OSIRIS-REx: NASA’s landing on an asteroid
OSIRIS-REx at Bennu (artist impresion). Credit: NASA Goddard

OSIRIS-REx: NASA’s landing on an asteroid

14/11/2018Written by Steph Neumann

Everything you need to know about a daring new asteroid rendezvous.

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Mapping Bennu (artist impression) Credit: NASA/Goddard/University of Arizona

It’s been two years since the launch of NASA’s mission to an asteroid, and now the OSIRIS-REx spacecraft has an asteroid called Bennu in its sights and is getting ready to arrive on 3 December 2018.

Ahead of the headlines, here’s all you need to know about this ambitious new mission.

Mission in a nutshell

Asteroids are debris left over from the formation of our Solar System and may be carrying the precursors to the origin of life. By studying what asteroids are made of, we hope to answer one the oldest and most frequently asked questions: where did we come from?

Sometimes asteroids come to us as meteorites, but their fiery descent and landing on Earth can destroy information about water or organic materials. There’s no substitute for studying asteroids in their native habitat, but that means going out there and collecting samples.

In order to get a better idea of what materials are present on asteroids, OSIRIS-REx has three main objectives when it visits asteroid Bennu:

– Map the surface of Bennu. OSIRIS-REx has three cameras – one for short-range mapping, one for long-range telescopic imaging, and one for capturing images of the collected samples.

– Find out what Bennu is made of. Scientists want to know more about the kinds of chemicals that exist on Bennu, especially if there are any organic compounds on the surface.

– Bring back bits of Bennu. OSIRIS-REx has a robotic arm and hand called TAGSAM. This will be used to collect the samples of Bennu that will be analysed back on Earth.

Why choose Bennu?

Why choose Bennu?
Image Credit: NASA/GSFC
Why choose Bennu?

101955-Bennu is an asteroid just under half a kilometre wide, or about as wide as five rugby pitches arranged end-to-end. Its orbit often crosses Earth’s orbit, meaning that Bennu is one of the objects that could collide with Earth sometime in the future.

There are over half a million asteroids in the Solar System. Why, then, choose Bennu for a mission like OSIRIS-REx? There are several reasons:

– It’s close to Earth. Bennu has an orbit very similar to that of Earth’s. It’s slightly more elliptical, so that it only crosses Earth’s path occasionally. This closeness makes Bennu very accessible for sample return missions like OSIRIS-REx.

– It’s big. Small asteroids spin faster than larger ones. An asteroid less than about 200m wide spins so fast that any loose material is thrown off it. This includes any visiting spacecraft. At 492m wide, Bennu is large enough for a comfortable landing.

– It’s made of the right stuff. Studies have shown the Bennu is a fairly primitive, carbon-rich asteroid. Carbon is a vital element for life and it’s thought that we may find these kinds of organic molecules on Bennu.

Are we there yet?

Are we there yet?
OSIRIS-REx journey. Credit: Phoenix7777 using JPL data
Are we there yet?
Looking back at Earth. Credit: NASA/OSIRIS-REx

OSIRIS-REx launched on 8 September 2016, as NASA’s first mission to land on an asteroid. Fast forward two years and we’re still asking, ‘are we there yet?’.

So where is OSIRIS-REx and when will it get there?

OSIRIS-REx has travelled billions of kilometres in the past two years to rendezvous with Bennu.

In August 2018 OSIRIS-REx began a series of thruster burns to slow it down enough to enter orbit around Bennu. But we’re still talking about incredibly fast speeds. Bennu orbits around the Sun at 63,000 miles per hour and OSIRIS-REx has to match this speed almost exactly to enter orbit!

OSIRIS-REx is due to arrive at Bennu on 3 December 2018.  But the mission is already starting to hit the headlines as Osiris snaps pictures of the asteroid from afar.

On the way

On the way
Jupiter and three moons. Credit: NASA/OSIRIS-REx
On the way
Asteroid Bennu rotation. Credit: NASA/OSIRIS-REx

During its travel, OSIRIS-REx hasn’t exactly been sleeping on the job.  One of the first photographs sent by OSIRIS-REx was of Jupiter and three of its moons: Callisto, Io, and Ganymede, taken on 12 February 2016 when the craft was 76 million miles away from Earth.

On 22 September 2017, OSIRIS-REx took a colour picture of Earth during its flyby about 170,000 kilometres away.  This picture was taken using short exposure times due to the brightness of Earth.  Three days later OSIRIS-REx took a picture of the Earth and Moon from 3 million miles away.

And finally on 17 August 2018, OSIRIS-REx took its very first snap of Bennu, 1.4 million miles away from the target.

On 2 November 2018, OSIRIS-REx captured this stunning set of images of Bennu as it rotated, revealing its diamond shape in all its glory. As the craft travels closer it will give the mission team a chance to start learning about the asteroid’s shape, size, surface features and surroundings ahead of the landing.

Haven’t we just landed on another asteroid?

Haven’t we just landed on another asteroid?
Rover 1a and Rover 1b. artist impression. Credit: JAXA

Good spot! OSIRIS-REx won’t be the first mission to land on an asteroid. Japan’s Hayabusa 2 mission recently stole the show by touching down not one but three mini landers on an asteroid called Ryugu.

Following these successful landings, in spring 2019, the Hayabusa 2 spacecraft will detonate a crater in the surface of Ryugu to expose and collect fresh material. The spacecraft itself will then descend to the surface and collect three different samples of rock. It will depart the asteroid in December 2019, and return its precious samples to Earth in 2020.

OSIRIS-REx will be the first US asteroid landing, and certainly the first landing on asteroid Bennu!

Mission timeline

Mission timeline
Credit: NASA/OSIRIS-REx
Mission timeline
OSIRIS-REx sample collection. Credit: NASA

As OSIRIS-REx zooms in on its asteroid target, we’re going to be hearing a lot more about this daring mission. The current mission timeline is:

3 December 2018 – Arrival at Bennu. After some exploratory flybys, OSIRIS-REx will enter into orbit around Bennu at the end of the year, imaging and collecting data about this asteroid close up. Scientists will use this information to select the best landing site.

July 2020 – Landing. Once a landing site is selected, OSIRIS-REx will lower onto Bennu’s surface and collect about 150 grams of dust and rock using its TAGSAM blaster. Landing will be more of a ‘kiss and go’ rather than long-term stay on the surface.

March 2021 – Departure. OSIRIS-REx will leave Bennu for a journey back to Earth.

September 2023 – Return to Earth. OSIRIS-REx will send the samples back to Earth via return capsule and parachute, while the main spacecraft enters a stable retirement orbit around the Sun.

To follow updates on the OSIRIS-REx mission, follow the mission’s webpage or twitter.

To find out more about asteroids and to touch a meteorite, visit Our Solar System gallery at the National Space Centre.

About the author: Steph Neumann is a physics student at the University of Leicester and a former Science Interpreter at the National Space Centre.