Scientists Have Found “Earth-Like Water” On Comets

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Scientists have long thought water came to Earth as part of a collision with a planetisimal or via asteroids, which are often thought to have brought life to Earth as well. While comets are mainly icy bodies, in-depth studies showed that the icy water on their nuclei isn’t the best candidate for a water-bringer. However, a team of researchers say “Earth-like water” on comets could reshape our knowledge about the origin of water on Earth, according to a statement on

An international team of scientists which consists of CNRS researchers at the Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres and the Laboratory of Space Studies and Instrumentation in Astrophysics found a family of hyperactive comets which consist of Earth-like water. Their findings were published in the journal Astronomy & Astrophysics, and they’re based on measurements of the comet 46P/Wirtanen taken by NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA).

According to popular theories in astronomy and astrophysics, Earth was formed from a collision of celestial bodies known as planetesimals, which were scattered across the early solar system as it was forming billions of years ago. Those bodies were poor in water, so researchers believe water was brought by a larger planetesimal or smaller objects such as asteroids.

Researchers traced terrestrial water using isotopic ratios1, especially the ratio in water of deuterium (a neutron-equipped version of hydrogen), to hydrogen, which is known as the D/H ratio.

They continued their research on the comet 46P/Wirtanen as it approached Earth in December and then analyzed it with the SOFIA airborne observatory on a Boeing aircraft. Researchers found that it was the third comet which displayed D/H ratio behavior. All three comets were classified as hyperactive comets, which means that as they approach the sun, they release more water than the area of their nucleus should allow.

“We have identified a vast reservoir of Earth-like water in the outer reaches of the solar system,” lead author Darek Lis of NASA’s Jet Propulsion Laboratory said in the space agency’s news release. “Water was crucial for the development of life as we know it. We not only want to understand how Earth’s water was delivered, but also if this process could work in other planetary systems.”

Hyperactive comets are a special family of comets whose water vapor is derived from icy grains expelled into their own atmosphere as they approach the sun. This process makes their D/H ratio similar to that of terrestrial water, compared to comets whose gas halos are made only out of their own surface ice. However, researchers suggest that the Earth-like water on comets doesn’t indicate that the ice is present in their own nucleus. If this hypothesis is correct, then the water in all nuclei in comets could be similar to terrestrial water, which might reshape our thoughts of the origin of Earth’s water.

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