# Biology 1002B Lecture Notes - Photometer, Methods Of Detecting Exoplanets, Shining Light

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Published on 21 Apr 2013
School
Western University
Department
Biology
Course
Biology 1002B
Professor
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Lecture 26: The Drake Equation
1. All of the terms (and the rationale underlying their suggested values) of the Drake Equation.
N = Ns × fp × ne × fl × f i × fc × L
N = Number of advanced civilizations in our galaxy
Ns = Number of stars = 100 billion
fp = the fraction of those stars that have planets = 0.5 (observational data support)
ne = number of planets that can potentially support life = 2
fl = the fraction of those planets that develop life = 1
fi = the fraction of planets that develop intelligent life = 0.1
fc = the fraction of planets willing and able to communicate = 0.1
L = average lifetime of a civilization (hard to achieve)
2. Mechanism by which the “transit method” detects extrasolar planets
To determine what fraction of stars have planetary systems
Ground base, telescope, hubber
Kepler mission
o Detect presence of planets around
distant stars
Detect sensitive changes in
apparent of a star
o Giant mirror that gathers light on bottom
o Photometer that sits in the middle
42 CCD
Photons of star light convert to
electrical current
o Heliocentral orbit orbiting sun and not Earth
o Fixed and not scanning the sky
o Looking at 100 000 stars
o Do those stars have planets around them?
Transit method
o The graph will oscillate
Rhythmic oscillating in apparent star brightness as orbiting planets move between
kepler and star
o When a planet transits/moves in front of a star
Dim the light
Measure at least 3 times (proof) takes few years to be sure transit is a planet
o Orbital time (distance)
Planets closer to the centre has a shorter orbital time
Can calculate the distance from the parent star
o Transiting time
Calculate the orbital distance
Important to life
o Radius of planet and star
o Light grey atmosphere
o Dark grey body of planet
o Kepler can detect the star light alone and the star light passing through the atmosphere
Shining light through different gases changes spectrum
Figure out atmospheric composition (molecular and atomic characteristics)
o Detection of other planets in orbit
See how other planets exert forces on each other
Planet formation is a natural consequence of star formation
Star formation of planets coincide
3. Characteristics of planets that are thought to be conducive to the development of life.
Interested in earth size planets (similar mass)
o Must be big enough for a gravitational pull to develop an atmosphere of heavy elements (N, H2O)
o Jupiter and neptune are big heavy gas planets
Gravitational pulls keeps light elements such as helium and hydrogen
Does not help develop life
Distance from the parent star and size of planet
Water in a liquid state defines the habitable zone
o Planet at the temperature so water can be liquid
o All planets capable of developing life, it will develop life
o Suggests liquid water one time flowed on Mars
No evidence life elsewhere in solar system since no liquid water elsewhere so only Earth
o Having bacteria and plants is not good enough for evidence of life
Need to be intelligent and generate radiowaves or some sort of communication
Is the incident shallow or deep in the angle of sunlight
o The temperature is greatly affected
4. Structure of water that explains its properties
The periodic table is universal
Water is fundamental to life
Hydrogen bonding which gives water an unique property is universal
o No hydrogen bonding between hydrogen and sulfide
o Hydrogen sulfide turns liquid to gas well below zero
o If there was no hydrogen bonding, water would be a gas well below zero