Title: ASTR 330: The Solar System
1ASTR 330 The Solar System
- Lecture 10.5
- Review 1
- for
- Mid-Term Exam 1
Dr Conor Nixon Fall 06
2ASTR 330 The Solar System
- Review 1 What have we learned?
- Lecture 1 Introduction to course dates, times,
advice, rules etc. - Lecture 2 Our place in space planetary motion,
eclipses. - Lecture 3 The Sun nuclear energy, solar lines,
solar activity. - Lecture 4 The planets densities, atmospheres,
spectroscopy. - Lecture 5 Spectral windows, albedos,
telescopes, future technology. - Lecture 6 Solar System Formation nebula
collapse, planetesimals. - Lecture 7 8 Meteorites. Types, radioactivity,
half-life. - Lecture 9 Asteroids
- Lecture 10 Comets
Dr Conor Nixon Fall 06
3ASTR 330 The Solar System
- Lecture 2 History and Perspective
- Early ideas about the planets wandering
stars. - The ecliptic path of the Sun across the sky,
through the zodiac.
- The seasons equinoxes, solstices.
- Phases of the Moon, and what causes them
eclipses. - Geocentric universe Aristotle.
- Retrograde motion of the planets epicycles,
Ptolemy. - Heliocentric universe Copernicus.
Dr Conor Nixon Fall 06
Picture credit wikipedia.org
4ASTR 330 The Solar System
- What is a total solar eclipse?
- Terminology
- Umbra and penumbra
- Totality
- Baileys beads
- Diamond ring
- What is a lunar eclipse?
Dr Conor Nixon Fall 06
5ASTR 330 The Solar System
- Lecture 2 Laws of Planetary Motion
- Keplers three laws of planetary motion
- Law of Orbits Each planet moves in an
elliptical orbit about the sun, with the Sun at
one focus of the ellipse. - Law of Areas An imaginary line connecting the
Sun with a planet sweeps out equal areas in equal
times as the planet moves about the sun. - The Law of Periods The square of the period of
any planet is proportional to the cube of the
semi-major axis of orbit. T2 K a3 - Galileos discoveries.
- Newtons ideas on gravity
- inverse square law of universal gravitation.
- Escape velocity.
Dr Conor Nixon Fall 06
6ASTR 330 The Solar System
- Basic definitions parallax, Kelvin temperature
scale (celsius 273). - Matter
- Atoms and elements.
- Atomic structure the nucleus protons and
neutrons electrons. - Hydrogen and Helium.
- Molecules and compounds.
- Light photons, waves and particles, speed of
light, mass of light. - EM spectrum types of EM radiation, from Radio
to Gamma.
Dr Conor Nixon Fall 06
7ASTR 330 The Solar System
- Parts of the Sun
- Core where nuclear fusion occurs temperature
15 million K. Energy is released as gamma
radiation. - Radiation zone the next layer of the Sun out
from the core gamma ray photons are repeatedly
absorbed and re-emitted. - Convection zone the level immediately below the
visible surface globs of solar liquid rise and
fall by convection, transporting energy. - Photosphere the visible surface of the Sun
5800 K. - Chromosphere the layer immediately above the
photosphere visible during eclipses as a pink
color. - Corona the very outer part of the Sun, merging
with the solar wind. Very hot 4 million K. Gas in
ionized.
Dr Conor Nixon Fall 06
8ASTR 330 The Solar System
- Lecture 3 Solar Lifetime Activity
- The Sun consumes 4x106 tons of matter/second,
converting H to He with a small fraction lost to
pure energy. This is the Suns power source. - Einsteins formula E mc2 gives the relation
between a small amount of mass and a large amount
of energy. The fuel source will last an estimated
10 billion years or more. - The Sun exhibits several types of activity
- Sunspots dark patches on the photosphere,
which are in fact only 1000 K cooler than the
rest of the photosphere. Caused by material
trapped in magnetic fields. 11-year cycle.
Migrate to equator. - Flares huge eruptions from the surface,
associated with the breaking of magnetic field
lines. Energy is released from radio to X-ray. - CMEs huge ejections of matter from the corona
into the solar wind, which are related to solar
flares.
Dr Conor Nixon Fall 06
9ASTR 330 The Solar System
- Sizes and densities we categorize the planets
into 3 groups - Terrestrial small size, high density Mercury,
Venus, Earth, Moon, Mars. - Giant large size, low density Jupiter, Saturn,
Neptune, Uranus. - Icy/KBO small size, low density Pluto and
Charon, KBOs. - Composition clues
- Mercury is same density as Earth, should be less
(smaller gravity) if same protosolar proportions
of the elements. - Giant planets are less dense than Earth, should
be more (more gravity). - We solve this riddle by concluding that planets
have different compositions. Closer to the sun,
more heavy elements.
Dr Conor Nixon Fall 06
10ASTR 330 The Solar System
- Lecture 4 Forms of Matter
- For the planets, it is sometimes useful to think
of four principle components gas, ice, rock and
metal. - Rocks and minerals
- A rock is an assembly of one or (usually) more
different minerals. - Minerals may be elemental (e.g. Gold, Graphite)
or compound (SiO2). - Rock types igneous (e.g. basalt), sedimentary
(e.g. limestone), metamorphic (e.g. marble). - Atmospheres ways for a planet to acquire an
atmosphere - Direct capture from original solar nebula
(priordial or primary). - Outgassed from rocks after differentiation
(secondary). - From later cometary impacts (secondary).
Dr Conor Nixon Fall 06
11ASTR 330 The Solar System
- Ways to lose an atmosphere
- Thermal escape from exosphere the thermal
energy of the molecule is enough to surpass the
escape velocity of the planet. - Impacts comet or asteroid impacts may blast
atmosphere into space. - Ablation by solar wind particles.
- What affects which molecules escape? (i) mass of
planet (ii) mass of molecule (iii) temperature.
Dr Conor Nixon Fall 06
12ASTR 330 The Solar System
- Lecture 5 Planetary Astronomy
- Remote sensing vs in situ investigations.
- Spectroscopy visible (solar) and infrared
(planetary). - Spectral windows absorption and transmission in
the Earths atmosphere. - Meaning of albedo percentage of light reflected.
- Infrared spectral lines give information on
- Temperature
- Composition
- Pressure
Dr Conor Nixon Fall 06
13ASTR 330 The Solar System
- Telescopes
- Size - affects both spatial resolution, and
amount of light collected, (or faintness of
objects which can be detected). - Sites - high and dry sites are best Antartica,
Atacama desert in Chile, Mauna Kea in Hawaii,
space! - Future techniques and technology
- Segmented giant mirrors (e.g. Keck I and II).
- Adaptive optics, to correct for atmospheric
twinkling. - Optical interferometry, to improve spatial
resolution dramtically without having to build an
impractically large single mirror. - Space telescopes - best seeing of all sites.
Dr Conor Nixon Fall 06
14ASTR 330 The Solar System
- Lecture 6 Solar System Formation
- Facts we can use composition
- the Sun is mostly H and He, most of the mass is
in the Sun, therefore the nebula was mostly H and
He. - The inner planets do not now have much in the way
of volatiles probably never had much. - Other facts orbits and rotations
- Planets mostly orbit in the same plane,
near-circular orbits. - Planets orbit Sun in same direction.
- Sun rotates in same direction as planets orbit.
- Nebular theory of Laplace.
Dr Conor Nixon Fall 06
15ASTR 330 The Solar System
Figure Universities Corp. For Atmospheric
Research (UCAR)
Dr Conor Nixon Fall 06
16ASTR 330 The Solar System
- Planetesimals to Planets, Proto-sun to Sun
Picture credit James Schimbert, U. Oregon, Eugene
Dr Conor Nixon Fall 06
Picture NASA
17ASTR 330 The Solar System
Picture credit NASA GSFC
- Left-overs asteroids, comets, EKOs/KBOs
Dr Conor Nixon Fall 06
Picture Johns Hopkins University
Graphic SWRI
18ASTR 330 The Solar System
- Major mineralogical types (1) Stony (2) Iron
(3) Stony-Iron. - Types by origin/history (1) Primitive
(chondrite) (2) Differentiated (achondrite) (3)
Breccias. - Primitive meteorites are all stones either (i)
carbonaceous, or (ii) other stones. - Differentiated meteorites can be any of the
mineralogical types. - Breccias are typically crustal material from
asteroids or planets. May be primitive or
differentiated. - Types by landing/detection (1) Falls (2) Finds.
- Finds have a skewed distribution towards iron or
stony-iron meteorites.
Dr Conor Nixon Fall 06
19ASTR 330 The Solar System
- Lecture 7 Finding Meteorites
- Famous meteorite falls include
- LAigle Fall (1803, France) the fall which
first drew scientific attention to meteorites. - Allende Fall (1969, Mexico) the first big fall
since the space race began. Dated to be very old
(4.56 Gyr). - Murchison Fall (1969, Australia) a large fall
of carbonaceous chondrite material, in which was
found organics, inc. amino acids. - The Antarctic is a very happy hunting ground for
meteorites, not only because they are easily
spotted on the ice, but also because movements of
the ice sheets tend to concentrate meteorites
against natural barriers.
Dr Conor Nixon Fall 06
20ASTR 330 The Solar System
- We can determine meteorite origins by
photographing their path across the sky from
several different locations, and calculating the
trajectory. E.g. Peekskill meteorite. They turn
out to be from the main asteroid belt. - Primitive meteorites are old (4.5 Gyrs) with
chondrules, possibly iron grains (H, L, LL) and
quite often are breccias. - Carbonaceous chondrites are a special class of
primitive stones, which are less dense, contain
more volatiles and carbon. - Tagish Lake and Murchison are famous C.C.
meteorites, which have been found to contain
amino acids. - We know these molecules are from space by their
chirality. - IPD or Brownlee particles come from comets.
Dr Conor Nixon Fall 06
21ASTR 330 The Solar System
- Lecture 8 Differentiated Meteorites
- Differentiated meteorites lack chondrites hence
are called achondrites. - Iron meteorites contain up to 10 nickel. When
polished they show a crisscross Widmanstatten
pattern due to slow cooling (below right). - These meteorites come from bodies (typically
asteroids) which have undergone differentiation
a fractional separation under heat and gravity.
Dr Conor Nixon Fall 06
Graphic SaharaMet, RR Pellison Photo NEMS
22ASTR 330 The Solar System
- Lecture 8 Stony-Irons, Basalts
- Stony-iron meteorites are thought to come from
the boundary layer between the iron core and
stony mantle of differentiated parent bodies. - Stony-irons can be dated due to the their
silicate (stony) component, and hence an age for
similar iron meteorites can be determined. - Ages for differentiated bodies are 4.4 to 4.5
Gyr, not much younger than the solar system
hence differentiation took place early on. - Eucrites are meteorites which have been found to
come from the crust of the asteroid Vesta. - Basalts tend to be lighter rocks from the
asteroid crust. Some basalts however have been
determined to some from Mars.
Dr Conor Nixon Fall 06
23ASTR 330 The Solar System
- Radioactivity (mostly) refers to the process of
nuclear transformation, from one unstable
parent isotope to a daughter isotope which is
usually more stable. - Alpha decay occurs when a helium nucleus is
emitted, moving the nucleus 2 steps up the
periodic table. - Beta decay takes place when a neutron is
transformed into a proton and an electron, moving
the nucleus 1 step down the period table. - Gamma radioactivity is not an isotope
transformation at all, rather the emission of a
high-energy EM photon by the nucleus.
Dr Conor Nixon Fall 06
Picture www.impcas.ac.cn
24ASTR 330 The Solar System
- Lecture 8 Dating Meteorites
- Radioactive dating uses the observation that the
parent to daughter nuclear ratio decreases over
time. By measuring the ratio in a sample, and
using a sister isotope to estimate the original
amount of the daughter product, we can estimate
the age of a sample. - The half-life of a radioactive isotope is the
time it takes for half of the parent nuclei to
spontaneously decay to the daughter product. - The solidification age is the time since the
sample was last molten. - The gas retention age is the time since the
sample was last mechanically disturbed, e.g. by a
shock or impact.
Dr Conor Nixon Fall 06
Picture Univ. of South Carolina/CSE
25ASTR 330 The Solar System
- First asteroid discovered in 1801 Ceres (still
the largest) in the gap region between the
orbits of Mars and Jupiter. - Missing planet found but Juno, Pallas and Vesta
detected soon after. Exploded planet? - Asteroid population follows a 1/D2 population
(number decreases with increasing size) rather
than the expected 1/D3 population. - Hence, we know most of the mass in the main
asteroid belt less than 1/20 mass of Moon. - Measuring asteroid orbits (by astrometry) and
rotation rates (by light curves) was relatively
easy. Measuring actual sizes and masses was
harder. Could use either occultation, or
spectroscopy to get sizes.
Dr Conor Nixon Fall 06
26ASTR 330 The Solar System
- Lecture 9 Asteroid Orbits
- Asteroids orbit the sun between 2.2 and 3.3 AU,
with periods of 3.3 to 6 years. Collisions are
rare (several per 10,000 years).
- Gaps in the distribution of asteroid semi-major
axes are known as resonance or Kirkwood gaps. - The gaps are caused by Jupiters gravity.
Asteroids with a certain SMA have a fixed period
by Kepler (3). - Orbits which cause the asteroid to repeatedly
pass Jupiter in the same place are unstable.
Dr Conor Nixon Fall 06
Picture JPL/SSD Alan B. Chamberlain
27ASTR 330 The Solar System
- Lecture 9 Families and Classes
- Asteroids which have similar spectroscopic
properties and similar orbits are said to form a
family. - We also note that some asteroids are bright with
silicate features in the spectrum, while others
are dark with water signature, hence 3 types - C-TYPE carbonaceous dark, with water
primitive (e.g. Ceres) - S-TYPE stony, with silicates primitive (e.g.
Eros) - M-TYPE (rare) metallic radar-bright (e.g.
Psyche) - C-type (75) are outer edge of main belt, S-type
(25) inner edge. - Densities are not useful indicators of
composition, e.g. Psyche.
Dr Conor Nixon Fall 06
28ASTR 330 The Solar System
- Lecture 9 Asteroids contd.
- Asteroids are also found
- In the Lagrangian L4 and L5 points of Jupiters
(and Mars) orbit, called Trojans. - In Earth crossing orbits NEAs/NEOs.
- In elliptical orbits Centaurs.
- Trojans and centaurs are redder than main-belt
asteroids. - Visits
- Gaspra (1991) by Galileo. Found irregular
object, craters. - Ida (1993) by Galileo. Found moon (Dactyl), more
cratered than Gaspra. - NEAR-Shoemaker at Mathilde found very dark,
slow rotating object. - NEAR-Shoemaker at Eros orbited and landed.
Found flat-bottomed craters filled with dust.
Dr Conor Nixon Fall 06
29ASTR 330 The Solar System
- Comets are small primitive bodies from the outer
solar system. - Whereas asteroids are mainly rock and metal,
comets are mainly ice.
- When comets approach the inner solar system
their volatiles evaporate forming a temporary
atmosphere (coma) and tail. - Plasma or ion tail is ionized volatile material.
- Dust tail is dust particles released by
vaporization of the volatiles.
Dr Conor Nixon Fall 06
Figure credit thursdaysclassroom.com
30ASTR 330 The Solar System
- Lecture 10 Comets - contributions
- Tycho Brahe made important contributions to
cometary science in the 16th century. By parallax
he showed that the comet was further than the
Moon, hence not in Earths atmosphere. Also
showed that the comet head is as big as the
Earth. - Halley was the first to find convincing proof of
cometary re-occurrence. He successfully predicted
the return of his namesake in 1758.
- Comets follow elliptical orbits, and these are
often inclined with respect to the planet orbits. - Long (200 yrs) and intermediate (30-200 yrs)
period comets come from Oort cloud. Short period
comets are from Kuiper belt.
Dr Conor Nixon Fall 06
Diagram Tim Stauffer
31ASTR 330 The Solar System
- Lecture 10 Composition etc
- Largest component of comets is water ice. Also
perhaps 10 CO, plus CH4, NH3, CO2 and others. - Molecules quickly ionized or dissociated (broken
up) by solar radiation after leaving the nucleus,
see H2O, CH, CH2, OH, NH etc.
- Tail colors
- Hydrogen envelope is blue due to H emission.
- Plasma tail is blue due to CO fluorescence
(straight tail). - Dust tail is yellow due to reflected sunlight
(curved tail).
Dr Conor Nixon Fall 06
Picture Nanjing University Astr.
32ASTR 330 The Solar System
- Lecture 10 Comet missions and fates
- Comet close-up missions
- Giotto/Vega missions to Halley (1986). Found a
dark (4 albedo) small nucleus (16x8x8 km). - Deep Space 1 passed Borelly in 2001 darker than
Halley. - Stardust passed Wild-2 in Jan 2004.
- Also note S-L 9 impact with Jupiter.
- Possible fates of a comet
- Total evaporation
- Dead comet
- Collision
- Gravitational ejection
Dr Conor Nixon Fall 06
33ASTR 330 The Solar System
- What is meant by a geocentric universe? A
heliocentric one? - Give a major contribution to astronomy by each of
the following Aristotle, Ptolemy, Copernicus,
Kepler, Galileo, Newton. - How old is the Sun, and what is the name of the
mechanism which powers it? - Name the three visible layers of the Suns
atmosphere, and give an approximate temperature
for each. - What information can we tell about a planet from
infrared spectral lines? - Give three examples of volatile species in the
solar system, and say where they could be found.
Dr Conor Nixon Fall 06
34ASTR 330 The Solar System
- Why did the gas cloud collapse to a disk and not
a point why did everything not fall into the
Sun? - Why are the inner planets volatile-poor while
the outer planets are volatile-rich? - Name three famous meteorites, and say what they
are famous for. - Why are the Allan Hills in Antarctica a good
place to hunt for meteorites? - What is the meaning of (a) parent nucleus (b)
daughter nucleus (c) half-life? - Basaltic meteorites are another type of
differentiated meteorite. What does the term
mean? From what part of the parent body do
basalts come?
Dr Conor Nixon Fall 06
35ASTR 330 The Solar System
- What are the three main asteroid types?
- What are resonance gaps, and why do they occur?
- Give the general properties of comet orbits are
their orbits similar to those of the planets? - It has been stated that comets are actually very
dark. How come we can see them?
Dr Conor Nixon Fall 06