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MIT's REXIS and Bennu Water Surface

This mosaic image of the asteroid Benn consists of 12 PolyCam recordings collected on December 2 by the OSIRIS-REx spacecraft from the 15-mile (24km) range. The picture was obtained at a 50 degree angle between the aircraft, the asteroids and the sun. Credits: NASA / Goddard / University of Arizona

After flying in space for more than two years, NASA's OSIRIS-REX aircraft (origin, spectrum interpretation, resource identification, security regulatory researcher) recently entered the orbit around their target, the asteroid Bennu. It is believed that asteroids like Bennu are the remains of debris created in our solar system. So in the first mission of the kind that NASA flew, OSIRIS-REX asks to take the sample and bring it to Earth.

With several instruments on the aircraft, MIT is a student built by a student named REgolith X-Ray Spectrometer (REXIS), which will provide data for selecting sampling sites as well as other mission goals, including the characterization of the asteroid and its behavior and comparing them with observations on Earth. REXIS is a joint project of the Department of Earth, Atmosphere and Planetary Science (MIT), the MIT Department of Aeronautics and Astronautics (AeroAstro), the Harvard University Observatory, the Astrophysics and Space Research Institute of MIT Kavli and the MIT Lincoln Laboratory.

Shortly after arriving in Benn, scientists of OSIRIS-REX announced they identified water on the asteroid, which could affect the choice of sampling sites. EAPS talked with Richard Binzel, an asteroid expert at MIT and a co-investigator of the mission that led the development of REXIS – on the role of the instrument and what this discovery means for future use of similar devices. Binzel is also a professor of planetary science at EAPS with a joint appointment at AeroAstro and associate professor of Margaret MacVicar.

Q: What is the purpose of REXIS, as part of the OSIRIS-REx mission?

A: The mission goal of OSIRIS-REx is to get an untouched sample from the asteroid surface, Bennu, which has some of the most original survival chemistry since the very beginning of our solar system. The asteroid is like a weather capsule, which tells us what the condition of our solar system was when it came to 4.56 billion years ago.

The goal of REXIS is to map the Bennu composition as a support mission, selecting the place for that pattern. The goal is to go to the asteroids and spend it for a year in detail studying to determine which place can give us the highest scientific return. It is about progressive assessment and characterization of the asteroid: We will go through the orbits that descend gradually down to the point where we see the surface in exceptionally good detail – such as crater and bramble characteristics. So we know where to touch the surface, take the pattern and bring it safely to the aircraft.

To do this, on OSIRIS-REx, there are a number of instruments: visible cameras and spectrometers mainly in visible and close infrared wavelengths that map the asteroid surface, along with MIT's REXIS, a REgolith X-ray spectrometer. REXIS complements all other instruments and contributes to the rest of the data by looking at the X-ray. No other instrument on OSIRIS-REX will see the X-ray surface. So this is quite unique in the planet's research, and the fact that they built the students is even more incredible.

One of our goals is to confirm the mapping of minerals by other instruments. Visible and close infrared spectrometers are sensitive to the mineral composition of the surface, and REXIS measures the individual atomic elements that are present. One of the things we want to achieve is to see if the atomic elements we measure in accordance with the minerals that other instruments measure and vice versa.

Q: How does REXIS work?

A: REXIS works by exploiting the solar X-ray emission. Some of these X-ray rays hit the asteroid and interact with atoms on the surface: they absorb and change the energy level of electrons in the atoms. When the atoms return to their basic state, they radiate the X-ray photon, meaning that the X-rays from the sun caused the asteroid to shine or fluoresce.

REXIS measures the energy and placenta of X-ray that fluoresces from the surface of the asteroid, and energy tells us what are the atoms present. The X-ray photon energy emitting atom corresponds exactly to the energy between the two electronic orbits. Each atom has its own unique energy signature, so we can conclude the elemental composition of the asteroid surface.

We will look for things like iron, silicon, oxygen and sulfur – some of the very basic building blocks of planetary bodies. We will be able to measure the number and determine the composition of this asteroid.

We now perform all types of calibration measurements and learn about the instrument's characteristics in space: the ways it works as expected and the differences. It's part of the sun-tracking instrument design and calibrating asteroid observations, taking into account all the variations of the sun. REXIS has two parts: one part is the main spectrometer measuring the X-rays emitted from the asteroid surface; the other is a small solar X-ray monitor or SXM, and is constantly looking at the sun's output, which varies in time ranges from minutes, hours, and days. So if we look at one place on the asteroid and see this huge X-ray fluorescence, we'll know if that is an asteroid that's special in that place, or it's just a solar torch that has happened. At the same time. We also observe the cosmic X-ray background or CXB and calibrate the sensitivity of our instrument by observing a stable, powerful source of X-rays in the sky called Cancer.

We also calibrate REXIS measurements by laboratory measurements of meteorites, and we will be able to determine which type of meteor is most desirable. If we see any variations on the surface, we will be able to tell which regions have the most similarity to known meteorites, and this can lead us to where we will get our sample.

Q: NASA announced that they found evidence of water on Bennu. What does this mean for REXIS and where did the sample take?

A: Mission OSIRIS-REX found evidence of the presence of hydrated minerals on the surface of the asteroid Benn. These minerals arise when water molecules react with rock material and become part of the crystal structure. Meteorite studies show that this process took place very early in the history of the Solar System. This discovery tells us that Bennu's surface has not been heated at temperatures that are high enough to break down these minerals and release water. It seems that Bennu contains this primordial water, providing clues as to how this material was shipped to Earth, leading to a viable world.

This is a tempting news for REXIS because it is one of the atomic elements we are looking for for oxygen, which, of course, is the main ingredient of water, and REXIS has the potential to confirm the findings of these water molecules in minerals Benn. .

Many factors go into the decision to sample. First of all, we need to determine which parts of the surface are safe to go, to know that the aircraft can move, get a pattern, and come back safely. Then, from all safe regions, which are scientifically most interesting – based on what we call a scientific value map. The goal is to have a complete understanding of the composition of the asteroid surface and any variability. Then we want to find a sampling site that we think has the most original organic chemistry since the beginning of the solar system, so the water on the Bennu that was signed by the water was very interesting for the sample.

At the moment we are still quite far from the asteroid and we are slowly moving towards lower orbital distances. By REXIS we will reach the orbital distance to begin our scientific operations in June of this year. Then REXIS will print the composition of the asteroids in the sense of its atomic elements. When we get the sample back, we will be able to check if REXIS is right. If so, this means that we can send a REXIS-like device anywhere in the Solar System and get a reliable impression of detail about the detail of these objects.

If REXIS is successful, it shows that with a small instrument you can get great science. Our nickname for REXIS is, "a small spectrometer that he could."

Explore further:
A student-built experiment integrated with NASA's mission to OSIRIS-REX

Massachusetts Institute of Technology

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