What a surprising comet this has been, even from the start when discovered in September 2012. It has defied predictions. It was hyped as the comet of the century. One thing is certain. It got a lot of attention and continues to surprise.
ISON plunged toward the sun gaining speed and brightness. During the hours before closest approach, or perihelion, it brightened, then dimmed and seemed to no longer have a tail. The highest resolution imagery during the closest approach distances by the SDO spacecraft didn’t show anything. It started to show a tail and increasing brightness as it departed. That was a surprise. This 15 sec video records the approach, perihelion, and departure. Replay it several times. Look for ISON to dim as it neared the Sun. Notice it is barely visible upon re-emergence. Then, it brightens considerably. The black disc in the center has an image of the Sun superimposed. The disc blocks the bright sunlight from entering the camera and obscuring the view.
Here are three frames for comparison as ISON departs the Sun. The comet appears to brighten. This puzzled astronomers. They thought it had been destroyed during the intense heat of the close pass. These images are from late Thursday night the 28th and early to midday Friday the 29th.
This next image is from very late Friday to early Saturday 30th UT. It appears to show ISON again dimmer. What is will do the next few days is not known.
One of the more informative articles about ISON came from Karl Battams at the U.S. Naval Research Laboratory in Washington, DC. He is an astrophysicist and computational scientist based in the solar physics group at NRL. Here is the link to his blog post late Thursday night after he had intensely followed ISON and tried to field questions and give reasonable answers. I offer a few quotes.
I’ll just say this upfront right now: whatever you read in the following blog post, please feel free to assume it is completely incorrect and the truth is actually quite contrary to what I’m saying. It has been – and continues to be – one of those days. So this will be a relatively brief blog post because we’re up to our necks in media inquiries and attempting to do real science to figure out the mystery that is comet ISON.
Right now, here’s our working hypothesis: As comet ISON plunged towards to the Sun, it began to fall apart, losing not giant fragments but at least a lot of reasonably sized chunks. There’s evidence of very large dust in the form of that long thin tail we saw in the LASCO C2 images. Then, as ISON plunged through the corona, it continued to fall apart and vaporize, and lost its coma and tail completely just like Lovejoy did in 2011. (We have our theories as to why it didn’t show up in the SDO images but that’s not our story to tell – the SDO team will do that.) Then, what emerged from the Sun was a small but perhaps somewhat coherent nucleus, that has resumed emitting dust and gas for at least the time being.
This has been fun to watch. Many of us have waited with high expectations for over a year wondering what it would do. It was exciting to watch the astronomy community come together and focus their attention with powerful instruments on the comet. It was great to have a wealth of internet tools available to all for watching the events unfold. I have also enjoyed sharing what I have found with readers. Someday, we will be blessed with another comet, or an eclipse, or something else unexpected. I can’t wait.