Global Courant
After traveling billions of miles, NASA’s The OSIRIS-REx mission has reached its peak in a small black capsule that shot through the sky before landing in the Utah desert.
Inside is likely the largest sample of dust and rock ever returned by an asteroid. Extracted and brought back from an asteroid called Bennu with great engineering ingenuity, scientists will now study in search of clues about the origins of the solar system and life itself.
The seven-year mission took OSIRIS-REx to a carbon-rich near-Earth asteroid, where it orbited Earth for two and a half years. The surface was mapped and properties such as density and spin were measured. This ‘mess’ asteroid also has a (very) small chance of ever impacting Earth, so obtaining complex measurements of its orbit and other dynamics was also a goal of the mission.
The origin of the solar system – and life
Most asteroids are the rocky remains of failed planets and destructive collisions in the early solar system, orbiting between Mars and Jupiter. They vary drastically in size, shape and composition, and discovering what they are made of can help us learn more about how the planets formed.
These primitive bodies – some of which are more than 4.5 billion years old – may also shed light on the origins of life, because they tell us about the distribution of water, minerals and other elements such as carbon.
There is also an element of self-interest in studying these asteroids, to understand the risk they could pose if they come Earth’s way.
Using telescopes on Earth, we can get a rough idea of what an asteroid’s surface is made of. However, to perform an in-depth chemical analysis, we need to have some actual samples.
Most of the asteroid samples we have are meteorites: chunks of space rock that crashed to Earth. There are more than 70,000 meteorites in collections around the world, but we know the origin of less than 0.1% of them.
Furthermore, we know that the samples we have are not very representative of the types of asteroids in space. Part of the reason for this is that some types of asteroids are better than others at surviving the fiery descent through the atmosphere.
But some meteorites do not appear to match any known type of asteroid. So where do they come from?
With the help of special camera networks such as that of Australia Desert Fireball Network we can observe incoming asteroids, retrieve meteorite samples and track their paths through space to determine their origins. This process is possible deliver relatively uncontaminated samples to the laboratory.
Still, it is very difficult to link a meteorite to a known parent planet, or even to some type of asteroid observed with a telescope.
Bringing pieces of space back to Earth
Sample return missions are the gold standard for analyzing the composition of alien bodies. They can bring pieces of another planet or asteroid to Earth to study.
The first such mission was to the moon, bringing back lunar samples for analysis. We have discovered that the moon is made of the same material as the Earth, and that it was probably formed from orbiting debris after a giant impact.
Sample return missions are technically very challenging. Not only does a spacecraft have to travel hundreds of millions of miles from Earth, but it also has to match its speed to its target (not just zoom past), find a safe landing site, land to collect a sample (without crashing), sample in a sealed capsule, take off again and return to Earth. Much of this process must be autonomous, because the time delay for communication with Earth is too long for remote operation.
OSIRIS-REx collected a sample of Bennu in 2020. Photo: NASA via AP/The Conversation
Aside from the lunar samples returned by the Apollo missions, OSIRIS-REx is the fourth mission to return extraterrestrial material to Earth.
NASAs Stardust mission, launched in 1999, returned microscopic samples from the trail of Comet Wild-2. The Hayabusa Mission, launched in 2003 by the Japanese space agency JAXA, returned less than 1 milligram from asteroid Itokawa. JAXAs Hayabusa2 (launched in 2014) returned 5.4 grams of sample from asteroid Ryugu.
NASA estimates that OSIRIS-REx has returned about 250 grams of asteroid Bennu, by far the largest sample ever recovered. We’ll know for sure once the sample is carefully examined at the Johnson Space Center in the coming days.
The sound of fireballs
We and our colleagues at Curtin University are deeply involved in the global effort to find out what asteroids are really made of. We have participated in or analyzed samples from all of these sample return missions and led the Global Fireball Observatory.
There are six OSIRIS-REx mission scientists from Curtin (including one of us – Nick Timms), and they will be among those receiving the first wave of samples in the coming weeks.
The return of the capsule also had its own incredible scientific value. It was essentially a man-made fireball.
Fireballs, or really bright shooting stars from large space rocks, are quite rare and impossible to predict. This is why we use special camera networks to observe large areas of the sky (the Desert Fireball Network observes almost three million square kilometers of the Australian sky every night).
When objects from space enter the atmosphere and travel much faster than the speed of sound, they ignite the air to create a fireball and also cause other, less studied phenomena such as shock waves – which can be dangerous.
Returning a sample is a great opportunity to deploy seismic sensors and other instruments to analyze the shock wave, which can tell us more about the physics of reentry and why some meteorites survive while others do not.
This is done for the Hayabusa2 sample return in 2020, and researchers from Sandia Labs and the University of Southern Queensland had detectors set up in Utah for the OSIRIS-REx return.
What’s next?
Like Hayabusa2, the OSIRIS-REx spacecraft itself is not yet ready. Both spacecraft have dropped their precious samples back to Earth and continued with the goal of future asteroid fly-bys.
The mission, now renamed “OSIRIS APEX”, has already started targeting an asteroid called Apophis, which it will intercept not long after the asteroid passes by Earth in April 2029.
Eleanor K. Sansom is a research assistant, Curtin University And Nick TimmsColleague Professor, Curtin University
This article is republished from The conversation under a Creative Commons license. Read the original article.
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