Goal: To understand life in
our galaxy.
Objectives:
1) To understand the Basic building blocks for life
in general
2) To learn about What type of stars and planets
to look for if we want to find life
3) To understand How to find these planets
4) To examine The search for intelligent life
5) To learn about The Drake equation
Brainstorm!
• Try to find 6 characteristics of the most
basic life (note this is life in general – so if
you can think of a life form that does not
need it, it is not a basic building block).
• Note also this is not for human life, just the
most basic life (like bacteria).
• Finally, this is for life as we know it.
Lets find them in our solar system!
• Venus – too hot, not enough water, very
unpleasant.
• Earth – I am not 100% sure, but I think we may
have those building blocks on that planet.
• Moon – maybe some ice at the pole, but nope
not going to find life there.
• Mars – very tempting to be optimistic. It has
most of what you need (underground water,
frozen surface, but below that…). However, it is
lacking in Nitrogen.
I think the best place to look:
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Is a moon of Jupiter called Europa.
About the size of our moon.
No atmosphere.
However, due to tidal heating, underneath
about 1-10 miles of frozen surface lies a
gigantic underground ocean!
• It has all the possible blocks for life – so
does it have life?
• We need to send a probe there to find out.
SIM PlanetQuest
• Is a NASA mission scheduled to launch in 2015 (which
means you should expect it about 2020…).
• What this instrument will do different is that it will be an
interferometer.
• An interferometer is a telescope that is slit into two or
more parts and spread out over a large area.
• What this does is effectively gives you a bigger diameter
to your telescope.
• Since resolution ONLY depends on diameter, and not the
amount of light your collect, this can give you very good
resolution.
Why not done already
• One complication, you have to be able to
know the distance between telescopes
accurate to the wavelength of light.
• For radio this is easy because the
wavelengths are long.
• For infrared and optical this is hard
because the wavelengths are very tiny.
• For more info go to:
http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm
What it will do
• With a really good resolution you can measure
the positions of stars very accurately.
• Measure their positions once every month or so
and you can watch the stars move with time.
• Some of this will be due to parallax motion (due
to the earth’s motion around the sun).
• Some will be due to “proper” motion – which is
the motion of the star with respect to our sun.
• Once you subtract those out you get the orbital
motion – yes you will be able to watch the star
orbit around an imaginary point.
Advantages
• Can be used on any star.
• Can be used to detect planets as small as
the earth!
• Can be used to find planets further away.
• Disadvantage – you are still finding the
planet indirectly.
• You have no real info on the planet other
than its mass and orbital characteristics.
We want to find LIFE!
• To do this we have to look at a planet.
• However, planets are so small that we
have no hope of actually imagine their
surface features from many light years
away – sorry no finding oceans and
continents.
• So what can we do?
Chronographs
• When you have multiple detectors for
measuring light you can determine how
you add those together.
• If you are clever you can get them to add
together.
• If you are even more clever you can get
them to cancel out!
Blocking the star
• To image a planet directly you have to get
rid of all the light from the star.
• If you can do that then you have a better
shot at imagine a planet.
• If you can image the planet you can take
its spectrum.
• What will the spectrum tell you about the
planet?
Which molecule, if found in some
abundance, would indicate that
there was some form of life on the
planet?
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A) Carbon Dioxide
B) Nitrogen
C) Water
D) Ozone
What determines the makeup of
the atmosphere?
• There are 3 processes:
• 1) geological – volcanoes mostly.
• Volcanoes spew water, Carbon Dioxide,
Nitrogen, and Sulfur Dioxide into the
atmosphere
Interactions with the sun
• Two ways here:
• 1) UV rays can break apart molecules.
• This will form some oxygen in an atmosphere for
example, but only trace amounts.
• As we saw for the earth, this can also break
apart water molecules.
• 2) Solar wind – if a planet has no sizable
magnetic field certain gasses (such as water
vapor) will be removed from the atmosphere.
Biological
• This is the one we want to search for.
• If there are molecules that are a result of
biological processes, are short lived, and
do not occur much naturally, if we find
them, we have found life!
• Note this will be life in general, like
bacterial and plant life, not intelligent life.
• So, what do we look for?
Smoking guns for life?
• Nitrogen can be useful.
• However, it is difficult to detect, and many
atmospheres have it naturally (Venus +
Mars have 3%, and Titan has mostly
Nitrogen).
• How about molecular Oxygen (O2)?
• Well, it is even more difficult to observe.
• Very trace amounts are produced
naturally, so you would have to show a lot
of it (like our 26%) to be able to say it was
life induced, but we still can’t detect it…
The true guns
• Methane and Nitrous Oxide
• Methane does not survive long in an atmosphere as it
gets destroyed by UV rays.
• NO tends to react with Oxygen or goes to molecular
Nitrogen.
• Either way both are too trace to be seen with the
instruments coming out.
• However OZONE is the key!
• To have significant amounts of Ozone you need a lot of
free Oxygen, which means life!
• Also, Ozone is fairly easy to detect!
With what will we find it?
• Now that we know what to look for, what
will actually be doing the looking?
• NASA’s Terrestrial Planet Finder (TPF for
short) should be able to do all of this and
is scheduled for completion in 2020.
• However, their funding is being cut, so
there is a chance it won’t get off for awhile
(2030?).
• Anyhow, within our lifetimes we should be
able to find life outside our solar system!
Intelligent life
• This is great for life in general, but what
about ET?
• There is an agency that is searching for
intelligent life:
• SETI (Search for Extra Terrestrial
Intelligence).
What does SETI look for?
• SETI scours the radio section of the
electromagnetic spectrum.
• SETI tries to find signals that could not
occur naturally.
• Some examples include beamed
transmission, repeated patterns, very
narrow band emission, or anything else
that can only be created intentionally by an
alien civilization.
Suppose we find life, then what?
• If it is unintelligent life – we can do
NOTHING!
• Lets suppose we sent a craft to the alpha
Centauri system at a speed of 0.1 c.
• It would take 43 years to get there…
• The large distances make interplanetary
travel unlikely for a long time – and even
then very impractical.
How far away will life be?
• Do figure this one out we will use what is
called the Drake Equation.
• The Drake Equation is just a giant unit
conversion basically…
• There are a few forms to it.
• We will be examining an offshoot here…
Number of stars in galaxy
• 400 billion
However, how many of those stars
can have planets with intelligent
life?
• Big stars die too fast – not enough time to
evolve and a lot of UV light
• Small stars have planets tidally locked
• Slow rotation of planet means no magnetic
field which means no life on surface
So, need
• Stars like our sun
• Only about 10% are like our sun
• 2/3rds of those are in binary systems
• So, that leaves about 10 billion possible
intelligent life bearing suns
What fraction of those have
planets?
• This is the last of the factors that we know
well.
• It seems that 50-90% of stars form a
planet system.
• But even if it is only 1 in 10 then we still
have 1 billion useful planetary systems.
How many planets or moons like
our Earth in a region where you
can have life (in general)?
• This one is tricky.
• Stars with too low metals won’t form big enough
planets.
• Stars with too much metal will form hot Jupiters.
• Also, some of these systems will have more than
1 planet in a habitable zone (we have 3)
• If we say 1 planet per say 10 systems then we
still have 100 million Earth like planets in a
habitable zone.
What fraction of those have
actually developed life?
• Here we have to guess.
• Is life really easy to form when conditions
are right or were we fortunate?
• If only 1 in a thousand form life though that
is 100,000 planets with life on it!
What fraction of those have
develop intelligent life?
• This one is the biggest guess.
• However if only 1 in a thousand develop
intelligent life that is 100 intelligent
civilizations in just our own galaxy.
For what fraction of their planet’s
life do they use technology that we
could use to communicate with
them?
• We have only been at this for 60 years.
• Even if the average is a million years well there would
have to have been 5000 civilizations for us to be able to
detect one.
• So that would now mean that we would need 50 galaxies
such as ours to find another intelligent civilization such
as ours.
Light speed!
• Instead of going there, lets just
communicate (if we can figure out how to
do this and we both have a wish to).
• How long will it take us to get a response?
Universe
• Remember there are about 100 billion
spiral galaxies in the observable universe!
• It would be very unlucky, a great shame,
and a big waste of space if we truly were
alone in the universe.
• Will we find life – probably (and maybe
within our own solar system too) – and
maybe within our lifetimes!
• Intelligent life? Well, we shall see.
Conclusion
• We have found what a planet needs to be
capable of supporting life.
• We have found what to look for to determine if a
planet has life.
• We have estimated the # of intelligent
civilizations in our galaxy.
• Sadly, getting from place to place is really hard
(after all as we found at the start of the
semester, the distances between stars is really
big).