Science & Technology

Experts confirm that a second interstellar visitor is zipping through solar system

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 have now confirmed the existence of another one.

The comet, originally 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.

Based on an analysis of night-by-night observations, the International Astronomical Union announced today that the comet is “unambiguously interstellar in origin,” coming in from far beyond our solar system. The IAU also gave the object a new name to befit its interstellar status: 2I/Borisov.

The IAU and NASA say 2I/Borisov should reach its closest point to the sun on Dec. 7, at a distance of about 180 million miles. That’s tens of millions of miles beyond the orbit of Mars — well out of harm’s way, as far as Earth is concerned. The IAU says it expects the comet to be at its brightest in the southern sky in December and  January. But even then, it will take a moderate-sized telescope to spot it.

“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,” Davide Farnocchia of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory said earlier this month in a NASA status report. “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 worked 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 2I/Borisov has a fuzzy appearance and a short cometary tail. NASA says observations from the University of Hawaii indicate the comet’s nucleus is somewhere between 1.2 and 10 miles wide.

Before 2I/Borisov, the only interstellar object astronomers knew about was a cosmic interloper known as ‘Oumuamua — so they’re not sure what to expect from the second one. But if it’s 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.

UW astronomer Lynne Jones discussed the case of 2I/Borisov 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.

Spectral observations from Apache Point and elsewhere could reveal the chemical composition of 2I/Borisov, telling astronomers whether there are dramatic differences in the makeup of material from other stars. The IAU said the 34-foot Gran Telescopio Canarias in the Canary Islands has already obtained a spectrum of the object “and has found it to resemble those of typical cometary nuclei.”

Studying such objects could well provide a new way of investigating processes in planetary systems beyond our own, the IAU said. And who knows? Maybe 2I/Borisov will turn out to be another flying cigar, this time sporting a trail of cosmic smoke.

This is an updated version of a report first published at 10:59 a.m. PT Sept. 13.

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