Comet ISON to Fly By Mars

On October 1st, Comet ISON will pass closer to Mars than it ever will to Earth. The Red Planet’s rovers and orbiters are ready to send home postcards of the event.

Comet ISON's Mars fly-by
NASA's new animation shows Comet ISON's path through the inner solar system.
NASA's Goddard Space Flight Center Scientific Visualization Studio
In one week the (in)famous Comet ISON will make its closest approach to Mars, flying just 10.8 million km (6.7 million miles) from its surface on October 1st. All Martian eyes will be watching, including Curiosity’s, though a postcard-perfect picture is far from guaranteed.

Curiosity and Opportunity will both be watching as ISON passes overhead, but the most likely detection will come from the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter. That camera resolves 1-meter (3-foot) features on the Martian surface, but the unprecedented sharpness of its daylit landscapes doesn’t necessarily mean it will do well on a dim glow in darkest space several million km away. NASA already planned a test observation for August 20th, and unfortunately (but not unexpectedly), Comet ISON remained just below the detection threshold.

“For missions like MRO that are designed to look at a planet around which they are orbiting, turning their instruments in the opposite direction and trying to detect a fuzzy iceball is not something that’s done on a whim,” writes Karl Battams on the Comet ISON Observing Campaign blog. “It has to be meticulously planned, prepared for, and tested.”

Mars Reconnaissance Orbiter
The Mars Reconnaissance Orbiter, sailing some 15,000 miles above the Red Planet's surface, will attempt to capture Comet ISON's close passage.
MRO is also planning to look during another three observing windows: on September 29th, and October 1st and 2nd. Mars Express was scheduled to start looking yesterday (September 23rd), and the Swift spacecraft’s Ultraviolet/Optical Telescope will take observations on October 1st. For the full list of planned professional observations of Comet ISON, see CIOC’s Observation Calendar.

Regardless of how the observations of Comet ISON turn out next Monday, they promise to be good practice for Comet Siding Spring, which will come 216 times closer (within 110,000 km of the Red Planet) in October 2014.

By the Numbers

The Mars flyby is the first of several close encounters:

  • Oct. 1st: Comet ISON sails 10.8 million km from the Martian surface
  • Nov. 19th: ISON will pass closest to Mercury, with Messenger as its witness.
  • Nov. 28th: Comet ISON whips through the outer solar corona, passing within 1.2 million km of the Sun’s visible surface.
  • Dec. 26th: Assuming the comet survives its graze past the Sun, it’ll pass 64.2 million km from Earth (167 times farther than the Moon).

Watch this animation from NASA's Goddard Space Flight Center Scientific Visualization Studio to see two views of the comet’s trajectory through the inner solar system:

Or play with this interactive model of Comet ISON's orbit from visualization company INOVE.

News, Solar System
Monica Young

About Monica Young

Monica Young, a professional astronomer by training, is web editor of Sky & Telescope, where she creates, manages, and maintains website content, and contributes to the magazine.

9 thoughts on “Comet ISON to Fly By Mars

  1. Kevin Heider

    C/2013 A1 (Siding Spring) is expected to pass 0.00089 AU (133,000 km; 83,000 mi) from the center-point of Mars.

  2. Kevin Heider

    ISON’s closest approach to Mercury is 2013-Nov-19 at a distance of 0.24207 AU (36,213,000 km; 22,502,000 mi).

    From the surface of Mercury ISON would be 107 degrees from the Sun in the constellation of Orion.

  3. Michael-MartinMike Martin

    I’ve been watching ISON for about a couple of months now And it seems to be in Cancer quite a bit. Any reasoning in back of this. Clear Sies. Mike

  4. Kevin Heider

    ISON is still 2.3AU (2.3 times further from Earth than Earth is from the Sun), so apparent movement against the background sky will be slow. From 2013-Apr-27 to 2013-Aug-02 ISON was in Gemini. From 2013-Aug-03 to 2013-Sep-24 it is in Cancer. As of 2013-Sep-25 ISON is entering Leo.

  5. Anthony BarreiroAnthony Barreiro

    @ Mike Martin — where are you and what are you using to observe Comet ISON? What does it look like? As soon as the Moon wanes I’m going to give it a try.

  6. Bill

    Will all observations of ISON from Mars be lost due to the government shutdown, or were they able to program the probes ahead of time? All NASA websites seem to be down.

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