Upgrade to remove ads
SETI, Life Out There
Terms in this set (12)
With so many possible abodes, simple forms of life are probably relatively common. However, the odds of finding intelligent life may be much lower.
Simple Life vs. Complex Life
Simple organic molecules are abundant in the Solar System and beyond. Simple single-celled life forms dominate life on Earth (Focus of mars and Europa).
Why Care about Extraterrestrials?
Pros: Extraterrestrials increase awareness of our place in the cosmos, answers the question of if we are alone, and it is practical knowledge gained over time.
Cons: It is common wisdom that complex life is rare, two-way communication takes too long, we have trouble dealing with each other and other species on this planet, and searching costs money.
Where should we look? Where might we find planets that could harbor complex life?
We need liquid water (habitable zones) according to our understanding of life.
The evolution of complex life takes a long time so we need to look at stars of moderate ages.
We also need C-H-N-O-P-S. This limits us to stars that formed after the first generation of stars, maybe later
Evolution of the Universe
Initially, the universe consisted almost entirely of H,He, and Li. Everything else was formed in fusion reactions inside stars and was ejected when they died.
Early stars could have no terrestrial planets, and if Jovian planets require accretion cores to form up, there were no Jovian planets either.
It took a while to form enough heavy elements for plants or life. The length of time depends on where you are since that sets the star-formation rate.
More massive starts burn their hydrogen fuel faster and thus have much shorter lives even though they have more of it.
If the evolution of complex life takes ~3 Gyr, then we have to limit our search of stars less than ~1.5 solar masses (F2).
What should we look for?
Could we be detected by extraterrestrials?
Directly: Images. electromagnetic leakage: (Radio, TV, military,...)
Indirectly: O2 (or O3 )detected in Earth's atmosphere, pollutants, human-made chemicals in the atmosphere.
Views of Earth
Views of Earth as it could be seen from an extra-terrestrial telescope (hundreds of km of resolution): No obvious sings o intelligent life at these scales.
Views of Earth as seen from a very high resolution orbiting satellite (a few tens of meters of resolution): We can see geometric patterns.
Spectra of Earth-like planets
The key is Ozone absorption at 9.6 um. This requires oxygen, which requires photosynthesis.
Detecting Life From a Distance
The radio signal modulates as the Earth rotates and propagates outwards at the speed of light.
Earth is inside a radio bubble of 100ly. Can watch I Love Lucy from 60ly.
Sagan: "Extraordinary claims require extraordinary proof"
Healthy Skepticism is good. Much of what we learned is based on models and/or interpretation.
Independent confirmation of facts, debate on the evidence, arguments from authority carry little weight, Occam's Razor (If there are two hypothesis that explain the data equally well, choose the simpler), is it testable? (Baloney Detection)
Science is all about gathering the facts as best we can, explaining what we have learned, and changing theories when they fail.
An open mind, and the ability to form fact-based judgments are invaluable in today's world.
YOU MIGHT ALSO LIKE...
ASTR 1141 Chapter 1
Astronomy Ch 18
Chapter 1: A Universe of Life?
A universe of life
OTHER SETS BY THIS CREATOR
Introduction to American Government