Goal: To understand life in our universe.

Objectives:1) To understand the Basic building blocks for life

in general2) To learn about What type of stars and planets

to look for if we want to find life3) To understand How to find these planets4) 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:

• 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?

• 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?

• A) 2 billion• B) 20 billion• C) 200 billion• D) 2 trillion

What fraction of those are like our sun?

• A) 100%• B) 10%• C) 1%• D) 0.1%• E) 0.01%

What fraction of those have planets?

• 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)?

• A) 100%• B) 10%• C) 1%• D) 0.1%• E) 0.01%

What fraction of those have actually develop life?

• A) 100%• B) 10%• C) 1%• D) 0.1%• E) 0.01%

What fraction of those have develop intelligent life?

• A) 100%• B) 10%• C) 1%• D) 0.1%• E) 0.01%

What fraction of those develop and utilize (intentionally or

unintentionally)?

• 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

• 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).