Comet Photos: First Close-ups of Peanut-Like Hartley 2

Comet-Hunter Closing In
Photograph courtesy NASA/JPL-Caltech/UMD
After a nearly 2.9-billion-mile (4.6-billion-kilometer) voyage, NASA's EPOXI mission spacecraft has survived its risky rendezvous with comet 103P/Hartley 2 and has beamed back the first close-up images of the comet.
This montage of five pictures, for example, shows Hartley 2's nucleus as the craft was flying toward and under the icy body on Thursday. The images progress in time clockwise, starting at top left.
Initial views of Hartley 2 show a comet the likes of which mission scientists have never seen before, including an odd peanut or bowling pin shape and dozens of superactive jets spewing gas and dust like firehoses.
The odd textures of the surface of the nucleus—visible in the images above—have also caught many experts' eyes: The thick, rough ends of the comet are bisected by a much thinner central region that is noticeably smoother.
"We think the jet activity at the ends of the nucleus run along natural ridges, and may end up eroding the surface and creating clumps of material at the far ends of the comet," said Jessica Sunshine, EPOXI team scientist.
"In the center there doesn't seem to be any jet activity at all, creating a possible natural reservoir." Sunshine speculates that the smooth region may be filled with fine grains of dust that originated from the active regions near the comet's poles and were drawn by gravity to the middle.
(See more pictures of comet Hartley 2.)
—Andrew Fazekas
Published November 5, 2010
First Encounter With Hartley 2
Photograph courtesy NASA
The EPOXI mission probe's high-gain antenna began beaming pictures back to Earth just 20 minutes after the craft flew through the comet's halo of gas and dust, passing 435 miles (700 kilometers) from the surface of the nucleus, on Thursday.
In the picture above—one of the first snapped during the brief encounter—jet activity appears to be concentrated near the far right end of the comet, the side facing the sun. (See more comet pictures.)
"What we are seeing is the sun heating that portion of the comet and the dust from the surface being driven off into space by the gas jets," Sunshine said. Mission scientists believe that most of the outgassing seen during the encounter is from carbon dioxide originating from within the comet—but it's still unclear how the gas is escaping.
"We are pretty sure that the sources are subsurface, but what physical structure is involved, we simply don't know yet."
Published November 5, 2010
Hartley 2 Fireball?
Photograph by Wally Pacholka, TWAN
A bright meteor streaks over Sedona, Arizona, in November. The "shooting star" is among a handful that may have come from dust blown off of comet Hartley 2. A circle marks the comet's position in the sky.
When a comet approaches the sun, it heats up unevenly, throwing dust, ice, and bits of rock into space. If this debris enters Earth's atmosphere, the material burns up in a fiery display. (Read about an annual meteor shower that may produce a meteor storm next year.)
This month astronomers collected a handful of reports of fireballs that appear to radiate from the same region of sky that Hartley 2 is passing through, suggesting that the comet created a minor meteor shower.
Published November 5, 2010
Cyanide Comet
Photograph courtesy Byron Bergert
In the weeks leading up to EPOXI's encounter with Hartley 2, a Jupiter-size halo of gas and dust formed around the comet's 1.2-mile-wide (2-kilometer-wide) nucleus. Above, the comet appears as a hazy green blob, as seen in a backyard-telescope picture taken on October 6 in Florida. (Related: "'Biggest' Comet Measured.")
The cometary atmosphere is thought to have been produced by cyanide-laced gases escaping from the comet's surface as the object heated up on approach to the sun.
In September, observers on the ground noticed a significant enlargement of the comet's outer atmosphere within a ten-day period. Astronomers estimate that a few million tons of poisonous cyanide gas were steadily released into space during this event.
Published November 5, 2010
Welcome, Hartley 2
Photograph by Per-Magnus Hedén, TWAN
A family in Sweden stands under a starry sky in a long-exposure photograph taken in October. An arrow indicates the faint dot of comet Hartley 2.
Discovered in 1986 by Australian astronomer Malcolm Hartley, the mountain-size ball of ice and dust completes an orbit of the sun every 6.5 years. But only in the last few months has the comet brightened enough to be easily visible through backyard telescopes and binoculars.
Hartley 2 made its closest approach to Earth since its discovery on October 20, coming within 11 million miles (18 million kilometers) of our home planet.
Published November 5, 2010
EPOXI Mission Accomplished
Illustration courtesy NASA/JPL-Caltech
Now that the Hartley 2 encounter is complete, dwindling fuel supplies will likely end the comet-chasing career of the EPOXI mission probe, seen above in an artist's rendering. NASA next plans to use the craft as an astronomical observatory to study extrasolar planets.
The probe snapped thousands of images during the comet encounter, which will soon be available for study. Mission scientists expect that the flood of data will provide new information about the material spewing from Hartley 2's surface, as well as the processes that form comets in general. (Related: "Comet Swarm Delivered Earth's Oceans?")
"The smallest and most active comet we have ever laid our eyes on is really turning out to be full of surprises," Sunshine said. "We really have a lot of work ahead of us."
Published November 5, 2010