WASHINGTON (Reuters) - The reddish cigar-shaped object called ‘Oumuamua spotted last year tumbling through space is a comet, scientists said on Wednesday, solving the mystery over how to classify the first interstellar object found passing through our solar system.

This artist’s impression shows the first interstellar asteroid, `Oumuamua as it passes through the solar system after its discovery in October 2017. European Southern Obervatory/M. Kornmesser/Handout via REUTERS/Files

Astronomers said they closely examined the trajectory of ‘Oumuamua, which measures about a half-mile (800 meters) long, as it speeds through our cosmic neighborhood after being evicted somehow from a distant star system.

They found that it is deviating slightly from a path that would be explained purely by the Sun’s gravitational pull because of what apparently is a very small emission of gas from its surface, indicative of a comet.

‘Oumuamua (pronounced oh-MOO-uh-MOO-uh) initially was pegged as a comet, but it lacks the tail of gas and dust characteristic of many comets, and some scientists argued that it was perhaps a dry asteroid.

“It does not display any tail in any observation we obtained,” said astronomer Marco Micheli of the European Space Agency’s SSA-NEO Coordination Centre in Italy, who led the study, published in the journal Nature.

“However, our analysis shows that the amount of emitted gas that is needed to generate this extra force we see would have been so small as to be invisible in our observations,” he said in an email.

This “extra force” acting on the object’s trajectory amounts to only about 0.1 percent of the Sun’s gravitational attraction.

‘Oumuamua was first detected last October by the University of Hawaii’s Pan-STARRS1 telescope. Its name refers in the native Hawaiian language to a messenger arriving from a great distance.

It previously slingshot past the Sun traveling at roughly 196,000 miles per hour (315,000 km per hour) and is heading out of the solar system in the direction of the constellation Pegasus. ‘Oumuamua as of last month was roughly the same distance from the Sun as Jupiter.

Astronomers suspect that more visitors from other star systems will be discovered passing through our solar system.

“The discovery of ‘Oumuamua is an absolute first in the field, and it provided our first opportunity to study an object coming from another star and planetary system,” Micheli said. “The existence of these objects was expected, but seeing one for the first time, and being able to study it in detail, is a unique chance to know more on these distant systems, and how they formed.” </s> Astronomers around the world were positively tickled last year when we detected our first interstellar object inside the solar system. The object was named ‘Oumuamua, a term of Hawaiian origin meaning “a messenger from afar arriving first.” Telescopes around the world turned to watch as our visitor rocketed off into oblivion, and scientists eventually decided it was an asteroid. However, some new data calls that assessment into question. ‘Oumuamua may have been a comet after all.

The scientific community has long expected an interstellar visitor to show up, and ‘Oumuamua was undeniably from another star. It shot past us with such haste there was no way it could have started in our solar system — even a gravity boost from Jupiter wouldn’t have given a local object matching speed and trajectory.

So, ‘Oumuamua’s appearance wasn’t a shock, but the 800-meter cigar-shaped object still wasn’t exactly what we expected. Scientists believed the first interstellar object in our solar system would be a comet. If other solar systems are anything like ours, there should be a cloud of comets at the very edge. It wouldn’t take much for these objects to break away and sail through interstellar space. However, ‘Oumuamua looked more like an asteroid than a comet.

The hallmark of a comet is the way the icy body heats up as it passes close to the sun, leading to the formation of a “coma.” That’s why comets have tails and asteroids don’t. ‘Oumuamua didn’t have a visible tail. Researchers from the University of Hawaii Institute for Astronomy (where ‘Oumuamua was discovered) have kept watch on the object using the Hubble Space Telescope, and the latest data suggests something other than gravity has affected its path.

Astronomers have attempted to determine if the solar wind or radiation could have tweaked ‘Oumuamua’s trajectory using computer models, but nothing fit with the observations. The best explanation was outgassing. The process that produced a comet’s coma as it heats up. The release of gas can actually nudge the orbit. If that’s what caused the change to ‘Oumuamua’s orbit, it would have to be a comet.

There are still a lot of unanswered questions. We didn’t see a coma, so maybe a journey through interstellar space alters comets in some way. Or perhaps ‘Oumuamua is an asteroid, and there’s some mechanism at work that we’ve never seen before. We might never know — ‘Oumuamua is leaving, and it isn’t coming back. </s> Remember that cigar-shaped interstellar object that whizzed through our Solar System last year? It was pretty weird, right? Well, new research shows ‘Oumuamua is even stranger than we realized.



‘Oumuamua, pronounced “oh-MOO-ah-MOO-ah,” is a comet and not an asteroid, according to research published yesterday in Nature. That’s not a huge revelation, as many scientists had already assumed as much. What’s special about this new paper, however, is that it offers tangible evidence to bolster the case.

Seems like a fine point, but there’s a big difference between asteroids and comets. Both types of objects are leftovers from the formation of the Solar System, but where asteroids are composed of metals and rocky material, comets are made from ice, dust, and rocks. Typically, comets have elongated orbits that take them to the outer reaches of the Solar System, but as they venture inwards, the Sun’s rays cause gas and dust to shear off, producing a glowing cloud of material called a coma and a visible tail.

In the case of ‘Oumuamua, the dark, 2,620-foot-long object was detected on October 19, 2017 using Hawaii’s Haleakala Observatory, and scientists have been tracking it ever since. ‘Oumuamua came to within 20.5 million miles (33 million km) of Earth before heading back toward interstellar space—and it appears to be in a hurry. By combining data collected from the NASA/ESA Hubble Space Telescope, the Canada-France-Hawaii Telescope, ESO’s Very Large Telescope, and the Gemini South Telescope, a team led by Marco Micheli from the European Space Agency noticed something odd about ‘Oumuamua: It’s moving faster than expected.

The extra speed isn’t ludicrous by any means, but it’s still measurable. ‘Oumuamua is still slowing down thanks to the gravitational influence of our Sun, but not at the rate expected by celestial mechanics. The reason, say the authors of the new study, is that ‘Oumuamua is still venting material from its surface. Solar heating is producing an effect called outgassing, and the material ejected from the object’s surface is creating a tiny amount of thrust. It’s like a built-in propulsion system, but one that only becomes active inside the warm, cozy realms of a star system.



To make sure the acceleration effect was not being caused by something else, the researchers considered scenarios like solar wind, a collision with another object, its mass being different than calculated, and other known or suspected astrophysical phenomena. However, “these explanations are all either physically unrealistic or insufficient to explain the observed behavior,” write the authors in the study.

“Also, the unlikely theory that ‘Oumuamua is an interstellar spaceship was rejected: the smooth and continuous change in speed is not typical for thrusters and the object is tumbling on all three axes, speaking against it being an artificial object,” according to Hubble press release. As a related aside, research from late last year came to the same conclusion.



The suspected presence of outgassing was the smoking gun needed to prove that ‘Oumuamua is a comet and not an asteroid.

“We think this is a tiny, weird comet,” said Micheli in a press release. “We can see in the data that its boost is getting smaller the farther away it travels from the Sun, which is typical for comets.”

Now, you’re probably thinking, “What the hell, Dvorsky, a minute ago you said comets produce a visible coma and tail when they get close to the Sun! But ‘Oumuamua doesn’t exhibit any of this!” Fair point, but there is a good reason for this, one demonstrating how freakin’ weird this object really is.

‘Oumuamua, the researchers speculate, is venting unusually large, coarse dust grains. Micheli’s team is theorizing that small dust grains, which that typically litter the surface of comets, eroded during the course of ‘Oumuamua’s epic journey through interstellar space (we have no idea how old this object is, so who knows how long it’s been careening through the Milky Way, which formed 13.5 billion years ago). All that’s left on this comet are the larger dust grains. If ‘Oumuamua is producing a cloud composed of these large particles, it would be too dim for Hubble to see it. But the unexpected deviation in its acceleration suggests these grains are very much there, and that ‘Oumuamua is, or was, in an outgassing phase during its brief time in our Solar System.

Sadly, this new result means it’s going to be exceptionally tough for astronomers to figure out where in the galaxy this object came from. If it had been an asteroid with a boring and predictable speed, scientists should have been able to backtrack its trajectory to its star system of origin. But with its variable speed, that’ll now be a physics task of herculean proportions, and probably something best suited for a future supercomputer.

It came, we saw, it’s quickly leaving. But we’re still learning some amazing things about this messenger from afar. </s> An interstellar asteroid that drifted past our sun recently has been confirmed to have originated from another solar system.

Our solar system has many visiting chunks of space debris passing through, but we have never found one that has come from another solar system – until now.

A team of astronomers has identified one such cosmic traveller, dubbed 1I/2017 or ‘Oumuamua (the Hawaiian word for scout).

According to The Guardian, the object was first spotted travelling past the sun last month.

At first glance, it looked very similar to the comets and asteroids seen in our own solar system. However, unlike this space debris, ‘Oumuamua’s orbit was calculated as being impossible to achieve by one that originated in our own system and could be one of as many as 10,000 that are nearby.

The object is believed to be an incredibly dark red colour, with 96pc of all light that hits it being absorbed.

The appearance of red means that it contains organic, carbon-based molecules. This could add even greater credence to the theory of transpermia, whereby comets and asteroids containing organic molecules could have collided with Earth and ‘seeded’ life here.

Findings on ‘Oumuamua have been published by two sets of researchers from the University of Hawaii and UCLA, respectively.

The team from Hawaii calculated that ‘Oumuamua is just 400 metres long with a rotation once every 7.3 hours.

The UCLA team estimated that the other 10,000 or so objects similar to the asteroid could be located closer to our sun than Neptune, with three objects arriving and three leaving our solar system on a daily basis.

By better understanding how ‘Oumuamua and other objects like it enter our solar system, we can learn more about how planets formed in their native star system. </s> The first known interstellar visitor to our Solar System, 'Oumuamua, which buzzed past the Sun last September, has proven evasive to define. First it was a comet. Then it was an asteroid. Then it was maybe both.

Now a new team of researchers led by the European Space Agency has delivered their verdict: 'Oumuamua, according to their analysis, is probably a comet after all.

If you have whiplash, you're not alone - but on the other hand, its interstellar origins notwithstanding, 'Oumuamua is unlike any object we've ever seen before.

It was first spotted on October 19 last year, 40 days after it had already made its closest approach to the Sun, and it immediately got scientists abuzz. Its velocity indicated that it had come from somewhere far outside our Solar System - and that it had been travelling for hundreds of millions of years.

It was also an unusual shape - up to 400 metres (0.25 miles) long, and distinctly cigar-shaped. It could be up to 10 times as long as it is wide - which was never before seen in an asteroid or comet.

Figuring out whether it's an asteroid or a comet, however, has proven extraordinarily tricky. At first, based on preliminary observations, astronomers thought it was a comet. But comets contain ice, the sublimation of which creates the tail as they zoom through space.

'Oumuamua showed none of the characteristics associated with comets. It was reddish in colour, and showed no signs of dust around it - indicating that it was composed of dense rock and metal, reddened by cosmic radiation, and contained no water or ice.

In December, a team of researchers announced that 'Oumuamua's organic-rich crust could conceal a comet-like icy core - concluding that the object is a planetesimal with a well-baked crust (it sounds like a delicious pie now).

But, according to ESA astronomer Marco Micheli and colleagues, there's one more aspect that seriously seems to indicate comet, and it hadn't yet been factored in.

The international team analysed both ground- and space-based observations of 'Oumuamua as it traversed our Solar System, and they found something strange. Its arc could not solely be explained by the effect of gravity exerted by the Sun or other objects. Which means it seems to be behaving… like a comet.

"The motion of all celestial bodies is governed mostly by gravity, but the trajectories of comets can also be affected by non-gravitational forces due to cometary outgassing," the researchers wrote in their paper.

They detected non-gravitational acceleration, mainly directed away from the Sun, in 'Oumuamua's trajectory. This may not have been caused by cometary outgassing, but it is consistent with the behaviour of comets.

Just to be sure, the team carefully examined other potential causes, including things like solar radiation pressure, various external forces, and interaction with solar wind. They even accounted for "geometric effects" which could happen if 'Oumuamua wasn't one solid object, but several chunks flying together.

After all that, they concluded "comet-like outgassing to be a physically viable explanation, provided that 'Oumuamua has thermal properties similar to comets."

As for the lack of dust cited as a reason for 'Oumuamua's asteroid designation, the team noted that this could be explained by an atypical dust-grain size distribution, a low dust-to-ice ratio, or changes to the object's surface sustained over its long journey from its mysterious origin point.

If it is a comet, that would have an impact on 'Oumuamua's hypothesised origins. A study earlier this year found that its most likely starting point was a binary star system, since that would be the most likely to eject an asteroid, as opposed to a comet, which apparently the Solar System flings about into interstellar space willy-nilly.

It may actually be impossible to tell whether 'Oumuamua is a comet or an asteroid based on our current observations. However, it's moving away from us at speed, and we've probably missed the boat to send a probe to study it in situ.

But, if there's a next time - another interstellar visitor in the future - our understanding could benefit greatly from knowing about it ahead of time, and having the infrastructure in place so that we could intercept it with a probe.

Whether such a visitor is similar to 'Oumuamua or vastly different, these observations could help us understand the physical properties of interstellar objects - and how much of 'Oumuamua's uniqueness is because of its long, lonely and possibly violent journey through the vastness of space.

So who votes for hedging our bets and calling it a cometsteroid?

The team's research has been published in the journal Nature. </s> The traveler, which was given the name `Oumuamua, Hawaiian for "messenger from afar," was first discovered in 2017 by researchers with the Panoramic Survey Telescope Rapid Response Systems (Pan-STARRS), located on Maui. From the moment researchers spotted the oddly shaped object, they weren't exactly sure how to classify it: first it was a comet, then an asteroid, before astronomers deemed it simply an interstellar object.

But now, thanks to the hard work of researchers led by the European Space Agency, `Oumuamua is back to being considered a comet, since it's not solely being guided by the sun's gravity as a planet or asteroid would be, according author Marco Micheli, the lead author on the study.

​"Unexpectedly, we found that `Oumuamua was not slowing down as much as it should have due to just gravitational forces," Micheli told USA Today. "We think this is a tiny, weird comet… we can see in the data that its boost is getting smaller the farther away it travels from the sun, which is typical for comets."

"It's definitely an exciting discovery," he added.

According to Micheli, after analyzing `Oumuamua's trajectory, researchers determined that the 800-meter-long object wasn't solely being pushed on its journey by a gravitational pull of the sun, planets and any other solar system objects.

By slapping the comet label on the mysterious object, researchers are better able to explain `Oumuamua's non-gravitational acceleration, since comets are propelled by outgassing, Space.com reported.

Though `Oumuamua isn't your typical comet, as it lacks a coma — the cloud of gas and dust that envelops around the nucleus of the comet — the mystery remaining behind the object now is its origin. </s> On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar asteroid, named 1I/2017 U1 (AKA 'Oumuamua).

In the months that followed, multiple follow-up observations were conducted that allowed astronomers to get a better idea of its size and shape, while also revealing that it had the characteristics of both a comet and an asteroid.

Interestingly enough, there has also been some speculation that based on its shape, 'Oumuamua might actually be an interstellar spacecraft (Breakthrough Listen even monitored it for signs of radio signals!).

A new study by a pair of astronomers from the Harvard Smithsonian Center for Astrophysics (CfA) has taken it a step further, suggesting that 'Oumuamua may actually be a light sail of extra-terrestrial origin.

The study – "Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration?", which recently appeared online – was conducted by Shmuel Bialy and Prof. Abraham Loeb. Whereas Bialy is a postdoctoral researcher at the CfA's Institute for Theory and Computation (ITC), Prof. Loeb is the director of the ITC, the Frank B. Baird Jr. Professor of Science at Harvard University, and the head chair of the Breakthrough Starshot Advisory Committee.

To recap, 'Oumuamua was first spotted by the Pan-STARRS-1 survey 40 days after it made its closest pass to the Sun (on September 9th, 2017).

At this point, it was about 0.25 AU from the Sun (one-quarter the distance between Earth and the Sun), and already on its way out of the Solar System. In that time, astronomers noted that it appeared to have a high density (indicative of a rocky and metallic composition) and that it was spinning rapidly.

While it did not show any signs of outgassing as it passed close to our Sun (which would have indicated that it was a comet), a research team was able to obtain spectra that indicated that 'Oumuamua was more icy than previously thought.

Then, as it began to leave the Solar System, the Hubble Space Telescope snapped some final images of 'Oumuamua that revealed some unexpected behavior.

After examining the images, another international research team discovered that 'Oumuamua had increased in velocity, rather than slowing down as expected. The most likely explanation, they claimed, was that 'Oumuamua was venting material from its surface due to solar heating (AKA outgassing).

The release of this material, which is consistent with how a comet behaves, would give 'Oumuamua the steady push it needed to achieve this boost in velocity.

To this, Bialy and Loeb offer a counter-explanation. If 'Oumuamua were in fact a comet, why then did it not experience outgassing when it was closest to our Sun?

In addition, they cite other research that showed that if outgassing were responsible for the acceleration, it would have also caused a rapid evolution in 'Oumuamua's spin (which was not observed).

Basically, Bialy and Loeb consider the possibility that 'Oumuamua could in fact be a light sail, a form of spacecraft that relies on radiation pressure to generate propulsion – similar to what Breakthrough Starshot is working on. Similar to what is planned for Starshot, this light sail may been sent from another civilization to study our Solar System and look for signs of life. As Prof. Loeb explained to Universe Today via email:

"We explain the excess acceleration of `Oumuamua away from the Sun as the result of the force that the Sunlight exerts on its surface. For this force to explain measured excess acceleration, the object needs to be extremely thin, of order a fraction of a millimeter in thickness but tens of meters in size. This makes the object lightweight for its surface area and allows it to act as a light-sail. Its origin could be either natural (in the interstellar medium or proto-planetary disks) or artificial (as a probe sent for a reconnaissance mission into the inner region of the Solar System)."

Based on this, Bialy and Loeb went about calculating the likely shape, thickness, and mass-to-area ratio that such an artificial object would have. They also attempted to determine whether this object would be able to survive in interstellar space, and whether or not it would be able to withstand the tensile stresses caused by rotation and tidal forces.

What they found was that a sail that was only a fraction of a millimeter thick (0.3-0.9 mm) would be sufficient for a sheet of solid material to survive the journey through the entire galaxy – though this depends greatly on 'Oumuamuam's mass density (which is not well-contrained).

Thick or thin, this sail would be able to withstand collisions with dust-grains and gas that permeate the interstellar medium, as well as centrifugal and tidal forces.

As for what an extra-terrestrial light sail would be doing in our Solar System, Bialy and Loeb offer some possible explanations for that. First, they suggest that the probe may actually be a defunct sail floating under the influence of gravity and stellar radiation, similar to debris from ship wrecks floating in the ocean. This would help explain why Breakthrough Listen found no evidence of radio transmissions.

Loeb further illustrated this idea in a recent article he penned forScientific American, where he suggested that 'Oumuamua could be the first known case of an artificial relic which floated into our Solar System from interstellar space.

What's more, he notes that lightsails with similar dimensions have been designed and constructed by humans, including the Japanese-designed IKAROS project and the Starshot Initiative with which he is involved.

"This opportunity establishes a potential foundation for a new frontier of space archaeology, namely the study of relics from past civilizations in space," Loeb wrote.

"Finding evidence for space junk of artificial origin would provide an affirmative answer to the age-old question 'Are we alone?'. This would have a dramatic impact on our culture and add a new cosmic perspective to the significance of human activity."

On the other hand, as Loeb told Universe Today, 'Oumuamua could be an active piece of alien technology that came to explore our Solar System, the same way we hope to explore Alpha Centauri using Starshot and similar technologies:

"The alternative is to imagine that `Oumuamua was on a reconnaissance mission. The reason I contemplate the reconnaissance possibility is that the assumption that `Oumumua followed a random orbit requires the production of ~10^{15} such objects per star in our galaxy. This abundance is up to a hundred million times more than expected from the Solar System, based on a calculation that we did back in 2009. A surprisingly high overabundance, unless `Oumuamua is a targeted probe on a reconnaissance mission and not a member of a random population of objects."

According to Loeb, that there's also the fact that 'Oumuamua's orbit brought it to within 0.25 AU of the Sun, which is a good orbit for intercepting Earth without experiencing too much solar irradiation. In addition, it came to within 0.15 AU of Earth, which could have been the result of orbital corrections designed to facilitate a flyby.

Alternately, he states that it is possible that hundreds of such probes could be sent so that one of them got close enough to Earth to study it. The fact that the Pan STARRS-1 survey barely detected 'Oumuamua at its closest approach could be seen as an indication that there are many other such objects that were not detected, bolstering the case for 'Oumuamua being one of many such probes.

Considering that astronomers recently concluded that our Solar System has likely captured thousands of interstellar objects like 'Oumuamua, this opens the possibility for future detections which could help prove (or disprove) the case for an interstellar light sail.

Naturally, Bialy and Loeb acknowledge that are still too many unknowns to say with any certainty what 'Oumuamua really is. And even if it does happen to be a piece of natural rock, all other asteroids and comets that have previously been detected have had mass-to-area ratios orders of magnitude larger than the current estimates for 'Oumuamua.

That, and the fact that radiation pressure appears to be capable of accelerating it, would mean that 'Oumuamua represents a new class of thin interstellar material that has never before been seen. If true, that opens up a whole new set of mysteries, such as how such material was produced and by what (or whom).

While it has been beyond the reach of our telescopes for almost a year now, 'Oumuamua is sure to remain the subject of intense study for many years to come. And you can bet astronomers will be on the lookout for more of them! After all, "the Ramans do everything in threes", right?

This article was originally published by Universe Today. Read the original article. </s> Asteroid ‘Oumuamua was a cigar-shaped asteroid so unusual that some astronomers suggested it was built by an alien civilisation.

Now an international group of scientists have released the results of a new investigation of the strange object, which is zooming out of the solar system at 114,000 kilometres per hour.

It is the first space rock discovered in our solar system that appears to have originated from another part of the galaxy

‘Ouamuamua was spotted last year and later scanned for radio signals to make sure it was not an extraterrestrial probe.

Although the results of this probe proved it was natural in origin, astronomers have argued about whether it was an asteroid or a comet ever since.

MORE: How do you pronounce ‘Oumuamua and what does it mean?

Telescopes first spotted the mysterious red-tinged object last October as it zipped through the inner solar system.

Neither a coma nor tail was spotted behind our first confirmed interstellar guest, which are the hallmarks of an icy comet.

Now the Hubble Space Telescope has been used to examine the object in great detail.

Italian astronomer Marco Micheli said new observations show ‘Oumuamua being propelled through space by gasses shooting out from behind it, which is a process called ‘outgassing’ that’s common in comets.

The release of what’s believed to be gaseous carbon monoxide, carbon dioxide and water applied only a tiny force on the object (about 1,000 times smaller than the effect of the sun’s gravity), the researchers said.

The team’s measurements ‘were so precise that we could actually see the change in position caused by the outgassing,’ said co-author Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies at Jet Propulsion Laboratory in Pasadena, California.

‘It’s a definitely exciting discovery,’ said Micheli of the European Space Agency.

Micheli said computer models suggest objects typically are ejected during the formation of planetary systems, and that most of these castaways should be comets given their location on the frigid outskirts of their systems. Only a tiny fraction should be asteroids, by scientists’ best calculations.

Had it been an asteroid, it would have been ‘extremely lucky to beat these odds’ – or it would have underscored scientists’ misunderstanding of the early solar system, Micheli said.

Discovered by a telescope in Hawaii, Oumuamua is a Hawaiian word which means messenger from afar, or scout.

Now it’s long gone and our chances of knowing exactly what it was have disappeared with it.

The University of Toronto’s Alan Jackson, who reported in March that Oumuamua likely came from a two-star system, remains unconvinced of its true identity.

‘But this is certainly an interesting new piece of information for us to chew on,’ he said in an email.

Astronomers from the University of Hawaii spotted ‘Oumuamua – named after the Hawaiian term for ‘scout’ or ‘messenger’ – in October passing the Earth at about 85 times the distance to the moon.

It is the first object discovered in the solar system that appears to have originated from another part of the galaxy. Although thought to be an asteroid, ‘Oumuamua’s elongated cigar shape hundreds of metres in length but only one-tenth as wide is highly unusual for a typical space rock.

‘We think this is a tiny, weird comet,” said Marco Micheli from the European Space Agency.

‘We can see in the data that its boost is getting smaller the farther away it travels from the Sun, which is typical for comets.’ </s> An artist's illustration of the interstellar object 'Oumuamua' (ESA/Hubble, NASA, ESO, M. Kornmesser)

CAPE CANAVERAL, Fla. (AP) - Our first known visitor from another star system has now been identified as a comet.

A European-led team makes the case in Wednesday's edition of the journal Nature.

Telescopes first spotted the mysterious cigar-shaped object last October as it zipped through the inner solar system. Since then, astronomers have flip-flopped between comet and asteroid.

Neither a coma nor tail was spotted, hallmarks of an icy comet. But Italian astronomer Marco Micheli (Mee-KAY-lee) and his team report that the object's path and acceleration are best explained not just by gravity, but also gases shedding from a comet.

It's long gone, as are the chances of knowing conclusively what it was.
The first known interstellar object to pass through the Solar System, ʻOumuamua, has been identified as a very inactive comet and not an asteroid, as previously thought.