In space, where large objects hurtle in past one another at hundreds of thousands of miles per hour, a distance has a tendency to shrink compared to how we perceive it here on Earth. On October 19, comet C/2013 A1, or Siding Spring, will pass Mars at a distance of approximately 87,000 miles, less than half the distance between the Earth and its moon.

NASA scientists are bracing for a “once-in-a-lifetime” event with the comet hurtling near its Mars rovers and orbiters at 126,000 miles per hour. It will reach its closest distance to Mars at 2:27 p.m. Eastern Time, say NASA experts.

The nucleus of the comet will miss the orbiters working around Mars, but the material shedded by the comet as it passes by raises concerns, as it will crash toward Mars at 35 miles per second. At that velocity, a particle one-fiftieth of an inch in diameter can knock an orbiter out.

NASA anticipates that the Mars atmosphere, while thinner than that of the Earth, will protect the rovers Curiosity and Opportunity from damage by shed particles. The three orbiting craft, however, will have no such protection. NASA has three orbiters currently working near Mars: Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Atmosphere and Volatile Evolution orbiter. These will be maneuvered to the opposite side of the planet during and for a short while after the comet flyby.

The proximity of the comet to Mars will provide for an unprecedented opportunity for astronomers to study the comet and its effect on the Martian atmosphere.

“This is a cosmic science gift that could potentially keep on giving, and the agency’s diverse science missions will be in full receive mode,” said John Grunsfeld, astronaut and associate administrator for NASA’s Science Mission Directorate. “This particular comet has never before entered the inner solar system, so it will provide a fresh source of clues to our solar system’s earliest days.”

Experts say that the Siding Spring comet is from the “Oort Cloud,” a proposed region of space surrounding our sun from which many comets are thought to originate. Siding Spring is made of a swarm of icy objects believed to be remnants of the birth of our solar system.

Scientists will be observing and the comet with Earth- and space-based telescopes including the Hubble Space Telescope, along with the Chandra, Kepler, Spitzer, and Swift telescopes. Terrestrial observations will be made via the Infrared Telescope Facility on Mauna Kea, Hawaii. The comet’s approach has been monitored using NASA’s asteroid-hunter, the Near-Earth Object Wide-field Infrared Survey Explorer, which will also monitor the flyby.