PCS 581 Lecture Notes - Lecture 11: Breakthrough Listen, Pioneer 10, Nuclear Weapon
Lecture 11:
Locations of Life?
Some kind of life might be possible subsurface
oLots on Earth, maybe Mars, maybe Europa
Could we detect subsurface life?
Two possibilities of life: surface (earth) or subsurface (ocean moon like Europa)
How do we detect subsurface life? You have to get under the surface – for many it will be
a big challenge at least a 100 years
There might not be a point searching
How detect life on another planet’s surface? Detecting the atmosphere
Detecting Extrasolar Life
Spectroscopy can probe chemical abundances in atmospheres
oWhich Technique? Transit
oAbsolute cutting-edge science
Can contain results of life, photosynthesis (mostly microbes)
Visible from space, at huge distances
During a transit as planet passes between us and the stars – the light would go through the
planet’s atmosphere and we can detect that through spectroscopy
Day will come when we will study the atmosphere of exoplanets orbiting other stars
Its giving you what is in the atmosphere
We have already done some of this
Very hard to do – all the detection so far is heavily debated – that was the case for
everything back then – hopefully in 20 years we’ll be able to tell how many has breathing
atmosphere
Matter of practice and technology – as soon as we find it there will be experts saying it is
something else
Life Around a Star
Life arose on Earth within at least a few hundred million years
Which live shorter lives? high mass
Is it less than a few hundred million years? Yes
oOnly 1% of all stars
Planet itself will need a stable orbit around its star – should we rule out binary, triple or
cluster stars? No
oBut maybe less appealing candidates
Earth formed around the same time as the sun
They can live up to a few million years – that clearly is not going to work out – if star
lives that short there is no way it will harbor life – rule them out – thankfully they’re so
rare that making it rule out is easier
Not rule out binaries because we have found planets that orbit three stars orbiting each
other – proxima
Less appealing – we are looking for stars that are similar to our sun
find more resources at oneclass.com
find more resources at oneclass.com
The Habitable Zone
Region in which a terrestrial planet of the right size would be not too hot, not too cold,
but just right for liquid surface water
oSmaller stars have zones that are narrower
Affects odds of having a planet in the zone…? No
oSmaller stars are very common
If we want to see surface life – planets with no stars can have life if it is hot enough
We look at the surface – has to be liquid, not too cold, and not too hot
Small stars are cooler, so the planets want to nestle in and are tightly packed – they can
also have planets
Smaller stars are 100x more common than big stars
Two reasons to look for smaller stars: common, and second because easier to see planets
because the star is dimmer, orbits will be smaller
Downsides: they are often really unstable, and dangerous for life – since habitable zones
are very near for those stars
We only know one type of life – so we can’t completely rule out possibility of life in
those star planets
Exoplanet Periodic Table
We found a lot and had a lot of success
Kepler still has more
Biased towards hot Jupiters
Without bias – super earths are the most common types of planets
Earth sized planets are pretty common but hard to find because so small
The Rare Earth Hypothesis
Seems like we’re finding billions of good candidates
But what if Earth is just the luckiest planet?
oAnd of course, we’d be born on the luckiest planet
oOtherwise we wouldn’t be alive to question it
Still possible earth would be rare
Possible that earth could be alone – seems unlikely because if there are a lot of universes
than that does not mean we’re perfect
A Galactic Habitable Zone?
Too close to the centre: too many supernovae going off, too much radiation
Too far out: not enough heavy element enrichment
Even within the galaxy – areas of the galaxy not habitable
In the inner there may be too many supernovas and denser and can’t have life
In the outskirts, lot less supernovas meaning little elements to have planets and can’t
sustain life
We don’t have the data yet – so we don’t know
Who section galaxies would have to be ruled out
find more resources at oneclass.com
find more resources at oneclass.com
The Impact of Protection Racket
In the early solar system, Jupiter scattered most newborn asteroids & comets out to the
Oort Cloud, or into the Sun
Are we lucky to have Jupiter, at all?
oMaybe Jovians are to be expected in any system with Earth-like planets?
When Jupiter formed it took control of the asteroids and cleaned everything up in the
solar system
And if something hits solar system it will be hit
Jupiter has been protecting us from birth to the end of its life – maybe we’re lucky to
have Jupiter
Rocky planets formed inside frost line and frost giants in the outside
Our Perfectly Balanced Climate?
We’ve had liquid water for 4 billion years
Periods of hothouse or snowball Earth, but only temporary
oVenus and Mars had permanent versions
Pieces of “luck”: plate tectonics and our Moon...?
Earth is pretty special
We have the moon and we’re lucky to have it – we got it through a giant impact
IF moon essential not a lot of worlds won’t have it – meaning we’re pretty lucky
Plate tectonics refreshing CO2 – had a very regulated atmosphere until human came along
We never boiled or froze - we never got too bad and always bounced back
Maybe we’re special
Rare?
Maybe Earth was lucky... Very lucky, and unique
oCan’t really know until we investigate similar worlds
oAnd out of billions of possible worlds, wouldn’t some others be just as lucky?
Or, maybe Earth wasn’t lucky, and we will find other planets that are far more
habitable...
Investigate similar worlds - Only way to know is analyze their atmosphere – how many
are habitable?
Something we can answer by analyzing atmosphere
Searching for Life?
We can think about habitability
We can search for worlds, and even analyze their atmospheres to discover “breathers”
But we all know what we’d really like to find...
One thing to find breathing atmosphere but we want to find aliens – we want to find
things like us – we don’t want to be alone – we want to find someone we can talk to
Searching for Extraterrestrial Intelligence
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Some kind of life might be possible subsurface: lots on earth, maybe mars, maybe europa. Two possibilities of life: surface (earth) or subsurface (ocean moon like europa) You have to get under the surface for many it will be a big challenge at least a 100 years. There might not be a point searching. Can contain results of life, photosynthesis (mostly microbes) During a transit as planet passes between us and the stars the light would go through the planet"s atmosphere and we can detect that through spectroscopy. Day will come when we will study the atmosphere of exoplanets orbiting other stars. Its giving you what is in the atmosphere. We have already done some of this. Very hard to do all the detection so far is heavily debated that was the case for everything back then hopefully in 20 years we"ll be able to tell how many has breathing atmosphere.
