A once-in-a-million-year close encounter comes to Mars on Sunday. A comet will zoom past the red planet, and space observers are ready.
A flotilla of spacecraft will enjoy a ringside seat, precariously close as the speeding mountain-sized snowball barnstorms the red planet and swings its debris-filled tail around the nearby world.
Comet Siding Spring (C/2013 A1) will make the historically close approach to Mars, passing only 87,000 miles (140,000 kilometers) away at 2:28 p.m. EDT on October 19. That makes the flyby an astronomical squeaker, since it is less than half the distance that separates Earth from the moon. In fact some astronomers expect Mars to pass through the debris tail of the comet, although NASA officials downplayed that possibility at a recent space agency briefing.
Discovered by Australian comet hunter Robert McNaught early last year, the comet has been tracked by NASA as it falls in toward the inner solar system, allowing scientists to refine the comet’s exact trajectory.
Duck and Cover
While NASA initially worried about a small risk of collision with Mars, it has since ruled out any chance of impact. Instead, spacecraft and rovers will see the closest approach of a comet with our neighboring planet ever observed. Because the comet is speeding by at a whopping 126,000 miles per hour (202,800 kilometers per hour), mission controllers are still a bit nervous for the safety of their spacecraft circling Mars.
As the comet violently sheds material into space at the time of closest approach, no one knows how much gas and dust will be left in its wake. And because Mars might travel through the debris tail of the comet, mission controllers from the U.S., European, and Indian space agencies are taking precautions against any possible impacts. When particles the size of sand grains travel at high speeds and hit spacecraft, they can damage electronics and fuel lines, even to the point of rendering them unusable.
Mission engineers will rely on a “duck and cover” strategy with their orbiters, sending them to the opposite side of the planet for 20 minutes during the peak danger time—about an hour and half after the comet’s closest approach. Mars itself should shield the spacecraft from any debris.
Cosmic Time Capsule
Comets are exciting for astronomers to study up close because they are considered time capsules left behind from the birth of the solar system nearly five billion years ago.
Astronomers are champing at the bit, too, because they believe this to be a long-period comet that originates from the Oort cloud, a giant frozen reservoir of billions of comets that envelopes the solar system far beyond Pluto.
Every once in while one of these ice balls receives a gravitational tug out of its slumber, which sends it dive-bombing the sun, only to head back out again to the Oort cloud. Astronomers think this might be Siding Spring’s first trip into the inner solar system in at least a million years. And this would be our first chance ever to see one of these mysterious long-period comets up close.
If true, that means the comet is a pristine remnant of the solar system’s early formation. Analysis of the icy visitor may reveal chemistry that harks back to the birth of the planets, including the Earth.
If you want to follow the action live, tune in for some live webcasts from telescopes here on Earth, via SLOOH astronomy outreach venture’s double broadcast. The first broadcast begins at 2:15 p.m. EDT (1815 GMT) on Sunday, October 19, and the second starts at 8:30 p.m. EDT (0030 October 20 GMT). You can also check out the Virtual Telescope Project, which will feature live views of the comet as it passes Mars, beginning at 12:45 p.m. EDT (1645 GMT).