Aug 8, 2023 - Science

Asteroids deliver answers about the solar system's evolution

Illustrated collage of a researcher looking through a microscope on a starry background surrounded by circles and orbits.

Illustration: Aïda Amer/Axios

Asteroids, comets and meteorites are increasingly essential to scientists' understanding of our solar system.

Why it matters: These objects are proxies for the elements and chemicals present in the early solar system.

  • Scientists want to study them to find out how water was possibly delivered to Earth and how the planets came together initially, which could have implications for understanding distant star systems and the search for life beyond Earth.
  • Many of these small bodies are ancient, NASA's Jeff Grossman, the program scientist for the OSIRIS-REx mission to an asteroid, tells Axios. "Very little has happened to them since the earliest days of the solar system."

What's happening: Meteorites collected on Earth and pristine samples of asteroids and comets brought back from space are deepening scientists' understanding of these small objects and our universe as a whole.

  • A sample of asteroid Ryugu brought back to Earth in 2020 contains stardust older than our solar system and is rich in volatile gases that could help explain how those gases got to early Earth, helping to form our atmosphere.
  • A team of researchers claims a meteorite found in the Sahara desert in Morocco might be a rock ejected from Earth 10,000 years ago that found its way back to our planet thousands of years later. If confirmed, the space rock could help reveal how meteors are changed over time while in space.
  • Scientists are also using observations made during meteor showers — like the Perseid meteor shower this week — to learn more about the compositions of the comets that create them.

How it works: Asteroids and comets are thought to be leftovers from the dawn of planet formation in the solar system.

  • Some of these objects are thought to be fragments of the iron cores of planetesimals that didn't come together to form major planets. Others are rubble piles of material that represent the remnants of violent collisions.
  • Unlike Earth, with its constantly churning crust, asteroids and other small bodies are largely frozen in time, acting as time capsules that can reveal the early solar system's composition.
  • "It's very difficult to study this part of Earth's history. You can only look basically at evidence that's left in the rocks that are much younger," Grossman said. Asteroids and other relatively small objects are a source of "information about this epoch of the solar system."

The intrigue: "Although we probably have samples of over 100 asteroids in the meteorite collection, we don't know where those come from, except for a small number of them," Grossman said.

  • "It's almost like studying Earth rocks gathered randomly from around the Earth and not telling you where they're from and asking you to understand those histories."
  • Meteorites have also been altered by their trips through the atmosphere, potentially destroying some of the molecules that were within the space rock before it came to Earth.
  • By actually retrieving samples of asteroids and bringing them back to Earth, scientists know exactly where they came from and what they're made of, ending the guessing game created by retrieving meteorites that have already fallen to Earth.

What to watch: The OSIRIS-REx mission to asteroid Bennu is scheduled to deliver a large sample of the space rock back to Earth next month, giving scientists a way to learn more about the building blocks of life in the solar system.

  • The Lucy mission is on its way to explore Trojan asteroids near Jupiter, and Psyche is expected to launch in October to explore a strange metallic asteroid that might be the dead core of an early planet.
  • The United Arab Emirates is planning to send its first mission to the asteroid belt, expected to launch in 2028.
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