Coming attraction: Evidence is mounting for detection of a second interstellar visitor

A two-color composite image from the Gemini North Multi-Object Spectrograph in Hawaii shows Comet C/2019 Q4 (Borisov). Blue and red dashes are images of background stars that appear to streak due to the comet’s motion. (Gemini Observatory / NSF / AURA Image / Travis Rector)

Two years after astronomers made their first detection of a celestial object that came into our solar system from the neighborhood of another star, they think they’ve spotted another one.

The comet, known as C/2019 Q4 (Borisov), was discovered on Aug. 30 by Gennady Borisov at the MARGO observatory in Crimea, a region that’s contested by Ukraine and Russia. C/2019 Q4’s origin hasn’t yet been fully confirmed, but each night brings further evidence that its path traces back to far beyond our solar system.

In a Thursday update, NASA reports that C/2019 Q4 is 260 million miles from the sun and will reach its closest point to the sun on Dec. 8, at a distance of about 180 million miles. That’s tens of millions of miles beyond the orbit of Mars.

“The comet’s current velocity is high, about 93,000 mph, which is well above the typical velocities of objects orbiting the sun at that distance,” said Davide Farnocchia of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory. “The high velocity indicates not only that the object likely originated from outside our solar system, but also that it will leave and head back to interstellar space.”

Farnocchia has been working with other astronomers, including experts at the European Space Agency’s Near-Earth Object Coordination Center, to nail down the comet’s precise trajectory. It’s heading for the inner solar system from above — that is, celestial north — at a 40-degree angle to the solar system’s ecliptic plane.

The observations made to date indicate that C/2019 Q4 has a fuzzy appearance, suggestive of a cloud of gas and dust that could be resolved into a tail as the object comes closer. NASA says observations from the University of Hawaii indicate the comet’s nucleus is somewhere between 1.2 and 10 miles wide.

C/2019 Q4 should be detectable using moderate-sized amateur telescopes at the time of peak brightness in December. The next few weeks of observations should nail down (or knock down) C/2019 Q4’s interstellar status. But Karl Battams, an astrophysicist at the Naval Research Laboratory who’s an expert on eccentric comets, is sounding increasingly confident:

So far, astronomers have confirmed the existence of only one interstellar object, known as ‘Oumuamua — so they don’t know what to expect from what may be the second one. But if C/2019 Q4 is anything like ‘Oumuamua, they’re in for a wild ride.

Even though ‘Oumuamua is now on its way out of the solar system for good, with fading opportunities for observation, the astronomical community is still debating whether it’s an asteroid, a comet or an alien probe.

‘Oumuamua’s weirdest quality is its extreme length, compared to its width. By some measures, the ratio of length to width is 10 to 1, which would make the object look either like a giant cigar or an appropriately sized starship.

Astronomers at the University of Washington played a role in estimating the size and shape of ‘Oumuamua, and are looking into C/2019 Q4 as well.

Assuming C/2019 Q4 is of interstellar origin, spectral observations could reveal its chemical composition, telling astronomers whether there are dramatic differences in the makeup of material from other stars. And who knows? Maybe it’ll turn out to be another flying cigar, this time sporting a trail of cosmic smoke.

Update for 4:30 p.m. PT Sept. 13: UW astronomer Lynne Jones discussed the case of C/2019 Q4 in an email forwarded to GeekWire. Jones is involved in the preparations for the Large Synoptic Survey Telescope, or LSST. She’s associated with the UW’s DIRAC Institute, which is developing analytical tools for LSST data. Here’s what Jones had to say:

“It’s pretty amazing to find another object with such an interesting orbit — another likely interstellar object so soon after the first has really interesting implications for how many of these kinds of things we may find in the future as bigger full-sky surveys (like LSST) start up. It’s also interesting to me that this object is so different from ‘Oumuamua — it’s cometary instead of rocky, and has a much higher eccentricity. Luckily it will be visible for much longer than ‘Oumuamua as well — we will have about a year to study this object in more detail.

“UW is involved with follow-up observations, partly through obtaining additional observations at Apache Point Observatory [in New Mexico] that will improve the orbit measurement, but primarily are intended to help determine the size of the comet (which can also be used to look for any indications of a light curve, indicating a rotation period which can help constrain its shape). We hope to obtain more observations with APO in the near future to further characterize the comet.

“UW is also involved with the Zwicky Transient Facility (ZTF), and obviously this is very interesting for that survey as well — it wasn’t observed with ZTF, but there are some follow-up resources associated with the ZTF survey which have been used to observe C/2019 Q4 as well, to measure a color for the comet.”

In a follow-up tweet, Jones noted that there’s a large team of astronomers on the case. She gave a special shout-out to Bryce Bolin, who’s working at the DIRAC Institute as a senior research fellow with the B612 Foundation’s Asteroid Institute.

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