[meteorite-list] Deep Impact Observes Comet C/2012 S1 (ISON)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 5 Feb 2013 12:55:33 -0800 (PST)
Message-ID: <201302052055.r15KtXRt025371_at_zagami.jpl.nasa.gov>

http://epoxi.umd.edu/3gallery/cometISON.shtml

DIF Observes ISON

Comet ISON, just discovered in September 2012, is expected to become
more observable by amateurs
<http://science.nasa.gov/science-news/science-at-nasa/2013/18jan_cometison/>
later this year. As part of an extended observing campaign, the comet
was imaged by the Deep Impact Flyby (DIF) spacecraft over a 36-hour
period in mid-January while the comet was 5.1 AUs from the sun and 5.3
AUs from DIF. 146 images were collected using a clear filter in the MRI
<http://deepimpact.umd.edu/tech/mri.html> every 15-minutes from Jan 17
03:40 UT to Jan 18 16:20 UT. Scientists have many ways of processing and
analysing the images. Here we highlight two ways the 146 images were
used. (North is up, East is to the left, and the Sun is to the left.)

      
Technique 1: Stack and Add

[Image of comet ISON as imaged by DIF 17-18 Jan 20113]
Image 1: This image of comet ISON (C/2012 S1) combines all 146
80-second clear filter exposures for a total integration time of 11680
seconds (about 3.25 hours). Individual frames were shifted to align the
comet at the center before coadding. By keeping the comet centered and
adding all of the images together, the stars effectively get smeared so
the long streaks are the trails of background stars.

Although the comet is 5.1 AU from the Sun and 5.3 AU from the
spacecraft, and required a long exposure, it shows a diffuse nucleus and
an anti-sunward tail indicating that it is already active. Although the
tail appears short and stubby in this image, it is at least 65,000 km
long and, due to projection effects, could be significantly longer.

      
Technique 2: Align and animate

Animation 1: Movie of comet ISON (C/2012 S1) on January 17-18, 2013 as
seen from the Deep Impact spacecraft. Here the 146 images are once again
aligned on the comet at center. But instead of adding all of the images
into one, each image is shown sequentially. The most obvious is the
motion of the comet. But by measuring the brightness of the comet in
each frame, we can see the brightness of the coma changing by about 6-7%
over the course of the sequence.

Image 1/Video Credit:* NASA/JPL-Caltech/UMD (Tony Farnham)

Comet ISON in relation to DIF, Sun, and Earth

At the time the 146 images were collected, the comet was 5.1 AU from the
Sun and 5.3 AU from the spacecraft.


Comet ISON background

What sets comet ISON apart from most other comets is that it is a
sungrazer, a class of comet that passes very close to the Sun's surface.
On November 28, 2013, comet ISON will reach perihelion (its closest
point to the Sun) at a distance less than 3 solar radii. Although they
are numerous, most comets of this class are very small and faint, and
don't survive their close approach to the Sun. Those that do, however,
tend to be very spectacular. ISON became active when it was over 5 AU
from the Sun (beyond Jupiter's orbit), which means it is different from
more typical sungrazers and may have a nucleus large enough to survive
its perihelion passage.

Because ISON could potentially become the next "Great Comet",
astronomers around the world are planning studies to characterize its
behavior leading up to, and hopefully following, its solar passage. Of
particular interest will be observations of ISON when it is very close
to the Sun where extensive comet studies are rare. NASA is participating
in this campaign and the data collected by Deep Impact represent the
first spacecraft observations to be obtained in the effort.


      Other links

    * NASA Science News: Comet of the Century?
      <http://science.nasa.gov/science-news/science-at-nasa/2013/18jan_cometison/>
    * SOHO comet movies
      <http://sohowww.nascom.nasa.gov/gallery/Movies/comets.html>
    * Sungrazing Comets <http://sungrazer.nrl.navy.mil/>


Where is comet ISON?

Orbit Viewer applet originally written and kindly provided by Osamu
Ajiki (AstroArts), and further modified by Ron Baalke (JPL).
original page

<http://neo.jpl.nasa.gov/orbits/epoxi1.html>

If you'd like to check out the interactive orbital displays for other
comets and asteroids, please visit the NEO Program

<http://neo.jpl.nasa.gov/orbits/>.


Where do I look in the sky?

The above graphic is pretty cool, but how will it tell me where to look?

Be sure to take a look at Reading an Orbital Diagram
<http://aop.astro.umd.edu/where/howto.shtml> to get some basic
background on interpreting this graphic and what the sliders and other
adjustments do.
Received on Tue 05 Feb 2013 03:55:33 PM PST