Mars has been a blue planet many times

Minerals show the way to the water

The new findings are the result of years of observations by the ESA satellite Mars Expresswhich has been orbiting Mars since 2003, and NASA Mars Reconnaissance Orbiterwhich began its observations in 2005. Only now do we have a complete overview of the measurements and their impact.

The satellites contain all kinds of minerals on Mars AppointedMeasurements revealed up to a hundred thousand areas that had been under water for a long time.

Liquid water leaves a sediment in the form of small mud particles that sink to the bottom. And when the water evaporates at a certain point, large amounts of salt are left behind.

To the surprise of the researchers, it turned out that the salt layers are deeper than the clay layers in some places. This means that the water must have returned many times, after millions or even billions of years of drought.

We simply thought of Mars. The water did not disappear overnight, but returned many times for shorter or longer periods of time,” says John Carter of the University of Aix-Marseille in France, who collaborated on a project to map the surface of Mars.

Close-ups of Mars being wet

Our knowledge of Mars’ wet past is only about 50 years old. Before that, planetary scientists thought Mars had always been a dry wasteland, just like the Moon.

That changed in 1971, when the first close-ups from the Mariner 9 satellite showed riverbeds dried up. This indicates that it was raining on the red planet.

This new insight was supported by two Viking probes that entered Mars orbit in 1976 and sent landers to the surface. They found traces of roaring rivers that carved deep gorges in the landscape.

It also found that many meteorite craters in the planet’s early days contained lakes, and evidence has been found that the vast northern lowlands of the Fastitas Borealis around the North Pole were once covered by a shallow ocean.

Finally, measurements from Viking probes indicated that the northern ice cap contained water in the form of ice. Subsequent measurements showed that this also applies to the southern ice sheet.

The theory that Mars was warm and wet in its first billion years was conclusively proven in 2004, when the rover Opportunity and Spirit found deposits in ancient craters that could have formed only in water.

Four years later, NASA sent the Phoenix probe to Facitas Borealis. The rover scraped the top inch of soil with its robotic arm and found the ice left behind when the ocean receded.

The Mars Express and Mars Reconnaissance Orbiter satellites were already mapping the surface of Mars at that time.

Satellites measure thermal radiation

Both satellites are equipped with spectrophotometers. these machines To measure The thermal radiation that a surface reflects when exposed to sunlight. The wavelengths of radiation show which minerals a surface contains.

Mars Express mapped the entire planet at a resolution of 200 meters per pixel, and the Mars Reconnaissance Orbiter made detailed maps of particularly interesting regions at a pixel size of just 10 meters.

Before these two satellites mapped the surface of Mars, we knew there were 1,000 mineral regions that formed in liquid water. Now there are 94,083.

Minerals formed by water are dated by counting the number of impact craters in a given area. The fewer pits, the smaller the surface. This indicates that water was flowing on Mars only two billion years ago.

The fact that water has returned several times in Mars’ history shows that the climate there was noticeably warmer than the average temperature of -60 degrees Celsius that Mars now experiences at several periods.

This conclusion was recently supported startlingly by the Chinese rover Zhurong, which is active in the Martian crater Utopia Planitia, the largest crater in the solar system.

The rover has a radar that can see up to 100 meters deep on the bottom, and measurements It revealed two layers with larger stones at the bottom and smaller stones at the top.

The two layers show that the crater experienced major floods 3 and 1.6 billion years ago, respectively.

Chinese planetary scientists believe that the frozen salty groundwater melted and went to the surface. This may have been due to sudden warming from asteroid impacts or volcanic eruptions.

Radar measurements add another 400,000 years to the history of water on Mars. This means that the planet had good conditions for life not only in its early days, but also billions of years later.

The water disappeared through the thin atmosphere

Although Mars has known liquid water many times, the planet eventually lost its water because the atmosphere became increasingly thin.

With no atmosphere to trap the sun’s heat, the blue planet turned into the red planet we know today.

However, Mars is not completely dry. Water minerals on the surface show where the soil is most likely to hold the most water. As a result, satellite maps can also influence the possibility of building manned bases on Mars in the future.

So far, the northern Plain of Vastitas Borealis, where ice lies just below the surface, has been the best candidate. The big drawback is that it is very cold at -97°C.

Closer to the equator, the climate is more friendly, with temperatures between -70 and 20 degrees Celsius. There is no ice here, but data from the two satellites indicate that the Meridiani Planum plain contains many hydrated minerals that could serve as a source of water for a Martian colony.

Satellite observations are not only important for our understanding of Mars’ history and for planning future Mars bases — they can also help us track past life on Mars. We know from Earth that water is a prerequisite for life, so satellite maps show where to look for signs of life best.

A vivid example of this is the Jezero crater, where once there was a large lake with a river delta. Here, NASA’s Perseverance rover is now collecting drill cores, which will go to Earth in 2033 for analysis in advanced laboratories.

Perhaps by then, we will have evidence that Mars was not only wet, but fertile as well.