Title: Elements of the Solar System, Exploring Extrosolar Planets and Evolution of Planetary Systems
1Elements of the Solar System,Exploring
Extrosolar PlanetsandEvolution of Planetary
Systems
2The Astronomical Unit (AU)
- The appropriate length unit for studying the
Solar System is AU - AU is the average distance between the Sun and
the Earth - 1 AU 150 Million km8 light minutes
31-The Solar System
4Not only the Sun and the Planets
- The Sun
- Planets (terrestrials and Jovians)
- Moons of the planets
- Meteorites
- Astroid belts
- Comets
- Oort Cloud
- Kuiper Belt
- Interplanetary dust
5Mass Distribution
- Sun 99.85
- Planets 0.135
- Comets 0.01 ?
- Satellites 0.00005
- Minor Planets 0.0000002 ?
- Meteoroids 0.0000001 ?
- Interplanetary Medium 0.0000001 ?
- Simply Sun 99.9 0.1 Jupiter
6The Nine Planets
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
- Pluto(?)
MNEMONIC My Very Educated Mother Just Sent Us
Nine Pizzas
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9Imagening the distances
- Imagine the Solar System being a soccer ground
(about 100 m long). - The Sun would be a glaring orange in the centre.
- Pluto would encircle the sun at the edge of the
soccer ground, having the size of a dust
particle. - The Earth would be 1,30m away from the orange,
having the size of a sesame seed.
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11Bodes Relation
- a simple rule that gives the distances of the
planets from the Sun
where N0, 3, 6, 12, 24for Mercury, Venus,
Earth, Mars, etc.
12 Planet N Bodes Law Radii
True Orbital Radii
Mercury 0 (04)/10 0.4 AU 0.39 AU
Venus 3 (34)/10 0.7 AU 0.72 AU
Earth 6 (64)/10 1.0 AU 1.00 AU
Mars 12 (124)/10 1.6 AU 1.52 AU
____ 24 (244)/10 2.8 AU _______
Ceres 24 2.88 AU
Jupiter 48 (484)/10 5.2 AU 5.2 AU
Saturn 96 (964)/10 10.0 AU 9.5 AU
Uranus 192 (1924)/10 19.6 AU 19.2 AU
Neptune ? ? 30.1 AU
Pluto 384 (3844)/10 38.8 AU 39.5 AU
13What does Bodes Law tell us?
- Bode's Law predicted that there should be a
planet between the orbits of Mars and Jupiter. - The "missing planet" turned out to be the
asteroid belt.
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15Obliquity of the Planets
16The orbit of the planets lie on a plane (except
for the Plutos)
17Terrestrial Planets
- The inner four planets at the center of the solar
system - Mercury, Venus, Earth, Mars
- They all are small, rocky, rotate slow, they
have small number of moons. - Metal cores.
18Jovian Planets
- Outer planets of the Solar System
- Jupiter, Saturn, Uranus Neptun
- They are made of gas/liquid/ice
- No solid surface
- Small solid core (rock)
- They have rings
- Large number of moons
19Terrestrial and Jovian Planets
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22Interiors of Jovian Planets cross-cuts
23Interiors of Jovian Planets cross-cuts
Saumon Guillot (2004)
24Gas giant planets Jupiter Saturn
- Dominant composition
- Hydrogen Helium, like the sun
- Surface clouds ammonia ice, water ice....
- Deep in interior liquid metallic hydrogen
- Even deeper rocky core of 10...15 M?
- These are model results which depend on equation
of state of hydrogen - For Saturn this is certain (unless models are
wrong) - For Jupiter the uncertainty includes Mcore0
25Ice giant planets Uranus Neptune
- Dominant composition
- Water Ammonia Methane ices
- Only atmosphere contains H, He (in total only
minor) - Uranus
- 25 Iron Silicates
- 60 Methane Water Ammonia
- 15 Hydrogen Helium
- Neptune
- 20 Iron Silicates
- 70 Methane Water Ammonia
- 10 Hydrogen Helium
26Thermal emission of Jupiter and Saturn
- Jupiter and Saturn emit more radiation than they
receive from the sun. - They are not massive enough for nuclear burning
(need at least 13 Mjup) - Kelvin-Helmholz cooling time scale much shorter
than current age (at least for Saturn) - Possible solution
- Helium slowly sediments to center, releases
gravitational energy
27Why UN ice, JS hydrogen?
- Theory
- All four formed at similar location, first
forming a rockice core by accumulating icy
bodies - Somehow U N were moved outward and did not
accrete much gas anymore - J S remained and accreted large quantities of
hydrogen gas
28Summary - What do the inner planets look like?
- They are all
- rocky and small!
- No or few moons
- No rings
29Summary - The Jovian Planets
- They are all
- gaseous and BIG!
- Rings
- Many moons
30Quantitative Planetary Facts
31What are Moons?
- Moons are like little planets that encircle the
real planets. - Usually, they are much smaller than planets.
- Planets can have no moons (like Mercury and
Venus), one moon (like Earth) or up to a very
large number of moons (e.g. gt63 for Jupiter). - Mars (2), Saturn (gt34), Uranus (gt27), Neptun
(gt13), Pluto (1)
32Asteroids
- Small bodies
- planetoid, minor planet
- Their mass is not sufficient to make them
spherical - Many of the asteroids are part of the asteroid
belt between Mars and Jupiter. - Believed to be left over from the early evolution
of the solar nebula. - Largest object Ceres is about 1000 km accross
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34Asteroid Belt
- The doughnut-shaped concentration of asteroids
orbiting the Sun between Mars and Jupiter - More that 200000 asteroids
- Total mass, a few 1024 g, is 1/30 of the Moon.
- if the estimated total mass of all asteroids was
gathered into a single object, this object would
be less than 1,500 kilometers across
35The Origin of the Asteroid Belt
- The asteroid belt may be material that never
coalesced into a planet, perhaps because its mass
was too small the total mass of all the
asteroids is only a small fraction of that of our
Moon. - A less satisfactory explanation of the origin of
the asteroid belt is that it may have once been a
planet that was fragmented by a collision with a
huge comet.
36Kirkwood Gaps
This slide is not essential for the exam and can
be skipped
- If you plot the radius of the orbits of the
asteroids you do not get a smooth bell-curve'
shape. There are concentric gaps in the asteroid
belt known as Kirkwood gaps. - These gaps are orbital radii where the
gravitational forces from Jupiter do not let
asteroids orbit (they would be pulled into
Jupiter). - For example, an orbit in which an asteroid
orbited the Sun exactly three times for each
Jovian orbit would experience great gravitational
forces each orbit, and would soon be pulled out
of that orbit. - There is a gap at 3.28 AU (which corresponds to
1/2 of Jupiter's period), another at 2.50 AU
(which corresponds to 1/3 of Jupiter's period),
etc. The Kirkwood gaps are named for Daniel
Kirkwood who discovered them in 1866.
This is an example of resonance. This resonance
phenomenon has Jupiter passing by any asteroid in
the Kirkwood gaps every two or three asteroid
years, depending on which gap. The repeated
tugging induces an asteroid into larger, longer
orbits closer to Jupiter. Eventually, however, an
asteroid's resonance with Jupiter disappears as
its orbit increases.
37Comets
a white dust tail and a blue gas (ion) tail.
- A comet consists of a tiny nucleus with diameter
less than 10 km. The nucleus is made up of frozen
gases and dust. - Eccentric orbit around the Sun.
- Most comets spend most of their time at vast
distances from the Sun. - When they approach the Sun, some gases will be
vaporized and an extended coma will then be
produced (of size 100000 km). - The tail can be up to 1AU long.
- Orbits of a comet may be open or close. A comet
with an open orbit will only visit the Sun once.
However, a comet with a closed orbit (actually it
is elliptical) will visit the Sun again and
again. Perhaps, the most famous one is the Comet
Halley, it has a closed orbit with a period of 76
years.
38Comet Tails
- When a comet moves close to the Sun, the solar
wind (charged particles ejected from the Sun) and
the Sun's radiation pressure push the dust and
gases of the comets away, this will result in a
beautiful long tail. - From this, we know why the comet tail is always
pointing away from the Sun.
The dust trail is made of particles that are the
size of sand grains and pebbles. They are large
enough that they are not affected much by the
Sun's light and solar wind. The gas tail, on the
other hand, is made of grains the size of
cigarette-smoke particles. These grains are blown
out of the dust coma near the comet nucleus by
the Sun's light.
39Comet Orbits
40Meteoroids, Meteors and Meteorites
- When asteroids collide with one another they can
produce small fragments known as meteoroids. - If a meteoroid enters the atmosphere of the
Earth, it glows due to heat generated by
friction. These are called meteors. - If the rock survives the trip through the
atmosphere and strikes the surface of the Earth,
the remnant is called a meteorite. - Only 2 documented cases in which a person is hit
by a meteorite.
41Two documented Cases
This slide is not essential for the exam and can
be skipped
- Annie Hodges of Sylacauga, Alabamawas napping on
her couch on November 30, 1954 when an
eight-pound meteorite crashed through the roof.
It bounced off a large console radio and hit her
in the arm and then in the leg, leaving her
bruised but okay. - On the afternooon of June 21, 1994, Jose Martin
and his wife, Vicenta Cors, were driving in Spain
from Madrid to Marbella. As they zoomed past the
town of Getafe, a three-pound meteorite smashed
through their windshield on the drivers side,
ricocheted off the dashboard, and bent the
steering wheel, breaking the little finger on
Martins right hand. It then flew between the
couples heads and landed on the back seat. Other
than the broken little finger, they were okay.
42Meteor Shower
- Comets exposed to the heat of the inner solar
system slowly disintegrate - This is another source of meteoritic material
- When the Earth passes through the debris left in
a comets orbit, the result is a metor shower of
micrometeorites.
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44Perseid Meteor Shower
- Usually the best meteor shower of the year.
- It starts in August 10 and peaks the following 2
days - Specs of rock that have broken off the comet
Swift-Tuttle.
August 10, 1998
45November 13, 1833
46Kuiper Belt Oort Cloud
- Kuiper Belt is a "junkyard" of countless icy
bodies left over from the solar system's
formation. - Kuiper Belt is shaped like a disk.
- The Kuiper Belt extends from inside Pluto's orbit
to the edge of the solar system. - Kuiper Belt was discovered in 1992
- There are at least 70,000 "trans-Neptunians" with
diameters larger than 100 km in the radial zone
extending outwards from the orbit of Neptune (at
30 AU) to 50 AU. - The Oort Cloud, which is much further (50000 AU),
is a vast spherical shell of billions of comets.
47Kuiper Belt Oort Cloud
48Kuiper Belt Oort Cloud
49When is a planet not a planet?
Recently, the International Astronomical Union
(IAU) had a fierce to try to iron out the
definition of a planet. They decided that a
planet
- Is in orbit around the Sun.
- Has sufficient mass for their self-gravity to
overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape.
- Has cleared the neighbourhood around its orbit.
Objects that pass the first two tests, but fail
the third, and which are not themselves
satellites of other planets, are now called dwarf
planets.
50Quaoar and Sedna new planets?
Quaoar is a Kuiper belt object discovered by
Trujillo and Brown in 2002 with the Palomar
Telescope. It orbits outside Pluto and was the
largest Solar System object discovered since
Pluto in 1930. Its diameter is about 1300km (half
the size of Pluto), and it is on a very circular
orbit currently one billion miles outside
Pluto. Sedna is a similar object that is even
further away, and takes over 10,000 years to
orbit the Sun. It was discovered in 2004 by the
same astronomers.
512003UB313, aka Xena
In 2003, a Kuiper-belt object was found which is
bigger than Pluto. It even has its own moon! Its
orbital period is 560 years on a highly-inclined
orbit. Although colloquially known as Xena, it
is called 2003UB313 until an official name is
decided.
522-Formation of the Solar System
53- How was the Solar System Formed?
- A viable theory for the formation of the solar
system must be - based on physical principles (conservation of
energy, momentum, the law of gravity, the law of
motions, etc.), - able to explain all (at least most) the
observable facts with reasonable accuracy, and - able to explain other planetary systems.
- How do we go about finding the answers?
- Observe looking for clues
- Guess come up with some explanations
- Test it see if our guess explains everything (or
most of it) - Try again if it doesnt quite work, go back to
step 2.
54Planetary Nebula or Close Encounter?
- Historically, two hypothesis were put forward to
explain the formation of the solar system. - Gravitational Collapse of Planetary Nebula (Latin
for cloud) - Solar system formed form gravitational collapse
of an interstellar cloud or gas - Close Encounter (of the Sun with another star)
- Planets are formed from debris pulled out of the
Sun during a close encounter with another star.
But, it cannot account for - The angular momentum distribution in the solar
system, - Probability for such encounter is small in our
neighborhood
55Common Characteristics and Exceptions of the
Solar System
We need to be able to explain all these!
56Common Characteristics and Exceptions
57The Nebular Theory of Solar System Formation
Interstellar Cloud (Nebula)
It is also called the Protoplanet Theory.
58A Pictorial History
Gravitational Collapse
Condensation
Interplanetary Cloud
Accretion
Nebular Capture
59Pre-main Sequence Evolution
60The Interstellar Clouds
- The primordial gas after the Big Bang has very
low heavy metal content. The interstellar clouds
that the solar system was built from gas that has
gone through several star-gas-star cycles.
61Collapse of the Solar Nebula
Gravitational Collapse
Denser region in a interstellar cloud, maybe
compressed by shock waves from an exploding
supernova, triggers the gravitational collapse.
- Heating ? Prototsun ? Sun
- In-falling materials loses gravitational
potential energy, which were converted into
kinetic energy. The dense materials collides with
each other, causing the gas to heat up. Once the
temperature and density gets high enough for
nuclear fusion to start, a star is born. - Spinning ? Smoothing of the random motions
- Conservation of angular momentum causes the
in-falling material to spin faster and faster as
they get closer to the center of the collapsing
cloud. ? demonstration - Flattening ? Protoplanetary disk. Check out the
animation in the e-book! - The solar nebular flattened into a flat disk.
Collision between clumps of material turns the
random, chaotic motion into a orderly rotating
disk. - This process explains the orderly motion of
- most of the solar system objects!
62Condensation of the Solar Nebula
- Composition of the Solar Nebula
- As the protoplanetary disk cools, materials in
the disk condensate into planetesimals - The solar nebular contains 98 Hydrogen and
Helium (produced in the Big Bang), and 2
everything else (heavy elements, fusion products
inside the stars). - Local thermal environment (Temperature)
determines what kind of material condensates. - Water and most hydrogen compounds have low
sublimation temperature, and cannot exist near
the Sun. They exist far away from the Sun. - Metals and rocks have high sublimation
temperature, and can form near the Sun. - Frost line lies between the orbit of Mars and
Jupiter.
63The Four Phases of Matter
- There are in fact more than three phases of
matter. - Plasma when the temperature is very high, high
energy collision between atoms will knock the
electrons lose, and they are not bounded to the
atoms anymore
Core and corona of the Sun and stars
Surface of the Sun and stars
Surface of Earth
White dwarfs, CMB
64Transition Between Phases
Liquidation
Evaporation
Solid
Liquid
Gas
Solidification
Condensation
Condensation
Sublimation atoms or molecules escape into the
gas phase from a solid.
65Initially, small dust and ice particles in the
early solar nebula collided, sticking
electrostatically. As this accretion process
continues, gravity plays a greater role in
forming these planetesimals. These can be as
large as asteroids. Within a few million years,
some of these planetesimals have grown to
hundreds of kilometers and are nearly spherical
as a result of their self gravitation. They start
to affect the orbits of nearby planetesimals,
increasing the number of collisions.
66Accretion Formation of the Terrestrial Planets
- Accretion The process by which small seeds grew
into planets. - Near the Sun, where temperature is high, only
metals and rocks can condense. The small pieces
of metals and rocks (the planetesimals) collide
and stick together to form larger piece of
planetesimals. - Small pieces of planetesimals can have any kind
of shape. - Larger pieces of planetesimals are spherical due
to gravity. - Only small planets can be formed due to limited
supply of material (0.6 of the total materials
in the solar nebula). - Gravity of the small terrestrial planets is too
weak to capture large amount of gas. - The gas near the Sun were blown away by solar
wind.
Click it!
67Solar Winds
- Solar wind is the constant outflow of gas from
the Sun - Evidences of Solar Wind
- Tails of Comet always point away from the Sun,
indicative of the existence of solar wind. - SOHO (SOlar and Heliospheric Observatory) C2 and
C3 movies. - Effects of Solar Wind on Planet Formation
- At certain stage of the planet forming process,
Solar winds blow away the gases in the planetary
nebula, ending the formation of the planets.
68Nebula Capture Formation of the Jovian Planets
- In the regions beyond the frost line, there are
abundant supply of solid materials (ice), which
quickly grow in size by accretion. - The large planetesimals attract materials around
them gravitationally, forming the jovian planets
in a process similar to the gravitational
collapse of the solar nebula (heating, spinning,
flattening) to form a small accretion disk. - Abundant supply of gases allows for the creation
of large planets. - However, the jovian planets were not massive
enough to trigger nuclear fusion at their core.
69The Results of Selective Condensation
- Not much light gases were available for the
formation of planets near the Sun, but small
amount of metals and rocks are available - The planets close to the Sun are small and rocky
- There are abundant supply of light gases farther
out - The planets far away from the Sun are big and
composed of gases of hydrogen components - These processes can explain the two types of
major planets, their size differences, locations,
and composition.
70Origin of Comets and Asteroids
- Asteroids
- Rocky leftover planetesimals of the inner solar
system. - Most of the asteroids are concentrated in the
asteroid belt between the orbit of Mars and
Jupiter. - Jupiters strong gravity might have disturbed the
formation of a terrestrial planet here. - Jupiter also affects the orbit of these asteroids
and sent them flying out of the solar system, or
sent them into a collision cause with other
planets. - Comets
- Icy leftover planetesimals of the outer solar
system. - Comets in between Jupiter and Neptune were
bullied away from this region, either collide
with the big planets, or been sent out to the
Kuiper belt or the Oort cloud. - Comets beyond the orbit of Neptune have time to
grow larger, and stay in stable orbit. Pluto may
be (the biggest) one of them.
71Explaining the Exceptions Impact and Capture
Heavy Bombardment There were many impact events
during the early stage of the solar system
formation process, when there were still many
planetesimals floating around.
- Evidences of Impact
- Comet Shoemakers collision with Jupiter
- Surface of the Moon and Mercury,
- More in Chapter 7
- Effects of Impact
- Tilt of the rotation axis of planets (Venus,
Uranus) - Creation of satellites (May be our moon)
- Exchange of materials (Where did the water on
Earth come from if most of the gases were blown
away by solar wind after Earth was formed?) - Catastrophes (Where did all the dinosaurs go?)
72Where did the moons come from?
- Giant Impact
- Our moon may have been formed in a giant impact
between the Earth and a large planetesimal - Captured Moons
- Phobos Deimos of Mars may be captured
asteroids. - Triton orbits in a direction opposite to
Neptunes rotation
Capture of Comet Shoemaker by Jupiter
73The Age of the Solar System
- Through radioactive dating, the age of the solar
system is determined as 4.6 billion years - Potassium-40 (an isotope of Potassium K19)
decays to Argon-40 by electron capture, turning a
proton in its nuclei into neutron (thus changing
its chemical properties) - Potassium-40 exists naturally
- Argon is an inert gas that never combine with
anything, and did not condense in the solar
nebula - By determining the relative amount of
Potassium-40 to Argon-40 trapped in rock, we can
determine the age of rock, assuming that there
were no Argon-40 initially
74Formation of the Solar System
- Formed 4.568 Gigayears ago (age of oldest known
solids in solar system) - Mars formed about 13 Megayears later
- Earth formed 30 to 40 Megayear later
- Leading theory for formation of the moon is that
about 100 Myr after the birth of the solar system
Earth was hit by a Mars-size object. The heavy
cores of both objects formed the new Earth and
the light silicate crusts formed the moon. - Jovian planets (Jupiter, Saturn, Uranus, Neptune)
must have formed in less than 10 Myrs (life time
of gaseous protoplanetary disks)
75Radioactive Dating Using K-40
- For every 1.25 billion years, half of the
Potassium-40 decay and turn into Argon-40 - 1.25 billion years is called the half-life of
Potassium-40.
76The Formation Of Solar System Simulations
Simulations from www.astronomyplace.com. Check
them out!
History of the Solar System, Part 1
History of the Solar System, Part 2
Orbit in the Solar System, Part 4
History of the Solar System, Part 3
77Do we Have a Viable Theory?
- YES!
- We can explain most of the properties of the
solar system, including the exceptions. - We used only good physics.
- Testing Our Theory against other solar system
- Can we find protoplanetary disks (before planets
were formed)? - Can we find other solar system?
- If we do find other solar system, does our theory
explain the other solar system?
78Evidences Of Protoplanetary Disks
Do we have any evidence of the existence of
planetary nebulae outside of the solar system?
We now have many observational evidences of the
existence of the protoplanetary Disks.
Hubble Space Telescope image of the dust disk
surrounding Beta Pictoris
Each disk-shaped blob is a disk of material
orbiting a star
79Origin of the Solar System Key Concepts
- How the Solar System formed
- (1) A cloud of gas dust contracted to form a
disk-shaped solar nebula. - (2) The solar nebula condensed to form small
planetesimals. - (3) The planetesimals collided to form larger
planets. - When the Solar System formed
- (4) Radioactive age-dating indicates the Solar
System is 4.56 billion years old.
80- Clues to how the Solar System formed
How things move (dynamics) - All planets revolve in the same direction.
- Most planets rotate in the same direction.
- Planetary orbits are in nearly the same plane.
81(1) A cloud of gas and dust contracted to
form a disk-shaped nebula.
- The Solar System started as a large, low-density
cloud of dusty gas. - Such gas clouds can be seen in our Milky Way and
other galaxies today.
82- The flat, rapidly rotating cloud of gas and
dust was the solar nebula. - The central dense clump was the protosun.
- Similar flat, rotating clouds are seen around
protostars in the Orion Nebula.
83- The contraction of the solar nebula made it spin
faster and heat up. (Compressed gas gets hotter.)
Temperature of solar nebula
gt 2000 Kelvin near Sun lt
50 Kelvin far from Sun.
84(2) The solar nebula condensed
to form small planetesimals.
- Approximate condensation temperatures
1400 Kelvin metal (iron, nickel)
1300 Kelvin rock (silicates)
200 Kelvin ice (water, ammonia,
methane) - Inner solar system over 200 Kelvin, only metal
and rock condense. - Outer solar system under 200 Kelvin,
ice condenses as well.
85- As the solar nebula cooled, material
condensed to form planetesimals
a few km across. - Inner Solar System
Metal and rock solid
planetesimals Water, ammonia,
methane gas. - Outer Solar System
Metal and rock solid planetesimals
Water, ammonia, methane solid,
too. - Hydrogen and helium and gaseous everywhere.
86(3) The planetesimals collided to
form larger planets.
- Planetesimals attracted each other
gravitationally. - Planetesimals collided with each other to form
Moon-sized protoplanets.
87- Protoplanets collided with each other (and with
planetesimals) to form planets. - Inner Solar System
- Smaller planets, made of
- rock and metal.
- Outer Solar System
- Larger planets, made of
- rock, metal and ice.
- In addition, outer planets are massive enough to
attract and retain H and He.
88- Collisions between protoplanets were not gentle!
- Venus was knocked upside-down, Uranus and Pluto
sideways. - Not every planetesimal was incorporated into a
planet. - Comets leftover icy planetesimals.
- Asteroids leftover rocky and metallic
planetesimals.
89- How does this nebular theory explain the
current state of the Solar System? - Solar System is disk-shaped
It formed from a flat solar nebula. - Planets revolve in the same direction
They formed from rotating nebula. - Terrestrial planets are rock and metal
They formed in hot inner region. - Jovian planets include ice, H, He
They formed in cool outer region.
90More Protoplanetary Disks
MAUNA KEA, Hawaii (August 12, 2004) The sharpest
image ever taken of a dust disk around another
star has revealed structures in the disk which
are signs of unseen planets. Dr. Michael Liu,
an astronomer at the University of Hawaii's
Institute for Astronomy, has acquired high
resolution images of the nearby star AU
Microscopii (AU Mic) using the Keck Telescope,
the world's largest infrared telescope. At a
distance of only 33 light years, AU Mic is the
nearest star possessing a visible disk of dust.
Such disks are believed to be the birthplaces of
planets.
http//www.ifa.hawaii.edu/info/press-releases/Liu0
804.html
913-Extra-solar Planets
92Do you believe solar systems like our own are
common or rare among sun-like stars in the disk
of the Milky Way galaxy? Why?
We expect to find planetary systems around other
systems because of the Copernican Principle.
93Are there more planets in the Universe?
- Yes, there are other planets, so-called
extra-solar planets (around stars other than the
Sun). - But it is very difficult to spot them, since they
are far far away. - Recall that a planet is much smaller than a star.
- How can planets of other stars be spotted then?
94Planets of other stars
- There are three main ways that astronomers search
for these planets - Doppler method
- Transit method
- Gravitational (micro)lensing
95Doppler Method
- The planet will pull the star into a small
circle about the center of mutual mass, called
the system barycenter. On the sky, the star will
move from side to side.
If you observe a star very accurately with
Doppler instruments, you may be able to measure
a slight wobble around the center of mass.
This can indicate a planet.
96Radial Motion of Stars due to Planets
97- Astrometrically (via a positional wobble)
- Spectroscopically (via blueshifts and redshifts
of absorption lines)
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99Astrometric (Wobble) Detections
If a stars position on the sky (proper motion)
wobbles with time, it could be due to an unseen
companion. Only Jupiter-mass planets have
enough mass to be detected in this way.
100First Success 1995
101Transiting Planets
- If you can observe many stars, you may sometimes
see one get slightly fainter for a little while.
This happens if a planet passes between us and
the star like a mini-eclipse.
102Transiting Extra-solar Planets
103Gravitational Lensing Detections
If a star/planet moves exactly in front of a
background star, the brightness of the background
star can be greatly magnified by the
gravitational lens effect.
104Detection via microlensing
OGLE-2003-BLG-235
Foreground faint (invisible) star passes across
background faint (invisible) star. Gravity of
foreground star amplifies background star.
Brightening of background star. If planet is
present around foreground star, AND one is lucky
that it also passes background star one sees
blip in the signal.
105Detection via microlensing
OGLE-2003-BLG-235
106Extrasolar planets to date
- First extrasolar planet was discovered around a
neutron star in 1991 - First extrasolar planet orbiting a normal star
was found in 1995 by Michel Mayor and Didier
Queloz of the Geneva Observatory in Switzerland
orbiting the star 51 Pegasi - More than 200 planets have been discovered see
http//www.obspm.fr/encycl/catalog.html - It is estimated that there are at least 20
billion planetary systems in our Galaxy.
107What has been found?
108More Known Planets
109Whats wrong with this picture?
These are all Jupiter-sized planets orbiting very
close to the star!
110Selection Effect
- Actually, our methods of detecting extra-solar
planets can find only massive planets that are
close to the stars. - So it is not surprising that all we have found
are such planets. - But we still need one explanation...
111But, why are these large planets so close to the
stars?
- According to our planetary nebular theory, large
planets can only be formed far away from the host
star, behind the frost line, where there are
abundant quantities of gasesSo, why do we see
these large planets so close to the stars? - Possible Explanation
- Maybe these planets were formed far away from
the stars as our planetary nebular theory
predicts. But for some reason (say friction
between the planets and the dense planetary gas)
caused the planets to lose their orbital angular
momentum and migrate toward the stars. - (Planetary migration is an active research field)
112Eccentricity of Planets
From Review by G. Marcy Ringberg 2004
113Is The Nebular Theory OK?
- We have evidences for the existence of
protoplanetary disks! - We have found many extrasolar planetsby indirect
methods. - We have not found any solar system like ours!
- All the extrasolar planets we found so far are
large, Jupiter-sized (or larger) planets. - All these planets are located very close to the
host star, inconsistent with the nebular theory.
- Why we dont find any solar system like ours?
- May be we just havent found them yet!
- Possible Explanation ? Detection Limit
- Larger planets at close distance to the host
stars produce larger Doppler effect and intensity
dropSmaller planets far away from the star
produce much smaller effect, and are more
difficult to detect.
114Summary
- We have a viable theory to explain the formation
of our solar system. - We have evidences that planetary nebulae exist in
other star systems. - However, we have not found a solar system similar
to ours outside of our own. - Extrasolar planets we found so far do not agree
with our theory The physics of our theory is
fundamentally correct, but details of the model
may need adjustment
115Links
- http//www.solarviews.com/eng/homepage.htm
- http//www.solarsystem.org.uk/
- http//learn.arc.nasa.gov/planets/
- http//solarsystem.nasa.gov/planets/
- http//pds.jpl.nasa.gov/planets/
- http//exoplanet.eu/
- http//exoplanets.org/
- http//observe.phy.sfasu.edu/courses/ast105/lectur
es105/ - http//liftoff.msfc.nasa.gov/academy/space/solarsy
stem/solarsystemjava.html