I’m still catching up on my research after having something of a rough start to the year. A few months ago, I saw headlines saying that water had been discovered in the TRAPPIST-1 system. A whole lot of water. Too much water, in fact. Normally where there’s water there could be life, but according to the news articles I read back in February, the TRAPPIST-1 planets have so much water that life probably could not exist there (not enough carbon, not enough minerals).
But now I’ve finally read the actual research, and I’m really glad I did because a lot of journalists in the popular press clearly did not. This paper, titled “Inward Migration of the TRAPPIST-1 Planets as Inferred From Their Water-Rich Compositions,” ends thusly:
[…] while these planets may be habitable in the classical definition, any biosignature observed from these planets system may not be fully distinguishable from abiotic, purely geochemical sources. Thus, while M-dwarfs may be the most common habitable planet-host in our Galaxy, they may be the toughest on which to detect life.
In other words, these planets very well might be able to support life, but we may not be able to detect that life if it’s there.
This reminds me of a paper Carl Sagan wrote in the 1990’s showing how difficult it is to conclusively prove there is life on Earth based solely on observations made by a passing NASA spacecraft.
Earth’s oceans in particular do an outstanding job masking the usual biosignatures we would be looking for. As far as that NASA spacecraft could tell, Earth’s oceans appeared to be completely lifeless.
So if the planets of the TRAPPIST-1 system really are as that inward migration paper describes them—15% to 50% water, with their surfaces covered entirely by ocean—then we are going to have a really difficult time finding life there. But that is not the same as saying there’s no life there to find!