Earth-type and icy moons are what we know best, but these worlds outweigh them by far.
It's easy to think of Earth as a water world, with its vast oceans and beautiful lakes, but compared to many worlds, Earth is particularly wet. Even the icy moons of Jupiter and Saturn have far more liquid water than Earth. Earth is unusual not because it has liquid water but because it has liquid water in the warm habitable zone of the Sun. And as a new study in Nature Communications shows, Earth could be even more unusual than we thought.
Water is one of the more common molecules in the universe. Hydrogen is the most abundant element in the cosmos, and oxygen is easily produced as part of the stellar CNO fusion cycle. So we would expect water-rich planets to be plentiful in stellar systems. But that isn’t to say liquid water will be plentiful. In our Solar System, two kinds of worlds have liquid water. Earth and gas giant moons.
Like other warm terrestrial planets such as Venus and Mars, Earth had liquid water in its youth. Mars was too small to retain its water. Much of it evaporated into space, while some froze into its surface crust. Venus was large enough to retain water, but its extreme heat boiled much of it off into its thick atmosphere. We still aren’t entirely sure how Earth managed to retain its oceans, but it was likely a combination of a strong magnetic field and an extra helping of water from asteroids and comets during the heavy bombardment period.
The icy moons of Jupiter and Saturn are another story. They were far enough from the Sun that they retained the water of their formation. They quickly formed a thick layer of ice to prevent water from evaporating into space. But these moons are small worlds and would have very quickly frozen solid were it not for the tidal forces exerted by their gas giant. FULL STORY from Inverse
No comments:
Post a Comment