Washington: A Planetary Science Institute researcher has for the first time observed that the nucleus of Comet Hartley 2 is tumbling at a changing rotational rate.
These findings, as well as information gleaned from a recent NASA EPOXI spacecraft flyby of Comet 103P/Hartley 2, are expected to offer new insights as researchers strive to better understand comets and the role they could possibly play in aiding human solar system exploration, said Nalin H. Samarasinha, senior scientist at PSI and lead author of a paper titled “Rotation of Comet 103P/Hartley 2 from Structures in the Coma”.
"Understanding the makeup of comets has immediate relevance to planetary exploration efforts. Small bodies of the solar system such as asteroids and comets could potentially act as way stations, as well as to supply needed resources, for the human exploration of the solar system," Samarasinha said.
"For this purpose, it is necessary to know the properties and the character of these objects to maximize our investment," added Samarasinha.
The research team analyzed images of the rotationally excited, or tumbling, Hartley 2 comet taken during 20 nights between Sept. 1 and December 15, 2010 using the 2.1-meter telescope at Kitt Peak National Observatory near Tucson, Ariz.
A blue filter that isolates the light emitted by cyanogen (CN) molecules was used to observe CN features in the coma of the comet, Samarasinha said. This showed clear variations over time scales ranging from a few hours to over several days. The coma is the extended "atmosphere" of the comet that surrounds the solid nucleus that consists of ice and dirt.
"The rotational state of a comet`s nucleus is a basic physical parameter needed to accurately interpret other observations of the nucleus and coma. Analysis of these cyanogen features indicates that the nucleus is spinning down and suggests that it is in a state of a dynamically excited rotation," he said.
"Our observations have clearly shown that the effective rotation period has increased during the observation window," he added.
Hartley 2, a relatively small comet with a 2-kilometer long nucleus, is highly active for its size, he said. It is experiencing rotational changes due to torque caused by jets of gases emitting from the icy body.
The study appears in Astrophysical Journal Letters.