A comet will give Mars a historically close shave next weekend, and NASA aims to be ready for the dramatic cosmic event.

The space agency has already trained a number of its science assets on Comet Siding Spring, which will zoom within 87,000 miles (139,500 kilometers) of Mars on Oct. 19 about one-third the distance between Earth and the moon. And NASA's fleet of Red Planet orbiters and rovers will be watching on the big day, studying the comet and its influence on Mars' atmosphere.

ANALYSIS: Why a Mars Comet Impact Would be Awesome

"On October 19, we're going to observe an event that happens maybe once every million years," Jim Green, director of NASA's planetary science division, said during a news conference today (Oct. 9). "We're getting ready for a spectacular set of observations." [See photos of Comet Siding Spring]

First-Time Visitor

Comet Siding Spring, also known as C/2013 A1, was discovered in 2013 by astronomer Rob McNaught using Australia's Siding Spring Observatory. The comet is making its first trip through the inner solar system from the frigid, faraway Oort Cloud, which lies about 50,000 astronomical units from the sun. (One astronomical unit, or AU, is the average distance between Earth and the sun about 93 million miles, or 150 million km).

Because Siding Spring has never been "heat-treated" before, the incoming comet likely remains largely unchanged since its formation 4.6 billion years ago, researchers said. So studying its composition and behavior should provide clues about the conditions that existed at the birth of the solar system.

NEWS: Mars Missions Preparing for Thrilling Comet Close Shave

"That's one of the reasons we study comets they're the remnants of our solar system's formation," said ?Padma Yanamandra-Fisher, a senior research scientist at the Space Science Institute's Rancho Cucamonga branch in California.

Observations by a number of missions, including NASA's Hubble, Swift, Spitzer and NEOWISE spacecraft, have already returned some data on Siding Spring. For example, researchers think the comet's core is between 0.5 miles and 5 miles (0.8 to 8 km) in diameter. Further, the fuzzy cloud (or coma) surrounding Siding Spring's nucleus is about 100,000 miles (160,000 km) wide at this point, and its tail stretches for about 300,000 miles (480,000 km), scientists said.

Continue reading here:

NASA Mars Missions Prepare for Historic Comet Flyby