M&P Exam 01 Flashcards
State 3 facts about Mercury that could possibly threaten its definition as a planet if the definition were the one from the 2006 IAU.
Mercury is very small (smaller than some moons like Titan & Ganymede)
Mercury’s orbit is highly eccentric & egg-shaped
Mercury does not have a substantial atmosphere - exosphere of atoms blasted off by solar wind
You have 5 steel spheres with diameters of 0.01, 0.1, 1.0, 10, and 100 mm. Show those diameters on linear and logarithmic scales.
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You determine the number of stars in a galaxy by measuring the rotation rate, applying Kepler’s laws to get the mass and then dividing by the average mass of a star. In one or two short sentences, why might the answer be too high?
The mass will likely be too high due to taking the average mass of a star. Mass refers to all parameters that contribute to mass like dark matter, gas and dust. Most mass comes from dark matter. Instead, after finding the rotational velocity, measure the radius, R and find the rotational period. Finally, use Kepler’s 3rd law to get an accurate mass.
State 3 properties of water that make it important for human life.
pH neutral = good medium for chemical reactions
Water has highest “latent heat” for cooling - energy transfer
Water is denser than ice - ice floats, melts, more liquid - maintain stable water temperature
Draw the graph of average molecular velocity (vertical axis) versus temperature with logarithmic axes for He, H2O, O2, and CO2 gases. Then add ozone (O3) to the graph.
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The graph in a) can help predict a planet’s atmospheric chemical conditions. State 3 other factors that might affect that composition.
Subsurface water
Stellar winds that strip atmosphere
Stellar UV that dissociates H2O
Planet’s escape velocity
Use a diagram of forces and one sentence to explain why a rotating gas cloud tends to collapse to a disk.
Vertical gravitational force components cause the rotating cloud to collapse to a disk as it is unbalanced.
Describe 3 effects caused by the early sun that caused the difference in composition between the Terrestrial and Jovian planets.
Photon Pressure pushes lighter elements outward
- Terrestrials: Overabundance of lighter elements outside, leaving heavier elements in the center.
- Jovians: Further from the sun, so they retain a lot of the lighter elements & they accumulate in their atmospheres
Chemical Sticking of Planetesimals that gravitationally collect in orbit (temp & density dependent)
- Terrestrials: planetesimals are close together & gravitationally collect, sweeping up debris
- Jovians: further apart = less collisions in Jovians, gaseous
Accretion & Cooling
- Terrestrials: form molten Terrestrial planets that then solidify (more surface area = cools faster (αR^2) - heavier elements sink
- Jovians: Turbulent eddies trap planetesimals which collect into warm liquid jovians… chemical & temperature differentiations occur
Why was it essential to NASA to determine a more accurate value of the AU before 1962?
Accurate measurements of AU are needed to navigate to other planets, such as Venus in the Mariner Missions.
Describe three reasons why radar was not used in 1961 to determine the distance to Mars.
Mars is much further away
Mars disk is much smaller
Time between Mars conjunctions is larger than Venus (Venus more frequent)
Mars signal return takes longer
Explain, with 2 short sentences or equations & a diagram, why the solar energy flux at a planet must be divided by 4 to determine the average flux over its whole atmospheric surface.
Geometric Correction: body of radius r receives piR^2 area of sunlight, but energy is heating 4piR^2 of total surface area.
Solar flux must be divided by 4 to get average input flux heating the planet = 655
With 2 short sentences, explain why much more solar radiation energy passes through the atmosphere of Venus than the ground radiation energy does. Be specific but numbers are not necessary.
Venus’ atmosphere is 96% CO2 and is transparent to incoming solar radiation. It is highly opaque to infrared radiation emitted by the surface. This traps heat through the greenhouse effect & prevents ground radiation from escaping.
What parameters make up a planet?
Size
Shape
Mass
Orbital Tilt
Orbital Eccentricity
Chemical Composition
Orbital Domination
Energy Source
Atmosphere
What is the definition of a planet according to IAU 2006?
A planet a) orbits the sun, b) has enough mass to assume nearly spherical shape, c) clears its orbital neighborhood
What are some problems with the IAU 2006 definition?
Pluto becomes a dwarf planet, Earth has not cleared its orbital debris (no planet has) because of meteorites, why is Jupiter not classified as a brown dwarf binary?, becoming spherical depends on more than just mass.
Why is Pluto considered a dwarf planet?
It is not massive enough & it has an incredibly eccentric orbit, passing into the Kuiper Belt.
Why is Jupiter not considered a brown dwarf binary star?
There is no clear reason.
What is the Drake equation? Give answers.
A means of measuring the number of planets with intelligent life in our universe today (Nc)
N* = # of stars in our universe today (10^11)
fp = fraction of stars that have planetary systems (1)
NL = # of planets ever suitable for life in a planetary system (1)
fL = fraction of suitable planets that ever evolve life (1)
fi = fraction of life-bearing planets that ever evolve intelligence (10^-1)
ft = fraction of a star’s lifetime that intelligence survives (10^-2)
What is the original drake equation?
of intelligent civilizations in our galaxy that can communicate with us today (Nc)
R* = rate of star formation in our galaxy
fp = fraction of stars that have planetary systems
NL = number of planets ever suitable for life in a planetary system
fL = fraction of suitable planets that ever evolve life
fi = fraction of life-bearing planets that ever evolve intelligent life
fc = fraction of intelligent life forms that ever produce interstellar signals
L = how long do they reproduce that communication
How do we estimate the number of stars in a galaxy?
Determine the rotational velocity, v near the outer edge using angle of inclination
Find the rotational period using the radius, p = 2piR/v
Use Kepler’s 3rd law to determine the mass, Mp^2/R^3
Draw the rotational velocity curve for typical galaxies.
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How does dark matter affect the calculation of the number of stars?
It has no effect on mass since all mass affects rotational velocity. Reduce the number of stars by 80% if dark matter does NOT produce stars or planets.
What are some methods of exoplanet detection?
Pulsar Timing
Microlensing
Transit
Doppler
Direct Imaging
What are the requirements for life?
Liquid Water
- pH neutral = good for chemical reactions
- Liquids have latent heat for cooling
- Water is denser than ice - stabilizes water temperature
Protective Envelope
- Solar wind particles strip the atmosphere & are diverted by the magnetic shield
- Short wavelength, high energy light is blocked by atmosphere (UV)
Define a habitable zone.
Depends on parent star type - brightness, temperature, mass
- Not too hot or too cold for liquid water
- Not too much uv radiation & stellar wind particles
- Far enough away to be tidally locked
What are the principles of atmospheric retention?
Surface temperature vs. gravity
- Assume gases are produced from warm surface
- Higher surface temp = molecules move faster = escape
- More surface gravity = must move faster to escape
- Equipartition of energy: all particles in a gas have same kinetic energy
- Massive molecules move slower at a given temperature
How do we calculate escape velocity?
sqrt (2GM/R)
Describe the relationship between an object’s escape velocity and a molecule’s average velocity.
- Velocity of molecules decreases as surface temperature decreases
- Heavier molecules move slower than lighter molecules
- Plot escape velocity & surface temp of moons/planets
- If body is above molecular line, its escape velocity is > molecule’s average velocity (holds onto that gas)
When were the earliest traces of life on Earth found?
3.5 billion years ago
What are some problems with calculating the fraction of life bearing planets that evolve intelligence? That ever evolve life? The fraction of a star’s life that intelligence exists?
What is intelligence? What is life? We have not died yet, so we don’t know the fraction of a star’s life that we live. How did life form? Intelligent civilization longevity, conditions on exoplanets.
What is the answer to the Drake Equation?
100,000,000 bodies in any galaxy that have intelligent life today
What are some other forms of the Drake Equation?
Niu = NgNc – # of bodies with intelligent life in our universe today (10^18)
Nicu = Niufc – # of planets with life in our universe that can communicate with us (10^12)
Describe the factors that cause a cloud to collapse?
High temperature, molecules move faster = more pressure = cloud dissipates
High mass, more gravity = molecules move faster to escape = cloud collapses
Define Jeans Mass, how do we measure its parameters?
Critical mass for a cloud to collapse. Set kinetic equal to potential energy – Mj = 45T^(3/2)n^(-½)
If a cloud’s mass is less than Mj, why are there stars?
Molecular clouds undergo fragmentation into denser cores.
Describe the steps to star formation.
Disk Formation:
- Angular momentum conserved, faster rotation = vertical forces cause cloud to collapse
- Central gas temperature increases to fuse H to He and increases gas pressure
Collapse of inner cloud stops = stable star
H & He Outward:
- Photon pressure from star pushes H & He outward
- UV ionization & solar win also push them out = overabundance of H & He
Chemical Sticking:
- Molecules form planetesimals (temperature & density dependent)
Inner Disk Accretion & Cooling
- Planetesimals gravitationally collect in orbit to form molten terrestrials
- Terrestrials solidify
- More volume (αR^3) – slower
- More surface area (αR^2) – faster
Outer Disk Accretion – Jovians
- Planetesimals further apart = collisions are seldom
What evidence is there for the age of our solar system?
Zircon - 4.375 bil yrs
Meteorites
Oldest moon rocks
4.57 bil yrs old
What is Radiometric Dating?
Radioactive nuclei decay to another element with a known half-life, Tau
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What are the problems with circular orbits?
There are less collisions & planetesimals will not be made. Early debris could have been in eccentric orbits that were forced circular by gravitational forces.
What are the cardinal locations of an inner planet?
Superior Junction
Inferior Junction - Venus is closest
Greatest Eastern Elongation (evening)
Greatest Western Elongation (morning)
What is AU?
Average distance between Earth & sun – leads to every astronomical distance: geometric parallax > cepheid variable > hubble constant > stellar brightness based on distance to stars
How do we find AU?
Solar Parallax: Earth’s radius + solar parallax angle
Orbital Periods of Earth & Venus: Kepler’s 3rd => ratio of their orbit sizes
Transits of Venus: Observers at 2 latitudes see different transit durations
Distance & Position of Venus
What is RADAR & how is it used to measure AU?
Radio Detection & Ranging used to accurately measure AU. Sends out pulses & receives echoes in wavelengths.
Why was it difficult to detect Venus by RADAR & what mistake was made in 1958?
Soviets jam radio systems – NOMAC reduce noise
1958: LL sent 5 pings & measured AU = 149,467,000 (132,000 km too small)
2 pings 0.24 sec apart, thought the higher ping was the real one
Who achieved the first radar echo from Venus? Who did it?
JPL (GALCIT) Mariner Mission
- 2 radio dishes (Bistatic – pulses sent & received at once… no need for switching to receive mode & estimating timing)
- 1961 – continuous wave transmission
AU = 149,599,000
Today AU = 149,597,870.700
How does distance affect radar echo brightness?
Α 1/R^4. Mars would be 1.7% strength of Venus.
How was Venus’ rotation velocity measured using radar?
Power spectra of radar echoes, bandwidth of echoes indicates rotation velocity at equator. Bright feature seen at red shifted side. If in retrograde (rotation cancels revolution), no wavelength shift.
How do we calculate planet temperature without the greenhouse effect?
Calculate Solar Energy Flux onto the atmosphere
Predict Solar Energy Flux at Venus
SEF @ Earth = 1370 W/m^2 & Venus is 0.723 Earth’s distance from the sun
SEF is α 1/R^2 => SEF @ Venus = 2620 W/m^2 (1370/0.523)
- Geometric Correction: body of radius, r receives πR^2 area of sunlight, but energy is heating 4πR^2 of surface area
Divide SEF by 4 => Average Input Flux Heating the Planet = 655
Albedo Correction – Light reflected by top of atmosphere
Albedo = average ratio of intensity of reflected to incident light
Venus Albedo = 0.75
Surface Input Flux = 655(1-0.75) = 164 W/m^2
Set equal to flux radiated by warm surface to get equilibrium temp
Venus Temperature From Energy Flux (𝜎 = 5.57x10^-8)
Stefan-Boltzmann: radiated energy, F = 𝜎T^4
Surface Input Flux = Radiated Flux
T = (F/𝜎)^(¼) = 232k
How do we correct for the greenhouse effect to get a planet’s temperature?
Depends on Atmospheric Absorption Factor
- Surface flux increased to correct for outgoing atmospheric absorption
g = Fraction of surface radiation blocked by atmosphere
Escape Flux = surface flux radiated x (1 - g)
@ Equilibrium, escape flux = input flux = surface flux (1-g)
Surface Flux = (input flux)/(1-g)
Describe Venus’ greenhouse effect.
CO2 blocks & absorbs heat from the planet = greenhouse effect making Venus very hot.
How do we predict g (surface radiation blocked by atmosphere)?
Blackbody Radiation & Wien’s Law: wavelength at peak intensity is α 1/T
Photosphere = 5,500k, solar radiation peak = 500nm (green)
Venus atmosphere = 96% CO2 (transparent to solar radiation, sunlight heats efficiently)
T = 730k
Peak ground radiation at 4 microns u (infrared)… CO2 is opaque to Venus ground radiation (infrared), so it absorbs heat emitted from surface
Because Venus radiated energy is blocked, there is a strong greenhouse effect… 724k
Venus is @ Equilibrium
What is the runaway greenhouse effect?
Trapped heat = more surface outgassing = more opacity = more trapped heat. When atmospheric escape from exosphere = outgassing = reaches equilibrium
How did Venus get so much CO2?
Inner solar nebula had water
- Strong solar uv light dissociated water
- Hydrogen escaped & stripped by solar wind
- O2 combined with carbon to form CO2
- CO2 transparency to visible & opacity to IR = stronger greenhouse effect = high temperature
Describe the problem with Phosphene on Venus.
- 14 september 2020: PH3 linked to life, may be no abiotic way for its production on Venus
- PH3 denser at mid latitudes… needs abiotic source to be produced
How much of Earth’s mass is water?
0.02%
Describe the problems with Earth’s water.
Where did Earth’s water come from?
- Water ice existed in cold interstellar space, but inner regions of the early solar disk were hot
- water dissociation should have occurred
- Hydrogen would have been pushed out by solar wind & radiation (no water)
- Earth would have been at boiling point
- Hydrogen has isotopes (H) & (D)
- Earth has 7 times ratio of D/H
When did it thaw to liquid?
- % of He in stellar cores increases with age => He falls to center, forcing core outward & expands => increase in star size = Brighter
- Faint Young Sun Paradox
- Earth sun was only 73% its brightness: should have been frozen
What are some solutions to Earth’s water?
Water from Comet Nuclei
- Made of water ice, D/H is very different from Earth (Hartley), isotopes do not work
Water from Meteorites
- Carbonaceous 20% water, D/H too high
- Enstatite (H rich), earth’s building blocks would have 20 times more H
- Asteroid Collisions found hydrated rocks in asteroids (not enough)
Describe the problems and solutions to the Sun’s angular momentum.
- Sun has 99.85% of solar system’s mass, but only 0.3% angular momentum
Solutions:
- Sun’s rotation slowed way down (due to solar wind)
- Sun’s surface rotates much slower than inner layers (due to solar photons)
- Less angular momentum in Oort cloud
- 99.9% of system’s mass was lost after sun formed
How did the Earth-moon system lose angular momentum?
Earth should be spinning 304 times faster. Believe Earth formed by impact => angular momentum lost from impactor
How do the tides on Earth affect its rotation & the moon’s orbit?
Earth’s tides slowed earth’s rotation & accelerated the moon’s orbit
How does the rotation of Earth’s inner core differ from its outer core?
Solid metal inner core rotates eastward slightly faster than the surface. Liquid metallic outer core rotates westward due to IC magnetic field.
What is precession?
Wobble of Earth’s rotational axis that traces a cone shape over 26,000 years. Does not affect the plane of Earth’s orbit (ecliptic), but changes orientation of Earth’s axis relative to other stars.
What are the Planes of Reference?
Tilted 23.5°
Ecliptic Plane: Sun’s apparent annual path due to our orbit
Equatorial Plane: Imaginary extension of Earth’s equator
Seasonal Markers & the Sun
Summer Solstice (June 21): Sun is 23.5° above celestial equator
Winter Solstice (Dec 21): Sun is 23.5° below celestial equator
Equinoxes (Mar 21 & Sep 21): Sun is at equator
Sun appears to move 1° eastward each day due to Earth’s orbit & shifts 23.5° N to S and back over 1 year.
Star Chart
Centered on Equatorial: ecliptic appears as sin wave
Centered on Ecliptic: equator is a flipped sin wave… Sun’s apparent annual path due to our orbit
Time & Years
Tropical Year: time it takes for the sun to return to the same position relative to celestial equator (equinox to equinox)… defines our calendar years.
Sidereal Year: time it takes for earth to complete one full orbit… longer because precession shifts position of the equinox westward along the ecliptic. Shortens tropical year by 20 minutes.
Precession & Coordinate System
Right Ascension: longitude… remains parallel to celestial equator
Declination: latitude… does not change as Earth rotates hourly
Designed to remain aligned with Earth’s equatorial plane.
Why not use fixed stars as 0,0?
Precession causes celestial equator to shift over time, coordinate system would not align with Earth’s equator.
Astrology & Precession
Zodiac signs in astrology are no longer aligned with original constellations due to westward shift of sun’s position due to precession
Ophiuchus (Nov 29 - Dec 18)
Why does the theoretical evolution of a star during its main sequence lifetime present a problem for our history of the evolution of life on Earth?
The early sun was only 73% of its brightness, so any water should have been frozen. However, geologic records show that liquid water was present very early on.
We might assume there is more mass in the Oort cloud than we expected, but it would probably make the sun’s angular momentum problem even worse. Explain why.
More mass in the oort cloud would increase the total angular momentum of the solar system. A smaller amount of angular momentum is in the sun itself.
State two ways you could eliminate Earth’s axial precession by changing details about it or its rotation or its orbit.
NO MOON. The sun’s axial precession is largely influenced by lunar gravity. Make the earth a perfect sphere so that precession stops.
Describe how you can derive the difference, in days, between tropical and sidereal years, just from the period of Earth’s axial precession alone.
Period = 360° orbital revolution / 0.83 westward shift of vernal equinox = 26,000. Shift per sidereal year: 360/26,000 = 0.014°/year. Time difference: 365.256 days / 360 = 1.014 days.
