The Jovian Planets Jupiter Saturn (from Cassini probe) Uranus Neptune (roughly to scale) Earth.

The Jovian Planets

Jupiter Saturn (from Cassini probe)

Uranus Neptune

(roughly to scale)

Earth

Discoveries

Jupiter and Saturn known to ancient

astronomers.

Uranus discovered in 1781 by William

Herschel.

Neptune discovered in 1845 by Johann Galle. Predicted to exist by

John Adams and Urbain Leverrier because of

irregularities in Uranus' orbit.

Jupiter

Saturn

Uranus

Neptune

318

95

15

17

Mass (MEarth)

11

9.5

4

3.9

Radius (REarth)

(0.001 MSun)

Orbit semi-major axis

(AU)

Orbital Period(years)

5.2

9.5

19.2

30.1

11.9

29.4

84

164

Basic Properties

Optical – colors dictated by how molecules reflect sunlight

Infrared - traces heat inatmosphere, therefore depth

So white colors from cooler, higher clouds, brown from warmer, lower clouds. Great Red Spot – highest.

Jupiter's Atmosphere and Bands

Whiteish "zones" and brownish "belts".

Other Jovian planets: banded structure and colors

More uniform haze layer makes bands

less visible. Reason: weaker gravity allows

clouds torise higher and

spread out to create more uniform layer

Blue/green of Uranus and blue of Neptune due to methane.

Colder than Jupiter and Saturn, their ammonia has frozen and

sunk lower. Methane still in gas form. It absorbs red light and

reflects blue.

- Zones and belts mark a convection cycle. Zones higher up than belts.

-- Zones were thought to be where warm gas rises, belts where cooled gas sinks. Now less clear after Cassini, which found rising gas only in the belts!

- Winds flow in opposite directions in zones vs. belts. Differences are

hundreds of km/hr.

- Jupiter's rapid rotation stretches them horizontally around the entire planet.

Storms on Jovian Planets

Jupiter's Great Red Spot: A hurricane twice the size of Earth. Has persisted for at least

340 years. Reaches highest altitudes.

New storm “Oval BA”

"white ovals" - may last decades

"brown ovals" - only seen near 20° N latitude. Not known why. May last

years or decades

Neptune's Great Dark Spot: Discovered by Voyager 2 in

1989. But had disappeared by 1994 Hubble observations.

About Earth-sized.Why do these storms last

so long?

Jupiter

Can't observe directly. No seismic information. Must rely on physical reasoning and connection to observable phenomena.

Core thought to be molten or partially molten rock,maybe 25 g/cm3, and of mass about 10-15 MEarth .

Jupiter’s Composition: mostly H, some He, traces of other elements (true for all Jovians). Gravity strong enough to retain even light elements. Mostly molecular.

We only see the upper regions of the atmosphere. Spectroscopy of reflected sunlight reveals which molecules present. We find Hydrogen, Helium, Methane, Ammonia, some water, a few others.

All of these molecules should produce white clouds. The molecules responsible for the colors we see in the bands and spots are not known.

Internal Structure

Rapid rotation causes Jupiter and Saturn to bulge:

Gravity

without rotation

with rotation

Gravity

Jupiter and Saturn rotate every ~10 hours. Radius at

equator several % larger due to bulge.

Differential Rotation

Rotation period is shorter closer to the equator:

Jupiter

Saturn

Uranus

Near poles At equator

9h 56m

10h 40m

16h 30m

9h 50m

10h 14m

14h 12m

How do we know? Tracking storms at various latitudes, or using Spectroscopy and Doppler

shift.

Moons of Jovian Planets

The Galilean Moons of Jupiter

Closest to Jupiter

Furthest from Jupiter

(sizes to scale)

Radii: 1570 km (Europa, slightly smaller than our Moon), to 2630 km (Ganymede - largest moon in

Solar System).

Orbital periods: 1.77 days (Io) to 16.7 days (Callisto).The closer to Jupiter, the higher the moon density: from 3.5 g/cm3 (Io) to 1.8

g/cm3 (Callisto). Higher density indicates higher rock/ice fraction.

Io Europa Ganymede Callisto

Io's Volcanism

More than 80 have been observed. Can last months or years.

Ejecta speeds up to 1000 m/s. Each volcano ejects about 10,000 tons/s

Rich in S, SO2. S can be yellow, orange, red, black depending on temperature. Frozen SO2 snowflakes are white.

Voyager 2 (1979) Galileo (1996)

Activity causes surface to slowly change over the years:

Volcanic activity requires internal heat. Io is a small body. Should be cold and geologically dead by now. What is source of heat?

First, Io and Europa are in a "resonance orbit":

Day 0

Europa

Io

Day 1.77

Europa

Io

Day 3.55

Europa Io

The periodic pull on Io by Europa makes Io's

orbit elliptical.

Jupiter

Jupiter

Jupiter

Europa “pulls Io outward”

here.

Ioorbital speed slowe

r

orbital speed faster

- Io “tidally locked” like our Moon. Tidal bulge always points to Jupiter. So angle of bulge changes faster when Io is closer to Jupiter.

(exaggerated ellipse)

-But Io rotates on its axis at a constant rate, so cannot keep bulge exactly-pointed at Jupiter at all times during orbit.

- So bulge moves back and forth across surface => stresses => heat => volcanoes

Europa may have Warm Water Ocean beneath Icy Surface

860 km

42 km

Icebergs or "ice rafts" suggest broken and reassembled chunks.

Dark deposits along cracks suggest eruptions of water with dust/rock

mixed in (Europa’s density => 90%rock, 10% ice).

Fissures suggest tidal stresses.Hardly any impact craters.

What is source of heat? Same as Io: resonant orbits with Ganymede and Io make Europa's orbit elliptical

=> varying tidal stresses from Jupiter => heat.

Warm ocean => life?

Further down: rocky/metallic layers

Io pulls Europa inward here.

Ganymede pulls Europa outward

here.

Saturn's Titan: A Moon with a Thick Atmosphere

Surface pressure is 1.6 times Earth’s, T=94 K. Atmosphere 98% Nitrogen,also methane, ethane, benzene, propane, etc. Evidence for methane rain, a few lakes of methane/ethane, drainage channels, liquid-eroded rocks, an icy

volcano (active? replenishing the methane?). Mostly dry now – rain and liquid flow may be episodic (centuries?).

Surface from Huygens

probe

Origin of atmosphere: internal heat from natural radioactivity may escape surface through volcanoes. Atmosphere trapped by Titan’s cold temperature

and relatively high gravity. Interior: rocky core and water mantle.

Taken during Huygens’ descent

From Cassini-Huygens mission

Saturn's Rings (all Jovians have ring systems)

- Inner radius 60,000 km, outer radius 300,000 km. Thickness ~100 m!

- Composition: icy chunks, <1 mm to >10m in diameter. Most a few cm.

- A few rings and divisions distinguishable from Earth. Please read how the gaps

form.

Voyager probes found that rings divide into 10,000's of ringlets.

Structure at this level keeps changing. Waves of matter move like ripples on a pond.

Origin of Cassini Division: another resonance orbit Approximate radius of Mimas'

orbit

Mimas' orbital period is twice that of particles

in Cassini division. Makes their orbits

elliptical. They collide with other particles and end up in new circular orbits at other radii. Cassini division nearly

swept clean.Other gaps have similar

origins.

Origin of Saturn's Rings:

If a large moon, held together by gravity, gets too close to Saturn, tidal force breaks it into pieces, at a radius called the Roche Limit. Rings inside Roche Limit => pieces can’t reassemble into moon.

Not clear whether rings are as old as Saturn or much younger (about 50 million years).

Unclear. Total mass of ring pieces equivalent to 250 km moon. Perhaps leftover debris from moon building? A shattering collision? A captured object? Regardless, a large moon could not survive so close to Saturn:

Rings of other Jovian Planets

The rings of Uranus.Discovered by "stellar

occultation".

Jupiter, Uranus, Neptune rings much thinner, much less material. Formed by breakup of smaller bodies? Also maybe "sandblasting" of material off moon

surfaces by impacts.

Given rings have short lifetime and all Jovian planets have them, their formation must be common.

Neptune's moon Triton is spiraling in to the planet and should produce spectacular ring system in 100 million years.

The Jovian Planets

Jupiter Saturn (from Cassini probe)

Uranus Neptune

(roughly to scale)

PlutoPredicted to exist by remaining irregularities in Uranus' orbit.

Discovered in 1930 by Clyde Tombaugh (1905-1997).

Irregularities later found to be incorrect!

Model created from Hubble images. This is the most detail

we have.

Discovery image of Pluto's moon Charon

(1978)

Two more moons found in 2005

with the Hubble.

Mass 0.0025 MEarth or 0.2 x mass of Moon

Radius 1150 km or 0.2 REarth

Density 2.0 g/cm3 (between Terrestrial and Jovian densities. More like a Jovian moon)

Basic Properties of Pluto

Icy/rocky composition

Moons: Charon: radius about 590 km or 0.1 REarth .

Pluto and Charon tidally locked. Nix and Hydra about 30-100 km. Origin of Pluto

Now known to be just the largest known of a class of objects in the outer reaches of the Solar System. These objects are Kuiper Belt

Objects.

The Kuiper Belt Objects

Over 1000 found since 1992. Probably 10,000's bigger than 100 km exist.

Icy/rocky.

Orbits tend to be more tilted, like Pluto's.

Leftover planetesimals from Solar System formation?

Oort Cloud is a postulated huge, roughly spherical reservoir of comets surrounding the Solar System. ~108 objects? Ejected planetesimals.

Oort Cloud

A passing star may dislodge Oort cloud objects, plunging them into Solar System, where they become long-period comets.

If a Kuiper Belt object's orbit takes it close to, e.g., Neptune, its orbit may be changed and it may plunge towards the inner Solar System and become a short-period comet.

Radius 1200 ± 50 km or at least as big as Pluto. Icy/rocky composition, like

Pluto.

The New “Dwarf Planet” Eris

It too has a moon,Dysnomia

(Keck telescope)

Asteroids

Rocky fragments ranging from 940 km across (Ceres) to < 0.1 km. 100,000 known.

Most in Asteroid Belt, at about 2-3 AU, between Mars and Jupiter. The Trojan asteroids orbit 60 o ahead of and behind Jupiter. Some asteroids cross Earth's orbit. Their orbits were probably disrupted by Jupiter's gravity.Total mass of Asteroid Belt only 0.0008 M

Earth or 0.07 Mmoon. So it is not debris

of a planet.

Probably a planet was trying to form there, but almost all of the planetesimals were ejected from Solar System due to encounters with Jupiter. Giant planets may be effective vacuum cleaners for Solar Systems.

Gaspra Ida and Dactyl

The Sun

The Sun in X-rays over several years

The Sun is a star:

a shining ball of gas powered by nuclear fusion.

Luminosity of Sun = 4 x 1033 erg/s = 1 LSun

(amount of energy put out each second in form of radiation, = 1025 40W light bulbs)

Mass of Sun = 2 x 1033 g = 330,000 MEarth

= 1 MSun

Radius of Sun = 7 x 105 km = 109 REarth = 1 RSun

Temperature at surface = 5800 K => yellow (Wien’s Law)

Temperature at center = 15,000,000 K

Average density = 1.4 g/cm3

Density at center = 160 g/cm3

Composition: 74% of mass is H

25% He 1% the rest

Rotation period = 27 days at equator

31 days at poles

The Interior Structure of the Sun(not to scale)

Let's focus on the core, where the Sun's energy is generated.

Review of Atoms and Nuclei

Hydrogen atom:

_

+proton

electron

_

++

_

Helium atom:

The proton is the nucleus

The nucleus is 2 protons + 2 neutrons

What binds the nuclear particles? The “strong” nuclear force.

Number of protons uniquely identifies element. Isotopes differ in number of neutrons. Helium example: 4He: 2p + 2n. 3He: 2p + 1n

Review of Ionization

+

Radiative ionization of H

_

Energetic UV Photon

"Collisional Ionization" of H

+

__

+

Core of Sun is hot: gas is completely ionized by energetic collisions

What Powers the Sun

Nuclear Fusion: An event where nuclei of two atoms join together.

Need high temperatures.

Mass of nuc. 3 is slightly less than mass of (nuc. 1 + nuc. 2). Thelost mass is converted to energy. Why? Einstein's conservation of

mass and energy, E = mc2. Sum of mass and energy always conserved in reactions. Fusion reactions power stars.

Chain of nuclear reactions called "proton-proton chain" or p-p chainoccurs in Sun's core, and powers the Sun.

Energy is produced. Elements can be made.

nuc. 1 + nuc. 2 → nuc. 3 + energy (radiation)

neutrino (weird particle)

deuteron (proton + neutron bound together)

positron (identical to electron but positively

charged)

proton

proton

1) proton + proton → proton+neutron + neutrino + positron

(deuteron)

+ energy (photon)

photon

{

In the Sun's Core...

2) deuteron + proton → 3He + energy

He nucleus, only 1 neutron

3) 3He + 3He → 4He + proton + proton + energy

Net result:

4 protons → 4He + neutrinos + energy

Hydrostatic Equilibrium: pressure from fusion reactions balances gravity, allows Sun to be stable.

Mass of end products is less than mass of 4 protons by 0.7%.Mass converted to energy.

600 million tons per second fused. Takes billions of years to convert p's to 4He in Sun's core. Process sets lifetime of stars.

How does energy get from core to surface?

core

"radiative zone":

photons scatter off nuclei and

electrons, slowly drift outwards:

"diffusion".

"surface" or photosphere: gas

density low enough so photons can escape

into space.

photon path

"convection zone"

some electrons bound to nuclei => radiation can't get through =>

heats gas, hot gas rises, cool gas falls

Can see rising and falling convection cells in photosphere => granulation. Bright granules hotter and rising, dark ones cooler and falling. (Remember convection in Earth's atmosphere,

interior and Jupiter).

Granules about 1000

km across

Why are cooler granules dark? Stefan's Law: brightness α T4

The (Visible) Solar SpectrumSpectrum of the Sun shows:

1) The Black-body radiation

2) Absorption lines (atoms/ions absorbing photons at specific wavelengths).

10,000's of lines from 67 elements, in various excited or ionized states.

Again, this radiation comes from photosphere, the visible surface of the Sun. Elements weren’t made in Sun, but in previous stellar generations.

Sunspots

• Roughly Earth-sized• Individual spots last ~2 months• Usually occur in pairs • Follow solar rotation

They are darker because they are cooler (4500 K vs. 5800 K).

Related to loops of the Sun's magnetic field.

radiation from hot gas flowing along magnetic field loop at

limb of Sun.

44

Objects Seen in Transit

Transit of Venus 6/8/04Photo: J. Lodriguss

Venus transit with bird, 4-frame composite

Rafael Navarro and Ismael CidTres Cantos, Madrid, Spain

45

Transit of ISS and Shuttle Atlantis, 50 min after undocking,

September 17th 2006 at 13h 38min 50s UT. Taken from the ground at Mamers (Normandy)

France. Takahashi TOA-150 refractor (diameter 150mm, final

focal 2300mm), Baader helioscope and Canon 5D.

Exposure of 1/8000s at 50 ISO, extracted from a series of 14

images (3 images/s) started 2s before the predicted time. Image

copyright Thierry Legault.

http://www.vt-2004.org/photos/vt-photos-top01.html#iss

46

Transit of ISS and Shuttle Atlantis, 50 min after undocking,September 17th 2006 at 13h 38min 50s UT.

• Sunspot numbers vary on a 11 year cycle.

• Sun's magnetic field changes direction (flips) every 11 years.

• Maximum sunspot activity occurs about halfway between reversals.

• We just passed through a sunspot minimum (c. 2009). Sunspot activity now on the rise again.

• High levels of sunspot activity correlate with other active Sun behavior -- flares, coronal mass ejections (CMEs), prominences.

• Solar flares can disrupt radio communications on Earth, are hazardous to astronauts in space (high levels of radiation), and can even permanently damage spacecraft in orbit.

Above the photosphere, there is the chromosphere and...

The Corona

Best viewed during eclipses.

T = 106 K

Density = 10-15 g/cm3 only!

We expect X-rays from gas at this temperature.

X-ray brightness varies over 11-year Solar Cycle: coronal activity and sunspot activity go together.

Yohkoh X-ray satellite

The Solar Wind

At top of corona, typical gas speeds are close to escape speed => Sun losing gas in a solar wind.

Wind escapes from "coronal holes", seen in X-ray images.

Wind speed 500 km/sec (takes a few days to reach Earth).

106 tons/s lost. But Sun has lost only 0.1% of its mass from solar wind.

Active Regions

Prominences: Loops of gas ejected from surface. Anchored in sunspot pairs. Last for hours to weeks.

Flares: A more energetic eruption. Lasts for minutes. Less well understood.

Prominences and flares occur most often at maximum of Solar Cycle.