APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

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APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by APOD Robot » Tue Mar 26, 2024 4:05 am

Image Comet Pons-Brooks' Ion Tail

Explanation: Comet Pons-Brooks has quite a tail to tell. First discovered in 1385, this erupting dirty snowball loops back into our inner Solar System every 71 years and, this time, is starting to put on a show for deep camera exposures. In the featured picture, the light blue stream is the ion tail which consists of charged molecules pushed away from the comet's nucleus by the solar wind. The ion tail, shaped by the Sun's wind and the comet's core's rotation, always points away from the Sun. Comet 12P/Pons–Brooks is now visible with binoculars in the early evening sky toward the northwest, moving perceptibly from night to night. The frequently flaring comet is expected to continue to brighten, on the average, and may even become visible with the unaided eye -- during the day -- to those in the path of totality of the coming solar eclipse on April 8.

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Roy

Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Roy » Tue Mar 26, 2024 12:31 pm

Still pushing the "comet is a dirty snowball" theory despite pictures, impacting one, & actually landing on one??? We know betteer.

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Chris Peterson » Tue Mar 26, 2024 1:40 pm

Roy wrote: Tue Mar 26, 2024 12:31 pm Still pushing the "comet is a dirty snowball" theory despite pictures, impacting one, & actually landing on one??? We know betteer.
Comets are a mix of rocky material, mostly silicates and carbonates, and volatile ices. Nothing wrong with calling that a "dirty snowball"... although depending on the mixture of rock to ice, some are better described as "snowy dirtballs". The particular constituents in a pristine comet are probably determined mainly by where they formed in the early Solar System. The composition changes over time for those comets that approach the Sun closely enough to lose material.
Chris

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Ann » Tue Mar 26, 2024 2:16 pm

Chris Peterson wrote: Tue Mar 26, 2024 1:40 pm
Roy wrote: Tue Mar 26, 2024 12:31 pm Still pushing the "comet is a dirty snowball" theory despite pictures, impacting one, & actually landing on one??? We know betteer.
Comets are a mix of rocky material, mostly silicates and carbonates, and volatile ices. Nothing wrong with calling that a "dirty snowball"... although depending on the mixture of rock to ice, some are better described as "snowy dirtballs". The particular constituents in a pristine comet are probably determined mainly by where they formed in the early Solar System. The composition changes over time for those comets that approach the Sun closely enough to lose material.
This one looks like a dirty snowball to me, with its fine tail.

Also, in view that it made its first recorded appearance in the skies of the Earth in 1385, and that it has returned every 71 years, I must say that this particular comet appears to be particularly gassy. :wink:

Ann
Last edited by Ann on Tue Mar 26, 2024 2:41 pm, edited 1 time in total.
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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Chris Peterson » Tue Mar 26, 2024 2:20 pm

Ann wrote: Tue Mar 26, 2024 2:16 pm
Chris Peterson wrote: Tue Mar 26, 2024 1:40 pm
Roy wrote: Tue Mar 26, 2024 12:31 pm Still pushing the "comet is a dirty snowball" theory despite pictures, impacting one, & actually landing on one??? We know betteer.
Comets are a mix of rocky material, mostly silicates and carbonates, and volatile ices. Nothing wrong with calling that a "dirty snowball"... although depending on the mixture of rock to ice, some are better described as "snowy dirtballs". The particular constituents in a pristine comet are probably determined mainly by where they formed in the early Solar System. The composition changes over time for those comets that approach the Sun closely enough to lose material.
This one looks like a dirty snowball to me, with its fine tail.

Also, in view that it made its first recorded appearance in the skies of the Earth in 1385, and that it has returned every 71 years, I must say that this particular comet appears to have a lot of wind. :wink:

Ann
I think we might be seeing a very faint dust tail below the comet, but mostly it is the ion tail that is dominating things, which means that most of what's coming off this comet is volatile gases and not dirt!
Chris

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by captainwiggins48@aol.com » Tue Mar 26, 2024 3:06 pm

A bit of wordplay by APOD, visible 'during the day'. West's Comet (1976) had a nucleus that was actually visible in full daylight as a tiny brilliant companion to the sun. As far as I know, and am still astonished, I'm the only person who witnessed the event after viewing this magnificent comet during the previous night.

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Chris Peterson » Tue Mar 26, 2024 3:33 pm

captainwiggins48@aol.com wrote: Tue Mar 26, 2024 3:06 pm A bit of wordplay by APOD, visible 'during the day'. West's Comet (1976) had a nucleus that was actually visible in full daylight as a tiny brilliant companion to the sun. As far as I know, and am still astonished, I'm the only person who witnessed the event after viewing this magnificent comet during the previous night.
C/2006 P1 McNaught (2007) was even brighter than West, and was also visible in full daylight.
Chris

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Roy

Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Roy » Tue Mar 26, 2024 5:43 pm

Chris Peterson wrote: Tue Mar 26, 2024 1:40 pm
Roy wrote: Tue Mar 26, 2024 12:31 pm Still pushing the "comet is a dirty snowball" theory despite pictures, impacting one, & actually landing on one??? We know betteer.
Comets are a mix of rocky material, mostly silicates and carbonates, and volatile ices. Nothing wrong with calling that a "dirty snowball"... although depending on the mixture of rock to ice, some are better described as "snowy dirtballs". The particular constituents in a pristine comet are probably determined mainly by where they formed in the early Solar System. The composition changes over time for those comets that approach the Sun closely enough to lose material.
I would invite you to look at the Rosetta spacecraft pictures of comet Churyumov-Gerasimenko , APODs of 28Nov2021 and 15Sep2014. The comet is dark as coal, and hard rock. If i recall correctly, Rosetta's landing probe was pronged, hoping to dig in to the "dirty snowball", but it bounced off the rocks.

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Chris Peterson » Tue Mar 26, 2024 6:33 pm

Roy wrote: Tue Mar 26, 2024 5:43 pm
Chris Peterson wrote: Tue Mar 26, 2024 1:40 pm
Roy wrote: Tue Mar 26, 2024 12:31 pm Still pushing the "comet is a dirty snowball" theory despite pictures, impacting one, & actually landing on one??? We know betteer.
Comets are a mix of rocky material, mostly silicates and carbonates, and volatile ices. Nothing wrong with calling that a "dirty snowball"... although depending on the mixture of rock to ice, some are better described as "snowy dirtballs". The particular constituents in a pristine comet are probably determined mainly by where they formed in the early Solar System. The composition changes over time for those comets that approach the Sun closely enough to lose material.
I would invite you to look at the Rosetta spacecraft pictures of comet Churyumov-Gerasimenko , APODs of 28Nov2021 and 15Sep2014. The comet is dark as coal, and hard rock. If i recall correctly, Rosetta's landing probe was pronged, hoping to dig in to the "dirty snowball", but it bounced off the rocks.
A dark surface can occur on both ice and rock. And it is entirely reasonable that the outermost layer of a comet would show mostly rock, as that will be the layer where most of the volatiles will have evaporated away.

Comets are low density- much less than rock.
Chris

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Roy

Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Roy » Tue Mar 26, 2024 6:45 pm

To know density, you need to know composition and volume. Where are you getting these figures?

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Chris Peterson » Tue Mar 26, 2024 6:53 pm

Roy wrote: Tue Mar 26, 2024 6:45 pm To know density, you need to know composition and volume. Where are you getting these figures?
You don't need to know anything about composition. You need the volume and the mass. Volume is generally a direct observation, either optically or with radar. In the case of Churyumov-Gerasimenko, the mass was accurately measured by the way its gravity affected the Rosetta lander and orbiter. In other cases mass has been estimated by observing how comet orbits are perturbed by Jupiter or Saturn.
Chris

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Roy

Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Roy » Tue Mar 26, 2024 10:37 pm

Chris Peterson wrote: Tue Mar 26, 2024 6:53 pm
Roy wrote: Tue Mar 26, 2024 6:45 pm To know density, you need to know composition and volume. Where are you getting these figures?
You don't need to know anything about composition. You need the volume and the mass. Volume is generally a direct observation, either optically or with radar. In the case of Churyumov-Gerasimenko, the mass was accurately measured by the way its gravity affected the Rosetta lander and orbiter. In other cases mass has been estimated by observing how comet orbits are perturbed by Jupiter or Saturn.
I looked at the Wikipedia entry for the C-G comet. The mass is stated as 9.982x10^12 kg. Volume is stated as 18.7 km^3. Density is stated as 0.533 gm/cm^3. That is half the density of water. Ice would be twice thast density, rock five times that. The mas calculation is too small, or the volume calculation is too large - however them

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Re: APOD: Comet Pons-Brooks' Ion Tail (2024 Mar 26)

Post by Chris Peterson » Tue Mar 26, 2024 10:39 pm

Roy wrote: Tue Mar 26, 2024 10:37 pm
Chris Peterson wrote: Tue Mar 26, 2024 6:53 pm
Roy wrote: Tue Mar 26, 2024 6:45 pm To know density, you need to know composition and volume. Where are you getting these figures?
You don't need to know anything about composition. You need the volume and the mass. Volume is generally a direct observation, either optically or with radar. In the case of Churyumov-Gerasimenko, the mass was accurately measured by the way its gravity affected the Rosetta lander and orbiter. In other cases mass has been estimated by observing how comet orbits are perturbed by Jupiter or Saturn.
I looked at the Wikipedia entry for the C-G comet. The mass is stated as 9.982x10^12 kg. Volume is stated as 18.7 km^3. Density is stated as 0.533 gm/cm^3. That is half the density of water. Ice would be twice thast density, rock five times that. The mas calculation is too small, or the volume calculation is too large - however them
You are overlooking porosity. Like most asteroids, comets are highly porous.
Chris

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