1. Extraterrestrial Life

2. Extraterrestrial Life
The Day the Earth Stood Still (1951)
Forbidden Planet (1956)

3. Extraterrestrial Life

4. Extraterrestrial Life

5. The Search for Extraterrestrial Intelligence (“SETI”)
Is there simple, basic life elsewhere?
Is there intelligent life elsewhere?
Are there intelligent, communicative civilizations elsewhere?
If there are, how do we find out about them?

6. Is there simple, basic life elsewhere?
Nobody knows, but, to guess, almost surely yes, and maybe even quite close
In the past 25 years, as we’ve explored Mars, Jupiter, and Saturn up close, the probability has increased that there may be simple extraterrestrial life even in our own Solar System!

7. Mars

8. Mars
There is reasonably good evidence that there was once liquid water flowing on the Martian surface
A global climate change event long ago evidently violently changed this
Today’s surface Martian soil seems to have water ice mixed in: as much as 2% of the soil may be ice in some regions
Could very simple life exist subsurface even today? Maybe….

9. Jupiter’s Moons
One of the larger Moons, Europa, probably has a large subsurface ocean of liquid water

10. Saturn’s Moons
Titan
Enceladus

11. Saturn’s Moons
The largest moon, Titan, has a dense atmosphere of nitrogen (98%), which is also the largest constituent of the Earth’s atmosphere (80%)
Titan has a huge surface ocean of liquid methane
Sunlight shining on methane can create complex organic molecules

12. Saturn’s Moons
A smaller moon, Enceladus, almost definitely has a subsurface ocean of liquid water

13. Life in our Solar System?
At least three other planets show strong evidence that they have, or had, liquid water on the planet or a satellite
The moons of Jupiter and Saturn have a perpetual source of energy input due to tidal heating
Similarly harsh environments on Earth do have thriving simple life

14. Hydrothermal Deep Sea Vents on Earth
No sunlight
Chemically toxic surroundings
Biologically very active: bacteria, worms, clams, shrimp!

15. How about outside the Solar System?
Can’t observe the chemistry of other Solar Systems directly (yet; JWST may help)
Are the raw materials for life even present elsewhere?
Even if they are, are there environments conducive to allowing those materials to organize into life?

16. Molecules outside the Solar System
All life as we know it depends on organic molecules built into complex chemical structures
Like atoms, molecules can be excited by light of certain specific wavelengths

17. Molecules outside the Solar System
These wavelengths usually fall in the radio or infrared part of the spectrum
Radio and IR observations of the interstellar medium, and also protostars and young stars, reveal hundreds of complex molecules

18. Building blocks of amino acids and DNA!

19. How do these complex molecules form in interstellar space
How do these complex molecules form in interstellar space? Why are they not destroyed by UV light from stars?
Hint: strong signals from molecular gas are almost always found
in the same direction where the interstellar dust is particularly
thick.

20. Interstellar Dust & Molecules go together
Dust apparently “catalyzes” the formation of molecules: provides a working surface for them to assemble
Dust shields the newly formed molecules from destructive UV starlight
Very cold temperature of interstellar medium is ideal environment to form molecular bonds, which are fragile

21. So, the building blocks of life are everywhere
So, the building blocks of life are everywhere. But are there environments conducive to allow those materials to organize into life? Occasionally? Commonly?

22. Are planets common around other stars?
One hint: rotation of stars
Our Sun rotates slowly (25 days), even though it should have spun up during protostellar collapse
What happened to the excess spin?
It went into the planetary orbits: the Sun has all the mass, but the planets have all the angular momentum

23. Measuring rotation in other stars
The hottest 5% of all stars are found to have narrow lines, and thus rotate rapidly: they may not have shed planets during protostellar collapse
The remaining 95% rotate slowly, like the Sun: they are good candidates for planets

24. Direct Observation of Extrasolar Planets: The Kepler satellite

25. Results from Kepler
Thousands of extrasolar planets found; many stars have multiple planets like our Sun
The easiest to find are massive planets like Jupiter, with short orbital periods; these hot planets with no solid surface are not suitable for life as we know it
A few planets of mass comparable to Earth in the “Goldilocks zone” are starting to appear

26. The raw materials – complex organic molecules – are everywhere in the Galaxy
Probably the majority of stars have planetary systems, and there are likely a large number of Earth-like planets in temperate orbits
So: what fraction develop life?? And how about intelligent life?

27. The Drake Equation
A means to estimate the number “N” of intelligent, communicative civilizations in our Galaxy

28. N = ns x fp x fs x fd x fi x fc x fl
The Drake Equation
N = ns x fp x fs x fd x fi x fc x fl
ns the number of stars in our Galaxy
fp the fraction of stars with planets
fs fraction of planets suitable for life
fd fraction of suitable planets where life does develop
fi fraction of planets where life is intelligent
fc fraction where intelligent life is communicative
fi fraction of star’s lifetime that civilization remains

29. N = ns x fp x fs x fd x fi x fc x fl
The Drake Equation
N = ns x fp x fs x fd x fi x fc x fl
ns the number of stars in our Galaxy = 2 x 109
fp the fraction of stars with planets = 0.5
fs fraction of planets suitable for life = 0.1
fd fraction of suitable planets where life does develop = 0.1
fi fraction of planets where life is intelligent = 0.5
fc fraction where intelligent life is communicative = 0.5
fi fraction of star’s lifetime that civilization remains = ??
N = 2.5 x 106 x fl

30. fl = fraction of a star’s lifetime that a civilization remains
On Earth, our own civilization has had the ability to beam a radio message anywhere in our Galaxy for about 100 years; we “just” become communicative, compared to stellar lifetimes
Our Sun’s total main sequence lifetime will be about 1010 years; the Sun is now about halfway through that lifetime: 5 x 109 years remain
Assuming our civilization remains intelligent and communicative for the rest of the Sun’s main sequence lifetime, for us, fl = 5 x 109/1010 = 0.5

31. N = 2.5 x 106 x fl
If fl = 0.5, then N = 1.25 x 106 !! There are more than a million technical, communicative civilizations active today, scattered throughout our Galaxy
On average, the closest one to us could be about 100 pc (= 300 lt-years) away

32. fl = fraction of a star’s lifetime that a civilization remains
However, a nuclear war could in just a few months easily end all life on earth permanently
Then fl = 100 years / 1010 years = 10-8
Then N = 2.5 x 106 x fl = << 1
In that case, we expect no other technical, communicative civilizations other than our own anywhere in our Galaxy today

33. By far the largest uncertainty in estimating the number of intelligent, communicative civilizations elsewhere in our Galaxy today is a social and diplomatic issue, not an astronomical one!

34. If we are optimists, how do we communicate?
Our current technology allows us to send and receive radio messages anywhere in the Galaxy
Other wavelengths are also possible, but not as cheap or easy
Should we listen? Or send?

35. If we are optimists, how do we communicate?
It’s certainly easiest and cheapest to listen
But, if everyone listens, and no one sends…..