On May 11, NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft will depart asteroid Bennu, and start its two-year long journey back to Earth. OSIRIS-REx is NASA’s first mission to visit a near-Earth asteroid, survey its surface and collect a sample from it.
In October 2020, the spacecraft briefly touched asteroid Bennu, from where it collected samples of dust and pebbles. Bennu is considered to be an ancient asteroid that has not gone through a lot of composition-altering change through billions of years, which means that below its surface lie chemicals and rocks from the birth of the solar system.
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Therefore, scientists and researchers are interested in studying this asteroid as it might give them clues about the origins of the solar system, the sun, the Earth and the other planets.
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 for known asteroids, the remnants from the formation of the solar system over 4.6 billion years ago.
Bennu is an asteroid about as tall as the Empire State Building, located 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 potentially hazardous asteroids.
Bennu is named after an Egyptian deity. The name was suggested 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.
So far, we know that Bennu 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 percent 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 creation, 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 allow them to enter the Earth’s neighbourhood.
Bennu is believed to have been born in the Main Asteroid belt between Mars and Jupiter and because of gravitational tugs from other celestial objects and the slight push asteroids get when they release absorbed sunlight, the asteroid is coming closer to Earth.
In October 2020, the spacecraft contacted the surface of the asteroid successfully and fired a burst of nitrogen gas meant to stir rocks and soil. Once the surface was disturbed, the spacecraft’s robotic arm captured some samples. The spacecraft’s engineers have also confirmed that shortly after the spacecraft made contact with the surface, it fired its thrusters and “safely backed away from Bennu”.
When the spacecraft finally returns in September 2023, it will bring back the largest sample collected by a NASA mission since the Apollo astronauts collected samples of Moon rock.
“There is no straight path back to Earth. Like a quarterback throwing a long pass to where a receiver will be in the future, OSIRIS-REx is traveling to where the Earth will be. The spacecraft will circle the Sun twice, covering 1.4 billion miles (2.3 billion kilometers) over to catch up with Earth,” NASA said in a statement.
Scientists will use the asteroid samples to study the formation of the solar system and of habitable planets such as Earth. NASA will also distribute a part of the samples to laboratories worldwide and will reserve about 75 per cent of the samples for future generations who can study it with technologies not yet created.
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. It also utilised this time to survey the surface and identify potential sites to take samples.
The spacecraft contains five instruments meant to explore Bennu including cameras, a spectrometer and a laser altimeter.
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