Mercury, the closest planet to our Sun, may actually have deposits of water ice.
That's according to new data from NASA's MESSENGER space probe, which scanned for signs of water ice in some of the planet's permanently-shadowed craters.
MESSENGER found evidence of of hydrogen-rich layers "tens of centimetres thick."
"The buried layer has a hydrogen content consistent with nearly pure water ice," David Lawrence, one of the lead scientists on the project, said in a release.
Although the planet is first in line from the Sun, it's actually not the hottest.
Venus holds that crown, with a surface temperature pushed up past the 460C mark by a runaway greenhouse effect.
Still, Mercury's daytime high is still a little over the 400C mark, but the presence of water ice has been suspected for decades.
As the planet orbits the sun, its rotational tilt is less than one degree, meaning parts of the polar regions never see sunlight.
With almost no atmosphere to hold in heat, and very long nights, temperatures on the planet's dark side can plunge to less than -170C.
NASA says the new findings raise more questions -- including whether it's possible Mercury may be harbouring liquid water.