This is Mars as it might have appeared during the height of its last ice age!
Of all planets in the Solar System, Mars has the climate most like ours. Both Mars and Earth are sensitive to small changes in the shape of its orbit and the tilt of its axis.
On Earth, when the axis tilts more, the poles warm up and ice ages end
. But a 2003 paper in Nature
did simulations and found that Mars works the other way! When its axis tilts more, the poles warm up, and the polar ice caps start to evaporate... bringing more water to the whole planet. But since Mars is below freezing most of the time, that brings ice
all the way down to 30° latitude in both hemispheres, as shown here.
From about 2.1 million to 400,000 years ago, the increased tilt of Mars' axis made its poles warmer. But the tilt has been less since then. This is making the poles colder, so water vapor has been leaving the zone between 30° and 60° latitude, and collecting in the ice caps.
If you haven't read Kim Stanley Robinson's trilogy Red Mars
, Green Mars
, Blue Mars
, you really should. It's a sprawling tale of the terraforming of Mars, packed with fascinating digressions. Now I want White Mars
The photo is from here:http://photojournal.jpl.nasa.gov/catalog/PIA04933
It was prepared for the December 18, 2003, cover of the journal Nature
. The simulated surface deposit is superposed on a map based on altitude measurements by Global Surveyor and images from NASA's Viking orbiters of the 1970s.
The paper is here:
• James W. Head, John F. Mustard, Mikhail A. Kreslavsky, Ralph E. Milliken and David R. Marchant, Recent ice ages on Mars, Nature 426
(18 December 2003), 797-802.#spnetwork