Comet Hartley 2

June 15, 2011
An optical image of Comet Hartley 2, taken by the the NASA EPOXI (Deep Impact) mission between Nov. 3 and 4, 2010, during the spacecraft's flyby of comet Hartley 2. Credit: NASA/JPL-Caltech/UMd

( -- The comet Hartley 2 is a relatively small and elongated comet - only about 0.6 x 0.4 kilometers in size. It orbits the sun every 6.46 years, getting as close to it as 1.05 astronomical units (the Earth is at a distance of 1 AU) and as far away as 5.88 AU; Hartley 2 was discovered in 1986. In 2007, NASA decided to direct its Deep Impact satellite to visit Hartley 2, having completed its primary mission to study the comet Tempel 1. Hartley 2 was chosen because of its small size — about 100 times smaller in volume than Tempel 1 — and its odd propensity to shoot out relatively large amounts of gas and dust, a feature that makes it quite different from other known comets.

The mission reached Hartley 2 on November 4, 2010, and the results of its measurements, together with those from a multi-wavelength, multi-observatory campaign, appeared this month in the Astrophysical Journal Letters. CfA astronomer Scott Wolk was part of a large international team studying the comet during this period. He worked in particular with X-ray observations of Hartley 2 using the Chandra X-ray Observatory.

Hartley 2 had been flagged as a very active emitter of gas and material, but the astronomers found that most of this activity was actually coming from a large halo of fluffy, icy grains rather than from the nucleus of the comet itself, making the comet itself somewhat less strange.

Chandra detected X-ray emission due to the impact of atoms in the solar wind with molecular gas surrounding the comet. Models of the comet's overall behavior show that carbon dioxide gas evaporating from the comet is the dominant driver of its activity, at least once the comet gets near to its closest approach to the sun; this is the first time that carbon dioxide gas has been identified as being the dominant driving source of activity in a comet. The results shed new light on comets - the objects that are suspected of having brought water to the Earth in the early days of the solar system - and on the nature of the young solar system itself.

Explore further: Image: Comet Hartley 2 approaches Earth

Related Stories

Image: Comet Hartley 2 approaches Earth

September 30, 2010

A pale green interloper among the stars of Cassiopeia, Comet Hartley 2 shines in this four-minute exposure taken on the night of Sept. 28, 2010, by NASA astronomer Bill Cooke.

NASA spacecraft on final approach toward comet

November 2, 2010

( -- The EPOXI mission spacecraft has refined its path toward a Nov. 4 flyby of comet Hartley 2, successfully performing its final maneuver today at 8 a.m. PDT (11 a.m. EDT). The spacecraft burned its engines ...

Primordial dry ice fuels comet jets

November 10, 2010

One of the biggest comet findings coming out of the amazing images and data taken by the University of Maryland-led EPOXI mission as it zipped past comet Hartley 2 last week is that dry ice is the 'jet' fuel for this comet ...

Recommended for you

NASA selects investigations for future key planetary mission

October 1, 2015

NASA has selected five science investigations for refinement during the next year as a first step in choosing one or two missions for flight opportunities as early as 2020. Three of those chosen have ties to NASA's Jet Propulsion ...

Dawn team shares new maps and insights about Ceres

October 1, 2015

Mysteries and insights about Ceres are being discussed this week at the European Planetary Science Conference in Nantes, France. NASA's Dawn spacecraft is providing scientists with tantalizing views and other data about the ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.