Explanation: From somewhere else in the Milky Way galaxy, Comet 2I/Borisov is just visiting the Solar System. Discovered by Crimean amateur astronomer Gennady Borisov on August 30, 2019, the first known interstellar comet is captured in these two recent Hubble Space Telescope images. On the left, a distant background galaxy near the line-of-sight to Borisov is blurred as Hubble tracked the speeding comet and dust tail about 327 million kilometers from Earth. At right, 2I/Borisov appears shortly after perihelion, it's closest approach to Sun. Borisov's closest approach to our fair planet, a distance of about 290 million kilometers, will come on December 28. Even though Hubble's sharp images don't resolve the comet's nucleus, they do lead to estimates of less than 1 kilometer for its diameter.
Comet Hale-Bopp in true color. Photo: Fred Espenak.
True color comet pictures will show that the comet has a greenish coma ("head"), a yellow-white, diffuse dust tail and a streaky blue gas tail. As for Comet Hyakutake, it was remarkably dominated by its blue gas tail, and we never saw a yellow dust tail developing. As for Comet Hale-Bopp, its greenish coma was swamped by its bright yellowish dust tail.
Comet Borisov is seen to be "all blue". Such comets don't exist. If we are seeing the coma of the comet, it should be greenish, and if we are seeing the dust tail, it should be yellow-white. The reason why a comet's coma is greenish, as well as the reason why a comet's gas tail is blue, has to do with the way certain certain chemical compounds (such as carbon monoxide) are ionized by the Sun. The dust tail, by contrast, is made up of larger particles that are shed by the comet and illuminated by the Sun.
Comet Borisov in false color. NASA, ESA, D. Jewitt (UCLA).
Compare Comet Borisov with Comet Holmes. Comet Holmes had a very bright, egg-white dusty coma. A faint green glow surrounded the coma. A faint blue gas tail is seen to be disconnected from the comet in Tony Cook's picture.
As for Comet Borisov... what can I say? Hubble imaged it. Let me guess... Maybe through a 606 nm filter? Or even an 814 nm filter? The picture of Comet Borisov and a background galaxy has probably been imaged through two filters, but Hubble won't tell us which ones. Or maybe even the comet-galaxy picture is a single filter image, and the image has just been processed to show the comet and the galaxy as differently colored.
Ann
Edit: It is the fact that we are not told what filter was used to image Comet Borisov that makes me most irritated.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 9:49 am
by Boomer12k
"Welcome to the Solar System" from Earth... "Hope you enjoy your visit."
:---[===] *
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 11:05 am
by Geo1138
Ann,
I found a captioned image and it gave the filter info as...
Well, I assume that the "lp" part of the name of the filter means "long pass". That would suggest that the filter lets through as many wavelengths as possible, so that it is impossible to distinguish any colors.
Thanks!
Ann
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 1:17 pm
by BDanielMayfield
Ann, you have made an assumption that this comet's true color(s) would match the color of common comets coming from Sol's system. Is that a safe assumption though? Probably, but isn't it possible that this interstellar comet has a chemical makeup differing enough from our typical comets to effect its appearance just a bit?
Reports however suggest that the chemicals coming off Borisov are much like those coming off our comets. This is what the wikipedia article currently has to say about its composition:
2I/Borisov's composition appears to be similar to that of Solar System comets. A preliminary (low-resolution) visible spectrum of 2I/Borisov was similar to typical Oort Cloud comets.[24][25] Its color indexes also resemble the Solar System's long period comets.[21] Emissions at 388 nm indicated the presence of cyanide (formula CN), which is typically the first detected in Solar System comets including comet Halley[9]. This was the first detection of gas emissions from an interstellar object.[26] The detection of diatomic carbon has also been reported,[27] but not confirmed, with the ratio C2 to CN being less than 0.3.[28] This resembles a carbon-chain depleted group of comets, most of which are Jupiter family comets.[27] Atomic oxygen has also been detected, from this observers estimated an outgassing of water at a rate similar to Solar System comets.[29][30]
Hopefully though in upcoming days we will be getting even better images, both for esthetics and for checking its chemistry.
Bruce
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
.
<<Jelly beans are small bean-shaped sugar candies with soft candy shells and thick gel interiors. The confection is sold in a wide variety of colors and flavors, and is made primarily of sugar. It has been claimed that jelly beans were first mentioned during 1861, when Boston confectioner William Schrafft urged people to send his jelly beans to soldiers during the American Civil War. It was not until July 5, 1905, that jelly beans were mentioned in the Chicago Daily News. The advertisement publicized bulk jelly beans sold by volume for nine cents per pound. Most historians contend that jelly beans were first associated with celebrations of Easter in the United States sometime during the 1930s due to their egg-like shape.>>
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 4:20 pm
by geckzilla
The comet is pretty faint. I've got a raw (with cosmic rays removed) image of the original comet next to the galaxy. You can see the galaxy overall is brighter than it. To get the comet to a comparable brightness with the galaxy, they had to take a stack of three longer exposures without the galaxy, and then combine it with this shorter one that features the galaxy. In reality though, the comet's coma was much fainter than the extended parts of the galaxy.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 5:28 pm
by Psnarf
290 million km is somewhere in the middle of the asteroid belt. https://svs.gsfc.nasa.gov/4758
Collision would be nice, maybe send some pieces our way to study?
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 5:32 pm
by alter-ego
geckzilla wrote: ↑Sat Dec 14, 2019 4:20 pm
The comet is pretty faint. I've got a raw (with cosmic rays removed) image of the original comet next to the galaxy. You can see the galaxy overall is brighter than it. To get the comet to a comparable brightness with the galaxy, they had to take a stack of three longer exposures without the galaxy, and then combine it with this shorter one that features the galaxy. In reality though, the comet's coma was much fainter than the extended parts of the galaxy.
Thanks, geck. That clears up a question I had. I didn't understand one image description I read that said the image is a composite of separate exposures. Looking at the raw image it's obvious a composite is needed.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 5:50 pm
by Chris Peterson
Ann wrote: ↑Sat Dec 14, 2019 7:26 am
:bang: False color APOD! :bang:
To be clear, this is not a false color image. It is a pseudocolor image- the source data is single channel (grayscale), with the original intensity values replaced with color values. This is done because it allows us to see and interpret more structure than we can do using intensity alone. Many different pseudocolor mappings are used to enhance structural details that would otherwise not be apparent.
(With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.)
Here is a set of different pseudocolor mappings, all using the same grayscale data that is underneath today's APOD image.
_
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 6:56 pm
by mostly cloudy
As always, a good and spirited color discussion. The photo colors make the pictures more interesting, but it’s helpful to know what is going into the processing.
Kudos to Mr Borisov... at least Crimean nights are warm in August; I am always in awe of the thousands of dedicated human eyes scanning the night skies of Earth all year round.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sat Dec 14, 2019 8:30 pm
by BDanielMayfield
Chris Peterson wrote: ↑Sat Dec 14, 2019 5:50 pm
With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.
Is that fact significant? That is, is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Chris Peterson wrote: ↑Sat Dec 14, 2019 5:50 pm
With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.
Is that fact significant? That is, is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?
No, not particularly significant for a small comet with a 2 AU perihelion. Not all comets show an obvious ion trail. It's likely most active comets have them, but that doesn't mean they'll be bright enough to detect. The dust trail is generally a lot brighter.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Chris Peterson wrote: ↑Sat Dec 14, 2019 5:50 pm
With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.
Is that fact significant? That is, is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?
No, not particularly significant for a small comet with a 2 AU perihelion. Not all comets show an obvious ion trail [sic]. It's likely most active comets have them, but that doesn't mean they'll be bright enough to detect. The dust trail [sic] is generally a lot brighter.
https://en.wikipedia.org/wiki/The_Iron_Trail wrote:
<<The Iron Trail is a 1921 American silent adventure film directed by Roy William Neill and written by Dorothy Farnum. The film stars Wyndham Standing, Thurston Hall, Reginald Denny, Alma Tell, and Harlan Knight. The film was released on October 30, 1921, by United Artists. The plot details the competing efforts to build railways into interior Alaska in the early part of the 20th century.>>
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Chris Peterson wrote: ↑Sat Dec 14, 2019 5:50 pm
With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.
Is that fact significant? That is, is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?
No, not particularly significant for a small comet with a 2 AU perihelion. Not all comets show an obvious ion trail. It's likely most active comets have them, but that doesn't mean they'll be bright enough to detect. The dust trail is generally a lot brighter.
Thanks for that dependably sensible reply Chris.
As for your comment Art, “often accused of posts that are cents-less”, ‘nough said.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
BDanielMayfield wrote: ↑Sat Dec 14, 2019 8:30 pm
Is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?
No, not particularly significant for a small comet with a 2 AU perihelion. Not all comets show an obvious ion trail. It's likely most active comets have them, but that doesn't mean they'll be bright enough to detect. The dust trail is generally a lot brighter.
Thanks for that dependably sensible reply Chris. As for your comment Art, “often accused of posts that are cents-less”, ‘nough said.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Ann wrote: ↑Sat Dec 14, 2019 7:26 am False color APOD!
To be clear, this is not a false color image. It is a pseudocolor image- the source data is single channel (grayscale), with the original intensity values replaced with color values. This is done because it allows us to see and interpret more structure than we can do using intensity alone. Many different pseudocolor mappings are used to enhance structural details that would otherwise not be apparent.
Well, the term used to be false color. I like it. Anyway, the Hubble people could have said that it was a false (or pseudo) color image. They could have said that the image of the comet and the galaxy was processed to show these objects as differently colored. And they could have said that the comet was really much fainter than the galaxy. And they could have named the filter they used for the images.
(With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.)
Yes, that's exactly what it looks like. No streakiness from an ion tail can be seen at all. By the way, thanks for the remainder that the gas tail is really called the ion tail.
Here is a set of different pseudocolor mappings, all using the same grayscale data that is underneath today's APOD image.
_
borisov_pseudocolor.gif
Thanks, that's interesting.
Ann
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sun Dec 15, 2019 5:05 am
by RocketRon
So, will we be ready to put a probe onto a future visitor,
to analyse what its made of.
Now that could be interesting ??
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sun Dec 15, 2019 5:06 am
by RocketRon
This may require more than a few days notice, of course.....
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Chris Peterson wrote: ↑Sat Dec 14, 2019 5:50 pm
With this comet, we see no ion tail. All of the light around the coma is scattered off of dust particles.
Is that fact significant? That is, is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?
No, not particularly significant for a small comet with a 2 AU perihelion. Not all comets show an obvious ion trail. It's likely most active comets have them, but that doesn't mean they'll be bright enough to detect. The dust trail is generally a lot brighter.
Comet Arend-Roland, with its distinctive anti-tail,
photographed by the American astronomer Alan McClure on 24 April 1957.
Wikipedia calls the cometary tails tails. But it does say (in the caption under the first picture) that a comet's antitail can be call a dust trail.
Ann
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
Posted: Sun Dec 15, 2019 1:45 pm
by BDanielMayfield
RocketRon wrote: ↑Sun Dec 15, 2019 5:05 am
So, will we be ready to put a probe onto a future visitor,
to analyse what its made of.
Now that could be interesting ??
RocketRon wrote: ↑Sun Dec 15, 2019 5:06 am
This may require more than a few days notice, of course.....
That would require better rockets, RocketRon. Or more likely, some propulsion system(s) that is better than rockets at supplying high delta V. Interstellar visitors will always be moving faster than objects bound to our system, so they will be harder to catch.
Re: APOD: Interstellar Comet 2I/Borisov (2019 Dec 14)
RocketRon wrote: ↑Sun Dec 15, 2019 5:06 am
So, will we be ready to put a probe onto a future visitor, to analyse what its made of.
Now that could be interesting ??
This may require more than a few days notice, of course.....
That would require better rockets, RocketRon. Or more likely, some propulsion system(s) that is better than rockets at supplying high delta V. Interstellar visitors will always be moving faster than objects bound to our system, so they will be harder to catch.
Smaller payloads and better detection systems (no offense Borisov) will soon make this a reality:
https://en.wikipedia.org/wiki/2I/Borisov#Exploration wrote:
<<The higher hyperbolic excess velocity of 2I/Borisov of 32 km/s makes it even harder to reach for a spacecraft than 1I/'Oumuamua (26 km/s). According to a team of the Initiative for Interstellar Studies, a two-ton spacecraft could theoretically have been sent in July 2018 to intercept 2I/Borisov using a Falcon Heavy-class launcher, but only if the object had been discovered much earlier than it was. Launches after the actual discovery date would require a significantly larger launcher such as the Space Launch System (SLS) and Oberth manoeuvres near Jupiter and near the Sun. By September 2019, even an SLS-class launcher would only be able to deliver a 3 kg payload (such as a CubeSat) into a trajectory that could intercept 2I/Borisov in 2045 at a relative speed of 34 km/s. According to congressional testimony, NASA may need at least five years of preparation to launch such an intercepting mission.>>
Interstellar Comet 2I/Borisov
False color APOD! 
