Tag: interstellar comet

Interstellar Comet Borisov Looks Weirdly Familiar

The gas cyanogen has been detected in 2I/Borisov’s coma—a historic detection of a gas commonly found in regular comets.

Artist’s impression of a cometary nucleus. [ESA]

It’s official, the solar system is playing host to its second confirmed interstellar visitor only two years after the strangely-shaped `Oumuamua was spotted receding into interstellar expanse. While `Oumuamua was historic in that it was the first confirmed interstellar comet to be discovered, according to a new study (which has yet to be peer reviewed), this newest interstellar vagabond is potentially more significant:

“For the first time we are able to accurately measure what an interstellar visitor is made of, and compare it with our own solar system,” said Alan Fitzsimmons of the Astrophysics Research Center, Queen’s University Belfast, in a statement.

So, why are astronomers so excited about 2I/Borisov?

A (Cometary) Star Is Born

In late August, the comet was discovered by Gennady Borisov, an amateur astronomer in Crimea, and initially designated “C/2019 Q4” because, well, it looked like a regular comet. It was only after repeated observations by Borisov, and confirmed by other amateur and professional astronomers, that the object’s path and speed through the solar system could be realized. It turned out to be traveling fast.

Like, really, really fast.

Clocked at a breakneck pace of 93,000 miles per hour (150,000 kilometers per hour), astronomers realized that C/2019 Q4 was a special kind of comet. While it was found to possess the characteristics of a regular comet (it has a faint coma and tail) there is no way that it’s gravitationally bound to our Sun. Its trajectory is hyperbolic. In other words, it didn’t originate in our solar system—it’s an alien visitor.

This simple animation depicts the comets path through our neighborhood; there’s little ambiguity in the fact that it doesn’t intend to hang around for very long:

With only a slight tug by our Sun’s gravity, the interstellar visit will careen out of the solar system in a few months. [NASA/JPL-Caltech]

Last week, these factors all culminated in the International Astronomical Union (IAU) officially classifying C/2019 Q4 as the second unambiguous interstellar comet discovery to date. It was therefore reclassified as “2I/Borisov” (1I/`Oumuamua being the first, of course). It’s thought interstellar junk passes through our solar system all the time, but only two comets (to date) have been confirmed to have an interstellar origin, suggesting our observational techniques are improving.

Now, the really neat thing about 2I/Borisov is that it’s a lot more active than `Oumuamua; the latter produced very little in the way of a discernible coma or tail after its discovery. Borisov, however, is being far more generous, already allowing astronomers to grab a crude spectroscopic snapshot of the gases being vented into space.

A Mysterious Interstellar Time Capsule

After being thwarted by the glare of the Sun on Sept. 13, an international team of astronomers was able to use the William Herschel Telescope on La Palma in the Canary Islands in the morning of Sept. 20 to measure the light that was being scattered off the gases in its tenuous coma. Follow-up spectral analysis by the TRAPPIST-North telescope in Morocco was also used.

Measuring the spectrum of Borisov allows us to understand the chemical composition of the ices that are fizzing into space as they are slightly heated by our Sun’s radiation via a process known as sublimation. And this is profoundly awesome.

To capture the spectra of any comet reveals the chemicals it contained when it formed billions of years ago. In our solar system, comets are considered to be icy time capsules; they formed from the solar nebula when the Sun was a proto-star and the planets were just starting to accrete from the surrounding protoplanetary disk of ancient debris. To see the chemicals contained within the vapor of these fizzing “dirty snowballs” gives us a five-billion-year-old glimpse of what the solar nebula and its system of baby planets would have contained.

2I/Borisov as imaged by the Gemini North Telescope on Hawaii. [GEMINI OBSERVATORY/NSF/AURA/INTERNATIONAL ASTRONOMICAL UNION]

Borisov wasn’t formed in our solar nebula, however, it was formed from the nebula of a distant, unknown star of unknown age. We have little idea as to where or when it originated (though there’s little doubt that astronomers will use data from the European Gaia space telescope to try to figure out a rough estimate, as they did with `Oumuamua).

Surprisingly Familiar

While previous observations of the comet’s nucleus have revealed a reddish tinge that is similar to the long-period comets that originate from our solar system’s Oort Cloud (such as Hale-Bopp and Hyakutake), the new study has been able to identify another familiar trait: its venting gases contain cyanogen. This chemical is a simple, yet toxic molecule containing one carbon atom and a nitrogen atom (CN). Cyanogen is commonly found in regular comets born in the solar system.

The researchers were also able to make an estimate of the ratio of the dust to gas that is being blasted from the comet’s nucleus and, you guessed it, it is roughly in agreement to what you’d expect a regular comet to generate.

All of these findings point to an unexpected conclusion, as the researchers highlight in their paper: “If it were not for its interstellar nature, our current data shows that 2I/Borisov would appear as a rather unremarkable comet in terms of activity and coma composition.” In other words, if it wasn’t for its extreme speed, 2I/Borisev would look like a regular comet from our solar system.

Does this mean all comets from any star system have similar compositions? That doesn’t seem possible, considering we know other stars and their associated nebulae their comets would have formed from contain different chemicals to our own. It could just mean that Comet Borisov was ejected from a nearby star that formed in the same stellar nursery as our Sun five billion years ago and should therefore contain approximately the same chemicals. But for now, it’s too early to say.

Obviously, more work needs to be done and, fortunately, we have time. The comet will reach perihelion (point of closest approach to the Sun) in early December, and astronomers are predicting maximum nucleus activity in December and January before it starts to recede into the interstellar night.

So, watch this space.

Sadly, ‘Oumuamua Isn’t Piloted by Joyriding Aliens

An international team of experts have teamed up to conclude that the interstellar visitor isn’t what we hoped it was.

An artist’s impression of the strangely-elongated interstellar object ‘Oumuamua that zoomed through our solar system in 2017 [ESO/M. Kornmesser]

It probably comes as no surprise that the scientific consensus of ‘Oumuamua’s origins have concluded that it is a natural object, despite how funky and alien spaceship-looking the interstellar visitor at first appeared. According to a new study published today in the journal Nature Astronomy, the findings of 14 international experts have been pooled to categorically say that ‘Oumuamua isn’t an artificial object piloted by an intelligent extraterrestrial species, but instead “has a purely natural origin.”

“The alien spacecraft hypothesis is a fun idea, but our analysis suggests there is a whole host of natural phenomena that could explain it,” said the team’s leader Matthew Knight, from the University of Maryland, in a statement.

This most recent study comes hot on the heels of a fair amount of speculation that the spinning cigar-shaped object, which was detected by the Pan-STARRS1 telescope in Hawaii on Oct. 19, 2017, could be artificial. One of the more vocal advocates of this possibility, Avi Loeb of Harvard University, investigated the idea that ‘Oumuamua may be an interstellar probe that used our sun’s radiation pressure for a boost in velocity as it flew through the inner solar system. While the world’s media loved this concept (as did I), many scientists balked and emphasized the need to take the Occam’s razor approach and instead focus on natural explanations, not aliens. But, as pointed out by Loeb, while more likely explanations existed, considering the most extreme ones is still a part of the scientific process.

“This is how science works,” said Loeb in an interview for The Harvard Gazette late last year. “We make a conjecture … and if someone else advances another explanation, we will compare notes and the next time we see an object of this type we will hopefully be able to tell the difference. That’s the process by which science makes progress.”

Deep down, we all had the sense that the interstellar visitor likely wasn’t aliens (though it did spawn some wonderful debates about mind-boggling interstellar distances, the challenges of visiting other star systems, and why ET would bother popping by for a whistle-stop tour without saying “hi”), but this new study convincingly sounds the death knell for the possibility of aliens taking a joyride through our galactic neighborhood.

The new study is clear, in which the researchers write: “Here we review our knowledge and find that in all cases, the observations are consistent with a purely natural origin for ‘Oumuamua.”

So, what does the study conclude?

The object is most likely an ancient interstellar comet that randomly encountered our solar system after drifting through interstellar space for millions of years. The mechanisms by which ‘Oumuamua was ejected from its star system of birth remains up for debate, but the study’s authors point to the likelihood of a Jupiter-like world that may have gravitationally ejected the object when it strayed too close, helping it achieve escape velocity and a future lost deep in the interstellar expanse—until it encountered our solar system.

Even the behavior of the ancient comet as it traveled through the inner solar system agrees with theoretical predictions. The small boost in velocity as it made close approach to our sun was caused by ices (entombed under ‘Oumuamua’s surface) being heated and vented into space as a vapor (and not aliens hitting the gas). This behavior in comets is well-known, but the problem with ‘Oumuamua is that it exhibited few signs of being a comet—it didn’t develop a tail nor did it develop a coma, two clues of its cometary nature. But this object is different from the comets we know; it has been drifting through the galaxy for eons, perhaps it lost the majority of its ice in previous stellar encounters, or perhaps it contained little in the way of volatiles during its formation. Comets and asteroids also have a lot more in common that the textbooks may tell us, so perhaps it did vent small quantities of vapor to give it a boost, but not enough for astronomers to observe a tail and coma. In short, ‘Oumuamua shares similar traits to other objects that exist in our solar system

“While ‘Oumuamua’s interstellar origin makes it unique, many of its other properties are perfectly consistent with objects in our own solar system,” added Robert Jedicke of the University of Hawai’i’s Institute for Astronomy (IfA) and collaborator in the Nature Astronomy study.

The key thing that makes ‘Oumuamua so captivating, however, is not how it behaved when it entered the solar system and used the sun to change its course, it’s that we know it came from interstellar space, the first of its kind that we’ve ever encountered. Undoubtedly, the solar system has been visited countless times by junk that has been shed by other stars in our galaxy—there’s a lot of stars carrying around a lot of comets and asteroids, after all, they’re probably scattered around the Milky Way like baby’s toys being thrown out of strollers—but this is the first, special interstellar visitor that we’ve only just had the ability to detect.

The best news? There will be more.

Humanity is rapidly advancing through a “golden age” for astronomy and, if these interstellar vagabonds are as common as we now believe, we’re on the verge of detecting many more of them. For example, the Large Synoptic Survey Telescope (LSST), which is being constructed in Chile, is expected to become operational in 2022 and it will be so powerful that astronomers predict at least one ‘Oumuamua-like object will be spotted per year. Once we grasp how often these things turn up, perhaps we’ll be prepared enough to have a robotic spacecraft intercept one to see what these visitors from other stars really look like instead of depending on distant observations.

Of course, this whole episode could be a cautionary tale. Perhaps our advanced alien neighbors disguise their spacecraft to look like passing comets to get a closer look of primitive intelligences such as ourselves.* ‘Oumuamua being identified as an interstellar comet is exactly what they want us to believe…

*This was inspired by a tweet I read this morning, but I forgot who tweeted it and it appears I didn’t “like” it, so it’s since been lost to the twitterverse. Thank you to whomever tweeted it, it formed the seed to this blog!

If Aliens Pilot Interstellar Object ‘Oumuamua, They Snubbed Us

The Seti Institute has monitored the object for radio transmissions, just in case it isn’t natural

We humans are a sensitive bunch. We keep pondering the question: “are we alone?” If we consider the answer is a “yes,” we then start having an existential crisis over our place in the universe. But if the answer is a “no,” a can of worms open and we start asking even more questions. “If they’re out there, where are they?” “Isn’t it a bit weird we haven’t heard from our extraterrestrial neighbors?” “Are they just too far away for us to communicate?” and my personal favorite: “Have they consciously decided not to communicate with us because we’re considered not worth communicating with?!” The Fermi Paradox is certainly as paradoxical as they come.

Cue a random object that cruised through our solar system last year. The interstellar visitor zoomed right into our interplanetary neighborhood, used the Sun’s gravity for a cheeky course correction, and then slingshotted itself back out into deep space. The whole thing happened so quickly that astronomers only noticed when the thing was speeding away from us at high speed.

Naturally, we took a hint from science fiction, remembering Arthur C. Clarke’s classic novel “Rendezvous With Rama” — when a huge artificial object appears from interstellar space and a brave team of astronauts are sent to intercept it. Might this interstellar object also be artificial? After all, it has an odd, tumbling shape (like a spinning cigar) and the precision at which it flew past us with the trajectory it did (using the Sun to change its direction and speed of travel) just feels artificial.

So, with the help of the SETI Institute’s Allen Telescope Array (ATA) in California, astronomers decided to take aim at the departing object from 
Nov. 23 and Dec. 5, 2017, when it was 170 million miles from Earth. The objective was to listen out for artificial radio transmissions that might reveal any kind of extraterrestrial intelligence. By monitoring frequencies from 1 to 10 GHz (at 100 MHz intervals), the ATA would be able to detect a very low powered onmidirectional transmitter, with a transmitting power as low as 10 Watts — the approximate equivalent to a citizen band radio.

According to the SETI study to be published in the February 2019 issue of Acta Astronautica, no signals were detected. Though this is obviously a blow for working out whether this thing was being actively piloted by some kind of intelligence, it does narrow down the true nature of the object, that has since been named ‘Oumuamua — which, in Hawaiian, roughly means “scout,” or “messenger.”

“We were looking for a signal that would prove that this object incorporates some technology — that it was of artificial origin,” said Gerry Harp, lead author of the study, in a SETI Institute statement. “We didn’t find any such emissions, despite a quite sensitive search. While our observations don’t conclusively rule out a non-natural origin for ‘Oumuamua, they constitute important data in assessing its likely makeup.”

Although this doesn’t prove ‘Oumuamua isn’t an alien spacecraft, it does put limits on the frequencies it could be transmitting on, if it is transmitting. And even if it isn’t transmitting, it doesn’t mean it’s not artificial. Could it be an ancient spacecraft that’s been sailing the interstellar seas for millions or billions of years, long after its intelligent occupants have died? Or long after its artificial intelligence has run out of energy? 

Or — and this is the big one — did it zoom through our solar system, aware of our presence, and not bother communicating with us? If that scenario played out, we need to re-open that can o’ worms and try to understand where we stand in the universal ecosystem of competing intelligences. Perhaps we are the cosmic equivalent of an ant colony; our intelligence just isn’t worth the time when compared with the unimaginable alien intelligences that have the technology to send ‘Oumuamuas to probe distant star systems for life.

Alas, it’s probably a case of Occam’s razor, where the simplest explanation is most likely the correct one: ‘Oumuamua is probably a strange-looking asteroid or ancient comet that was randomly shot at us by some distant star system and astronomers were lucky to detect it. But, we still need to ponder the least likely explanations, you just never know…

The Solar System Just Had an Interstellar Visitor. Now It’s Gone

Comet-PanSTARRS-1
Hello, goodbye interstellar comet. The hyperbolic orbit of Comet C/2017 C1 as plotted by JPL’s Small-Body Database Browser (NASA/JPL-Caltech)

Update: At original time of writing, C/2017 U1 was assumed to be a comet. But Followup observations by the Very Large Telescope in Chile on Oct. 25 found no trace of cometary activity. The object’s name has now been officially changed to A/2017 U1 as it is more likely an interstellar asteroid, not a comet.

Astronomers using the PanSTARRS 1 telescope in Maui may have discovered an alien comet.

Comets and asteroids usually originate from the outermost reaches of the solar system — they’re the ancient rocky, icy debris left over from the formation of the planets 4.6 billion years ago.

However, astronomers have long speculated that comets and asteroids originating from other stars might escape their stars, traverse interstellar distances and occasionally pay our solar system a visit. And looking at C/2017 U1’s extreme hyperbolic trajectory, it looks very likely it’s not from around these parts.

“If further observations confirm the unusual nature of this orbit this object may be the first clear case of an interstellar comet,” said Gareth Williams, associate director of the International Astronomical Union’s Minor Planet Center (MPC). A preliminary study of C/2017 U1 was published earlier today. (Since this statement, followup observations have indicated that the object might be an asteroid and not a comet.)

According to Sky & Telescope, the object entered the solar system at the extreme speed of 16 miles (26 kilometers) per second, meaning that it is capable of traveling a distance of 850 light-years over 10 million years, a comparatively short period in cosmic timescales.

Spotted on Oct. 18 as a very dim 20th magnitude object, astronomers calculated its trajectory and realized that it was departing the solar system after surviving a close encounter with the sun on Sept. 9, coming within 23.4 million miles (0.25 AU). Comets would vaporize at that distance from the sun, but as C/2017 U1’s speed is so extreme, it didn’t have time to heat up.

“It went past the sun really fast and may not have had time to heat up enough to break apart,” said dynamicist Bill Gray. Gray estimates that the comet is approximately 160 meters wide with a surface reflectivity of 10 percent.

But probably the coolest factor about this discovery is the possible origin of C/2017 U1. After calculating the direction at which the comet entered the solar system, it appears to have come from the constellation of Lyra and not so far from the star Vega. For science fiction fans this holds special meaning — that’s the star system where the SETI transmission originated in the Jodie Foster movie Contact.

For more on this neat discovery, check out the Sky & Telescope article.