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U-M astronomy is aiding in the comprehension of this swift, ancient, and massive comet that originated beyond our galactic vicinity

An international group of astronomers, including a doctoral candidate from the University of Michigan, were the first to announce the identification of only the third recognized interstellar object visiting our solar system on July 3.

Now, two of the scientists involved—Aster Taylor from the U-M Astronomy Department and Darryl Seligman from Michigan State University—have produced a recent study beginning to define this distant object, named 3I/ATLAS.

Interstellar objects are formed outside our solar system and travel through it without establishing a consistent orbit around the sun. 3I/ATLAS and its two previous counterparts have opened exceptional, priceless opportunities for scientists to acquire insights about remote areas of our galaxy.

“This is what we aim for—discovering objects like this, raising public awareness about them, and creating enthusiasm,” stated Aster Taylor, a Fannie and John Hertz Fellow in U-M’s Department of Astronomy.

This public enthusiasm, in turn, sustains momentum for funding and the development of new tools for future discoveries. For instance, the Vera C. Rubin Observatory, which is backed by the U.S. National Science Foundation and the U.S. Department of Energy, became operational this summer. While it did not discover 3I/ATLAS, it’s anticipated to identify one or two new interstellar objects annually, said Taylor.

“It’s an exciting time to find fascinating objects,” noted Taylor. “We’re thrilled about three, but if we can reach 10 or more of these, we’ll have a substantial sample and we’ll definitely be excited about that.”

Both studies are accessible as preprints on arXiv. Taylor and Seligman also penned an op-ed regarding the discovery for Space.com.

Details at a glance

The identification of 3I/ATLAS was facilitated by NASA’s Asteroid Terrestrial-impact Last Alert System. ATLAS is composed of four telescopes—two located in Hawaii, one in Chile, and another in South Africa—that automatically survey the entire sky multiple times each night for moving objects.

ATLAS’s name suggests a crucial fact about this object: It is not destined for a terrestrial impact. In other words, it will not collide with Earth. In fact, it will not approach us closer than our distance to the sun.

Moreover, it is probably a comet, stated Taylor. It is surrounded by something known as a coma, a diffuse cloud of gas and dust enveloping its rocky core. As 3I/ATLAS approaches the sun, that coma might develop and unveil intriguing hints regarding its composition.

“3I/ATLAS likely harbors ices, particularly beneath its surface, and those ices may begin to activate as it gets closer to the sun,” remarked Seligman, a postdoctoral researcher at MSU. “However, until we detect specific gas emissions like H2O, CO, or CO2, we can’t definitively identify what types of ice or the quantities present.”

In the ensuing months, space telescopes such as Hubble and JWST will focus on 3I/ATLAS to explore these and other queries about its size, rotation, and response to heat.

“We have images of 3I/ATLAS that aren’t entirely clear, and it appears blurrier compared to the other stars in the same frame,” explained James Wray, a professor at the Georgia Institute of Technology who contributed to the discovery. “The object is quite distant, and thus, our understanding is limited.”

Nevertheless, the researchers have determined some significant characteristics from their initial observations. Specifically, 3I/ATLAS is more rapid, larger, and older than its predecessors, 1I/’Oumuamua and 2I/Borisov.

3I/ATLAS has a hyperbolic speed of just under 60 kilometers per second—about 130,000 miles per hour—compared to 26 for ‘Oumuamua and 32 for Borisov. Its diameter is currently estimated to be up to 10 kilometers, or 6 miles, which would be 100 times that of ‘Oumuamua and 10 times that of Borisov.

However, Taylor believes these values will decrease as astronomers gain more accurate observations of 3I/ATLAS. Such a considerable size would suggest that galaxies are significantly more proficient at generating these types of objects than is physically feasible.

Lastly, while ‘Oumuamua and Borisov are estimated to be millions of years old, 3I/ATLAS seems to be between 3 billion and 11 billion years old.

“That’s a broad range,” noted Taylor. “But 11 billion years is quite old. It’s nearly as ancient as the galaxy.”

This is yet another figure that Taylor suspects will ultimately be closer to the lower end of the spectrum. Nevertheless, it will provide intriguing insights into how our galaxy was forming stars, planets, and other objects in its earlier epochs.

The identification

Taylor was enlisted for the project during travels to help validate 3I/ATLAS as an interstellar object and to initiate early characterizations. And…
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There was a tight timeline. If the ATLAS team had detected 3I, it was likely that other astronomers had, too, and the team aimed to verify their theories and disseminate the information first.

“I was completely on holiday in Fiji with my family when this was revealed. Upon hearing the news, my immediate thought was, ‘Okay, that’s my next couple of days,’” Taylor remarked. “It’s tremendously exhilarating, but it’s also more demanding than one might expect.”

Seligman had a bit more heads-up, but not significantly. Information began to circulate within the group on July 1.

“I caught wind of the object prior to going to bed, but we didn’t possess much data yet,” Seligman stated. “When I awoke around 1 a.m., my associates, Marco Micheli from the European Southern Observatory and Davide Farnocchia from NASA’s Jet Propulsion Laboratory, were emailing me to suggest that this was likely legitimate. I began sending out notifications advising everyone to direct their telescopes to observe this object.”

Larry Denneau, a participant in the ATLAS team, evaluated and submitted the discovery findings from the European Southern Observatory’s Very Large Telescope in Chile shortly after it was detected.

“We’ve experienced false alerts before regarding intriguing objects, so we understand not to become overly enthusiastic on the first day,” Denneau noted. “However, the incoming data was entirely consistent, and late that night it appeared we had something genuine.”

John Tonry, another ATLAS member and professor at the University of Hawaii, played a key role in the design and development of ATLAS, the survey responsible for uncovering 3I.

“It’s immensely rewarding every time our diligent work surveying the sky uncovers something novel, and this comet, having journeyed for millions of years from another star system, is especially intriguing,” he expressed.

Once 3I/ATLAS was verified, Seligman and Karen Meech, faculty chair for the Institute for Astronomy at the University of Hawaii, both facilitated the communication process and collaborated on assembling the data for the paper submission.

“As soon as 3I/ATLAS was identified as likely interstellar, we quickly mobilized,” Meech explained. “We activated observing time on significant facilities such as the Southern Astrophysical Research Telescope and the Gemini Observatory to obtain early, high-quality data and establish a groundwork for in-depth follow-up studies.”

Other contributors to this research encompass the European Space Agency Near-Earth Objects Coordination Centre in Italy, California Institute of Technology, Auburn University, Universidad de Alicante in Spain, Universitat de Barcelona in Spain, European Southern Observatory in Germany, Villanova University, Lowell Observatory, University of Maryland, Las Cumbres Observatory, University of Belgrade in Serbia, Politecnico di Milano in Italy, University of Western Ontario in Canada, Universidad Diego Portales, Santiago in Chile, and Boston University.

Authored with Emilie Lorditch from Michigan State University

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