Even in our own solar system, he says, there are reasons for believing that the picture is more complicated. Yesterday, we mentioned a recent finding that rocky alien planets orbiting red dwarfs (the favored sites for exoplanet life) might in fact feature too extreme temperatures, based on recent research on one of them (–273 degrees Celsius on the night side and 767 degrees C on the day side, which implies little or no atmosphere to moderate it.).
Anyway, our physics color commentator offers some thoughts:
This report is about the Holy Grail of exoplanets–finding a planet with liquid water on it. So far, the thinking goes, a planet has to orbit its host star at just the right distance so that the temperature is between the freezing and boiling point of water. This “Goldilocks Zone” is further away for big hot stars, and close in for small cool stars. Most stars in our galaxy are smaller/cooler than our Sun, so there are better chances of finding a planet in the GZ for these “red dwarf” stars. Indeed, this is exactly what the planet finder mission is discovering.
But the kicker is that when a planet is very close to its host star, the tidal forces are also much greater. It is tidal forces that lock our Moon’s rotation so that only one side ever faces the Earth. The same thing happens to planets orbiting a red dwarf–only one side ever faces the star, and that side gets hot, too hot for water, whereas the dark side gets too cold for liquid water.
Some optimists had theorized that if such a planet had a thick atmosphere with strong winds, then the heat could be distributed to the cold/dark side, and perhaps liquid water could still exist. So this paper takes a hard look at one such planet as it orbits its star, and tries to measure the temperature. As far as they can tell, the planet’s dark side is the temperature of space (4K), while the hot side is 1000K (or 750C). It doesn’t look promising for water.
What I find odd, is that in our own solar system, Saturn is far outside the “Goldilocks Zone” yet it has a moon, Enceladus, that is emitting steam jets filled with hydrocarbons. So this fixation on GZ seems overrated. Or to say it differently, life can live in far more extreme environments than the astrobiology community want to consider. It is almost as if this fixation with the GZ is intended to turn a qualitative observation into a quantitative field worthy of funding. The danger of being overly-quantitative is not just the overreliance on models, or the higher risk of failure, but rather the real probability that “certainty” blinds one from observing the actual phenomenon.
It’s not what you don’t know that hurts you, it’s what you do know that ain’t so.
Rob Sheldon is the author of Genesis: The Long Ascent
See also: Bad news about life on rocky alien planets.
Kreidberg’s team estimated that the promising planet had temperatures of –273 degrees Celsius on the night side and 767 degrees C on the day side, which implies little or no atmosphere to moderate it.