Wandering through the realms of the cosmos, pondering its huge vastness

Successful Close Encounter with a ‘Space Peanut’: EPOXI’s flyby to Comet Hartley 2

credit: JPL/NASA

Just a few hours ago, NASA’s EPOXI mission spacecraft successfully flew past comet Hartley 2 at 6:59:47 a.m PDT (13:59:47 Universal Time) Thursday, Nov. 4.

The Deep Impact probe zoomed to within 435 miles (700 kilometers) of Hartley and  it took incredible images of the comet’s solid nucleus. The close encounter marked just the fifth time that a spacecraft has ever visited a comet.

Experts say initial images from the flyby provide new information about the comet’s volume and material spewing from its surface. The small but active comet is full of surprises, with spinning jets, geysers of cyanide gas, and a strange, irregularly-shaped core. The nucleus is only about 2.2 km (1.4 miles) across, so there’s not much mass in it, which means that it has weak gravity. In fact, the round ends of the nucleus are bumpy and rough, indicating material is loosely aggregated there.

EPOXI is an extended mission that uses the already in-flight Deep Impact spacecraft. Its encounter phase with Hartley 2 began at 1 p.m. PDT (4 p.m. EDT) on Nov. 3, when the spacecraft began to point its two imagers at the comet’s nucleus. Imaging of the nucleus began one hour later.

I watched the coverage of this event through an online live steaming available at NASA TV. I was updating my Facebook and Twitter account as I was waiting for updates and images of the closest approach. After more than an hour since the webcast began, the first images that were taken many hours before close encounter were  received. They depicted the comet nucleus as little more than a point of light, with the fuzzy coma surrounding it. I was saving screenshots every now and then as the images came in.


First snapshot of Comet Hartley! Notice the jets that were clearly visible streaming from the peanut-shaped comet nucleus. This shape is common in asteroids and comet nuclei, according to astronomers.

Moments later, a few of the close-approach images were finally shown. I was really amazed upon seeing its odd peanut-shaped body with an irregular and contoured surface. Images are available here and here. According to NASA EPOXI’s tweet, the 55 images taken about every 15 minutes were 256 x 256 subframes and the 5 close approach are full frames 1024 x 1024.

This image montage shows comet Hartley 2 as NASA’s EPOXI mission approached and flew under the comet. The images progress in time clockwise, starting at the top left.  This was taken by EPOXI’s Medium-Resolution Instrument. The sun is to the right.  Image credit: NASA/JPL-Caltech/UMD

A nice animation of the five close-approach images above 🙂 image credit: planetary.org

Those bright streamers of light are jets of gas shooting away from the comet, formed when frozen material on the comet surface gets heated by the Sun, expands, and shoots away.


This image shows many features across the comet's surface. The length of the comet is indicated. There are two obvious regions of jet activity associated with rough terrain. Image credit: NASA/JPL-Caltech/UMD

These are medium-resolution; hi-res ones will be coming soon.

Scientists are interested in comets because they’re icy leftovers from the formation of the solar system about 4.5 billion years ago. Studying them could provide clues to how Earth and the planets formed and evolved.

Congratulations to the EPOXI team for a successful commetary encounter  and for sending amazing  images!😀



Related links:

NASA EPOXI Flyby Reveals New Insights Into Comet Features

NASA Image Gallery

Hartley 2 compared to other comets, and in motion 3D

Jets are clearly visible streaming from the peanut-shaped comet nucleusJets are clearly visible streaming from the peanut-shaped comet nucleus

3 responses

  1. An additional answer from Dr. Perry Esguerra, a physicist from the National Institute of Physics here in the Philippines.

    “300 kg of water is only 0.3 cubic meter – this is a reasonable value for a comet that is roughly 2km x 1km x 1km.”

    November 6, 2010 at 6:20 pm

  2. peter

    Thanks for this informative summary of the coverage. One question: how does a comet that is 1.25 miles long and 3/4 wide produce “180 to 300 kg (400 to 660 lb) of water per second.”



    November 6, 2010 at 9:57 am

    • Hi Peter!

      I’m not an expert on the subject, but I’ll try to give you an answer based on what I found.
      Comets are largely composed of water. In fact, a study claims that comets have contained vast amounts of liquid water in their interiors during the first million years of their formation. There was even a theory that the Earth´s oceans were formed by water from comets. A typical comet contains 10^13 kg of water ice. So in my opinion, it is likely that a comet about the size of Comet Hartley is capable of producing such amount of water.

      Hopefully, we could get better explanations to this.🙂

      November 6, 2010 at 5:20 pm

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