Moons and Planets Final
It took a year of observing Pluto to determine its orbit accurately. We then learned it is closer than predicted. How did this lead to a re-evaluation of its mass, and in general terms, what was that re-evaluation?
#1 - from the (false) perturbations on Neptune #2 - had watched the orbit long enough to get its distance => too small for its brightness #3 - discovered moon Charon => use Kepler's 3rd Significant drop it mass from Jupiter sized to .00216 earth masses orbit -->High eccentricity and crosses Neptune's - High inclination angle to the other planets
Suppose Mars had a moon half the diameter of Earth's Moon, with an atmosphere just like Earth's atmosphere, and a 24 hour rotation period. What would we predict its average surface temperature to be?
...T = (i(1-a)/4(1-g)σ)1/4 a = planet albedo (ratio of reflected to incident light) σ = Stephan-Boltzmann constant R = planet radius i = solar radiation at the planet (energy/sec/unit area)
How many TRAPPIST 1 exoplanets have we detected, how many of those are Earthlike, which ones are in the habitable zone, and considering the star, explain whether you would expect another to become habitable within about a billion years or so, and which one it would be.
7 planets, 3 in habitable zone(e, f, and g) *** ultra cool dwarf? small?
It has been estimated that there are 500 billion exoplanets in our galaxy. If that is so, use the solar system as a model to calculate the probably number of habitable bodies in our galaxy
8 planets (2 or 3 of which may be habitable) 3/8(500 billion) = 187 billion 500 million
How would you define "planet"? Your answer can be a list of required properties if you want, and can include some of the ones in the current official definition, but not all 3 of them. b) List what solar system bodies might be difficult to categorize by your definition, and why
A celestial body that: 1- orbits the sun and 2-has sufficient mass to assume a nearly spherical shape and also is not a satellite (moon) of another object maybe larger than a certain size (diameter)? Something like Pluto (nearly spherical rocky object orbiting sun, not a moon) which was determined to not be a planet would, by my definition, be a planet. This could include a lot of other too small object
"Radius exclusion laws" are sometimes used in calculating the probability that Bode's law is not just a coincidence. In that context, what does "Hill radius" mean, why is it a factor, and how is it related to the "fractional Hill radius"?
A particle on a stable orbit cannot approach a planet more closely than k Hill radii for some k, using Hill radius h We can extend this criteria to two adjacent planets with non-zero mass by summing their respective Hill radii For non-circular orbits, we also expect that the aphelion distance of the inner planet is less than the perihelion distance of the outer one. The planets are separated by a Hill radius even at their closest possible approach: The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites.
What is the major constituent of the lakes and seas on Titan, how is it supplied to them, and how much of the atmosphere also consists of that substance?
Atmospheric Methane: 5% Because of the liquid methane on the surface, Titan has a similar cycle to the water cycle on Earth ● Methane rain will typically accumulate near the poles but the most extreme storms will usually occur at around 60 degrees latitude ● These rainstorms have been found to fairly rare, less than once during a Titan year, but they are always quite extreme ● There is evidence to suggest that, like Earth, serious variations in temperature and moisture trigger extreme weather
When you make a graph of average molecular velocity vs. gas temperature using logarithmic scales for both, each molecule is represented by a straight line. With a few equations, show why that is true
Ave molecule kinetic energy: E=3kT/2=mv^2/2 => vαT^1/2 - For each mol. mass m, logv α ½logT log v α ½logT => straight lines on log-log graph
How do we know Oumuamua came from outside the solar system, and why do we think it's long and thin?
Calculations based on trajectory show that the object came from the constellation Lyra Suggests origin from the star Vega 'Oumuamua travelled at about 59,000 mph average speed At this speed, it took so long that for 'Oumuamua to complete its journey that Vega was in a different position when it left! Its exact origin therefore remains a mystery Acceleration outgassing makes calculating the origin location increasingly difficult
What does the Jeans Mass signify, and in one sentence, how do we derive an equation for it (you can answer mathematically with an equation or two, or conceptually with words)?
Critical mass for cloud collapse: the "Jeans Mass", Mj Determine the gravitational potential energy of the cloud, Eg - And the total kinetic energy of the molecules in the cloud, Ek - Set them equal: Eg = Ek , and solve for the cloud mass
Why do the Jovian planets have higher percentages of H and He than the Terrestrials?
During sun formation, H and He are forced outward - Sublimation of inner disk ices by solar heat => atomic H & He - Photon pressure from young Sun pushes H & He outward - UV ionization followed by solar wind electromagnetic forces also push H & He outward
Slide #7 of the "Origins of the Solar System Moons" set states that the Apollo rock samples ruled out the Fission, Capture and Co-formation theories. For each theory, explain why, using one sentence for each. (Use the web for more information if you need to.)
Fission: in its protoplanetary stage a chunk of Earth flew off into space and formed the moon The lunar samples are older than the Pacific Ocean Capture: The moon came from another part of the solar system and was pulled in by Earth's gravity The Moon is almost chemically identical to Earth so it would be unlikely that they formed far apart Co-formation: The Earth and Moon formed at the same time through accretion by a giant spinning disk of matter The outer layer of Earth's crust is 200 million years old and therefore cannot be source of the moon
Describe two reasons it is difficult to determine the mineralogical composition of asteroids. A few sentences for each reason should be enough.
Geologic differentiation occurs during large impacts in space and when objects enter our atmosphere • As a result, until recently we have never had a sample of an asteroid that was unaffected by "space weathering" or differentiation when it crashed into Earth • While the total elemental composition may remain unchanged the mineralogical structures are heavily modified • This makes spectral analysis difficult Spectral analysis is difficult to use on asteroids because they are small and typically have a low albedo (especially c type asteroids) • On top of this meteorites are usually differentiated making it difficult to match spectral analysis
Explain why Earth's axial precession does not affect the alignment of the physical seasons with calendar dates, and also why it does affect the coordinates of every star.
Our "tropical" year is defined by passages of the sun across the celestial equator (the equinoxes) - So every year, the sun is the same angle above or below the equator on the same calendar date - So the synchronization of the physical seasons to the calendar dates is not affected by precession So the Vernal Equinox location precesses too - Precession shifts the Vernal Equinox westward 0.83 minutes of arc/year along the ecliptic (Remember, its' the equator that precesses, not the ecliptic)
Draw a horizontal line to represent a timeline from 1980 to 2019. Choose 5 of the SETI programs and projects and mark their ranges of operation dates above or below the line. If the beginning or end of operation is uncertain, mark it with a questions mark
Sentinel, META and BETA 1983-1999 SERENDIP 1979-? Active SETI 2010? Project Phoenix 1995-? Wow! 1977
Describe one major difference between the runaway greenhouse effect on Venus, and the increased greenhouse effect we fear on Earth.
Venus possibly began to heat up due to greater proximity to sun. On earth main reason is increase in atmospheric CO2 On Venus, Water evaporated into atmospher was major GHG responsible-- Not CO2 like on Earth
What basic parameters about an exoplanet and/or its orbit do we need to know in order to decide if it's "Earth like"? And which of those can we determine directly by the Doppler method of detection, and which by the transit method of detection?
What's earthlike? Radius: 0.1 - 2.0 Earth radii Mass: 0.001 - 10.0 Earth masses (=> density => composition) In its Habitable zone?: Depends on orbit size Atmosphere?: Depends on mass, radius and orbit size mass, radius, and orbit from transit orbital period and velocity from doppler
Explain Carl Sagan's "Faint Young Star Paradox". 3 or 4 short sentences should do it.
When did our water become liquid? The early sun was ~70% its present brightness All water on the early earth should have been frozen - But the geologic record shows liquid water very early
We might colonize Venus someday, suspended from balloons high in the atmosphere. First, calculate the mass of a balloon 100 meters in radius, with a wall thickness of 1cm, and material density of 1gm/cm3 . Then propose a way to fill the balloon with a gas lighter than Venus' atmosphere, after arrival at Venus.
a balloon filled with Nitrogen and Oxygen from Earth would be lighter than the Venusian air. mass= volume * density = (4/3)pi(r^3) * density
State 3 pieces of evidence for the theory that the K-T extinction was caused by an asteroid or impact. Also state one other possible cause for the extinction.
discovered a thin layer of iridium, a very rare element on Earth, laid down at precisely the K-T boundary. This layer is found worldwide, on continental shelves and ocean floors. • This iridium clay layer has about the same concentration as of iridium as meteorites. The K-T boundary clay in North America contains high levels of spherules, which are formed when the impacted rock is blasted into the air and melted, and as it falls forms droplets which are immediately frozen into glass spheres . • Just above this clay layer is the layer with high iridium concentrations and shocked quartzite, which is formed when quartz crystals suddenly succumb to a pulse of great pressure. • All of these are found to be 65 million years old, exactly at the K-T Boundary Eruption theory: Also happening at the K-T boundary was a large amount of volcanic activity between the Indian and African tectonic plates. Large quantities of Basalt covered what is now the Deccan Plateau of Western India. This created the lava beds known as the Deccan Traps, which today are located under the Indian Ocean. • The Deccan eruptions lasted roughly 1 million years, straddling the KT boundary and released ash and aerosols high into the atmosphere.
There is an error in my "Martian Water" slides applying the conditions on Mars to the phase diagram of water. Find the error, state what it is, and how Mars might be different if the figure in error were in fact correct.
max pressure is 0.1 not 0.001 more room to allow for liquid water
Draw a sketch of the shape of Ultima Thule as best you can. Show the rotation axis, label the two "binary" parts, and explain why we think it has the shape it has
see notebook
Describe 3 pieces of observational evidence for "Planet X"
to use the perturbations of transNeptunian objects and even the orbit of Neptune to predict the orbit size and eccentricity of Planet X A dwarf planet officially known as 2015 TG387 was discovered four years ago The orbit of The Goblin fits perfectly with the models if Planet X does exist in the far reaches of the solar system In a paper by Batygin and Brown, they discuss the orbital clustering that happens with distant Kuiper Belt objects These objects are typically found to have semi-major axes that are 250 AU or greater The odds found by Batygin and Brown that the this happens by random is 0.2% Other astronomers have now found more evidence in the Kuiper Belt and say the odds of these random orbits is 0.0001%
List the 5 steps for avoiding an asteroid collision with Earth, and write one sentence for each describing why that step is important
• Finding the meteorite determines the time before the impact.. • Tracking it. Sometimes, the asteroid is "lost" after its first sighting. • It can take even months of observations to determine the trajectory of the body. • This trajectory may have chances of hitting the Earth. • Characterize it. With telescope and eventually spacecraft observations we can gather data from the meteorite: shape, mass, size, spinning rate... It is also possible to scale them according to the impact risk: • Deflect/destroy it. The trajectory of a body on the space depends only on its position (gravitational potential energy) and velocity (kinetic energy). regarding the expression above we can conclude that the most realistic way would be changing the velocity of the asteroid. • Coordinate. Even if it is divided in pieces or deflected from the initial target, there may be a collision with causalities. • The change in the target point when deflecting can create international tension. • Due to this asteroids is not a one nation problem. Cooperation is necessary for both avoiding the collision or minimizing its consequences and for the aftermath repairing
Briefly describe two completely different theories for how Triton got its retrograde orbit. A sentence or two for each is enough.
• This theory proposes that Triton got its orbit by colliding with another satellite which was already orbiting Neptune • The constraints to this event are: • This theory requires this satellite to be large enough to slow down Triton, • But small enough to not destroy it • Mass is estimated to be about 0,01 · 𝑀� • Triton could have been slowed down by the aerodynamic drag force of the gas disk around Neptune • After its velocity was decreased enough, it would have been captured. • Models predict Neptune had a protosatellite nebula with a mass close to 40 times the mass of Triton • Triton's orbit should had been elliptical
Examine the March, 2011 dimming event of Tabby's star in those slides. With diagrams, show what kind of transit event could cause such a dimming pattern. It should explain the gradual dimming, the sudden onset of re-brightening, and the asymmetric light curve.
•Significant multi-day dimming events occurred, implying something large crossed in front of the star •Transits lasted up to a week •Asymmetric light curves •Light was blocked up to 22% at one point •Data checked for errors and was validified Rings of extremely fine dust may have originated from circumstellar material •Would have dispersed starlight as observed •Would explain the gradual dip Possibly a huge swarm of comets passing the star in an elliptical orbit •Consistent with observations •Unlikely as thousands of comets would be needed to show what observations show us •Best model at the time and was published Megastructure that would hypothetically surround a star in order to harness its power output using solar panels •Since it would surround the star it would block light •Structure would be unfathomably big
How did we first determine there is molecular hydrogen (H2) in the plumes of Enceladus, and why is that particularly important for the possibility of life there?
● 2008 - Cassini does a flyby within 16 miles of the surface, directly sampling the plumes ● Chemical analysis of the sample detects large amounts of water, ammonia, carbon dioxide, salt, and hydrogen Hydrogen points towards there being hydrothermal activity ● Hydrothermal vents on Earth are great homes for life, so why not on Enceladus?
Briefly describe two completely different theories for how Uranus got its tilted rotation axis. A sentence or two for each is enough
● Giant impacts were really common in the early solar system. ● It's easy to model a non-contrived collision that ends up with Uranus being tilted as it is. ● The most current dynamics for this collision are a 1-3 earth mass impactor and a strongly of-center impact, well before the moons of Uranus formed. It's possible for a planet to be tilted a lot by gravitational interactions with other planets. ● This is likely what happened for Saturn: resonances with Neptune gave it its 27 degree tilt ● For one such model for Uranus, it requires a large moon being ejected from the system during the Nice Model outer planet migrations ● This isn't a widely accepted hypothesis - the paper it is from is a preprint, and it doesn't account for other features Uranus has that impacts seem to account for
