NASA spacecraft arrives at Bennu asteroid

By Andrew Warren, Glen Nagle

4 December 2018

3 minute read

Grey asteroid spinning in front of black background

Asteroid Bennu seen through its full rotation by OSIRIS-REx’s cameras
Credit: NASA/Goddard/University of Arizona

Since its launch in September 2016, NASA’s OSIRIS-REx spacecraft has travelled more than 2 billion kilometres across the solar system towards an asteroid named Bennu, and at around 4am AEDT this morning the spacecraft officially arrived in Bennu’s orbit.

At just 500 metres across, Bennu is about the same size as the length of five football fields, which makes it the smallest object ever to be orbited by a spacecraft.

During the final hours before reaching Bennu’s orbit, the Canberra Deep Space Communication Complex – which we manage on behalf of NASA – provided the mission scientists with one of the final contact opportunities with their spacecraft before it arrived.

We’ve been proud to have played our part in OSIRIS-REx’s journey so far, but its mission is really only just beginning.

The Canberra Deep Space Communication Complex will lock four of its giant antenna dishes onto Juno's signal.

The Canberra Deep Space Communication Complex will be in contact with the spacecraft throughout the mission.

What’s OSIRIS-REx doing while it’s hanging out at Bennu?

OSIRIS-REx (which stands for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) has been slowly approaching Bennu for several weeks, and it’s now just 2 kilometres above the asteroid. It will spend the next two-and-a-half-years performing a detailed study of the asteroid with every instrument it has available.

The spacecraft will analyse the composition and structure of the carbonaceous asteroid, and in February 2019 it will also begin to map Bennu’s surface to find the best place to collect a sample.

After it chooses the best collection site, it will briefly touch the surface of Bennu to retrieve a sample of up to 2kg of regolith (dirt and rocks), before returning to Earth, where it’s scheduled to arrive in September 2023.

Our team in Canberra and our two sister Deep Space Network stations around the world in Spain and the United States will be with the mission every step of the way.

This artist's concept shows the OSIRIS-REx spacecraft contacting the asteroid Bennu with the Touch-And-Go Sample Arm Mechanism or TAGSAM.

This artist’s concept shows the OSIRIS-REx spacecraft contacting the asteroid Bennu with the Touch-And-Go Sample Arm Mechanism or TAGSAM. Credit: NASA’s Goddard Space Flight Center

What’s so important about this rock?

Bennu is a 4.5 billion year old asteroid which may hold clues to life on Earth and importantly, information necessary for our future survival on this planet.

Images of Bennu appear to show that it’s a ‘rubble pile’, a collection of rocks and boulders that have accumulated under gravity over billions of years, and scientists are hopeful that they’ll find water-bearing minerals that contain organic compounds, which are the building blocks of life on earth.

Scientists are also keen to learn more about the asteroid’s trajectory and its physical and chemical properties to gain critical insights into what to do to mitigate any future collision scenarios.

Bennu travels around the Sun every 1.2 years, and its path occasionally cross the Earth’s orbit. Given what astronomers know of the asteroid’s orbit, there is currently a 1 in 2700 chance that it could impact Earth in the mid to late 22nd century.

Bennu isn’t a ‘dinosaur-killer’ type asteroid, but could potentially cause significant damage if it were to blast through our atmosphere and hit anywhere on the planet.

Knowing more about asteroids like Bennu will help unlock the secrets of the formation of the early solar system, give further insights into the story of life on Earth, and provide greater knowledge to protect ourselves from potential threats from space.