NASA
On November 26th, the "Insight" Mars probe successfully landed on the Martian Eleusion plain and began to detect the internal structure and phenomena of Mars. The Eurexian Plain, where the "Engrave" landed, is a huge volcanic plain near the equator of Mars, only about 600 kilometers from the Gaelic crater landing on the "Curious" Mars.
Just a few days ago, the National Aeronautics and Space Administration (NASA) also announced the planned landing site for the next-generation Mars rover "Mars 2020." The Jezero crater stood out from the three alternative landing sites and became the destination of the Mars 2020 Mars.
Although Mars's size is smaller than that of the Earth, it is still not an easy task to select a suitable landing point for a valuable Mars probe on its surface of about 140 million square kilometers. It requires engineers and scientists to interact with each other. Cooperate with each other.
Engineering constraints are the primary consideration
Like Earth, the surface of Mars has a variety of topography, with an endless plain, a 6,000-meter-long canyon and the first peak of the solar system with a drop of 27,000 meters. For a car driver on Earth, parking on a flat ground is obviously easier than parking the car on a slope because there is no need to worry about the car slipping or implementing a relatively complex ramping process at the start. For a rover, landing on a relatively flat terrain is also a less risky and more successful option. There are obvious north-south differences in the terrain of Mars. The southern hemisphere is full of undulating mountains and valleys, as well as large and small craters, and the terrain in the northern hemisphere is relatively flat. Therefore, with the exception of detectors with special missions, most of the Mars Landing Detectors landed in the northern hemisphere and near the equator.
When the detector is landing, it generally needs to decelerate by interacting with the atmosphere. At the final stage of the landing, the power provided by its own engine is used to achieve a soft landing. The atmosphere of Mars is relatively thin. If the geographic elevation of the landing site (similar to the concept of altitude on Earth) is too high, then the detector has not been in contact with the surface of Mars before it is fully decelerated by the atmosphere. Therefore, it is generally necessary to select a region with a lower elevation as a landing site.
Detectors working on Mars for a long time use solar cells to generate electricity. At the same time, light sensors used to navigate and detect obstacles also require better lighting conditions. Mars' high latitudes do not have sufficient light, so Mars probes mostly choose to land in areas with latitudes less than 30 degrees. Good lighting conditions at low latitudes also result in a milder day and night temperature difference, which does not cause extreme day and night temperature differences and nighttime low temperatures like in high latitudes, making it easier for detectors to maintain their own thermal balance.
If the detector accidentally landed on a rock-filled area, it would cause a lot of trouble for the detector's work. Rocks can damage the detector's landing buffer mechanism and hinder the normal operation of the retarding engine. At the same time, for the Rover, the rocks that are scattered will also hinder their movement. Therefore, it is generally necessary to select a place where the rock is scarce as a landing point.
In addition to detectors landing on Mars, MRO, MAVEN and other detectors provide us with global information about Mars in a way that flies around Mars. Using the orbiter's probing data, scientists and engineers can make judgments about whether the various areas of Mars meet these hard constraints and give possible landing point options.
Scientific goals help select locations
The scientific goal of recent Mars exploration is to look for evidence of current or existing life on Mars. Through previous research, scientists have realized that if a region on Mars used to be a delta formed by submarine, lake basin, riverbed, or river alluvial, then there is likely to be an environment in which life can be born. In addition to being able to send back the most accurate images of the surface of Mars, the detectors that fly around Mars can also use the multi-band spectrometers and altimeter instruments to bring more information about the surface topography and rock composition of Mars. Scientists can use Mars' global data to select potential landing sites based on the specific scientific goals of each landing detector. Later, through constant encryption detection and comparison discussions, narrow the landing site candidate range and determine the landing point actually used.
Take the "Curious" rover as an example. The Rover was originally scheduled to launch in 2009, and the work of selecting a landing site began in 2006. NASA issued a notice to the members of the Mars Exploration Project Analysis Group to collect landing sites, and scientists from various research institutions began to select jobs. Soon, the scientists submitted 33 alternative landing site options. Based on this, NASA adjusted the detection plan around the Mars probe to further obtain more detailed remote sensing observations of the 33 optional landing sites.
A year later, the scientists again held a seminar to use the data already obtained to select the landing site. The selection focuses on four factors: the ability to acquire geological features, evidence of appropriate life, the presence of biometrics, and the ability to assess the potential of life at the site. After three days of discussion, the number of candidates for the landing site was reduced to six.
Interestingly, the Gail crater landing site actually used by Curious has already been eliminated in this round of PK. However, in 2008, the CRISM spectrometer on the MRO detector brought new rock composition detection data. Analysis of these data shows that there are a large number of minerals in the Gaelic crater that can only be formed in a water-rich environment, meaning that there were lakes. In addition, the geomorphological features of the site indicate that it has been frequently washed away by floods.
These new situations have aroused great interest among scientists and re-listed the Gael impact crater as an alternative landing point. At this point, the Curious task was postponed to 2011 for other reasons, and scientists gained longer time to make a more full assessment of the landing site.
In 2010, after the last seminar, scientists still did not agree on the selection of landing sites. Therefore, the strengths, weaknesses, and recommendations of the four candidate points, including the Gaelic crater, were summarized in a four-page document submitted to NASA headquarters for final decision by NASA officials. Since the successful landing, "Curious" has brought a lot of new scientific discoveries. In June this year, evidence of the existence of organic molecules was also found, indicating that the selection of the Gaelic impact crater as a landing site was quite successful.
Manned landing has more requirements
At present, research on landing sites for manned landings on Mars is also underway. Like the detectors, the manned mission also requires a soft landing on a relatively flat terrain. The lower elevation of geography, the flat terrain, and the absence of large amounts of rock require consistency with unmanned landing sites. In addition, there are more factors to consider when manned to land on Mars.
Due to the high cost of carrying the Earth from Mars, it is difficult for astronauts to carry large amounts of water to Mars under current technical conditions. The water they need to survive on a daily basis must be taken locally on Mars. At the same time, water can also be used by astronauts to produce crops on Mars, generating oxygen for their breathing and hydrogen that can be used as a fuel for the spacecraft.
On Mars, there are two ways to produce large amounts of water. One is by breaking down the hydrated minerals, and the other is by drilling the ice on Mars. Intuitively, cutting the ice layer seems to be an easier and straightforward option. However, the ice on Mars is generally found in the cold polar regions, where the low temperatures will pose greater challenges to the astronauts' survival and the normal operation of the landing spacecraft. Extremely low temperatures also mean that it takes more energy to cut the ice. In addition, when astronauts take off from the Martian polar region and return to Earth, they cannot get the "help" of Mars rotation as they did at the equator. Therefore, the search for areas rich in hydrated minerals at low latitudes is currently considered a more reasonable option. (Li Huichao)
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