A new analysis of the interstellar visitor 3I/ATLAS reveals it is releasing a significant amount of water vapor at an unusually large distance from the Sun. This unexpected activity challenges current understanding of how comets behave and provides new insights into the composition of objects from other star systems.
Using NASA’s Neil Gehrels Swift space telescope, astronomers detected strong ultraviolet emissions from the comet. These emissions are a clear indicator of hydroxyl gas (OH), a chemical byproduct formed when water molecules are broken apart by sunlight. The findings suggest the comet is actively shedding water, a process typically observed much closer to a star.
Key Takeaways
- Interstellar comet 3I/ATLAS is ejecting water vapor at a rate of approximately 88 pounds per second.
- This activity was observed at a distance of three astronomical units (AU) from the Sun, where water ice is expected to remain frozen.
- The discovery was made by detecting hydroxyl gas (OH), a byproduct of water, using NASA's Swift space telescope.
- The finding implies that the chemical ingredients for life may be common in planetary systems beyond our own.
A Puzzling Observation from a Distant Visitor
Astronomers observed 3I/ATLAS before it passed behind the Sun from our vantage point on Earth. The data, collected in ultraviolet light, could only be captured from space because Earth's atmosphere absorbs these wavelengths. The results of this observation were published in a new study in The Astrophysical Journal Letters.
The amount of hydroxyl gas detected indicates that the comet is releasing water at a torrential rate. Researchers calculate the output to be about 88 pounds per second, a volume comparable to a fully open fire hose. What makes this discovery particularly noteworthy is the comet's location when the observation was made.
Distance and Temperature
The water ejection was recorded when 3I/ATLAS was three astronomical units (AU) from the Sun. One AU is the distance between the Earth and the Sun, approximately 93 million miles. At three times that distance, solar radiation is generally considered too weak to cause significant sublimation of water ice on a comet's nucleus.
Typically, comets from our own solar system must travel much closer to the Sun for their water ice to sublimate, transitioning directly from a solid to a gas. This process is what creates a comet's glowing halo, or coma, and its characteristic tail. The behavior of 3I/ATLAS suggests a different mechanism is at play.
Rewriting Cometary Science
The unexpected activity from 3I/ATLAS adds to a growing list of surprising discoveries from interstellar objects. Each visitor has displayed unique characteristics, forcing scientists to reconsider their models of planetary and cometary formation.
"Every interstellar comet so far has been a surprise," said Zexi Xing, a postdoctoral researcher at Auburn University and lead author of the study. "'Oumuamua was dry, Borisov was rich in carbon monoxide, and now ATLAS is giving up water at a distance where we didn’t expect it."
These differences suggest that the conditions in other star systems could be vastly different from our own. The chemical makeup of 3I/ATLAS, which appears to have a high ratio of carbon dioxide to water, further distinguishes it from comets originating in our Oort Cloud or Kuiper Belt.
Possible Explanations for Water Release
Scientists are still exploring why 3I/ATLAS is releasing so much water so far from the Sun. One leading hypothesis is that sunlight is not directly heating the comet's core, or nucleus. Instead, it may be warming smaller ice grains that have already been ejected from the nucleus.
As these tiny grains of ice drift into the coma, they are more easily heated by solar radiation, causing them to vaporize and release water molecules. This process would explain the high rate of water ejection at such a great distance. This also implies the comet must contain a substantial reservoir of water to sustain this activity.
A Messenger from Another Star System
Interstellar objects like 3I/ATLAS offer a rare opportunity to study material from faraway planetary systems without leaving our own. By analyzing their composition, astronomers can learn about the chemical environments around other stars.
The Origin of 3I/ATLAS
Astronomers believe 3I/ATLAS originated near the center of the Milky Way galaxy. It was likely ejected from its home star system by a gravitational event, such as a close pass with another star. Based on its trajectory, scientists estimate the comet could be billions of years old, possibly predating our own Sun by as much as three billion years.
The presence of water is particularly significant because it is a key ingredient for life as we know it. The discovery reinforces the idea that the building blocks for life may not be unique to our solar system.
"When we detect water — or even its faint ultraviolet echo, OH, — from an interstellar comet, we’re reading a note from another planetary system," said Dennis Bodewits, a physics professor at Auburn University and coauthor of the study. "It tells us that the ingredients for life’s chemistry are not unique to our own."
This finding supports the broader scientific search for habitable environments beyond Earth, suggesting that water is a common component throughout the galaxy.
Future Observations Planned
Currently, 3I/ATLAS is positioned behind the Sun, making it impossible to observe from Earth. However, spacecraft stationed near Mars have been able to track its journey. The comet is expected to become visible again to Earth-based telescopes in late November.
Scientists are eager to conduct further observations as it re-emerges. Continued study of its behavior and composition will provide more clues about its origin and the processes that govern comets from other star systems.
As Zexi Xing noted, each new interstellar visitor is a learning opportunity. "Each one," he added, "is rewriting what we thought we knew about how planets and comets form around stars." The ongoing analysis of 3I/ATLAS will undoubtedly contribute new chapters to that story.