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Transcript
Are we Alone? - The Search for Life
beyond the Earth.
Ian Morison
Emeritus Professor of Astronomy
Gresham College
Star-stuff
Ring
Nebula
M1
The
Crab
Nebula
Elsewhere in our own Solar
System
We could find other simple life-forms
here.
Canals on
Mars?
The Face on Mars!
Valleys and Volcanoes
Olympus Mons
Islands and
Channels
Viking on Mars
• Two Viking Spacecraft landed on Mars in 1976 to search
for evidence of life.
Spirit and Opportunity
Martian Dust Devils
Phoenix Lander
Jupiter
4 major moons – discovered
by Galileo
Io
Europa
Ganymede
Callisto
Io
Jupiter’s Moon Europa
Breaking up of the surface
• Icebergs!
Water Plumes!
Searching for Life!
Finding Evidence of Simple Life
on other Planets
Can we see any exo-planets?
A real problem due to the
overwhelming brightness of the star
orbited by the planet.
Infrared observations by one of the
KECK telescopes
HR 8799 with
three planets
HST using a coronograph
• The Hubble Space
Telescope has
observed a planet in
orbit around the star
Formalhaut.
Indirect Detection Methods
The RADIAL VELOCITY or
DOPPLER WOBBLE method
51 Pegasi b
• The first planet
detected around a
normal star.
• Period just 4 days!
• A gas giant very close
to its star.
Planetary Transits
Detect the transit of a
planet as it crosses
the face of the star.
This results in a
slight drop in
luminosity.
This can only work
if the orbital plane of
the planet includes
the Earth.
HD 209458 transit
HD 209458 b
• 150 light years
from Earth.
• Planet orbits
every 3.5 days.
• 4 million miles
from its star.
• Atmospheric
temperature
~2000K.
Evidence for Life?
We could detect evidence of life by
observing the spectra of the planet’s
atmosphere.
Study the Infra-Red Spectrum
What does it tell us?
SETI
The Search for Extraterrestrial
Intelligence
The Seminal Paper
• In 1959 Giuseppe Cocconi and Phillip Morrison published
a paper in Nature in which they pointed out that given two
telescopes of the size of the newly built 250ft Mk1 Radio
Telescope at Jodrell Bank it would, in principle, be
possible to communicate across inter-stellar distances.
Where to look? Locations
• They suggested that any
search should target the
nearest Sun-like stars as
these live long enough and
are hot enough to allow life
a chance to evolve on a
planet at a suitable distance
from them.
• A target list was provided including Tau Ceti and
Epsilon Eridani.
Where to look? Frequency
• They pointed out that the background noise (atmosphere,
Galaxy, CMB etc.) was a minimum between ~1 to 10 GHz.
• This band included the (radio) Hydrogen Line at 1.4 GHz
and the OH Lines at ~ 1.6 GHz.
• The band from 1.4 to 1.6 GHz is called the Water Hole
Project Ozma
• In 1960 Frank Drake and his colleagues at Green Bank,
West Virginia, used the Tatel 85ft telescope to make the
very first SETI observations in what was called Project
Ozma.
Project Ozma
• They were given use of a new, state of art, low noise
parametric amplifier and made observations over a 400
KHz band around the Hydrogen Line at 1420 MHz.
• They observed Tau Ceti and Epsilon Eridani for a total of
two months, but only detected the, then top secret, U2 Spy
plane!
The Voyager Record
Numbers and
DNA
Continental
Drift
Birth
Arecibo Radio Telescope
Arecibo Message
How does what we have learnt about
other planetary systems affect the
likelyhood of other life being present
in our galaxy?
The Drake Equation
Number of Stars born per year in
the Milky Way
• Recent estimate of current SFR = 7
stars/yr
Fraction of Sun-type stars
• ~73-84% of the stars in
the Milky Way are M
type – too cool
• Upper limit of 21% of
stars in the Milky Way
are like our Sun.
So about 1 suitable star is born
per year
Fraction of Sun-type Stars with
Planets
• We do not yet know.
• As time goes by we will be
able to detect many more.
• There may be 10-30% of
stars with planetary systems.
Fraction of stars with terrestrial
planets within their solar systems
• Again we do not know – but
we are finding many solar
systems where we do NOT
believe there can be EarthLike planets.
• Hopefully this is because
solar systems like ours are
rather hard to find!
Number of Planets in a Star’s
Habitable Zone
• 8 planets; many satellites
• Earth, Mars; (Europa)
Fraction of habitable planets where
life arises
• Wild optimism: the
fraction where life arises
= 100%
Simple Life could be very
common.
How often will simple life evolve
into intelligent life?
This, in my view is the most difficult
part of this equation to estimate.
• Our Moon has
stabilised our
rotation axis
Its formation
gave us a
thinner crust.
• Recycling of CO2
COMETS
Fraction inhabited by intelligent
beings
• One needs, we believe,
a very long time to
allow life to evolve.
• Really difficult to
estimate how often a
planet will have a
temperate climate for
long enough
Perhaps our human race is rather
special.