Transcript Extra-Solar Planets

There are ~200 billion stars in our galaxy…
…one of them is our Sun.
Are there other planets in the universe?
Is there another Earth out there?
2
Giordano Bruno (1548-1600)
Believed that the Universe was infinite and that
other worlds exists.
He was burned at the stake for his beliefs.
Extra-Solar Planets
Exoplanet - A large body orbiting a
star other than the Sun.
Topics in this lecture:
•Review of planet formation
•The Habitable Zone
•Basic properties of discovered exoplanets
•Hot Jupiters
•Super-Earths
How to make a planet
• Large, cool cloud of gas and dust
– Gas makes the star, dust is necessary for planet
formation
– Dust is usually made of metals (Fe, Ni, Al), rocks
(silicates) and ices (solid H2O, CH4, NH3)
– Mostly H and He (these two elements make up
about 98% of our Solar System)
• Cloud begins to collapse under its own selfgravity
How to make a planet
Nebular Hypothesis
a) Solar Nebula
b) Contraction into rotating disk w/ hot center
c) Dust grains accrete to form larger and larger
particles
d) Large particles sweep out more material to form
planetesimals
e) Planetesimals eventually collide to form planets
The Habitable Zone
The region around a star within which the
requisite conditions for the existence of life
can be met.
Typically these conditions include:
– Suitable temperature for liquid water
– Existence of water itself
– Appropriate cosmo-chemical composition
– Are there other conditions or different ones? Are
these necessary and sufficient conditions for life?
The Habitable Zone
Depends on:
• Distance to parent star
• Type of parent star
• ATMOSPHERE
– Albedo
– Greenhouse effect
– Dynamics (=atmospheric motions)
Overview of Exoplanets
Planet (IAU definitions of Planet, Dwarf Planet and Small Solar System Bodies)
(1) A "planet” is a celestial body that:
(a) is in orbit around the Sun,
(b) Reached hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighborhood around its orbit.
(1) A "dwarf planet" is a celestial body that:
(a) is in orbit around the Sun,
(b) Reached hydrostatic equilibrium (nearly round) shape,
(c) has not cleared the neighborhood around its orbit, and
(d) is not a satellite.
(1) All other objects except satellites orbiting the Sun shall be referred
to collectively as "Small Solar System Bodies".
Limited by search size...
Imagine, if you shrunk our solar system
to a little larger than a quarter:
Our whole Solar
System
Our Milky Way Galaxy
would be this big
would be the size of
the United States.
From: http://planetquest.jpl.nasa.gov/Navigator/material/sim_material.cfm
And the neighborhood
where we’ve found new
planets would only be
the size of Manhattan.
You can even see some of the stars
that have planets in the night sky…
From:
…if you know where to look
From:
Overview of Exoplanets
Discovery
• First discovered extrasolar planet: 1988
• Number to date: 405
• Largest: 25 MJ
• Smallest: 0.006 MJ (7x10-5 MJ possible comet)
• Closest to parent star: 0.0172 AU
• Furthest from parent star: 670 AU
• Detection methods: numerous
Exoplanet Detection Methods:
5 proven methods
- Astrometry & Radial Velocity Method : 235 systems
- Transit Method: 46 systems
- Microlensing Method: 6 systems
- Pulsar Timing Method: 3 systems
1) Astrometric Method
Astrometric Method: Astrometry consists of measuring a
star's position in the sky and observing the ways in
which its position changes over time.
If the star has a planet, then the gravitational influence of
the planet will cause the star to move in a tiny circle.
Astrometric Method
Astrometric Method: Pro’s and Con’s
Pro’s:
1 telescope can search many stars at a time
Con’s:
Does not work for far away stars (Can’t see the motion)
Difficult to detect Terrestrial planets (not sensitive enough)
Process is slow (needs to observe multiple orbits)
Radial Velocity Method
Doppler Effect - The change in frequency of a wave as
perceived by an observer moving relative to the wave
source.
If a wave source is moving TOWARD an observer, the waves tend to “pile up”,
INCREASING the frequency, or pitch.
If a wave source is moving AWAY FROM an observer, the waves tend to
“spread out”, DECREASING the frequency, or pitch.
Radial Velocity Method
Blue Shift - Object is approaching
Red Shift - Object is receding
Radial Velocity Method
Radial Velocity Method (Doppler Method) This method measures slight changes in a star's velocity
as the star and the planet move about their common
center of mass.
Astronomers can detect this motion by analyzing the
spectrum of starlight due to the Doppler shift in the stars
spectrum.
The larger the planet and the closer it is to the host star, the faster the star
moves about the center of mass, causing a larger color shift in the spectrum of
starlight. That's why many of the first planets discovered are Jupiter-class (300
times as massive as Earth), with orbits very close to their parent stars.
Radial Velocity Method
Radial Velocity Method: Pro’s and Con’s
Pro’s:
Can be used on far away stars
Con’s:
Can only observe 1 star at a time (with high tech spectrographs)
Difficult to detect Terrestrial planets (not sensitive enough)
Process is slow (needs to observe multiple orbits)
3) Transit Method
From the vantage point of the Earth, the planet of HD 209458 moves across the
face of its star once every few days. It is so close that it is being vaporized by
the star.
Transit Method
Transit Method: Planet passes in front of parent star and
dim’s the light
Instuments detect this periodic dip in brightness.
Period and depth of the transits, orbit and size of the
planets can be calculated.
Transit Method
Transit Method
Transit Method
Transit Method: Pro’s and Con’s
Pro’s:
Can be used on far away stars
Can detect Terrestrial Planets (Method is sensitive enough)
Can determine atmospheric composition
Con’s:
Can only detect ~1% of all solar systems (angles need to exactly
align)
Process is slow (needs to observe multiple orbits)
Also called Photometric Method
Gravitational Microlensing Method
If a planet transits EXACTLY through the center of the
parent star, gravity from the planet will bend the starlight
Like a lens. The lensed light is magnified, and the star
appears to briefly brighten.
Telescopes can watch for the brief brightening of a star
to detect a planet.
Gravitational Microlensing Method
Pro’s:
Sensitive enough to detect terrestrial planets
Con’s:
The chances of a planet microlensing are very rare.
Extremely sensitive instruments need to be used.
Hot Jupiters
• Large planets, orbiting close to parent star
• Too close to be in the Habitable Zone
• Still some interesting atmospheric chemistry
and physics
– Silicate rain?
– Tidal locking causing interesting atmospheric
waves?
– All atmospheric chemistry/physics is still
speculative
Super Earths
• Terrestrial (“rocky”) planet
• More massive than Earth, less massive than
Jupiter (ranges used in the literature range
from 1 ME – 10 ME)
• Not necessarily “habitable”, as the name
might suggest
• Host stars are metal-poor
• Some super-Earths have been found in the
habitable zone around main sequence stars
Good Examples of Stellar Systems
• Gliese 876
a) Parent star:
– M3.5 V, T=3480 K, L=0.0124 Lsun
b) Gas Giant
– M=2MJ, a=0.208 AU
c) Gas Giant
– M=0.62 MJ, within orbit of Gliese 876 b
d) Super Earth
– Inside orbits of both Gliese 876 b and c
The Gas Giants in this system are within the Habitable
Zone, the Super Earth is too close (hot) for liquid
water.
Good Examples of Stellar Systems
• Gliese 581
a) Parent star:
– M3 V, T=3480 K, L=0.013 Lsun
b) Gas Giant (Neptune-sized)
– M=16 ME, a = 0.04 AU
c) Rocky Planet
– M=5 ME, a = 0.07 AU, within habitable zone (Temperature could
be as low as -3 oC or as high as 500 oC, due to runaway
greenhouse akin to Venus)
d) Super Earth
– M=7 ME, a = 0.22 AU, within habitable zone
e) Super Earth
– M=1.9 ME, a=0.03 AU
The Drake Equation
Where should we search for extraterrestrial life? How should we search?
What is required to have life? Complex life? Life we could communicate with?
The “Drake Equation” simply organizes these supposed requirements into separate
factors, a sort of list of possibilities for our consideration.
We want to estimate the likelihood that there are stars with planets with life that
developed into complex “intelligent” technological forms that might be
sending or receiving signals.
What we really want is the total number of them, because that tells us how far we
might have to search.
The Drake equation assigns a symbol for each one of these key factors, representing its
probability of occurrence, and multiplies all of them together. It is not something that is
actually solved, or that you will have to work with except to see a few basic things.
The Drake Equation:
At the end you should see this “equation” as a map of our class
topics:
N =R
fpl
nhab
Stars ? Planets? Habitable
planets?
fL
fC
Origin Complex
of life? life?
fT
L/T
Intelligence, Lifetime
technology? of civilization
Kardeshev Scale
• Type I Civilization: Utilize all the Energy of Planet
– Widespread Use of Fusion Power
– Alternative Energies
• Type II Civilization:
– Utilize all the Energy of Parent Star
– Create and harness energy from black holes
• Type III Civilization:
– Harness energy from multiple star systems and
galaxies
Kardeshev Scale
• A tiered category for civilizations based on the
amount of power available to them
• Type 0
• Type I
• Type II
• Type III
• Type IV
Type 0
• Primary Energy Attained From Burning Fossil
Fuels
• Sensitive to environmental, societal, and
biological pressures
• Extreme danger of extinction
Example: Planet Earth at Present
Type I
• Utilizes resources of entire planetary system
• Use of fusion power for energy needs
• Still Sensitive to extinciton
Type II
• Extract energy from multiple stellar systems
• Capable of Stellar engineering
• Very Low Extinction Risk due to spread
Type III
• Able to utilize the resources of an entire
galaxy
• Travel through wormholes possible
• Capable of galactic scale influence and
engineering
Type IV
Utilize all galaxies in the entire universe as an
energy source
Control matter, energy, time, and space
Effectively Immortal
Planet Earth at Present
• .7 on Kardashev Scale
The Drake equation is just a symbolic way of asking what the
probabilities are that a sequence of events like those below
(and more) might occur in other planetary systems.