Download Lecture 25

ASTR368
Exoplanet Detections
Kepler
Extra-Solar Life
Life in the Universe (Chapter 24)
http://grooveshark.com/s/Is+There+Anybo
Out+There/541wYk?src=5
Other Possible Necessities for Life
A large planet like Jupiter to clear out asteroids?
A large moon?
A magnetosphere?
The right location in a Galaxy?
Impacts and Habitability
Some scientists argue
that Jupiter-like planets
are necessary to reduce
rate of impacts
If so, then Earth-like
planets are restricted to
star systems with
Jupiter-like planets
Climate and the Moon
The planet should spin
relatively quickly so
day/night temperatures
aren’t too dramatically
different
The Earth has an
unusually large Moon
Tidal pools are
ultimately caused by the
Moon and may be
necessary for life
Magnetospheres
Magnetosphere protects a planet from a stellar
wind, which may disrupt formation of life
Constraints on Galaxy Location
Some scientists argue
that proportions of
heavy elements need to
be just right for
formation of habitable
planets
If so, then Earth-like
planets are restricted to
a Galactic habitable zone
The Drake Equation
How likely is this process?
How special is the Earth?
Frank Drake
The Drake Equation
How likely is this process?
How special is the Earth?
R* is the average rate of star formation in our Galaxy
fp is the fraction of those stars that have planets
ne is the average number of planets that can support life
fℓ is the fraction of the above that develop life at some point
fi is the fraction of the above that develop intelligent life
fc is the fraction of civilizations that develop a technology
that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable
signals into space.
The Drake Equation (simplified)
Number of civilizations with whom we could potentially
communicate
N = NHP  flife  fciv  fnow
NHP = total # of habitable planets in galaxy
flife = fraction of habitable planets with life
fciv = fraction of life-bearing planets w/ civilization at
some time
fnow = fraction of civilizations around now.
We do not know the values for the Drake Equation
NHP : probably billions.
flife : ??? Hard to say (is it near 0 or near 1?)
fciv : ?????? It took 4 billion years on Earth
fnow : ?????? Can civilizations survive long-term?
What are we Doing to Find E.T.?
1) Space probes!
2) SETI searches
3) Locating extrasolar planets
But we’re not really trying too hard, all
things considered
Space Probes
Voyager 1+2, Pioneer 10+11 launched in the 1970s and
still going
Spacecraft take about 100,000 years to reach the
nearest stars.
http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html
Pioneer plaque
Voyager record
New Horizons
To infinity and beyond!
The Search for ExtraTerrestrial Life (SETI)
SETI searches the sky at radio frequencies for strong,
repeating signals IN OUR GALAXY
Nothing plausible so far….
SETI @ Home
We have even Sent a few Signals
Sent from Arecibo Telescope in 1974 to
globular cluster M13 by Frank Drake, Carl
Sagan and others
Fermi’s Paradox
Plausible arguments suggest that civilizations should be
common, for example:
Even if only 1 in 1 million stars gets a civilization at
some time  100,000 civilizations
So why we haven’t we detected them?
Solutions to Fermi’s Paradox
1) We are alone: life/civilizations much rarer than we
might have guessed.
Our own planet/civilization looks all the more
precious…
2) There are lots of other civilizations but lots of
stars. Someday we’ll meet them.
Anthropic Principle
The Universe appears to be fine-tuned for life (us).
If the parameters of the Universe (e.g., the force of
gravity) were only slightly different, stars and
galaxies would not form, and we would not be here.
The Anthropic Principle states that the Universe
appears fine-tuned to us, because we are here to
observe it. If we were not here, there would be no
one to report on whether the Universe is fine-tuned
or not.
Anthropic Principle
Modified anthropic principle (Schmidhuber):
The 'problem' of existence is only relevant to a
species capable of formulating the question.
Prior to Homo sapiens' intellectual evolution to
the point where the nature of the observed
universe - and humans' place within same spawned deep inquiry into its origins, the
'problem' simply did not exist.