Peter Watson

ET, phone homeAre we alone in the universe?

Peter Watson

The Good News

• We’ve found a lot of places to go

• Probably even life out there….

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The Bad news• We can’t get there

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The Really Bad news• We had better fix things here…

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The Really, Really Bad news• We may not have long enough

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Image Credit: ALMA (ESO/NAOJ/NRAO), NSF

HL Tauri from ALMA

Star has just got going: we can see the disc of hot gas forming planets

Peter Watson

An (almost) new-born star: β-Pictoris

• still surrounded by dust

• But it’s had time to form at least one giant planet

• so are planets common?

Peter Watson

Picture by Etienne Rollin

Now we are seeing lots of other solar systems

Like this! (except this is our sun and Venus, June 5)

Kepler• observed 150000 stars

every 30 mins.

• Note 0.1 % change• 4 hours• symmetrical shape

Vega

Deneb

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How many?• 6 planets known since pre-history

• Uranus: 1781

• Neptune: 1846

• Pluto: 1931

Note: even this is an underestimate:Kepler has 2321 candidates, 61 74 confirmed

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21/10/2019

• https://apod.nasa.gov/apod/ap151205.html

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•Orbit has to be aligned with earth

•Need to see several transits

•Does best with large planets, close to star

•“hot Jupiters”

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Kepler 11 has at least 6 planets

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•Kepler 22b: first earth-sized planet in Goldilocks zone (not too hot, not to cold!)

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So planetary systems are common: do they look like ours?

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• Lot of stars have hot Jupiters

• Some don’t know they should be in circular orbits!

• HD80606b goes from 500°C to 1200°C in 6 hours

• Lots go backwards

Not really

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•CoRoT-7b

•mass ~ five Earth, radius~ 1.7 Earth

•year lasts ~20 hours

•FAR too hot (1500°)Peter Watson

•Planets in orbit round binary (double-star) systems: Kepler 16b

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• ~Earth sized planet + ~Neptune sized planet

• Every 97 days approach to ~1.5 million km

Kepler 36

Credit: Harvard-Smithsonian Center for Astrophysics/David Aguilar

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Kepler-47

• First Binary Star 2-Planet System

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• Maybe we need a planet called Vulcan.

• Star Trek puts it round the star 40-Eridani: quite sensible

• Green ring is “habitable zone”

On the other hand ...

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Water planet: K2-18B

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And now.. (Feb 2017)• TRAPPIST-1 system

Transiting Planets and Planetesimals Small Telescope

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• 7 planets, all within orbit of Mercury

• Several in Goldilocks zone

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And now..• Like this!

• Star is cool red dwarf

• Not what we would expect for life support

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• There may be many planets that don’t orbit stars

• A real αστήρ πλανήτης (astēr planētēs), meaning "wandering star"

• Except we have defined planets to be in orbit round stars!

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• Seems likely ALL stars have planets

• We haven’t had time to observe orbits of longer than a year or so

• Maybe more than 100 billion planets in the Milky Way

• Many similar to Earth

Conclusions

So let’s

go

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So what does this do for alien life?

•Where are they?

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The Wow signal• 1977 from Big

Ear observatory (Ohio)

• Very big signal, never repeated

• Before GUI’s!

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Search for Extraterrestrial Intelligence

• Vast amounts of data from Arecibo are never analysed

• If aliens are smart enough to communicate over large distances AND too dumb to use cable, we could pick up their signals

A depressing corollary

• Fermi’s question: where are they?

• if the universe is full of planets (it is) and some have liquid water (almost certainly) and evolution is universal (why wouldn’t it be?)…..

• Why isn’t the galaxy full of inhabited planets with intelligent species who want to talk to us?

Peter Watson

The Drake Equation• How many advanced civilizations are there in our

galaxy (50 billion stars)?

• # of new stars born each year = 10

• fraction of stars with planets = 100%

• # of habitable planets/system = 0.5

• probability that life evolves =100%

• prob. that life develops intelligence =5%

Peter Watson

• prob. that intelligent life can communicate across space =5%

• lifetime of intelligent civilization =3500 yrs

• # of times a civilization could re-develop =1

• Total number of civilizations in our galaxy at the moment?

• http://www.as.utexas.edu/astronomy/education/drake/drake.html-old

•42!!!!!!!!!!!!•Well, you decide which number I got wrong!

An image that is embedded in our sub-conscious

•No evidence that Nature is working towards more complex and intelligent beings

•Steven Jay Gould has pointed out that this is probably temporary: viruses have much better survival values than humans

• Note whole orders of living beings have disappeared from the earth for no apparent reason.

• E.g Burgess shale

•

•this is Opabinia

• this is Orthrozanclus Maybe intelligence isn’t such a great idea!

• Maybe intelligent species last a really short time

Hiroshima Aug 5 1945

Hiroshima Aug 6 1945

In summary:

• There are lots of planets

• No known or foreseeable technology will get us to a extra-solar planet

• Total absence of any evidence for extra-terrestrial life suggest it is very uncommon: pick your own reason why

• If you want to play your own games with the data, go to http://exoplanet.eu