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Tuesday, December 01, 2020

Explained: What is asteroid Bennu, and why is the NASA studying it?

Bennu is an asteroid about as tall as the Empire State Building and located at a distance of about 200 million miles away from the Earth.

By: Explained Desk | New Delhi | Updated: October 28, 2020 8:47:56 am
Asteroid Bennu, OSIRIS-REx, NASA asteroid Bennu,US spacecraft, Us spacecraft asteroid, rare rubble grab, science, asteroidThis Aug. 11, 2020 photo shows the sampling arm of the OSIRIS-REx spacecraft during a rehearsal for an approach to the "Nightingale" sample site on the surface of the asteroid Bennu. (NASA/Goddard/University of Arizona via AP)

On Tuesday, NASA’s OSIRIS-REx — Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — spacecraft briefly touched asteroid Bennu, from where it is meant to collect samples of dust and pebbles and deliver them back to Earth in 2023.

The asteroid was named after an Egyptian deity by a nine-year-old boy from North Carolina in 2013 who won NASA’s “Name that Asteroid” competition. The asteroid was discovered by a team from the NASA-funded Lincoln Near-Earth Asteroid Research team in 1999.

What is an asteroid?

Asteroids are rocky objects that orbit the Sun, much smaller than planets. They are also called minor planets. According to NASA, 994,383 is the count of known asteroids, the remnants from the formation of the solar system over 4.6 billion years ago.

Asteroids are divided into three classes. First, those found in the main asteroid belt between Mars and Jupiter, which is estimated to contain somewhere between 1.1-1.9 million asteroids.

The second group is that of trojans, which are asteroids that share an orbit with a larger planet. NASA reports the presence of Jupiter, Neptune and Mars trojans. In 2011, they reported an Earth trojan as well.

The third classification is Near-Earth Asteroids (NEA), which have orbits that pass close by the Earth. Those that cross the Earth’s orbit are called Earth-crossers. More than 10,000 such asteroids are known, out of which over 1,400 are classified as potentially hazardous asteroids (PHAs).

What is the OSIRIS-REx mission?

This is NASA’s first mission meant to return a sample from the ancient asteroid. The mission is essentially a seven-year-long voyage and will conclude when at least 60 grams of samples are delivered back to the Earth. As per NASA, the mission promises to bring the largest amount of extraterrestrial material back to our planet since the Apollo era.

The mission was launched in 2016, it reached its target in 2018 and since then, the spacecraft has been trying to match the velocity of the asteroid using small rocket thrusters to rendezvous it. It also utilised this time to survey the surface and identify potential sites to take samples.

On Tuesday, the spacecraft’s robotic arm called the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), made an attempt to “TAG” the asteroid at a sample site which was no bigger than a few parking spaces and collected a sample.

The spacecraft contains five instruments meant to explore Bennu including cameras, a spectrometer and a laser altimeter. The departure window for the mission will open up in 2021, after which it will take over two years to reach back to Earth.📣 Follow Express Explained on Telegram

Why are scientists studying asteroid Bennu?

Bennu is an asteroid about as tall as the Empire State Building and located at a distance of about 200 million miles away from the Earth. Scientists study asteroids to look for information about the formation and history of planets and the sun since asteroids were formed at the same time as other objects in the solar system. Another reason for tracking them is to look for asteroids that might be potentially hazardous.

It is for these reasons that scientists are interested in gathering information about this particular asteroid. Significantly, Bennu hasn’t undergone drastic changes since its formation over billions of years ago and therefore it contains chemicals and rocks dating back to the birth of the solar system. It is also relatively close to the Earth.

How do chemicals and rocks offer scientists clues about the solar system?

Because of Bennu’s age, it is likely to contain material that contains molecules that were present when life first formed on Earth, where life forms are based on carbon atom chains. Even so, “organic material like the kind scientists hope to find in a sample from Bennu doesn’t necessarily always come from biology. It would, though, further scientists’ search to uncover the role asteroids rich in organics played in catalyzing life on Earth,” NASA says.

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What do we know about the asteroid so far?

So far, we know that the asteroid is a B-type asteroid, implying that it contains significant amounts of carbon and various other minerals. Because of its high carbon content, the asteroid reflects about four per cent of the light that hits it, which is very low when compared with a planet like Venus, which reflects about 65 per cent of the light that hits it. Earth reflects about 30 per cent.

Around 20-40 per cent of Bennu’s interior is empty space and scientists believe that it was formed in the first 10 million years of the solar system’s formation, implying that it is roughly 4.5 billion years old. As per high-resolution photographs taken by the spacecraft, the surface of the asteroid is covered in massive boulders, making it more difficult to collect samples from its surface.

There is a slight possibility that Bennu, which is classified as a Near Earth Object (NEO), might strike the Earth in the next century, between the years 2175 and 2199. NEOs are comets and asteroids nudged by the gravitational attraction of nearby planets into orbits which allows them to enter the Earth’s neighbourhood.

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