Comet C/2013 A1, also known as Comet Siding Spring, will pass within about 87,000 miles (139,500 kilometers) of the Red Planet — less than half the distance between Earth and our Moon and less than one-tenth the distance of any known comet flyby of Earth.
Siding Spring’s nucleus will come closest to Mars around 2:27 p.m. EDT, hurtling at about 126,000 mph (56 kilometers per second). This proximity will provide an unprecedented opportunity for researchers to gather data on both the comet and its effect on the martian atmosphere.
Siding Spring came from the Oort Cloud, a spherical region of space surrounding our Sun and occupying space at a distance between 5,000 and 100,000 astronomical units (1 AU is the average Earth-Sun distance). It is a giant swarm of icy objects believed to be material left over from the formation of the solar system.
Siding Spring will be the first comet from the Oort Cloud to be studied up close by spacecraft, giving scientists an invaluable opportunity to learn more about the materials, including water and carbon compounds, that existed during the formation of the solar system 4.6 billion years ago.
Some of the best and most revealing images and science data will come from assets orbiting and roving the surface of Mars. In preparation for the comet flyby, NASA maneuvered its Mars Odyssey orbiter, Mars Reconnaissance Orbiter, and the newest member of the Mars fleet, Mars Atmosphere and Volatile EvolutioN (MAVEN), in order to reduce the risk of impact with high-velocity dust particles coming off the comet.
In addition, Earth-based and space telescopes, including NASA’s iconic Hubble Space Telescope, will be in position to observe the unique celestial object. The agency’s astrophysics space observatories — Kepler, Swift, Spitzer, Chandra — and the ground-based Infrared Telescope Facility on Mauna Kea, Hawaii —will be tracking the event.