'Mirage Planets' May Convince Us They're Habitable Long After Their Oceans Have Burned Away
In the search for extraterrestrial life, liquid water is essentially the holy grail. Life can be found on Earth almost everywhere that there is liquid water, and it has been all but assumed that the presence of liquid water is the most important criterion for a planet's habitability. Indeed, astronomers have found several "Earth-like" exoplanets recently, all of which seem to be habitable because they appear to potentially have a watery environment. But now, a new study from the University of Washington claims that some of these planets may be "mirage planets," or planets that manage to trick us into thinking they're habitable, but have actually been dry and lifeless for millions of years.
Astrobiologists often focus on red dwarf stars when searching for life on other planets, primarily because red dwarfs are many times dimmer than our Sun, and therefore their planets can be much closer to them than Earth is to the Sun and still support life. But according to the newest computer simulations, red dwarfs also have the disadvantage of being many times brighter and hotter early in their lives than they are when we observe them. If the planets around them formed while they were still in this hotter stage, then their oceans would likely have burned up long before now.
According to lead study author Rodrigo Luger, "Planets around these stars can form within 10 million years, so they are around when the stars are still extremely bright. And that's not good for habitability, since these planets are going to initially be very hot, with surface temperatures in excess of 1,000 degrees Celsius [1,832 degrees Fahrenheit]. When this happens, your oceans boil and your entire atmosphere becomes steam."
But these planets may be more problematic in our search for extraterrestrial life than other uninhabitable planets, because they may be able to convince us that they're inhabitable. Another marker we use to judge a planet's habitability is the amount of oxygen in the atmosphere, and the high-energy radiation emitted from red dwarf stars may split the water atoms from the boiled oceans into hydrogen and oxygen, leaving the atmosphere saturated with an incredibly high concentration of oxygen.
Luger added, "Because of the oxygen they build up, they could look a lot like Earth from afar, but if you look more closely, you'll find that they're really a mirage - there's just no water there. So, not only are these planets uninhabitable, but they can actually trick us into thinking they're inhabited."
Luger insisted, however, that further research is necessary to confirm the results of this study. And even if they are confirmed, it doesn't necessarily lead to any dire sweeping conclusions about the habitability of red dwarf star planets. "Although [these processes] threaten the habitability of planets around low-mass stars, it certainly does not rule it out. There's just so much we don't understand about habitability and the origin of life that it would be premature to draw any strong conclusions."