A comet soared past Mars today (Oct. 19) in a rare close encounter that researchers called a "once-in-a-lifetime" occurrence that could help scientists better understand the earliest days of our solar system.
Comet Siding Spring came within just 87,000 miles (139,500 kilometers) of the Martian surface at 2:27 p.m. EDT (1827 GMT) on Sunday, or about one-third of the distance between Earth and the moon.
The comet went past Mars at about 125,000 mph, NASA officials said.
All seven spacecraft operating on or around Mars were scheduled to observe the flyby, with the goal of learning more about comet composition and "behavior," according to Space.com.
"We cannot plan missions to comets like this, this one was discovered less than two years ago. It is incredible luck that it is saving us the trouble of going to it, as it flies by Mars, which is being explored by seven active robots," Mark Lemmon of Texas A&M University, a camera team member for NASA's Curiosity and Opportunity Mars rovers, said in a statement. "So this very much is a once-in-a-lifetime event, for us and our rovers."
Planetary scientist David Grinspoon, who tracked Comet Siding Spring flyby in real-time during a live webcast by the Slooh Community Observatory, compared the significance of the event with the impact of Comet Shoemaker-Levy 9 with Jupiter back in 1994.
"It's very rare," Grinspoon said of such a close encounter. "And it's certainly the first time that I can think of that I've seen it happen with Mars."
Scientists are now looking forward to use the orbiters' observations to gain insight into the origin of the solar system.
"We're glad the spacecraft came through. We're excited to complete our observations of how the comet affects Mars, and we're eager to get to our primary science phase", said Bruce Jakosky, NASA's principal investigator for its Maven spacecraft.
NASA orbiters will transfer pictures and data of the flyby sometime this week. The comet has moved on and Earth is not at any kind of risk from the comet.