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Lesson9a - Formation
Comets and their effect
Comet Hayukatake
Comet
Halley up
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Comet Hartley2 from Deep Impact Space Probe
Comet Compositions
• Water Ice (H2O)
• Dry Ice (CO2)
• Dust and Rock
• In the vacuum of space (no air pressure) what
is the state of H2O and CO2?
.
1. Gas.
2. Gas or a liquid, depending on the
temperature
3. Gas or Solid, depending of the
temperature
4. Gas, Liquid or Solid depending on the
temperature
5. Solid.
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Comets are on highly elliptical orbits
• A comet spends most of its time far from the
Sun where temperatures are very low.
• When it passes close to the Sun, the comet
heats up and the volatile gasses (H2O and CO2)
begin to evaporate. There is no liquid state.
• As the gasses explode outward they drag dust
along with them.
• Comets first develop a Coma and then a tail.
Gas tail
Dust tail
When the comet leaves the Sun,
will it look like this….
• 1)
Or this?
• 2)
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2. #2
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It’s this one… Solar Wind and
Radiation drives the tail.
• 2)
Comet’s tail always points away
from the Sun
• In the vacuum of space the only thing pushing
on the tail is the solar wind and the light
coming from the Sun. The tail has to always
point away from the Sun, regardless of how
the comet moving.
• Charged particles in the solar wind exert a
force on the gas molecules
• When dust particles absorb sunlight they
receive a push as well.
Gas tail
Dust tail
Elemental abundances in the
Universe
• Other than hydrogen and some helium, all
other elements are made inside stars.
• When stars die they expel these elements
back out into space where new objects
incorporate them.
• Carbon and Oxygen are about 10 times more
abundant than any other element, except for
hydrogen and helium.
• Both of these elements are made in stars
where 3 Helium nuclei are fused into one
Carbon, and an additional Helium makes
Oxygen.
• What we find in the Solar System is lots water,
carbon dioxide, and methane. H2O, CO2, CH4
• But not in the inner Solar System. It looks like
Earth has lots of water because of the oceans,
but this is a tiny fraction of the Earth’s mass.
• What is the difference with Mercury, Venus,
Earth and Mars compared to the rest of the
Solar System?
.
1. The inner planets are
geologically active
2. The inner planets are
rocky planets
3. The inner planets all
have atmospheres
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The Frost line for water
Close to Sun, H2O, CO2, and CH4 are all gasses.
Beyond the orbit of Mars these are solids.
• What does the Sun do to comets that
evaporate their water and dry ice?
• What does the Sun do to comets that
evaporate their water and dry ice?
• The solar wind drives these gasses away from
the Sun, causing a tail to form from the comet.
• The Solar Wind drives the gasses out to the
outer parts of the Solar System. Just like it
does for the tail of a comet.
• In the outer solar system the volatiles are in
the form of ice. Ices can stick together and
make larger bodies.
• Jupiter originally was a mixture of rocky
material and ice. It grew large enough to be
able to hold onto hydrogen and helium. It
then became a gas giant.
• Outer solar system moons and comets are
covered in ice.
• In the inner solar system it was cool enough
for iron and silicate compounds to form and
make rocky material. But not cool enough for
ice to accumulate.
• The inner planets were devoid of these
volatile compounds.
• In this scenario of solar system formation,
Earth should have virtually no water.
• Where do you think most of the water on
Earth came from?
.
1. Water was trapped in the
rocks and later released.
2. Water came from volcanic
activity
3. Water came from
collisions with comets.
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• Today it is thought that virtually all the water
on Earth came from collisions with icy bodies.
• Many of these bodies probably came to Earth
from the migration of Neptune and Uranus
caused by the 1:2 resonance of Jupiter and
Saturn.
• Even more interesting, comets have been
found to contain amino acids. The building
blocks of proteins and DNA.
• Comets might have seeded the Earth with the
compounds of life.
Importance of comets
• Life needs water. Comet collisions provide
this.
• Comets have amino acids, life needs this.
• It seems to be the case that without the giant
planets in the solar system, we (humans)
would not be here today. The planets shot
almost all of the small icy bodies out into the
Oort cloud.