The Osiris-Rex spacecraft is on its way back to Earth, having thwacked — briefly — the surface of an asteroid called Bennu last year to scoop up samples. It will arrive home in 2023, ejecting a capsule full of samples that may help eager scientists decipher the origin of Earth’s water and life.
But the spacecraft will have plenty of fuel left. Its mission team wondered: Could it go somewhere else?
Yes, it turns out. And not just anywhere, but one of the most famous near-Earth asteroids: Apophis.
“We were pretty excited when we found out we could go there,” said Michael Nolan from the University of Arizona, the science team chief on the mission, who presented findings this week at the fall meeting of the American Geophysical Union in New Orleans.
Apophis was once thought to be the asteroid that posed the greatest threat to Earth. After its discovery in 2004, astronomers rated its chance of hitting our planet in 2029 as high as 1 in 37, the highest in recorded history for any asteroid. At 1,000 feet across, it would not end life on Earth if it hit but would decimate an area hundreds of miles across.
“It was very scary,” Nolan said.
Updated analysis later showed that the asteroid, which dances around Earth’s orbit, would not impact our planet. But it will still make a close pass in April 2029 at a distance of 20,000 miles, inside the orbits of some geostationary satellites, and close enough that it will be visible to the naked eye in Europe, Asia and Africa.
By coincidence, if mission controllers on Earth directed Osiris-Rex to complete three flybys of the planet after dropping off its samples, it would be able to reach Apophis. When the asteroid flies through Earth’s skies, Osiris-Rex would be just an hour behind, ready to sidle up in June 2029.
“It’s sort of a fluke,” Nolan said.
While Apophis poses no threat to Earth — at least for the next century or so — studying it could tell scientists a great deal about asteroids of this size. No other mission is planned to visit Apophis in 2029, although there are proposals to do so.
Next month the Osiris-Rex team will put forward its proposal to NASA to extend the mission, with a decision expected by April. If it goes ahead, the spacecraft will spend 18 months studying Apophis after it arrives.
While orbiting Apophis, Osiris-Rex would swoop down over the surface to take high-resolution images. This would include looking for evidence of landslides caused by the gravitational tug of Earth as the asteroid flew past.
The spacecraft would also attempt to descend to the surface and use its thrusters to blast a hole in its surface. The goal would be to expose underground material, helping to work out what the asteroid is made of.
“Apophis is compositionally the kind of asteroid that’s most likely to become a hazard,” Nolan said. “The material properties will help us understand what its structure is.”
This in turn could inform a future mission to save Earth from Apophis or another asteroid. By working out its mass, density and structure, scientists will know how spongy or hard the asteroid is, telling them how best to deal with similar objects.
“We really need to understand what we’re dealing with,” said Jim Bell, an astronomer at Arizona State University who is not involved in the Osiris-Rex mission. “Is this a solid hunk of rock? Can we change this thing’s orbit? Could we destroy it, blow it up into tiny bits, if we had to take some drastic measures?”
NASA’s ongoing Dart mission, which launched last month, is performing a not-too-dissimilar experiment by slamming into a small asteroid to see if scientists can change its orbit.
Davide Farnocchia, from NASA’s Center for Near Earth Object Studies at the Jet Propulsion Laboratory in California, said the close pass of Apophis was an “amazing opportunity” to observe an asteroid of this size up close. It would also lead to better understanding of whether Apophis poses a future threat to Earth.
After Apophis, Osiris-Rex might even have enough fuel to visit yet another asteroid. Or, it could be placed on the surface of Apophis and act as a “tracking beacon,” Nolan said.
Budget constraints or other issues, such as concerns that Osiris-Rex could inadvertently alter the orbit of Apophis and make it a threat to Earth, could dictate whether the extended mission is approved. But it could prove an exciting next chapter for the mission.
“It’s once in a millennium that something this big comes to Earth,” Bell said. “We should take advantage of that.”
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