Transcript a Kuiper Belt object?

9.2 Comets
• Our Goals for Learning
• How do comets get their tails?
• Where do comets come from?
How do comets
get their tails?
Comet Facts
• Formed beyond the frostline, comets are icy
counterparts to asteroids.
• “Dirty snowballs” = the nucleus
• Most comets do not have tails.
• Most comets remain perpetually frozen in
the outer solar system. Only a few enter the
inner solar system, where they can grow
tails.
When a comet nears the Sun, its ices can sublimate into gas and
carry off dust, creating a coma and long tails.
Comets eject small particles that follow the comet around in its
orbit and cause meteor showers when Earth crosses the comet’s
orbit.
Meteors in a shower appear to emanate from the same area of sky
because of Earth’s motion through space
Where do comets come from?
Only a tiny number
of comets enter the
inner solar system most stay far from
the Sun
Oort cloud:
On random orbits
extending to about
50,000 AU
Kuiper belt:
On orderly orbits
from 30-100 AU in
disk of solar
system
How did they get there?
• Kuiper belt comets formed in the Kuiper belt: flat
plane, aligned with the plane of planetary orbits,
orbiting in the same direction as the planets.
• Oort cloud comets were once closer to the Sun,
but they were kicked out there by gravitational
interactions with jovian planets: spherical
distribution, orbits in any direction.
What have we learned?
• How do comets get their tails?
• The vast majority of comets do
not have tails. Only those few
comets that enter the solar
system grow tails. As the comet
approaches the Sun its nucleus
heats up. Some of the comet’s
ice sublimates into gas, and the
escaping gases carry along some
dust. The gas and dust form a
coma and two tails: a plasma
tail of ionized gas and a dust
tail. Larger particles can also
escape, becoming the particles
that cause meteors and meteor
showers on Earth.
What have we learned?
• Where do comets come from?
• Comets that enter the solar
system come from one of two
reservoirs in the outer solar
system: the Kuiper belt and the
Oort cloud. The Kuiper belt
comets still reside in the region
beyond Neptune in which they
formed during the birth of the
solar system. The Oort cloud
comets are thought to have
formed in the region of the
jovian planets, and were kicked
out to the great distance of the
Oort cloud by gravitational
encounters with the planets.
9.3 Pluto: Lone Dog
or Part of a Pack?
• Our Goals for Learning
• What is Pluto like?
• Is Pluto a planet or a Kuiper belt object?
Pluto: the exception
• Not a gas giant like the other outer planets.
• Has a very elliptical, inclined orbit.
• By far the smallest planet, and smaller than
several moons.
• Has a surprisingly large moon Charon, probably
formed by a huge collision of another object
with Pluto when the solar system was forming.
• Also has two smaller moons: Nix and Hydra.
Pluto will never collide with Neptune because
of a 3:2 orbital resonance.
What is Pluto like?
• 1978 discovery of Pluto’s moon Charon:
Pluto’s mass from Newton’s version of
Kepler's Third Law (like Fall computer lab).
• It has a thin nitrogen atmosphere that will
refreeze onto the surface as Pluto’s orbit
takes it farther from the Sun.
• 2005 discovery of small moons Nix & Hydra.
• Pluto will be visited by the New Horizons
spacecraft in 2015 (launched January 2006).
Hubble Space Telescope’s direct
view of Pluto & Charon
Brightness variations during eclipses of Pluto by Charon
(or vice versa) show dirty ice on surfaces - like comets.
Is Pluto a planet?
a Kuiper Belt object?
something else?
Come to think of it...
what is a planet?
Is Pluto a planet or a Kuiper Belt
object?
• Pluto is well beyond Neptune, in the Kuiper
Belt.
• Inclined orbit is typical of Kuiper Belt
comets.
• Composition is typical of Kuiper Belt
comets, but not any of the other planets.
Is Pluto a planet or a Kuiper Belt
object?
• Kuiper Belt objects have similar orbital
resonances with Neptune.
• Kuiper Belt comets can have moons.
• Kuiper Belt objects Triton (captured moon
of Neptune) and Eris (formerly code-named
Xena) are even larger than Pluto. Even
larger Kuiper Belt objects may be
discovered in the future, which may lead to
confusion in calling them `dwarf planets'.
International Astronomical Union
definition of a planet (as of 2006)
• Planets must be big enough to be “nearly round”
due to self-gravity, and must have “cleared the
neighbourhood around their orbit” of similarly
sized objects (8 planets)
• Dwarf planets are big enough to be spherical due
to self-gravity, but have not cleared their orbits of
similarly sized objects [think belts], and are not
moons of larger objects (Ceres, Pluto, Eris)
• All other objects directly orbiting the Sun are
“small solar system bodies”.
What have we learned?
• Is Pluto a planet, dwarf planet,
• What is Pluto like?
or Kuiper belt object?
• Pluto is much smaller than
any other planet, with an orbit • Whether Pluto should be called
more elliptical and more
a “planet” (dwarf or regular) is a
inclined to the ecliptic plane
matter of opinion, but its
than that of any other planet.
properties suggest that it is a
It is made mostly of ices and
Kuiper belt object.
has a very thin atmosphere of
• Its composition and orbital
gases that are expected to
freeze onto the surface as
properties match those of other
Pluto moves farther from the
Kuiper belt objects and do not
Sun in its 248-year orbit. It
fit in with the other planets. It is
has a large moon, Charon,
among the largest known Kuiper
with a slightly lower density
belt objects today, but there may
than Pluto, suggesting that
be larger ones still awaiting
Charon may have been
discovery.
formed in a giant impact.