Scientists still have a lot to learn about the Red Planet. In the meantime, InSight and Perseverance devices send unprecedented data to Earth about everything that is detected on Mars. Thanks to this, scientists received the key to understanding the evolution of the Red Planet and its differences from the Earth.
InSight and Perseverance devices send unprecedented data to Earth on everything from Marsquakes to information about the inner layers of the Red Planet.
If people on Earth are fighting an intense fight against the covid-19 pandemic, suffering from record heat and trying to figure out how to make sure that they do not run out of water, then our spacecraft on Mars live much quieter. (It also helps that they don't have to breathe.) Parked on the Martian surface, the Insight lander listens for the quakes, while the Perseverance rover rolls around in search of life.
This week, scientists unveiled a series of scientific findings based on information gathered from brave robots. Today they have published three articles in Science magazine, prepared by dozens of scientists from around the world. In them, the researchers talk about the clever ways of using the seismometer of the "Insight" apparatus, with the help of which they were able to look deep into the depths of the Red Planet. This instrument enriched them with unprecedented knowledge of the Martian crust, mantle and core. Scientists have mapped the innards of another planet for the first time. And yesterday, a second group of scientists held a press conference at which they announced the preliminary results of the research work of the Perseverance rover, and also talked about the next steps that it will take in studying the surface of the crater Jezero. This crater was once a lake and could have become the home of ancient microbial life.
Scientists still have a lot to learn about the Red Planet. “It's built with the same building blocks as Earth, but very different from it,” said University of Cambridge seismologist Sanne Cottaar, who wrote a paper for Sainz on three new studies. - There is a lot of evidence that the evolution of Mars was in many ways different. And now, as scientists form the inner image of the layers of the planet, we have new ways to understand how Mars was formed, and how it came into being."
When comparing two planets, many interesting questions arise. For example, why does the Earth have a magnetic field, while Mars seems to have disappeared? Why are there so many volcanoes on Earth, and they are very scattered, and on Mars, volcanoes are larger and more concentrated? (With a diameter of 602 kilometers and an altitude of almost 26 kilometers, Mount Olympus is the largest known volcano in the solar system.) The formation of Mars was probably accompanied by numerous cataclysms, but now everything is calm on its surface. And unlike Earth, there is little volcanic activity. (However, in May, scientists presented evidence of such recent activity.) Only by looking deeper beneath the surface will researchers be able to better understand such oddities of Mars, and along with the features of a similar Earth.
But before plunging into the avalanche of this scientific literature, we need to take a short course on the structure of Mars and the apparatus "Insight" exploring it. Compared to the Earth, the Red Planet is geologically quite calm. Because our planet has tectonic plates, which are huge chunks of land that move over the underlying mantle, its surface literally explodes with activity such as volcanoes and catastrophic earthquakes. There are no tectonic plates on Mars, because its core formed and quickly cooled down at the very beginning of the existence of the Red Planet. Today, Mars is shaken by small tremors, likely caused by the shrinking planet that continues to cool.
The task of the Insight lander is to detect such marsquakes using a seismometer, which it has been doing since February 2019. This instrument provides scientists with an exceptionally rich variety of seismic data, especially for two phenomena - P-waves (compression waves) and S-waves (shear waves), which occur as a result of Marsquakes. “P-waves are longitudinal seismic waves, like sound in the air, and they are the fastest waves propagating in planetary bodies,” says Brigitte Knapmeyer-Endrun, seismologist at the University of Cologne, who is the lead author of the study on modeling the Martian bark. “We also have secondary waves, S-waves, or shear waves. This movement is more like the trembling of guitar strings."
Crucially, S-waves are slower than P-waves. Therefore, when a Marsquake occurs, the Insight probe seismometer registers them a little later. “The difference between the appearance of S-waves and P-waves gives us an idea of the location of seismic activity, how far it is from our station,” says Knapmeier-Endrun. These waves also differ depending on the medium through which they pass and from which they are reflected. P-waves pass through solid rocks, liquids and gases, and S-waves only through solid rocks.
By analyzing the waves reaching the Insight seismometer, scientists can get an idea of the inner composition of Mars. Since S-waves cannot penetrate the liquid core, all of their energy is reflected entirely from the core-mantle boundary. Think of it as binary for computers. Only two elements, ones and zeros, can be combined to create extremely complex programming. Likewise, the two types of waves combine to paint a complex picture of Martian entrails. “We also look at the difference in arrival time, which allows us to determine the thickness of a particular layer,” says Knapmeier-Endrun.
Using such methods, she and her colleagues were able to determine the thickness of the bark. Previously, scientists had to use orbiting satellites to measure differences in gravity and topographic properties across the planet. In this way, they tried to determine the thickness of the crust, eventually coming to the conclusion that it was 110 kilometers on average. “Now that measurements are taken from the inside, we can say that this was a clear exaggeration,” says Knapmeier-Endrun. Scientists now believe that the average crustal thickness is at most 72 kilometers.
Researchers believe this crust is made up of two or three layers. There is the topmost layer 10 kilometers thick, which, according to Insight measurements, turned out to be unexpectedly light. This is probably due to the fact that it consists of crushed rock left over from the impact of meteorites. The layer below sinks to a depth of about 20 kilometers. “Unfortunately, we are not sure what is next there, just the mantle or even the third layer of the crust. There is some uncertainty in this regard, and we have not yet been able to resolve it, - says Knapmeier-Endrun. "We can confidently say that the crust is not as thick as previously thought, and that its density is less."
Planetary seismologist Simon Stähler of the Swiss Higher Technical School of Zurich has spearheaded the study of Mars' hottest interior, its core. Although Stehler's team has no way of looking into the interior of the central part of the planet, the researchers were able to obtain some information by analyzing S-waves bouncing off the boundary between the core and the mantle. These vibrations, unable to penetrate into the liquid Martian core, return to the surface, and there they are captured by Insight receivers. “It takes a whopping 10 minutes,” says Stehler, referring to the time from the marsquake to the time it takes for the signal reflected from the core to be captured.Having measured this time interval, his team determined the depth of wave penetration, and based on this, measured the depth of the core itself. It turned out that it begins about 1,550 kilometers from the surface.
Scientists have found that the core density is surprisingly low, at just 6 grams per cubic centimeter. This is much less than they expected from a high-iron Martian center. “It's still a bit of a mystery to us why the nucleus is so light,” says Stehler. There should certainly be lighter elements, although it is not clear which ones. He and his team hopes over time to record the P-waves formed as a result of the Marsquake on the opposite side of the planet, directly opposite the place where Insight is located. Since these waves can penetrate the boundary between the core and the mantle, they will provide the receiver of the lander with information about the composition of the Martian core. But for this to work, explains Stehler, "Mars must meet us halfway and arrange such a Marsquake on the other side of the planet."
In their scientific work, the Stehler team reports that the radius of the core is 1830 kilometers. Another team, led by Amir Khan, a geophysicist from the Swiss Higher Technical School of Zurich, found that this size is so large that there is very little room for the mantle, like inside the Earth. This layer, which surrounds the core, performs the heat trapping task. The earth's mantle is divided into two parts, and between them there is a so-called transition zone. The top and bottom layers are composed of different minerals. “The mantle of Mars - I will say this somewhat disrespectfully - is a simplified version of the Earth's mantle, judging by its mineralogical composition,” says Khan, who became the lead author of the work on the description of the Martian mantle.
Previous estimates of the core radius were made using geochemical and geophysical data and indicated the absence of the lower mantle layer. But to confirm this, the scientists needed Insight seismological data. They became the key to understanding the evolution of the Red Planet, in particular, why it lost its magnetic field, which would protect the atmosphere and possible life from the harsh solar winds. For a magnetic field to appear, a temperature difference is needed between the outer and inner parts of the core. It must be large enough to create circulating currents that mix the core fluid and promote the formation of a magnetic field. But the core of Mars cooled down so quickly that these convection currents died out.
Khan's analysis also shows that Mars has a thick lithosphere, as the hard and cold mantle is called. This may provide an answer to the question of why the Red Planet does not have tectonic plates that provoke powerful volcanic activity on Earth. “If there is a very thick lithosphere, it is extremely difficult to break it down to create some kind of tectonic plates on the Earth,” explains Khan. "They may have been on Mars early on, but now they have definitely closed up."
While Insight “eavesdrops” on the internal vibrations of Mars, then Perseverance, rolling on its dusty surface, looks for signs of ancient life in the rocks, determines the places where samples of the surface layer are collected and studies the geological history of Jezero. "Exploration is not sprinting, it's a marathon," NASA's deputy chief scientific officer Thomas Zurbuchen said at a press conference Wednesday on the rover's early successes on the Red Planet. "Perseverance is just one step on a long and carefully planned journey to explore Mars that will combine robot and human efforts in the coming years."
At a press conference, scientists talked about what Perseverance does during its travels.“The challenge is figuring out exactly which direction we want to go and how we're going to fit everything into our schedule,” said Vivian Sun of NASA's Jet Propulsion Laboratory, a systems engineer there. According to her, the scientists decided to send Perseverance about a kilometer south of the landing site in order to collect the first rock samples. The collected samples will be stored in the body of the rover, and then it will lay them on the surface of the planet for subsequent transfer to Earth on a return flight.
Perseverance is equipped with a two-meter robotic arm with a range of new devices, including a technology demonstrator called MOXIE to test the ability to generate oxygen from the Martian atmosphere. It has already demonstrated its ability to convert small amounts of atmospheric carbon dioxide into oxygen. There are also sensors for assessing the current climate and high-resolution cameras to capture what is around the rover. “We're just being tortured by the dust devils,” said Caltech geochemist Ken Farley. These are really devilish gusts of wind, very similar, as he says, to earthly ones.
Some rocks in the photographs resemble hardened lake silt. This indicates that it is there that one should look for traces of past life in the form of fossilized biological signs. Scientists also want to understand whether the rocks in the crater are of sedimentary or volcanic origin. If this is the remnants of volcanic emissions, then using radiometry, you can determine their age. This will enable a better understanding of the geological history of the materials collected by Perseverance. Farley says the most surprising finding to date is signs of flash floods and changes in water levels. This suggests that the crater has gone through several stages of drying and filling with water in a liquid state.
Armed with new software based on artificial intelligence, Perseverance also broke the record for rovers to move independently across the planet's surface, and it did so on the second day of autonomous movement. “Autonomous propulsion today is almost as fast as human-driven movement,” said Jet Propulsion Laboratory robotics engineer Olivier Toupet. A human can remotely control a rover by moving it about 30 meters a day. He performs carefully calibrated maneuvers, avoiding obstacles, and artificial intelligence allows you to increase the speed of the device. The software creates a three-dimensional map of the surface on which the vehicle travels, allowing it to optimize and update its route in real time. According to Toupe, the maximum distance traveled on Mars autonomously is about 107 meters. Scientists expect Perseverance to quadruple that figure over the next few weeks.
After completing a southerly flank, the Perseverance will head northwest to the delta of an ancient river that once carried its waters into Jezero Crater. Then he will begin to fully use the instruments on board to determine the chemical and mineralogical composition of the local Martian rocks, as well as their shape and texture. This information will help scientists learn more about the ancient watercourse of this basin.
And the Insight, located several thousand kilometers away, will continue to register subsurface tremors and reveal the internal structure of this rocky planet, which scientists have been able to characterize using seismology. “This is a very young area of research for humanity,” says Kottar. “We look at the stars for much longer than at our feet.”