Winter in the northern hemisphere is synonymous with snow (at least in films and Victorian novels). The Earth is unusual because it has water can commonly be found on its surface in solid, liquid and gas form, and both solid and liquid water can rain/snow/sleet/drizzle from the sky. So what happens on other bodies in the solar system?
Most water on the surface of Mars is now trapped in its glaciers/ice caps, but what about snow? Whilst there is less water vapour in the Martian atmosphere than the Earth’s, Mars still has clouds made of ice crystals. These ice crystals can fall slowly out of the sky, but at night under the right conditions, snowstorms can occur. Most of this snow will vaporise before it hits the ground, and any that do make it to the ground will likely vaporise during the day.
Venus has the hottest surface temperature of any planet in the solar system. Water snow is not possible. The atmosphere of Venus contains lots of sulphur and temperatures hot enough to melt lead, it is so thick we can’t see the surface of the planet so we have collected radar data to understand what it looks like. One feature of this data is that on the tops of some high mountains there is an increase in the number of radio waves reflected, giving the appearance that the tops of mountains are brighter, just as snow on the top of mountains is brighter than the surrounding rock.
Whilst it is far too hot for snow on Venus, it is thought that these mountain tops are covered in a form of frost caused by metal sulphides, which forms only at high elevations and it’s this which makes is appear more reflective to radar.
Mercury, my main planet of study, doesn’t have snow-capped peaks, being too hot over the majority of the planet and no atmosphere. So the nearest feature to snow is ice in the craters close to the north and south poles, these craters are permanently in shadow protecting the ice from the boiling Sun. Without an atmosphere there isn’t any form of precipitation other than a daily micrometeorite shower.
Titan, a moon of Saturn is much to far out from the Sun to have water snow, and any water near the surface, just like in the bleak midwinter, is like a stone. It does snow on Titan, near the poles hydrocarbons can crystallize out in the atmosphere and then fall as snow down onto the surface.
Another moon of Saturn, Enceladus, is probably the most visually spectacular example, geysers on the south pole can be seen erupting water vapour into space. Some of this water is lost in orbit and forming the E ring of Saturn, but some of the water falls back down onto the surface as ice crystals. As this fall back it is happening without an atmosphere it doesn’t really count as snow but is a great excuse to show the stunning photos of the plumes.
There are lots of forms of snow around the solar system however maybe Earth still has some of the best snow views in the solar system. Happy Christmas/ Winter Solstice/ Saturnalia to all my readers!