WASHINGTON: A Nasa spacecraft, which scientists believe has collected samples from an asteroid, began its two-year journey back to Earth on Monday.

Nasa’s OSIRIS-REx spacecraft is attempting to complete a mission to visit Bennu, a skyscraper-sized asteroid some 200 million miles (320 million km) from Earth, survey the surface, collect samples and deliver them back to Earth.

Staff celebrated at the OSIRIS-REx control room in Colorado as the space vehicle pushed away from the asteroid, whose acorn-shaped body formed in the early days of our solar system. OSIRIS-REx arrived at Bennu in 2018.

The spacecraft found traces of hydrogen and oxygen molecules — part of the recipe for water and thus the potential for life — embedded in the asteroid’s rocky surface, said Dante Lauretta, the OSIRIS-REx mission’s principal investigator, in 2018.

The trip back to Earth will take about two years. The spacecraft will then eject a capsule containing the asteroid samples, which Nasa says will land in a remote area of Utah.

Nasa says samples will be distributed to research laboratories worldwide, but 75pc of the samples will be preserved at the Johnson Space Center in Houston for future generations to study with technologies not yet created.

The roughly $800 million, minivan-sized OSIRIS-REx spacecraft, built by Lockheed Martin, launched in 2016 to grab and return the first US sample of pristine asteroid materials. Japan is the only other country to have accomplished such a feat.

Asteroids are among the leftover debris from the solar system’s formation some 4.5 billion years ago. A sample could hold clues to the origins of life on Earth, scientists say.Osiris-Rex is “now moving away over 600 miles an hour from Bennu, on its way home,” Dante Lauretta, head of the mission, said on Nasa’s video broadcast of the event.

The spacecraft’s thrusters were engaged without incident for seven minutes to put the probe on the correct trajectory home, a journey of 1.4 billion miles (2.3 billion kiometres).

It is carrying more than 60 grams of dust and fragments from the asteroid, the largest sample collected by Nasa since the Moon rocks brought back by the Apollo missions.

To achieve this goal, the US space agency launched a high-risk operation in October 2020: the probe came into contact with the asteroid for a few seconds, and a blast of compressed nitrogen was emitted to raise the dust sample which was then captured.

The surprise for Nasa was the probe’s arm sank several centimetres into the surface of the asteroid, showing the scientists that “the surfaces of these rubble pile asteroids are very loosely consolidated,” said Lauretta.

The whole mission almost came to nought when Nasa realised a few days later that the valve of the collection compartment was failing to close, letting fragments escape into space.

But the precious cargo was finally secured after being transferred to a capsule fixed in the spacecraft’s centre.

In two and a half years, that capsule will be released a few hours before entry into the Earth’s atmosphere, and will be slowed down by a parachute system for its landing.

The samples will then be transported to Nasa’s Johnson Space Centre in Houston, but 75 percent will be kept intact to be studied by future generations, who will have advanced technologies that have not yet been created, the agency said.

The analysis should help scientists better understand the formation of the solar system and the development of Earth as a habitable planet.

Published in Dawn, May 12th, 2021