‘Oumuamua: What sent an interstellar comet zooming by our sun

(CNN) In 2017, ‘Oumuamua became the first observed interstellar object to pass through our solar system, and its sighting sparked questions scientists are still trying to answer.

The object, similar in shape to a cigar or a pancake, was the size of an asteroid and moved in a somewhat comet-like fashion, but lacked a comet tail.

Unlike comets, which can be several kilometers across, ‘Oumuamua is estimated to be 377 by 364 by 62 feet (115 by 111 by 19 meters).

The confusing movements have led some to speculate that the mysterious object may even be an extraterrestrial spacecraft.

Now, new research aims to close the book on the interstellar comet’s orbit with a simpler explanation. A study describing the findings was published Wednesday in the journal Nature.

An interstellar visitor

As planets form around stars, gravitational interactions tend to eject some of the small “leftovers,” such as comets and asteroids.

“Comets preserve a snapshot of what the solar system looked like when it was at the stage of evolution that protoplanetary disks are now,” study co-author Jennifer Bergner, assistant professor of chemistry at the University of California, Berkeley, said in a statement. “Studying them is a way to see what our solar system looked like early in its formation.”

These interactions send space rocks out of their planetary systems and into interstellar space, where they can travel for millions of years.

Scientists think that’s how ‘Oumuamua ended up passing through our solar system six years ago. The space object was first observed by the University of Hawaii’s Pan-STARRS1 telescope. The object, which had orbited the sun and was leaving our solar system, was named ‘Oumuamua, which means “a messenger who arrives first from afar” in Hawaiian.

This artist’s illustration depicts ‘Oumuamua moving toward the outskirts of our solar system after being heated by the sun.

Astronomers used telescopes around the world to watch the interstellar visitor for four months before it became too faint to observe.

But ‘Oumuamua did not fit well with the proposed scenarios. The object looked more like an asteroid, but space rocks like asteroids move because of gravity.

“Oumuamua was accelerating as it moved, which would require more than just gravity. The object appeared to be propelled, like comets when they are near the sun and the evaporation of their gas and dust by the heat of the sun causes a propulsive effect. The force of the ejected material also slightly changes the trajectory of comets, distinguishing them from asteroids and planets as they orbit the sun.

However, ‘Oumuamua did not look like a comet, nor did it have a tail or an envelope of gas and dust, called a coma, that all comets have.

Unraveling a space mystery

The sighting of Oumuamua sparked debate among astronomers as soon as it appeared.

“It was an exciting time in astronomy when ‘Oumuamua was first discovered, and it just got more and more intriguing as the more we learned about it, the harder it became to explain its behavior,” Bergner said. “As an astrochemist, my scientific interest in ‘Oumuamua developed as models began to emerge to explain its acceleration, which implied the object’s rather unusual chemical properties.”

Bergner heard a talk by Darryl Seligman, a National Science Foundation postdoctoral fellow at Cornell University in Ithaca, New York, about the types of molecules that can provide the best acceleration. The two began working together on ways to test acceleration theories for the interstellar comet.

Together, Seligman’s deep understanding of Oumuamua and Bergner’s background in ice phase chemistry allowed them to come up with a new theory.

The pair envisioned ‘Oumuamua as a water-rich comet traveling through the interstellar medium, or the space between stars. Over time, the reddish object was bombarded by radiation, which formed hydrogen inside the comet.

Bergner found previous research from decades past that found ice could turn into molecular hydrogen, suggesting that a comet’s snowball-like structure could trap hydrogen in bubbles within the ice.

The sun’s heat would then force the bubbles to release the gas in a fan-shaped spray.

“When the body warms, the water ice restructures into a more stable and compact form, and the trapped gas can escape,” Bergner said. “This may explain ‘Oumuamua’s behavior, but it doesn’t need to invoke any exotic chemistry or physics.”

As hydrogen gas released from the interstellar comet, it accelerated the small object. The fact that there was no dusty coma around ‘Oumuamua can also be explained using the same scenario.

“Even if there was dust in the ice matrix, you’re not sublimating the ice, you’re just rearranging the ice and then letting (hydrogen) escape. So the dust won’t even come out,” Seligman said. “What’s beautiful about Jenny’s idea is that this is exactly what should happen with interstellar comets. We had all these silly ideas, like hydrogen icebergs and other crazy things, and this is just the most plausible explanation. general.”

The search for interstellar objects

Observatories like the James Webb Space Telescope can help astronomers learn more about where comets formed in planetary systems beyond our system, as well as the composition of these exocomets, Bergner said.

When the Vera C. Rubin Observatory in Chile begins operations in 2025, it will aim to detect several interstellar comets like ‘Oumuamua each year, allowing astronomers to better understand the nature of comets from other planetary systems.

“Comets and asteroids in the solar system have probably taught us more about planet formation than what we have learned from the actual planets in the solar system,” Seligman said. “I think interstellar comets can tell us more about extrasolar planets than the extrasolar planets we’re trying to get measurements of today.”

(Extrasolar planets exist outside our solar system.)

Rubin Observatory’s Legacy Survey of Space and Time, or LSST, program will observe the skies over the Southern Hemisphere for 10 years.

“If we had LSST online before ‘Oumuamua’s transit through the inner solar system, we would have detected it much earlier in its trajectory,” Seligman said. “We might have had the opportunity to send a space mission to intercept and rendezvous with the object because it was so close to Earth. Therefore, in the future when we discover more interstellar objects, we will be able to send a dedicated space mission to an interstellar object.”