Transcript Goal: To understand life in our universe.

Goal: To understand life in
our universe.
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.
Looking for life outside our solar
system:
• To find life we first need to be able to find
planets.
• The problem is that at any wavelength the
star is at least a million – if not a billion
times brighter than the planet!
• So, right now we really can’t image the
planet directly – at least in most cases.
• So, how can we find planets?
Planet hunting
• The easiest way to find a planet is from the
wobble of the star.
• As the planet orbits both planet and star orbit
around the center of mass (such that the each
mass times their distance from the center of
mass is the same).
• For Jupiter orbiting the sun the center of mass is
5 million miles from the center of the sun.
• So, over the course of 12 years the sun does an
orbit with a radius of 5 million miles!
How do we find this?
• We examine the velocity of the star moving towards and
away from us.
• If an alien species were looking along the plane of our
solar system they would be able to see our sun moving
towards them at one point at a velocity of 0.13 km/s
• This is a pretty small velocity, and tough to actually
observe, but is possible.
• 6 years later the velocity would be -0.13 km/s (moving
away from them).
• From this you get the orbital period – which gives you
orbital distance.
• The speed gives you the mass of the planet.
What we mostly find
• The first 100 planets found were mostly
large planets (Jupiter sized and bigger).
• Most of these were close to the sun
(Earth’s orbit or less).
• Many were very close to the sun – called
hot Jupiters.
• These are not necessarily the norm, but
they are the easiest to find, so we found
them first.
Finding smaller planets
• Eventually we want to find Earth sized
planets.
• We are getting to smaller and smaller and
will continue to do so.
• However, to do better we need to go to
space!
Interferometer
• A telescope slit into two or more parts and spread out
over a large area.
• Effectively gives telescope a bigger diameter
• 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
• Have 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.
What it will do
• Separates the star and planet on image (but star
is still so much brighter will not see the planet)
• 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.
• 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 21%) 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!
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…
How many stars are in the Milky
Way galaxy?
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A) 2 billion
B) 20 billion
C) 200 billion
D) 2 trillion
What fraction of those are like our
sun?
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A) 100%
B) 10%
C) 1%
D) 0.1%
E) 0.01%
What fraction of those have
planets?
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A) 100%
B) 10%
C) 1%
D) 0.1%
E) 0.01%
What fraction of those have planets
or moons like our Earth in a region
where you can have life (in
general)?
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A) 100%
B) 10%
C) 1%
D) 0.1%
E) 0.01%
What fraction of those have
actually develop life?
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A) 100%
B) 10%
C) 1%
D) 0.1%
E) 0.01%
What fraction of those have
develop intelligent life?
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A) 100%
B) 10%
C) 1%
D) 0.1%
E) 0.01%
What fraction of those develop and
utilize (intentionally or
unintentionally)?
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A) 100%
B) 10%
C) 1%
D) 0.1%
E) 0.01%
So, we have a number of expected
civilizations!
• But how far are they from us?
• Lets take the radius of our galaxy (50,000
light years across) and divide by the
expected # of civilizations.
• Now, if we travel at 10% the speed of light
when do we get there?
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?
Relativity
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Things look grim!
However, relativity to the rescue!
As you go faster, your clock slows down.
So, the time you experience is changed by
a factor of γ (γ = 1 / (1 – v2/c2))
• So, if v = 0.9999 c then a short time can
go by for the explorers (although a lot of
time passes by for planet Earth).
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).