Scientists Think These ‘Kidney Beans’ Could Prove That Mars Once Supported Life

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Scientists Think These ‘Kidney Beans’ Could Prove That Mars Once Supported Life

They may resemble kidney beans, but formations on the northern hemisphere of Mars are actually sand dunes covered in carbon dioxide frost

How cold winters are on Mars depends on the tilt of its axis. The more tilted towards the sun the northern hemisphere of the Red Planet is, the warmer it gets and vice versa.

The CO2 ice turns to vapor and rises to the atmosphere when it grows warm enough. Periods during which this greenhouse gas created a thicker atmosphere meant the possibility of liquid water on Mars, which could have sustained life.

Formations that look like jumbo-sized kidney beans (or blobs of chocolate syrup, depending on your palette) may be indicators of whether

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in the distant past.

Recently imaged by the

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(High-Resolution Imaging Science Experiment) camera on NASA’S Mars Reconnaissance Orbiter (MRO), these “kidney beans” are actually sand dunes frozen in place by carbon dioxide frost.

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behave like

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. They migrate as winds blow sand from one side to the other, slowly crawling across the surface. Frost that settles on them during the Martian winter in the northern hemisphere prevents them from moving until they thaw.

By imaging the dunes, scientists can figure out how much CO2 frost forms on the dunes during the Martian winter. When temperatures grow warmer in the spring, the frost sublimates, transitioning from a solid to a gas without a liquid phase and vanishing into the atmosphere.

The amount of frost depends on

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on its axis. How much it

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affects temperatures in its northern and southern hemisphere during certain times of year. For now, the Red Planet tilts only slightly more than Earth.

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is thought to remain mostly stable because of the gravitational effects of our moon.

However, the moons of Mars, Phobos and Deimos, are not massive enough to exert gravitational forces strong enough to stabilize its tilt. Through simulations, scientists have found that the tilt of Mars can change significantly over time—it can go from having almost no tilt at all to to a tilt of over 80 degrees. While these simulations can only go back so far before they run into problems with accuracy, running them for spans of hundreds of millions, even billions of years can at least help with estimating how much Mars tilted at a certain point in time. While a low tilt means the polar regions stay cold, a high tilt will increase how directly the north or south pole faces the sun.

So how can tilt determine

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? The hemisphere tilted most towards the sun will experience long summers during which both carbon dioxide and ice sublimate and stay in the atmosphere. CO2 and water vapor are both greenhouse gases. Whenever the planet is warmer, the atmosphere is thicker, trapping heat and raising the surface pressure, which makes it possible for water on the surface to stay in liquid form instead of ice. If Mars ever had some form of life, it is most likely to have survived during these warmer eras.

Mars may have been more like Earth billions of years ago. It once had a thick atmosphere, much like our planet, which would have allowed liquid water to flow on the surface. Unlike Earth, its smaller size means a smaller iron core that kept it from generating a strong enough magnetic field to hold on to that atmosphere. The sun-blasted Red Planet is now too hostile an environment to sustain life (at least

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).

If we keep observing the changes in ice on Mars, such as frozen dunes that look suspiciously edible, maybe they will finally reveal whether life could have once thrived there.

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