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.
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.
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.
“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.”
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.