable planet”. After all, at this point, we have only one example to work with. However, there are many places in our solar system where life might exist and there are billions of solar systems out there that we can look at.
While we might not know what is “habitable” researchers are constantly working on what might make one planet more or less habitable than another. If nothing else this could make the process less random and help scientists to focus on the best candidates.
The latest research, from NASA and the European Space Agency (ESA), published in the Journal of Geophysical Research focused on the role of a magnetosphere in protecting planets from solar winds.
The relationship between a planet and its sun is obviously important. Life, as we know it, requires some heat but not too much. Beyond light and heat however, the sun also emits a constant flow of particles called the solar wind. This wind washes over everything in its path on its route to deep space.
The sun also periodically erupts in a coronal mass ejection (CME). On Earth the planets magnetosphere protects the planet from the solar winds and the CMEs, but particularly severe ones can still disrupt communication systems.
Some planets, such as Venus, don’t have a magnetosphere and this can have disastrous consequences.
According to researchers, on December 19, 2006 a small, slow moving CME was observed ripping large amounts of oxygen from the atmosphere of Venus and pulling it into space.
“What if Earth didn’t have that protective magnetosphere? Is a magnetosphere a prerequisite for a planet to support life? The jury is still out on that, but we examine such questions by looking at planets without magnetospheres, like Venus,” said Glyn Collinson, first author on the paper at NASA’s Goddard Space Flight Center in Greenbelt, Maryland in a statement.
Collinson began by examining data from the ESA’s Venus Express, which visited Venus for 8 years beginning in 2006. Collision found that on December 23, 2006 the atmosphere of Venus leaked oxygen at a near-record density. The data showed that something unusual was happening with the solar wind at the same time.
Next Collinson recruited Lan Jian of NASA Goddard who specializes in solar wind events. Looking at historical data, Jian found the weak CME that occurred on December 19, just four days before the event on Venus.
For the event to be related it would have required the solar winds to move at 200 miles per second, which is extremely slow for a CME.
CMEs fall into two categories, those fast enough to move a shockwave in front of them and those that move “like a fog rolling in”. Fast CME’s have been observed at planets other than Earth, slow CMEs have not.
“The sun coughed out a CME that was fairly unimpressive. But the planet reacted as if it had been hit by something massive. It turns out it’s like the difference between putting a lobster in boiling water, versus putting it in cold water and heating it up slowly. Either way it doesn’t go well for the lobster,” said Collinson.
The researchers think that the effects of the small ‘fog-like’ CME built up over time, dragging prt of Venus’s atmosphere into space. The research doesn’t show that such an event would occur with every small CME, only that it is a possible effect.
This, in turn, makes it less likely that a planet without a magnetosphere would be habitable in any way that we understand.
Venus, it should be noted, was not high on the ‘hospitable’ list to begin with. Venus is 10 times hotter than the Earth, with a poisonous atmosphere so dense that no spacecraft has survived on the planets surface for more than two hours. It is not known how much the lack of magnetosphere and CMEs contributed to this harsh environment.
