Oct 20, 2022 - Science

Asteroid science is rewriting the solar system's history

Illustration of a marble bust of an asteroid on a pedestal with stars in the background

Illustration: Sarah Grillo/Axios

New studies, missions and rich data about asteroids are giving scientists a sharper picture of the solar system's history.

Why it matters: Asteroids are leftovers from the dawn of the solar system that carry a record of the materials that built planets. They could help piece together how the solar system formed — and how life-generating water arrived on Earth.

  • These space rocks can also threaten our planet, and while strikes are rare, scientists stress that understanding these objects is key to keeping Earth safe.

Driving the news: A trio of papers published today analyzed samples from the asteroid Ryugu returned to Earth in 2020 by the Hayabusa2 spacecraft.

  • Scientists found new evidence that the asteroid's parent formed on the far outskirts of the solar system, offering potential clues into Earth's history.

How it works: The composition of asteroids is studied by analyzing meteorites that fall to Earth or more pristine samples taken from the asteroids themselves. Previous analysis of Ryugu samples found the minerals and chemicals in the asteroid are similar to those in a type of meteorite (CI chondrites) formed in the outer solar system.

  • But just because the asteroid and CI chondrites formed from the same materials doesn't necessarily mean they formed in the same place, says Timo Hopp, a scientist at the Max Planck Institute for Solar System Research and a co-author of two of the new papers.
  • Materials move through the solar system — and understanding when, where, and how is key to unraveling the history of Earth.
  • The isotopes, or types of an element, in an asteroid or meteorite are fingerprints pointing to where the materials formed and can be used to trace their path through the solar system.

Details: In the new papers, international teams of scientists measured the abundance of noble gases, including helium and neon, in Ryugu samples as well as the isotopes of elements in the asteroid.

  • They found Ryugu is rich in volatile gases, which could help scientists to understand how volatile gases were first delivered to Earth, where they played a key role in forming the planet's life-supporting atmosphere.
  • Another recent study of the zinc content of meteorites found the origin of Earth's volatile elements is, in part, from the outer solar system.

The isotopes of iron found in Ryugu and CI chondrites are distinct from those found in other meteorites that formed in the outer Solar System, suggesting they formed in a different reservoir farther from the Sun, according to one of the studies.

  • Other meteorites are thought to be from asteroids formed in the same nursery as Jupiter and Saturn.
  • But the compositions of Ryugu and the CI chondrites suggest their predecessors were born elsewhere, possibly near Uranus and Neptune, the authors write.
  • They then somehow moved from the edge of the solar system to the surface of Earth.

The intrigue: The findings also mean Ryugu and the CI chondrites could "share a common heritage with Oort cloud comets," the authors write. The Oort cloud is a massive layer of ice and dust 4.6 trillion miles away from the Sun and just in the grip of the Sun's gravity.

  • That is a "tantalizing" idea, says Kevin Walsh, a scientist at the Southwest Research Institute who studies asteroids.
  • Comets are considered the most primitive bodies in the solar system. If some asteroids end up being thrown out to the edge of the solar system where they form comets, "it would be a big key for us to unlock in understanding the dynamical history of the solar system," Walsh says.

Yes, but: The amount of carbon in Ryugu samples suggests its parent body didn't form from comets, according to a paper published last month.

  • Hopp says the properties of comets are different from those of Ryugu and other asteroids, but that may be because they changed since they formed and traveled through the solar system.
  • A challenge is there isn't much data about comets. A mission to return comet samples from the Oort Cloud probably isn't possible in our lifetime, Hopp says.
  • Instead, they propose retrieving samples from asteroids that may have formed in the Kuiper Belt beyond Neptune.

The big picture: Learning more about asteroid compositions isn't just about understanding the history of the solar system.

  • Knowing the makeup of asteroids in Earth's neighborhood is key to determining how best to deflect them if one is ever found on a collision course with Earth.
  • Scientists think some asteroids are metal-rich and dense, while others are effectively rubble piles of loosely packed rocks floating through space together.
  • The means of deflecting an asteroid may change depending on its composition.

Between the lines: The DART spacecraft successfully deflected an asteroid recently, but researchers still have a lot to learn about how to best throw an asteroid off course if needed.

  • A new tool developed by researchers at MIT could help map out the interior of asteroids, making it easier to know the most effective way of throwing them off-course.
  • “If you know the density distribution of the asteroid, you could hit it at just the right spot so it actually moves away,” Jack Dinsmore, who helped develop the tool, said in a statement.

What to watch: NASA's OSIRIS-REx spacecraft is set to return a sample from a different asteroid to Earth in September 2023, which will give scientists clues about the variety of asteroids and compositions that exist in the solar system.

  • NASA was also expected to launch another asteroid mission this year to the strange asteroid Psyche — thought to possibly be the iron core of a long-dead planet — but technical problems have delayed it. It's not clear when, or if, the mission will get off the ground.

Go deeper: Asteroids help trace water's journey across the solar system

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