Less than a year ago, astronomers spotted a comet that originated in the far reaches of our solar system passing through our solar system. The object, known as 3I/ATLAS, is only the third confirmed interstellar visitor to date, and scientists are now uncovering clues about the extraterrestrial environment in which it formed.
A new study led by researchers at the University of Michigan suggests that the comet formed in conditions far colder than those that shaped our solar system. The discovery came from analysis of the comet’s unusual water composition, which revealed an unusually high concentration of deuterium, a heavier form of hydrogen.
The research was published in the journal Nature Astronomy and received support from NASA, the US National Science Foundation, and Chile’s National Agency for Research and Development.
“Our new observations show that the conditions that led to the formation of our solar system are very different from how planetary systems evolved in different parts of our galaxy,” said Luis Salazar Manzano, lead author of the study and a doctoral student in UM’s astronomy department.
Alien comet contained unusual “heavy water”
A water molecule is made up of two hydrogen atoms and one oxygen atom, giving water the familiar formula of H2O. In normal water, hydrogen atoms contain only protons. However, some water contains deuterium, an isotope of hydrogen that contains both protons and neutrons.
Researchers discovered that 3I/ATLAS contains very large amounts of this deuterium-rich water. Although small amounts of heavy water exist on Earth and in comets in our solar system, the levels found in 3I/ATLAS were dramatically higher.
“The amount of deuterium relative to ordinary hydrogen in water is higher than what has been observed so far in other planetary systems or planetary comets,” Salazar Manzano said.
The comet’s deuterium ratio was about 30 times higher than what has been measured in comets in our solar system, and about 40 times higher than the ratio found in Earth’s oceans, the researchers said.
Clues about the frozen birthplace
Scientists use deuterium levels as a kind of chemical fingerprint that reveals the conditions in which a celestial object was formed. By comparing these ratios with those found in nearby locations, researchers can deduce the environment in which comets were formed.
The researchers concluded that 3I/ATLAS likely formed in a much colder region with lower radiation levels than the environments that formed the solar system’s planets and comets.
“This proves that whatever conditions led to the formation of our solar system are not ubiquitous throughout the universe,” said study co-leader Teresa Paneque Carreño, assistant professor of astronomy at UM. “It may sound obvious, but it’s one of those things you have to prove.”
How scientists studied 3I/ATLAS
The researchers said this study was only possible because astronomers detected 3I/ATLAS early enough to conduct detailed follow-up observations.
After the discovery, Salazar Manzano and his collaborators secured observation time at the MDM Observatory in Arizona, where they detected some of the first signs of outgassing from the comet (MDM stands for the observatory’s original partners, the University of Michigan, Dartmouth College, and the Massachusetts Institute of Technology).
Salazar Manzano then teamed up with Paneque Carreño, who brought expertise with Chile’s Atacama Large Millimeter/Submillimeter Array (ALMA). ALMA’s instruments are sensitive enough to distinguish between deuterium water and ordinary water, allowing the research team to accurately measure the ratio of deuterium water to deuterium.
Researchers say this is the first time scientists have successfully performed this type of water analysis on an interstellar object.
“Being at the University of Michigan and having access to these facilities was key to making this research possible,” Salazar Manzano said. “We are part of a team that is extremely talented in multiple disciplines and extremely experienced, and we all complemented each other so much that we were able to analyze and interpret these datasets.”
More interstellar visitors could be found
The study also indicates that astronomers may soon be able to chemically analyze additional interstellar objects to better understand how planetary systems form across our galaxy.
So far, scientists have identified only three known interstellar objects entering our solar system, but researchers expect that number to increase as more advanced observatories begin exploring the skies.
Paneque Carreño stressed that preserving dark night skies is essential to spotting these faint visitors.
“We need to pay attention to the night sky and keep it bright and dark so we can detect these small, faint objects,” she said.
Additional support for this research was provided by the University of Michigan Fellows Association and the Heising-Simons Foundation. ALMA is operated through a partnership between the European Southern Observatory, NSF, Japan’s National Institutes of Natural Sciences, and the Republic of Chile.
