Announcements

1
Announcements

• Assignments were very good this week!
• Let me know this week if youre planning to do a
  presentation rather than a report

2
The Search

• An overview of the Mars Rover Mission
• Gas Giant Planets
• Sketch of a Gas Giant
• Who's who in the Outer Solar System
• Formation of Gas Giants
• Formation of GG moons
• Tidal Forces
• Visits to the Planets
• How Unique is Earth?

3
The Mars Rovers

• Identical pairs of rovers sent to opposite sides
  of Mars
• Spirit and Opportunity
• Each has a 1220 day' (sol) since on opposite
  sides of Mars, it is always day for one of the
  two
• Primarily geology mission.

4
The Mars Rovers

• Launched in June/July 2003
• 3 Stages
• Get off out Earth's surface
• Get out out Earth's orbit
• Head towards Mars

5
The Mars Rovers

• Began landing in Jan 2004
• Entered atmosphere at 12,000 mph (Chicago -gt San
  Francisco in 9 minutes)
• Broke using heat shield, parachute.
• Took pictures on decent to gauge horizontal
  velocity
• Deployed airbags
• Fired retro-rockets
• Bounced a lot

6
The Mars Rovers

• Once landed and stable, base unfurled
• Rover, which was also folded up, unfurled

7
The Mars Rovers
8
The Mars Rovers

• Four Science Goals
• Determine whether Life ever arose on Mars
• Characterize the Climate of Mars
• Characterize the Geology of Mars
• Prepare for Human Exploration

9
The Mars Rovers

• Search, characterize rocks soils that hold
  clues to past water activity and geologic process
• Determine distribution, composition of minerals,
  rocks, and soils surrounding the landing sites.
• Perform "ground truth" of surface observations
  made by orbiters
• Search for iron-containing minerals that indicate
  water
• Geological clues to the environmental conditions
  that existed when liquid water was present.
  Assess whether those environments were conducive
  to life.

10
The Mars Rovers

• Cameras
• Panoramic Camera (Pancam)
• Microscopic Imager (MI)
• Engineering cameras Hazcams and Navcams
• Spectrometers
• Miniature Thermal Emission Spectrometer
  (Mini-TES)
• Mössbauer Spectrometer (MB)
• Alpha Particle X-Ray Spectrometer (APXS)
• Rock Abrasion Tool (RAT)
• Magnet Array

11
Gas Giant Planets

• Overview
• Who's Who
• Formation
• Moons
• Tidal Forces

12
Our Solar System

• Almost all of mass of planets are in the 4 giant
  planets

13
The Giants

• The Giants are sometimes all called Jovian'
  planets after Jupiter
• After more exploration showed their diversity,
  this term lost favor

14
The Giants

• The giant planets inhabit the outer solar system
  (5-30 AU)
• This means they get less energy from the Sun (4
  - 0.1) per area
• Top of cloud cover of planets is very cold
  (-170oF --- 350oF)

15
The Giants

• The giant planets can be weighed very accurately
  by measuring the speed of their moons.
• Much heavier than Earth, but not so heavy
  considering their size
• Densities 600 1600 kg/m3, compared with Earth's
  5700 kg/m3
• Mostly made of gas/liquids?

16
The Birth of Giants

• In outer solar system, cooler
• Less evaporative stripping of volatile gasses
• If sufficiently massive cores form, can keep even
  volatile gasses
• These gasses will be representative of the very
  early solar system

17
The Birth of Giants

• Since early solar system is largely composed of
  Hydrogen, so will gas giants
• Rocky or Icy or Slushy core
• High-hydrogen atmosphere has some similarities to
  atmosphere in Miller-Urey experiment
• Can form lots of organics

18
The Birth of Giants

• Large rotating liquid metal region means large
  magnetic field
• Jupiter Significant field extends out size of
  the Sun!
• Can seriously effect nearby objects.

19
The Birth of Giants

• Large mass -gt high pressure, temperature at
  center
• Temperature at center of Jupiter 4 times
  surface of Sun!
• Collapse from origin of planet still slowly
  continuing
• Releases heat energy
• These planets have a source of heat

Jupiter in Infrared
20
The Birth of Giants

• Gas giants emit more heat than they absorb from
  Sun
• At earlier times, would have been much hotter
• Moons, which are nearby, heated by their nearby
  planet
• Many of these moons are large (planet-sized)
• Moons might be interesting for life?

Jupiter in Infrared
21
The Composition of Giants

• Structure of gas giant atmospheres depends on
  mass of planet
• Lower planet mass -gt lower interior pressure -gt
  may not be high-pressure enough to make hydrogen
  into a liquid metal.
• Rock/Ice cores surrounded by Hydrogen/Helium gas

22
The Moons of Giants

• Planets large enough that many moons were also
  formed
• Many of them planet sized in their own right
• Get heat from planet
• Some (Io/Jupiter) effected by planets magnetic
  field
• Atmosphere? (Titan, Saturn)
• Water? (Europa, Jupiter)

23
The Moons of Giants

• Formation like planets around sun
• Rotating body, disk forms
• Moons generally along plane of rotation of planet

24
Tidal Forces

• Tidal forces familiar from Earth
• Not due simply to gravitational attraction (that
  would just move the whole body) but the
  difference in gravitational force across the body
• Gravity inverse square
• Tidal forces inverse cube
• REALLY matters how close the object is

25
Rings

• Most of the gas giants have rings
• Jupiters are very small, probably transient, and
  made largely of dust
• Too close to planet, tidal forces are strong
  enough to disrupt moons or prevent them from
  forming
• Result is material scattered in orbit around
  planet

26
Visiting the outer Solar System

• Pioneer
• Voyager I/II
• Galileo
• Ulysses
• Cassini-Huygens

27
Pioneer 10,11

• Launched in 1972
• Camera, equipment for measuring gas/magnetic
  fields in the solar system, radiation
• Now ghost ships
• Carry plaque in case ever discovered
• Plaque designed by Carl Sagan

28
Voyager I/II

• Launched in 1977
• Carry cameras, equipment for measuring
  gas/magnetic fields in the solar system
• Now at 90 AU (8.4 billion miles)
• Still send trickle of data
• Will continue transmitting until 2020 (not
  enough sunlight to power equipment)

29
Voyager I/II

• Carries a golden record
• Has needle, instructions on how to play it on
  cover
• Contents assembled by Carl Sagan
• Contains music, greetings in 55 langaguges,
  natural/atmospheric sounds, written greetings

http//www.jpl.nasa.gov/flash/voyager_record/index
.htm
30
Voyager I/II

• Travelled past Jupiter, Saturn
• Voyager II then flew by Uranus and Neptune
  Voyager I stopped by Titan (largest moon of
  Saturn), trajectory then sent it out of plane of
  galaxy

31
Ulysses

• Sent to examine magnetic field, radiation from
  Sun, esp. poles
• Sent to Jupiter for slingshot out of plane of
  ecliptic
• Also obtained magnetic field data from Jupiter

32
Galileo

• Launched 1993
• Study Jupiter's atmosphere, satellites,
  magnetosphere for 2 years.
• Made encounters with asteroids
• Arrived at Jupiter, Dec 1995
• Significantly advanced our knowledge of the
  Galilean moons
• At end of mission was burned up in Jupiter's
  atmosphere to avoid contaminating moons

http//www.jpl.nasa.gov/videos/quicktime/galileo.q
tl
33
Galileo

• Took pictures of direct impact of comet into
  Jupiter in 1994

34
Cassini-Huygens

• Will arrive at Saturn later this year (July)
• Already taking pictures
• Will send a probe (Huygens) to Titan

35
Planets of Interest

• Where might life be?
• Gas Giants?
• Moons?
• Europa
• Titan
• Iapetus

36
Gas Giants

• Convection is a fundamental process
• Happens everywhere
• Fluid heated at bottom rises, cools, falls back
  down
• Gas giants have hot centers
• Large-scale motions
• Mix material

37
Gas Giants

• Makes it difficult to imagine life forming
• No real surface to live on
• Chemicals constantly being mixed around
• No originally contained environment (protocell')

38
Moons

• Gas giants have planet-sized moons
• At least one (Titan) has a significant atmosphere
• Another (Europa) very likely has liquid salty
  water under a layer of ice

39
Europa

• Very suggestive it has a liquid underneath
• No cratering
• Many fractures, ridges on surface
• What would this mean for life?
• If some source of energy on inside (geothermal,
  chemical), very real possibility of some sort of
  life

40
Titan

• Very Cold
• Massive, Cold enough to have an atmosphere (1.5 x
  as dense as ours!)
• No oxygen
• No liquid water
• Hydrogen rich
• Interesting organic chemistry
• Lakes of hydrocarbons?
• Huygen probe 2005

41
Iapetus

• Moon of mystery
• Side facing away from Saturn is very, very dark
• Much less light reflected than bright side
• How did this happen?
• What is the dark material?

42
How Unique is Earth?

• What is special about Earth?
• How important/rare are those things?
• How many such planets are there likely to be?

43
Earth

• Atmosphere
• Large surface gravity
• Reasonable temperature
• Rocky srface
• Large moon
• Lots of heavy elements

44
How Important/Rare are these?

• Heavy elements
• Likely ubiquitous in planets around Pop I stars

45
How Important/Rare are these?

• Rocky Surface
• Can happen if there is heavy elements (see above)
• Probably true of all planets close enough to have
  liquid water
• (But planet migration)

46
How Important/Rare are these?

• Atmosphere
• Requires not too close to sun
• Requires massive enough planet

47
How Important/Rare are these?

• Reasonable Temperature
• Goldilocks zone
• Needs to be right distance to star

48
How Important/Rare are these?

• So we require
• Rocky Planet
• Of the right mass
• At the right distance from the star

49
Habitable Zone

• Corresponds to further than Venus to about Mars
  distance for our Sun
• Using inverse-square law, could calculate for
  other stars
• Main requirement liquid water in the presence of
  an atmosphere.

50
Habitable Zone Binary Stars

• About half of all stars are in binary systems
• Stars orbit a common center of mass (more on that
  next week)
• Can planets have reasonable orbits in such
  systems?
• Yes, but must orbit one star or be far away from
  both
• Figure 8 orbits arent stable

51
Reading for Next Class (Apr 23)

• Chapter 17 The Discovery of Extra-Solar Planets
• Techniques for finding planets
• Results
• Looking closer
• Atmospheres?
• PlanetQuest