16-sec-action, 334 mn km away: Osiris to grab 1st asteroid sample on Oct 20

A well-preserved time capsule from the early solar system, asteroid Bennu could hold answers to the origin of our sun, its planets, and ultimately life as we know it

It was in 1957 when a small Soviet spacecraft reached the escape velocity to leave the planet and enter the Earth's orbit. Six decades since the Sputnik-I's path-breaking achievement, OSIRIS-REx is set to sneak in and return samples from an asteroid — 334 million km away from the Earth.

The spacecraft will make its first attempt to collect the dust, mineral sample on October 20.

Nasa's Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft will perform the historic event as the robotic spacecraft descends to asteroid Bennu’s boulder-strewn surface, touch down for a few seconds and collect a sample of the asteroid’s rocks and dust to begin a journey home where scientists will conduct elaborate studies on the alien material.

. The mission’s target is Bennu, a carbon-rich near-Earth asteroid that is also potentially hazardous to Earth. (Source: Nasa)

The mission was launched in September 2016 from Cape Canaveral in Florida and the spacecraft arrived at its destination, asteroid Bennu, on December 3, 2018, covering over two billion km of cosmic distance.

The 16-second TAG manoeuvre

The mission will perform the first attempt of its Touch-And-Go (TAG) sample collection event when a series of manoeuvres will bring the spacecraft down to site Nightingale, a rocky area 52 ft (16 m) in diameter in Bennu’s northern hemisphere, where the spacecraft’s robotic sampling arm will attempt to collect a sample. The National Aeronautics and Space Administration (Nasa) said in a statement: "Site Nightingale was selected as the mission’s primary sample site because it holds the greatest amount of unobstructed fine-grained material, but the region is surrounded by building-sized boulders." The sample collection site is the size of just about a few parking blocks.

During the 4.5-hour sample-collection event, the spacecraft will perform three separate manoeuvres to reach the asteroid’s surface. With the thrusters coming to life, the spacecraft will begin a downward trajectory on the asteroid, leaving the orbit in which it has been for close to two years. As the spacecraft descends, touches down on the surface, and fires one of its three pressurised nitrogen bottles, the agitated gas will lift Bennu’s surface material, which will then be caught in the spacecraft’s collector head. After this brief touch, OSIRIS-REx will fire its thrusters to back away from Bennu’s surface and navigate to a safe distance from the asteroid — all of this in just 16 seconds.

Why Bennu?

Bennu is a diamond-shaped pile of rubble floating in space, but there’s more to it than meets the eye. The asteroid is just one of the nearly 780,000 asteroids in our solar system, but what makes it unique and appealing is its proximity to the Earth. Unlike most other asteroids that circle the Sun in the asteroid belt between Mars and Jupiter, Bennu circles the Sun nearly in the same plane as the Earth making its closest approach every six years. Size is another aspect, most asteroids spin on their axis which makes it difficult to approach them by spacecraft. However, Bennu has a diameter of 492 metres, a bit more than the height of the Empire State Building in New York City, and it rotates once every 4.3 hours.

The mission’s Touch-And-Go (TAG) sample collection event is scheduled for Oct. 20, 2020 on site Nightingale. (Source: Nasa)

A well preserved time capsule from the early solar system, scientists suspect that microscopic grains of dust on the surface could be the same ones that spewed from dying stars which coalesced to make the Sun and the planets nearly 4.6 billion years ago. That has also sparked a debate over clues of the origin of life.

During its scan of the asteroid, the spacecraft saw carbon-bearing, organic material widespread on the surface, including the sample site, Nightingale. These findings indicate that hydrated minerals and organic material will likely be present in the collected sample. Nasa scientists also found that Nightingale's regolith (dust and surface material) has only recently been exposed to the harsh space environment, meaning that the mission will collect and return some of the most pristine material on the asteroid.

The return home and delivery

Following its maiden attempt on October 20, scientists will verify the success of the mission on October 22 as they snap images of the TAGSAM head to see whether it contains Bennu’s surface material followed by a spin manoeuvre on October 24 to determine the mass of the collected material. If unsuccessful, the spacecraft has enough pressurised nitrogen for two more attempts at the alternative site Osprey in January 2021.

The spacecraft was launched on ULV Atlas rocket to the asteroid. (Source: NASA)

The spacecraft is tasked with collecting at least 2 oz (60 grams) of Bennu’s rocky material to deliver back to the Earth – the largest sample return from space since the Apollo programme. OSIRIS is set to depart Bennu's orbit on a return trajectory in 2021 and deliver samples to the Earth station on September 24, 2023.