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Meet the people trying to help. Environment COP26 nears conclusion with mixed signals and frustration. Environment Planet Possible India bets its energy future on solar—in ways both small and big. Hartley 2 last reached perihelion closest approach to the Sun in Hartley 2 orbits the Sun within the asteroid belt, which lies between the orbits of Mars and Jupiter.
Hartley 2 is a Jupiter-family comet. A Jupiter-family comet is defined as having an orbital period of less than 20 years and one that has been modified by close passages with the gas giant.
During its flyby, the spacecraft came within miles kilometers of the comet. Hartley 2 was the fifth comet to be visited by spacecraft and was the second encounter made by this particular spacecraft. Comet Hartley's core is also not uniform, but is made up of water ice with methanol, carbon dioxide and possibly ethane.
The release of these gases occur at different locations on the comet. For example, carbon-dioxide-driven jets shoot from the ends of the comet, with most occurring from the small end. Water vapor is released from the mid-section with very little, or no carbon dioxide or ice. The comet's surface is dotted with glittering blocks that are approximately feet 50 meters high and feet 80 meters wide. These surface features appear to be two to three times more reflective than the surface average.
The planned rendezvous will not be the first comet encounter for the NASA probe. In the spacecraft, then known as Deep Impact, sent an impactor careening into Comet Tempel 1 to excavate a crater and get a glimpse of its composition. The views expressed are those of the author s and are not necessarily those of Scientific American. John Matson is a former reporter and editor for Scientific American who has written extensively about astronomy and physics.
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