The unsolved mystery of Mars

Geomorphological differences between the northern and southern hemispheres

Since Viking 1976 and Global Prospector discovered the whole terrain of Mars 20 years later, we know that the surface topography of the northern and southern hemispheres of Mars is very different. The northern hemisphere is almost smooth and flat, with few craters, while the southern hemisphere is covered with many craters. This fact shows that the southern hemisphere is an older terrain than the northern hemisphere. Tarsis mountain area in equatorial region caused by large-scale volcanic activity. There is a huge difference in landforms between the northern and southern hemispheres of Mars, and the cause has always been an unsolved mystery. American scientists recently published an article in the journal Nature, arguing that the violent impact of external forces such as asteroids or comets is the reason for the difference between the north and the south of Mars. They believe that billions of years ago, asteroids or comets violently hit young Mars, causing huge differences in the surface. However, some scientists believe that although the latest research results provide more arguments for collision theory, other possibilities, such as the geological movement of Mars itself, cannot be completely ruled out.

The Mystery of Huge Sandstorm

Humans have observed huge sandstorms on Mars through Mariner 9 and Viking probes, and global prospectors have also observed large-scale sandstorms covering almost Mars at 200 1. Large-scale sandstorms mostly occur in winter and spring in the southern hemisphere. For example, a sandstorm occurred in June of 200 1 year. At first, it was just a dust cloud over the Geras Basin in the southern hemisphere, and then its volume increased slightly, but on June 27th, the storm started raging and the dust cloud expanded rapidly. By early July, the dust cloud had spread outside the basin and covered the whole of Mars. The sandstorm didn't end until the end of September, but the dust rolled up at the top was still floating in the atmosphere, so by June165438+1October, Mars seemed to be stationary.

It's vague.

The atmosphere of Mars is very thin, only one tenth of that of the earth. Theoretically speaking, the large-scale wind represented by the atmospheric circulation model is not easy to blow up under the conditions of Mars, so it is difficult to raise dust from the surface. Despite this, in fact, large-scale sandstorms have occurred. Why is this?

So far, no one can give a correct explanation to the question "How the sandstorm on Mars swept the world quickly", but people tend to have a theory that the dust particles in the air absorb sunlight and make the surrounding air heat up rapidly. Strong winds roll up more dust on the surface of Mars, causing the temperature to rise further. This circulation mechanism makes a small area of dust clouds eventually evolve into a global sandstorm on Mars.

In contrast, there is no global sandstorm on the earth. This is because there is no global desert like Mars on the earth, and sandstorms are self-reliant. Secondly, the temperature of the earth is mainly controlled by the heat energy contained in water vapor, and the dust particles in the air have little influence on the temperature. On Mars, the situation is completely different, because dust absorbs sunlight, which will cause dry air to suddenly heat up, and then form a strong wind and raise more dust.

The mystery of water existence

As we all know, people are most interested in the existence of water when exploring Mars, because water is related to the existence of life. Inferring from the topography of river traces such as the "valley network" all over Mars, there was a lot of water on Mars. Recently, NASA's Phoenix lander found evidence of water ice outside the polar ice sheet of Mars. This discovery is undoubtedly a key first step to understand whether the surface of Mars is habitable.

Now, scientists are convinced that there used to be a lot of liquid water on Mars. But where does the water come from? The most likely explanation is that it comes from groundwater rich in sulfuric acid. This is because the spectrogram of rocks sent back by Spirit shows that as much as 40% of rocks are sulfate. Groundwater permeates upward through volcanic rocks, sometimes flooding the surface of Mars, forming shallow lakes or shallow seas. Then, the water evaporated, leaving a thin layer of sulfate on the ground. This process may happen many times on Mars. So it accumulated into a thick rock layer containing sulfate.

Some scientists believe that the lowlands in the northern hemisphere used to be oceans. In addition, there is still water in Geras Basin or Alti Lei Ping Plain. So, where did the abundant water go? It is now confirmed that the water existing on Mars is only polar ice and a little water vapor in the atmosphere. Water has evaporated, but has it dispersed into space? Or did it seep into the ground? Or is it still in the form of frozen soil?

Many scientists believe that water seeps into the ground, which coincides with the observations of Odyssey probe. In fact, one of the observation purposes of this "Odyssey" is to find the existence of water on Mars. Gamma rays were used in this observation.

Spectrometer. When the Odyssey probe passed Mars for the first time while lowering its flight orbit, the gamma-ray spectrometer detected neutrons and gamma rays emitted from the soil north of the Antarctic, thus knowing the hydrogen concentration on the surface and near-surface layer, which indicated that there were signs of water ice on Mars, and knew the quantity of permafrost and its seasonal changes.

So, how do we know the existence of hydrogen atoms from neutrons and gamma rays? As we all know, there is no dense atmosphere on Mars. When it is hit by strong cosmic rays, its surface will release a strong neutron stream. These neutrons will collide with the nuclei of various elements when crossing the near-surface layer of Mars. When the neutron hits the hydrogen nucleus in water, it will slow down and release some heat energy. If it is absorbed by other atoms such as hydrogen, it will emit gamma rays. Therefore, if the amount of thermal neutrons is small and the amount of gamma rays is large, it is considered that the concentration of hydrogen is high.

The data sent back by the gamma-ray spectrometer show that there are fewer thermal neutrons in the southern hemisphere south of 60 degrees south latitude, while the amount of gamma rays released by hydrogen-absorbing neutrons increases. In addition, there are similar areas in parts of the northern hemisphere. These facts show that there is permafrost about 1 m from the surface in the area south of 60 degrees south latitude, and there seems to be a lot of ice. If this inference is

If it is correct, these areas will be the exploration targets in the future mission to explore the traces of life in permafrost.

Mystery of magnetic field disappearance

1996, "Global Explorer" used atmospheric braking to enter the circular orbit of Mars. Unexpectedly, one side of the solar panel was not completely opened, which led to the prolonged air braking time. Because it is closer to the surface of Mars than the predetermined distance, accurate magnetic measurement can be made. As a result, Global Prospector found magnetic interference zones in some places in the southern hemisphere.

There is no magnetic field on Mars now, but we know that part of the magnetic field in the past is preserved in rocks, and according to different

Locally, the magnetic direction is reversed, resulting in interference fringes. This kind of magnetic interference fringe also exists on the seabed of the earth, which is the evidence of plate tectonic theory.

The existence of remanence on Mars indicates that this planet once had a magnetic field. However, due to the nuclear cooling of early Mars, the magnetic field disappeared. Because the magnetic interference fringes can only be seen in the southern hemisphere, but not in the northern hemisphere, scientists believe that the topography in the northern hemisphere is formed after the disappearance of the magnetic field, or the abnormality caused by the mixing of heat and water inside makes the magnetism disappear. To sum up, we only know that there was a very strong magnetic field on Mars, something created interference fringes, and the magnetic field disappeared at some time. As for why there are no magnetic interference fringes in the northern hemisphere, why are there only some places in the southern hemisphere? None of these questions have been answered by humans.