PTYS 214 – Spring 2011

Homework #9 available for download on the class website DUE on Thursday, Apr. 14

Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/

Useful Reading: class website “Reading Material” http://en.wikipedia.org/wiki/Moons_of_Jupiter http://en.wikipedia.org/wiki/Tidal_acceleration

Announcements

Quiz #8

Total Students: 19Class Average: 3.0Low: 1.5High: 4

Quizes are worth 20% of the grade

Planetary Sciences Graduate Teaching Assistant Excellence Award

Planetary Science Department initiative to promote, recognize and reward exemplary performance among graduate teaching

assistants assigned to PTYS undergraduate courses

If you think your PTYS-214 Teaching Assistant qualifies for the award, please fill out a nomination form describing:1) Why you are nominating the TA2) How the TA has contributed to your learning experience

Nomination forms and the drop box are located on the table outside your classroom, room 308

The Teaching Assistants for PTYS214-2 are:

Lissa Ong & Devin Schrader

Extra Credit Presentation

Genevieve Connor

Kyle Thompson

Moons of Jupiter

− Best known are the four large Galilean satellites:

Io, Europa, Ganymede, Callisto

− Smaller, significant moons are Thebe, Amalthea, Adrastea,

Metis, Himalia

− Jupiter has 63 confirmed satellites

CallistoCallistoGanymede

Europa

Io

Amalthea

Thebe

JUPITER

Galilean Moons

SatelliteDiameter*

(km)Density*(kg/m3)

Revolution & Rotation

(days)

Avge Surface Temperature (K)

Io 3,642 3530 1.77 130

Europa 3,130 3020 3.55 102

Ganymede 5,268 1940 7.15 110

Callisto 4,806 1,850 16.69 134

*Earth’s Moon: diameter= 3,476 km density= 3340 kg/m3 Locked in 1:2:4

Resonances

Synchronous Rotation

Synchronous rotation Almost all Galilean moons always keep the same face turned toward their planet (like our Moon)

This means that the satellite takes as long to rotate on its axis as it does to execute one revolution around its planet

Natural consequence for any moon that orbits close to its planet Revolution

around body

Rotation on its axis

Non-rotating Body

Rotating Body inSynchronous Rotation

Connected to tidal effects on a body

Example: The Earth-Moon System

Tidal Friction Moon’s gravity exerts a small amount of drag on the Earth causing tidal friction

This friction gradually slows the Earth’s rotation (1 second every 50,000 years)

Effect of Earth’s gravity is much stronger on the Moon

Earth raises much stronger tides on the Moon

Tidal friction is more severe

Moon slows down its rotation much faster

End result: Synchronous rotation

Why Synchronous Rotation

Tidal Friction on Galilean SatellitesGalilean Satellites are already locked in synchronous rotation, but:

Satellites orbits arenon-circular

tidal bulges vary inheight (because of

the change in the satellite’s distance from Jupiter)

Extra tidal friction (heating)

Some tidal heating is also produced by the varying orbital velocity (libration)

Why are the Galilean satellite orbits not circular?

1:2:4 ResonancesEach time Ganymede orbits Jupiter once, Europa orbits Jupiter twice and Io orbitsJupiter 4 times

Strongly enhance the bodies mutual

gravitational influence

It is a very important source of energy for the Jovian moons since the solar energy flux is so weak

How weak?

Io is more volcanically active than the Earth!

Why is tidal heating important?

Tidal heating depends on the distance from the parent planet

Io (the innermost of the Galilean Satellites) is too close to Jupiter and has too much tidal heating

Callisto (the outermost) is too far from Jupiter and has little tidal heating

Callisto has a very old heavily cratered surface

Tidal Heating on Io Tidal forces alternatively squeeze and stretch

Io’s interior, generating enormous amounts of heat

Io's solid surface can rise and fall by about 100 m ! (the highest ocean tides

on Earth only reach ~20m)

Io’s surface is peppered with hundreds of volcanoes, high

mountains, lava flows No impact craters!

Image sequence of two volcanic plumes 100 km (62 mi) high (Voyager 2)

Io’s ActiveSurface

Eruptions at Tvashtar Catena

(Nov. 1999)

Hot lava!(hotter than on Earth)

(Galileo Images)

(Feb. 2000)

Eruption at Kilawea Volcano, Hawaii

Life on Io?

Io provides an environment very hostile to life

1. It has practically no atmosphere, so right above the surface the temperature is very cold, but its surface, with all its volcanoes, is frequently molten, therefore it is super hot!

2. Io receives a huge amount of radiation from Jupiter but it has little or not atmosphere to shield its surface from it

Europa

Second closest to Jupiter and the smallest of the four Galilean moons

Spectroscopic observations indicate a surface made of water ice

Very few impact craters – the surface has to be very young

Pwyll (~50 km across)

Magnetic field measurements

Data from the magnetometer on board of Galileo (launched in 1989, mission terminated in 2003) show that Europa’s magnetic field varies in direction and strength in response to Jupiter’s magnetic field

Europa has an induced magnetic field !

This requires a near-surface, electrically conducting global layer, consistent with a salty ocean beneath its crust

(an iron-core would not produce an induced field as strong)

Similar data suggest that also Ganymede and maybe even Callisto may have subsurface oceans

Europa surface features

Magnetic field measurements demonstrated that Europa has an ocean but how thick is the ice layer?

Surface features provide strong argument in favor of relatively shallow ice layer

– Ridges and bands (lineaments)

– Chaotic terrain

Europa’s surface

(Galileo image)

Ridges

“Mountains”

“Chaos”

“Mountains”

“Chaos” regions (Galileo image)

Areas where the ice appears to have been broken apart and "rafted" into new positions(similar to the disruption of pack-ice on polar seas during spring thaws on Earth)

Long linear features usually a kilometer wide, a few hundred meters tall, and hundreds or thousands of kilometers long

Ridges(Galileo image)

Ridge formation: Tidal squeezing model− Diurnal tides open and close cracks in ice− While the crack is open, water and slush enter the crack

and this material is then squeezed up

Europa in a nutshell

~ -170°C

~ 0°C

volcanism

Life on Europa: Surface

Life on the surface of Europa is practically impossible

Why?

1) Temperature: -170°C (-223°C to -148°C)

too low for any psycrophile we know on Earth!

2) No atmosphere no chance for stable liquid water

3) Radiation from Jupitera deadly dose of charged particles bombard Europa’s surface continuously (not even Deinococcus Radiodurans could survive!)

Life on Europa: Subsurface

Life may be possible in the subsurface ocean

Best location: close to hydrothermal (volcanic) vents on its ocean floor(assuming they exist!)

Complexity of life: mainly limited bythe amount of available energy to sustain it

On Earth, the bulk of energy comes from photosynthesis

Could photosynthetic life occur on Europa?

Possibly at location of cracks, if

liquid water (warmer than

the surrounding ice) can get close to the

surface

Maybe…

Ganymede Largest moon of the Solar

System (larger than Mercury!)

Surface is characterized by light and dark regions; bright regions appears younger than the dark, heavily cratered areas

Magnetic field measurements from Galileo indicate a steady magnetic field, similar to Earth’s, and a varying component, similar to Europa

Maybe an ocean under a thick ice crust!

Less tidal heat than Europa, some more radiogenic heat (larger size)

Europa Jupiter System Mission!Announced in February 2009 as a joint project between NASA and ESA

Two independent spacecrafts: − Jupiter Europa Orbiter: built by NASA − Jupiter Ganymede Orbiter: built by ESA

Estimated launch/arrival: 2020/2026Planned Instruments:

− Ice-penetrating radars to detect either the ice-water boundary (Europa) or pockets of warm ice (Ganymede) − Laser altimeters to detect changes in satellites shape as they orbit Jupiter− Various imaging instruments