Martian Spring

Spring is just about to give way to summer here in the northern hemisphere. In the northern hemisphere of Mars, though, spring is just beginning. In fact, today is the spring equinox.
For the most part, Mars has seasons for the same reason that Earth does — the planet is tilted on its axis. So as Mars orbits the Sun, its northern and southern hemispheres take turns receiving more sunlight.
Right now, Mars is tilted at about 25 degrees — almost the same angle as Earth. But that hasn’t always been the case. Over a period of a hundred thousand years or so, its tilt can vary dramatically.
At times, the planet’s axis can stand almost straight up and down. At that angle, every point on the planet receives about the same amount of sunlight every day of the year.
In that configuration, the polar ice caps get thicker and thicker. Most of the carbon dioxide in the atmosphere freezes onto the ice caps, so the atmosphere gets much thinner.
At the other extreme, Mars may be tilted about two-thirds