Transcript Asteroids

Large moons of the solar system: Titan
• Titan is the only moon in the solar system which has an
atmosphere.
• The atmosphere is mostly nitrogen and thicker than even
Earth’s atmosphere.
• The pressure near the surface is not too different from the
pressure in this room on Earth, but the temperature is just
slightly above the boiling point of liquid nitrogen.
• It is so cold, however, that methane and ethane in the
atmosphere can form liquid droplets and form rain.
• Titan is the only moon in the Solar System that has rivers and
lakes. They are not full of water, but of methane and ethane
liquids, probably with dissolved organic material.
Titan, as seen by the Cassini spacecraft
false color on the left, infrared on the right
Rivers were seen on the surface of Titan as the probe
“Huygens” descended to the surface. It landed and took
pictures of the surface of a streambed (right).
Radar sweeps of the
North pole of Titan,
taken by the
Cassini spacecraft,
showing lakes of
methane and ethane.
Flat areas in radar
images are probably
liquid surfaces, and
are colored blue to
resemble features
on Earth. The radar
image has no color
in reality. (late 2007)
A lake (or sea) near the North pole of Titan, taken by
Cassini, compared to Lake Superior on Earth (right).
Lakes near the north pole of Titan
Titan’s
Atmosphere.
Triton
Triton, the
large moon
of Neptune,
may be a
captured
Kuiper-belt
Object (KBO).
Medium-sized moons
of the solar system
• There are 12 medium-sized moons of
the solar system, mostly around Saturn
and Uranus.
• These have a variety of features, and
some are truly strange because they
are some kind of aggregate object.
The Cassini spacecraft has returned detailed
pictures of many of these smaller moons of Saturn.
• We will just look at some in alphabetical order.
• Notice that most of these are icy objects but are large
enough to be round and have lots of craters.
• In addition, some of them show cracking like the
moon Europa of Jupiter.
• Enceladus seems to be producing ice and water
vapor and this contributes to the “E” ring of Saturn.
Medium-sized Saturnian Moons, compared to the Earth’s Moon
Dione
Enceladus
Enceladus
A series
of holes
can be
seen in
the cracks
Enceladus
appears to
be releasing
jets of water
vapor and
ice crystals,
in this
false-color
image,
which may
be adding
to Saturn’s
E ring.
Iapetus the trailing
side has
regions
which are
losing water
to the white
areas.
Rhea
another
view of
a bright
crater –
probably
relatively
recent.
Tethys
Phoebe, an example of a smaller moon.
(which might be a captured KBO !)
Moons of Uranus and Neptune (except Triton)
Ariel,
a moon of
Uranus
Miranda (a moon of Uranus) appears fragmented
and jumbled together from various pieces.
Ch. 8
Dwarf Planets
and
Small Solar
System Bodies
There are several kinds of objects in our Solar System
Terrestrial planets and Jovian planets, with satellites (moons)
Dwarf planets (which can also have moons) and
“small solar system bodies” – asteroids, comets and meteoroids
Objects are still being classified: Kuiper Belt Objects, Plutoids,
Plutinos, Trans-Neptunian Objects (TNOs), Oort cloud objects
The period of Pluto’s orbit is 248 years.
Pluto and Charon are almost like a double planet.
Pluto has at least four smaller moons.
The Pluto–Charon Orbit is so unusual that it probably means
Charon is captured, and not co-evolved with Pluto
Eris is a dwarf planet even further than Pluto.
Asteroids: three major groups
The Asteroid belt
Trojan Asteroids
Near-Earth Objects (NEOs)
This is a plot
of actual
positions of
known comets
and asteroids
(April 1, 2005).
This shows the
inner solar
system, out
to Jupiter.
Notice most of
these are in
the asteroid
belt between
Mars and Jupiter.
Expanding
the first
plot, we get
a plot of
known comets
and asteroids
in the region
around the
Earth.
Fortunately,
there aren’t
very many
of these
Near Earth
Objects
(NEOs).
This is the
view from the
side, i.e., in
the ecliptic
plane, of the
plot of the
objects in
the inner
solar system.
Ceres, the largest asteroid, is also a dwarf planet.
Asteroids and meteoroids
are small “rocky” objects
The main difference
between the two is size.
Some asteroids have been studied up close.
Asteroid Eros
Asteroid Eros
was imaged by a
spacecraft which
then landed on it
and sent back
data on its
composition.
Close-up pictures of Eros crater and surface.
Crater about 3 mi across
Photo of area 12 m across
The DAWN spacecraft was in orbit around Vesta, the
second-largest of the asteroids in the Asteroid Belt, for
almost a year.
DAWN is now in orbit around Ceres, the largest asteroid
(and also the only dwarf planet in the asteroid belt).
http://www.nasa.gov/mission_pages/dawn/main/index.html
http://dawn.jpl.nasa.gov/
http://en.wikipedia.org/wiki/4_Vesta
http://dawn.jpl.nasa.gov/mission/dawn_fact_sheet.pdf
Vesta
Lagrange points
are places where
asteroids will be
trapped in the
orbit of Jupiter.
These are called
Trojan Asteroids.
This is another
plot of actual
positions of
known comets
and asteroids
(April 1, 2005).
This shows the
outer solar
system, with
the orbit of
Jupiter and its
Trojan asteroids.
Notice there is
another belt
of objects out
past Neptune.
This shows the
outer solar
system, past
the orbit of
Jupiter.
This is the view
from the side,
i.e., in the
ecliptic plane.
Notice that the
comets are
coming from
all directions,
but the other
objects are in
the ecliptic plane.
Dwarf Planets and
Small Solar-System Bodies
• In 2006 three objects—Pluto, Ceres, and Eris—were
classified as dwarf planets. Later, we added Haumea
and Makemake to the list, so there are 5 at present.
• Pluto is classified as a Kuiper Belt Object (KBO) and
is also a dwarf planet.
• Other objects orbit the Sun beyond Neptune. For
example, at least 1277 KBO’s have been observed. A
few potential Oort cloud objects have also been
identified.
• http://solarsystem.nasa.gov/planets/index.cfm
Halley’s Comet was last seen in 1986. The orbital
period is 76 years, so it will be back in 2062.
Comet Tails: ion tail and dust tail
Comet Hale-Bopp (1997) had two distinctive tails:
http://antwrp.gsfc.nasa.gov/apod/ap050522.html
A Comet Trajectory
is usually a very
narrow ellipse,
with eccentricity
near 1.0
Some comets appear
to come from almost
100,000 A.U.
from the Sun,
in a region called
the Oort cloud.
Comet Reservoirs:
the Oort Cloud
and
the Kuiper Belt
(pronounced Kye-per)
Halley’s Comet nucleus, a photo taken by a passing
spacecraft in 1986.
Short-period comets
result when a comet
is deviated from a
highly-eccentric
orbit by the influence
of a Jovian planet.
Fragmentation of a
comet can occur
as it passes Earth.
Meteor Trails in the night sky
Meteor Showers
are usually due
to old comets.
There is definite proof
that some are due to
known comets.
Others are probably
fragments of asteroids.
List of meteor showers:
http://en.wikipedia.org/wiki/Meteor_showers#Notable_meteor_showers
Meteorite – a meteor which reaches the ground
Various types: stony, iron-nickel, carbonaceous
Stony meteorites
Broken to reveal a dark crust
and a rough fracture surface
Cut and polished
to reveal iron inclusions
Iron meteorites
Cut and polished to
Reveal crystalline form
Rough, as-found
Carbonaceous chondrite
meteorite
Allende meteorite
fragment, found
after a fall in Mexico
Ruler is 15 cm
What Killed
the
Dinosaurs?
This is an artistic
representation of
an asteroid
impact in the
Yucatan region
over 65 million
years ago.
Tunguska event, Siberia, June 30,1908
Tunguska Debris, Siberia, 1908
Barringer Crater in Arizona – a meteor crater
Manicouagan Reservoir: a crater in Canada
Approximate frequency of random impacts
Near Earth Objects – NEOs
are monitored by NASA
There is an automated system to scan the sky for near-Earth
objects and report them to a computer system. These use some
reflector telescopes with one meter diameter mirrors.
http://www.ll.mit.edu/LINEAR/
These and other reports are fed into a computer program called the
JPL Sentry system: http://neo.jpl.nasa.gov/risk/
For further descriptions: http://neo.jpl.nasa.gov/
It is important to know about the most serious hazards. For
example, Asteroid 1950 DA may collide with Earth in the year 2880
(1 in 300 chance): http://neo.jpl.nasa.gov/1950da/ and so people
should keep track of this object in the future.