Glossary term: Comet Nucleus

Description: A comet nucleus is the core of a comet. This is a solid object, similar to a dirty snowball, made with ice and rocky, dusty particles. Far from the Sun the nucleus is the sole component of the comet. Closer to the Sun a comet's nucleus is heated due to sunlight. This causes the surface ice to sublimate. The sublimated ice and the dust embedded in it are ejected and surround the nucleus as a coma with a tail pointing away from the Sun.

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The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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This comet nucleus looks like two large, bumpy lumps joined together. A small jet of material is being blown off the nucleus

Comet 67P/Churyumov-Gerasimenko

Caption: Comet 67P/Churyumov–Gerasimenko's nucleus is a "dirty snowball" made of a mixture of frozen materials and dust. It is shaped like two large lobes: one 4.1 km × 3.3 km × 1.8 km, the other 2.6 km × 2.3 km × 1.8 km. These lobes are connected by a small bridge. When a cometary nucleus such as this nears the Sun its frozen, icy material is heated, turning into gas. This, combined with the embedded dust, provide the material for the comet's characteristic coma and tail.
Credit: ESA/Rosetta/NAVCAM credit link

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