APOD: Comet Pons-Brooks' Swirling Coma (2024 Mar 18)

[APOD Robot]

Comet Pons-Brooks' Swirling Coma

Explanation: A bright comet will be visible during next month's total solar eclipse. This very unusual coincidence occurs because Comet 12P/Pons-Brooks's return to the inner Solar System places it by chance only 25 degrees away from the Sun during Earth's April 8 total solar eclipse. Currently the comet is just on the edge of visibility to the unaided eye, best visible with binoculars in the early evening sky toward the constellation of the Fish (Pisces). Comet Pons-Brooks, though, is putting on quite a show for deep camera images even now. The featured image is a composite of three very specific colors, showing the comet's ever-changing ion tail in light blue, its outer coma in green, and highlights some red-glowing gas around the coma in a spiral. The spiral is thought to be caused by gas being expelled by the slowly rotating nucleus of the giant iceberg comet. Although it is always difficult to predict the future brightness of comets, Comet Pons-Brook has been particularly prone to outbursts, making it even more difficult to predict how bright it will actually be as the Moon moves in front of the Sun on April 8.

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[Ann]

Comet Pons-Brooks' Swirling Coma. Image Credit & Copyright: Jan Erik Vallestad

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Amazing amazing!!

Is that red stuff hydrogen alpha? Chris?

Ann

[T3chy9]

Not Ha. Comet's don't really have emission lines. Usually comets would have absorption lines, so even less Ha (Kirchhoff's Laws and Spectroscopy). Comet's can be wildly different so the cop-out answer is "it's always possible!".

In my opinion the intensity of the red and the swirl structure as a whole is largely processing artifacts. That is not to say comets can't have a spiral structure, just that what is seen here is (very) overblown.

[Knight of Clear Skies]

In my opinion the intensity of the red and the swirl structure as a whole is largely processing artifacts. That is not to say comets can't have a spiral structure, just that what is seen here is (very) overblown.

The spiral structure has been noted by other others and does appear to be real. There is a good write-up by the astrophotographer here which also shows a conventionally processed image form the same data:

https://www.astrobin.com/eqxd1j/B/

"Evidence is mounting that 12P is "cryovolcanic." The comet's surface is peppered with geysers which spew plumes of dust and icy gas into space when fragile vents are exposed to sunlight. These exhaust plumes naturally form spirals as the comet rotates."

The spiral structure is very faint compared to the coma and tail, hence the false colour version to show it more clearly.

Here's another image that shows the spiral:

https://spaceweathergallery2.com/indiv_ ... _id=203962

[T3chy9]

That is not to say comets can't have a spiral structure, just that what is seen here is (very) overblown.

Yes, I thought I was sufficiently clear about that. To date however the image you linked is the second observer reporting such a feature to that extent. It's not too difficult to use similar settings to produce a similarly sharpened result.

I mean seriously, look at it. Wouldn't you expect to see some sort of Doppler shift esq appearance? Some non uniformity in the spiral?

[thekelbell]

Hello, I'm a newbie to astronomy in general, so apologies if I ask any silly questions.

I'm wondering about why this comet in particular has a spiral shape. The APOD description said that it was caused by rotation of the comet--- but wouldn't all comets be rotating as they fly through space? Why is this comet, in particuar, rotating in such a way as to cause a spiral shape?

Thanks,
Kel

[Chris Peterson]

Hello, I'm a newbie to astronomy in general, so apologies if I ask any silly questions.

I'm wondering about why this comet in particular has a spiral shape. The APOD description said that it was caused by rotation of the comet--- but wouldn't all comets be rotating as they fly through space? Why is this comet, in particuar, rotating in such a way as to cause a spiral shape?

Thanks,
Kel

This comet has a very volatile surface and/or subsurface, resulting in large amounts of outgassing as it approaches the Sun. Most comets release their volatiles and dust much more slowly, and much more evenly over their surfaces, so the effects of their rotation aren't really visible. 12P appears to be releasing at least some through vents, like geysers. These streams of concentrated material appear to spiral because of the rotation of the nucleus.

[thekelbell]

This comet has a very volatile surface and/or subsurface, resulting in large amounts of outgassing as it approaches the Sun. Most comets release their volatiles and dust much more slowly, and much more evenly over their surfaces, so the effects of their rotation aren't really visible. 12P appears to be releasing at least some through vents, like geysers. These streams of concentrated material appear to spiral because of the rotation of the nucleus.

Oh, I see, thanks! That's really cool

Do we know what 12P is made of, and what its material differences are compared to most comets?

[T3chy9]

I stand partially corrected - according to more sources the spiral structure is quite visible, at least to a camera. Enough to give this image credibility. I still think it's overprocessed as the spiral shape probably isn't that well defined, and specifically the gradients between the spirals not that pronounced. But very cool!