For a particle just half of a millimeter across, the detritus from Comet Sliding Spring is causing an awful lot of headaches for NASA. All three of its Mars orbiters need to be moved, as they fear a collision with the tiny particles could damage the spacecraft.

The nucleus of the comet itself is not the issue – it will miss Mars by about 82,000 miles – but that’s not the issue. As a comet travels through space, it spews tiny particles at speeds of up to 35 miles per second. At that rate, even the smallest piece of space dust could severely damage the delicate observational systems.

“Three expert teams have modeled this comet for NASA and provided forecasts for its flyby of Mars,” explained Rich Zurek, chief scientist for the Mars Exploration Program at NASA’s Jet Propulsion Laboratory in Pasadena, California. “The hazard is not an impact of the comet nucleus, but the trail of debris coming from it. Using constraints provided by Earth-based observations, the modeling results indicate that the hazard is not as great as first anticipated. Mars will be right at the edge of the debris cloud, so it might encounter some of the particles — or it might not.”

It would be a very expensive risk to take. Though not a risk to the orbiters, Sliding Spring’s nucleus will come closer to Mars than any comet ever has to Earth. The greatest risk to NASA’s equipment would come about 90 minutes after the nucleus has passed and last for approximately 20 minutes.

The Mars Reconnaissance Orbiter (MRO) already made one adjustment on July 2, with another planned for August 27. The Mars Odyssey orbiter has a similar move planned for August 5. The Mars Atmosphere and Volatile Evolution (MAVEN) won’t even enter orbit until September 21, but its team has an adjustment planned for October 9. Sliding Spring is expected to make its pass on October 19.

It’s not all bad news, though. Because the comet will pass so close to Mars, NASA intends to use the orbiters to get unprecedented views of its nucleus, tail and any effects it might have on Mars’ atmosphere. Because this comet has not been observed in our solar system, scientists are excited to get their hands on a fresh set of data.