Details on Comet Hartley 2 and EPOXI
The Comet Hartley 2 or 103P Hartley 2, made a close flyby to Earth on November 4, 2010. This small, peanut shaped comet was met by NASA’s Deep Impact probe, whose new mission was recently renamed EPOXI. The probe passed by the comet at 7:01 am PDT, flying through the comet’s diffuse corona at approximately 27,500 miles per hour, and came within 435 miles of it’s icy core. For more details about Hartley 2 see: Facts About the Hartley 2 Comet, Andy D
The EPOXI Mission
This mission is only the fifth time in history that a spacecraft has gotten close enough to photograph the heart of a comet. Five new photographs were taken and beamed back to NASA’s Jet Propulsion Lab at 8:02 am that morning. Deep Impact observed the comet, sending information back to astronomers, and began taking pictures 18 hours before the flyby occurred, when the comet was 496,000 miles away. Further information on the Deep Impact can be found at: The Deep Impact Probe Mission, Andy D
Astronomers had to wait nearly an hour before receiving pictures from Deep Impact after the nearest approach, because the probe could not aim its antennas toward both Earth and the comet at the same time. The probe stored the photographs in its memory until it had passed the comet and turned toward Earth to send the pictures to scientists.
Scientists discovered the comet was not on a stable orbit, so it was unpredictable in its direction. They decided instead of steering the probe manually, they switched to Autopilot or AutoNav, which means the probe would face the brightest object near it, excluding the Sun. According to EPOXI flight director Rich Reiber, without using AutoNav, there would have only been a 0.1 percent chance of taking a picture of the nucleus.
Deep Impact is the first spacecraft in history to have visited two comets. The first mission to a comet was when Deep Impact visited Tempel 1 in July 2005. The primary mission was to create a crater on the surface of the comet to see what the comet was made of. In fact, this is the third special mission for this probe, and the reason for the mission name change. While Deep Impact is still the spacecraft’s name, EPOXI as the mission name is a combination of two names, EPOCH for extra solar planetary observation mission, and DIXI, for Deep Impact Extended Investigation.
The Comet - Hartley 2
Australian astrophotographer, Malcolm Hartley in 1986, discovered Hartley 2. The comet appeared as a smudge on a photographic plate. Hartley 2 is a small comet at only 1.36 miles across, and one of the smallest to be visited by a spacecraft. An interesting fact about this comet is, it spews much more gas and dust than any known larger comet.
The comet has two jets that stream toward the Sun and give the comet its boost. The orbit is difficult, if not impossible to predict because of these jets, which act like rocket thrusters. Scientists believe Hartley 2 was created about 4.2 to 4.5 billion years ago, beyond planet Neptune’s orbit. The comet is made up of icy dust, gas and ancient materials thought to be left over from the formation of the Solar System. Scientists study comets to understand how the Solar System was formed and to comprehend their composition.
Views of Comet Hartley 2
Images By: NASA/EPOXI Mission: https://www.nasa.gov/mission_pages/epoxi/images/version1/index.html
Wired Science: New Super Close-Up Images of Comet Flyby, Lisa Grossman: https://www.wired.com/wiredscience/2010/11/epoxi-comet-flyby/
PBS Newshour: NASA Snaps Photos of Comet Hartely 2, Vanessa Dennis and Jenny Marder: https://www.pbs.org/newshour/rundown/2010/11/comet.html
NASA:EPOXI Encounter With Comet Hartley 2: https://www.nasa.gov/mission_pages/epoxi/images/version1/index.html