Asteroids may hold the key to the origins of water in the solar system

A pair of missions to two asteroids near Earth are beginning to provide new information about when, where and in what form water first existed in the solar system.

Why is this important: Water played a key role in the formation of planets – and the emergence of life that evolved on at least one world thereafter.

  • “Asteroids, on some level, were carriers of water throughout the solar system,” says Kevin Walsh, a scientist at the Southwest Research Institute who studies asteroids.
  • The “children and grandchildren” of those asteroids that drifted closer to Earth can be studied to learn more about the primordial asteroids that first carried water, he says.
  • Signs of water can be spotted in chemically altered asteroid materials when rocks and dust interact with water.

Driving the news: NASA’s OSIRIS-REx spacecraft collected about 250 grams (about half a pound) of rock and dust from the surface of near-Earth asteroid Bennu in October 2020, a team of scientists that includes Walsh reports today in the magazine Science. The sample will be brought back to Earth next year.

  • Bennu is about 500 meters (1,640 feet) wide, orbiting the Sun at an average distance of 105 million miles – and sometimes relatively close drift towards the earth.
  • The spacecraft created a plume of debris and a 9-meter-long (30-foot) crater as it collected the sample. By analyzing both the particles lifted in the process and the forces experienced by the spacecraft, the researchers found that the material is finer, less dense and looser than the surface, report Walsh and his colleagues in a separate paper in the magazine Scientific advances.
  • The particles landed on the spacecraft’s spectrometer, giving the team the opportunity to study their infrared signals. Previous research has postulated that the material is likely rich in magnesium-containing minerals formed through interactions with water, similar to some “chemically primitive” meteorites found on Earth. They report that the latest analysis proves it.

The big picture: Small rocky bodies like Bennu are thought to be fragments of the first asteroids in the solar system.

  • Evidence suggests that these early-stage asteroids formed just tens of millions of years after the solar system began 4.5 to 4.7 billion years ago, when a cloud of gas and of dust collapsed and formed the Sun.
  • As rocks orbiting the Sun accreted into the outer solar system, ices and gases were also drawn into their mix. As the bodies got bigger, there was more heat, more pressure, and more compression of rocks and fluids.
  • And “very quickly these bodies became geologically active,” says Harold Connolly, professor of geology at Rowan University and co-investigator and mission sample scientist on OSIRIS-REx. Water was ‘an agent of change’ in the early solar system that helped make the planets the geologically active worlds they are today – ‘something that life can actually evolve on’, he adds. he.

As the asteroids hit together in the early outer solar system, chunks of rock broke off and reaccumulated to form “rubble pile” asteroids like Bennu.

  • Its current composition is thought to have been established on a larger carbon-rich parent asteroid within 10 million years of the start of the solar system, by NASA.
  • “The whole history of the solar system is hidden in these little little piles of rubble,” says Walsh. “You can walk back to the original asteroids.”

A mission apart by the Japanese space agency JAXA, published an analysis from a sample returned from asteroid Ryugu in late 2020.

  • It corresponded to a rare type of meteorite which landed in Tanzania in 1938.
  • Radioisotope dating indicates that the material was changed when ice melted into water that circulated through the asteroid about 5.2 million years after the solar system formed, the the team reported.

The plot: For Bennu, “We don’t know where he came from or who he might be related to,” Walsh says.

  • OSIRIS-REx can provide images from the asteroid down to its individual rocks and craters. The randomly scattered boulders spotted on the asteroid are different from the rest of the rocky material.
  • “It tells us that it’s interacting with something that wasn’t primarily its main parent. It speaks to the wild history of the belt – and probably the collisions of [Bennu’s] own.”
  • Connolly, who is also a co-investigator on the JAXA mission, says that Bennu and Ryugu could be cousins, but this hypothesis cannot be confirmed until the pieces of Bennu are on Earth.

What to watch: JAXA’s two sample return missions – Hayabusa1 and Hayabusa2 – returned samples that were found to match the most abundant and rarest meteorites on Earth.

  • The big question is where Bennu fits in, says Connolly.

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