Transcript Extra-Solar Planets

A105
Stars and Galaxies
Today’s APOD
Solar Lab
after
class today
 Final Exam –
Tuesday, Dec. 12
12:30-2:30 PM
Swain West 119
Final Exam…
• Open Book – Bring Text
–Part I – Multiple Choice
–Part II – News Articles
–Part III – Short Written Summary
• Comprehensive/emphasis on
galaxies, cosmology, life
elsewhere
Today’s Topics
• Planets around other stars
– how do we find them
– what are they like?
– what kinds of stars have planets?
• How likely it is that life exists elsewhere
than Earth? (Drake Equation)
• How would we detect life on other
planets?
Our Solar
System
Gas Giants
Terrestrial
Planets
Ice Giants
Searching for Planets
• Nearly 200 “extra-solar” planets have
been discovered
• How are planets discovered?
Radial velocity
Transits
– Gravitational lensing
– Wobbles in stars’ positions
Discovering
Planets
from
Spectra
o Remember the Doppler Shift!
o Absorption lines shift left or right if
stars move toward or away from us
o Planetary orbits cause stars’ radial
velocities to change
Periodic velocity changes due to orbiting planet
Velocity vs. Time
VERY high precision is needed
to measure these very small
velocity changes
Velocity (meters per second)
Velocity of 51 Peg
80
60
40
20
0
-20
-40
-60
-80
0
About 7 orbits in 30 days
10
20
P=4.2 days
Time (days)
30
40
A Planet around e Eridani
 A planet orbits the star e Eridani at
a radius of 3.2 A.U.
 e Eridani is similar to our Sun
 e Eridani is only 10.5 light years away
 The planet is similar to Jupiter
 The planet orbits e Eridani in 7 years
 e Eridani has at least one more planet
u And has at least 3 planets
terrestrial
planets
Planetary Transits
If the Earth lies in the same
plane as the orbit of a planet
we see a transit
•The planet passes across
the face of the star
•Some of the starlight is
blocked by planet and the
star appears dimmer
Seeing
planets
near stars
is hard
Looking for an Earthlike planet around a
nearby star is like standing on the East
Coast of the United States and looking for a
pinhead on the West Coast — with a VERY
bright grapefruit nearby.
• Very large telescopes will help
This photo shows an image
of the faint star GQ Lupi
taken in the infrared. The
faint object to the right of the
star is a possible planetary
companion. It is 250 times
fainter than the star itself
and it located 0.73
arcsecond west. At the
distance of GQ Lupi, this
corresponds to a distance of
roughly 100 astronomical
units. The planet probably
has a mass of about 2 x
Jupiter.
Imaging
Planets?
• Orbiting the
brown dwarf
~225 light years
away
• Young, about
1000K
• Further from its
“sun” than Pluto
is from ours
(brown dwarf is
blocked out)
Another
possible
planet
Location
of brown
dwarf

Possible planet
Properties of KNOWN ExtraSolar Planets
•
•
•
•
All are gas giants like Jupiter and Saturn
Most are larger than Jupiter
Many orbit close to their parent stars
Some are in systems with multiple planets
Known Planets Are Close to Stars
Hot Jupiters
These hot Jupiters form
further out, and migrate
inward as they eject
smaller bodies from their
planetary systems
Selection Effects
• Close-in, massive planets are easier to
detect
• Far-out planets and light-weight planets
are MUCH HARDER to detect
• So far, we’ve only been able to detect
massive, close-in planets
• Techniques, sensitivity are improving
• Terrestrial planets soon!
The
Habitable
Zone
Too hot!
Too cold!
•The planet needs to be the right
distance from the star. WHY?
•The star needs to have the right mass.
WHY?
A planet needs the right star!
Constraints on star systems:
1) Old enough to allow time for evolution (rules
out high-mass stars - 1%)
2) Need to have stable orbits (might rule out
binary/multiple star systems - 50%)
3) Size of “habitable zone”: region in which a
planet of the right size could have liquid
water on its surface.
Even so… billions of stars in the Milky Way seem
at least to offer the possibility of habitable worlds.
You are
here
There are 400 Billion Stars in our
Galaxy. How many harbor life?
How common is life of any kind in the Milky Way?
Very Rare
Rare
Common
Very Common
How common is intelligent, technological life?
Very Rare
Rare
Common
Very Common
The Drake Equation
• Start with 1011 stars in the Milky Way…
• What fraction of the stars are similar to the Sun?
• What fraction of solar type stars have planets?
• What fraction of solar type stars with planets have planets in the
habitable zone?
• On what fraction of these planets will life emerge?
•
On what fraction of these will intelligence emerge?
•
What fraction of these will develop technology?
• What fraction of a star’s life will a technological civilization survive
(assume a solar-type star remains on the main sequence for 1010
years)?
The Drake Equation
What are the odds that there are intelligent, advanced,
communicative civilizations out there? How many can we
expect to exist in all of the Milky Way Galaxy?
Make your own calculation of the
number of intelligent,
communicative, technologically
advanced civilizations in the
Milky Way.
All stars in the
Milky Way
fraction with planets?
fraction in the habitable zone?
fraction with simple life?
with technical society?
with intelligence?
with long-lasting technology?
= NHP  flife  fciv  fnow
We do not know the
values for the Drake
Equation
NHP : probably billions.
flife : ??? Hard to say (near 0 or near 1)
fciv : ??? It took 4 billion years on Earth
fnow : ??? Can civilizations survive long-term?
Search for Extra-Terrestrial Intelligence
SETI experiments look for deliberate signals from E.T.
Can We Find Extra-Terrestrial
Intelligence?
• Looking for SIGNALS is the easiest way
• We can also transmit a signal (but it’s a long wait
for the answer...)
• Different kinds of signals to listen for:
– local communication signals: on Earth, this includes
TV, radio, etc.
– communication between the planet and another site,
such as satellites and spacecraft
– A BEACON signal used to try to communicate with
other civilizations.
Can Earth Be
Heard from
Space?
• YES! Earth has been broadcasting TV and radio
communications for the last 50 years. ET civilizations
up to 50 light years away could be picking us up.
• We can “listen” but radio wavelengths may be best
– Biggest collecting area - Arecibo telescope.
– The background sky is the quietest at wavelengths of about
0.1 mm. At shorter wavelengths, emission from the galaxy is
loud, and at longer wavelengths, interstellar clouds absorb the
signals
Message to M13
Nov 1974
• Message was beamed from the
Arecibo radio telescope
– toward the M13 star cluster
– 24,000 light-years away
– a 1679 (23 x 73) pulses and spaces
• The message was transmitted only
once and was intended to serve as
a exercise in how we might go
about trying to contact extraterrestrials.
Message to
M13
• Formed a picture showing
when arranged in a rectangle
– numbers 1-10
– elements, chemicals of life
– a DNA molecule
– a stick figure of a human
– solar system
– diagram of radio telescope
Searching for ET
• NASA funded SETI until 1993
• Present efforts all privately funded
– SETI Institute (Frank Drake)
• seti@home -- help analyze SETI data
– Planetary Society
• META (million channel extraterrestrial assay) -scans one million channels in the band
• BETA (billion channel version of META)
• 84 ft. dish antenna at Harvard Univ.
• connected to supercomputers that look for nonrandom patterns in the signals (most of the signals
come from natural sources such as stars)
• 250 megabytes of data each second
Your computer can help! SETI @ Home:
a screensaver with a purpose.
Visiting ET?
• With foreseeable technology, we can achieve
speeds of 10% of the speed of light
• We can travel 10 light years in 100 years
• We can reach the nearest star in 43 years
• Allow each new colony 5000 years to duplicate
the technology
• Colonies could spread out about 50 light years
every 25,000 years
How long to colonize?
Assume 100,000 years
per 20 parsec hop
Total time to cover the
Galaxy:
1500 hops x 100,000 years
= 150,000,000 years
The Fermi Paradox
•
•
•
•
Emil
Konopinski
LANL Fuller Lodge
Cafeteria
Enrico Fermi
Edward Teller
Herbert York
Emil
Konopinski
LANL Tech
Area
Enrico
Fermi
The Fermi Paradox
The Drake Equation – A few
hundred technical civilizations
150,000,000 million years
to colonize the Galaxy
WHERE IS EVERYBODY?????
Where is Everyone?
• Some factors in Drake equation may be
much smaller than we believe – is life, or
intelligent life, very rare?
• Do civilizations hide to avoid a “galactic
scourge?”
• Do technological civilizations selfdestruct?
• Is no one more advanced than we are?
• The Zoo hypothesis…
Possible solutions to the paradox
Civilizations are common but
interstellar travel is not. Perhaps…
 Interstellar travel more difficult than we
think
 Desire to explore is rare
 Civilizations destroy themselves before
achieving interstellar travel
These are all possibilities, but not very appealing…
Possible solutions to the paradox
We are alone: life/civilizations much rarer
than we might have guessed.
•
Our own planet/civilization looks all the more
precious…
OR - There IS a
galactic
civilization…
… and some
day we’ll meet
them…
Difficulties of
Interstellar Travel
•
•
•
•
Far more efficient engines are needed
Energy requirements are enormous
Ordinary interstellar particles become like cosmic rays
Social complications of time dilation
Traveling to Another Star?
• Distances between stars are much greater than
we can imagine
• Sci-fi books and movies have dramatized space
travel to make it seem possible
– Interstellar travel may never happen
– Even the Voyager spacecraft (some of the fastest
ever flown) traveled at only 20 km/s through space not even 1% of the speed of light. They would take
60,000 years to reach even the nearest star
100.000000%
Maximum Speed Achieved
10.000000%
0.100000%
0.010000%
Space Shuttle
0.001000%
Automobile
0.000100%
Plane
0.000010%
Train
Horse
1000
100
10
1000
100
10
Years
Before
Present
YEARS BEFORE
1
Now
0.000001%
0.1
0.01
0.001
10
100
1000
Years
From
Now
YEARS
AFTER
% Speed of Light
1.000000%
Can we travel to new worlds?
•
•
•
Within the lifetime of today’s children
we will be able to send robotic
spacecraft to visit our nearest
neighbors
At 10% of the speed of light (30,000
km/sec) travel time will be about 100
years
Then wait another 10-20 years for
the data to return
SOLAR LAB!
Kirkwood Obs.
NOW!