Transcript Announcements A to K to the Planetarium right now

Announcements
Students with last names starting from A to K go
to the Planetarium right now
L to Z – Thursday (11:00 a.m.)
1- 3 March: Brooks Observatory tours
7:30-8:30 p.m. – extra credit
Bring back your ticket with your name on the back
March 2-18
Instructor: Anatoly Miroshnichenko
E-mail: [email protected]
The lecture notes are available from:
http://ardbeg.astro.utoledo.edu/~anatoly/
astr1010/2004/materials.html
Chapter 9
The Giant Planets:
Jupiter, Saturn, Uranus, Neptune
• Internal Structure
• Atmospheres
• Magnetospheres
• Satellites and Rings
Jovian Planets: Basics
• Distance: 5-30 AU
– Much farther from Sun than terrestrial planets
– Much colder (100-50 K)
• Mass: 10-100 Earth masses
– Much more massive than terrestrial planets
• Jupiter & Saturn are similar
– Size (about 10 Earth diameters)
– Composition: mostly hydrogen and helium
• Uranus & Neptune are similar
– Smaller than Jupiter & Saturn
– Less hydrogen and helium
Basic Parameters
Planet
Jupiter
Dist.
A.U.
5.20
Mass
MEarth
317
Radius
REarth
11.2
Density Composition
g/cm3
1.33
H, He
Saturn
9.53
90
9.4
0.70
H, He
Uranus
19.2
14
4.11
1.32
Neptune 30.1
17
3.92
1.64
H compounds
rock, H, He
H compounds
rock, H, He
Appearance
• Jovian planets show “banded” appearance
– due to atmosphere
– we see only cloud tops
• Rotation quite fast (hours)
– Jupiter: 10 hrs
– Saturn: 11 hrs
– Uranus: 17 hrs
– Neptune: 16 hrs
Clouds
• Clouds on Jupiter & Saturn
composed of ammonia ice (NH3)
• different colors due to differing cloud composition
Saturn’s clouds deeper; less visible
• Clouds on Uranus & Neptune
– composed of methane (CH4)
• produces blue-green color
Axial Tilt & Seasons
• Jupiter
only 3º axis tilt; no real seasons
Seasons on Uranus
• Saturn
27º tilt; normal seasonal
variation
• Neptune
29º tilt; similar to Saturn
• Uranus
98º tilt -on its side![collision?]
extreme seasons! each 21 yrs
long
Planet Interiors
Jupiter
Jupiter – Comet Encounter
Comparing Jovian Planet Interiors
Density and size – Jovian planets have very low
densities and similar radii
The smallest stars are even smaller in radius
than Jupiter, but ~80 times more massive
Uranus and Neptune have higher densities and a
different chemical composition (hydrogen
compounds and rocks and less pure H and He)
Planet Density
Jovian Planet Atmospheres
No solid surfaces
Jupiter atmosphere
Content: Almost entirely H and He + trace amounts
of methane (CH4), ammonia (NH3), and H20.
Jupiter’s weather occurs in troposphere where
clouds can be formed of ammonia crystals and
other compounds
Jupiter’s Atmosphere
Wind is driven by the planet’s rotation.
Jupiter’s rotation is so fast that the atmosphere
breaks up into many swirling bands.
The bands of rising air are called zones
The adjacent bands of falling air are called belts
Belts and Zones on Jupiter
Great Red Spot is the most dramatic weather
pattern in the Solar system (size of 2 Earths)
The Great Red Spot
Atmospheres of Other Planets
Different colors are due to trace gases or colored
compounds, produced by chemical reactions
Saturn has almost the same color as Jupiter
Uranus and Neptune are blue (due to methane
which absorbs red light and transmits blue)
Saturn has belts and zones
Neptune has bands and a high-pressure storm
Great Dark Spot
Uranus has slowly changing weather
Magnetospheres
Magnetosphere consists of planet’s magnetic field
and particles trapped within them.
Jupiter’s magnetic field is 20,000 times stronger
than Earth’s. It deflects solar wind at 40 Jupiter
radii (3 million km).
The charged particles from Jupiter’s magnetosphere
bombard surfaces of Jupiter’s moons which leads to
release of their atmospheric gases
Magnetospheres
Jovian Planet Moons
There are more than 100 known moons orbiting
Jovian planets (J-52, S-30, U-21, N-11)
Three main groups of jovian moons:
Small moons - less than 300 km in diameter
Medium-size - 300-1500 km
Large - more than 1500 km
Medium and large moons have circular orbits that
lie close to the equatorial planes of their parent
planets
Jupiter Moons
Pre-visit expectations: cold and geologically dead
Voyager missions: the moons are active!
Four Galilean moons: Io, Europa, Ganymede, Callisto
Io has many volcanoes and no impact craters
Europa – no craters, fractured surface, icebergs
Ganymede – grooves on surface, magnetic field
Callisto – a heavily cratered iceball
Io
Eruptions erased
all Io’s impact
craters.
Reasons for Geological Activity
Io has an additional heating source – tidal heating
Tidal heating is due to the Io’s orbit ellipticity.
Io is continuously flexed by Jupiter.
Source of the orbit ellipticity – orbital resonances
Periodical lining up of the three closest satellites
of Jupiter (Io – 4 orbits, Europa – 2 orbits,
Ganymede – 1 orbit)
Tidal Heating
Orbital Resonance
Europa
Recently formed crust
No craters
• tidal heating work
Visible icebergs suggest
the presence of an ocean
below the surface.
Latest news: the ocean
may be made of acids
Rings and Gaps
Two of Saturn’s rings can be seen from Earth
In fact, there are as high as 100,000 individual rings
and gaps
Rings and gaps are caused by grouping of particles
at some orbital distances which are being forced out
at others.
Gaps can be created by gap moons located within
rings. They clear up gaps around their orbits.
Rings of Saturn
Telescopic view
Rings of Saturn (Voyager image)
Rings of Saturn (close up)
Rings of Jupiter, Uranus and Neptune
These rings are much fainter than that of
Saturn and were discovered after 1977.
The rings of Uranus and Neptune were
discovered during a stellar occultation.
Rings are similar to each other. They lie in
their planet’s equatorial plane, particle orbits
are almost circular, gaps are due to gap moons.
Saturn’s rings have larger size, higher
reflectivity, and greater number of particles.
Origin of the Rings
Ring particles may not last very long.
They are ground into dust in a few million years.
It should be a source of new ring particles.
The most likely one is collisions of small moons
and impacts between meteorites and small moons.
In the beginning, there were many more moons
around jovian planets. Gradual dismantling of the
moons created the ring systems.
Summary of Jovian Planets
• Jovian planets larger, more massive than terrestrial
• Composition:
– mostly hydrogen (H) and helium (He)
– dominated by hydrogen
– also large amounts of ices (water, ammonia,
methane)
• Why So Large?
– basic reason is distance from sun
• cooler temps allowed ices (volatiles) to freeze
Role of Volatiles
• Inner solar system is hot:
–volatiles are gaseous; not available for planet core formation
–planet cores
• only rock (no ice)
• smaller, less massive (1 earth mass)
• Outer solar system is cold:
– volatiles are solid; available for planet core formation
– planet cores
• both rock and ice
• bigger, more massive (10 earth masses)
• Massive cores have larger gravity; can capture gas
– Jovian planets have massive atmospheres (lots of H and He)
– Terrestrial planets have minimal atmosphere (little H and He)
Summary
Jovian planets are dynamic worlds with rapid
winds, huge storms, strong magnetic fields, and
interiors where common materials strangely
behave.
Jovian moons are geologically active because of
their ice compositions.
Ring systems were formed from small moons.
Study of jovian planets brought new concepts of
ice geology, tidal heating, and orbital resonances.