Asteroid-Bound OSIRIS-REx Set to Begin New Quest for Life's Origins

The ambitious seven-year mission will visit the asteroid Bennu and bring back samples scientists think might contain the building blocks of life.

The countdown has begun for NASA’s OSIRIS-REx mission. It is set to visit an asteroid, pick up a sample and bring it back to Earth.

The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) is a part of NASA’s New Frontiers Program. It is the third mission to be selected as a part of this programme, after Juno to Jupiter and New Horizons to Pluto and beyond. The team behind OSIRIS-REx includes scientists from France, Germany, Italy, the UK, the US and Canada.

The mission was selected to sample the asteroid named 101955 Bennu, commonly called as just Bennu, orbiting the Sun very close to Earth. Unlike typical asteroids, such as the ones floating around in the belt between Mars and Jupiter, Bennu orbits the Sun in an orbit nearly the same as Earth’s. In fact, it’s so close to us that the 500-metre-wide rock’s orbit will bring it within the Moon’s orbit in 2135. It is also classified as a ‘potentially hazardous object’ because it just might smash into Earth someday. But you can breathe easy for now: scientists think that day is at least 300 years away.

Bennu was selected to be the target because it is distinctively black and carbonaceous, an indication that it holds organic compounds we are interested in. Such asteroids are essentially remnants from the early Solar system, debris thrown out during the formation of the Sun and the planets. Their composition is thought to have been unchanged through billions of years. These remnants also suffer minimal space weathering –effects of radiation, high energy rays, and solar wind – and therefore hold a perfect record of conditions that existed when Earth formed. Scientists believe they contain amino acids and sugars, chemical compounds presumed to be the primary building blocks for life on Earth. These compounds have also been found in meteorites before.

All this means that scientists believe analysing the likes of Bennu could give us great insights into the formation of the Solar System and whether space-rocks might have played a significant role in seeding our planet with life.

If that’s true, would we technically be aliens ourselves?

The mission objectives for OSIRIS-REx are:

  • Return and analyse a sample of Bennu’s surface
  • Map the asteroid
  • Document the sample site
  • Compare observations at the asteroid to ground-based observations

The truck-sized spacecraft will be launched into space by an Atlas V rocket on September 8 for a two-year cruise to Bennu.

Halfway through its journey towards Bennu, OSIRIS-REx will prepare to sling past us on September 23 next year, using our planet’s gravity to throw itself toward Bennu. This will increase the speed of the craft from the launch velocity of 19,000 km/hr to nearly 103,000 km/hr. A year after this space-acrobatics, when the probe is about two million km from Bennu, it will slow down to match the asteroid’s speed (101,000 km/hr).

The procedure towards a rendezvous will begin on August 17, 2018. The craft will first start flying in tandem near Bennu before easing into an orbit around it. After reaching the asteroid on March 18, 2019, OSIRIS-REx will begin extensive surveying and mapping of Bennu to determine a location for the sampling of the grey, dusty body.

On July 4, 2020, OSIRIS-REx will descend slowly towards the asteroid, extending a robotic arm named TAGSAM, for Touch-And-Go Sample Acquisition Mechanism. The arm is fitted with a sampler head that looks like a bottle cap. This will hold particles from the asteroid.

When TAGSAM is just a few centimetres away from Bennu, it will let loose a small burst of nitrogen gas to stir up and disturb the surface. The puff will kick up loose grains and small pieces of debris. Some of this will collect in the sampler head. Once that’s done, the TAGSAM arm will retract into the craft, dropping the sample safely in a container to be stowed away for us. The probe will carry enough nitrogen to attempt this exercise thrice, with the arm remaining in physical contact with the asteroid for all of five seconds every time. The craft is capable of carrying up to two kilograms of asteroid material back to Earth.

On March 3, 2021, scientists estimate that OSIRIS-REx will prepare to depart from Bennu, shooting its thrusters out and flying away at the speed of about 1,100 km/hr. After a little over two years of hurling through space, it will reach close to Earth on September 24, 2023, safely holding samples of a tiny, far away body.

When it is close to the planet, the craft will jettison the sample return capsule for re-entry and push away, setting itself in orbit around the Sun. The ejected sample container that is protected in a heat shield will make contact with our atmosphere at a numbing 44,640 km/hr, burning its way towards us. It will continue falling freely till it’s about three kilometres from the surface, when parachutes will deploy for a soft landing. This landing and recovery will take place in the Utah Testing and Training Range, in the desert region in North America, over seven years after the spacecraft’s launch.

Wondrous as the mission sounds, it pays to note that OSIRIS-REx is visiting an asteroid so very close to us and yet returning a sample after seven years. Scientists can’t launch such missions frequently – so they’ll dig as deep into the Bennu sample as they can go with their chemical tools. They’ll be looking for amino acids and other organic compounds, but not for microbes or any kind of primitive life-forms. In fact, the approval for the mission was granted only after scientists could say with some level of cerntainty that microbes do not exist on Bennu. The Planetary Protection Act (Article 9) has heavy restrictions on re-entry vehicles that might contaminate Earth with alien microbes!

A call for naming the asteroid now called Bennu was put out in 2013. The winner was a nine-year-old boy called Mike Puzio, who stated that the craft, with its arm extending out, resembled the Egyptian bird Bennu, thought to be an inspiration for the phoenix. The name was chosen because it aptly went with the theme of the craft named after Osiris, an Egyptian deity himself.

The connections are plenty and interesting, as principal investigator Dante Lauretta noted on his blog three years ago. Osiris, the Egyptian god of afterlife, is said to have sprinkled seeds around the Nile and caused it to flood, thus spreading agriculture. It is believed that asteroids like Bennu possibly seeded life on Earth. Osiris was killed by his brother Set, who shut his body tightly in a coffin and threw it into the Nile. OSIRIS-REx has a capsule that is sealed tight and will be thrown into Earth. Lastly, when Osiris’s body was recovered, Set chopped it up and spread the pieces throughout the world. The samples from OSIRIS-REx will be distributed to the international scientific community for analysis.

In its initial days, the mission was just called OSIRIS. Then, when Lauretta’s team decided to up the ante and have OSIRIS sample the asteroid’s regolith – surface rock of a body – they decided to add a form of “regolith explorer” to it. Remembering how the dinosaurs died due to an asteroid impact, Lauretta added “REx” to the name. It makes for good irony: now a dinosaur is rushing at enormous speeds towards an asteroid.

Sandhya Ramesh is a science writer focusing on astronomy and earth science.

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