There could be snow on Mars. Here’s how

Evidence found at Hale Crater suggests the presence of liquid water on Mars. Image: Getty/NASA.

Given that there are ambitious plans to colonise Mars in the near future, it is surprising how much we still have to learn about what it would be like to actually live on the planet.

Take the weather, for instance. We know there are wild fluctuations in Mars’s climate – and that it is very windy and at times cloudy (though too cold and dry for rainfall). But does it snow? Might settlers on Mars be able to see the red planet turn white? A new study surprisingly suggests so.

Mars is clearly cold enough for snow. It has ice – the amount of which has varied significantly over time. When its axis is tilted at only a small angle relative to its orbit, its surface is ice-free except for the polar caps. This is the situation today, when its axial tilt is 25⁰ (similar to Earth’s 23⁰ axial tilt).

However, possibly because Mars lacks a large moon to stabilise its spin, there have been times when its spin axis was tipped over by up to 60⁰ – allowing the polar ice caps to spread, maybe even to the extent that there was abundant ice near the equator.

NASA’s Phoenix Mars Lander didn’t see snow on the ground. Image: NASA/JPL-Caltech/University of Arizona/Texas A&M University.

Mars emerged from its most recent ice age about 400,000 years ago. Since then, its polar caps have been small, and any ice surviving near the equator has been buried under dust.

The planet’s atmosphere is of low pressure and very dry. Although it is still possible for clouds to form at an altitude of several kilometres, until now it has been generally believed that any true snowfall would not reach the ground. The clouds, resembling Earth’s cirrus clouds, are believed to form when the small amount of water vapour in the atmosphere condenses (directly from vapour to ice) onto grains of dust lofted skywards during storms.

Shots by the Curiosity rover of cirrus clouds (made of tiny crystals of water-ice) on Mars.

Winter wonderland?

Being only a few micrometres in size, ice particles falling from the clouds would would drop at about only a centimetre a second. This allows more than enough time for them to evaporate before reaching the ground (strictly speaking, the process should be called “sublimation”, because the ice goes directly to vapour, without melting first). Overnight and seasonal frost spotted on Mars have been explained by water-ice particles falling quickly because they had been made temporarily larger and heavier by an outer coating of frozen carbon dioxide from the atmosphere.

Seasonal frost (or snowfall?) in gullies on a crater wall on Mars, at 60⁰ N. This view is about 800 metres wide. Image: NASA/JPL/University of Arizona.

The new study, published in Nature Geoscience, has found a way in which tiny specks of water-ice could travel down to the ground without this strange frozen carbon dioxide coat. If correct, this would mean genuine snow on Mars – just like that on Earth. The team used measurements from two orbiting spacecraft (the Mars Global Surveyor and Mars Reconnaissance Orbiter) to study how temperature varies with height in the martian atmosphere. They found that at night, the lower atmosphere below ice clouds can become unstable, because it becomes less dense below than above.

This leads to rapid downdrafts of air, travelling at about 10 metres per second, which could carry ice crystals to the surface too quickly for them to “evaporate”. However, the snow layer would probably be thin and not last too long before it sublimes back into the atmosphere – where it could form new clouds and snowfall.

The phenomenon is similar to what is known on Earth a “microburst”, when a localised 60mph (97km per hour) downdraft below a thunderstorm can be powerful enough to flatten trees. The same process can also be responsible for intense snowfall at a particular location, by carrying snowflakes groundward in a blast, punching through the near-surface layer of air that would normally be warm enough to melt them.

A microburst on Earth.

Snow has not yet been observed in the process of actually reaching the ground on Mars, but it has been seen falling through the sky. NASA’s Phoenix lander, which landed at 68⁰ N in 2008 and became famous for finding ice below the surface when it scraped the dirt away, studied the sky above too. It used a LIDAR (like radar but relying on reflections from a laser beam) to probe the atmosphere, and on at least two nights observed curtains of falling snow hanging below the cloud layer.

Frost or a light dusting of snow seen at the Viking 2 lander site, Utopia Planitia, Mars. Image: Vandencbulek Eric/creative commons.

The ConversationIf a downdraft powerful enough had occurred, then maybe one morning Phoenix would have woken up to a winter wonderland, instead of the usual red landscape – at least for a few hours.

David Rothery is professor of planetary geosciences at The Open University.

This article was originally published on The Conversation. Read the original article.


 

 
 
 
 

What’s up with Wakanda’s trains? On public transport in Black Panther

The Black Panther promotional poster. Image: Marvel/Disney.

Black Panther is one of the best reviewed superhero films of all time. It’s instantly become a cultural touchstone for black representation in movies, while shining a positive light on a continent almost totally ignored by Hollywood. But never mind all that – what about the trains?

The film takes place in the fictional African country of Wakanda, a small, technologically advanced nation whose power comes from its main natural resource: huge supplies of a magical metal called vibranium. As is often the case in sci-fi, “technologically advanced” here means “full of skyscrapers and trains”. In other words, perfect Citymetric territory.

Here’s a mostly spoiler-free guide to Black Panther’s urbanism and transport.

City planning

It’s to the credit of Black Panther’s crew that there’s anything to talk about here at all. Fictional cities in previous Marvel films, such as Asgard from the Thor films or Xandar from Guardians of the Galaxy, don’t feel like real places at all, but collections of random monuments joined together by unwalkably-wide and sterile open spaces.

Wakanda’s capital, the Golden City, seems to have distinct districts and suburbs with a variety of traditional and modern styles, arranged roughly how you’d expect a capital to be – skyscrapers in the centre, high-rise apartments around it, and what look like industrial buildings on its waterfront. In other words, it’s a believable city.

It’s almost a real city. Image: Marvel/Disney

We only really see one area close-up: Steptown, which according to designer Ruth Carter is the city’s hipster district. How the Golden City ended up with a bohemian area is never explained. In many cities, these formed where immigrants, artists and students arrived to take advantage of lower rents, but this seems unlikely with Wakanda’s stable economy and zero migration. Did the Golden City gentrify?

Urban transport

When we get out and about, things get a bit weirder. The narrow pedestrianised sand-paved street is crowded and lined with market stalls on both sides, yet a futuristic tram runs right down the middle. The tram’s resemblance to the chunky San Francisco BART trains is not a coincidence – director Ryan Coogler is from Oakland.

Steptown Streetcar, with a hyperloop train passing overhead. Image: Marvel/Disney.

People have to dodge around the tram, and the street is far too narrow for a second tram to pass the other way. This could be a single-track shuttle (like the former Southport Pier Tram), a one-way loop (like the Detroit People Mover) or a diversion through narrow streets (like the Dublin Luas Cross City extension). But no matter what, it’s a slow and inefficient way to get people around a major city. Hopefully there’s an underground station lurking somewhere out of shot.


Over the street runs a *shudder* hyperloop. If you’re concerned that Elon Musk’s scheme has made its way to Wakanda, don’t worry – this train bears no resemblance to Musk’s design. Rather, it’s a flying train that levitates between hoops in the open air. It travels very fast – too fast for urban transport, since it crosses a whole neighbourhood in a couple of seconds – and it doesn’t seem to have many stops, even at logical interchange points where the lines cross. Its main purpose is probably to bring people from outlying suburbs into the centre quickly.

There’s one other urban transport system seen in the film: as befitting a major riverside city, it has a ferry or waterbus system. We get a good look at the barges carrying tribal leaders to the ceremonial waterfalls, but overhead shots show other boats on the more mundane business of shuttling people up and down the river.

Transport outside the city

Unfortunately there’s less to say here. Away from the city, we only see people riding horses, following cattle-drawn sleds, or simply walking long distances. This is understandable given Wakanda’s masquerading as a developing country, but it makes the country very urban centric. Perhaps that’s why the Jabari hate the other tribes so much – poor transport investment means the only way to reach them is a narrow, winding mountain pass.

The one exception is in freight transport. Wakanda has a ridiculously developed maglev network for transporting vibranium ore. This actually follows a pattern seen in a lot of real African countries: take a look at a map of the continent and you’ll see most railways run to the coast.

Image: Bucksy/Wikimedia Commons.

These are primarily freight railways built to transport resources from mines and plantations to ports, with passenger transport an afterthought.

A high-speed maglev seems like overkill for carrying ore, especially as the film goes out of its way to point out that vibranium is too unstable to take on high-speed trains without careful safety precautions. Nevertheless, the scene where Shuri and Ross geek out about these maglevs might just be the single most relatable in any Marvel movie.

A very extravagant freight line. Image: Marvel/Disney.

Perhaps this all makes sense though. Wakanda is still an absolute monarchy, and without democratic input its king is naturally going to choose exciting hyperloop and maglev projects over boring local and regional transport links.

Here’s hoping the next Black Panther film sees T’Challa reforming Wakanda’s government, and then getting really stuck into double-track improvements to the Steptown Streetcar.

Stephen Jorgenson-Murray tweets as @stejormur.

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