NASA is busy readying its considerable arsenal of scientific instruments, spacecraft and rovers for a close encounter with comet C/2013 A1 on Sunday, Oct 19. The comet's closest approach with a planetary body will be with Mars, at which point it will miss the Red Planet by only 87,000 miles (140,013 km), less than half the distance between Earth and our moon, traveling at speeds of up to 126,000 mph (202,777 km/h).
C/2013 A1, also referred to as Siding Spring, originated in the Oort Cloud, a doughnut-shaped region of space containing over a trillion icy bodies, located far beyond the orbit of Pluto. Material contained in the Oort Cloud is thought to be more or less unaltered since the birth of the solar system. This essentially makes Siding Spring an icy time capsule, a detailed analysis of which could provide a once-in-a-life-time opportunity to understand the formative period of our immediate celestial neighborhood.
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"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," stated astronaut and associate administrator for NASA’s Science Mission Directorate John Grunsfeld. "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."
In all, NASA is tasking 16 spacecraft, observatories and rovers with harvesting as much data as possible from the Martian encounter. Most of the agency's assets will be targeted on the comet itself, studying C/2013 A1's composition, size and rotational speed as well as a host of other characteristics. However some assets, like the recently-arrived Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter, will be examining how the comet's close proximity to the Red Planet affects the Martian atmosphere as Siding Spring skims past.
The potential scientific gains to be made through observing such an event are hard to quantify, but it is worth noting that there are also risks. Each of NASA's assets currently orbiting or traversing Mars are the product of thousands of man hours and millions of dollars, and some may be put in danger with the passing of the comet.
Rovers on the surface of the planet such as Curiosity and Opportunity will be protected by the Martian atmosphere, however the agency has decided to alter the orbits of some of its spacecraft in an attempt to move them a little farther out of harm's way. NASA believes that the period of greatest risk to its orbiters will begin roughly an hour and a half after the comet's closest approach, with the danger receding 20 minutes later.
"The hazard is not an impact of the comet nucleus itself, but the trail of debris coming from it," stated Rich Zurek, chief scientist for the Mars Exploration Program. "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."
Regardless of the risks, it cannot be argued that we are in the midst of a golden age for understanding the characteristics of these enigmatic celestial wanderers. Data collected by the Rosetta orbiter and her Philae lander of 67P/Churyumov-Gerasimenko, paired with the observations of Siding Spring, are bringing us ever closer to understanding the nature of our early solar system.
The following NASA video outlines the potential dangers to agency assets orbiting Mars.