Martian Christmas Crystals
December 25, 2006
Earth and Mars are the only planets in our solar system having polar ice caps that expand and contract in response to changes in the seasons. On Earth, the polar caps are composed of water-ice (snow crystals). However, on Mars, the extreme low temperatures at the polar cap regions result in the precipitation of frozen carbon dioxide crystals (Martian snow/frost). On Mars north polar cap, water-ice snow is also known to occur (based on results from spectral observations). The carbon dioxide crystals shown above were produced in the cold stage of a Scanning Electron Microscope (SEM). Compared to 6-sided hexagonal snow crystals, frozen carbon dioxide crystals are 8-sided octahedrons (bi-pyramid form). They're also considerably smaller than the snow crystals we're most familiar with. One other thing, they don't dress-up store windows as nicely during the holidays.
It's not known whether or not Old Santa wears a little green suit on Mars, but his coursers should have a relatively easy time getting airborne -- escape velocity on Mars is less than 1/2 of that for Earth.
Merry Christmas and Happy Holidays!
Jim Foster and Martin Ruzek