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How do we define extraterrestrial life? What are we looking for?
Life beyond Earth; life that doesn’t originate from Earth
Looking for any sign of life- be it simple, complex, or intelligent
Is the universe a rational place?
Yes. The universe acts UNIFORMLY and RATIONALLY
Are there worlds beyond the solar system?
Yes, exoplanets, which are planets orbiting a star that isn’t our sun
How do we define a habitable world?
We’re asking whether it offers environmental conditions under which life could arise or survive, not whether it actually harbors life…
First requirement is WATER!
The moon, venus, mars
Liquid water is present on or in “select” planets, but several moons, too!
LIQUID WATER ON THE SURFACE
VOLCANISM
PLATE TECTONICS
MAGNETIC FIELD
What is geocentrism?
Basically just the belief that Earth is the center of the universe, and the sun the moon and the stars all revolve around it
What is the history of geocentrism?
Ok
So,
ancient greeks try to put system of rules together, relied partly on observations and want to explain the rising and setting of the sun, moon, planets, and stars
they produced the 1st scientific model of the universe: GEOCENTRIC MODEL
Aristotle supported it, argued that the Earth was at the center because it was heavy and unmoving- his student Ptolemy developed geocentric model called Ptolemaic system
PTOLEMAIC MODEL:
Retrograde motion isn’t simple and requires orbits-on-orbits (epicycles)
High precision prediction requires orbits-on-orbits-on-orbits
Makes pretty good predictions (within about 1-2 degrees)
Geocentricism then basically ended with Nico Copernicus, as he presented the heliocentric model… GALILEO AND KEPLER later provided evidence to confirm this, which led to the gradual abandonment of geocentricism
What are the pros of geocentrism?
essential for understanding the history of astronomy
highlights evolution of scientific thought, showing how science corrects itself over time
What is the history of heliocentrism?
Aristarchus of Samos (310-230 BCE)
Determined relative sizes of the Earth, Sun, and Moon
He also produced a simpler heliocentric model… if a smaller moon orbits Earth, then a smaller Earth likely orbits the sun
Earth is on an orbit (moving), which is a big deal that’s going to need proof
PARALLAX SHOULD EXIST. BUT IT ISN’T OBSERVED, SO HELIOCENTRICITY IS WRONG
Copernicus Revolution: Nicholas Copernicus (1540)- REVIVES HELIOCENTRICITY
Tycho Brache (1580ish)- made the most precise naked eye observations of planetary positions
Accurate to 21/60th of a degree (about 0.017 degree), sun angular diameter of about 0.5 degree, parallax of proxima cen (0.77 arcsec)
Johannes Kepler (1650): Using tycho’s model and discovered that the helio model works best
What prevented heliocentrism from being quickly accepted?
Opposition to established beliefs
Galileo and church and stuff
What is a parallax
Wha are Kepler’s Laws of Planetary Motion?
Planets orbit in ellipses, not circles
Planets’ orbital speeds vary
Larger orbits have slower speed- longer orbital periods
What is aphelion?
A planet’s farthest point away from the sun
What is perihelion?
A planet’s closest point to the sun
Average of a planet’s perihelion and aphelion distances = the length of its semimajor axis (planet’s average distance from the Sun)
What is a look-back time?
Amount of time that has passed since the light from a distant object was emitted
What is the sun’s look-back time?
8.3 mins
What is the circumference of the Earth?
about 1/7th of a second (at light speed)
How long is a trip to the moon?
1.25 seconds
Sun is about 4,000 times further away from us than the moon is
how far away is pluto
about 5.5 hours away (at light speed)... 330 minutes and 11 hour orbit
What is an element defined by
the number of protons
what is an element
atoms with the same amount or number of protons
what is an isotope
same number of protons, but different number of neutrons
what is an atomic #
the number of protons
what is an atomic mass #
the number of protons and neutrons
what is an ion
an atom with a non-zero net charge
what do Organic molecules contain
Organic molecules contain carbon (and usually also hydrogen)
what is a molecule
2 or more atoms that are bonded together
what is a compound
molecules that are made from atoms of 2 or more atoms
what are the 3 types of spectra
continuous spectrum, absorption spectrum, and emission spectrum
what is continuous spectrum produced by
Is produced when light contains a broad and uninterrupted range of wavelengths or colors
Emission from hot dense objects
Blackbody radiation- hotter objects appear more blue and cooler ones emit less and appear more red
There’s no gaps between wavelengths
what does continuous spectrum tell us
TEMPERATURE… hotter objects emit more blue light (shorter wavelengths), while cooler objects emit more red light (longer wavelengths) aka blackbody radiation
Luminosity and size
Tells us about the temperature and energy output of dense, hot objects like stars.
what is absorption spectrum produced by
Light source
Gas in the way
Electron excitation
The absorption spectrum is produced when light passes through a cooler gas, causing certain wavelengths (colors) of light to be absorbed by the atoms or molecules in the gas. This process creates dark lines, called absorption lines, in the continuous spectrum of the light.
what does absorption spectrum tell us
Chemical composition of gasses
Surface conditions of stars
Movement
Exoplanet atmospheres
Reveals the chemical composition, temperature, movement, and conditions of the cooler gas surrounding hot objects, like a star's atmosphere or an exoplanet’s atmosphere.
what is emission spectrum produced by
When atoms or molecules emit light at specific wavelengths. This happens when an atom's electrons move from a higher energy level to a lower one, releasing energy in the form of light.
Excitation
Electron decay
Wavelength of light
what does emission spectrum tell us
Chemical composition of gasses
Temperature and density
Nebulae (gas clouds) and stellar formation
Provides information about the composition, temperature, and density of hot, low-density gases, like nebulae or stellar atmospheres.
what are the 2 types of planets?
1. Near to the sun
Mercury, venus, earth and mars (MVEM)
4 terrestrial (solid and dense) planets
Solid surfaces with no or very few moons
2. Farther from the sun
Jupiter, saturn, uranus, and neptune (JSUN)
Gas giants/jovian planets/ice giants
No solid surfaces with many moons… H, He
Characteristics of asteroids
Asteroids are basically chunks of rock and metal that orbit the sun but are much smaller than planets
Characteristics of meteors
typically made up of rocks, metal, or a combination of the two
How is the universe “moving” ?
Gravity and gravitational forces/pull
How do stellar lifetimes change?
Stars do not last forever.They are born, live, and die.A star is“born”when hydrogen fusion begins in its central core, and it lives as long as it can generate energy through fusion. A star “dies”when it finally ceases to produce energy by any kind of fusion.
How do stellar masses change?
Spend most of their lives fusing hydrogen into helium
Rock types and how they form/change
Igneous, sedimentary, metamorphic
Also split into silicates and carbonates
Layering of different rocks gives us this record- younger rocks are near the surface and are increasing age with depth
Fossils embedded in the geological record- gives us an understanding of the history of life on Earth
Rocks allow reconstruction of Earth’s surface history- allows us to look over a 46 year old “geological record”
What is radiometric dating
The most reliable method for measuring the age of a rock, fossil, or other solid object… relies on careful measurement of an object’s proportions of various atoms and isotopes
Idea is to determine the age of a rock or something from the ratio of parent and daughter nuclei within it, which depends only on the DECAY RATE and LENGTH OF TIME over which he decay has been occurring
Is governed by the laws of quantum physics
what is alpha decay
Large atomic nucleus ejects a helium nucleus, which consists of 2 protons and 2 neutrons
what is Beta decay/electron capture
Nucleus emits or absorbs an electron, causing one of its neutrons to turn into a proton, or a proton to turn into a neutron
what is a half-life?
The TIME IT TAKES FOR HALF OF PARENT TO DECAY INTO DAUGHTER; time it would take for half the atoms in a sample of the substance to decay
What has radiometric dating told us?
OLDEST INTACT ROCKS: 4.02GYRS
OLDEST EARTH ROCK FRAGMENTS (ZIRCON CRYSTALS): 4.38GYRS
Age of the solar system: about 4.5 billion
What are decay rates known for?
Many isotopes
What happened during the Hadean Eon?
The atmosphere is built by these volcanoes/arise from volcanic eruptions
Outgassing of trapped gasses
Massive amounts of H20 and CO2 are given off during volcanic eruptions… as well as N2, H2, H2S, SO2
So, the atmosphere builds up and water vapor condenses
water vapor turns into rainfall- causes oceans and lakes to fill up
H2O leaving behind a CO2 dominated atmosphere, which leads to high temperatures
Surface of Earth undergoing bombardment (ended about 3.8Gyrs ago)
Ultimately, there’s reason to believe that life started at the end of the Hadean Era
in the process of all of this, the surface is continually reshaped by VOLCANISM, PLATE TECTONICS, AND EROSION
In the process and events of the Hadean Ion, what is the surface continually reshaped by, and what are these things driven by?
in the process of all of this, the surface is continually reshaped by VOLCANISM, PLATE TECTONICS, AND EROSION
All of these are driven by the planet’s internal heat- Earth’s internal structure reflects this
All internal Earth must have been molten at some point
What are the original heat sources?
gravitational energy
radioactivity
impacts
Why it worked:
Ongoing radioactivity and good insulation (Mars has much less “stuff” (thermal energy/mass than Earth does), which is why they aren’t Earth
Residual heat drives gravitational energy, which leads to this ongoing radioactivity and good insulation
What was the atmosphere like during/in the Hadean Era
Volcanic gasses
lack of oxygen
water vapor
high pressure
temperature
How old is the continental crust?
4 billion years old
Continental crust (granite) is always floating, granite gets deformed and rearranged, and slowly grows and is added to
How old is the seafloor crust? (basalt- igneous)
Is very young and has very young material (200 million years old)
Is like a conveyor belt
Seafloor is created and destroyed
How is the magnetic field made
The liquid outer core of the Earth generates the magnetic field
Magnetic field is created whenever an electric charge is in motion
What does the magnetic field do?
Forms a protective barrier, which protects the atmosphere from erosion by solar wind particles
protects the surface against bombardment by high-energy particles
Keeping/maintaining an atmosphere- what does gravity do?
Keeps constant pull on planets in atmosphere
What is solar wind stripping?
Solar wind stripping is the process by which the solar wind removes gas from a planet’s atmosphere over time
refers to process where charged particles' from the Sun’s solar wind directly interact with and strip away atmospheric particles
PARTICULARLY IMPACTS PLANETS WITH WEAK MAGNETIC FIELDS
What is thermal escape?
loss of atmospheric particles due to high temperatures, where molecules gain enough energy from heat to be able to escape velocity and leave the planet’s gravitational pull
Occurs when atmospheric molecules gain enough kinetic energy due to high temperatures, ALLOWING THEM TO REACH ESCAPE VELOCITY AND LEAVE THE PLANET’S ATMOSPHERE
Search for Extraterrestrial Intelligence is…
Search for intelligent, communicating civilizations
what does astrobiology focus on?
1. Studying the conditions conducive to the origin and ongoing existence of life
2. Looking for these conditions on other planets in our solar system and around other stars
3. Looking for the occurrence of life elsewhere
What did Anaximander do
Earth is surrounded by the celestial sphere
The sun and the stars are placed on the sphere, moving around the Earth
Was successful at explaining MOST astrological phenomenon, except for planets
Sun, moon, and the planets are all on their own spheres (circles) centered on Earth
You can’t change from a circle (perfect)
Their orbital velocity thus cannot be changed
Assumption = Earth is centered, there are circular orbits and constant/consistent/uniform speeds
What did Aristarchus of Samos 310-230 BCE do
Determined relative sizes of Earth, Sun, and Moon
He also produced a simpler heliocentric model… if a smaller moon orbits Earth, then a smaller Earth likely orbits the sun
What did Tycho Brache do?
made the most precise naked eye observations of planetary positions
was accurate to about 21/60th of a degree
Who, using Tycho’s model, discovered that the helio model works best?
Johannes Kepler
What did Galileo do?
First person to use telescope
His telescope observations point to the helio model, starts understanding the physics of motion
Observes: moon orbiting jupiter, phases of venus, Galileon satellites
What did Newton do?
Discovers physical principles behind kepler’s laws and mathematically describes them
3 laws of motion
first to realize an attractive force could explain multiple phenomena
FOUND THAT STRENGTH OF FORCE DEPENDS ON MASSES AND SEPARATION (DISTANCE)
Fg = G
Inverse square law
Successfully predicts comet orbits and the existence of Uranus
What are Newton’s 3 laws of motion?
Law of Inertia (First Law): An object at rest stays at rest, and an object in motion stays in motion with a constant velocity unless acted upon by an external force
Law of Acceleration (Second Law): The force acting on an object is equal to its mass multiplied by its acceleration (F = ma)
Law of Action and Reaction (Third Law): For every action, there is an equal and opposite reaction
What did William of Ockham do
Says that entities must not be multiplied beyond necessity
Idea of simplicity also goes back to Aristotle and his student Ptolemy
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