Stunning Images of an Alien Comet Passing Mars [Slide Show]
Orbiters and rovers deliver the first up-close look at a once-in-a-lifetime interplanetary encounter
![Stunning Images of an Alien Comet Passing Mars [Slide Show]](https://static.scientificamerican.com/sciam/cache/file/137A92C3-E7AD-486B-9E90D62DD5DB64A8.jpg?w=590&h=393)
Stunning Images of an Alien Comet Passing Mars [Slide Show]
- STRANGERS IN THE NIGHT On Sunday, October 19, 2014, an interplanetary robotic fleet watched as Comet Siding Spring swooped within about 130,000 kilometers of Mars. That’s only one third the distance between Earth and the moon, and the closest anyone’s ever observed a comet approach a planet without hitting it. This composite image from the Hubble Space Telescope combines images taken over two days to illustrate the angular separation between the comet and the Red Planet at the point of closest approach. Credit: NASA, ESA, PSI, JHU/APL, STScI/AURA
- SEARCHING FOR THE NUCLEUSThe Hubble telescope has been checking-in on Siding Spring for more than a year during the comet’s journey toward Mars from the outer solar system. Three images (taken in 2013 on October 29 and in 2014 on January 21 and March 11) captured the comet when it was between 500 and 600 million kilometers away from Earth, and show its slow evolution as its volatile elements boil off in the sunlight. Siding Spring’s nucleus is too small to be seen in these images, hidden within the comet’s nearly 20,000-kilometer-wide coma of gas and dust.
- A NEW VIEW OF AN ICY WORLD Unlike most comets we’re familiar with, which circle the sun in orbits of tens or hundreds of years, Comet Siding Spring’s orbit spans more than a million years, originating in the Oort Cloud, a spherical shell of icy debris at the outskirts of our solar system. No comet direct from the Oort Cloud has ever been seen in such detail before. Here, the HiRISE camera on NASA’s Mars Reconnaissance Orbiter captures the first close-ups of Siding Spring’s nucleus, revealing it to be only a half-kilometer wide. This composite image shows two of the best HiRISE snapshots of the comet, with each shot split in two. The upper photos show Siding Spring’s nucleus and gassy inner coma, whereas the lower shots are more exposed, revealing the much fainter outer coma and the beginnings of the comet’s tail. Further studies of these images should soon reveal more detailed information about the comet’s origins and composition. Credit: NASA/JPL-Caltech/University of Arizona
- SIDING SPRING IN THE SKIES OF MARS NASA’s Opportunity rover snapped this labeled image of Siding Spring shortly before daybreak on Mars, some two-and-a-half hours before the comet’s closest approach. These and other images taken by the rovers are the first snapshots of a comet taken from the surface of another planet. Credit: NASA/JPL-Caltech/Cornell Univ./ASU/TAMU
