Exploring Asteroids to Understand Life

By Mike Howie

Scientists in Japan and the United States are studying small near-Earth asteroids with robotic spacecraft to learn more about the origins of life in our solar system. Both Hayabusa2, launched by the Japanese Aerospace Exploration Agency (JAXA) in 2014, and OSIRIS-Rex, launched by NASA in 2016, are now circling their asteroids and searching for safe sampling sites.

Turning Old Failure into New Success

These are not the first missions attempting to sample asteroids. JAXA’s first Hayabusa mission visited an asteroid called Itokawa in 2005, but it was nearly a disaster. The largest solar flare ever recorded damaged the spacecraft’s solar panels and one of its four engines before it ever reached the asteroid. Once it arrived at Itokawa, two of its three reaction wheels failed, leaving the craft unstable, and the rover it released to land on and study the asteroid’s surface missed its target and floated into space. The bullet meant to stir up dust for collection didn’t fire, making it unclear if the craft gathered any samples, and all of the engines failed on the journey back to Earth.

While it was several years late, Hayabusa made it home in 2010 carrying 1,534 grains of dust from Itokawa and valuable lessons on how to successfully visit and sample an asteroid. The sample it collected proved that most of Earth’s meteorites come from stony, carbon-poor asteroids. And the spacecraft’s failures directly influenced the design of Hayabusa2.

With more landers and reaction wheels, stronger engines, a better communications system, and a redesigned collection tube that can gather samples even if the bullet doesn’t fire, Hayabusa2 is now visiting a new asteroid: Ryugu. It’s one of only five asteroids of the right size, composition and orbit to provide the answers JAXA scientists are looking for.

Time Capsules in Space

Ryugu is a carbon-rich asteroid, a type thought to be mostly unchanged since forming at least 4.6 billion years ago. Just a few grains from Ryugu could help us learn more about the early days of our solar system and the origins of life.

Using a spacecraft called OSIRIS-REx, NASA scientists are studying a similar asteroid called Bennu. While the Americans want to learn more about our origins, they’re also assessing Bennu’s threat to life on Earth. Due to a phenomenon called the Yarkovsky effect, the asteroid has a 1 in 2,700 chance of hitting the Earth in the late 22nd century — one of the highest probabilities of any known asteroid.

The Yarkovsky effect explains how sunlight can alter an asteroid’s orbit. As asteroids float through space, they absorb energy from the sun in the form of light on one side. When that side faces away from the sun, the energy is released as radiant heat that alters the asteroid’s orbit. This phenomenon makes it difficult to predict exactly where an asteroid will end up. By studying Bennu’s surface material, the scientists will gain a greater understanding of how it absorbs and emits heat, allowing them to make a more accurate prediction of where the asteroid will go.

By flying such similar missions at the same time, the JAXA and NASA scientists find themselves in a friendly competition. While Hayabusa2 launched and plans to return to Earth first, OSIRIS-Rex is larger and plans to gather more sample. But each of the teams is still cheering for the other, and in 2014 they signed a memorandum promising to share their data, software and samples. Both missions are going smoothly, and the success of either could lead to fascinating news for the entire scientific community.