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.


 

 
 
 
 

CityMetric is now City Monitor! Come see us at our new home

City Monitor is now live in beta at citymonitor.ai.

CityMetric is now City Monitor, a name that reflects both a ramping up of our ambitions as well as our membership in a network of like-minded publications from New Statesman Media Group. Our new site is now live in beta, so please visit us there going forward. Here’s what CityMetric readers should know about this exciting transition.  

Regular CityMetric readers may have already noticed a few changes around here since the spring. CityMetric’s beloved founding editor, Jonn Elledge, has moved on to some new adventures, and a new team has formed to take the site into the future. It’s led by yours truly – I’m Sommer Mathis, the editor-in-chief of City Monitor. Hello!

My background includes having served as the founding editor of CityLab, editor-in-chief of Atlas Obscura, and editor-in-chief of DCist, a local news publication in the District of Columbia. I’ve been reporting on and writing about cities in one way or another for the past 15 years. To me, there is no more important story in the world right now than how cities are changing and adapting to an increasingly challenging global landscape. The majority of the world’s population lives in cities, and if we’re ever going to be able to tackle the most pressing issues currently facing our planet – the climate emergency, rising inequality, the Covid-19 pandemic ­­­– cities are going to have to lead the way.

That’s why City Monitor is now a global publication dedicated to the future of cities everywhere – not just in the UK (nor for that matter just in the US, where I live). Our mission is to help our readers, many of whom are in leadership positions around the globe, navigate how cities are changing and discover what’s next in the world of urban policy. We’ll do that through original reporting, expert opinion and most crucially, a data-driven approach that emphasises evidence and rigorous analysis. We want to arm local decision-makers and those they work in concert with – whether that’s elected officials, bureaucratic leaders, policy advocates, neighbourhood activists, academics and researchers, entrepreneurs, or plain-old engaged citizens – with real insights and potential answers to tough problems. Subjects we cover include transportation, infrastructure, housing, urban design, public safety, the environment, the economy, and much more.

The City Monitor team is made up of some of the most experienced urban policy journalists in the world. Our managing editor is Adam Sneed, also a CityLab alum where he served as a senior associate editor. Before that he was a technology reporter at Politico. Allison Arieff is City Monitor’s senior editor. She was previously editorial director of the urban planning and policy think tank SPUR, as well as a contributing columnist for The New York Times. Staff writer Jake Blumgart most recently covered development, housing and politics for WHYY, the local public radio station in Philadelphia. And our data reporter is Alexandra Kanik, whose previous roles include data reporting for Louisville Public Media in Kentucky and PublicSource in Pittsburgh, Pennsylvania.

Our team will continue to grow in the coming weeks, and we’ll also be collaborating closely with our editorial colleagues across New Statesman Media Group. In fact, we’re launching a whole network of new publications, covering topics such as the clean energy transition, foreign direct investment, technology, banks and more. Many of these sectors will frequently overlap with our cities coverage, and a key part of our plan is make the most of the expertise that all of these newsrooms combined will bring to bear on our journalism.

Please visit citymonitor.ai going forward, where you can also sign up for our free email newsletter.


As for CityMetric, some of its archives have already been moved over to the new website, and the rest will follow not long after. If you’re looking for a favourite piece from CityMetric’s past, for a time you’ll still be able to find it here, but before long the whole archive will move over to City Monitor.

On behalf of the City Monitor team, I’m thrilled to invite you to come along for the ride at our new digs. You can follow City Monitor on LinkedIn and on Twitter. If you’re interested in learning more about the potential for a commercial partnership with City Monitor, please get in touch with our director of partnerships, Joe Maughan.

I want to thank and congratulate Jonn Elledge on a brilliant run. Everything we do from here on out will be building on the legacy of his work, and the community that he built here at CityMetric. Cheers, Jonn!

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Sommer Mathis is editor-in-chief of City Monitor.