Huge comet outburst reported, 17P/Holmes Options

[djellison]

They would be able to see it - without a shadow of a doubt - IF it's the same shape and size as seen from Mars as it is from Earth. It's not THAT much closer when at Mars - much of the distance from Earth to the Holmes is the out-of-ecliptic distance - perhaps it's 1/3rd closer. But even at the Earth range, it would be easily visible in Navcam as a bright star, and possibly even resolved as a tiny fuzzy dot in Pancam.

However - we are far from the heady days of >850 Whrs when we did astronomy from atop Husband Hill - so it'd be quite an 'ask' in terms of power etc.

As for other spacecraft observing it - they could do - not sure if they'd want to go the effort involved though.

Doug

[ynyralmaen]

Again, no idea of brightness, sorry.

On the Yahoo group comets-ml, a subscriber named perryhelion estimates it as magnitude +1.2 from Mars.

[AndyG]

Settings: 400ASA, "cloudy", "centre spot metering...

Should have used the Flash, Stu - and come back a few minutes later to open the shutter!

Andy

[nprev]

Please be sure to warn us if anyone employs a flash powerful enough to light up Holmes; think we'd all appreciate having time enough to take cover...

Couldn't see it last night, BTW; it actually got cloudy in LA, and we have a 30% chance of rain! (This is astonishing to us old US people, because of course we know that it never rains in southern California... )

[ugordan]

Please be sure to warn us if anyone employs a flash powerful enough to light up Holmes; think we'd all appreciate having time enough to take cover...

That's why he spelled Flash with a capital F

[ed_lomeli]

On Wednesday and Thursday last week, at first glance, the yellow color was most striking to me. The yellow color is still there but not as intense. I've taken video on 3 days through a 4 inch refractor with a webcamera, sometimes dodging the clouds.

http://www.youtube.com/watch?v=qtw-ncS75uo

[nprev]

Hey, that's neat, Ed; thank you!

Question though: Why isn't there any apparent motion relative to the stars in the field? Is this thing receding almost directly away from our line of sight (since it seems to be getting dimmer)? Not a criticism, it's just interesting...never seen a comet do that before.

[ilbasso]

Glorious! Had a beautiful view of it this evening. I even persuaded my wife, who has a broken knee, to make the trek with her walker out into our driveway to see it, using my 20x80 binoculars. The comparison to M13 is apt, but this is MUCH brighter. Sky and Telescope calls this "the strangest comet to burst onto the celestial scene in our lifetime." I believe it!

[ed_lomeli]

Hey, that's neat, Ed; thank you!

Question though: Why isn't there any apparent motion relative to the stars in the field? Is this thing receding almost directly away from our line of sight (since it seems to be getting dimmer)? Not a criticism, it's just interesting...never seen a comet do that before.

The comet reached perihelion with the Sun back in May so its distance from the Sun has been increasing while Earth will reach its closest approach to the comet (1.62 A.U.) between November 5-7th. Holmes is currently both moving away from Earth and getting closer to Earth, huh? Incidental with the timing of the comet's outburst, if I have it right, the Earth's orbit must be taking us in the same direction as the comet but at a slightly higher relative velocity thus allowing us to try to catch up until next week; after then, the comet's relative velocity will not be offset by Earth's velocity. BTW, that was 110 consecutive frames of raw video @ 2.75 sec/frame.

The dimming, a wild guess, the source of the dusty material may've ended its eruptive phase, but the expansion of the material already ejected would continue, resulting in a shell of debris, which would eventually dissipate.

[alan]

The comet reached perihelion with the Sun back in May so its distance from the Sun has been increasing while Earth will reach its closest approach to the comet (1.62 A.U.) between November 5-7th. Holmes is currently both moving away from Earth and getting closer to Earth, huh?

I haven't taken a look at its orbit but I suspect Holmes can both recede from the sun and be getting closer to Earth if its orbit is bringing it closer to the ecliptic.

[mhoward]

It's huge! I had only a rough idea where to look, and noticed it as a fuzzy star, even in the bright-sky suburbs here. Through 10x50 binoculars, it's amazing! Much bigger and brighter than I was expecting.

[ElkGroveDan]

I've been putting it off, but it's a perfect night here. We had a small thunderstorm pass over and then the skies cleared.

It sure is easy to find. Face Northeast and look up with binoculars.

Just wow.

[dvandorn]

Using Ed's excellent video as my reference, it looks to me like the nucleus -- the actual cometary body -- is located significantly to the upper left of the center of the apparently spherical coma around the comet.

In addition, although my eyes may be playing tricks on me, I can convince myself that I see the faintest of traces of linear features within the coma emanating from the nucleus "in" to the somewhat denser center of the coma.

I ask myself about the dynamics of such a violent eruption. I'd have to guess that such a cloud of gas and dust, which has expanded to be larger than Jupiter in physical size, would have to have quite a bit of mass entrained within it. In other words, it seems like an *awful* lot of mass shot off that comet all at once. And if the faint linear features I think I can see are really there, then the mass shot out in a pretty straight linear column, forming a center of an expanding cloud at the place where the comet *was* when the explosion occurred, not anywhere near where the comet is *now*... the energy of the release being sufficient to separate the comet from the center of the expanding cloud.

Are there models out there that allow for such an energetic release of material from a comet? Could you actually get the pressures and temperatures in the ices and dust and rocks that make up the comet for an explosion of this magnitude?

Or do we need to be thinking about impact processes, here?

Obviously, you can postulate an impactor within the Solar System both big enough and with a large enough relative speed in re the comet to have done this. Can you also postulate an endogenous process that would account for it as easily?

-the other Doug

[Stu]

Just been enjoying some gorgeous views of the comet here before dawn breaks over the Lake District... it's a remarkable sight in my humble 4.5" reflector, and I'm pretty sure that the coma looked lop-sided this morning, not so much spherical as last night, more like a gibbous Moon... anyone else think that?

[ed_lomeli]

In addition, although my eyes may be playing tricks on me, I can convince myself that I see the faintest of traces of linear features within the coma emanating from the nucleus "in" to the somewhat denser center of the coma

I don't think your eyes were deceiving you An image showing what appear to be inner jets.
http://www.digitalsky.org.uk/comets/2007-1...Holmes_800n.jpg

Measurements made before Holmes outburst estimate its nuclear diameter to be 3.4 km. And whatever portion of the nucleus, I'm guessing a small portion, that was released is spreading over a huge area with a coma that could extend from tens of thousands of miles or more from the nucleus. Measurements of Comet Halley by Giotto, for example, provided a nucleus size of "15 by 8 km, an estimated total volume of 500 cu km, a mass of 10 to the 17th grams, bulk density from 0.1 to 0.8 gram/cu cm, and a surface temperature of 300 to 400 K for the inactive crust that seems to cover 90 percent of the nucleus." Hale-Bopp's nuclear diameter was estimated to be somewhere between 40-70km.

An interesting image which appears to show a blue-green gaseous outer halo and the dusty inner halo. http://www.spaceweather.com/comets/holmes/...e-Lawrence1.jpg

(post edited to remove excessive quoting - doug)