Bad astronomy | Have we finally found liquid water on (well, under) Mars? Maaaaaaaybe.

Planetary scientists have announced that they have found evidence that a substantial amount of liquid water exists in a place below the surface of Mars.

!!!

Let me be clear from the beginning: The evidence is pretty good, but not 100% conclusive. There are warnings, which I will explain below. But looking at their work, I have to admit that it sounds (ironically) solid. If I were to bet, I would say that they indeed found a lake of shallow but wide liquid water buried deep beneath the surface of Mars.

And it's really amazing.

The observations come from the Spacecraft Mars Express of the European Space Agency. which is in orbit around the fourth rock of the Sun since late 2003. It is equipped with the usual fleet of cameras and detectors to scan Mars, to map it in an optical and mineralogical way, and to study the environment of the planet. 39, space close to Mars. [19659002] It also has a radar instrument called the Mars Advanced Radar for the underground and ionospheric sounding (MARSIS). This device is a 40-meter-long pole (consisting of two 20-meter dams that move away from the spacecraft) that sends radar pulses (radio waves) to the lower planet. Depending on the composition of the surface and the length of the wave used, the impulse is reflected on the surface and is returned to the spacecraft. The time it takes to go down and save can be used to measure the distance to the feature; the distance to the top of a mountain and the back is shorter than at the bottom of a valley, so that the pulse takes less time for the first and more for the last one. MARSIS can be used as an altimeter in this way to make a topological surface map of Mars.

But there is more. Some radar wavelengths penetrate the surface, passing directly through the material. It can be weakly or strongly reflected by some materials under the surface, allowing scientists to build a depth map of Mars up to several kilometers! The resolution is not great – it creates a band on an area about 3 to 5 kilometers wide – but several passes can be used to build enough signals to make decent maps of what lies below.

The south pole of Mars has a huge ice deposit beneath the surface called South Polar Layered Deposits (SPLD), extending over more than one thousand kilometers in diameter. This ice is almost pure water, mixed with dust in varying amounts (about 10-20% in places). Part of this hundred kilometers crosses the surface, forming the south polar polar ice cap, which is again mainly ice water, although it has a thick ice of carbon dioxide (" "dry ice") a meter or It is known for some time that liquid water could exist under the Martian surface. The heat emanating from the inside of the planet is bubbling, and the heat of the illuminated surface goes down. Depending on the thermal gradient (how the temperature changes with the depth, which depends on the material), this means that in some places on Mars the temperature allows the ice to melt. In general, it is about 1 to 2 kilometers deep.

Years ago, it was thought that the SPLD was too thin to hold liquid water, but MARSIS mapped the area (called Southern Planum, or Southern Plains). in fact up to 3.7 kilometers thick in places! Hmmmm.

And now, finally (well, hopefully), paydirt. Or paywater. 29 passes from MARSIS on an area show something very interesting: A deposit of 20 km of equipment about 400 km from the South Pole that reflects the radar very well. According to the delays of the pulsation, this substance is about 1.5 km below the surface and is distributed in a very thin layer of a thickness of only a few tens of centimeters

There are several materials that could produce radar reflections beneath the surface. , including ice with hot water, CO2 ice, or even liquid CO2 (which needs a high pressure to stay liquid, or it goes directly from a solid to a gas). However, either they are not reflective enough to create the signal seen, or the physical conditions necessary to create the signals are quite unlikely.

The most likely substance of a long shot that can exist there and be so reflective is the simplest: liquid water

So even though it's the way to bet it is not a lock. It is difficult to know exactly how the radar penetrates the surface, which can interfere with the signal and make it difficult to determine the composition of the subsoil. However, again, all that is considered liquid water is the best way to explain what we see.

Some people call it a lake, which is right, but at 20 km deep, more like a thin layer.

Always. It's really exciting! We have known ice-water on Mars for decades (the ice caps make it pretty obvious) as well as ice just below the surface at surprisingly low latitudes. But the liquid water has been wildly elusive. This new result seems much more likely to exist.

Research authors note that the low resolution of MARSIS means that smaller layers of liquid water (ponds, I guess) could exist also under the surface of Mars and be invisible to the instrument. This could be almost anywhere, but most likely at high latitudes. Hopefully the instruments of the future generation will be able to find these and map them.

So what does it mean for life? At this point everything would be speculated, but it is interesting to note that Mars once had lakes, seas and oceans on its surface, billions of years ago. These evaporated or were absorbed by the materials below when the atmosphere of the planet was sandblasted by the solar wind of the Sun, so that the surface water did not not last long.

Long enough for life to emerge? Who knows? But if that was the case, and that there was always liquid water under the surface, it would be a very, very interesting place to drill and get samples.