When it snows on Earth, it can be one of the most beautiful, magical sights, or it can signal the onset of traffic chaos and school closures!
But what about snow beyond Earth? One place scientists are sure it snows is Mars, although it isn't the same sort of snow that we experience on Earth.
Mars has four seasons, just like Earth, which means it has winter too, just like Earth.
But Mars's orbit is twice as long as Earth's – it takes about 687 days to go around the Sun – despite a Martian day being about the same as an Earth day.
That lengthy orbit means Mars's seasons last twice as long as Earth's
Winter on Mars sees snow, ice and frost arrive as the Red Planet is plunged into extreme cold.
If you thought Earth's winters were bad, well temperatures on Mars can plummet down to -123°C (-190° F) at the planet's poles.
What snow is like on Mars
Snow on Mars is well documented, using data captured by the rovers and orbiters that have been exploring the Red Planet for decades.
Martian snow is made up of water ice and carbon dioxide, or dry ice, according to NASA.
And it doesn't form thick layers of snow like we see in the coldest places on Earth: instead water-ice snow becomes a gas before it even touches the ground – it sublimates – because Mars's atmosphere is so thin.
Dry-ice snow on Mars does hit the ground, though.
"Enough snow falls that you could snowshoe across it," says Sylvain Piqueux, a planetary scientist at NASA’s Jet Propulsion Laboratory in Southern California.
"If you were looking for skiing, though, you’d have to go into a crater or cliffside, where snow could build up on a sloped surface."
Where it snows on Mars
NASA says it only snows on Mars at the planet's poles, when there's enough cloud cover and when it's pointed away from the Sun. In other words, at night.
There are plenty of images online showing snow and frost on Mars, as you can see in this article.
But why are there no pictures of it actually snowing on Mars?
NASA says it's because rovers on the surface can't get to the regions of Mars where snow would be falling.
And, frustratingly, cloud cover makes it rather tricky for Mars orbiters to see snowfall happen in real time.
How we know it snows on Mars
NASA’s Mars Reconnaissance Orbiter has been able to detect carbon dioxide snow falling on Mars, however.
It's equipped with an instrument called the Mars Climate Sounder that can see wavelengths of light beyond what the human eye can see.
This has enabled it to peer through the clouds and detect CO2 snowfall.
And in 2008, a team of scientists used NASA's Phoenix lander to detect snow falling from Martian clouds.
A laser instrument on Phoenix designed to study interactions between Mars's surface and its atmosphere detected snow falling from clouds about 4km (2.5 miles) above its landing site.
Data showed the snow vaporising before reaching the ground, leading mission scientist Jim Whiteway, of York University, Toronto, to proclaim: "Nothing like this view has ever been seen on Mars."
Snowflakes shaped like cubes
Dry-ice snowflakes on Mars are cube-shaped and smaller than the width of a human hair, according to planetary scientist Sylvain Piqueux.
This is to do with how water molecules bond when they freeze, NASA says. And while snowflakes on Earth have six sides, snowflakes on Mars have four.
"Because carbon dioxide ice has a symmetry of four, we know dry-ice snowflakes would be cube-shaped," Piqueux says.
"Thanks to the Mars Climate Sounder, we can tell these snowflakes would be smaller than the width of a human hair."
Frost on Mars
Frost on Mars is much more common and widely-documented than snow on Mars, and on the Red Planet, frost can be made of water or carbon dioxide.
Even as far back as the 1970s, NASA's Viking landers captured images of frost on Mars.
But in 2024, the European Space Agency announced that two of its spacecraft had seen frost even at the planet's equator, in the Martian tropics.
This frost was found on top of the Tharsis volcanoes, home to Olympus Mons, the tallest volcano in the Solar System.
The frost is as thick as a human hair and in total amounts to 150,000 tonnes of water, equivalent to 60 Olympic swimming pools.
And, once winter is over on Mars, much of the snow and frost thaws out, leaving incredible surface features like the so-called spiders on Mars.
