Announcements

1
Announcements

• Late HW 6 due right now.
• All HW 6 should be graded by tomorrow (including
  the late work).
• So, I should have all points tallied, and can let
  you know where you stand, just email or stop by.
• Extra Credit should be graded by Monday, so
  points next week should be complete, minus the
  final exam. (email if you want to know where you
  stand)
• No office hours today. Email if you want to see
  me.
• Do course evaluations, please
• www.courses.umd.edu/online_evaluation

2
The Final

• May 17th 130-330
• Room 2400 CSS building (this room).
• The final is worth 300 points out of the 1000 for
  the class. 30 of the grade.
• It is CUMULATIVE! Covering all material covered
  in the lectures AND book.

3
The Final

• The format will be similar to Tests 1 and 2.
• About half short answer,
• One quarter T/F and,
• One quarter essays.
• It will mostly (2/3) cover recent material
• Large/Small Satellites, Rings, ExoPlanets, Planet
  Formation, Life and Space Missions.
• The rest will be material from Tests 1 2,
• Meteorites, Comets, Asteroids, Planets, The Sun.

4
Exam Conduct

• Closed book, no notes or textbooks allowed.
• Bring your own pens and pencils, no whiteout or
  anything.
• NO talking or communicating in anyway once the
  finals have been distributed.
• Cheating will not be tolerated. If you are
  seen/heard cheating you may be asked to leave the
  exam room, and the case will be referred to the
  Head of Classes in the Astronomy Department. All
  credit for the exam will be lost, and the case
  may be sent to the University level.

5
Pluto

• Time to finalize our discussions of Plutos
  planet-hood.
• At the beginning of the class, when surveyed, you
  responded,
• Yes 17
• No 19
• Maybe 2
• The reasons given went from detailed orbits to
  not wanting to change textbooks.

6
Pluto

• Reasons it could be a planet?
• Its size and shape it is large enough to reshape
  itself, hydrostatic equilibrium.
• Orbits the Sun?
• Has Moons?
• History? Tradition?
• Around 53 objects could be considered to be in
  hydrostatic equilibrium, including one MBA.
• Reasons it might not be a planet?
• Its orbit, eccentric, inclined.
• It is in resonance with Neptune.
• It is just one of many bodies in the Kuiper Belt.

7
Pluto

• A big problem in this debate is that the most
  clear-cut measurable is size, which can be
  related directly to hydrostatic equilibrium.
• Likewise, the unclear concept of clearing its
  orbital neighborhood troubles some.

• So, one kinda-scientific approach to this
  actually uses some math to clear up this last
  point, depending on a planets position in the
  Solar System, and its size, it must
• Accrete the small bodies nearby, or (red line)
• Eject the small bodies nearby (blue line)

8
Test 1 Material

• Phases of the Moon
• Seasons
• Eclipses
• Keplers laws
• Law of Orbits elliptical orbits
• Law of Areas same area is swept out in same
  times
• Law of Periods T2a3
• The zones of the Sun, and radiation, the
  spectrum.
• Various aspects of the Sun, flares, sunspots..
  Energy consumption/production.

9
Test 1 material

• The planets in terms of size, density, and
  composition.
• Mercurys high density,
• The low densities of the outer planets.
• Telescopes their locations and observing in
  different wavelengths and spectral windows
• Solar System Formation, in terms of
• Composition distribution of H and He,
• Orbits and Rotation all in the same direction
  and plane.
• The collapsing cloud which ends up as a rapidly
  spinning disk due to angular momentum

10
Test 1 material

• Meteorites Stony, Iron, Stony-Iron
• Primitive (chondrite), Differentiated
  (achondrite) and Breccias.
• Primitives are all stony, and often contain
  chondrules. Carbonaceous Chondrites are a special
  class of primitive stones, and contain more
  volatiles and carbon.
• Differentiated meteorites are typically 4.4-4.5
  Gyr old (we get their age by radioisotope
  dating).
• Asteroids
• Size distribution- most mass in large asteroids
  (1/20 mass of the moon).
• Gaps in the Main Belt due to Jupiter.
• C-type are carbonaceous and dark, outer belt
• S-type are stony, with silicates, primitive,
  inner belt.
• M-type are metallic.
• Comets are small primitive bodies from the outer
  SS.
• Mostly ice, their volatiles evaporate near the
  Sun, creating two tails.

11
Test 2 Material

• The Moon 1 mass of Earth, 3.3 gcc, almost all
  rock.
• 8 reflectance in maria, 15 in highlands.
• Cratering density tells us about ages of
  different regions, young maria, and old
  highlands.
• Tidally locked with Earth, causes tides
• Mercury has a strange spin-state, 32 resonance
  due to elliptical orbit.
• Orbits in 88 days, rotates in 59 days, one day is
  176 days.
• Has an old surface, and is mostly a metal core,
  might have lost its rocky crust in an impact.

12
Test 2 Material

• Earths atmosphere
• Troposphere, stratosphere, mesosphere,
  thermosphere, magnetosphere.
• Greenhouse effect heats the surface, by trapping
  IR radiation.
• Tectonics- a function of plate moving about on
  the lithosphere.
• Venus has craters, but not basins must have been
  active since the LHB.
• Atmosphere is 97 CO2, with runaway greenhouse.
• 80 of surface is lava plains, some volcanoes,
  and pancake domes, and coronae.

13
Test 2 Material

• Martian surface features.
• Huge Valles Marineris
• Tharsis Uplift, huge shield volcanoes.
• Impact Basins Hellas.
• Mars is not very dense, having a core of Iron
  Sulfur, instead of Iron Nickel.
• Water on Mars
• Runoff and Outflow channels
• Gullies
• Martian Atmosphere

14
Test 2 Material

• Jupiter and Saturn show bands of colors, and have
  similar interiors
• H gas, liquid molecular H, metallic H, and
  rock/ice cores.
• Both have strong equatorial winds.
• Similar cloud layers, Ammonia ice, Ammonium
  hydrosulfide ice, water ice.
• Neptune and Uranus
• Interiors Liquid H and He, Compresses Water,
  rocky cores.
• Cooler atmospheres, with more heavy elements, no
  helium rain effect.
• Both have oddly oriented magnetic fields.

15
Large Satellites

• The large satellites we considered were,
• The Galileans - Io, Europa, Ganymede, Callisto
• Saturns Titan,
• Neptunes Triton.
• Each is large enough to be a planet, were they
  not orbiting a gas giant.

16
The Galileans

• The density of the Galileans increases with
  proximity to Jupiter
• Io 3.6 All rock.
• Europa 3.0 Differentiated, 10 ice
• Ganymede 1.9 Differentiated, half ice/half rock
• Callisto 1.9 Not differentiated, half ice/ half
  rock
• Surface features also vary wildly, heavily
  cratered old surfaces on the outer moon
  (Callisto), and super-young surfaces in near
  Jupiter (Io).
• The cratering record is altered due to
• Gravitational focusing, and
• The effects of impacting into ice.
• Reflectance of the surfaces also vary with
  distnace, as purity of water ice on surface
  changes, CAllisto 18, Ganymede 25-50,
  Europa 70

17
The Galileans

• Each moon has unique surface features and
  markings. Which tells a lot about their
  histories.
• Io and, to a lesser degree, Europa are tidally
  heated, due to a Mean Motion Resonance (421)
  with Ganymede.
• Ganyemedes period 7.16 days
• Europas period 3.55 days
• Ios period 1.77 days
• This Resonance excited eccentricities in the
  orbits of Io and Europa, creating tidal heating.
  This causes all of the volcanism at Io.
• The tidally induced volcanism drives sulfur to
  the surface and into a loose atmosphere.

18
Titan-Saturns big Moon.

• With a density of 1.9 gcc, it is physicall
  similar to Callisto and Ganymede BUT,
• IT HAS A HUGE ATMOSPHERE!
• Radio occultation found an atmosphere of 1.5
  bars, mostly Nitrogen, but also with lots of
  Methane.
• The atmosphere is evolving, constantly losing
  hydrogen from broken Methane, and other
  hydrocarbons which condense on the moons
  surface.
• We also see craters and other surface features on
  Titan, and The Huygens probe saw signs of
  drainage channels.

19
Triton

• Triton is in a retrograde orbit around Neptune.
  This is why we think it is captured.
• Tritons density is 2.1 gcc, very similar to
  Pluto and the rest of the KBOs.
• Triton is very reflective, so it is very cold,
  37K. There are frozen volatiles on top of frozen
  water ice.

20
Small Satellites

• We covered both regular and irregular small
  satellites.
• Regular low eccentricity, low inclination,
  ALWAYS prograde.
• Irregular High eccentricity and/or high
  inclination, possibly retrograde.
• The orbital properties of the satellites tells us
  a lot about their origins.

21
Saturns medium sized moons

• Saturn has 6 medium-sized moons, generally with
  densities between 1.1-1.4 gcc, so mostly (2/3)
  water ice and 1/3 rock.
• Mimas Looks like Death Star. Retained the shape
  of the huge impact, so always very cold.
• Enceladus - Very active plumes. Ejects material
  making up the E-ring. Tiger Stripes
• Tethys Has a huge, weathered impact crater,
  suggesting some heating in the past. Ithaca
  Chasma.
• Dione Heavily cratered trailing side, possible
  heavy impact altering its spin state in the past.
• Rhea - 60 reflective, very old surface.
• Iapetus Crazy, super-dark side is on the
  leading hemisphere. Trailing hemisphere is very
  bright 50 reflective.

22
Medium-sized moons at Uranus

• Uranus has 5 medium-sized moons, which are
  slightly denser than those at Saturn, between
  1.3-1.6 gcc.
• All named for English literature characters.
• The albedos are consistently between 20-30
  reflectance, so they are covered with dirty-ice
  water.
• Oberon Outermost, heavily cratered, old
  surface.
• Titania a few large impact basins, huge
  trenches and rifts, caused by expansion.
• Umbriel very dark with a few bright spots from
  fresh craters.
• Ariel very bright, with huge craters from
  expansion.
• Miranda crazy half melted surface is bizarre.
• Nereid has a very eccentric orbit, and likely
  captured.
• Proteus is oddly shaped and very close to Uranus.

23
Small moons at Saturn

• Saturn has some interesting small moons,
• Janus and Epimetheus are co-orbitals, every 4
  years they swap orbits during a close encounter.
  Their orbits only differ by 50 km.
• Saturn also has two cases of satellites with
  Trojans, moons orbiting at their Lagrange
  points, similar to the Jupiter Trojans.
• Both Jupiter and Saturn have families of
  irregular small moons, with highly inclined
  orbits and large eccentricities. Each family are
  likely remnants from one parents captured
  asteroid.

24
Rings

• Saturns rings are 100,000s of kms wide, and only
  20 meters thick!
• Each ring shows lots of structure, essentially
  lots of ringlets.
• Rings C and D, are very faint inner rings.
• C-ring has two gaps occupied by ringlets.
• The B-ring is the brightest and most massive
  ring.
• It stretches from 32,000 km 57,000 km unbroken.
• The particles are sized from 10s of cm to meters
  in size.

25
Rings

• In between the B and A rings is the Cassini
  division.
• The division is very large (4,000 km), and full
  of small faint rings and ringlets.
• The A-ring is very large with two gaps,
• Encke and Keeler.
• This ring shows lots of wave features, spiral
  bending and spiral density waves.
• The F-ring is a very thin ring full of braids and
  bright patches. It is eccentric and its width
  varies from 30-500 km.
• It is shepherded by two moons, pan and
  prometheus.
• The G-ring is very thin and faint. It is only 8
  km wide.
• The E-ring is very wide, and is formed from the
  material from Enceladus.

26
Rings at Uranus/Jupiter/Neptune

• The Rings at Uranus were found via occultation in
  77. They a series of thin dark rings, probably
  made of carbonaceous material.
• These rings are circular and narrow, less than 10
  km wide.
• Jupiters rings are extremely faint. They likely
  come from the small moons adrastea and Metis.
• Jupiter also has gossamer rings, bounded by
  Amalthea and Thebe.
• Neptune has 3 rings, which have bright arcs in
  them.

27
Ring origins/Compositions

• The possible origins for rings are
• Break-up of a satellite,
• Material is unable to form due to tidal fields.
• The wide rings at Saturn should lose very small
  particles and erode in 100s of millions of years.
  Since we see plenty of small particles they are
  likely replenished by large km-sized particles,
  which are now being discovered.
• Saturns rings are icy, as are its satellites,
• Jupiters rings are silicate, matching its inner
  satellites.
• Uranus and Neptune have dark carbonaceous rings,
  which dont match the icy satellites

28
Formation Facts

• Age ? 4.6 Gyr old, from meteorite dating.
• Rotation ? Planets rotate in the plane of the
  Suns equator, in the same direction.
• Angular momentum ? The Sun has all the mass, the
  planets have the Angular Momentum.
• Composition ? inner planets are silicate based,
  outer are heavy on volatiles, from temperature
  gradient in primordial disk.
• Asteroids ? Leftovers from planet formation, show
  signs of composition gradient.
• Meteorites ? primitive meteorites formed in the
  disk, some contain interstellar grains.
• Comets ? Composed of water-ice and other trapped
  gases.

29
Formation Facts

• 8. Isotopes ? isotope ratios vary with distance
  from Sun..
• 9. Volatiles ? Volatiles have reached the inner
  planets via comets, probably during the LHB.
• 10. Retrograde rotation ? 2.5 retrograde rotating
  planets point to important role impacts have
  played in planets formation.
• 11. Satellite Systems ? Giant planets have
  regular satellite systems, suggesting formation
  in a disk.
• 12. Irregular Satellites ? All giant planets have
  captured satellites
• 13. Giant planets ? The giant have cores with
  10-15 Earth masses of rock and ice, 3 of 4 show
  heat excess.

30
Extra Solar Planets

• First ones were discovered via precise Pulsar
  timing.
• Methods for detecting planets around Solar-type
  stars are
• Astrometric, observing motion of star
• Radial Velocity- observing redshift from Doppler
  effect
• Transit brightness dip from planet crossing in
  front of star.

31
Radial Velocity

• This method relies on the movement of the star
  around the system barycenter, creating a
  redshift/blueshift signature in the stars
  spectra.
• This method is responsible for most discoveries.
• It determines Orbital Period, semi-major axis,
  and eccentricity of orbit, and multiple planets,
  and minimum mass of planet.
• This method more easily finds close-in and large
  planets.
• AND, we now have a handful of ExoPlanets that are
  very close to stars and more massive than
  Jupiter.

32
Transits

• These are very hard to obtain, due to slim odds
  of correct geometry and very slight dimming due
  to relative sizes involved.
• These discoveries of Hot Jupiters requires new
  ideas on planet formation, or planet migration.
• Planets can migrate, via angular momentum
  transfer with disks of material, BUT they must
  stop migrating somehow,
• Tidally locked rotation,
• Or planets just get eaten all the time.

33
Life in the Solar System

• Life defined as
• Metabolism
• Reproduction
• Miller-Urey created Amino Acids, but we also find
  them on meteorites and GMCs.
• We find fossils dating to 3.5 Gyrs ago on Earth.
• Signs on Earth point to life forming in a
  reducing atmosphere and evolving to the oxidizing
  atmosphere which came about about 2.2 Gyr ago via
  photosynthesis.
• Venus is too close to Sun, hence it lost its
  water via Runaway Greenhouse Effect,
• Mars is likely too small to have held enough
  atmosphere amidst impacts.

34
Spacecraft.

• We need spacecraft for exploration. They provide
  potential for in situ experiments, otherwise
  impossible.