Comets for Elementary astronomy

1. Comets and the Outer Solar
System

2. Comets
They originate far from
the Sun and follow
highly elliptical orbits.
A comet is made of dirty ice, a few
kilometers across. Comets
have been referred to as
'dirty snowballs.’
Comets contain dust, ice,
carbon dioxide, ammonia,
methane and more.
Astronomers think comets
are leftovers from the
material that initially formed
the solar system about 4.6
billion years ago.
(Comets have tails of gas and dust
when they come near the Sun.)

3. Parts of a Comet
Dust Tail Usually fuzzy looking and is curved because the
individual dust particles are taking up their own separate orbits
around the Sun. It forms closer to the Sun.
Ion Tail: Atoms that have gained or lost electrons. Consists of
straight streamers. It forms first and can be as long as the size
of the Earth's orbit.
A coma is the atmosphere that
comes from a comet’s heated
nucleus. It is Vaporizing gas
and dust.
The nucleus, “dirty snowball” is
the only permanent part of the
comet although it has never
been seen. The brightness of
the comet can depend on how
large the nucleus diameter is.

4. 1997’s incredibly bright and
gorgeous Comet Hale-Bopp.
The dust tails look white or a
teeny bit yellowish, due to
reflected sunlight, while the ion
tail glows blue or green,
depending on the primary
constituents of the gas.
Carbon monoxide tends to emit
blue light, while carbon
molecules glow a ghostly green.
A comet’s tail can stretch for tens of millions of kilometers.
But, despite their length, tails are incredibly low density, as low
as a few hundred atoms per cubic centimeter. The air you
breathe is a million billion times denser!

5. Growth of Tail
Closer to the Sun, the gas
evaporates and the dust that was
held together by the frozen gas is
released. The Solar wind pushes
these materials away from the Sun
to form tails.
Farther from the
Sun than the planet
Mars, comets are
simply balls of
frozen gas and dust
and do not have
tails.
Notice that the
tail leads the comet
on its trip away
from the Sun.

6. Comets go around the Sun in a highly elliptical orbit. They can spend
hundreds and thousands of years out in the depths of the solar system
before they return to Sun at their perihelion. Like all orbiting bodies,
comets follow Kepler's Laws - the closer they are to the Sun, the faster
they move.

7. 2014 by an European mission, Rosetta
went into orbit around the comet
67P/Churyumov- Gerasimenko, and
found it to be a bizarre little object
looking very much like a cosmic rubber
ducky.
The surface is completely devoid of craters; clearly the surface is very young.
Images show jets of gas emitted from very specific places on the surface, and
there are wide circular pits here and there which may be gas vents, growing
wider over time as the ice below is depleted.

8. The Stardust spacecraft flew into the coma of a
relatively new comet, Wild-2 in 2004, and took
this picture of the nucleus while collecting dust
samples for return to earth: