Tadpole Comet Swims Under Deep Impact’s Gaze

Video of Comet C/2012 S1 ISON compiled from images taken by NASA’s Deep Impact spacecraft on Jan. 17-18, 2013.

Comet ISON looks like a tadpole in the video, but we all know that tiny tadpoles grow into big green frogs. So will the comet when it brightens to naked eye visibility later this year. Well, not a frog exactly. A great comet is more like a colossal tadpole with a long, bright tail that can stretch many degrees across the sky.

NASA’s Deep Impact probe, the one that gave us amazing closeup pictures of comets Tempel 1 and Hartley 2, is back in the business of comet watching. NASA directed the spacecraft to track and image Comet ISON as part of a campaign to learn all we can about this frozen ball of ice and dust during its first trip to the inner solar system.

Comet ISON photographed on Jan. 20, 2013 using the Vatican Observatory’s 72-inch telescope. A short tail, fuzzy coma (comet atmosphere) and bright nucleus are visible. Inside the nucleus is the comet body itself, believed to be about 2 miles across. We can’t see it directly because it’s shrouded by its own gas and dust. Click photo to learn more. Credit: Carl Hergenrother

Like Comet C/2011 L4 PANSTARRS, ISON is believed to come from the Oort Cloud, a gigantic, spherical reservoir of comets in the distant outer solar system that reaches a third of the way to the nearest star system, Alpha Centauri. As the sun travels around the center of the Milky Way galaxy, gravitational nudges from neighboring stars can give an Oort Cloud comet a little push and send it falling toward the inner solar system.

The ensuing sun-bound voyage is THE definition of a slow boat to China. It takes millions of years for a comet like ISON to inch toward the inner sanctum, but when these first-timers finally get a taste of the sun’s heat, pristine, dust-laden ices are quick to vaporize.

Artist depiction of Oort Cloud, sphere filled with millions of inactive comets extending some 9 trillion miles from the sun. In 1932 and again in 1950 astronomers Ernst Opik and Jan Hendrik Oort postulated the existence of the cloud to explain where comets with long orbital periods originate.

When the photos were taken, ISON was 493 million miles from the spacecraft or about as far as Jupiter is from the sun. Despite this vast distance, we can already see a haze of gases called the coma from vaporizing ice and a short tail more than 40,000 miles long pointing southeast. Amateur astronomers have recorded a similar appearance with telescopes and cameras here on Earth.

Comet ISON is a hot topic whether you’re a professional astronomer, amateur or brand new to skywatching because it belongs to a special group of comets called sungrazers. As the name implies, these comets passed exceptionally close to the sun before swinging back out into the depths of space. ISON will arc only 130,000 miles from the sun or a little more than half the Earth-moon distance on November 28, 2013. Assuming the comet doesn’t break to pieces under the intense heat and gravitational stress, we should see a long-tailed spectacle with the naked eye both before and after closest approach.

Comet McNaught (C/2006 P1) was our most recent “Great Comet”. As the photo attests, it was a spectacular sight in mid-January 2007 for skywatchers in the southern hemisphere. Some predict Comet ISON has what it takes to become the next great comet. Credit: NASA

Although I don’t have the details on the comet’s size, many astronomers believe ISON is big enough to survive intact and make for a great show this fall and winter in both northern and southern hemispheres.

Have no fear about any effects on Earth except for jaws dropping in wonder (assuming predictions hold true); Comet ISON will only come as close as 40 million miles on Dec. 26, 2013.

14 Responses

      1. karen Homes

        Great – thank you Astro Bob ……… Look forward to reading it .
        Im a big fan !! and read your blog daily.

      2. Dean

        Bob, how can someone assume a 0 impact risk? Unless you are able to calculate all orbits of all particles and masses in the universe simultaneously and validate that there is no way any series of impacts or gravitation influences would result in any of them ever impacting Earth, that statement cannot be made. While near term impact risks can be calculated, I would assume that longer term risks are not so easy?

        1. astrobob

          Hi Dean,
          Since the questioner was referring to this apparition only, that would be an accurate assessment. I agree that future apparitions might result in probabilities greater than zero. Just to be completely accurate however, I probably should have said “essentially 0”. One must be careful with words like ‘zero’, ‘forever’ and ‘never’ 🙂

  1. Steven

    Love your daily articles Astrobob, I really do. And I so hope ISON will be visible. Seeing photos of a comet is one thing, but actually seeing it in the sky… I can still clearly remember seeing Jupiter for the first time trough a telescope, wow.

    Btw, I hope it’s okay to go offtopic here, but is there already an explanation for the latest ‘strange thing’ found by Curiosity? Don’t get me wrong: no doubt there’s a normal explanation for it, but it does looks weird doesn’t it? http://mars.jpl.nasa.gov/msl-raw-images/msss/00173/mcam/0173MR0926019000E1_DXXX.jpg (near the bottom)

    1. astrobob

      That is a cool object Steven. First time I’ve seen it. I know Curiosity is in area where there are number of rocks on “pedestals” due to erosion processes. My first guess is that – a pedestal rock that’s been polished by the wind. Anyone else want to hazard a guess?

  2. Wayne Hawk

    Aloha Astro Bob and Everyone!

    Seems that you’re getting one inquiry about 2012 DA14 almost every day! This NEO appears to be causing just as much concern as the “Mayan Doomsday” myth. Another reason some folks may be watching this more closely is due to the fact that a television show (on NatGeo, Discovery or History) that aired very recently described the “dinosaur killing” asteroid and how it is impossible to predict exactly when the next one will hit, “possibly extinguishing all of human life”. Having those kinds of TV shows on with NEO’s entering earth’s atmosphere closer than the satellites don’t exactly make the general populous feel “calm” about these things. You know the media will “milk” all they can out of this one…anything for “ratings” it seems. Remember the movie “Network”? Everytime I see something where a human being gets hurt and everyone thinks it is funny, I can’t help but think of that movie. But I digress…

    I really wanted to comment on how amazed I am that the Vatican has a 72 inch telescope and an observatory! I know it’s been there for quite some time (the observatory, not the 72 inch telescope), but look how long after Galileo it took before it was finally an accepted fact that the earth wasn’t the center of the universe and it was built/allowed! Now we get some great photos from the Vatican that Galileo would have loved to see.

    Sometimes I can’t help wondering just how much further along the technological path we’d be if organized religion stuck to “faith” and kept its nose out of science. I know, old argument. In any event, I’m sure happy we finally got out of the “dark ages” and even the Vatican can accept the universe as God made it.

    1. astrobob

      It’s interesting that the Catholic Church has been more supportive of science than some other major faiths. There’s even a Vatican astronomer and he curates a large collection of meteorites belonging to the same.

  3. Edward M. Boll

    As of Feb.6, I hope toward a magnitude of 6.0 for Bressi, 3.1 for Lemmon and -0.4 for Panstaars as of their brightest.

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