A comet with a retrograde orbit found by the NEOWISE Space Telescope

Infrared image of the comet C/2014 C3 (NEOWISE) (Image NASA/JPL-Caltech)
Infrared image of the comet C/2014 C3 (NEOWISE) (Image NASA/JPL-Caltech)

The NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) Space Telescope discovered his first comet after starting its new mission last year. On February 14, 2014, during one of its scans of space in search of objects that can cross the Earth’s orbit, it found a comet, which has been designated C/2014 C3 (NEOWISE). Astronomers quickly realized that it’s a weird comet because its orbit is retrograde.

The NEOWISE mission started a few months ago but the spacecraft was launched in 2009: it’s the space telescope originally known as WISE. Its name was changed after NASA reactivated it to search for near-Earth objects (NEOs), asteroids and comets whose orbits cross that of the Earth and are therefore potentially dangerous.

The comet C/2014 C3 (NEOWISE) was identified when it was at a distance of about 230 million kilometers (143 million miles) from Earth. Its orbit hasn’t yet been calculated with precision but it seems to have come from the region of the outer planets. It’s a very eccentric orbit whose duration is about 20 years that brings it also above the ecliptic plane. Its tail extends at present to about 40,000 km (25,000 miles).

The NEOWISE Space Telescope observed the comet C/2014 C3 (NEOWISE) for six times within half a day before it went out of its sight. This allowed to establish that its orbit is retrograde, which means that it’s orbiting the Sun in the opposite sense from the Earth and the other planets.

The discovery made ​​by the NEOWISE Space Telescope was later confirmed by follow-up observations made by other ground-based telescopes. Thanks to them, it was possible to establish that the comet C/2014 C3 (NEOWISE) isn’t a NEO therefore it isn’t dangerous for the Earth. It remains interesting from a scientific point of view because it’s really strange for its retrograde orbit. Presumably, it’s the result of some gravitational interference occurred who knows when that strongly altered its original orbit.

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