Comet Hartley 2 Flyby Surprises! Credit: NASA, JPL-Caltech, University of Maryland, EPOXI Mission
Visited last fall by NASA’s Deep Impact spacecraft during its EPOXI mission was comet Hartley 2.
Scientists have published their findings about the flyby – offering some new twists to the encounter of a cometary kind. On its EPOXI mission the Deep Impact spacecraft flew by Hartley 2 on Nov. 4, 2010.
According to research published in the June 17 issue of the journal Science, it turns out that Hartley 2 is in a hyperactive class of its own compared to other comets visited by spacecraft.
The EPOXI science team’s new, in-depth analysis of the images and data taken during the flyby confirms its earlier finding that carbon dioxide is the volatile fuel for Hartley 2’s ice-spewing jets.
Hyperactive!
“Hartley 2 is a hyperactive little comet, spewing out more water than other comets its size,” said University of Maryland Astronomer Michael A’Hearn, who is lead author on the Science paper and principal investigator for the EPOXI and Deep Impact missions.
Researchers have also found that:
— The smooth, relatively inactive waist of the peanut shaped comet is likely re-deposited, and thus evolutionary rather than primordial material
— Hartley 2 has an ‘excited state of rotation’ because it spins around one axis, but also tumbles around a different axis; and
— On its larger, rougher ends, the comet’s surface is dotted with glittering, blocky objects that can reach approximately 165 feet (50 meters) high and 260 feet (80 meters) wide.
During the spacecraft’s flyby of the comet — with closest approach of 431 miles (694 km) on November 4, 2011 — carbon dioxide driven jets were seen at the ends of the comet with most occurring at the small end.
The water ice particles driven out by these jets created a “snowstorm” through which the spacecraft flew. In the middle region or waist of the comet, water was released as vapor with very little carbon dioxide or ice.
Redistribution on a comet
These findings indicate that material in the waist is likely a product of the activity at the ends of the comet, the researchers say.
“We think the waist is a deposit of material from other parts of the comet, our first evidence of redistribution on a comet,” said University of Maryland Astronomy Professor Jessica Sunshine, who is deputy principal investigator for the EPOXI mission.
“The most likely mechanism is that some fraction of the dust, icy chunks, and other material coming off the ends of the comet are moving slowly enough to be captured by even the very weak gravity of this small comet. This material then falls back into the lowest point, the middle,” said Sunshine in a University of Maryland press statement.
Mystery objects
The study notes that another EPOXI discovery is that on the knobby ends of Hartley 2, particularly the smaller end, the surface terrain is dotted with block-like, shiny objects, some as big as a block-long, 16-story-tall building — tops of 165 feet (50 meters) high and 260 feet (80 meters) wide.
The new study says that the objects appear to be two to three times more reflective than the surface average.
“These are spectacular features, but at this point we don’t know whether these are deposits or growths…or something else,” Sunshine said.
Launched in January 2005, the Ball Aerospace constructed spacecraft made history when it smashed a probe into comet Tempel 1 on July 4th of that year.
Following the conclusion of that mission, a Maryland-led team of scientists won approval from NASA to fly the Deep Impact spacecraft to a second comet as part of an extended mission named EPOXI (Extrasolar Planet Observation and Deep
Impact Extended Investigation).
By Leonard David