Our solar system's second known interstellar visitor doesn't seem to be in one piece anymore.
Photos of the interstellar Comet Borisov taken by NASA's Hubble Space Telescope on March 28 and March 30 show an elongated nucleus that appears to have two distinct components, astronomers announced in a note Thursday (opens in new tab) (April 2). That's a very different situation than the one Hubble observed on March 23, when the nucleus was a single entity.
These two pieces are about equally bright (opens in new tab), but that doesn't mean they're of equivalent size, said UCLA astronomer David Jewitt, who led the new observations.
Related: Interstellar comet: Here's why it's got scientists so pumped up
"Actually, it turns out almost never to be that case," Jewitt told Space.com, referring to similar observations of native-born comets.
"Usually, the main nucleus drops off a piece, and the piece is small compared to the main nucleus — it contains a tiny fraction of the total mass," he said. "But, because it was just plucked out of the nucleus, it's pretty icy. And the ice fizzes and sublimates like crazy, making it a good producer of dust."
Dust is what Hubble is picking up in these photos. So, it's unlikely that Borisov is breaking apart in a significant way, Jewitt added. He estimated that Borisov may have just lost 0.1% to 1% of its total mass, comparing the probable scenario to a car that just dropped a side mirror.
Still, the researchers don't know for sure that this is the case; it's possible that something more dramatic just happened. Jewitt and his colleagues hope to figure it out, and additional Hubble observations could do the trick.
For example, further Hubble imagery could show researchers how fast the shed fragment is accelerating away from the main nucleus and how long it remains observable. Both of these data points would provide clues about the size of the newly liberated shard, Jewitt said.
Comet Borisov was detected in August 2019 and made its closest approach to the sun in December. It's not necessarily surprising to see a chunk fly off the comet now, four months after this perihelion passage, Jewitt said; the timeline is consistent with two prominent models of comet shedding.
In one of those models, comets begin spinning faster after close solar approaches because the heating they experience causes significant, and asymmetrical, mass loss. It may take several months for the spin-up to get dramatic enough for pieces to go flying off into space, Jewitt said.
In the other model, this same heating causes pressure to build up inside comet nuclei. Eventually, the pressure reaches a pocket of supervolatile ice, such as carbon monoxide or carbon dioxide, resulting in a blowout. And, again, this may take some time. (But comets may be too leaky for this explanation to be viable in most circumstances, Jewitt said.)
There's also the possibility that Comet Borisov got hit by something. But an impact is unlikely to be the explanation, Jewitt said, given how empty space is and how strange Borisov's orbit is compared to objects that were born in our solar system.
Borisov is the second known interstellar body ever spotted in our solar system. The first was the mysterious object 'Oumuamua, whose multilayered weirdness has prompted speculation that it may be an alien spacecraft of some sort.
'Oumuamua was already barreling toward the outer solar system when it was detected. Borisov had not yet rounded the sun in August 2019, meaning astronomers have been able to track it for longer stretches and in greater detail.
This tracking, however, has been compromised recently by the coronavirus pandemic, which has shut down many ground-based telescopes.
"It's entirely possible that the virus is going to kill the comet for most astronomers," Jewitt said.
But Hubble is still operating despite the outbreak, and this iconic eye in the sky is well suited to observe Borisov. Indeed, even the biggest ground-based scopes don't have the resolution required to detect the recent shedding event, Jewitt said.
"So, really, only [the Hubble] Space Telescope can see this sort of thing," he said.
- We could chase down interstellar Comet Borisov by 2045
- 'Oumuamua: The solar system's 1st interstellar visitor explained in photos
- 1st color photo of interstellar comet reveals its fuzzy tail
Mike Wall is the author of "Out There (opens in new tab)" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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Let's hope the SOBs are sensitive to the coronavirus!
Remember this one?
Now let us explore the alien spaceship connection, a scout ship. How many confirmed exoplanets? 4241, The Extrasolar Planets Encyclopaedia Question: if this is an alien scout ship, we have 4241 exoplanets, which one did it come from?
Question. How long did it take for the scout ship to travel just 4 light-years to reach our solar system? At a constant velocity of 30 km/s, the trip is 40,000 earth years.
Question: is flat earth science and astronomy more secure than reports of 2I/Borisov as an alien spaceship?
Hale-Bopp was a spectacular comet visible but some, claimed an alien space ship with that comet too with bad results., https://www.space.com/19931-hale-bopp.html
Seems we need to plan for this alien invasion. We need to assemble all the highest tech weapon systems, like scram-jets mounted with maximum yield nukes for an minimally effective response. It will at least show them we are not helpless. Kinetic high speed rail-guns and any lasers they have been working on need to be brought in and give them hell. We might be able to bluff our way out of this if they think we are too advanced for their risk/reward. Some of these aliens could be wimps. Look at the Ferengis. They wouldn't hang around after one nuke went off.........We can only hope they are of a similar character, or coronavirus will look like a hangnail.
If aliens, we are in big trouble. Any species advanced enough to travel the stars is going to consider us a nuisance or something to poke at with a stick, at best.
All prior comets are believe derived from the solar system. If this object is truly from inter-stellar space, it should be referred to as an interstellar object with cometary appearance. I don't think it should be called a comet. I see from Wiki that they agree. This object is now known as 2I/Borisov, indicating the second interstellar visitor.
FYI, 2I means the 2nd interstellar comet observed now, I for interstellar like 1I/2017_U1, 'Oumuamua.
2I/Borisov has a fuzzy, coma shape too. Very common optical observation of comets using telescopes. My stargazing log records 52 comet sightings I made going back to April 1997 and April 1996, Hale-Bopp and Hyakutake. The most recent comet I observed is C/2019 Y4 (Atlas) on 30-March-2020 using my 10-inch Newtonian. From my stargazing log -
"Observed 2000-2200 EDT. Sunset 1929 EDT. I was able to view the comet again tonight but this time using the XT10i telescope. Very good views using 35-mm PO, 32-mm plossl, and 14-mm Delos eyepieces. Early in the evening I used the 35-mm PO and viewed Venus. Brilliant nearly half-moon shape, poked me in the eye :) This was a lovely early spring evening outdoors. I observed 3 polar orbiting satellites while I viewed the comet. 2 with unaided eyes, one passing through Auriga about as bright as Capella, the other passed across the FOV while I viewed the fuzzy coma of the comet. Not very bright but more distinct brighter core at 86x using the 14-mm Delos. Plenty of stars visible in the FOV with the comet too and using the 35-mm PO, I could see HIP40215 star and the comet in same FOV near 34/35x and 1.8-degree true FOV. The comet and star a bit more than 1-degree apart in angular separation near 2030 EDT or 0030 UT. While I observed in the east pasture, the waxing crescent Moon lit up the fields, I was bathed in moonlight. Very ethereal observing like this. Venus below the Pleiades was quite a sight in western sky tonight. Orion out and Leo."
I will stay the course charted by astronomy that 2I/Borisov is indeed a comet and not aliens visiting our solar system, plotting an invasion :)--Rod
They will totally ignore our presence, quickly and efficiently collecting from Antarctica the ice they need for their G and Ts, and departing happily to the next item in the Galactic Zoo.