Scientists have made the first measurements of water in samples collected from the surface of an asteroid, according to a new study.
The Japanese space probe Hayabusa completed a sample return mission from the asteroid Itokawa, retrieving 1,500 particles. Another mission, Hayabusa2, is conducting a sample return mission on the asteroid Ryugu.
A study detailing the analysis of five of the particles from the asteroid samples was published Wednesday in the journal Science Advances. The samples were collected from an area on Itokawa known as the Muses Sea, which is smooth and dusty.
“We found the samples we examined were enriched in water compared to the average for inner solar system objects,” said Ziliang Jin, lead study author and postdoctoral scholar in Arizona State University’s School of Earth and Space Exploration, in a statement.
Each sample is only about half the thickness of a human hair, so an ion mass spectrometer was used to study the tiny mineral grains.
There was no intention to study the samples for evidence of water until two researchers from Arizona State, Jin and Maitrayee Bose, proposed it.
In two of the five particles, Jin and Bose found pyroxene, a mineral that is known to contain water. Further study showed that the samples were rich in water, even though Itokawa is dry.
Itokawa is an S-type asteroid, one of the most common objects found in the asteroid belt. Even though these objects are on the small side, they also maintain the materials they formed with.
“They originally formed at a distance from the Sun of one-third to three times Earth’s distance,” Bose said.
Itokawa is shaped like a peanut and completes an orbit around the sun every 18 months, swinging through Earth’s orbit and then going beyond Mars. The asteroid is 1,800 feet long and between 700 and 1,000 feet wide.
The asteroid looks like a pile of rubble being held together by force. It’s a fragment of a much larger body that was once 12 miles wide, but it went through some rough changes. At one point, it encountered high temperatures that heated it to 1,000 or 1,500 degrees Fahrenheit. Multiple impacts eventually shattered it.
Two of the fragments, known as lobes, merged about 8 million years ago. The researchers believe that the samples were buried at least 328 feet inside the much larger parent body before it broke apart.
When the asteroid broke into pieces, it’s likely that the sample grains were exposed to radiation and impacts by micrometeorites. And yet, they retain water. The minerals are also similar in composition to those found on Earth.
“This means S-type asteroids and the parent bodies of [non-modified asteroids] are likely a critical source of water and several other elements for the terrestrial planets,” Bose said. “That makes these asteroids high-priority targets for exploration.”
The two researchers estimate that asteroids like this impacting Earth early in its history could have delivered as much as half of our ocean water, according to the study.
This tells us not only about planets in our own solar system but about what else we might find outside it.
“Sample-return missions are mandatory if we really want to do an in-depth study of planetary objects,” Bose said. “The Hayabusa mission to Itokawa has expanded our knowledge of the volatile contents of the bodies that helped form Earth. It would not be surprising if a similar mechanism of water production is common for rocky exoplanets around other stars.”