Nasa after bit of Armageddon asteroid
It could come straight from the pages of a Hollywood script – Nasa is to launch a probe to collect a sample of rock from an asteroid it fears could one day hit Earth.
Astronomers have found that the asteroid, called Bennu, crosses Earth’s orbit once every six years and is getting closer. In 2135 it will pass between the Moon and Earth – a hair’s breadth in space terms.
‘‘That 2135 flyby is going to tweak Bennu’s orbit, potentially putting it on course for the Earth later that century,’’ said Dante Lauretta, professor of planetary science at Arizona University.
Lauretta, who is Nasa’s principal investigator in charge of the Osiris-Rex probe mission to Bennu, which launches in September, said the chance of such an impact was small but significant.
The first task of Osiris-Rex will be to map every detail of the asteroid. It will then descend and hover above its surface to pick up some rubble, before flying back to Earth.
‘‘We need to know everything about Bennu – its size, mass and composition,’’ said Lauretta.
The asteroid was discovered in 1999 and has been studied intensively.
‘‘Bennu is a carbonaceous asteroid, an ancient relic from the early solar system that is filled with organic molecules,’’ said Lauretta.
‘‘Asteroids like Bennu may have seeded the early Earth with this material, contributing to the primordial soup from which life emerged.’’
Bennu is about 500 metres in diameter and travels around the sun at an average speed of 101,000kmh. The probe’s journey will involve an initial year of orbiting the Sun to build up speed before it slingshots back around Earth, using the planet’s gravity to align its orbit with the asteroid’s. They will rendezvous in August 2018.
Once there, Osiris-Rex will spend a year surveying the asteroid, studying its geology, and looking for sites where the rock is loose enough to retrieve a sample.
For scientists, the chance of obtaining chunks of a carbonaceous asteroid is exciting.
For the rest of us, however, Osiris-Rex’s most important task may be the measurements it makes of a bizarre and newly discovered force that can send asteroids careering around the solar system and potentially towards Earth.
‘‘The Yarkovsky effect is the force that acts on an asteroid when it absorbs sunlight and then radiates it back into space as heat. It acts like a small thruster, constantly changing its course,’’ said Lauretta. ‘‘Bennu’s position has shifted 160km since 1999.’’
It is these forces that make Bennu’s trajectory so hard to predict after 2135’s near-miss. It is expected to pass Earth at a distance of about 290,000km, close enough to alter the asteroid’s path so it may hit our planet on a future orbit.
‘‘We estimate the chance of impact at about one in 2700 between 2175 and 2196,’’ said Lauretta, whose team calculate such an impact would be equivalent to triggering 3 billion tonnes of high explosive.
Earth has been hit by asteroids and meteorites many times before. One such event may have formed the moon and another is thought to have wiped out the dinosaurs.
Efforts to save Earth from asteroids have featured in several Hollywood blockbusters, including the 1998 films Deep Impact and Armageddon.
Professor Mark Bailey, an expert on impact risks, said while the risk from Bennu was relatively small, the consequences of it hitting Earth could be enormous.
‘‘Bennu falls on the boundary, in terms of size, for an object capable of causing a global catastrophe,’’ he said.