1. Is Anyone Out There? Solving the Drake Equation
Write things that you think are important!

2. ? Q: Is there life beyond the earth?
How many of these planets have intelligent life?
How many are able to communicate with us?
(have adequate technology to send signals into space)
(How many of them want to?) ?

3. What this is not about:
Aliens visiting the earth
Alien abductions, UFOs, etc.
Us going to other planets in search of life
Justification: Traveling to other solar systems is hard. Much easier to use radio.
SPEED
TRAVEL TIME
COST
SPACE TRAVEL
Sloooow…
Looooong….
$$$$$$$$
RADIO COMMUNICATION
Fast! (c)
Long, but not as much
Cheap!

4. The Drake Equation N = R*fp*fe*fl*fi*fc*L
It identifies specific factors thought to play a role in the development of civilization able to communicate
Developed in 1960 by Frank Drake and others at SETI
(SETI: Search for Extra-Terrestrial Intelligence)
N = R*fp*fe*fl*fi*fc*L
N = # of communicative civilizations in our galaxy, right now

5. The Drake Equation N = number civilizations in our galaxy
R = rate of star formation (how many stars)
fp= fraction of stars that are have planets
fe= fraction of planets that are “earthlike”
fl = fraction of “earthlike” planets that develop life
fi = fraction of above that develop intelligence
fc= fraction of above that develop communication
L = lifetime of communicative civilization

6. Mathematical Aside: Fraction s
Most of the terms in the Drake Equation are in the form of fractions.
f=1 implies something that always happens
f=0 implies something that never happens
Values in between are things that might happen
f=0.5 means a 50/50 chance
f=0.1 means a 1 in 10 chance
f=10-3 is a 1/1000 chance
etc.

7. Astronomy factors

8. R: # of stars in the galaxy
This is well known to astronomers…
Rate of star formation x age of galaxy
Rs = billion = 2 to 4 × 1011
So far, so good…
M31, the Andromeda Galaxy
Astrophoto by Robert Gendler

9. Star needs to be like the Sun
Too cold
Too hot
JUST RIGHT
TAKE AWAY 90%
TAKE AWAY 25% MORE
LEAVES ABOUT 30 BILLION

10. fp: fraction of stars having planets
Q: Given one of the many stars in the galaxy…
What is the probability that it has planets?

11. fp: fraction of stars having planets
Until recently no exoplanets were known
First discovery 1995, then…
Today, almost 3500 exoplanets known!
250 known multi-planet systems!
The
Snowball
Effect!

12. fs-p: fraction of stars having planets
Searches still have a lot of bias
Cannot usually “see” the planets directly, only their effect on the parent star
Orbital inclination angle can be wrong
Parent star’s mass & brightness can affect detection…
Which stars do you choose for detailed study?
We don’t yet have a decent unbiased sample.
And it’s nowhere near complete.
But we can estimate…

13. fp: fraction of stars having planets
We now know that at least 50% of “typical” stars have planets. (fs-p = 0.5)
Infrared studies of discs around young stars indicate fp ~
But we can only detect a limited subset of planets…
So maybe they all do! (fp = 1)

14. fe: fraction of solar systems with an “earthlike” planet
Q: Given many solar systems, what fraction of these have “earthlike” planets?
If 1 (or more) in the “typical” solar system:
fe = 1 (or more)
If typical systems do not have an earthlike planet:
fe << 1

15. fe : factors to consider
Star:
Massive stars have short lifetimes…
not long enough to develop life.
Low mass star:
Not enough ionizing radiation,
“habitable zone” is very small,
Susceptible to outbursts (“flares”).
Distance from star:
Too close: TOO HOT!
Too far: TOO COLD!
Orbit too elliptical: Temperature varies too much!
Need a stable orbit over time!
Defines “habitable zone”

16. fe : factors to consider
Planet’s composition:
Need liquid H2O
(are NH3, CH4 etc. acceptable substitutes?)
Need an atmosphere!
Need organic (carbon) compounds
(silicon based life?)
No acidic / corrosive environment
Need elements heavier than hydrogen / helium
No “Population II” stars!

17. fe : factors to consider
Planet’s size
Too small -> less gravity -> no atmosphere -> no liquid H2O
Also, loses geothermal energy too fast
No magnetic field?
Too big – probably tend to be “gas giants” like Jupiter. No solid surface.
(Floating life forms?)

18. fe : factors to consider
Other factors
Moderate axial tilt
Moderate rotation rate
No spin-orbit lock?
Red dwarfs out?
Large moon necessary for the above?
What about moons of gas giants?
“Good Jupiter”
In the Galactic Habitable Zone?
No nearby supernovae, gamma emitters, etc. ?

19. fe: fraction of solar systems with an “earthlike” planet
Our own solar system has fe = 1
(Of course!!)
Stretching the definition, maybe fe = 2 or more:
Mars?
Europa?
Titan?
So far no truly “earthlike” planets have been found outside the solar system.
And only a few come close…
Guess from current data…. ~????
But current searches are biased against “earthlike” planets!
May be much higher!
But limited if red dwarf planets aren’t allowed (must be <0.2 or so)
Probably “borderline”
Outside habitable zone
But tidal interactions…
Kepler 186f
55 Cancri f ?
Proxima Centauri b
HD28185 b ?
Kepler 452b
Gliese 581 c/d ?

20. Biology Factors

21. fl: fraction of “earthlike” planets that develop life
Q: Given an “earthlike” planet…
What is the probability that it will develop life?

22. fl: fraction of “earthlike” planets that develop life
Simplest definition:
A living organism is something capable of replicating
Bacteria
Viruses
Other one-celled organisms
Need a self-assembling, self-replicating genetic code!
Earth-based life: DNA / RNA
Are there other possibilities?

23. fl: fraction of “earthlike” planets that develop life
If life always arises on “earthlike” planets, then fl = 1
Otherwise, fl < 1 (maybe << 1)
Only one known example of a planet with life!
Not much hard data to go on here…

24. fl : factors to consider
Two schools of thought:
School 1:
Even the simplest life is extremely complex!
Simplest organisms have about a million base pairs in DNA/RNA
Lots of things have to go “just right”
fl is “obviously” very small!

25. fl : factors to consider
School 2:
Building blocks of life are found in space and on other planets
Organic molecules
Water
Initial life on earth seems to have developed rather quickly…
fl might be large (possibly  1?)
But seems to have developed only once , not many times…
So it’s not just popping up everywhere!

26. fl : factors to consider
Life can survive under all sorts of conditions
Extremophiles!

27. fl : factors to consider
If life were to be found on Mars…
Implies fl is large! X

28. fi: fraction of planets with life that develop intelligent life
Q: Given a planet with simple life forms…
…things like bacteria…
…what’s the probability that intelligent life will eventually develop?

29. fi: fraction of planets with life that develop intelligent life
Simplest life forms: self-replicating organisms
But “copies” are not exact
Mutations
Those variants best suited to survive, best able to reproduce, are more likely to pass on their genetic code to the next generation
Natural selection
Over time those changes progressively accumulate
Evolution

30. fc: fraction of planets with intelligent life that develop communication
Given a planet with intelligent life…
What is the probability that they develop tools to communicate through space?

31. Sociology Factors

32. L: It’s all about the timing…
Given a planet with intelligent life forms that can communicate…
How long do they remain that way?

33. L: It’s all about the timing…
L : once a civilization becomes able to communicate, how long does it stay able to do so? ?

34. L: It’s all about the timing…
We only became able to communicate…
Early 1900’s: <100 years ago!
How much longer will we last?
5 billion years: sun turns into a red giant
Mass extinctions every ~100 million years
But will we even last that long…
What is our lifespan?

35. Values of N If 10,000 civilizations, then on average 100 ly apart
(Frank Drake’s Estimate)
If 1,000 civilizations, then on average 3000 ly apart
Could easily be 1(us)!
The real value of the Drake Equation is not in the answer itself, but the questions that are prompted when attempting to come up with an answer, and to identify areas of research!

36. They should be here!
Out of billion stars, if even a very small fraction develop technological civilizations, there must be a very large number of such civilizations. Even at a small fraction of the speed of light, the galaxy should have been completely colonized in no more than a few millions years.
With future proposed technology, it would take less than 1000 years to travel to the nearest stars (30-50 generations). Could take years preparing fo the next jump to the next star. And so on, and so on, and so on.

37. Fermi Paradox
In this scenario, it would take less than 100 million years to colonize the entire galaxy.
Since the galaxy is 12 billion years old, Earth should have been visited and colonized years ago
The absence of any evidence for such visits is the Fermi Paradox, named after physicist Enrico Fermi, who first asked the question in “Where are the aliens?”

38. Possible Solutions
Civilizations are extremely rare and we are the first one to arise
Perhaps most civilizations have destroyed themselves before they could explore the cosmos
They have deliberately concealed themselves
They don’t want to interfere with our development or they just don’t have interest in us

39. Another Solution
Life is scattered throughout the universe both physically and through time every few million years, on a distant planet, advanced civilized life will evolve and grow to the capacity that it can send out radio signals to other planets.
A few thousand years after that, life abruptly disappears and dies away, its radio transmissions going silent
This may be repeated innumerable times across the universe, but no two advanced civilizations ever develop close enough to each other and at the same time

40. Extra Info If you are interested in this topic of aliens
Or if you just want to know more before your test tomorrow
There are two good videos on mrhyatt.rocks under today’s section that you should watch
There are also little interactive things to play with where you can change the fractions for each factor
your test tomorrow!

42. your test…..
It’s over the solar system, planets, EXOPLANETS, & ASTROBIOLOGY
Which we started learning about in November!
Which was 3 months ago
So there is a lot of information to cover
Which translates into a lot of questions on your test
Which means you have a huge test
There were about 95 questions
BUT I GOT IT DOWN TO ~70
Don’t worry, MANY ARE EASY QUESTIONS
WHICH WILL HELP YOU EARN POINTS
AND MAKE HARDER QUESTIONS NOT WORTH AS MUCH!
SO TOMORROW YOU WILL NOT HAVE BELLWORK
YOU WILL COME IN, AND IMMEDIATELY START YOUR TEST
THE SOONER YOU GET HERE, THE MORE TIME YOU WILL HAVE TO FINISH IT
If you are absent, you need to come in and make it up
before or after school
Oh, and THERE IS A LIST OF VOCAB WORDS TO LOOK AT ON MRHYATT.ROCKS