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.


 

 
 
 
 

A growing number of voters will never own their own home. Why is the government ignoring them?

A lettings agent window. Image: Getty.

The dream of a property-owning democracy continues to define British housing policy. From Right-to-Buy to Help-to-Buy, policies are framed around the model of the ‘first-time buyer’ and her quest for property acquisition. The goal of Philip Hammond’s upcoming budget is hailed as a major “intervention” in the “broken” housing market – is to ensure that “the next generation will have the same opportunities as their parents to own a home.”

These policies are designed for an alternative reality. Over the last two decades, the dream of the property-owning democracy has come completely undone. While government schemes used to churn out more home owners, today it moves in reverse.

Generation Rent’s new report, “Life in the Rental Sector”, suggests that more Britons are living longer in the private rental sector. We predict the number of ‘silver renters’ – pensioners in the private rental sector – will rise to one million by 2035, a three-fold increase from today.

These renters have drifted way beyond the dream of home ownership: only 11 per cent of renters over 65 expect to own a home. Our survey results show that these renters are twice as likely than renters in their 20s to prefer affordable rental tenure over homeownership.

Lowering stamp duty or providing mortgage relief completely miss the point. These are renters – life-long renters – and they want rental relief: guaranteed tenancies, protection from eviction, rent inflation regulation.

The assumption of a British ‘obsession’ with homeownership – which has informed so much housing policy over the years – stands on flimsy ground. Most of the time, it is based on a single survey question: Would you like to rent a home or own a home? It’s a preposterous question, of course, because, well, who wouldn’t like to own a home at a time when the chief economist of the Bank of England has made the case for homes as a ‘better bet’ for retirement than pensions?


Here we arrive at the real toxicity of the property-owning dream. It promotes a vicious cycle: support for first-time buyers increases demand for home ownership, fresh demand raises house prices, house price inflation turns housing into a profitable investment, and investment incentives stoke preferences for home ownership all over again.

The cycle is now, finally, breaking. Not without pain, Britons are waking up to the madness of a housing policy organised around home ownership. And they are demanding reforms that respect renting as a life-time tenure.

At the 1946 Conservative Party conference, Anthony Eden extolled the virtues of a property-owning democracy as a defence against socialist appeal. “The ownership of property is not a crime or a sin,” he said, “but a reward, a right and responsibility that must be shared as equitable as possible among all our citizens.”

The Tories are now sleeping in the bed they have made. Left out to dry, renters are beginning to turn against the Conservative vision. The election numbers tell the story of this left-ward drift of the rental sector: 29 per cent of private renters voted Labour in 2010, 39 in 2015, and 54 in June.

Philip Hammond’s budget – which, despite its radicalism, continues to ignore the welfare of this rental population – is unlikely to reverse this trend. Generation Rent is no longer simply a class in itself — it is becoming a class for itself, as well.

We appear, then, on the verge of a paradigm shift in housing policy. As the demographics of the housing market change, so must its politics. Wednesday’s budget signals that even the Conservatives – the “party of homeownership” – recognise the need for change. But it only goes halfway.

The gains for any political party willing to truly seize the day – to ditch the property-owning dream once and for all, to champion a property-renting one instead – are there for the taking. 

David Adler is a research association at the campaign group Generation Rent.

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