This Tuesday, Oct. 1, NASA will again attempt to do something that has never been done before: photograph a comet from another world. Various spacecraft on the surface and in orbit around the Red Planet will have ringside seats to Comet ISON’s close pass as it continues its kamikaze dive toward the Sun. The comet is currently cruising into the inner Solar System, and on Oct. 1 it will come within 0.7 Astronomical Units ( 6.7 million miles) of Mars—about six times closer than it will ever come to Earth.
The comet, discovered by Russian astronomers in September 2012, is making its first appearance in our neighborhood and could become the most fantastic comet any of us will see in our lifetimes. Or, it could fizzle into nothing and be no more “spectacular” than comet Pan-STARRS was this past spring (barely visible to the naked eye, if at all). Being that ISON has never visited the Sun, the pristine matter from the earliest days of the Solar System’s formation still coats the comet’s surface, which presents an incredibly rare opportunity to researchers around the world to take advantage of the knowledge hidden in this time capsule from when the Solar System first formed. All of those secrets about the formation of the Solar System that are hidden within the comet are expected to explode into space (literally) as the comet heats up on its approach to the Sun.
Video Credit: ScienceAtNASA
But before ISON meets the Sun this Thanksgiving, it must pass Mars. NASA and European Space Agency satellites and rovers at Mars will be ready, positioning themselves and their cameras toward ISON as it plunges toward the Sun. The comet has already passed what is known as the “frost line,” as recent imaging shows a greenish color to the comet—a sure sign that solar heating is hot enough now to start vaporizing frozen water on ISON’s surface as it gets closer.
An unprecedented number of spacecraft (16 in all), as well as astronauts aboard the International Space Station and astronomers around the world, are working together to observe the comet as it passes through the inner Solar System. ISON’s visit is unique because no “first time visitor” has entered the inner Solar System at any point in recorded history, which presents a rare research opportunity. Both rovers, Curiosity and Opportunity, will be ready on Mars for ISON’s fly-by, although nobody knows whether or not they will see anything worth photographing because ISON is not as bright yet as astronomers had initially hoped. Not only that, but none of the spacecraft on or orbiting Mars has gear for imaging such a subject—their equipment is tailored for Martian observations, not comets. However, NASA’s Mars Reconnaissance Orbiter, or MRO, stands the best chance of photographing the comet’s pass, as it is equipped with a powerful telescope named HiRISE, which can detect the comet’s atmosphere (coma) and tail.
“The camera is designed for rapid imaging of Mars,” said Alfred McEwen of the University of Arizona, principal investigator for the HiRISE telescope. “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 opportunity to photograph ISON from Mars is not just an opportunity for pretty pictures, but also to determine, hopefully, the true size of ISON’s nucleus, which can help predict better how ISON will perform as it comes within 1 million miles of the Sun’s surface in late November. Perihelion, the time when the comet is closest to the Sun, will occur Nov. 28 when ISON dives to within 720,000 miles of the Sun’s surface. Nobody is sure if ISON will survive its suicidal plunge, but if it does astronomers expect quite a show in Earth’s night sky for several months after.
“If ISON’s nucleus is much bigger than 0.5 km, it will probably survive its Thanksgiving Day brush with the Sun,” said astronomer Carey Lisse of the Johns Hopkins University Applied Physics Lab. “It could turn into one of the most spectacular comets in many years.”