Transcript The Other Planets and Moons

The Other Planets and Moons
Inner planets
If hydrogen and helium are dispersed by the new star, only heavier
elements remain and a rocky planet forms.
Inner planets
– The inner solar system contains the Sun, Mercury, Venus, Earth
and Mars
Terrestrial planets
They are called terrestrial because they have a compact, rocky surface
like the Earth's.
Outer planets
If planets are big enough and cool enough, they can gravitationally
hold on to light gases and form gas giants.
Jovian planets
Jupiter, Saturn, Uranus, and Neptune are known as the Jovian
(Jupiter-like) planets, because they are all gigantic compared with
Earth, and they have a gaseous nature like Jupiter's.
Gas giants
The Jovian planets are also referred to as the gas giants, although
some or all of them might have small solid cores.
Pluto
• Pluto is also an outer planet, but
it is very different from the
others
Pluto and Charon
Comparison of inner and outer
planets
INNER
OUTER
• Smaller diameter
• Larger diameter
– except Pluto
• Smaller mass
• Larger mass
– except Pluto
• Higher density
– Comprised of heavier elements,
metals, and rock
• Lower density
– Jupiter and Saturn: H and He
– Uranus and Neptune: H, He, and
water
– Pluto rock and ice
Comparison of inner and outer
planets
INNER
• Have moons,
– except Mercury and Venus
OUTER
• Have moons
• Moons are irregularly shaped,
– except our Moon
• Moons are irregularly shaped
• Have surface exposed to space
– except Venus
• Surrounded by clouds
– except Pluto
• Not very reflective (low albedo)
• More highly reflective (high albedo)
Comparison of inner and outer
planets
INNER
• Orbits more closely spaced
OUTER
• Orbits more widely spaced
• Orbits nearly circular, except
Mercury
• Orbits nearly circular, except Pluto
• Orbits lie close to the ecliptic
– Mercury has greatest inclination
to the ecliptic (7 degrees)
• Orbits lie close to the ecliptic
– Pluto has greatest inclination to
the ecliptic (17.1 degrees)
Comparison of inner and outer
planets
OUTER
INNER
• Rotation is in the same direction as
orbital motion
– Except Venus
•
• Inclination of equator to orbit is
small
– Except Venus (177.3 degrees)
• Inclination of equator to orbit is
small
– Except Uranus (98 degrees) and
Pluto (18 degrees)
Orbital motion
– Except Uranus and Pluto
Planetary space missions
Voyager 1 & 2
Mars
• Mariner 2,3,4,9
– Mars fly-bys
• Viking 1,2
– Mars landers
Viking 1, 2
Mars
• Mars Global Surveyor
– Features look like they were
created by water
– Stationary lander and
surface rover, Sojourner
Mars Global Surveyor
Mars
• Mars Pathfinder
– The Pathfinder space
vehicle enters the Martian
atmosphere and descends to
the surface of the planet.
Mars Pathfinder
Moon
• Luna 1-24
• Apollo 11-17
• Clementine
• Lunar prospector
Luna 2, first to image Moon, 1959
Jupiter and Saturn
• Pioneer 10 and Pioneer 11
– Pioneers were designed to test the ability of spacecraft to survive
passage through the asteroid belt and nearly fried by ions trapped
in Jupiter’s magnetic field
– This info was crucial for the success of the Voyager missions
– They are headed off into interstellar space, being the first craft to
leave the solar system
Jupiter, Saturn, Uranus, Neptune,
Titan
• Voyager 1
– Jupiter
– Saturn
• Voyager 2
–
–
–
–
–
Jupiter
Saturn
Uranus
Neptune
Titan
Jupiter
• Galileo
– Observe Jupiter’s moons
and atmosphere
– The Galileo spacecraft as it
passed by Io, just prior to
Jupiter orbit insertion
Saturn
• Cassini
– Saturn orbiter and Titan
atmosphere probe
– Image shows the Cassini
orbiter with the Huygens
probe separating to enter
Titan's atmosphere.
Mercury
• Mariner 10
– Provided new information
about Mercury and Venus
– During its first flyby of
Venus, discovered evidence
of rotating clouds.
– During three flybys past
Mercury, it mapped about
half of the planet's surface,
during which time a thin
atmosphere and a magnetic
field were discovered.
Venus
• Venera 7,9
– first probe to return data
from the surface of another
planet (Venus) USSR
• Pioneer Venus
– High quality map of Venus
• Magellan
– By the end of the mission,
99% of the planet had been
mapped.
Magellan
Sizes of Planets
• This image
shows the nine
planets
approximately
to scale.
Obliquity of Planets
– This illustration shows the obliquity of the nine planets.
– Obliquity is the angle between a planet's equatorial plane and its
orbital plane.
Mercury
Mercury
• The planet Mercury resembles a
moon.
• Mercury's old surface is heavily
cratered like many moons.
Mercury is larger than most
moons but smaller than Jupiter's
moon Ganymede and Saturn's
moon Titan.
• Mercury is much denser and
more massive than any moon,
though, because it is made
mostly of iron.
Mercury
– Can’t tell too much from Earth-based images
– Mariner 10 imaged only 40%; so we don’t know what the other
60% looks like
– Lots of craters, evidence of lava flows, plains and cliffs (scarps)
formed when planet cooled
– Probably solid interior
Mercury
– Water ice at poles (from radio studies)
– No permanent atmosphere; H, He, Na, K, O2 continually
replenished
– Huge temp difference between day(700K) and night (100K)
• Earth temp range is only 11K!
– Iron core and magnetic field
• Rotates too slowly for dynamo to create magnetic field
• Still not understood where magnetic field comes from
3-D Mercury
• Only one spacecraft has visited Mercury, Mariner 10,
which passed Mercury three times in 1974 and 1975.
• Its resemblance to the Moon is only superficial.
• Craters are abundant, but a dense iron core, long scarps,
and vast lightly cratered plains indicate that the volcanic
and tectonic history of Mercury has been different from
that of the Moon.
Venus
Venus
– Similar to Earth but 30% closer to the Sun, which makes a lot of
difference!
– Evening star & morning star
– Only Moon and Sun are brighter
– Needed spacecraft to penetrate atmosphere to see what Venus is
like
Venus
– Yellow clouds of sulfuric acid
– Atmosphere is carbon dioxide and nitrogen from volcanoes (no
oceans to dissolve carbon dioxide)
– Hotter than Mercury even though it is farther from the Sun due to
the greenhouse effect
Venus
– Magellan mapped surface using radar techniques
– Flat, two highlands
– Less than 1000 craters compared to hundreds of thousands on
Moon and Mercury
– Believed that Venus’ surface is periodically replaced but no large
scale tectonic plate motion.
– Replaced by melting the crust by heat in the mantle every 700
million years
Venus
– Core is molten iron, but no magnetic field because it rotates
slowly.
– Venus has retrograde motion
• It rotates in the direction opposite to its rotation (sunrise is in
the West)
– No seasons because its axis of rotation is only within 3 degrees of
being perpendicular to the plane of its orbit about the Sun
3-D Venus
• Magellan used a radar imaging system to pierce the thick
cloud layers that obscure the surface, mapping 20% of
Venus in stereo (roughly equivalent to the dry land area on
Earth).
Mars
Mars
• Only planet whose surface features can be seen through Earthbased telescopes
• Volcanoes and canyons
• Volcanoes are huge; possibly due to hot spots as those that
created Hawaiian Islands BUT without any plate motion;
volcano stays above hot spot for a long time!
• Features created by water
• Now only water is frozen at poles, not on surface
Mars
• Additional evidence for water from SNC meteorites
– Contain gases in amounts found only in current Martian
atmosphere
– Contain water-soaked clay
• 95% atmosphere is carbon dioxide with N, Ar, O,and a tiny bit
of water vapor
• Mars’ axis is tilted almost same (25 degrees) as Earth’s
• Mars has seasons but they last twice as long at Earth’s
Mars
• Red color is from iron oxide dust
• 2 moons; Phobos and Diemos
• Moons were captured, not formed, like our Moon, by breaking
off a piece of the planet.
3-D Mars
• These stereo views were constructed from images obtained
by the Viking Orbiters between 1976 and 1980.
• Both Viking landers carried two cameras positioned 0.9
meters (2.7 feet) apart, providing excellent stereo
panoramas of the surface.
• Mars Pathfinder carried stereo cameras on both the lander
and on the Sojourner rover.
Jupiter
Jupiter
• 1300 Earth’s could fit in the volume of Jupiter
• Jupiter would need to be 75 times more massive to generate its
own energy like the sun and therefore be classified as a star.
• We see the clouds of Jupiter
• Jupiter rotates fastest of all planets (once every 10 hours)
Jupiter
• Clouds are storms, some last hours, some last centuries, like
the Great Red Spot.
• It is not known how such structures can persist for so long
• Upper atmosphere is ammonia and water crystals (white)
• Red, brown, orange colors in atmosphere due to sulfur
compounds which can assume many colors depending on
temp; others think it is due to phosphorous
Jupiter
• Jupiter’s surface and mantle are liquid
• Loses heat everywhere (not through volcanoes like the Earth
and some of the other planets)
• Heat brought to surface via convection currents
Jupiter
• Atmosphere has differential rotation
• Rapid differential rotation creates reddish (belts) and whitish
(zones) bands
• Hotter rising gas creates the light zones and cooler descending
gas creates belts
Jupiter
• Two frequencies of radio emission from Jupiter
– Decameter radiation
– Decimeter radiation
Jupiter
– Decameter radiation
• Electrical discharges associated with powerful electric
currents in Jupiter’s ionosphere
• Result from complex electromagnetic interactions
between Jupiter and its large satellites, especially Io
Jupiter
• Source of decimeter radiation
– Source of radiation is synchrotron radiation which is
emitted by high-speed electrons spiraling around a
magnetic field
– Two things are needed to account for the radiation
• A huge magnetic field 19,000 times stronger than
Earth’s
• A source of high energy charged particles
Jupiter
• Source of large magnetic field
• Jupiter’s molten iron core could not have created such
a strong field
• The hydrogen in Jupiter is compressed and so hot that
it forms liquid metallic hydrogen
Jupiter
• Source of large magnetic field
– Jupiter has 3 distinct regions
• Rocky core
• 40,000 km thick layer of liquid metallic hydrogen
• 20,000km layer of ordinary molecular hydrogen
Jupiter
• Source of large magnetic field
– So most of Jupiter is electrically conductive liquid metal
– Because of Jupiter’s rapid rotation, electric currents in this
liquid metal generate a huge magnetic field.
Jupiter
• So, Jupiter's magnetic field is larger than Earth’s due to
• More Rapid rotation (once/10 hours)
• Large metallic region is larger than Earth’s molten
core
Jupiter
• Source of high energy charged particles
– Jupiter’s magnetosphere is comprised of a plasma
– Due to the very high temperatures surrounding Jupiter
(temperatures much hotter than the Sun!), electrons are
torn off atoms leaving negative electrons and positively
charged protons (plasma)
– These high energy charged particles generate synchrotron
radiation as they are deflected by the strong magnetic field
of Jupiter
Jupiter
• Comet Shoemaker-Levy 9
fragmented in the tidal force
from Jupiter
• By watching impact debris from
the comet hit the surface of
Jupiter, astronomers learned
that the windspeed is more than
2200mph above the cloud layer
Jupiter
• At least 17 moons
– Four are called Galilean moons
– Io, Europa, Ganymede, and Callisto
• The geologic histories of these satellites are related to tidal
deformation of the satellites, which is severe enough to melt
large portions of Io's interior and may keep part of Europa's icy
shell liquid.
• Three rings
– Fine dust that is kicked out by Jupiter and Sun
– Replenished by material from its moons
3-D Jupiter
• The 3-D views shown here were constructed from images
obtained by Voyager 1 and 2 in 1979. (No useful 3-D
views of Europa were obtained by Voyager.)
• The geologic histories of these satellites are related to tidal
deformation of the satellites, which is severe enough to
melt large portions of Io's interior, and may keep part of
Europa's icy shell liquid.
Saturn
Saturn
• Second in size to Jupiter
• 22 moons
• Shares many of the same features as Jupiter
• Thick atmosphere, strong magnetic field, differential rotation, faint
bands, storms
• Also has liquid metallic hydrogen mantle surrounding solid core
Saturn
• Rings made of ice and ice-coated rock
• A ring a B ring separated by Cassini division (caused by combination
of gravitational forces of one of Saturn’s moons plus gravitational
force of the planet.
• Another gap in A ring called Encke division caused by a small moon
that orbits within the division
• Another ring (F ring) is kept intact by 2 shepherd satellites.
Saturn
• We see rings at different angles at different times with a 15 year
period, sometimes edge-on, sometimes from the top, sometimes from
the bottom
• Saturn is tilted on its axis,
just like Earth.
3-D Saturn
• The stereo views shown here were constructed from
images obtained by Voyager 1 and Voyager 2 in 1980 and
1981.
• The satellites of Saturn range from large boulders orbiting
near the massive ring system to the planet-sized cloudcovered Titan (which has not yet been imaged by
spacecraft).
Uranus
Uranus
• Voyager 2 could not detect any features
• Needed infrared images (from Hubble Space Telescope) to see Uranus’
system of belts and zones
• Has H and He atmosphere with methane and water ice crystals in the
upper atmosphere
• Methane absorbs red light, giving Uranus its blue-green color
Uranus
• Has retrograde rotation like Venus
• Axis of rotation tipped 98 degrees producing exaggerated seasons
• Three layers: liquid H and He, compressed liquid water, rocky core
• Strong magnetic field
• Magnetic axis does not go through center of planet
• Rings discovered by occultation of star
3-D Uranus
• Although no 3-D images are currently available for
Uranus, excellent 3-D views were obtained by Voyager 2
in January 1986 of three of its satellites: Miranda, Ariel,
and Titania.
Neptune
Neptune
• Similar to Uranus
• Methane absorbs red light, giving Neptune its blue-green color
• Neptune predicted due to its effect on Uranus before it was discovered
3-D Neptune
• Although no 3-D images are currently available for
Neptune (due to complex cloud motions between
exposures), some stereo coverage was obtained of Triton
by Voyager 2 in August 1989. Due to its icy composition,
however, relief on Triton rarely exceeds 1 kilometer.
Pluto
Pluto
• Discovered while looking for something that was allegedly disturbing
the orbit of Neptune
• Highly elliptical orbit
• Pluto and its moon almost the same size
Pluto
• Pluto is mostly brown.
• This picture captures the true
colors of Pluto as well as the
highest surface resolution so far
recovered.
• Image from University of Texas
McDonald Observatory and
University of Hawaii 88 inch
(2.2 m) telescope.
•
No spacecraft has yet visited
Pluto
Pluto
This map was created by tracking
brightness changes from Earth
of Pluto during times when it
was being partially eclipsed by
its moon Charon.
The map therefore shows the
hemisphere of Pluto that faces
Charon.
Pluto
Pluto's brown color is thought
dominated by frozen methane
deposits metamorphosed by
faint but energetic sunlight.
The dark band below Pluto's
equator is seen to have rather
complex coloring, however,
indicating that some unknown
mechanisms may have affected
Pluto's surface.
3-D Pluto
• Pluto, together with its large satellite Charon, is the only
planet not yet visited by spacecraft.
• This 3-D view of Pluto and Charon was created at LPI
using a map of Pluto's surface created from Hubble Space
Telescope (HST) images.
• The smallest features on the Pluto map are roughly 200
kilometers across. However, HST was not able to resolve
any detail on Pluto's large satellite Charon, which is
represented here by a gray sphere.