EAPS 10500 | Units 10-12 (Moons, Tides, and Rings; Exoplanets; Hazards of Space Travel) | Study Guide (Exam 4)
*-UNIT 11-*
*EXOPLANETS*
*-EXTRAS-*
*HOMEWORK AND LECTURE MATERIAL*
39. What happens to a moon if it migrates inside the Roche limit.
*If a moon migrates across the Roche limit, it is pulled apart by tidal forces and the particles orbits as ring.* Far outside the Roche limit, a moon is spherical Closer to the Roche limit, tidal forces begin to deform the moon *Crossing the Roche limit, the moon disintegrates and a ring forms as particles are stripped away*
57. How we potentially detected a moon orbiting an exoplanet.
*Kepler-1625b is a super Jupiter in the habitable zone (but not habitable). But it might have a moon, the first exomoon discovered, the size of Neptune, so also not habitable*. But if the exomoon had a moon — which would be called an exomoon moon — then maybe...
*-UNIT 10-*
*MOONS, TIDES, AND RINGS*
51. Why Mini-Neptunes are not likely to be habitable.
*Mini-Neptunes are large enough to have held onto hydrogen and helium atmospheres and thus would not be habitable by life* as we know it, though Super-Earths might.
35. The cause of gaps in Saturn's rings.
*Most of the gaps in Saturn's rings are caused by orbital resonances with Saturn's many moons* Saturn's Roche limit lies just on the edge of its rings. Inside the rings rages a constant battle of clumps of ice of forming due to electrostatic attraction and tidal forces working to rip them apart. *Ring moons are the other source of gaps in Saturn's rings as they collect ring material.*
11. Neptune's moon Triton's likely origin.
*Neptune's moon Triton is thought to have been captured:* - Orbit is tilted 23° from Neptune's equatorial plane - Comprised of mineralogy similar to Pluto
8. The capture theory of moon formation and the characteristics of a moon that would suggest it formed in this manner.
*Objects passing too close to a planet can be captured into orbit by its gravity* - Captured moons are identifiable by having orbits that are *not aligned with the planet's equator, are non-circular, and often retrograde.*
38. What the mass and volume of an exoplanet enable us to determine.
*Once we know a planet's mass* (from radial velocity method) *and its size* (volume; from transit method, which gives size)*, we can determine its density.* Density = mass/volume
76. The greatest danger to humans wishing to colonize Mars.
Traveling to and staying on Mars will *expose people to 100 times the radiation they experience on Earth*, making radiation the greatest danger to humans wishing to colonize it .
14. Evidence that our Moon formed from a giant impact.
(1) The Moon has *nearly identical chemistry to the Earth*, which can be explained by impact mixing. (2) The Moon's *crust formed from the slow cooling of a magma (molten) ocean*, consistent with a giant collision that caused the ejected rocks to have melted. (3) The Moon *has a very small core*, consistent with only Theia's and none of the Earth's core being ejected into orbit.
25. What spring and neap tides are and when they occur.
*(1) spring tides* - When the Moon and Sun tides align, high tides are highest and low tides are lowest. - These are known as "spring" tides and they occur during a new or full moon (twice each month). *(2) neap tides* - When the Moon and Sun tides are perpendicular, high tides are lowest and low tides are highest. - These are known as "neap" tides and they occur during first or third quarter moons (twice each month).
28. That most of the major moons in the Solar System are tidally locked.
*Almost all large moons in the solar system are tidally locked* - Pluto and Charon are tidally locked with each other Exceptions: - Saturn's moon Hyperion (resonance with Titan) - Pluto's four outer moons (resonances with each other)
24. Why there are high tides on two sides of the Earth at the same time.
*Because the Moon's gravity elongates the Earth, similar tides occur on two sides of the Earth simultaneously.* - The Sun also causes tides, but they are smaller despite its bigger mass because it is much further away.
74. How planets are protected from radiation.
*Our magnetic field deflects much of the radiation* from the Sun and the *atmosphere absorbs most of the rest* (causing the aurora lights)
60. Whether it is possible to view a double sunset from a planet surface.
*Planets in binary star systems would have* double sunrises and sunsets
29. That Pluto and its moon Charon are tidally locked to each other.
*Pluto and Charon are tidally locked to each other* and orbit about a point just above Pluto's surface. This results from *Charon's relatively big size compared to Pluto, which also leads both bodies to orbit about a point above Pluto's surface.* Pluto's outer four moons are not tidally locked due to orbital resonances with each other.
10. Pluto's moon Charon's likely origin.
*Pluto's moon Charon is thought to have formed from a giant impact:* - Prograde, circular, equatorial orbit - Orbits 8 Pluto diameters away - Comprised of similar mineralogy to Pluto Like Pluto, Charon is covered by various ices, has some young surface features, and few craters, suggesting recent tectonic activity.
40. Where the Roche limit is located around Saturn.
*Saturn's Roche limit lies just on the edge of its rings.* Inside the rings rages a constant battle of clumps of ice of forming due to electrostatic attraction and tidal forces working to rip them apart. Ring moons are the other source of gaps in Saturn's rings as they collect ring material.
13. Saturn's moon Enceladus's likely origin.
*Saturn's moon Enceladus is thought to have formed from co-accretion:* - Prograde, circular, equatorial orbit - Orbits 2 Saturn diameters away - Comprised of mineralogy much different than Saturn
31. The method of detection used by the Kepler Spacecraft.
*The Kepler Spacecraft used the transit method of exoplanet detection* - Kepler used a photometer that continually monitored the brightness of ~150,000 stars in a fixed field of view - Kepler identified planets crossing their stars by the slight dimming of the star's light
15. What the lunar dichotomy is.
*The far side of the moon has relatively high topography compared to the near side of the Moon.*- This is known as the *lunar dichotomy*. It possibly occurred because of a giant impact.
1. Which planets have moons
*The giant planets have lots of moons; Earth and Mars a few, and Mercury and Venus none.* This is because of planet size and distance to the Sun. - Earth = 1 moon - Mars = 2 moons - Jupiter = 80+ moons - Saturn = 80+ moons - Uranus = 27 moons - Neptune = 14 moons - Pluto = 5 moons
53. How habitable zones are influenced by star size/brightness.
*The hotter/brighter/bigger a star, the farther away the habitable zone* and vice-versa. Therefore, one must know the temperature of a star (based on brightness) before one can estimate where the habitable zone is located.
62. How many galaxies are estimated to exist.
*There are an estimated 4 trillion galaxies*, leading to a total of 4x10^21 stars
32. What the time between observed exoplanet transits represents.
*Time it takes to complete one orbit* (orbital period)
12. What is unique about Neptune's moon Triton.
*Triton is the only large moon in the solar system believed to have been captured.* - Since its chemistry is very similar to Pluto's, it was probably captured from the Kuiper belt. - The chance of such a capture suggest that there may be 1000 Tritons hiding in the Kuiper Belt.
61. About how many stars are estimated to be in our Milky Way galaxy.
*We believe our own Milky Way Galaxy also has about 1 billion stars*, which may be average for all galaxies
82. What would kill you first if you took off your helmet in space.
*You would suffocate* Eyes would not pop out in low pressure - No, our bodies can support large pressure differences. However, loss of air pressure usually leads to unconsciousness.
3. Current observations that conflict with impact theory of formation of our Moon.
A calculation of the impact of a Mars-sized object (Theia) into a young Earth forming a debris disc, that will later coalesce into our Moon. Not all of the Moon's current orbital characteristics appear consistent with giant impact theory, but they are: - The Moon started out orbiting much closer to the Earth and along its equator, but *tidal forces associated with the Earth's gravity have since pushed it away and the tidal forces associated with the Sun's gravity caused its orbital plane to rotate toward the ecliptic.*
67. What killed the Apollo 13 astronauts.
After an oxygen talk blew up in route to the Moon, *Apollo 13 astronauts used a gravitational assist from the Moon to successfully return home* The Apollo 13 astronauts rode home (except for reentry) in the Lunar Module (LM), the part built to land on the moon, because the command module was low on oxygen and power due to the explosion. NASA and the Apollo 13 astronauts had to overcome many significant problems in order to return safely - Needed to remove carbon dioxide from the Lunar Module that was only designed to house 2 astronauts for 48 hours (return took 3 astronauts for 133 hours). - The astronauts could not replenish drinking water provided by the Command Module's fuel cells. - Because of limited battery power, they could not turn on heaters, so the spacecraft dropped to 38 deg F. - The command module had not been designed to power up from full shutdown during in flight. - Had to manually steer the capsule since the guidance system was shut down.
27. About how many pictures of exist of Neil Armstrong on the Moon
An aside: *There are only two pictures of Neil Armstrong on the Moon* - Neil's reflection in Buzz Aldrin's helmet - Neil's back
63. How many potentially habitable Earth-like planets are out there.
An estimated 25% of all stars are stable enough to not over-radiate their planets and *an estimated 40% of all stars have a potentially habitable planet (similar size to Earth in the habitable zone). Thus, there are an estimated 4x10^20 potentially habitable planets* For every grain of sand on Earth... ...there are an estimated 50 Earth-like planets - If only 1 in a billion of those habitable planets developed life, there might be 400 billion (400,000,000,000) planets out there with life.
75. Where most cosmic rays originate from.
Another source of radiation are cosmic rays, energetic atomic nuclei traveling through space at near light speed *originating from supernovae throughout the galaxy.* - Apollo astronauts "saw" cosmic rays that collided with their optics nerves, causing "flashes" of light.
33. What a bigger drop in brightness mean for an exoplanet transit.
Bigger drop in brightness means *bigger planet (larger diameter)*
4. How Mars acquired its moons Phobos and Deimos.
Based on their orbits, *the moons of Mars, Phobos and Deimos, likely formed from a large asteroid impact.* - Phobos = 20 km across - Deimos = about 12 km across They have: - prograde orbits - circular orbits - equatorial orbits - close-in orbits Impact << debris ring forms around Mars << moons accrete from the ring
50. Characteristic of lava worlds.
Being an Earth-size planet is no guarantee of habitability as *rocky planets so close to their stars would be extremely hot and are thus called lava worlds.*
21. What is unique about Jupiter's moon Callisto.
Formed farthest from Jupiter, Callisto has the thickest shell of ice and water, as temperatures in the accretion disc this far out were lowest enabling lots of ice to accumulate. Despite being the size of Mercury, *Callisto's internal structure has not completely differentiated*. - This may be due to low accretion velocities (farthest/slowest orbit from Jupiter) and makes Callisto unique to all other large bodies in the Solar System.
48. Characteristic of hot Neptunes.
Hot Neptunes are *exoplanets the size of Neptune that orbit relatively close to their stars* and are thus hot compared to our ice giants
20. What is unique about Jupiter's moon Ganymede.
Ganymede, the largest moon in the solar system, has a thicker water/ice shell. *Ganymede's liquid iron outer core produces the only substantial magnetic field generated by a moon* in the Solar System.
40. The types of planets the gravitational microlensing method detects better than other methods.
Gravitational microlensing *detects small planets (Mars-sized), planets far from their stars (Jupiter distance orbits), and planets around far away stars better than other methods* Disadvantage: This observation cannot be repeated for a particular planet, since once the closer star passes the distant star, it will not pass it again.
39. How the gravitational microlensing detection method works.
Gravitational microlensing works the same way as a magnifying lens. Instead of glass deflecting light to make a bug look bigger, *a closer star warps space to the bend light of a more distant star and it make it look bigger.* The microlensing detection method *takes advantage of the way a gravitational field of a star bends the light of a more distant star*, magnifying its brightness. A planet orbiting the closer star will cause a deviation in the lensing process. The gravity of a planet orbiting the closer star causes a distortion in the magnification of the light of the more distant star
*-UNIT 12-*
HAZARDS OF SPACE TRAVEL
47. Where Hot Jupiters probably formed.
Hot Jupiters *probably formed out beyond their star's ice line, then migrated inwards due to gravitational interactions* with other gas giants.
46. The characteristics of Hot Jupiters.
Hot Jupiters are *gas giants similar in size to Jupiter, but orbiting very close to their stars* (well within Mercury's orbit) and are thus very hot. Hot Jupiters are the easiest exoplanets to detect as their large size and close orbit blocks significant sunlight and their large mass causes its parent star to wobble significantly. - Surface temperatures on the order of several thousand degrees. - Orbit their stars in a matter of days. - Probably tidally locked (one side always faces the star)
44. What the absorption spectrum of sunlight passing through our atmosphere reveals about the chemistry of our atmosphere.
If passed through a prism, light spreads out into a spectrum. *Missing colors show up as black lines, indicating specific gases are absorbing that part of the spectrum.*
7. The main factor that controls the percentage of ice to rock in the mineralogy Jupiter's major moons.
In the same way the ice line influenced the composition of the planets forming around the Sun, *there was an iceline around a warm Jupiter that influenced the composition of its major moons.* Io | [ice line] | then Europa, Ganymede, Callisto *(more ice from left to right, more rock to left of ice line)* - because temperature decreases with distance
66. What killed the Apollo 1 astronauts.
In 1967, *Apollo 1 experienced a fire during a test on the pad that killed 3 astronauts*. The fire spread rapidly due to the practice of using a pure oxygen environment in the capsule The practice of using pure oxygen during flight as opposed to a nitrogen/oxygen mix (our normal atmosphere) was because the required hardware is lighter and simpler. The practice was not changed until after the Apollo program due to the cold war pressure to get to the Moon first. A change was made to have an 80-20 oxygen-nitrogen mixture using adding outside air while on the ground. But only the oxygen was replenished in flight, meaning that the Apollo astronauts traveled to the Moon and back with a pure oxygen atmosphere. The Apollo 1 astronauts could not open their inward swinging capsule door during the fire, so the door was redesigned to swing outwards with explosive bolts.
69. What killed the Space Shuttle Columbia astronauts.
In 2003, the *Space Shuttle Columbia disintegrated during reentry killing all seven astronauts* after foam from the External Tank broke off and damaged tiles on the orbiter wing. The space shuttle was hit over 15,000 times by debris from the external tank and solid rocket boosters. Foam debris from the external tank caused more than 100 dents in the orbiter 5 years before the Columbia disintegrated upon reentry due to foam damage. NASA did not learn anything from the Challenger... - Like the O-rings, the problem with foam breaking off the External Tank had been known for years. The Columbia Accident Investigation Board concluded: "NASA's organizational structure and processes were sufficiently flawed and that a compromise of safety was expected no matter who was in the key decision-making positions."
58. How the relative mass of the stars in a binary system influence planet orbits.
In a binary star system of similar mass, the *distance of planets from the stars would vary greatly during each orbit, causing big changes in temperature probably not conducive to the evolution of life.* However, if one star in a binary system has most of the mass, and orbits close to the other, planetary orbits would not look much different than a single star system, and thus a planet in this system could be habitable. Planets in binary star systems would have double sunrises and sunsets
83. How low gravity affects the ability to walk.
It's *pretty much impossible to walk around an asteroid with only 1/100,000th the Earth's gravity* With Mars's gravity, *being 1/3 that of Earth's you could take longer steps* With the Moon's gravity *1/6 that of Earth, astronauts hopped and skipped around because it was easier than walking* — and they were wearing suits that weighed 180 lbs. on Earth!
9. How Jupiter acquired its small moons that orbit far from the planet.
Jupiter has many small moons with orbits that are retrograde (opposite the spin of the planet), not aligned with Jupiter's equatorial plane, elliptical, and are extremely far from the planet. - These orbital characteristics suggest *these moons were captured by Jupiter's strong gravity.* - As with Jupiter, Saturn's strong gravity has captured numerous small outer moons that are in highly variable orbits
18. The discoverer of the Galilean moons.
Jupiter's four largest moons (Io, Europa, Ganymede, and Callisto) are *called the Galilean Moons because they were first observed by Galileo Galilei in 1610* — the first moons discovered outside our own.
79. The consequences of prolonged weightlessness on the human body.
Long periods of weightlessness cause *muscles to atrophy, bones to become brittle, and the redistribution of body fluids, which can have effects on balance, blood volume, sight, breathing, brain function, heart function, and other yet unknown long-term effects.* - After a five month stay on the space station these astronauts were too weak to walk with Earth's gravity. - Regular resistance training is essential for maintaining bone and muscle mass in zero gravity
31. The fate of Mars's moon Phobos.
Mars's rotation is slower than Phobos' orbit, causes the tidal bulge to lag behind. As a result, Phobos's orbit is slowing down causing *Phobos to slowly orbit closer to Mars. It will eventually crash into Mars.*
32. The probable reason why Mercury and Venus do not have moons.
Mercury and Venus may have had moons in the past, but their *slow rotations would have led tidal forces to bring these moons crashing onto their surface* in a fairly short time span.
70. The dangers of micrometeoroids.
Micrometeoroids: *tiny pieces of space rock (millimeters or less) traveling at very high rates of speed* (measured in kilometers per second) that can cause a lot of damage. - Lunar sample from Apollo 16 shows numerous zap pits on its surface caused by micrometeorite impacts Micrometeoroids have damaged the space station, numerous satellites, and can harm astronauts. To avoid micrometeorite object damage (MMOD), this experimental shield is designed with two layers, an outer skin, which serves to break the micrometeoroid into a cloud of fragments and gas, which becomes easier for a rear wall, to capture or deflect what remains. - In the future, gecko-based robots might help repair micrometeoroid damage.
2. The giant impact theory of moon formation and the characteristics of a moon that would suggest it formed in this manner.
Moons can form from a collision of a large impactor that ejects mass into orbit to form a disc of material (ring) that then accretes into a moon. A moon that accretes from an impact debris disc will have a *prograde orbit* — in the same direction the planet spins. - Impact debris always orbits prograde because the angular momentum of the planet dominates (even if its spin axis changes). A moon that accretes from an impact debris disc will have a *circular orbit* - Tidal forces and collisions between particles circularize the debris disc and thus the orbit of the moon that forms. A moon that accretes from an impact debris disc will have *an orbit aligned with planet's equator* - With time, tidal forces circularize all moon orbits (unless other bodies influence orbits) A moon that accretes from an impact debris disc will have *a close-in orbit only a few planet diameters away* - Because of gravitational forces, most impact debris ends up in a close orbital disc from which the moon will form. A moon that accretes from an impact debris disc will have *similar chemistry as the planet* due to the mixing of impactor and planet materials - Impactors big enough to form debris discs tend to eject crust and mantle material from the planet, which then mixes with the impactor, leaving both with similar chemistries.
5. The co-accretion theory of moon formation and the characteristics of a moon that would suggest it formed in this manner.
Moons form from an accretionary disc of dust that is thought to often surround a newly formed giant planet (1) *Circular, prograde, and equatorial orbits* (2) *Can be both near & far from the planet*, since protoplanetary discs can extend much farther than impact debris discs (3) *Will have different mineralogies*, since there was no impact mixing (think gas giants) * This is the key factor in the difference between a giant impact moon and a co-accretion moon.*
56. What is unique about the exoplanet Proxima b.
Proxima Centauri b, the closest potentially habitable exoplanet, is only 4 light years away! At only 4.2 light years, *Proxima Centauri b is the closest potentially habitable planet we'll ever find.* - 30% bigger than Earth - Receives 30% less energy - Earth Similarity Index = 0.83
37. Which planets have rings.
Rings are extremely common: *all the giant planets have them* - Tidal forces are causing Triton to migrate toward Neptune. Eventually, it will cross the Roche limit and be ripped apart to form a spectacular ring around Neptune.
59. What a rogue planet is.
Rogue planets are *planets without a parent star, which happens when planets are expelled through gravitational interactions as solar systems first evolve.* An estimated 70% of all solar systems expel planets, possibly leading to a billion rogues planets in the Milky Way Galaxy — similar to the number of stars Rogue planets can be detected by gravitational microlensing when such planets pass in front of a more distant star's light. Most rogue planets discovered are brown dwarfs, 10 - 80 times bigger than Jupiter (and thus more easily observed), but not big enough to sustain nuclear fusion and become a star For the first time an Earth-sized rogue planet has been detected by microlensing
42. Why Saturn's moon Iapetus has a bulge around its equator.
Saturn's icy moon Iapetus has a 20 km high equatorial *ridge that is thought to be the result of a ring crashing down onto its surface.*
36. The average thickness of Saturn's rings.
Saturn's rings are made mostly of pure water ice particles, centimeters to meters in size. - Due to tidal forces *the rings align exactly with Saturn's equator and are on average only 10 m thick.*
73. What a solar flare is and whether it is capable of setting the Earth on fire.
Solar flares are *sudden, large energy releases from the Sun that carry especially high doses of radiation* - Spacecraft are very vulnerable to radiation blasts from solar flares...though fireworks like these are unlikely since radiation does not interact with objects and atmospheres as shown — though electrical systems could overload. *In the movies, solar flares are often incorrectly depicted as scorching the Earth. But we are in no danger of this happening because radiation does not ignite fires.*
81. How sound travels in space.
Sound in space? *There is no sound is space* Sound waves exist as vibrations in a pressured medium, such as air. There is no medium in space within which sound can travel.
71. What spacesuits are able to protect astronauts from.
Spacesuits have multiple layers of insulation to *protect astronauts from the micrometeoroids (Kevlar layer), and extreme cold and heat (±250°F), but not radiation*, which would require impractically thick, dense material.
55. What is unique about the exoplanet Teegarden's Star b.
Teegarden b is *about the same size and surface temperature as Earth. It orbits a quiet (no radiation pulses) low-mass red dwarf star only 12 light years away* - So, it is small and lasts 10s of billions of years given lots of time for life to evolve Teegarden's Star is so close to Earth that it is visible moving relative to most stars, which is how it was discovered. Because Teegarden's star is much less bright than the Sun, its habitable zone is very close and Teegarden b orbits it in less than 5 days, meaning it is likely tidally locked.
22. How a radar return signal is interpreted.
The Cassini Spacecraft also carried radar that can see through Titan's methane clouds and provide measurements of surface roughness and topography. (1) *Smooth* surfaces reflect radar waves away from the spacecraft, and thus appear *dark* (2) *Rough* surfaces reflect some of the radar waves back toward the spacecraft, and thus appear *bright.*
36. How the Doppler Effect works.
The Doppler Effect is the *apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.*
64. What the Drake equation calculates.
The Drake equation *calculates the number of civilizations we can expect to find in our galaxy with which communication is possible.*
54. The factors considered in the calculation of an exoplanet's Earth Similarity Index.
The Earth Similarity Index (ESI) rates a planet's potential habitability from 0 to 1 by comparing its *radius, density (these two define interior properties), escape velocity, and surface temperature (these two define surface properties)* to that of Earth.
30. Why the Moon is moving away from the Earth.
The Earth's faster rotation carries the tidal bulge a little ahead of the Moon's orbit. This causes the *Moon's orbit to speed up a little and go into a slightly higher orbit*. This is *causing the Moon to slowly drift away from the Earth at 4 cm/yr.*
65. Possible solutions to the Fermi Paradox.
The Fermi Paradox: The universe's billions of years of existence should have allowed plenty of time for intelligent, technological lifeforms to develop and broadcast their existence. Why, then, is the cosmos so quiet? *Possible solutions:* - *Transmissions from alien civilizations are too weak to pick up* because of vast distances. - *We are not looking in the right places* — space is vast, and we can only listen in a few directions at a time. - *Alien civilizations do not communicate in the radio spectrum like we do*, and thus we do not know how to recognize their signals yet. - *Civilizations always die out* and thus at any given time there are not enough to be easily detected. - *We are alone*
6. How Jupiter acquired its major moons.
The Galilean moons have prograde, circular orbits around Jupiter's equator and, most significantly, very different chemistry from Jupiter requiring they *formed from an accretionary disc.*
78. What the Kessler Syndrome is.
The Kessler Syndrome: *Collisions create debris which creates more collisions, etc. until the Earth is encased in a shell of orbiting debris, making it impossible for us to keep satellites in orbit* (goodbye, Internet, cell phone service, and GPS) and *no leaving the planet - forever.*
16. What the Late Heavy Bombardment was.
The Moon's topography reveals a tortured history Most of the big impact basins formed around 3.8 billion years ago, known as the *Late Heavy Bombardment.*
38. What the Roche limit is.
The Roche limit is *the distance from a planet where tidal forces are equal to the moon's own gravitational forces that work to keep it spherical.*
17. Why the South Pole-Aitken basin on the Moon is unique.
The South Pole-Aitken basin in the southern hemisphere is *the largest and oldest (4.3 Ba) recognized impact basin.*
68. Why the Space Shuttle Challenger exploded.
The Space Shuttle consists of an orbiter, an external tank with liquid oxygen and hydrogen fuel for the orbiter engines, and two solid rocket boosters that provide 80% of the lift for the first two minutes of flight. - The edge of a solid rocket booster segment showing one side of a field joint with o-rings in place. The aft joint failed upon ignition, then took 70 seconds to burn through a strut attaching the booster to the external tank. The detached booster then crushed the external tank releasing oxygen and hydrogen, which mixed and ignited. - Puff of smoke resulted, indicating O-ring failure upon ignition *Why the Space Shuttle Challenger exploded:* - The *program was aware of and ignored the implications of O-ring damage* on numerous recovered booster hardware. - The *launch took place under cold temperature conditions that had never been tested*, exasperating the O-ring problem. - *Managers at NASA and Morton Thiokol ignored the advice of engineers* that it was not safe to launch. Why a teacher (Christa McAuliffe) in space? - For political reasons: President Reagan wanted to appease a striking teachers union. Did this influence the disaster? - The White House probably put pressure on NASA to launch before Reagan's State of the Union address that evening.
41. How the direct imaging detection method works.
The direct imaging detection method *blocks the overwhelming glare of stars to reveal the reflected light of orbiting planets*
42. Which types of planets the direct imaging method detects better than other methods.
The direct imaging method *detects planets far from their stars better than other methods*
43. How we can infer the chemistry of an exoplanet's atmosphere.
The forefront and future of exoplanet research is understanding the chemistry of exoplanet atmospheres. If passed through a prism, light spreads out into a spectrum. *Missing colors show up as black lines, indicating specific gases are absorbing that part of the spectrum.*
52. What the habitable zone is.
The habitable zone is the range of orbits around a star within which *a rocky planet's surface temperature is warm enough to maintain liquid water on its surface.*
34. How tidal heating affects icy moons.
The icy moons of Jupiter's Europa and Saturn's Enceladus *also have elliptical orbits because of gravitational tugs of neighboring moons that cause tidal heating* sufficient to melt their icy lithospheres and create *subsurface oceans.*
35. How the radial velocity detection method works.
The radial velocity (or doppler) detection method *relies on the fact that the gravitational pull of an orbiting planet will cause a star to wobble* — move slightly toward the Earth (blue Doppler shift) and then slightly away (red Doppler shift) each time the planet orbits.
37. What the radial velocity method can provide that the transit method cannot.
The radial velocity detection method *gives us something that the transient method does not: the mass of a planet.*
72. What the solar wind is.
The solar wind is a *continuous flow of charged particles (radiation) from the sun that permeates the solar system.*
30. How the transit detection method works.
The transit detection method detects distant planets by *measuring the minute dimming of a star as an orbiting planet passes (transits) between it and the Earth.* - Dimming must occur at regular intervals to indicate a planet. - Only planets whose orbits are seen edge-on can be detected. - The transit method most easily detects big planets close to their stars.
34. Which types of planets the transit method detects most easily.
The transit method most easily detects *big planets close to their stars.*
41. The fate of Neptune's moon Triton.
Tidal forces are causing Triton to migrate toward Neptune. *Eventually, it will cross the Roche limit and be ripped apart to form a spectacular ring around Neptune.*
26. What is means for a moon to be tidally locked.
Tidal forces cause moons to become *tidally locked, where one side of the moon always faces the planet.*
33. Why our Moon does not experience as much tidal heating as Io.
Tidal heating occurs when moons continuously deform like an accordion Tides always cause a moon to deform. But if that moon is tidally locked in a circular orbit, the distorted shape of the moon remains the same as it orbits. Thus, no heat is produced. However, *if the moon is in an elliptical orbit (like Io around Jupiter), the tides will cause the moon to continuously change shape, which causes the interior of the moon to heat up.* - Io has an elliptical orbit because it is in resonance with Europa and Ganymede, which creates periodic gravitational tugs that keep the orbit from being circularized by tidal forces from Jupiter. - For every orbit completed by Ganymede, Europa completes 2 orbits and Io completes 4. - *Io's elliptical orbit causes tidal heating sufficient to melt its mantle, leading it to be the most volcanically active body in the solar system (400 active volcanoes).*
23. What is unique about Saturn's moon Titan.
Titan is the only moon in the solar system that has a thick atmosphere (mostly comprised of methane). It orbits outside the rings over Saturn's equator. Since we can't see Titan's surface through its clouds in visible light, the Cassini Spacecraft carried an infrared camera that observed infrared light from the Sun reflecting off bodies of liquid on Titan's surface — *methane seas!* False color Cassini radar view of Titan showing very smooth radar returns of its liquid methane lakes — making *Titan the only other body besides Earth in the solar system with liquid on its surface.*
45. Why we have so far found so few solar systems like ours.
We have so far found a continuous spectrum of exoplanet sizes and orbital periods, but *few look like our planets because our telescopes are not yet sensitive enough to detect exoplanets like our own*
80. How one can simulate the force of gravity on a spacecraft.
Weightlessness *can be countered by rotating a spacecraft, generating a centrifugal force that simulates gravity* - Running in a spinning spacecraft... This concept can be applied to an entire space station to simulate the force of gravity. - "Down" points outwards from the center of rotation. - The simulated "gravitational" force increases with spin rate and distance from the center of rotation. The proposed Gateway Spaceport looks suspiciously like the space station from the movie 2001, which was released in 1968. Objects not rotating with the spacecraft will not experience any centrifugal force and will not fall
49. What is likely to happen when Ice giants migrate closer to their stars.
When ice giants migrate toward their star and pass inside the ice line to become hot Neptunes (Neptune-sized exoplanets orbiting close to their stars), *their hydrogen and helium atmospheres may boil off, leaving a gas tail like that of a comet*
19. What is unique about Jupiter's moon Io.
With over 400 active volcanoes, *Io is the most volcanically active body in the solar system.* - Io gets its splotchy colors from volcanic plumes that rise to 200 km, showering the terrain with orange sulfur and rocky ash - Due to its low gravity, Io has mountains that rise as high as Mount Everest - In sharp contrast to Io, Europa has a thin shell of water ice with a subsurface ocean
77. How one could live on the Moon or Mars and be protected from radiation.
Without a substantial atmosphere or magnetic field, the best solution to protect ourselves on the Moon or Mars may be to *live underground.*
