The Mission To Visit A Killer Asteroid

Osiris-Rex launches in September

osiris rex spacecraft at Bennu
The Osiris-Rex spacecraft launches in September 2016. It will arrive at the asteroid Bennu 101955 in 2018.Nasa; Illustration by Pete Sucheski

Despite its small size, 101955 Bennu is one of the most dangerous ­asteroids in the solar system. In 2135, it will fly within about 186,000 miles of Earth, at which point, the odds of it striking us are an unsettling 1-in-2,700. Based on impact calculations, University of ­Arizona Lunar & Planetary ­Laboratory staff scientist Bashar Rizk estimates that if a person were within 5 miles of the asteroid’s impact, he or she would likely not survive. If Bennu were to hit a city, “­civilization would be wiped out; most buildings would collapse or ignite, or both,” Rizk says. “The fireball would be about 1,500 times as bright as the sun.”

That’s one reason why, NASA is ­sending a solar-powered spacecraft to rendezvous with the asteroid. Launching in September, the OSIRIS-REx (­Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) will fly about 1.2 billion miles to Bennu, then collect samples from the carbonaceous rock and measure how heat from the sun changes the asteroid’s trajectory. Understanding this effect will help to determine where the asteroid is headed, and it also might provide a method of defense: Scientists could use the sun’s heat to deflect Bennu from a collision course with Earth.

By The Numbers

20x8x10: Size, in feet, of OSIRIS-REx with wings deployed

200: Miles from Earth, in millions, that OSIRIS will meet Bennu

1: Total cost, in billions of dollars

1,600: Approximate diameter, in feet, of the asteroid

osiris rex sample collection
Osiris-Rex won't land on Bennu to collect its sample; instead it will extend its 10-foot arm and bump into it like a pogo stick while it sucks up a small sample of the carbonaceous asteroid. Then the arm will place the sample in a muffin-shaped capsule for its return journey to Earth. Scientists think asteroids like these may have seeded Earth with the necessary ingredients for life--or even life itself.Illustration by Pete Sucheski

Mission Timeline

September 2016: Launch from Cape Canaveral, Florida.

August-October 2018: Spacecraft cameras power up and try to locate Bennu­—from about 1.3 million miles away. The cameras will assess the asteroid's shape, spin rate, and whether it has any moons.

December 2018: Rendezvous with Bennu. From a distance of a few miles, the spacecraft will map the asteroid in unprecedented detail, identifying areas that might be easy to sample (as well as hazardous craggy rocks to avoid).

July 2020: The spacecraft's arm reaches onto Bennu's surface and sucks up 60 grams or more of asteroid material, which it stows in a sample-return capsule.

March 2021: OSIRIS-REx leaves Bennu, ­carrying the ­sample-return ­capsule back to Earth.

September 2023: The spacecraft delivers the sample, which parachutes for a soft landing in Utah. OSIRIS-REx will then bypass Earth and retire in a permanent orbit around the sun.

This article was originally published in the September/October 2016 issue of Popular Science, under the title "Visiting A Killer Asteroid."