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
Ganymede
Io
Europa
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 Earth-
Like 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 CO
2

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.