Asteroid Bennu

Context

NASA releases new images to show historic landing and sample collection on asteroid.

Background

After a four-year journey, NASA's robotic spacecraft Osiris-Rex briefly touched down on asteroid Bennu's boulder-strewn surface to collect rock and dust samples in a precision operation 200 million miles (330 million kilometers) from Earth.

The images taken provide a play-by-play sequence of the dramatic landing, which include Osiris-Rex's sampling arm breaking a large but fragile rock on contact.

NASA’s OSIRIS-REx Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer, spacecraft briefly touched asteroid Bennu. The collected samples of dust and pebbles will deliver on 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.

Asteroids

These are the rocky objects that orbit the Sun, much smaller than planets, hence sometimes they are 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.

These are divided into three classes, which are, those found in the main asteroid belt between Mars and Jupiter, 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 group 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.

Mission OSIRIS-REx

It is the first mission of NASA that aims 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 extra-terrestrial material back to our planet since the Apollo era.

It was launched in 2016, and reached its target in 2018, 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 20th Oct, 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.

Why the Asteroid Bennu was Chosen

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.

Proximity to Earth - It is closest asteroids to Earth are called Near-Earth Objects (NEOs). As the name suggests, NEOs are objects that orbit within 1.3 AU of the Sun. (1 AU = the distance between Earth and the Sun, or ~93 million miles) For a sample return mission like OSIRIS-REx, the most accessible asteroids for a spacecraft to reach are located between 1.6 AU and 0.8 AU. The ideal asteroid has an Earth-like orbit with low eccentricity and inclination.

Size - Small asteroids spin so fast thus lose its surface material. The ideal asteroid has a diameter larger than 200 m so that a spacecraft can safely come into contact with it and collect a sufficient sample.

Composition - Asteroids are divided into different types based on their chemical composition. The most primitive asteroids are carbon-rich and have not significantly changed since they formed nearly 4 billion years ago.

All these factors were complied by the asteroid Bennu and thus it was chosen.

Information That Can be Gathered by Asteroid Bennu

So far, the information provided by the mission we know that the 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 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.

Conclusion

By knowing the 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. The mission also helps us in knowing the hidden facts of our solar system.

Studying these materials will help us understand the primitive dust from which the solar system grew, and the range of organic compounds present. It will also tell us the physical properties of something that might hit the Earth, potentially helping us stop it.

Connecting the Article

Question for Prelims

Mission OSIRIS-REx is related to

(a) Atomic clock
(b) Asteroid Bennu
(c) Mars planet
(d) Jupiter planet

Question for Mains

How the space exploration missions like OSIRIS-REx mission, can contribute in the socio-economic development ?