Comet ISON is rocketing its merry way across the solar system toward the sun, scheduled to make its closest approach to Sol on Thanksgiving Day.
Several planets lie between ISON and Sol, and exactly a month from now, on October 1, it will be Mars’s turn.
"Comet ISON is paying a visit to the Red Planet," said astronomer Carey Lisse of the Johns Hopkins University Applied Physics Lab in a NASA statement. "On October first, the comet will pass within 0.07 AU from Mars, about six times closer than it will ever come to Earth."
AU stands for Astronomical Unit, the distance between the Earth and the sun.
Several instruments are in place to watch ISON’s Mars flyby, said NASA in the statement. Astronomers will glean information to determine the size of the comet’s nucleus and try to further refine predictions about whether it will survive its brush with the sun. The Mars Reconnaissance Orbiter is the best situated satellite for observing the comet as it cruises by the Red Planet, but a full 16 giant telescopes and satellites will be trained on the icy chunk.
Scientists were elated a couple of years ago when comet Lovejoy plunged into the sun and survived, sporting a brand-new tail when it emerged.
Depending on how large it is and how well it endures its journey into the sun’s atmosphere, comet ISON has the potential to shine as brightly as a full moon when the time comes. Study of the nucleus’s size could help predict what the comet will do and its likelihood of coming out alive.
If ISON fares as well as Lovejoy did, it will be an epic sight reminiscent of the shooting star that gave Tecumseh his name—only brighter and longer lasting.
NASA closely observed the comet on August 20 and will do so again on September 29 as well as October 1 and 2, when it is going right past Mars, the space agency said. By then it will have crossed the solar system’s frost line and be receiving enough heat from the sun that the nucleus will begin to melt and the tail will begin to form. The frost line is the distance from the sun at which the icy bits—which comprise 80 to 90 percent of the comet’s nucleus—begin to vaporize.
Once that happens, "the whole comet could erupt in geysers of gas," said Lisse in the NASA statement. "Mars orbiters will have a ringside seat."
Below, NASA goes more into depth.