As comet 3I/ATLAS continues its exciting journey through our solar system, scientists are still learning everything they can about this special space rock. It is only the second interstellar object ever tracked through our solar system and is among the fastest comets ever observed.
As the 3I/ATLAS nears its closest distance to Earth, an international team of astronomers now says the space rock may be covered in active, icy cryovolcanoes. If true, the evidence detailed in their pre-print study may force researchers to reconsider how comets form–not only in deep space, but our own solar system.
What is 3I/ATLAS?
Astronomers first detected the 3I/ATLAS in July and the comet has gripped global attention ever since. Since then, researchers around the world have aimed their telescopes and sensitive equipment arrays at it as the comet continues its 130,000 mile-per-hour journey through our stellar neighborhood. 3I/ATLAS offers us a never-before-seen glimpse at ancient, deep space comets. What’s more, the icy rock has never passed close enough to a star to be altered by its heat and radiation. This essentially makes it an untouched cosmic artifact dating back billions of years.
Apart from being the fastest comet ever observed (and also assuredly not an alien spacecraft), 3I/ATLAS also appears to display some unexpected surface activity. After monitoring the visitor for months, astronomers recorded a “sharp and lasting surge” in brightness as it reached around 2.5 astronomical units from the sun (roughly 185.9 million miles). The sustained level of brightness captured by their analysis indicates that 3I/ATLAS didn’t withstand a sudden explosion, but what appears to be an eruption across the comet’s entire water-ice surface layer.
Comet cryovolcanoes
They argue the most likely explanation for this brightness is cryovolcanism. Although volcanism on Earth is traditionally associated with scorching lava and fiery eruptions, cryovolcanism essentially operates similarly, but with the opposite materials. During cryovolcanism, liquid and vaporous water as well as other materials are ejected from inside a cosmic body. Astronomers have seen this type of behavior on moons like Jupiter’s Europa and Saturn’s Enceladus, but if confirmed, it represents a rarely seen event on comets.
The cryovolcanism on 3I/ATLAS is even more unique given the object’s origins. While eruptions are usually more acute, 3I/ATLAS lacks the protective, dusty mantle seen in our solar system’s comets. This would explain why its entire surface erupted in such a noticeable way.
Further examination of light reflected from the comet surface revealed that 3I/ATLAS likely resembles a rare type of meteorite called a carbonaceous chondrite. A carbonaceous chondrite is one of the universe’s oldest meteorites, and is heavy in metals such as nickel and iron. This composition could explain the comet’s cryovolcanism.
The study is still awaiting peer review, but its authors theorize that as 3I/ATLAS warmed and its surface ice began to melt, liquid corroded microscopic metal grains inside the rock. This would subsequently release more energy and gases like carbon dioxide, causing the frigid eruption.
Challenging the standard model
If true, 3I/ATLAS contradicts the standard model of comet formation. Instead of a more uniform amalgamation of rock, ice, and low amounts of metal, comets may begin their lives under a much more diverse set of circumstances.
“Interstellar visitors like 3I/ATLAS continue to challenge and refine our understanding of planetary-system formation and the chemical evolution of small bodies,” the study’s authors wrote, adding that, “each newly discovered object reveals unexpected properties that test and expand current models.”
