AST 10S Final Study Guide
Where were the Oort cloud objects formed?
-Spherical distribution with randomly-oriented orbits -Probably formed between Jupiter and Neptune -Thrown into outer solar system by gravitational interactions with Jovian planets
Be able to name two reasons why exoplanets are hard to detect.
1. Difficulties with angular separation From 10 light-years away, Earth would be 0.3 arcsecond in angular separation from the Sun - hard to resolve even with the largest telescopes 2. Difficulties with contrast Venus is bright in the evening/morning sky when Earth blocks the Sun's light From outside the Solar System, Venus's brightness competes with glare from Sun - one billion times brighter!
Know why the Jovian planets have strong magnetic fields
All of the Jovian planets have magnetospheres • Uranus's and Neptune's are really not aligned with spin axis (much more than Earth's) • Uranus's field is also off-center; not known what causes this
Understand how human activity can lead to climate change and that solar and volcanic activity alone cannot explain the current temperature changes
Big volcanic eruptions can temporarily lower temperatures (aerosols) Earth is apparently undergoing climate change for a new reason: Human activity is rapidly increasing the atmospheric concentration of carbon dioxide and other greenhouse gases. (The carbon dioxide cycle operates much too slowly to absorb these emissions on human time scales.)
Know how the combination of the Doppler and transit techniques can give the planet's mass and density
Combination of period between transits and radial velocity variation of star gives us the mass of the planet No ambiguity in orbit inclination - orbit is seen exactly edge-on (transit tells us this This combination also gives us density (size and mass)
What do we think produced Pluto's moons, and why do we sometimes call Pluto and Charon a "double planet"?
Comparable masses and compositions of Pluto & Charon make this a "double planet" system.
Know the two things that are needed to calculate the "no greenhouse" temperature for a planet.
Depend on distance from Sun and reflectivity (albedo)
Know how the signal from a transit (primary or secondary eclipse) can provide: The radius of the planet A spectrum of the planet (at least in the infrared) Information about the planet's atmosphere
Depth of transit depends on relative sizes of star and planet
Why are the compositions of Uranus and Neptune (lots of hydrogen compounds) different from those of Jupiter and Saturn (mostly hydrogen and helium)?
Details of nebular theory suggest that all 4 jovian planets started with about the amount of icy material at center - approximately 10x Earth's mass for all • Jupiter and Saturn formed first and could capture much more H and He gas before solar wind cleared out the nebula - Thus, they are mostly H and He • Uranus and Neptune didn't capture much gas - Thus they are mostly hydrogen compounds
Understand that convection leads to global wind patterns that, in the absence of rotation, would lead to one large convection circulation cell in each hemisphere
Global winds blow in distinctive patterns: •Equatorial: E to W •Mid-latitudes: W to E •High latitudes: E to W
Know the form that hydrogen can take in the interiors of these planets
High pressures inside Jupiter cause phase of hydrogen to change with depth. • Hydrogen acts like a metal at great depths because its electrons move freely • Metallic form may be liquid or some other weird state
In absence of rotation wind convection circulation.
Hot air would rise in the equator and move towards the poles with cold air from the poles moving towards equator.
Understand how observations of the Doppler shift of a star can reveal the following about a planet that is orbiting the star: The planet's orbital period. The planet's mass (or at least a lower limit to the mass) The eccentricity of the planet's orbit
If planet has a really large wobble, we can assume that the planet is really large If you can measure the stars period it tells you the planets the faster the star is moving, the heavier the planet must be
Astrometric method (astrometric "wobble") and know what astrometry is
If the star wobbles in position, it is certain that it is being orbited by a planet. gravity of planet, however weak it may be, is enough to pull its parent star as the planet orbits around it.
Know why comets form tails (at what point in their orbit does this happen?) and what forms the two tails that we typically see
Ion tail - Ionized gas pushed away from the comet by the solar wind - Points straight away from the Sun Dust tail - Dust released by vaporizing ice in the comet - Lags behind the comet along its trajectory
Know why the large moons are spherical while many of the small moons are not
Large moons are heated enough by gravitational contraction and radioactivity to melt and reform as spheres Small moons lose heat too quickly and never melt
What is a meteor shower?
Material ejected from comet stays on the same orbit When the Earth crosses these orbits, material falls into our atmosphere - meteor showers are comet showers!
Know that there are several other Kuiper Belt objects that are similar in size to Pluto and at least one (Eris) is bigger. Several of these have moons.
Mostly small objects, perhaps 70,000 with radii > 100 km Preferentially found beyond orbit of Neptune Primarily icy in composition, similar to comets Eris (discovered 2005) is 27% more massive than Pluto and up to orbits 100 AU away.
Understand how the Coriolis effect leads to global wind patterns that depend on latitude.
On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern and is important in the formation of cyclonic weather systems.
Where were the Kuiper belt objects formed?
Orbit in the same direction and (roughly) the same plane as the planets (donut-shaped distribution) -Past Neptune's orbit -Probably leftover planetesimals that formed in
What is the composition of Pluto?
Pluto probably consists of a mixture of 70 percent rock and 30 percent water ice. Internal structure: The dwarf planet probably has a rocky core surrounded by a mantle of water ice, with more exotic ices such as methane, carbon monoxide and nitrogen ice coating the surface.
What is the probable source of material for the rings of the Jovian planets?
Primary rings are likely the remains of a Titan-sized planet torn apart by tidal forces early in Saturn's history
Understand how the different temperature profiles of the Jovian planet atmospheres lead to the bands on Jupiter and the different colors seen among the planets
Rapid rotation means strong Coriolis effect Ammonium hydrosulfide clouds (NH4SH) reflect red/ brown. • Ammonia, the highest, coldest layer, reflects white. red bands are lower in altitude and are warmer and therefor brighter white bands are higher altitude clouds, which are cooler and emit less light • Strong Coriolis effect leads to many alternations • Saturn's layers are similar, but buried deeper in atmosphere (more subdued). - More haze (like smog) • Methane gas (CH4) in Neptune and Uranus absorbs red light but transmits blue light. • Blue light reflects off methane clouds, making those planets look blue. • Uranus probably looks whiter because the methane clouds are deeper in the atmosphere
What suggests that Triton is a captured Kuiper belt object?
Retrograde orbit - probably a captured Kuiper Belt Object
Know that the properties of at least some of the known exoplanets differ from those seen in the Solar System: - "SuperEarths" - "water worlds"
SuperEarth Planets are now being found with masses and sizes intermediate between Earth and Neptune - these are super-Earths Water world Other exotica possible: worlds completely covered in water, 50 sulfur, phosphorous, etc.
Can the presence of hot Jupiters be explained by a modification to the nebular theory of planet formation? If so, how?
The discovery of hot Jupiters has forced reexamination of nebular theory. • Planetary migration or gravitational encounters could explain presence of hot Jupiters.
Know that we are starting to be able to directly image planets through techniques such as coronagraphy and adaptive optics What is a "hot Jupiter"?
The so-called "hot Jupiters" are gas giant planets, similar in characteristics to the solar system's biggest planet, with orbital periods of less than 10 days. They have high surface temperatures as they orbit their parent stars very closely—between 0.015 and 0.5 AU—while Jupiter orbits the sun at 5.2 AU. Planetary migration or gravitational encounters could explain presence of hot Jupiters.
Understand why many of the moons of the Jovian planets are geologically active even though they are the size of Mercury or smaller.
Tidal heating plus heat from radio-active decay?
Know what is causing the heating at various levels in the Earth's atmosphere
Troposphere: • lowest layer of Earth's atmosphere • Warmed by infrared light from surface and convection • Temperature drops with altitude. Stratosphere: • layer above the troposphere • Warmed by absorption of ultraviolet sunlight (Ozone) • Temperature rises with altitude in lower part, drops with altitude in upper part. Thermosphere: • layer at about 100 kilometers altitude • X rays and ultraviolet light from the Sun heat and ionize gases. • Temperature rises with altitude. Exosphere: • highest layer in which atmosphere gradually fades into space • Temperature rises with altitude; atoms can escape into space. • Warmed by X rays and UV light
Why are Uranus and Neptune more dense than Saturn?
Uranus and Neptune are denser than Saturn because they have proportionally less H and He
Understand what a greenhouse gas does in terms of absorbing radiation
Visible light passes through the atmosphere and warms a planet's surface. The atmosphere absorbs infrared light from the surface, trapping heat
What is the difference between climate and weather?
Weather is the ever-varying combination of wind, clouds, temperature, and pressure. - Local complexity of weather makes it difficult to predict. Climate is the long-term average of weather. - Long-term stability of climate depends on global conditions and is more predictable.
Transit method
When a planet goes in front of the star, it will dim the light coming from it
Know that the places where energy (heat) is being deposited in the Earth's atmosphere determine the various levels of the atmosphere (troposphere, stratosphere, etc.)
Where light interacts with atoms and molecules
Know that differences in pressure can lead to winds
Winds are driven by pressure differences induced by differences in surface temperature (e.g., equator to pole)
Understand how these patterns change depending on rotation rate (e.g., Jupiter vs. the Earth)
air at the equator is hot air at the poles is cool gas in the equator gains energy (heat) and expands, air becomes less dense and rises gas at the poles cools down and becomes more dense and travels back down to the equator right in northern hemisphere and left in southern hemisphere air from equator will rise until about 30 degrees latitude but will lose steam and complete convection current by flowing back towards the equator in polar regions sinking air is flowing towards equator but around 60 degrees latitude it will begin warming and rise up to complete convection current the convecting flow of these two currents will create third current that will follow pattern (hadley cell)
Understand the Coriolis effect and what causes it
causes fluids to curve as they travel across or above Earth's surface wind appears to curve because of the Earth's rotation Air moves from high pressure to low pressure which causes a curve the equator has a low pressure warm air rises and is curved earth rotates from the east to the west from north: clockwise from south: counter clock wise
Know how the presence of an atmosphere with greenhouse gases can affect the surface temperature of a planet and what the effect on the Earth would be if there were no greenhouse gases.
if there were no greenhouse gases, the earth would not be able to effectively trap the heat from the sun and would become much cooler than it is now our atmosphere keeps our planet warm by trapping the energy we get from the sun. If no greenhouse, Earth would be 31°C colder (below freezing on average - so liquid water would be rarer on the surface).
Understand the concept of pressure, and why atmospheric pressure gets smaller as you go higher in the atmosphere?
pressure is higher at distances closer to the center - Has to support weight of all the air above - More room to separate and disperse at higher atmosphere
Understand the different formation processes for the large moons of the Jovian planets (e.g., the Galilean moons) vs. the small moons
small moons • Small moons have irregular orbits (some in opposite direction) • these are probably captured asteroids and comets • Most are "potato-shaped." larger moons created out of a sub nebula Large moons are heated enough by gravitational contraction and radioactivity to melt and reform as spheres Small moons lose heat too quickly and never melt
Know why we expect convection in the troposphere of the Earth's atmosphere, but not in the lower part of the stratosphere.
temperature declines with altitude in the troposphere but increases with altitude in the stratosphere.
Doppler method
when the star is coming towards us, it has a negative velocity and is blue shifted when the star moves away from us, it has a positive radio velocity and is redshifted if we measure how shifted the light is, we can figure out when the star has done a full orbit
Know that most meteorites are (parts of) asteroids, but that some can come from the Moon or Mars
• A few meteorites arrive from the Moon and Mars. • Composition differs from the asteroid fragments. • A cheap (but slow) way to acquire Moon rocks and Mars rocks
Why is Jupiter more dense than Saturn?
• Adding mass to a Jovian planet compresses the underlying gas layers. • The result is a more compact planet
What are asteroids made of, what determines their shapes, and where are most of them found?
• Asteroids are rocky leftovers of planet formation. • Asteroids are cratered and not round most found in asteroid belt between mars and jupiter
What causes the gaps in the asteroid belt?
• Asteroids in orbital resonance with Jupiter experience periodic nudges, which move the asteroids to new orbits or out of belt • Most of the time, the resonance creates a gap, but not always
Know what the composition of comets is and where they formed.
• Formed beyond the frost line, comets are icy counterparts to asteroids. • Nucleus of comet is a "dirty snowball." • Most comets do not have tails: only comets that enter the inner solar system grow tails. • Most comets remain perpetually frozen in the outer solar system.
Why is Jupiter the largest of the Jovian planets? - Why are the compositions of Uranus and Neptune (lots of hydrogen compounds) different from those of Jupiter and Saturn (mostly hydrogen and helium)?
• Formed past the frost line, so could build up big mass in hydrogen compounds and gas • Closest of the Jovian planets, so formed where the nebula was densest and had the most material • First to build up enough mass to capture gas for outer layers
Know about the very active volcanic activity on Io
• Io is the most volcanically active body in the solar system. • Caused by tidal stretching from Jupiter • Volcanic eruptions continue to change Io's surface.
How does the rotation of the Jovian planets affect their overall shapes?
• Jovian planets are not quite spherical because of their rapid rotation. - Gravity pulls into a spherical shape - But material near equator gets flung out from rapid rotation • Saturn is the most oblate planet: 10% wider at equator than at poles
Know that some asteroids have moons, which allow us to determine the masses of the asteroids.
• Measuring the orbit of asteroid's moon tells us an asteroid's mass - Kepler's 3rd Law
What is a meteorite, and how is it different from a meteor?
• Meteorite: a rock from space that falls through Earth's atmosphere • Meteor: the bright trail left by a meteorite
Know the basic composition of each of the four Jovian planets
• No solid surface - Instead the "surface" is the top of the clouds • Layers under high pressure and temperatures • Cores (~10 Earth masses) made of hydrogen compounds, metals, and rock
Know about the evidence that climate change is occurring: the temperature record the CO2 record
• Release of CO2 from oceans and via outgassing can raise temperatures - Thus, we see a clear link between CO2 levels and global temperatures in the past • CO2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again. • CO2 levels have increased by 20% in 50 years causes melting of ice sheets and rise of sea levels Human activity is adding carbon dioxide and other greenhouse gases to the atmosphere. While the carbon dioxide concentration also varies naturally, its concentration is now much higher than it has been at any time in the previous million years, and it is continuing to rise rapidly. Observations show that Earth's average surface temperature has risen during the last several decades. Computer models of Earth's climate show that an increased greenhouse effect triggered by CO2
• Understand that major impacts can have a devastating effect on life on Earth, but that they are fairly rare. Smaller impacts are much more common.
• Small meteors are quite common • Big ones are rare
What do we think cause gaps in the rings of Saturn?
• Some small moons create gaps within rings. • Orbital resonance with a larger moon outside ring can also produce a gap.
Know the locations and shapes of the Kuiper belt and Oort cloud
• The orbits of comets that enter the inner Solar System are extremely eccentric (flat oval) • Short-period comets originate in the Kuiper Belt • Long period comets originate from the Oort cloud: a distant reservoir 50,000-100,000 AU from the Sun •Kuiper belt objects - Orbit in the same direction and (roughly) the same plane as the planets (donut-shaped distribution) - Past Neptune's orbit - Probably leftover planetesimals that formed in that region Oort cloud objects - Spherical distribution with randomly-oriented orbits - Probably formed between Jupiter and Neptune - Thrown into outer solar system by gravitational interactions with Jovian planets
Why do many comets that we see in the inner part of the Solar System have highly elliptical orbits?
• The orbits of comets that enter the inner Solar System are extremely eccentric (flat oval) • Only a tiny number of comets enter the inner solar system. Most stay far from the Sun.
Know which moon is the only one with a thick atmosphere
• Titan is the only moon in the solar system to have a thick atmosphere. • It consists mostly of nitrogen (N2) with some argon (Ar), methane (CH4), and ethane (C2H6).
Why is Pluto not classified as either a terrestrial or Jovian planet? In other words, how is it different from the 8 major planets?
• highly inclined orbit • very small (compared to gas giants) • very ice-rich (compared to terrestrial planets) • several moons (in contrast to terrestrial planets)
Know what the Great Red Spot on Jupiter is
•Is a storm twice as wide as Earth •Unlike hurricanes on Earth, it is a high-pressure storm •Has existed for at least three centuries
