NATS 102, Sect. 12 – Fall 2006 : NATS 102, Sect. 12 – Fall 2006
Announcements Homework #4 available for download from the class web site
DUE OCTOBER 20
NATS102 Star Party: Monday Oct 16 5:45 – 7:30pm
Learn how to find the North Star, see Jupiter and Mercury, more
*Hmk #3 Extra Credit: 5pts – we’ll take presence
Oct 16, 7:30pm: Steward Observatory Public Evening Series
Dr. Alfred McEwen – Early results from the HiRISE on Mars
Reconnaissance Orbiter
Steward Observatory, Rm N210
Celinda out of town: Oct 3-13
Paulo out of town: Oct 9-13
Reading: Chapter 16 of the text book
Magic Trick! : Magic Trick!
Planets’ Moons : Planets’ Moons A moon is a natural body (of any size) rotating around a planet, and usually much smaller than its planet
Many moons are very small and may be asteroids captured by their planets There are
almost 140
known moons
in our Solar
System!
Jupiter has the
most moons of
any planet (63),
followed by
Saturn (33)
Moons of Jupiter : Moons of Jupiter Jupiter’s best known moons are the four large Galilean satellites:
Io, Europa,
Ganymede, Callisto
Smaller, significant moons are
Thebe, Amalthea, Adrastea,
Metis, Himalia Jupiter has 63 confirmed satellites
Jupiter's satellites are named for other figures in the life of Zeus
Galilean Moons : Galilean Moons *Earth Moon: diameter= 3,476 km
density= 3340 kg/m3 Miniature Solar system Locked in 1:2:4
resonances
Io : Io Innermost of the four Galilean satellites (closest to Jupiter)
Most volcanically active world in our Solar System
Peppered with hundreds of volcanoes, high mountains, lava flows – no impact craters!
Io’s Active Surface : Io’s Active Surface Image sequence of two volcanic plumes 100 km (62 mi) high
(Voyager 2) Eruptions at Tvashtar Catena (Feb. 2000) Telegonus Mensa, showing slumping, landslides, fracturing Mongibello Mons at
sunset
7 km high (Nov. 1999) Hot lava! (Galileo Images)
What fuels Io? : What fuels Io? Accretional heat: Io is too small to have left over accretional heat
Radioactive decay: not enough to generate the tremendous energy required to power the observed volcanic activity
Tidal heating!
Caused by the gravitational pull of Jupiter
combined with the other Galilean satellites
Galilean satellites are locked into “resonances”
- Each time Ganymede orbits once, Europa
orbits twice and Io orbits 4 times
- The resulting tidal forces alternatively squeeze
and stretch Io’s interior, generating enormous
amounts of heat
Io's surface can rise and fall by about 100 m
(300 ft! The highest ocean tides on Earth only reach
about 60 ft)
Molten material and gases rise through fractures
in the crust and erupt on the surface
Europa : Europa Second of the four Galilean satellites
Bright, smoothest surface of the Galilean satellites
The rock layer of Europa is surrounded by a shell of water (ice/liquid), and an icy crust
Europa’s surface : Europa’s surface Few craters… Europa’s complex surface
(Galileo image) Ridges Mountains “Chaos” Pwyll Grainne “Chaos regions”: area that have been broken apart and "rafted" into new positions
(similar to the disruption of pack-ice on polar seas during spring thaws on Earth)
Ganymede : Ganymede Surface is characterized by light and dark regions; bright regions appears younger than the dark, cratered areas
They may represent crustal plates, similar to Earth’s plates
It is heavily cratered especially in the dark regions implying an ancient origin of the surface Largest moon of the
Solar System
(larger than Mercury!)
Ganymede : Ganymede Khensu crater: dark-floored crater, 13 km in diameter “Nippur Sulcus”: younger, bright region overimposed on an older, darker region Ganymede’s dark region (Galileo+Voyager) A string of craters, similar to SL9 impact on Jupiter
Callisto : Callisto Second largest moon of Jupiter; about the size of Mercury
Most heavily cratered satellite in the Solar System; ancient surface, 4 billion years
No large mountains
Callisto : Callisto Chain of craters 620 km long, probably formed by a disrupted comet, like Shoemaker-Levy 9 (the largest crater is 40 km) Valhalla impact
structure:
bright central region
is 600 km in diameter;
concentric rings
extend to 3000 km
Surfaces of Galilean Satellites : Surfaces of Galilean Satellites Very active surface
No ice (too hot)
No craters Io Europa Ganymede Callisto Active surface
Ice shell (no rocks)
Few craters “Plates” of different age
Many craters Ancient surface
Heavily cratered
Slide16 : Minor Moons of Jupiter
Metis & Adrastea
- Small (40 & 20 km) and irregular, they are
in almost identical orbits
- They orbit Jupiter in 7 hours!
Amalthea
- Irregular in shape, 262 x134 km (163x83 mi), orbits Jupiter in 12 hours
- Reddest object in the solar system, maybe due to sulfur emitted by Io and deposited on its surface
Thebe
- Irregular in shape: 110 x 90 km (68 x 56 mi)
- Orbits Jupiter in 16 hours
Himalia
- Unusual angled orbit (probably a captured asteroid), about 170 km in size
Moons of Saturn : Moons of Saturn Titan is Saturn's largest moon
Mimas has an enormous crater –
probably caused by the impact
of a large body
Enceladus has a very bright, active surface; it may have active water volcanoes
Tethys has a canyon running three-quarters of the way around its surface; it may once have been split almost in half
Dione and Rhea have wispy white markings on one side
Hyperion is oddly shaped and
the length of its day is
constantly changing
Iapetus is half bright and half
dark
Titan : Titan Saturn’s largest moon, with a thick, “smoggy” atmosphere about 4 times denser than Earth’s atmosphere
Atmosphere is mainly nitrogen (N2) with few percent of argon (Ar) and methane (CH4)
Cold surface, 94K (-240ºF) Huygens probe showed evidence of
(past) fluvial processes
Radar Images (2006): Methane lakes!
Young surface, few craters so far Cassini Mission
Moons of Uranus : Moons of Uranus Most of the moons appear to be captured asteroids based to their size and orbit
Titania, with a radius of 789 km, is the largest
of Uranus moons; it has a large trench and few large impact craters
Miranda and Ariel seem to have
had violent pasts, and show
huge canyons as deep as
20 km All the moons are made of ice and
rock, with densities less than 2000
kg/m3 Titania Miranda
Moons of Neptune : Moons of Neptune Neptune has three main moons
Nereid, Proteus and Triton
plus five smaller moons; Triton and Proteus orbit close to Neptune, Nereid is in a distant orbit
Nereid is the Solar System object with the most eccentric orbit
Triton
- Only moon in our Solar System in a retrograde
orbit (orbiting in the direction opposite to
Neptune’s rotation)
- Coldest recorded object in our Solar System,
with a surface temperature of 38K (-391ºF)!
- Density of 2,066 kg/m3 contains more rock in
its interior than the satellites of Saturn and Uranus
- It has active geyser-like eruptions spewing
nitrogen gas and dark dust particles several
kilometers high
Satellites of Giant Planets : Satellites of Giant Planets Moons of the outer planets are ½ rock and ½ ice; only Io and Europa appear to also have an iron core
Most moons display heavily cratered terrains (old surfaces), with the exceptions of Io, Europa, Triton and Titan
Ganymede is the largest Satellite in our solar System, followed closely by Titan – both are bigger than Mercury!
No craters have yet been found on Io
Europa appears to have a deep ocean beneath its icy crust (Ganymede may have an ocean too!)
Titan supports an atmosphere second only to Venus’ (considering bodies with proper surfaces), which is rich with organics, and whose origin is unknown
Triton is the coldest recorded object in the Solar System with a surface temperature of 38K (-391°F)
Pluto : It has a large satellite, Charon, that is 1/2 Pluto’s size with a mass about 1/7 Pluto’s
Pluto’s density is 1800-2100 kg/m3, Charon’s density is lower, 1200-1300 kg/m3
Surface could be as cold as 33K
(-400ºF) but we have no measurements Pluto Dwarf Planet, located at the inner edge of the Kuiper Belt
Composition: 50% to 75% rock mixed with ices Hubble Space Telescope (1994) Pluto Charon Pluto orbits the Sun in 248.5 years and rotates on its axis in -6.4 days
Charon’s orbit is gravitationally locked with Pluto: 6.4 days (same as Pluto rotation)
Eris, a.k.a. UB313 : Eris, a.k.a. UB313 Dwarf Planet, located in the Kuiper Belt
Discovered in 2005, it caused a crisis of definitions in the astronomical community
Named after the Greek goddess of discord and strife…
Radius is estimated at 2400 km (largest object detected in the Solar System since the discovery of Neptune in 1846)
It has a moon named Dysnomia, estimated to be about 1/8 of Eris’ size 3 images (over 3 hours), Oct. 2003 Keck Telescope Image