Mars is, largely, a cold, dead world. There’s still some water left at the poles and in the thin air, but for the most part Mars appears quite dry. It wasn’t always this way, however. Billions of years ago, scientists think, Mars was covered in water—peppered with lakes, or maybe even large oceans.
These images show the planet on the last day of Martian spring in the northern hemisphere (just before summer solstice). The annual north polar carbon dioxide frost (dry ice) cap is rapidly sublimating, revealing the much smaller permanent water ice cap.
Yet today most of that water is gone. Researchers think that over the past few billion years the red planet’s water was probably blown off into space, carried away by the solar wind with the planet’s disappearing atmosphere. But new evidence drawn from meteorites here on Earth chunks of Mars that had been blasted into space suggests that Mars might also have vast underground reservoirs. Read more
