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Tonight, 320 million kilometers from us, NASA’s OSIRIS-REx spacecraft will briefly land on an asteroid, pick up some rocks from the surface, and then go on a long journey to bring them back to Earth, where they will be analyzed for find out. something else about how our solar system formed. The mission, which took years of preparation and planning, is one of NASA’s most ambitious in recent times and has caused many headaches for those responsible, now prepared for the most delicate and uncertain passage.
Asteroids
Asteroids are strange types: we can consider them close relatives of terrestrial planets, like ours, even if they are considerably smaller and rarely spherical. The hypothesis most widely shared by astronomers is that asteroids are what remains of the “protoplanetary disk”, the gigantic mass of dust and gas orbiting the Sun from which the planets and natural satellites of the solar system formed billions of millions of years ago. years. .
Asteroids are made up of minerals common on Earth, such as iron, while those made primarily of ice are known as comets. Sometimes an asteroid is what remains of an old comet, which has lost its ice as a result of cyclical passes near the Sun.
Almost all asteroids keep company in a part of space called the “main belt,” a large ring of debris that orbits the Sun, between the orbits of Mars and Jupiter, at a safe distance from Earth. Impacts and other events, however, can disturb the orbits of some of these space stones, leading them to approach or touch (in astronomical terms) our planet.
The main belt, in English “Asteroid Belt” (NASA)
Determining
Some of these are part of the so-called Apollo group, a set of celestial bodies that are kept under control because in the future they could interfere with Earth’s orbit: among them is also the asteroid 101955 Bennu, the target of OSIRIS-REx. We can imagine it as a small mountain that travels in space at a speed of about 28 kilometers per second: at its point of maximum extension it has a diameter of 565 meters and has an estimated mass of around 70 million tons.
OSIRIS-REx
The NASA probe has a central cubic body of 3 meters on each side, but with the solar panels open it reaches a maximum extension of more than 6 meters. It is equipped with various tools to study the surface of Bennu and map it, while at its bottom it has a particular mechanical arm to retrieve some rocky material from the asteroid.
OSIRIS-REx launched in 2016 and arrived at Bennu in 2018. Since then, it has orbited around it, tirelessly collecting data on its surface and revealing various surprises to mission leaders. Initially, Bennu was chosen because, seen by telescopes, it appeared to be an after all smooth asteroid, with a sandy surface that would have allowed the probe to land for sampling without particular problems. However, once it got close, OSIRIS-REx detected very different conditions: Bennu’s surface has numerous ridges and sharp rocks, which could complicate sampling by the probe.
Asteroid Bennu photographed closely by the OSIRIS-REx spacecraft (NASA)
The discovery didn’t catch the researchers so off guard, who had immediately contemplated the possibility that the asteroid was less smooth than it appeared from a distance. Mission times have been extended, allowing you to create highly detailed three-dimensional maps of Bennu, which OSIRIS-REx can now use to understand where it is in relation to the asteroid’s surface, and whether to continue the collection or give up. in case there is is the risk that something will go wrong.
In addition, the probe is at such a distance that it cannot be maneuvered in real time: the data it sends and receives takes an average of 18 minutes before crossing the hundreds of millions of kilometers that separate it from Earth. In a sense, OSIRIS-REx will have to do everything by itself, and only after several minutes will we know how things have gone on the asteroid.
Vitae
The planned site for the collection of rock material is a large crater called Nightingale: the researchers selected it, believing it could be a good place to collect samples containing traces of water and organic material. Of course, this does not necessarily mean that there are necessarily life forms on Bennu, as we know them, but it could indicate the presence of substances that are necessary to form it, such as carbon molecules. It may have been these ingredients, dating back to the formative period of our solar system, that later made it possible for life to form on Earth.
Withdrawal
Since the beginning of the year, those responsible for the mission have carried out two general tests to simulate the moment of taking the rocky material. To do this, they brought OSIRIS-REx closer to about 40 meters from the surface of the asteroid, making sure that all instruments were working correctly, including systems to automatically determine whether to continue with the attempt or stop it to avoid damaging the probe.
The OSIRIS-REx probe in a graphic elaboration, at the bottom you can see the robotic arm to take the material from the asteroid (NASA)
When in Italy it is past midnight (12:12), OSIRIS-REx will begin to approach Bennu extending its robotic arm. Upon touching the surface, the probe will emit a puff produced by a nitrogen canister, kicking up dust and rocks. These must then flow into a cylinder, which will be stored in the central body of the probe.
The sample will be transported on a long journey back to Earth, where researchers can analyze it to learn more about the asteroids.
OSIRIS-REx approach test to Bennu, carried out last August (NASA)
Unexpected
The mission brings with it many unknowns and therefore its leaders have studied various remedies to prevent it from becoming a failure. In addition to the automatic system to forgo sampling, the probe is equipped with three different nitrogen-containing cans, which can be used for as many attempts. If you interrupted the operation before starting the sampling, the probe would not even use nitrogen, so researchers have good scope for further attempts.
The problem is that, in the event of a sampling interruption, OSIRIS-REx would have to use its own retroreflectors to quickly zoom away from the asteroid. This maneuver would cause dust and rocks to lift off Bennu’s surface, likely rendering Nightingale Crater unusable for a second attempt. For this reason, the researchers identified more than one area that could be used for sampling, as an alternative to the main one for the attempt scheduled shortly after midnight.
More grams
NASA is not the first space agency to try to extract material from an asteroid. In recent years, the Japanese Hayabusa and Hayabusa-2 probes have successfully taken a few milligrams from a pair of asteroids. However, NASA’s mission plans to collect at least 60 grams of material, which should allow for more extensive and accurate research once the samples are on Earth.
To be honest, OSIRIS-REx has the capacity to collect up to 2 kilograms of rock material, but it will hardly collect such heavy samples. On board, the probe has systems to detect the weight of the removed material, an important detail to know from a distance if the collection was successful or not. If the systems indicate that they have collected up to 60 grams of material, the mission leaders can begin the rest of the program to transport them to Earth.
Return
If all goes according to plan, OSIRIS-REx will leave Bennu in March next year and then it will take two years to join us. The return of the container is scheduled for September 2023: stopped by a small parachute, its contents from the desert of a small world will land in the desert of Utah, in our world.
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