Transcript 38Life - NMSU Astronomy

Looking for life in the Universe
Solar System Sites
Attempts at Communication
Probability of Life
Detection of Planets
Recap
• Final assignments:
– Lab credit this week: Canvas evaluations, due before Monday
morning
– Homework this week: Canvas post-course assessment, due by
final exam time
– Final: Wednesday 12/11, 10:30-12:30
• Potential life sites in the solar system
– Look for locations where temperature allows for liquid water
– What affects temperatures of planets?
• Heating from Sun: balance of heat in = heat out
– temperature depends on distance from Sun and
composition/reflectivity of planets
• But this doesn’t seem to give the observed temperatures for
some planets, especially Venus, which is WAY hotter
• The Greenhouse effect: planetary atmospheres as blankets
that can increase the temperature
• Greenhouse effect and Earth: natural, man-made
greenhouse effect, and climate change
You will get a greenhouse effect
A. On any planet
B. On any planet with an atmosphere
C. On any planet with an atmosphere if the
atmosphere has gases that transmit visible
but block infrared light
D. On any planet with an atmosphere if the
atmosphere has gases that block visible but
transmit infrared light
E. On any planet with an atmosphere if the
atmosphere has gases than block both
visible and infrared light
….. But back to potential locations for life
on other planets …..!
From external heating + Greenhouse,
Earth seems to be about the only place
for liquid water now
– Venus too hot from Greenhouse
– Mars Greenhouse isn’t enough to make it
globally hot enough, although there are
locations on Mars that come close…
But there are other heat sources ….
Internal heat sources of
planets
• External heating from the Sun is from the
outside in
• Some heating can come from the inside out
• One source of internal heat: heat from
planetary formation
– When planets form, they are hot, because gravity
has accelerated particles to make them form
– Amount of internal heating varies from planet to
planet, probably both from initial heat and from
different cooling rates
If you put several potatoes of different sizes in
the oven, let them all heat up, then take
them out
A. They will all cool at the same rate
B. The inner parts of the smaller potatoes will
stay hotter for longer than the inner parts of
the bigger potatoes
C. The inner parts of the bigger potatoes will
stay hotter for longer than the inner parts of
the smaller potatotes
D. They will all stay hot forever
Internal heating of planets
• Bigger planets expected to stay hotter for
longer
• Earth is still hot in the center, evidence:
– volcanoes
– Magnetic field
– Plate tectonics
• Moon is not hot internally
– Surface is geologically “dead”
• Mercury is not hot internally
• Mars seems pretty dead, but perhaps not for
so long
Internal heating
• Based on this, expect that objects
smaller than Mars (roughly) are
probably cooled in their centers
• Surprise! Voyager flies by Jupiter,
takes pictures of moons, and sees
volcanoes on innermost large moon, Io!
Tides and tidal heating
• Another mechanism for creating internal heat: tides
• Tides come when you have an orbiting object
– Pull of gravity is stronger on closer side than on middle, so
closer side is pulled a little more
– Pull of gravity is stronger on middle than on far side, so far
side is pulled a little less
– Result: planet is “stretched” in the direction of the other
object, with near side towards the object and far side away
from it
Tides on Earth arise because the Earth is
stretched by the gravitational pull of
the Moon. How often do you expect a
high tide?
A. Once per day
B. Twice per day
C. Once per month
D. Twice per month
Tides and tidal heating
• On Earth, water flows to accommodate this stretching
--> tides on a two times per day cycle
• On Jupiter moons, tides are really strong
– Jupiter has a lot of mass, hence a strong
gravitational pull
– Moons are relatively close to Jupiter, so there’s a
big change of gravity from one side to the other
– “stretching” of the solid moons creates internal
friction that heats them up!
Solar System life sites
• Earth
• Venus too hot because of greenhouse effect
• Mars seems too cold now, but perhaps warmer in the
past?
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Evidence of past water, present water?
Evidence of past geological activity
Perhaps more greenhouse effect in past?
Evidence of life? ALH84001
Lots of current Mars exploration!
Solar System life sites
• Moons of Jupiter
– Io too hot
– Europa surface looks like ice
• Europa also has induced magnetic field
Life outside the Solar System
• For life outside the solar system, we
can’t find it by exploration
– Look for intelligent life by communication
– Look for observable tracers of life
• So far, nobody has contacted us, nor
have we received any signals!
Attempts at communication
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SETI project (also note SETI at home)
1974 Arecibo message to M13
Pioneer plaque
Voyager golden record
Communication time scales are very
long!
– Review: light years and distances in the
Milky Way