Comets

Dirty Snowballs?

Not Really

Comet HyukatakeComet Hyukatake

Comet West

Orbit• Most comets have a roughly circular

to slightly elliptical orbit and never enter the inner solar system.

• When they become disturbed, they dive into the inner solar system and take on a highly elliptical orbit shaped like a cigar.

• SOHO discovered that fragments of comets are falling into the Sun on a nearly daily basis.

Nucleus• Comets are a mix of ices and rock.• Ices include H2O, CO2, CO, CH4, NH3.• The side exposed to the Sun produces

jets in the areas where there are ices.• The ices are sublimated due to the

intense heating from the Sun.• As the ice is liberated, small rock

fragments and dust are also released.

Jets

Coma• The ices that become gas and the

form a roughly spherical region called the “coma”.(up to 1 million miles wide)

• This is also known as the head of the comet.

• The coma usually starts to develop when the comet nucleus gets inside of Jupiter’s orbit.

• The ices that become gas and the form a roughly spherical region called the “coma”.(up to 1 million miles wide)

• This is also known as the head of the comet.

• The coma usually starts to develop when the comet nucleus gets inside of Jupiter’s orbit.

• Coma

Tail• There are two types of tails to

most comets.

• Type I – This is gas tail created by the sublimated ices.

• Type II – This is a dust tail made of tiny rock fragments.

Type I Tail• The gas tail points

directly away from the Sun.

• It is pushed by the solar wind and pressure from the sunlight.

Type II Tail• The dust tail is

also pushed by the solar wind but it’s a heavier material, so it follows a combination of the jet direction and the solar wind.

Final Notes• Comets are very likely to be

similar to the planetesimals that the planets formed from.

• They may be our best hope to understand how our planet evolved in the earliest days of formation.