Nasa is planning to launch a probe to collect rock samples from an asteroid which may one day it hit Earth.
The asteroid, named Bennu, crosses Earth’s orbit once every six years and has gotten ever closer since it was discovered in 1999.
In 2135, Bennu will fly between the moon and Earth — a hair’s breadth in space terms.
That’s so close that gravity from the Earth could effect Bennu’s orbit, “potentially putting it on course for the Earth later that century,” said Dante Lauretta, a professor of planetary science at Arizona University.
Bennu is about 487 metres in diameter and travels around the sun at an average of 101,000 km per hour.
The chance of an impact is small but significant, and if it happens, would be equivalent to triggering three billion tonnes of high explosive, 200 times the strength of the atomic bomb dropped on Hiroshima.
“Bennu falls on the boundary, in terms of size, for an object capable of causing a global catastrophe,” Professor Mark Bailey of Northern Ireland’s Armagh Observatory told the Sunday Times.
NASA will launch the Osiris-Rex probe mission to Bennu in September.
The probe’s journey will involve a 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, the Sunday Times reports. They will rendezvous in August 2018.
Osiris-Rex will then spend a year mapping the asteroid and then hover above its surface to pick up some rubble, before flying back to Earth.
For scientists, the chance of obtaining chunks of a carbonaceous asteroid is exciting. “Bennu is a carbonaceous asteroid, an ancient relic from the early solar system that is filled with organic molecules,” Lauretta said. “Asteroids like Bennu may have seeded the early Earth with this material, contributing to the primordial soup from which life emerged.”
For the rest of the world, Osiris-Rex’s most important task may be the measurements it makes of a newly discovered force called the Yarkovsky effect, that can send asteroids careening around the solar system and potentially toward Earth.
This force makes Bennu’s trajectory hard to predict, but scientists know its position has shifted 160km since 1999.
“We need to know everything about Bennu — its size, mass and composition,” said Lauretta. “This could be vital data for future generations.”
Bertha R. Massie