If Mars had water, where did she go?

Professor of Physics and Assistant Director (Solar System) at the Mullard Space Science Laboratory of University College London

Mars has changed dramatically over the 4.6 billion years since its formation. About 3.8 billion years ago, Mars looked much more like Earth: volcanism, magnetic field, surface water, and thick atmosphere, at a time when life was already beginning on Earth. Evidence of the presence of old surface waters has accumulated – starting with Viking Orbit Imaging, a direct evidence in situ that water was at the surface, with an analysis of Opportunity minerals and Curiosity, evidence of Curiosity's neutral acid water, and rich minerals and clays on older surface regions, mapped by Mars Express.

Mars is now cold and dry, and its carbon dioxide atmosphere is thin, its surface environment is harsh and its thinning atmosphere is not protected by a global magnetic field. Mars Odyssey and Phoenix have found evidence of groundwater ice, Mars Reconnaissance Orbiter has detected recurring slope lines that may indicate traces of subsurface seepage water (or dustfall) and Last year, Mars Express found evidence of a liquid "water lake" under the South Pole using radar measurements.

All of this shows that the water has been and still is present on Mars – but some of the water has gone underground and another has escaped into space, as is the case. 39 have seen Mars Express and Maven. But the life potential on Mars was even better 3.8 billion years ago. That is why, with the ESA-Russia rover Rosalind Franklin (ExoMars), we will drill up to 2 m under the harsh Martian surface to look for signs of life in situ on the past or on the less likely present. In addition, Mars 2020 will collect samples for a possible return of Mars samples.

"Mars is now cold and dry, and its carbon dioxide atmosphere is thin, its surface environment is harsh and its thinning atmosphere is not protected by a global magnetic field."

Professor of Astronomy at the University of Vanderbilt and author of & # 39; Life on Mars, & # 39; from where is pulled underneath

If we take all the water from a planet, deposit it on the surface of the planet and spread it evenly over 100% of its surface, we will get what planetary scientists call a "global ocean". This concept helps us easily. visualize the total volume of water on this planet.

Robust estimates indicate that the total amount of water that planetary scientists have found on Mars, mainly in the ice caps, would create a global ocean from a depth of 70 to 100 feet. This is the amount of water we know today on Mars. We can say that with a lot of confidence.

We also know that Mars has lost a lot of water. By using the abundance of some trace gases in Mars' atmosphere, scientists estimate that there was once a world ocean with a depth of about 450 feet. Based on this evidence from atmospheric gases, we know that Mars lost 75% to 85% of the water with which it started. All this water is gone forever, lost in space. Again, I think we can say that with a lot of confidence.

However, if, in addition to evidence from atmospheric gases, we use visual evidence of a runoff of water on the surface of Mars, which is clear in the form of dry river valleys and canals. of exit that erase the old surface of the red planet. we can estimate that Mars has already had enough water to generate a global ocean from a depth of 1500 to 3000 feet. If we used this evidence from the ancient river valleys and outlet channels, we would necessarily conclude that 40% to 80% of the water started by Mars is not lost in space, any this water is hidden in the interior of Mars and not locked. in the polar ice. It's a lot of water.

In total, the evidence (in the current atmosphere) suggests that Mars lost 10% to 30% of the water that it had 4 billion years ago. Of the remaining 70% to 90% of its water stock, no more than 5% to 10% of this water was found in the polar ice caps. The remaining water, perhaps up to 90% of the water that started with Mars, is in underground reservoirs.

Timothy E. Dowling

Professor, Planetary Physics, University of Louisville

Mars is the only other planet in our solar system that can potentially be inhabited by humans. It is therefore not surprising that all the details, similar or different with the Earth, are studied closely. Even though Mars is smaller than the Earth, it has the same area in terms of dry lands (the Earth's surface being made up of two-thirds of oceans), which explains the size of the task of exploring the geology Of March.

After more than half a century of interplanetary exploration, we have plenty of independent evidence that water once poured heavily on the surface of Mars. In orbit (remote sensing), we have high resolution images showing the river features in the channels of the now dry rivers. We have detected aqueous chemistry of several types of minerals, which do not form without liquid water, and even smooth pebbles.

We even have brackish water films flowing today on the surface of Mars, where it is the warmest near the equator in the middle of the day. This was confirmed by spectroscopy, which detected the signal of hydrated salts – very diluted milk of magnesia! – well where these wet flows appear and not where they are not. But if not, where are all the surface waters on Mars?

Much of the answer, perhaps largely, is that Mars is not big enough to have a planetary magnetic field. The melted nickel-iron core of the Earth generates a dynamo that gives the original planet a powerful magnetic field that deflects the endless flow of harmful charged particles that flow from the sun, the solar wind. On the other hand, Mars has been hit hard by the solar wind, probably for billions of years. NASA's MAVEN spacecraft is currently in orbit around Mars, carrying out detailed measurements of this process. He confirmed that the solar wind regularly eliminates Mars' volatiles.

The picture that emerges is that every detail that can be enumerated for the Earth is beneficial to life, whether large or small, and that some are missing for life to appear and that it thrives almost impossible. Among the beneficial features of Earth that are missing on Mars include a powerful magnetic field, a large moon (to provide tides that shake the chemistry of the ocean and to stabilize the obliquity or tilt of the planet, and therefore its seasons), and plate tectonics (recycle oxygen and other resources in the oceanic crust). But the more we learn about Mars, the more intriguing the planet becomes.

The last big mystery is that there is a strong and uneven amount of methane in the atmosphere of Mars, much more than expected. On Earth, this is partly caused by geothermal sources, but mainly by the biosphere. Planetary scientists are currently studying ways to decipher the cause of excess methane on Mars, so stay tuned (and join us)!

"Mars is the only other planet in our solar system that has the potential to be habitable for humans."

Professor, Geological Sciences, University of Colorado, and Principal Investigator on the Mars (MAVEN) Mission on the Atmosphere and Volatile Evolution (MAVEN) whose research focuses on understanding the nature of planetary surfaces and atmospheres and on the opportunity to live in the universe.

The morphology of the surface shows signs of liquid water on the planet Mars. These elements resemble surface water runoff channels, lakes that fill old closed basins created by impact craters, a general degradation of the surface that best matches the presence. active hydrological cycle and flow characteristics that suggest the occurrence of large-scale floods.

In addition, minerals have been identified on the surface by rovers that can only be formed in the presence of liquid water. Some of them come in the form of "concretions", round nodules of minerals that form when water flows through the soil and can dissolve minerals and redeposit them elsewhere.

Today, on Mars, we have identified a type of chemical called "perchlorates" mixed with soil. These minerals can extract water vapor from the atmosphere and dissolve to produce small amounts of liquid water that is stable on the surface today at certain times of the day.

Features such as "ravines" and flow-like features, called "recurrent slope lines," may be due to recent water or runoff, are more controversial. And the radar has detected what appears to be a wet layer about a kilometer below the surface, near the South Pole, which may involve a layer of underground groundwater.

There is still water on Mars today, in the form of atmospheric water vapor, ice in the polar ice caps, ice buried below the surface in non-polar regions and water related to minerals in the world. There may also be additional water below the surface, perhaps in the form of groundwater that is widespread or spread around the world. Although possible, we have no direct evidence of its existence.

Each of these was detected using remote sensing observations or directly by imagery. Much of the water has been broken down into its atoms of hydrogen and oxygen and lost in space. We know this has happened because it leaves a distinctive signature: deuterium is a heavier form of hydrogen, having a neutron in addition to a proton; heavier, it escapes less easily in space and leaves the deuterium relatively more abundant in the remaining water on Mars. This enrichment in "D / H" indicates that between 85 and 95% of the water near the surface of Mars has been lost in space.

"There is still water on Mars today, in the form of atmospheric water vapor, ice in polar ice caps, ice buried beneath the surface in non-polar regions, and sea ice. Water bound to minerals in the world ".

Assistant Professor, Chemistry and Biochemistry, Georgia Tech, whose research focuses in particular on the development of instruments for in situ organic analysis in the search for extraterrestrial life, among others

Water on Earth is still unexplained. The general problem is that the solar system appears to be a giant distillation column, the volatile compounds being largely evaporated from planetary bodies that receive more heat and then grow on more distant and cold planetary bodies. The "ice line" for the water seems to be farther away than the Earth. Explaining why we have so much could be a bigger challenge than explaining why Mars has so little.

The small size of Mars can not be easily explained without the migration of Jupiter and Saturn inward then to the current positions. The initial position of Mars can not be known with 100% accuracy until our models and our understanding of the solar system are improved. . It is therefore difficult to know the magnitude of the Earth-Mars water ratio problem, since Mars could have been at any point relative to the Sun before the migration of Jupiter and Saturn to their present positions. .

Another problem is that Mars lost its magnetic field relatively early because of its relatively small size. As a result, the solar wind strikes the atmosphere, ionizes it, then projects free protons or molecular hydrogen, and even water vapor as a molecular cloud. The MAVEN mission is currently studying this interaction.

"The water is really the ink of the story of Mars."

Assistant Professor, Earth, Atmospheric and Planetary Sciences, Purdue University, whose research program uses NASA satellite and rover data, as well as laboratory and field work on Earth, to understand the surface processes that shaped Mars and the Moon.

The water is really the ink of the story of Mars. We see evidence of all kinds that Mars once had a very active water cycle on the surface, 3 billion years ago. We see river canals dug into the old uplands, with complex networks of tributaries that are only possible if the water comes in from everywhere, as one would expect if the rain or snow fell once in a while. area. These rivers flowed in craters and created deltas in dry lakes. The Curiosity rover explores one of the ancient lake basins of the Gale crater and has shown that the lake could be present for hundreds of thousands, even millions of years.

We know that the fluid that carved the canals and filled the crater lakes was water, not something more exotic, because we also observe minerals on the old surfaces of Mars that could not be found. be formed only in the presence of liquid water. Minerals, such as the salts that form when water evaporates, the clays that form when the water stays stuck for a long time, and the carbonates that form when the carbon dioxide of the atmosphere dissolves in the water. The next Mars rover of NASA, March 2020, will look for evidence of ancient life on Mars in the Jezero crater, where a dried up lake and delta could have deposited carbonates and trapped remnants of microorganisms.

We know that Mars had abundant water flowing to the surface 3 billion years ago, but now Mars is a cold, hyper-arid planet with very little liquid water on the surface. The reason for this change is that Mars has almost entirely lost the primitive atmosphere in the atmosphere and that the current atmosphere is too thin for the liquid water to be stable. NASA's MAVEN satellite has shown that the solar wind and other ongoing slow evacuation processes are not sufficient to explain the direction of the atmosphere; it is therefore likely that other processes such as the impacts of giant asteroids have made it possible to clean up the atmosphere. This has not happened here on Earth because the higher gravity and the active magnetic field help keep the atmosphere around.

Some of the water from ancient Mars was lost in space, but most of it was frozen underground. We see huge ice reservoirs buried at high latitudes, and NASA's Phoenix lander confirmed that there were pure ice deposits a few inches from the surface. If you melt all the ice on Mars, you could easily create an ocean. These ice deposits could be very important for future exploration and colonization of humans on Mars, as they could be an easily accessible source of water.