(ORDO NEWS) — Mars was once red with rivers. Traces of rivers, streams and lakes are visible all over the planet today. But about three billion years ago, they all dried up – and no one knows why.
Previously, many scientists assumed that the cause of the problems was the loss of carbon dioxide from the atmosphere, which helps Mars to keep warm.
But the new results suggest that the changes were caused by the loss of some other important component that kept the planet warm enough for running water.
In 1972, scientists were amazed to see photographs taken by NASA’s Mariner 9 spacecraft that circled Mars from orbit.
The pictures showed a landscape full of riverbeds – evidence that the planet once had a lot of water, although today it is dry as a bone.
Because there are no tectonic plates on Mars to move and bury rock over time, traces of ancient rivers still lie on the surface, like evidence thrown in a hurry.
This made it possible to analyze maps compiled from thousands of photographs taken from orbit by satellites.
Based on which trails intersect with others and how much they have weathered, the team of scientists compiled a chronology of how river activity changes with altitude and latitude over billions of years.
They were then able to combine that data with simulations of different climates and see which ones worked best.
Heat can come from the sun, it must be close enough to receive radiation, but not so close that the radiation destroys the atmosphere.
Greenhouse gases such as carbon dioxide and methane can trap heat near the planet’s surface. Water also plays a role: it can exist as clouds in the atmosphere or as snow and ice on the surface.
Snow caps usually act like a mirror, reflecting sunlight back into space, but clouds can either block or reflect light, depending on their height and composition.
Researchers have tested many different combinations of these factors, looking for conditions that could lead to a planet warm enough for at least some water to exist in rivers for more than a billion years, but then abruptly lose it.
But when they compared different models, they saw something amazing. Changing the amount of carbon dioxide in the atmosphere did not affect the result. That is, the driving force behind the change does not appear to have been carbon dioxide.
The new data is in good agreement with the scenario proposed, which says that a layer of thin icy clouds high in the Martian atmosphere acts like a translucent greenhouse glass, trapping heat.
The scientists speculated that if hydrogen was released from the planet’s interior, it could interact with carbon dioxide in the atmosphere, absorbing infrared light and heating the planet.
Scientists hope that studying what happened to planets like Mars could provide clues about planetary climates and how many more planets could be habitable.
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