When a comet
's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets.
In the cold depths of space, comets
are no more than chunks of frozen gases, ices and dust.
This past August, Rosetta finally met up with Comet
67P near Jupiter.
23 Science, reveal a thin layer of organic compounds dusted over the comet
C/ISON was discovered in September 2012 when it was farther away from the Sun than Jupiter, and was already active at such a great distance.
often used to be thought of as portents of doom since they appeared apparently from nowhere and occasionally coincided with major events.
As the comet
approaches, heat from the sun will vaporize ices in its body, creating what could be a spectacular tail that is visible in Earth's night sky without telescopes or even binoculars from about October 2013 through January 2014.
Designated C/2011 W3 (Lovejoy), it was discovered on 27 November 2011 by amateur astronomer Terry Lovejoy of Thornlands, Queensland, during a comet
survey using a 20 cm Schmidt-Cassegrain telescope, fitted with a CCD camera.
This particular comet
is thought to have its origins in the Oort Cloud with aphelion at 63,600 AU, but after its passage through the inner solar system, would have been perturbed by planetary encounters into an 11,800 year orbit with a semi-major axis of 518 AU.
73P/Schwassmann-Wachmann 3 orbits the sun every 5.4 years.
This device-carrying craft was set on a course toward Tempel 1, a comet
that orbits the sun every five and a half years.