Out of all the places in the solar system that NASA could look for ice, you would think that the planet closest to the Sun would be way down the list. It gets up to 450 degrees during the day, there is no atmosphere, no activity, nothing.
But Mercury ‘s tilt is almost directly up, I.e., it’s North Pole points directly up out of the solar system. It’s rotation is very slow, such that its year is 1 and a half ‘days’ (and its real solar day is actually 2 of its years) so it get baked on the dayside and cooled to -150 degrees on its night side. Put all this together and frozen water ice might survive. Especially at the poles.
Now, Nasa has confirmed this by capturing the first ever pictures of water ice on Mercury. It turns out that craters near the poles can be permanently shadowed from the Sun. Scientists have long thought this might be the case especially when radio telescopes scanning the planet found strongly reflected radar signals (a good sign that ice is present).
In this most recent study, scientists examined a number of impact craters near Mercury’s north pole and found that the deposits were made surprisingly recently. “The sharp boundaries indicate that the volatile deposits at Mercury’s poles are geologically young,” wrote the study’s authors in the journal Geology, “and either are restored at the surface through an ongoing process or were delivered to the planet recently.” Now we have definitely found ice on Mercury, we have to explain how it got there.
Like every discovery, it poses more questions.