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.