Giant space cigar: New observations show weird interstellar asteroid is ‘like nothing seen before’

Artist’s conception of the interstellar asteroid ‘Oumuamua. Image Credit: ESO/M. Kornmesser

A few weeks ago, something surprising happened when astronomers noticed an odd object moving quickly through the Solar System. Being on a large looping trajectory, it was first thought to be a previously unknown comet, but then calculations showed that it couldn’t have originated from within the Solar System, it must have come from somewhere else. Follow-up observations also showed that it was more like an asteroid, rather than a comet. Now, astronomers have published their most detailed findings yet, and this object, named ‘Oumuamua (Hawaiian, meaning scout or messenger coming from the past), is “like nothing seen before.”

The object was first seen on Oct. 19, 2017 by the Pan-STARRS 1 telescope in Hawaii, operated by the European Space Agency (ESO) and was then observed by multiple telescopes around the world. It had already passed closest to the Sun in its orbit and was now heading out of the Solar System again, so astronomers had to act fast to see it.

“We had to act quickly,” said team member Olivier Hainaut from ESO in Garching, Germany. “‘Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”

Combined multiple images from ESO’s Very Large Telescope and Gemini South Telescope showing ‘Oumuamua (circled). Other dots are the smeared trails of stars. Image Credit: ESO/K. Meech et al.
The light curve of ‘Oumuamua, showing how the object varied in brightness during three days in October 2017, by about a factor of ten (2.5 magnitudes), due to its very elongated shape. The object rotates every 7.3 hours. Image Credit: ESO/K. Meech et al.

Astronomers were able to measure both the object’s brightness and colour with ESO’s Very Large Telescope in Chile. By combining images from the FORS instrument on the VLT using four different filters, with those of other large telescopes, astronomers found that ‘Oumuamua varied dramatically in brightness by a factor of ten as it spun on its axis every 7.3 hours.

As Karen Meech noted, “This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”

In other words, this odd interstellar asteroid is shaped like a giant cigar, something not typically seen in our Solar System, and is estimated to be about 400 metres (1,312 feet) long. ‘Oumuamua appears to be dense, rocky or with high metal content, has little or no water or ice and a surface darkened and reddened due to the effects of irradiation from cosmic rays over millions of years.

“What a fascinating discovery this is!” said Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory, Pasadena, California. “It’s a strange visitor from a faraway star system, shaped like nothing we’ve ever seen in our own Solar System neighbourhood.”

Diagram depicting the trajectory of ‘Oumuamua through our Solar System. Image Credit: ESO/K. Meech et al.

“We are continuing to observe this unique object,” said Hainaut, “and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!”

Analysis of its orbit indicates that it most likely originated from the direction of the star Vega, traveling at around 95,000 kilometres/hour (59,030 miles/hour).

This is the first time that such an interstellar asteroid has been seen entering our Solar System, but astronomers estimate that there may be other ones about once per year or so.

“We have long suspected that these objects should exist, because during the process of planet formation a lot of material should be ejected from planetary systems. What’s most surprising is that we’ve never seen interstellar objects pass through before,” said Meech.

“We have been waiting for this day for decades,” said CNEOS Manager Paul Chodas. “It’s long been theorized that such objects exist – asteroids or comets moving around between the stars and occasionally passing through our solar system – but this is the first such detection. So far, everything indicates this is likely an interstellar object, but more data would help to confirm it.”

The discovery is reminiscent of the science fiction classic Rendezvous with Rama by Arthur C. Clarke where a huge cylindrical alien vessel enters the Solar System, initially mistaken for an asteroid. In this case, the object is probably natural based on what is known about it so far, but it is weird.

The new paper is available here (subscription/purchase).

This article was first published on Futurism.

 


What was the Solar System’s mysterious interstellar visitor last week?

Diagram depicting the trajectory of A/2017 U1 through the Solar System. Image Credit: NASA/JPL-Caltech

Last week, something unusual was detected moving through the Solar System, a small object which didn’t seem to behave like any known comets or asteroids. In fact, its behaviour suggested that it originated from outside of our Solar System. So what was this mystery interloper? While not 100 percent identified yet, it seems to be an interstellar asteroid or some similar rocky body.

A/2017 U1 was first discovered on Oct. 19 by the University of Hawaii’s Pan-STARRS 1 telescope on Haleakala, Hawaii. At first, astronomers thought it was probably a comet, but photometric analysis by telescopes showed that it lacked a coma, even as it was getting closer to the Sun. This suggested it was rocky and with little or no ice, and the observations also showed that the surface is quite red in colour, similar to some rocky objects in our own Kuiper Belt.

The object, now called A/2017 U1, was less than 400 metres (a quarter-mile) in diameter and moving remarkably quickly. It was also moving on an extreme trajectory, perpendicular to the orbits of the other planets, “above” the ecliptic. This, plus the speed, about 25.5 kilometres (15.8 miles) per second, indicated that it must have originated outside of the Solar System and was passing through when it was discovered.

“This is the most extreme orbit I have ever seen,” said Davide Farnocchia, a scientist at NASA’s Center for Near-Earth Object Studies (CNEOS) at the agency’s Jet Propulsion Laboratory in Pasadena, California. “It is going extremely fast and on such a trajectory that we can say with confidence that this object is on its way out of the Solar System and not coming back.”

According to Rob Weryk, a postdoctoral researcher at the University of Hawaii Institute for Astronomy (IfA), “Its motion could not be explained using either a normal solar system asteroid or comet orbit. This object came from outside our Solar System.”

The object crossed within Mercury’s orbit and made its closest approach to the Sun on Sept. 9. The Sun’s gravity caused it to make a “hairpin” turn, passing beneath Earth’s orbit on Oct. 19 at a distance of about 24 million kilometres (15 million miles). Now, it is leaving the Solar System again, travelling at 44 kilometres per second (27 miles per second).

Such objects were theorized to exist, moving between stars, but this would be the first that one was ever actually seen. That shouldn’t be too surprising, since there is already evidence for “rogue exoplanets,” planets which have been flung out of their solar systems and now wander through in isolation.

“We have long suspected that these objects should exist, because during the process of planet formation a lot of material should be ejected from planetary systems. What’s most surprising is that we’ve never seen interstellar objects pass through before,” said Karen Meech, an astronomer at the IfA.

“We have been waiting for this day for decades,” said CNEOS Manager Paul Chodas. “It’s long been theorized that such objects exist — asteroids or comets moving around between the stars and occasionally passing through our solar system — but this is the first such detection. So far, everything indicates this is likely an interstellar object, but more data would help to confirm it.”

Of course, the idea of a such an odd object suddenly appearing in the Solar System brings up other more interesting possibilities, such as an alien probe on a reconnaissance mission. In this case, however, based on analysis so far, it appears to instead be a small natural rocky or metallic body, similar to an asteroid. As astronomer Phil Plait had noted, the trajectory the object was on would actually be ideal for such a mission, but he is also pretty sure this one is natural.

A Bracewell probe is one such idea, an autonomous robotic interstellar space probe with a high level of artificial intelligence. The science fiction classic Rendezvous with Rama posited the possibility of an alien probe being mistaken for an asteroid.

In 1991, another odd object, 1991 VG, was discovered and for a while seemed, tentatively, like it might be an alien interstellar probe, but it also turned out to be an asteroid.

Now that A/2017 U1 is leaving the Solar System (unless it turns around of course!), there is limited time to keep observing it, unfortunately. But astronomers are busy trying to get all the data they can from this mystery visitor before it disappears for good.

This article was previously published on Futurism.

 

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