Where did Earth’s water come from? Maybe this ancient asteroid family will help us find out

A primitive family asteroids giving astronomers a glimpse into the past as they try to unravel the history of these tiny space rocks that are believed to have once existed gave water to World.

Life in Solar system be dangerous, with many impacts having occurred throughout history — for example, consider the huge impact who founded our moon or the many impacts that inspired the cratered surface of it mercury. Sometimes, mostly large asteroids asteroid beltlocated between Mars and Jupiter, too. When that happened, those asteroids would have broken into smaller pieces. Events like this can spawn several dozen smaller ones space rocks; of course, many pieces that originate from the same original object have some things in common, such as moving around in similar orbits. Astronomers call such groups of asteroids “families.”

More than 120 such families are known to exist in the asteroid belt. Some, such as the Vesta family named after the second largest object in the belt, viz 4 Henceforth, show evidence of chemical change. Because Vesta was so large, it also underwent a process called differentiation, whereby heavier elements moved to its core to form different layers, before being hit by another asteroid and partially broken up. .

Related: No asteroid impact needed: Newborn Earth made its own water, study finds

However, eight of the asteroid families retain their primordial chemistry. Astronomers are very interested in these pristine samples because their primitive compositions may provide insight into the conditions of our solar system when the generative asteroids of these families were formed. In other words, they could help us peer into the secret ancient Solar system. Therefore, University of Central Florida planetary scientist Noemí Pinilla-Alonso is leading a project called the Primitive Asteroid Spectroscopic Survey (PRIMASS) to tell the chemical composition of these asteroid families.

Now, finally, that work is complete thanks to Ph.D. student, Brittany Harvison, who undertook to study infrared observations of the Erigone family of primitive asteroids — the last family to be studied for the PRIMASS project. The Erigone family is comparatively young, as the collision that created it is estimated to have occurred only 130 million years ago.

“There are theories that the Earth may have received a fraction of its water from primitive asteroids in the early solar system,” Harvison said in his statement. “A big part of these theories is understanding how these primitive asteroids were transported into Earth’s path. So, exploring primitive asteroids in the solar system today could help paint a picture of what was going on in the years ago.”

Using near-infrared observations taken by NASAThe 3.2-meter Infrared Telescope Facility in Hawaii and the 3.58-meter Telescopio Nazionale Galileo in the Canary Islands in Spain, Harvison analyzed the composition of 25 members of the Erigone family. The group is named after its largest member, the 72-kilometer (44.7-mile) asteroid 163 Erigone.

​​​​Harvison found that 43% of the Erigone family, including 163 Erigone, are C-type carbonaceous asteroids, meaning they are rich in carbon. It is not surprising that so many of Erigone’s inhabitants are C-types as that is the most common type of asteroid in general, and one that often has evidence of hydrated or water-borne minerals. Therefore, C-type asteroids are prime candidates for bringing water to Earth.

As for the rest of the Erigone family, 28% are X-type asteroids that are probably of a different type that happen to have similar spectra to the rest of their family. B-types, which are a variety of carbonaceous asteroids, make up 11% of the Erigone family, while the unknown T-types make up 7%. There are also a number of L- and S-stone types that appear to be non-primitive intermediates rather than true members of the family.

Harvison’s main discovery, however, is that all members of the Erigone family have a similar basic composition that no other primitive asteroid family repeats. In fact, all families are unique and have their own different levels of hydration. Being able to match the asteroid families with the most water content will help point astronomers in the right direction in their search for the craters that brought water to Earth.

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Because the Erigones are so hydrated, they are now a prime target for the astronomers. As it happens, NASA’s Lucy space mission, which is in charge of Jupiterand Trojan asteroids, first visit the asteroid 52246 Donaldjohanson. Named after an American paleoanthropologist, this C-type asteroid is a member of the Erigone family, so scientists will be able to get a close look when Lucy flies past on April 20, 2025.

The PRIMASS team also wins time on the James Webb Space Telescope to look at the Erigone family (as well as other primitive asteroids) starting this summer. The results of JWST and Lucy will further reveal the history of these ancient materials and begin to fill the gaps in our knowledge of the time of the solar system – and of Earth.

Harvison’s research was published in the April 2024 issue of Icarus.

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