{"id":54889,"date":"2025-09-10T09:57:08","date_gmt":"2025-09-10T09:57:08","guid":{"rendered":"https:\/\/www.europesays.com\/ie\/54889\/"},"modified":"2025-09-10T09:57:08","modified_gmt":"2025-09-10T09:57:08","slug":"how-an-interstellar-interloper-spurred-astronomers-into-action","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/ie\/54889\/","title":{"rendered":"How an Interstellar Interloper Spurred Astronomers into Action"},"content":{"rendered":"

On 1 July 2025, astronomers detected a visitor from the deep reaches of space. At the time of discovery, the object was just inside Jupiter\u2019s orbit and was zipping across our solar system 4 times faster than the New Horizons probe sped past Pluto. It was first spotted by the Asteroid Terrestrial-impact Last Alert System (ATLAS<\/a>) in Chile, which was specifically designed to spot small, fast-moving objects like this. ATLAS sent out a public, automated alert<\/a>, and when astronomers saw it, they quickly went to work calculating the object\u2019s orbit and trajectory.<\/p>\n

That\u2019s when things got interesting. Backtracking the object\u2019s path showed that its origins were not in the Oort cloud<\/a>, the outermost region of our solar system responsible for most of the comets we see. Instead, the object\u2019s journey started a long time ago in a star system far, far away.<\/p>\n

The earliest observations of the object\u2014now labeled 3I\/ATLAS for being the third confirmed interstellar object (3I)\u2014showed a distinct coma or haze of material surrounding a dense center.<\/p>\n

\n

\u201cWe knew we were going to get a 3I. We didn\u2019t know when we were going to get a 3I.\u201d<\/p>\n<\/blockquote>\n

The trajectory of 3I\/ATLAS suggests that it will escape the modest gravitational clutches of the Sun in mid-2026, and that time frame has contributed to a flurry of activity among scientists in the emergent field focused on studying interstellar objects (ISOs). Teams of researchers have secured time on some of the most prominent telescopes around the world and in space, combed through telescope archives for \u201cprecovery<\/a>\u201d images, run computer models and simulations, and released nearly three dozen quick-look research papers<\/a> in astronomy\u2019s preferred preprint repository.<\/p>\n

\u201cWe knew we were going to get a 3I. We didn\u2019t know when we were going to get a 3I,\u201d said Michele Bannister<\/a>, who researches small solar system objects at the University of Canterbury in \u014ctautahi-Christchurch, Aotearoa New Zealand.<\/p>\n

The speed of discoveries about this interstellar visitor outpaced efforts made when the first and second interstellar objects were discovered: 1I\/\u2019Oumuamua in 2017 and 2I\/Borisov in 2019. One ISO might be a fluke, and two may be a coincidence, but three seemed inevitable. Astronomers took no chances in preparing for the likely arrival of another interstellar visitor.<\/p>\n

Teams\u2019 carefully laid plans have borne fruit, enabling rapid-response science, close international collaborations, and a united global effort to learn as much as possible about 3I\/ATLAS before it disappears forever.<\/p>\n

Planning for 3I<\/strong><\/p>\n

The arrival of \u2018Oumuamua<\/a> caught astronomers by surprise. It was the first discovery of its kind and wasn\u2019t spotted until it was on its way out of the solar system. Researchers had a mere 2 weeks to get all the data they possibly could, taking their best guesses about what telescopes, instruments, and wavelengths would provide the best data on such short notice.<\/p>\n

When something like \u2018Oumuamua<\/a> shows up, \u201cyou immediately write what\u2019s called a director\u2019s discretionary [DD] proposal,\u201d explained Karen Meech<\/a>, a planetary astronomer at the University of Hawai\u2018i\u2019s Institute for Astronomy. \u201cYou scramble, you write a proposal, you submit it. The [telescope] director reads it and makes a decision without a review panel.\u201d Bypassing a review panels speeds up the process but is less democratic.<\/p>\n

Having found one ISO, researchers started putting in DD proposals every semester in case another one showed up.<\/p>\n

\n

\u201cAstronomers are always trying to use these facilities as efficiently as possible.\u201d<\/p>\n<\/blockquote>\n

When Borisov<\/a> appeared 2 years later, it was immediately obvious that it was radically different from \u2018Oumuamua. The way observations were allotted on telescopes was also different\u2014facilities became overwhelmed with the sheer volume of DD proposals, Meech said. That led to duplicate observations and some teams\u2019 observations being bumped entirely when a newer, but identical, proposal came in. Telescopes have since worked out those kinks in the system to streamline the DD proposal process.<\/p>\n

Anticipating the inevitable detection of a third interstellar object, many ISO observers took a different approach: target of opportunity (TOO) proposals. TOO is a process commonly used in branches of astronomy that study unpredictable phenomena like supernovas, kilonovas<\/a>, gravitational waves, and gamma ray bursts. Researchers submit observing proposals for short observations of events that could happen at any time. If the event occurs, the team can trigger those telescope observations.<\/p>\n

\u201cMost collaborations, including ours, have preapproved dormant programs at the world\u2019s largest telescopes ready to be activated when a suitable [ISO] candidate is confirmed,\u201d said Ra\u00fal de la Fuente Marcos<\/a>, who researches small solar system objects at the Universidad Complutense de Madrid in Spain. Before \u2018Oumuamua, \u201csuch a discovery was considered highly unlikely. Now all the collaborations that have been involved in early data releases of 3I\/ATLAS have such systems.\u201d<\/p>\n

\u201cBasically, if you give us more than a semester to plan, we will plan,\u201d Bannister said. \u201cAstronomers are always trying to use these facilities as efficiently as possible.\u201d<\/p>\n

De la Fuente Marcos and his team imaged and obtained spectra of 3I\/ATLAS with the Gran Telescopio Canarias and the Two-meter Twin Telescope, both in Spain\u2019s Canary Islands. Their observing program was triggered a mere 6 hours after 3I\/ATLAS was confirmed as an interstellar object, allowing them to observe the comet from 2 to 5 July. Their results, published<\/a> in Astronomy and Astrophysics, were the first to show that 3I\/ATLAS\u2019s spectrum is red and dusty, not too dissimilar from dusty solar system comets.<\/p>\n

Teddy Kareta\u2019s observations were more serendipitous. Kareta<\/a>, a planetary scientist at Villanova University in Pennsylvania, already had time scheduled on the NASA Infrared Telescope Facility (IRTF<\/a>) for 3 and 4 July. He learned about 3I\/ATLAS the evening before his observing run and thought, \u201cThat\u2019s too cool to be real,\u201d he recalled.<\/p>\n

\u201cAnd then I woke up to about seven text messages, three missed calls, a dozen emails, most of which were saying, \u2018Hey, I noticed you\u2019re on the telescope because I checked the schedule\u2014 You\u2019re gonna go out, right?\u2019\u201d Kareta said.<\/p>\n

But the comet was coming in much faster than past ISOs and from a direction that made it challenging to observe.<\/p>\n

\n

\u201cIt was a very communal planning process, which I think for science often doesn\u2019t happen so quick and on the fly.\u201d<\/p>\n<\/blockquote>\n

\u201cPeople were coming up with observational plans on the fly,\u201d Kareta said. \u201cI pointed a 4-meter telescope at it for 2 full hours, and I think I got three useful images.\u201d<\/p>\n

There were plenty of emails, group chats, and Zoom calls trying to figure out the best telescope and camera settings.<\/p>\n

\u201cIt was a very communal planning process, which I think for science often doesn\u2019t happen so quick and on the fly,\u201d Kareta said. \u201cIt felt more like a readiness exercise than it did like a traditional kind of planning\u2026.You need as many hands on deck as possible to make it work at all.\u201d<\/p>\n

Kareta and his colleagues\u2019 infrared spectral observations, accepted for publication<\/a> in Astrophysical Journal Letters, suggest that the comet may have a complex grain size distribution, grain compositions unlike solar system comets, or both.<\/p>\n

A Broad Research Umbrella<\/strong><\/p>\n

By its galaxy-traveling nature, 3I\/ATLAS quite literally connects comet science with the study of stars, planetary systems, and the galaxy.<\/p>\n

ISO theorists have spent the time since Borisov\u2019s departure<\/a> working on a computer model that predicts the properties of interstellar objects across the galaxy. They had timed the release of their \u014ctautahi-Oxford model for the beginning of science operations<\/a> of the Vera C. Rubin Observatory and its Legacy Survey of Space and Time (LSST<\/a>), which is expected to discover<\/a> dozens of potential interstellar objects.<\/p>\n

\u201cWe knew that LSST and Rubin were going to find loads, but we just thought this was going to happen in 6 months\u2019 time, not now,\u201d said Matthew Hopkins<\/a>, who studies both ISOs and galaxy evolution at the University of Oxford in the United Kingdom.<\/p>\n

\n

Comet 3I\/ATLAS \u201creally did arrive with fantastic timing.\u201d<\/p>\n<\/blockquote>\n

Luckily, the model team, composed of people studying interstellar objects, comets, stars, and galaxy dynamics, was putting the finishing touches on a program that could analyze an ISO\u2019s speed and orbital information and predict where in the galaxy it may have come from.<\/p>\n

Comet 3I\/ATLAS \u201creally did arrive with fantastic timing,\u201d Hopkins said.<\/p>\n

The team jumped into action when the comet\u2019s orbital characteristics were announced. It was detected when it was 670 million kilometers (420 million miles) away, traveling at nearly 60 kilometers per second and coming in at a steep angle. Bannister, part of \u014ctautahi-Oxford\u2019s New Zealand contingent, said that her team was able to share its results so quickly because it had members scattered from western Europe to New Zealand. After working all day, the New Zealanders could hand off the research to European team members, whose day was just starting. By tag teaming the science, they submitted their analysis to Astrophysical Journal Letters about 84 hours after the comet\u2019s discovery. (It has since been published<\/a>.)<\/p>\n

\"AnThe orbit of 3I\/ATLAS will take it within the orbit of Mars, with close passes to both Mars and Jupiter. Credit: CSS, D. Rankin<\/a>; Video recorded and edited by Renerpho<\/a> via Wikimedia Commons, CC BY-SA 4.0<\/a><\/p>\n

\u201cEspecially for 3I, given that it was time sensitive, we definitely wanted to share our results as we had them,\u201d Hopkins said.<\/p>\n

The \u014ctautahi-Oxford model showed that because 3I\/ATLAS entered the solar system at a much steeper angle than either \u2018Oumuamua or Borisov, it likely came from a different region of the galaxy, a part known as the thick disk<\/a>. Though most young and middle-aged stars, including the Sun, live in the narrow thin disk of the Milky Way, many older stars live in the thick disk. The trajectory of 3I\/ATLAS suggests that it originated from a star system that could be more than 7.6 billion years old. Indeed, its parent star may already be dead.<\/p>\n

The age of 3I\/ATLAS has intrigued many researchers who study stellar populations, galaxy dynamics, the birth of exoplanetary systems, and astrobiology<\/a>, fields that are usually disparate and siloed.<\/p>\n

\n

\u201cIf you\u2019re studying interstellar objects, you\u2019re sitting cleanly at the division between planetary science and traditional astrophysics.\u201d<\/p>\n<\/blockquote>\n

\u201cIf you\u2019re studying interstellar objects, you\u2019re sitting cleanly at the division between planetary science and traditional astrophysics,\u201d Kareta said. \u201cAnd I think that means that people from both groups immediately know these are important.\u201d<\/p>\n

\u201cOur colleagues who do extragalactic science and supernovae are really excited to help with 3I, and so we\u2019re trying to trigger everything we can on the big telescopes,\u201d Meech said. Her group had been hoping to use the Keck II telescope<\/a> in Hawaii to obtain high-resolution infrared spectra of the comet, but the telescope had been experiencing technical issues. A student studying kilonovas had TOO time on the nearby James Clerk Maxwell<\/a> Telescope and donated it.<\/p>\n

\u201cHe said, \u2018You know what, [the kilonova is] not going to go off in the next 2 weeks. Let\u2019s use it for this,\u201d Meech recalled. \u201cAnd so we got five nights of observations on this object.\u201d Meech and her colleagues are still analyzing those data to understand the abundances of certain gases in 3I\/ATLAS\u2019s coma.<\/p>\n

The Long-Term Strategy<\/strong><\/p>\n

Several weeks after its initial discovery, it is clear that 3I\/ATLAS looks and behaves like a comet. It\u2019s now millions of kilometers closer to the Sun than it was upon detection in early July, and more recent observations, including from the Hubble Space Telescope<\/a>, James Webb Space Telescope<\/a>, Very Large Telescope<\/a>, and more, have shown a dusty coma emitted from the Sun-facing side and the beginnings of a traditional comet tail behind it.<\/p>\n

Most of the earliest 3I\/ATLAS papers are still undergoing peer review, and Kareta said that more research analyzing July observations will continue to trickle out. Too, groups that wrote early papers will be going back over their data to put them in context with newer information and provide deeper analyses of those initial quick looks.<\/p>\n

However, with the early rush of observations mostly completed, some scientists are turning their attention to what they want to learn about 3I\/ATLAS in the coming months.<\/p>\n

\u201cA lot of teams are still scrambling to get telescope time,\u201d Meech said.<\/p>\n

The comet will reach its closest approach to the Sun, a mere 35% farther than the Earth-Sun distance, on 29 October. Earth will lose sight of it in the Sun\u2019s glare in early September, but by mid-August, 3I\/ATLAS had already started outgassing, as predicted. Astronomers were eager to analyze the chemistry of the gases it emitted because that could give clues about its history<\/a>.<\/p>\n

\u201cStellar encounters this close are actually really rare for interstellar objects,\u201d Hopkins said. This is probably 3I\/ATLAS\u2019s first encounter<\/a> with a star since it was booted out of its own system, and its surface material has likely been frozen in time since then. \u201cWe can use that to learn some really cool things about the chemistry of its parent star halfway around the galaxy, even if it\u2019s dead.\u201d<\/p>\n

Spectra obtained from 3I\/ATLAS\u2019s coma in mid-August showed strong signs of water ice<\/a>, carbon dioxide<\/a>, nickel<\/a>, and cyanide<\/a>\u2014all expected of a comet emitting a mixture of gas and dust as it heats up. \u201cTypically for comets, the first thing you see is CN, cyanide, not because it\u2019s particularly abundant but because it interacts so strongly with sunlight,\u201d Meech said.<\/p>\n

\n

\u201cThere\u2019ll be a lot of happy arguments around \u2018Where did this form in the disk of its home star, and what does that tell us about the conditions that were like in that protoplanetary disk.\u2019\u201d<\/p>\n<\/blockquote>\n

Indeed, scientists are seeing an object not too unlike a domestic comet, and they\u2019ll continue to monitor its outgassing as it gets closer to the Sun.<\/p>\n

The outgassing of carbon monoxide would be particularly telling, as the compound freezes solid only in extremely cold conditions like those that exist in the outer reaches of a star system. So if 3I\/ATLAS outgasses carbon monoxide, Hopkins explained, it would be a strong hint that the object may have formed in the coldest outer regions of its system\u2019s protoplanetary disk.<\/p>\n

\u201cThere\u2019ll be a lot of happy arguments around \u2018Where did this form in the disk of its home star, and what does that tell us about the conditions that were like in that protoplanetary disk,\u2019\u201d Bannister added.<\/p>\n

Still, who knows? \u201cThese are representative fragments of star formation elsewhere. There\u2019s no reason that every protoplanetary disk has the same chemical distribution,\u201d Meech said.<\/p>\n

Every snapshot researchers get from now until 3I\/ATLAS\u2019s departure will help them put together a holistic, time series picture of the comet as it heats up and evolves. No one even knows whether it will survive its closest approach to the Sun in October.<\/p>\n

All eyes, and telescopes, will be trained on its predicted point of emergence in late November.<\/p>\n

Time Enough for Everyone<\/strong><\/p>\n

The biggest advantage that scientists have with 3I\/ATLAS that they did not have with 1I\/\u2019Oumuamua is time\u2014time not only to make more observations and analyses but to enable the widest participation possible.<\/p>\n

\u2018Oumuamua arrived in October, the middle of the academic semester. Scientists who could respond quickly tended to be senior-level researchers, those with fewer teaching responsibilities, and those at institutions with easier access to telescope facilities, Kareta explained. Early-career scientists, those involved with research programs, or those who had inflexible responsibilities were less able to contribute to the groundbreaking discovery in the two-ish weeks before the object disappeared.<\/p>\n

\n

\u201cThe longer we have to study it, that means more people can work on it, more brains can take a crack at the problem and\u2026leave their mark on this object.\u201d<\/p>\n<\/blockquote>\n

With 2I\/Borisov and now with 3I\/ATLAS, a monthslong observation window has enabled a larger, more diverse group of scientists from around the world to participate in observing, analyzing, and discussing this discovery.<\/p>\n

\u201cThe longer we have to study it, that means more people can work on it, more brains can take a crack at the problem and\u2026leave their mark on this object,\u201d Kareta said.<\/p>\n

And that can be only a positive thing for this nascent, but growing, field of science.<\/p>\n

\u201cWe\u2019re 7 years into this field of small-body galactic studies,\u201d Bannister said. \u201cThere\u2019s a whole different generation of people coming into this than were involved in 1I and even 2I. That\u2019s really exciting to see.\u201d<\/p>\n

\u2014Kimberly M. S. Cartier (@astrokimcartier.bsky.social<\/a>), Staff Writer<\/p>\n

Citation:<\/strong>\u00a0Cartier, K. M. S. (2025), How an interstellar interloper spurred astronomers into action,\u00a0Eos, 106, https:\/\/doi.org\/10.1029\/2025EO250329<\/a>. Published on 9 September 2025.<\/p>\n

Text \u00a9 2025. The authors.\u00a0CC BY-NC-ND 3.0<\/a>
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.<\/p>\n

\n\tRelated<\/p>\n","protected":false},"excerpt":{"rendered":"On 1 July 2025, astronomers detected a visitor from the deep reaches of space. At the time of…\n","protected":false},"author":2,"featured_media":54890,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[270],"tags":[582,8111,18,19,17,39902,39903,583,133,451,39904,1240,29902,39905,39906],"class_list":{"0":"post-54889","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-space","8":"tag-astronomy","9":"tag-comets","10":"tag-eire","11":"tag-ie","12":"tag-ireland","13":"tag-modeling","14":"tag-planetary-evolution","15":"tag-planets","16":"tag-science","17":"tag-space","18":"tag-space-planets","19":"tag-stars","20":"tag-telescopes","21":"tag-transdisciplinary-science","22":"tag-unsolved-mysteries"},"share_on_mastodon":{"url":"","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/54889","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/comments?post=54889"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/54889\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media\/54890"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media?parent=54889"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/categories?post=54889"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/tags?post=54889"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}