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7 Big Mysteries about Interstellar Object 3I/ATLAS
7 Big Mysteries about Interstellar Object 3I/ATLAS

Scientific American

time17-07-2025

  • Science
  • Scientific American

7 Big Mysteries about Interstellar Object 3I/ATLAS

Earlier this month astronomers were thrilled to discover only the third known interstellar object ever seen in our solar system. Now dubbed 3I/ATLAS, the suspected comet has just zoomed past the orbit of Jupiter, traveling so fast that it's bound to slip through our sun's gravitational grip. The high speed and hyperbolic trajectory of 3I/ATLAS means it must have come from another star and was cast adrift in the Milky Way by some unknown process before it eventually, by chance, briefly swooped by our sun. It will reach about the orbit of Mars before it boomerangs back toward interstellar space, never to be seen again, at the end of this year. That's why astronomers have been racing to study 3I/ATLAS since July 1, when Larry Denneau of the University of Hawaii first spied it using a telescope in Chile that's part of the globe-spanning Asteroid Terrestrial-Impact Last Alert System (ATLAS). Soon more powerful observatories, including the James Webb Space Telescope (JWST) and Hubble Space Telescope, will scrutinize the object—which, thanks to its alien, interstellar provenance may be the oldest comet anyone has ever seen. 'I didn't get any sleep for like 35 hours,' says Bryce Bolin of Eureka Scientific in California, who rushed to release a preprint paper and arrange additional observations following 3I/ATLAS's discovery. 'It ruined my weekend.' On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Stefanie Milam of NASA's Goddard Space Flight Center is part of a group that had reserved time on JWST to observe an interstellar object—if the researchers were fortunate enough for one to be discovered. But the group's luck was tested when it couldn't reach the lead of its program—Martin Cordiner, also at Goddard—to kick the observations into action. 'He was hiking in Maine when the object was discovered, and we could not reach him—he was completely off the grid,' Milam says. 'When he finally got back, his phone just blew up. I said, 'You're never allowed to go on vacation again!'' So why exactly are astronomers so eager to observe this object, and what do they hope to learn? Where did 3I/ATLAS come from? The first major question to answer about 3I/ATLAS is its origin. Tracing it back to an individual star is likely impossible, given the mixing of myriad stars in their orbits around our galaxy across billions of years. But we might be able to work out roughly the region it came from. One team of astronomers has already begun doing just that, using the high velocity of the object with respect to our sun—60 kilometers (37 miles) a second—to argue that it might have come from the vicinity of our galaxy's thick disk. This is a puffy torus of older stars moving at high velocities above and below the main flat plane of the Milky Way—which is where our sun serenely orbits. A thick-disk origin might mean that 3I/ATLAS is extremely ancient, more than eight billion years old. 'It's from a star that's potentially not even there anymore,' says Michele Bannister of the University of Canterbury in New Zealand, a co-author on the work. Aster Taylor of the University of Michigan performed a different age analysis based on the trajectory of 3I/ATLAS and suggests the object is 11 billion to three billion years old. 'We get similar answers,' Taylor says. Such estimates might soon be revised if subsequent observations can show just how much space weathering the object has endured during its interstellar sojourn. How big is it? Currently, 3I/ATLAS is inside the orbit of Jupiter and approaching the orbit of Mars, which it will cross in October, passing about 0.2 astronomical unit (one fifth the Earth-sun distance) from the Red Planet. Although early observations have led astronomers to categorize 3I/ATLAS as a comet, at the moment, it's not behaving exactly like one. The object doesn't display a large tail or enveloping coma of cast-off gas, only a hint of dust—but that is expected to change soon. As it traverses the asteroid belt between Mars and Jupiter and basks in the sun's radiance, its surface should warm enough to sublimate ice, venting sufficient material to form a large coma and perhaps a prominent tail. A substantial coma would be like a curtain drawn over astronomers' eyes, obscuring their view of the object and complicating efforts to gauge its dimensions. Before that happens, a team led by David Jewitt at the University of California, Los Angeles, is hoping to pin down its size with Hubble in August. (Other telescopes might be able to determine the size of 3I/ATLAS, too.) Initial estimates suggested 3I/ATLAS might be up 20 kilometers (12 miles) across—very big for a comet—but most astronomers now think it is much smaller. 'It's probably somewhere in the range of one or two kilometers,' says John Noonan at Auburn University in Alabama. That would be somewhat comparable in size to our first two interstellar visitors: 1I/ʻOumuamua, which was discovered in 2017 and was up to about 400 meters (0.25 mile) long, and 2I/Borisov, which was found in 2019 and was about one kilometer (0.6 mile) wide. If 3I/ATLAS turns out to be much bigger, 10 kilometers (six miles) or more, this would pose problems for preexisting estimates of many big interstellar objects reside in the galaxy. 'It's statistically extremely unlikely we should ever see something that size,' Noonan says. 'Theorists don't like that. But as an observer, I would love to see a really weird, big object.' How fast is it spinning? As well as its size, one of the key properties astronomers want to know about 3I/ATLAS is its rotation rate—something they might discern by watching the object's changing brightness as it spins. The spin of 3I/ATLAS could carry clues as to how the object was ejected from its home star in the first place. 'Certain ways of kicking these objects out tend to make them spin up,' Taylor says. A close pass of a gas giant planet, for instance, could easily set the object twirling while hurling it away from its home star. Conversely, a slow rotation period would suggest the object experienced a more gentle ejection. 'You could do this when stars die,' Taylor says. 'They lose a lot of mass, and so the gravitational force on objects at the outer edge of their system goes away. Those objects become unbound and just flow out into the galaxy.' The rotation period can also tell us more about the shape of 3I/ATLAS—a steady rotation suggests a fairly spherical form, whereas a fluctuating rotation speed might suggest a 'wonky shape,' Taylor says, like that of 'Oumuamua, which was estimated to be cigar- or pancake-shaped. What is 3I/ATLAS made of? If 3I/ATLAS really is an ancient cometary castaway that has been drifting through the galaxy for eons, it might be full of ice that has never been heated by a star. If so, then as it gets closer, the object might suddenly erupt into activity. While that could be bad news for measuring its size, it would aid efforts to determine 3I/ATLAS's chemical composition. JWST and Hubble would be best suited for the task of picking apart the different species of molecules that might erupt from 3I/ATLAS. Unfortunately, however, in October, when the object will be at its warmest, closest point to our star (called perihelion), Earth will be on the other side of the sun. This will make observations from our planet almost impossible. In November, post-perihelion, Noonan will use Hubble to study 3I/ATLAS and its emissions, looking for signs of substances such as hydroxide and hydrogen that can help clarify its composition. If the object is several billion years old, as predicted, then it might be rich in water because of the suspected formation environment around older stars. 'You would expect a lot of hydrogen coming from these water-rich irradiated objects, if this is really as old as [thought],' Noonan says. Milam and her colleagues, meanwhile, will use JWST in August and December to observe 3I/ATLAS before and after perihelion. Thanks to its keen infrared vision, JWST is better suited for teasing out the presence of molecules such as water, carbon monoxide, carbon dioxide and ammonia. 'We can really home in and see what this thing looks like,' she says. 'Borisov had a pretty boring chemistry, but it wasn't like any object in our solar system—there was hardly any water at all but a lot of carbon monoxide and hydrogen cyanide. With JWST, we're hoping to see a lot of carbon dioxide [on 3I/ATLAS], maybe even water, if it's as pristine as people are projecting.' Although the overall view from Earth degrades as the object approaches perihelion, some telescopes will be less visually impaired. Those operated by the Lowell Observatory in Arizona, for instance, are primed to observe 3I/ATLAS at dawn and dusk, when the sun is below the horizon. This will allow for studies even when the object will be close to our star from our planet-bound perspective. 'The Lowell Discovery Telescope is really well suited to observations close to the horizon,' says Nick Moskowitz, an astronomer at Lowell Observatory. 'We will be able to track it closer in to perihelion than other facilities.' An unlikely additional capability will be at Mars, where spacecraft such as NASA's Mars Atmosphere and Volatile Evolution (MAVEN) orbiter may be able to see 3I/ATLAS as it passes about 30 million kilometers (19 million miles) from the planet. 'It'll be pretty large and apparent in the sky,' Noonan says, providing the object kicks into activity as hoped. 'They'll be able to see the coma,' giving us an insight into 3I/ATLAS's activity near the sun that would otherwise be impossible to see from Earth. Will it survive? A big unknown about 3I/ATLAS is whether it will actually survive its close encounter with our sun. While 'Oumuamua did so, Comet Borisov was not so fortunate, with the object appearing to split and break apart on its way out of our solar system. The same fate could befall 3I/ATLAS. 'Borisov fragmented, which is pretty usual for comets,' Bannister says. All eyes will be on our latest visitor to see if the same thing happens again. An additional quirk of 3I/ATLAS's survivability is the impact of solar wind, which may snip away any cometary tail as it is ejected. By chance, the object is entering our solar system at quite a shallow angle, much flatter than that of most comets, which means it will experience stronger solar headwinds. Sarah Watson of the University of Reading in England and her colleagues are using this quirk to study how the solar wind traverses into the outer solar system. 'We can potentially calculate the speed of the solar wind,' she says, by noticing the impact of the solar wind on the purported comet's tail, if one materializes. Could we reach it? No spacecraft will be able to reach 3I/ATLAS. It is moving too fast and is too far from Earth for us to consider launching something in time. Yet an upcoming European Space Agency (ESA) mission called Comet Interceptor, set to launch in 2029, might attempt to visit another interstellar object, if we find one within its reach. The spacecraft will be positioned past the moon's orbit away from the sun and, if a suitable target is found, will be commanded to fire its engines and try and intercept the incoming alien object. If no suitable interstellar object is found, Comet Interceptor will instead be sent to one of several intriguing comets of our solar system. 'It is possible we could get an interstellar object, but we have to be really lucky,' says Colin Snodgrass, an astronomer at the University of Edinburgh, who is deputy lead on the mission. How many are there? One of our biggest outstanding questions about interstellar objects concerns their unknown abundance. The object 3I/ATLAS is our third interstellar visitor in eight years—a real but weak hint of how many are out there, waiting to be found. Predictions estimate there are trillions upon trillions of interstellar objects drifting around our galaxy, and perhaps one in our solar system at any given time—but they're typically just so faint that they're unlikely to be found by most telescopes. This is expected to change when a new telescope called the Vera C. Rubin Observatory begins a 10-year survey of the sky later this year. Rubin is expected to see somewhere between six and 51 interstellar objects in its 10-year survey. Seeing such a population will tell us 'how unique, or varied, planetesimal formation is across different parts of the galaxy,' Bannister says, referring to kilometer-scale objects thought to coalesce around newborn stars that become the feedstock for planets—and, when kicked to a system's hinterlands, become a reservoir of comets. One puzzling question is why we haven't seen much smaller interstellar objects, Moskowitz says. If smaller objects are more plentiful than larger objects, as scientists expect, then we should have seen some small interstellar objects entering our atmosphere, appearing as meteors streaking across Earth's skies at speeds and trajectories that clearly convey their interstellar origins. Detections of such objects have been claimed, but the evidence behind them has failed to convince most experts. The apparent absence of small interstellar interlopers 'is telling us something, but we don't know what that is yet,' Moskowitz says. 'I think that's going to be one of the major questions: Why are we seeing these big cometlike things coming through the solar system, but we're not seeing things that are smaller? It may have to do with the survivability of stuff out there in the galaxy, but we need more data.'

Here's How to Watch the Rare Total Lunar Eclipse This Week
Here's How to Watch the Rare Total Lunar Eclipse This Week

Yahoo

time12-03-2025

  • Science
  • Yahoo

Here's How to Watch the Rare Total Lunar Eclipse This Week

Originally appeared on E! Online Get ready, night owls. The first total lunar eclipse, also known as the Blood Worm Moon, will fully light up the sky soon—and fortunately, viewers can watch the phenomenon happen in real time. This year's celestial event won't be a quick one, so don't fill your schedule too much. The eclipse, which happens when the moon glows in a red-orange hue after passing by the darkest part of Earth's shadow, will start in the late hours of March 13 and reach its peak color on March 14, per NASA. More from E! Online Man Allegedly Stabs 18-Year-Old Man to Death After Finding Him In Bed With His Wife Christina Haack Celebrates Her Special 12-Year Milestone With Boyfriend Christopher Larocca Sudiksha Konanki Case: Person of Interest Identified by US Officials Amid Search for Missing Student Its totality will last for about 66 minutes, and will visibly shine across the Western Hemisphere, including North America, South America, Europe and Africa. (Hawaii and some parts of Alaska will miss the beginning of the penumbral phase—when the moon starts entering the Earth's outer shadow—but will be able to witness the rest of the event, according to Unlike the solar eclipse, which has to be viewed with special glasses to keep the eyes safe, this new celestial moment can be seen with the naked eye—or through binoculars, if viewers want a closer look. NASA recommends observing the eclipse in a dark spot away from bright lights. For those that can't watch the blood moon in-person, noted that several different livestreams will catch the event in full. These various options are necessary, considering this lunar eclipse is special. In fact, it'll mark the first time in three years since the moon glimmered in its scarce hue in 2022, and the next one won't appear again until 2026. The Blood Worm isn't the last rare occasion to grace the sky, as a new moon was pulled into the Earth's orbit last September. At the time, the phenomenon—known as an asteroid named 2024 PT5—was first spotted by NASA's Asteroid Terrestrial-Impact Last Alert System (ATLAS) initiative in early August, who calculated the floating rock's journey would last nearly two months. For the latest breaking news updates, click here to download the E! News App

Critical Mass: A cosmic close call that wasn't
Critical Mass: A cosmic close call that wasn't

New European

time12-03-2025

  • Science
  • New European

Critical Mass: A cosmic close call that wasn't

Relax. An asteroid 40-90 metres wide is almost certainly not going to hit the Earth in late 2032. Perhaps you weren't fretting about it anyway. The possibility of a planetary impact with asteroid 2024 YR4 wasn't a big worry even for those who knew about it. The chance of it hitting the Earth was always small, and even if it did, the consequences wouldn't have been catastrophic. An impact of this scale might do considerable damage locally, especially in a populated area. But such an event, were it to occur, would be predictable, so that any necessary evacuation could happen well in advance. And in any case, it would be far more likely to happen either in the oceans that cover two-thirds of the planet or in an unpopulated wild region. Such an outcome would be of considerable scientific interest, not to mention spectacular. Asteroid 2024 YR4 is one of the billions of rocky objects orbiting the Sun in the asteroid belt, a ring of debris that mostly occupies the region of space between Mars and Jupiter. Some of these objects follow orbits that can take them close to the Earth – and a few are 'Earth-crossing', meaning that their orbits intersect ours. That in itself doesn't mean they will hit the planet, however (or at least not in the foreseeable future), because an impact requires that both objects be in the same place at the same time. Tens of thousands of asteroids are known to come close to the Earth's orbit, and it's estimated that there may be around a thousand larger than 1km wide (and many more smaller ones) that are actually Earth-crossing. 2024 YR4 was first observed, as the name implies, on December 27 2024 by a telescope dedicated to such purposes, the Asteroid Terrestrial-Impact Last Alert System (Atlas) in Chile. The instrument's observations are linked up to automated warning systems including the European Space Agency's Aegis, so that anything potentially dangerous is immediately flagged up. Based on what scientists could deduce about the asteroid's orbit, the chance of an Earth impact initially looked small but not negligible; soon after its detection, this probability was estimated to be as high as 2.8%. But as the calculations have been refined using data from other telescopes, that chance fell. The probability is now estimated as 0.001% – one in 100,000. This makes it officially no longer on the risk list: it has been downgraded to zero on the Torino Impact Hazard Scale, introduced in 1999 to quantify such dangers. An asteroid 70 metres or so across is a hefty thing, but might seem minuscule compared with our planet. Yet such objects carry immense energy, and an impact would be more explosive than a thermonuclear blast. In 1908, an object – probably a stony asteroid of similar size to 2024 YR4 – is thought to have exploded 5-10km high in the atmosphere over the Tunguska region of Siberia, flattening around 800 sq miles of forest and rating eight on the Torino scale. The asteroid that is believed to have struck the Earth around 66m years ago off the coast of Mexico, causing global devastation that probably triggered or accelerated the extinction of the dinosaurs, was probably a whopping 10-15km across. Asteroid impacts of this sort are not inevitable – we might be able to deflect or even destroy them, as in the movies Deep Impact and Armageddon . The deflection of a 177-metre asteroid called Dimorphos was demonstrated in 2022 by Nasa, which sent the 600kg Double Asteroid Redirection Test (DART) spacecraft to hit the object head-on. It was a small effect, nudging Dimorphos into a slightly altered orbit around the 800-metre twin asteroid Didymos, which can come within 6m km of the Earth. 2024 YR4 is a reminder that we can't be complacent about the risks of planetary impacts. But in an age when zealots argue that a colony on Mars is an urgently needed back-up for humankind against a civilisation-ending impact, we need to keep them in proportion. An impact rating 10 on the Torino scale, 'capable of causing global climatic catastrophe that may threaten the future of civilisation as we know it', is thought to happen on average only every 100,000 years at most. The risk over the next several centuries is tiny – and by that time, who knows what we'll be able to do about such things, assuming we haven't wiped ourselves out in the meantime?

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