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Moon and Mars
This may sound a bit odd, but planetary scientists say it’s true. Since the last ice age ended on Mars, more than 20,000 cubic miles of ice have been added to the planet’s polar ice caps. And more is being added even today.
Here on Earth, the ice caps get bigger during an ice age. On Mars, though, the ice caps get smaller, while ice forms closer to the equator.
That’s because Martian ice ages are caused by a big change in the planet’s tilt on its axis. Right now, the tilt is almost the same as Earth’s. A couple of million years ago, however, Mars was tilted more severely — perhaps almost over on its side. That meant that the Sun was shining down on the planet’s poles. The solar heat vaporized much of the ice caps.
The water vapor froze back onto the surface at latitudes close to the equator, where there was much less sunlight to warm the surface. So instead of white “caps” at its poles, Mars probably had a “belt” of white around its middle.
That ice age ended about 400,000 years ago, when the planet’s tilt changed to roughly its current angle. So the polar ice caps have been getting thicker ever since. Radar aboard a Mars orbiter recently confirmed that scenario by peering deep into the northern ice cap — seeing layers of ice added over millions of years of Martian history.
Look for Mars to the lower left of the Moon this evening, shining like a bright orange star — a cold world that’s emerging from an even colder past.