Of Comet ISON

THE GHOST OF COMET ISON: On Friday, Dec. 6th, leading researchers from NASA’s Comet ISON Observing Campaign (CIOC) held an informal workshop at the Johns Hopkins Applied Physics Lab. One of the key questions they discussed was, Did Comet ISON survive? It might seem surprising that anyone is still asking. After all, the “comet” that emerged from the sun’s atmosphere on Thanksgiving day appeared to be little more than a disintegrating cloud of dust. This movie from the STEREO-A spacecraft (processed by Alan Watson) shows the V-shaped cloud fading into invisibility on Dec. 1st:

The answer hinges on the contents of that cloud. Is it nothing more than a cloud of dust–or could there be some some fragments of the disintegrated nucleus still intact and potentially active?

A key result announced at the workshop comes from SOHO, the Solar and Heliospheric Observatory. According to the spacecraft’s SWAN instrument, the comet stopped producing so-called Lyman alpha photons soon after its closest approach to the sun. Karl Battams of the CIOC explains what this means: “Without getting technical, Lyman-Alpha is a consequence of sunlight interacting with hydrogen, and if we are not seeing that interaction then it means that the levels of hydrogen (and hence ice) are extremely low. This is indicative of a completely burned out nucleus, or no nucleus at all.”

“The evidence appears strong that at some point approaching perihelion – whether days or hours – Comet ISON likely began to completely fall apart,” he continues. “What remains of ISON now is going to be either just a cloud of dust, or perhaps a few very depleted chunks of nucleus. Either way, it’s not going to flare up at this point and we should assume the comet’s show is over.”

“However, we do need to verify this,” says Battams. “Hopefully the Hubble team can come to the rescue! In mid-December, Hubble will be pointed in the direction of where ISON should be and they’ll try and image something. If no fragments are surviving, or they are tiny, then Hubble will not be able to find anything, but that negative detection will tell us something: namely that ISON is indeed gone for good.”


ISON & Encke Movie

UPDATE: New ISON and Encke Movie

Submitted by Karl Battams on Fri, 11/22/2013 – 15:52
Comets C/2012 S1 (ISON) and 2P/Encke continue to race through the solar system in this updated sequence! CLICK TO ANIMATE! [Image Credit: Karl Battams/NRL/NASA-CIOC]

Here’s the latest awesome movie I have of Comet’s ISON and Encke in the NASA STEREO-A HI-1 field of view! Click the image opposite and enjoy (it’s about 4.7MB so might take a moment to load)

I’ll spare you a repeat of the details I gave yesterday, and instead will just encourage you to read that blog post, in which I describe some of the background info here, including why this movie is so amazing and why it’ll just keep getting better!

There are a couple of new things I want to say here though. First I received a good question via Twitter that was along the lines of “where exactly is the Sun relative to all this?“. I briefly mentioned it yesterday but it’s worth elaborating on a tad. The Sun sits outside of the field of view of this camera, off to the right as you look at this movie. What I’m not showing you here (purely in the interest of small file sizes) is the full field of view of this camera. Here is a full field image, complete with a CME that appears to be blasting towards the comets… Will it hit them? We’ll have to wait and see, won’t we!

Second, I want to make a note of some interesting dynamics in ISON’s tail. You’ll see that Encke has kind of long waves in the tail, whereas ISON’s seems almost like high-frequency “puffs”. Off the top of my head I can think of two possible reasons, though one is really speculative.

The less speculative (and most likely) is that ISON is simply in a faster stream of the solar wind. Imagine holding a flag on a slightly breezy day. The flag will waft gently in the breeze. Now imagine holding it in really strong winds. The flag will be rippling violently, but those ripples will be smaller in amplitude. We need to look at solar wind velocities in that area to be sure, but that’s the guess I’m planting my flag [unintended] into.

The more speculative one would be that maybe it has something to do with ISON’s rotation. But I really don’t think ISON is rotating that fast or we’d have detected it from the ground. I also don’t know that a fast rotation would show up like that anyway. I’m really just thinking out loud on this one. If anyone asks you, I’d definitely stick with the solar wind speed argument for now – it’s much safer.

I don’t know when I’ll next get more data to update this movie. The STEREO spacecraft are far from Earth and they don’t send down this high-res data in realtime, or anything close to it. Hopefully some point tomorrow I’ll get some more but – just to forewarn you – it can take up to two or three days sometimes. If that happens, it’s because of DSN schedule conflicts and not because of some “omg it’s aliens” reason. Let’s please save the tin-foil for making turkey this week, not hats! [That’s a Thanksgiving Holiday reference, for you non-US folks.] Spacecraft data connections are spotty but we will absolutely do our best to get what we can, when we can. Keep checking back, and follow my Twitter feed (link below) for the latest updates.

frfom:    http://www.isoncampaign.org/karl/updated-ison-encke-movie

The Tail of Comet ISON

COMET ISON’S SUPER TAIL: Comet’s ISON’s recent outburst of activity has done more than simply brighten the comet. Whatever exploded from the comet’s core also created a spectacularly-long tail, more than 16 million kilometers from end to end. Scroll down to see the full extent of Comet ISON as photographed on Nov. 17th by Michael Jäger of Ebenwaldhöhe, Austria:

“The tail of the comet stretches more than 7o across the sky,” says Jäger. It’s almost as wide as the bowl of the Big Dipper.

Physically, ISON’s tail is about 12 times wider than the sun. So, when the head of ISON plunges into the sun’s atmosphere on Nov. 28th, more than 15 million kilometers of the comet’s tail will still be jutting into space behind it.

Because so much gas and dust is spewing from the comet’s core, it is impossible to see clearly what caused Comet ISON’s outburst on Nov. 13-14. One possibility is that fresh veins of ice are opening up in the comet’s nucleus, vaporizing furiously as ISON approaches the sun. Another possibility is that the nucleus has completely fragmented.

“If so, it will still be several days before we know for sure,” says Karl Battams, an astronomer with NASA’s Comet ISON Observing Campaign. “When comet nuclei fall apart, it’s not like a shrapnel-laden explosion. Instead, the chunks slowly drift apart at slightly different speeds. Given that ISON’s nucleus is shrouded in such a tremendous volume of light-scattering dust and gas right now, it will be almost impossible to determine this for at least a few days and perhaps not until the comet reaches the field of view of NASA’s STEREO HI-1A instrument on November 21, 2013. We will have to wait for the chunks to drift apart a sufficient distance, assuming they don’t crumble first.”

Monitoring is encouraged. Comet ISON rises in the east just before the sun. Amateur astronomers, if you have a GOTO telescope, enter these coordinates. Dates of special interest include Nov. 17th and 18th when the comet will pass the bright star Spica, making ISON extra-easy to find.