Two clusters of dark comets in our solar system could tell researchers where Earth’s oceans are located

The water that makes up the oceans served as an important element for the development of life on Earth. But scientists still don’t know where the water on Earth comes from in the first place.

One leading idea is that space rocks, such as comets or asteroids, supplied water to Earth through collisions. As a planetary scientist, I’m interested in the types of space objects that may have led to the formation of oceans. For the past few years, I’ve been studying a type of object that I call a dark comet, and it may just be the culprit. In new research published in December 2024, my colleagues and I discovered two classes of these elusive dark comets.

What is a comet?

The solar system has many small celestial bodies such as comets and asteroids. These space rocks were the basic building blocks of the planets of the early solar system, and the remaining remnants are the comets and asteroids we see today.

These objects are also the routes by which material is transported throughout the solar system. These tiny worlds can include debris, ice, organic matter, and more as they fly through space. That’s why researchers think they’re good candidates for delivering water, carbon dioxide, and other ice to Earth during its formation.

Traditionally, the difference between comets and asteroids is that comets have beautiful comet tails. These tails form because comets contain ice, but asteroids are not thought to contain ice.

As the comet approaches the Sun, these ices heat up and sublimate, turning them from ice to gas. The gases are heated by sunlight and blown off the comet’s surface in a process called outgassing. The release of this gas creates debris and small dust particles that reflect sunlight.

Asteroids, on the other hand, do not have cometary tails. Presumably, they resemble classical rocks without ice on their surfaces.

What is non-gravitational acceleration?

The release of gas from the comet’s surface creates a comet tail and a rocket-like recoil. The fast-moving gas pushes against the comet’s surface, which causes it to accelerate. This process drives the comet’s motion through space in addition to the motion set by the Sun’s gravity.

So when a comet releases gas, it creates what planetary scientists call non-gravitational acceleration, or motion that is not caused by the gravity of objects in our solar system. Planetary scientists typically measure a comet’s non-gravitational acceleration after detecting its tail.

What is a dark comet?

Our team has identified a class of small bodies in our solar system that incorporates some of the characteristics of both comets and asteroids. We called them dark comets.

These dark comets have comet-like non-gravitational acceleration, so they experience rocket-like recoil from the comet’s outgassing. However, it does not have the dusty tail that most comets have.

In other words, they look like typical asteroids, but gravity alone cannot explain their motion.

The first interstellar object, ‘Oumuamua, was the first comet- or asteroid-sized object discovered within the solar system from outside the solar system.

“Oumuamua exhibited this same strange combination of no dust tail and comet-like non-gravitational acceleration. This has led to many theories trying to explain what this object was. One possibility is that it was emitting gas like a comet, but did not produce a dust-like tail.

Since ‘Oumuamua was first discovered in 2017, my colleagues and I have identified other dark comets in our solar system. In our research, we discovered 7 new dark comets, bringing the total to 14.

Now that we’ve discovered more dark comets, we’ve realized that there are two types of them. The outer dark comet is even larger, measuring about a mile across and orbiting in a more elliptical orbit farther out in the solar system. The inner, fainter comets are smaller, typically 300 feet in size, and orbit in a circular orbit closer to Earth.

Contribution to the Earth’s oceans?

It is not yet clear exactly what these dark comets are. If the surface were not icy, it might not even be a conventional comet.

But the most likely answer to their non-gravitational acceleration is that they eject gas from water like comets, but do not produce dust-like tails. At least we don’t see the dusty tails when we observe them with telescopes.

If so, there should be many more of these yet-to-be-identified objects walking around like asteroids.

Scientists don’t know exactly where Earth’s water comes from, so if there really are a lot of dark comets with water near Earth, it’s likely that these dark comets brought water to the early Earth. Possibly.

These dark comets could tell researchers more about the origin of Earth’s oceans and the development of life on Earth.

Reasons to be excited about the future

This research is actually just the tip of the iceberg, as the discovery of these dark comets is just beginning in 2023.

The Vera C. Rubin Observatory’s Space-Time Heritage Survey will begin in 2025 and begin scanning the entire southern sky almost every night to find anything moving. The telescope is located atop a mountain in Chile’s Atacama Desert and contains the largest camera ever built.

This gives astronomers nearly five orders of magnitude more sensitivity in detecting moving objects in the night sky. It will help my colleagues and I discover many new dark comets in the near future.

Telescopes already in operation, such as the Hubble Space Telescope and the James Webb Space Telescope, could also help monitor outgassing and ice on the surfaces of the 14 dark comets my team has already identified.

Finally, the JAXA Hayabusa2 expansion mission is scheduled to rendezvous with one of the inner dark comets, 1998 KY26, in 2031. Therefore, we will be able to see the surface of the dark comet in great detail.

This article is republished from The Conversation under a Creative Commons license. Read the original article.