New studies find the interstellar comet 2I/Borisov is the most "pristine" ever discovered.
One of the only interstellar visitors ever discovered traversing our Solar System, the rogue comet 2l/Borisov, is also one of the most "pristine" such space objects ever. The comet, which was first spotted in 2019 by the amateur Ukrainian astronomer Gennady Borisov, likely never flew too close to any star including our sun, which left its composition very similar to how it was upon formation.
Comets, which are space bodies made of frozen gas, rock, and ice, are usually impacted by the heat and radiation they encounter on their way. What's attractive to scientists in studying comets that haven't changed much in their lifetimes is that they have a similar composition to the gas and dust that was present at the formation of the Solar System 4.5 billion years ago. Analyzing pristine comets can lead to a deeper understanding of the Solar System's beginnings and evolution.
The 2I/Borisov comet is only the second interstellar object ever found in our Solar System. The first one was 1I/'Oumuamua, detected in 2017.
The new study, based on observations from the European Southern Observatory's Very Large Telescope (ESO's VLT) in Chile, was led by Stefano Bagnulo of the Armagh Observatory and Planetarium in Northern Ireland.
"2I/Borisov could represent the first truly pristine comet ever observed," said Bagnulo.
The 2I/Borisov interstellar comet captured with the VLT.Credit:ESO/O. Hainaut
As reported in Nature Communications, his team used a technique called polarimetry, which measures the polarization of light, to study the space body. This helped the team compare 2I/Borisov to other local comets. The properties of the new comet were quite different from others they found in the Solar System, except for Hale-Bopp, a comet discovered in 1995 which is also considered very pristine.
The study's co-author Alberto Cellino from the Astrophysical Observatory of Torino, Italy, commented upon this connection, arrived at by analyzing polarization along with the comet's color:
"The fact that the two comets are remarkably similar suggests that the environment in which 2I/Borisov originated is not so different in composition from the environment in the early Solar System.".
In a fascinating nod to just how powerful Earth's top telescopes have become, another set of ESO researchers published a different study in Nature Astronomy on the comet's composition using data from the Atacama Large Millimeter/submillimeter Array (ALMA). This team, led by astronomer Bin Yang, was able to gather many clues about 2I/Borisov's makeup from its coma – the envelope of dust surrounding it. Inside the coma, they discovered compact pebbles, grains around one millimeter in size. They could also tell that the relative amounts of carbon monoxide and water in the comet changed significantly as it came closer to the Sun.
This indicated to them that the materials in the comet came from different places in the cosmos. Matter in the comet's home star system was likely mixed in a discernible pattern that related to how far the comet was from its star, found the scientists. This was possibly affected by the presence of giant planets, which stirred up materials in their system through strong gravity. Astronomers think this kind of process also took place in the early period of the Solar System's life.
"Imagine how lucky we were that a comet from a system light-years away simply took a trip to our doorstep by chance," remarked Yang.
In 2029, the European Space Agency plans to launch the Comet Interceptor project that would allow scientists to study comets that speed through our Solar System with even greater precision.
Unless you plan to try again in 6,800 years, this week is your shot.
- Comet NEOWISE will be most visible in the U.S. during the evenings from July 14-19, 2020.
- After July 23rd, NEOWISE will be visible only through good binoculars and telescopes.
- Look in the northwestern sky below the Big Dipper after dusk while there's a chance.
UPDATE: NASA is broadcasting a NASA Science Live episode highlighting Comet NEOWISE. NASA experts will discuss and answer public questions beginning at 3PM EST on Wednesday, July 15. Tune in via the agency's website, Facebook Live, YouTube, Periscope, LinkedIn, Twitch, or USTREAM.
Before last evening, July 14, 2020, the easiest way to see Comet NEOWISE — the brightest comet to zoom past Earth since 1977's Comet Hale-Bopp — from the United States was to catch it about an hour before sunrise. Now, however, you can see it in the evening, where it will remain for until the 19th. This is a definite don't-miss event — NEOWISE won't be coming back our way for another 6,800 years. It's the first major comet of the millennium, and by all accounts, it's unforgettable.
NEOWISE just got back from the Sun
Comet NEOWISE is named after the NASA infrared space telescope that first spotted it on March 27th. Its official moniker is C/2020 F3. It's estimated that the icy comet is about three miles across, not counting its tail.
NEOWISE is now heading away from our Sun, having made it closet approach, 27.4 million miles, to our star on July 3. The heat from that encounter is what's given NEOWISE its tail: It caused gas and dust to be released from the icy object, creating the tail of debris that looks so magical from here.
As NEOWISE moves closer to Earth, paradoxically, it will be less and less visible. By about July 23rd, you'll need binoculars or a telescope to see it at all. All of which makes this week prime time.
An evening delight
Image source: Allexxandar/Shutterstock/Big Think
First, find an unobstructed view of the northwest sky, free of streetlights, car headlights, apartment lights, and so on. And then, according to Sky & Telescope:
"Start looking about one hour after sunset, when you'll find it just over the northwestern horizon as the last of twilight fades into darkness."
It should be easy to spot since it's near to one of the most recognizable constellations up there, the Big Dipper. "Look about three fists below the bottom of the Big Dipper, which is hanging down by its handle high above, and from there perhaps a little to the right." Et voilà: Comet NEOWISE.
Says Sky & Telescope's Diana Hannikainen, "Look for a faint, fuzzy little 'star' with a fainter, fuzzier little tail extending upward from it."
The comet should be visible with the naked eye, though binoculars and a simple telescope may reveal more detail.
You may also be able to snap a photo of this special visitor, though you'll need the right gear to do so. A dedicated camera is more likely to capture a good shot than a telephone, but in either case, you'll need a tripod or some other means of holding the camera dead still as it takes a timed exposure of several seconds (not all phones can do this).
What happens after a heavy comet meal?
- A comet produces and unexpected explosive ejection of ice, dust, and gas.
- NASA's TESS satellites captures the whole thing by accident.
- The "burp" may have left a crater 65 feet across. That's quite a burp.
When NASA trained their Transiting Exoplanet Survey Satellite, AKA TESS, at Comet 46P/Wirtanen, they were merely looking for a body with which they could test out their system. TESS's mission is observing some 200,000 stars for evidence of exoplanets, but they knew the comet was going to pass through their observation window and that it would be bright. It seemed a good test case. Little did they expect they would catch it belch ice, dust, and gas.
A paper describing the TESS team's observations have been published in the November 22, 2019 issue of The Astrophysical Journal Letters.
Image source: NASA/JPL
According to the paper's lead author, astronomer Tony Farnham of the University of Maryland (UMD), "Wirtanen was a high priority for us because of its close approach in late 2018, so we decided to use its appearance in the TESS images as a test case to see what we could get out of it." "We did so, and we were surprised," he explained in a University of Maryland press release.
What came out of Comet Wirtanen was extensive. The team's early estimate is that about 2.2 million pounds of materials were expelled during the "burp," sufficient to leave a crater behind about 65 feet across. (Further analysis is ongoing.) Considering the diameter of the comet is believed to be about 1.2 kilometers, that's a significant cavity.
Comet burps have been seen before, but never observed in the entirety as TESS has done. The one-hour blast occurred on September 26, 2018 followed by a gradually increasing eight-hour period of brightness the astronomers suspect was actually light reflecting off of an expanding cloud of ejected ice, dust, and gas. In about two weeks the comet's brightness faded away.
Aside from catching the entirety of Comet Wirtanen's "indiscretion," what's remarkable about TESS's observations was the comprehensive manner in which they documented the entire outburst. The satellite takes detailed, composite images every 30 minutes, so, says Farnham, "With 20 days' worth of very frequent images, we were able to assess changes in brightness very easily. Such imagery That's what TESS was designed for, to perform its primary job as an exoplanet surveyor."
Comet Wirtanen's closest approach to Earth was long after the event, on December 26.
Of their good luck, he continues, "We can't predict when comet outbursts will happen. But even if we somehow had the opportunity to schedule these observations, we couldn't have done any better in terms of timing. The outburst happened mere days after the observations started."
Image source: NASA's Goddard Space Flight Center
TESS was launched aboard a Falcon X rocket on April 18, 2019 from Cape Canaveral. While the mission was originally intended to last just a couple of years, it's already been extended to 2022. Its goals are ambitious: The team hopes to find 10,000 alien worlds in just the first two years. It's off to a good start, having already found some.
Hopefully, this isn't the end of TESS's observations of comet burps. "We also don't know what causes natural outbursts," says Farnham, "and that's ultimately what we want to find."
NASA theorizes that burps may be caused by a thermal event that in which a heat wave reaches a pocket of volatile ices that expands and rapidly, explosively vaporizes. They also propose that it could be due to some more geological event, such as the collapse of a mountain that exposes that same ice to sunlight and heat.
Fanrham thinks that chances of further encounters are good: "There are at least four other comets in the same area of the sky where TESS made these observations, with a total of about 50 comets expected in the first two years' worth of TESS data. There's a lot that can come of these data. We're still finding out the capabilities of TESS, so hopefully we'll have more to report on this comet and others very soon."