Bennu, meet OSIRIS-REx. The NASA mission to catch an asteroid has reached a major milestone, with the spacecraft taking its first photographs of the target rock as it hurtles through space.
OSIRIS-REx, the Origins Spectral Interpretational Resource Identification Security – Regolith Explorer, was launched in 2016, around the time of Rosetta’s demise. It is heading to the near-Earth asteroid Bennu; when it reaches it, the space probe will spin around its rocky dance partner for some time, before paying a short visit to the surface. It will then return to Earth, taking some of Bennu back with it.
Bennu, a 500-meter-wide (1,650 feet) asteroid, was discovered back in 1999. It was chosen for interception by OSIRIS-REx, the first asteroid sample return mission in NASA’s portfolio, for several reasons. These include its primitive, unaltered composition, which may feature compounds that could be precursors to biological life; it is also large enough to have a decent-ish gravitational field, which means it won't regularly eject spacecraft-destroying material from its surface.
Thanks to its relative proximity to Earth, there is a very slim chance Bennu could impact Earth in the late 22nd century – although it’s nowhere near big enough to be an existential threat.
Most of its scientific objectives are related to the asteroid’s geology and geochemistry, but the OSIRIS-REx venture does have security implications. By understanding things like the Yarkovsky effect – where sunlight is absorbed then re-emitted as heat, which can slightly change an asteroid’s orbital path – we can better prepare for a future wherein, perhaps inevitably, we’ll have to deflect an object that threatens the planet.
OSIRIS-REx has traveled 1.8 billion kilometers (1.1 billion miles), about 12 times the Earth-Sun distance, to reach Bennu, although its curved path means it's "just" 108 million kilometers from Earth (67 million miles). It currently has 2.2 million kilometers (1.4 million miles) to go, and at that distance, it’s able to visualize the spacefaring rock in question.
“The mission team will spend the next few months learning as much as possible about Bennu’s size, shape, surface features, and surroundings before the spacecraft arrives at the asteroid,” Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson, said in a statement.
“After spending so long planning for this moment, I can’t wait to see what Bennu reveals to us.”
During this approach phase of the mission, the probe will see if it can spot any dust plumes or natural satellites around the asteroid, as well as taking a peek at its surface features and how it reflects or otherwise soaks up sunlight.
Over the next few months, as it gets ever closer, it’ll begin executing a series of maneuvers to sync up with Bennu’s orbit around the Sun, inevitably causing tensions at NASA to rise.
The asteroid’s dimensions makes it the smallest object that any spacecraft has orbited, let alone touched down on. Its low gravity will make establishing a close orbit more difficult than it otherwise would be.
If it does manage to tag along with Bennu this December, it will then spend the next 18 months or so mapping the asteroid from above, before quickly landing on the object and snatching away a sample in the summer of 2020. Then, it’ll leap up into space, and fly back to Earth, landing in the Utah desert in September 2023.
Although this is the first time a NASA mission will land on an asteroid and come back home, it’s not the first space agency in the world to achieve this feat. Back in 2010, Japan’s Hayabusa spacecraft brought back samples from asteroid 25143 Itokawa, and its sequel – Hayabusa2 – caught up with the dumpling-shaped asteroid Ryugu back in June this year.
NASA, however, was the first to orbit and land on an asteroid, accomplished by its Near Earth Asteroid Rendezvous (NEAR) mission in 2001.