Latest Updates on Comet ISONOnly a dim "ghost of ISON" survived the comet's November 2. Sun. The comet's head dwindled away as it raced through the Sun's greatest heat, but a headless streak emerged into spacecraft view out from the other side of the encounter. It's traveling along the comet's originally prescribed track but fading steadily, with no sign of cometary activity.
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Nothing will be visible by eye from Earth. UPDATES: December 1: Goodbye from SOHO, and a CBET summary. The dimming wisp of ISON's dust departed from SOHO's LASCO C3 field of view early today; it's at the 1 o'clock edge of this image.
If it appears a little brighter in images from the STEREO- A spacecraft, shown here, that's only because the camera is more sensitive. Dan Green of the International Astronomical Union's Central Bureau for Astronomical Telegrams published a long summary (Electronic Telegram No. Excerpts. The comet's nucleus apparently disrupted near perihelion, with the comet's head fading from perhaps a peak brightness of visual mag –2 some hours before perihelion to well below mag +1 before perihelion. M. Knight, Lowell Observatory.. SOHO coronagraph occulting disk on Nov. Nov. 2. 9. 9. 8. . K. Battams, Naval Research Laboratory, writes that, based on the most recent LASCO C3 images (Nov.
UT) . . . what remains is very diffuse, largely transparent to background stars, and fading; it appears that basically a cloud of dust remains. Z. Sekanina, Jet Propulsion Laboratory . The strong forward- scattering effect (phase angles near 1. Hubble will have a look for the remnant once it moves far enough from the Sun for Hubble to safely point at it, in mid- December. November 3. 0, 6 p.
EST: More fading, and Bortle revises his forecast. John Bortle withdraws his relatively optimistic forecast posted yesterday. He writes. The comet's appearance only suggests a progressive decline now. While ISON's photometric behavior up to and around perihelion did seem to mimic that of 1. Comet Seki- Lines, the failure of ISON's current cloud- like coma to exhibit any area of condensation as the cloud thins, and its fading and growing diffuseness, do not correspond to Seki- Lines' post- perihelion regeneration. To be similar in behavior with C/Seki- Lines, ISON would be developing an increasingly small, dense, very bright condensation within the coma. Likewise, the intensity and length of the tail(s) would be rapidly growing, just as we saw in the case of 2.
W3 Lovejoy following its perihelion. Following a 2- to 4- day blind period after the comet leaves spacecraft view, Bortle expects only a "large, low- surface- brightness, diffuse cloud showing just a trace of tail" — in other words a challenge object for skilled astrophotographers and image processers, not visual observers — if anything at all. November 3. 0, 9 a. EST: Fading continues; no activity.
Filip Fratev posts again (at 8: 1. UT this morning), "just measured another drop of 0. UT). Thus it is in the range of magnitude 3. The later LASCO C3 image from 1. UT shows the fading very obviously. He posts again at 1.
UT; "ISON's brightness has dropped rapidly. I estimated the comet as between about 4. Magnitude decrease was almost 0. Jacob Czerny notes that the comet remnant is fading at the rate expected of a simple, inactive debris cloud moving farther from the Sun's illumination. Watch Wicked Schoolgirls Online Freeform on this page.
In addition it is expanding, which means its surface brightness is dimming even faster than its total brightness. As for what looks like a new comet tail? That turns out to be well modeled by the trajectories of particles that ceased to be emitted at perihelion two days ago. Explains Hermann Böhnhardt (Max Planck Institute for Solar System Research), "If we assume in our calculations that the comet has emitted dust at perihelion, we can reproduce the current images quite well.".
Here's the latest blog article from the indefatigable cometary scientist Karl Battams: In ISON's Wake, a Trail of Questions. With great new movies from the STEREO A and B coronagraphs. Key takeaway. It does seem unlikely that there will be much to see in the night sky. I suspect that some of the outstanding astrophotographers around the world will be able to get something, but I doubt it will be as spectacular as before perihelion. I hope I'm wrong though. November 2. 9, 1. EST: A fading ghost.
At 1. 9: 5. 4 UT Filip Fratev (Bulgarian Acadamy of Sciences) wrote, "ISON [has] started to fade.. In] the last four hours it faded by more than 2 magnitudes and obviously is less bright.. I estimated the comet to be between 2. Four hours later Karl Battams of the Comet ISON Observing Campaign tweeted, "We can't tell if #ISON is in one piece or many. It's about mag 5 now and fading."November 2.
EST: A bold forecast. Longtime Sky & Telescope comet writer John Bortle, who's been covering these objects since the 1.
Here are some things I garner from the 1. UT image taken today by the SOHO LASCO C3 camera. Since yesterday's 'resurrection,' the comet's overall dust output has clearly increased dramatically as compared with its pre- perihelion situation. Likewise, early yesterday the dust production appeared to consist almost exclusively of 'very heavy' dust particles. My impression this morning from the latest SOHO and STEREO images is that the comet is now experiencing a huge and ongoing dust release in a broad range particle sizes. If this continues, it is a very hopeful sign for visual observers in days to come. I've mentioned several times that 1.
Comet Seki- Lines is the one other modern, dynamically 'new,' truly sunskirting comet whose photometric behavior is known in some detail. It likewise experienced a strange 'disappearance' right about the time of an anticipated brightness surge at perihelion, which had been expected to bring it to naked- eye daylight visibility at around magnitude –7. A quick glance at ISON's appearance in the 1. UT SOHO image jogged my memory that it looks very much like another comet photo I saw long ago . Comet Seki- Lines! One of the earliest post- perihelion photos of Seki- Lines was one taken by, I believe, the great comet photographer of the 1. Alan Mc. Clure. It showed a strangely wedge- shaped, large, brilliant coma forming the beginnings of a huge, broad, tail created by an obviously wide range in dust- particle sizes.
Sound familiar? "5. Although ISON's overall magnitude and degree of coma condensation appear reduced from last week, it still looks like a rather bright object that could well put a nice, if likely rather truncated, display between December 1st and 1. If (still a big if this early) ISON continues to exhibit intense dust production and retains sufficient ices to drive activity for a short time (perhaps less than a week could suffice), a broad tail of considerable size may quickly develop. As with 2. 01. 1- 1.
Comet Lovejoy, it would be impressive mainly from dark- sky observing sites due to rapidly diminishing surface brightness as the object withdraws from the Sun. The comet's 'head' will probably be tiny in comparison with the tail and might even be difficult to define with the unaided eye.". November 2. 9, 1. EST: "Reports of my death are exaggerated." After the comet seemed to vanish at perihelion yesterday, no one expected to be looking at a picture today like the one above! It sure looks like a comet from here.
The big question: is that bright thing just a cloud of dust and very fine rubble, soon to disperse?
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