Comet ISON Will Soon Pay Mars A Visit

Illustration showing NASA’s Mars Reconnaissance Orbiter studying Comet ISON from Mars orbit in late September and early October. ISON will pass 6.5 million miles from Mars, much closer than its Earth flyby on Dec. 26 of 39.9 million miles. Credit: NASA

On October 1, Comet ISON will pass within 6.5 million miles of the Red Planet. Wish I could be there with my scope. No worries. NASA already has a telescope lined up and ready to roll. It’s called the HiRise (High-Resolution Imaging Experiment) camera on the Mars Reconnaissance Orbiter. This 19.7-inch (0.5-m) scope has been busy since 2006 snapping high-resolution photos of the surface of Mars. At best it can see niggle out details about 1 foot (0.3m) across.

Comet ISON and Mars seen from Earth on Oct. 1 when the comet makes its close pass of the Red Planet. The view shows the sky facing east around the start of morning twilight. The comet should be about magnitude 11 and visible in a medium-sized telescope. The crescent moon’s a bonus. Maps: Stellarium

On Aug. 20, Sept, 29, Oct. 1 and 2, NASA will direct  the probe’s telescopic camera at Comet ISON. Since one of those dates has already passed, expect to see images of the first attempt soon. The two remaining Mars rovers – Opportunity and Curiosity – may also get a view depending on how bright ISON becomes. On Oct. 1, if my math is correct, the comet should shine at around mag. 2.5-3.0 from Mars, making it a naked eye object.

Comet ISON will shine at around magnitude 3 low in the northern sky in the constellation Lacerta the Lizard from the Curiosity rover’s location. The map shows the sky facing north at nightfall on Mars on Oct. 1, 2013. 

As you might guess, HiRise wasn’t sent to Mars to do astronomy. Since it’s target is the bright, sunlit surface of Mars below it, the camera was set up for shorter exposure unlike a typical camera-equipped telescope.

Illustration of Comet ISON’s bright nucleus and developing tail as it makes its closest approach to the sun this Thanksgiving. Credit: NASA

“The camera is designed for rapid imaging of Mars,” said the telescope’s principal investigator Alfred McEwen of the University of Arizona. “Our maximum exposure time is limited compared to detectors on other space telescopes. This is a major limitation for imaging comets. Nevertheless, I think we will detect Comet ISON.”

Comet ISON is now at the frost line, where water ice, which comprises 80-90% of a comet, begins to vaporize. Credit: NASA with additions by Bob King

The comet arrives at an auspicious time for study. It’s now crossing the “frost line” just beyond the orbit of Mars where water ice, the most common material in comets, starts to rapidly vaporize in sunlight. Scientists and amateurs alike are hoping this will boost the comet’s brightness and tail length.

Closeup study from Mars will hopefully give us a better idea of ISON’s size. I’ve seen diameter estimates of around 3 miles, but no one knows precisely. NASA comet specialists say that if it spans at least 0.3 miles (0.5 km) ISON will likely survive its close encounter with the blazing sun on Thanksgiving Day.

16 spacecraft and every scope Earth can muster will be directed at Comet ISON as wends its way in and out of the inner solar system and back to the icebox of the Oort Cloud. It’s all part of a worldwide ISON observing campaign. To find out more and how you can get involved, click HERE. NASA video including more about the Mars flyby HERE.

12 Responses

  1. Edward M. Boll

    If a .3 mile comet can survive, then a 3 mile wide comet should have no trouble. Estimates are between these 2 amounts.

  2. Edward O'Reilly

    Such a photograph of Comet Ison(apart from the beauty of the comet itself),will be historic – the first ever shot of a comet in an alien sky. Just adds to the mystique of this wispy visitor.

  3. Edward M. Boll

    I did not work my regular job this morning. I got to sleep in till almost 6. I drove School Bus. Stepping into the house at 9 AM, the warm, very blue sky was illuminated by the Sun. But that could not overwhelm the Moon which was clearly visible. Of course the Moon was only visible because of it’s vast elongation from the Sun. Even if ISON gets as bright as the Moon on Thanksgiving Day, it is not going to be easy to see, so close to the Sun.

  4. caralex

    Bob, can you explain how the image of Ison that’s circulating on the ‘woo-woo’ sites was made – the one that makes it look like a triangular craft? I know it’s something to do with parallax, and both its own and Hubble’s movement through space, and the stacking of images. However, I can’t picture it in my mind’s eye. Can you explain how it was made? Thanks.

    1. astrobob

      Hi Carol,
      Yeah, heard about that nonsense. The explanation is very clear – the comet moved during each exposure taken through a separated color filter. Here’s an excellent explanation with lots of pix:

    1. astrobob

      Dear Arjan,
      That won’t happen for two reasons. First, Mars has no global magnetic field. Even if did have a field equal to Earth’s, magnetic interaction between the comet and Mars would be insignificant. A refrigerator magnet has a stronger field that Earth’s. Gravitational interactions play a larger part, however in this case, with the comet passing over 6 million miles from Mars, even that’s a trivial effect.


    Morning Bob.

    ISON passed Mars and now the Sun is erupting in long duration filament ~Earth facing solar eruption in progress~

    _Notice actual positions for ISON,Mars,Earth,Sun.

    Be safe and aware ~Peace.

    1. astrobob

      The filament eruption is not related to Comet ISON and/or Mars. Eruptions like there are common. If this one turns out to be Earth-directed, it might possibly spark an aurora display.

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