Midterm 3 Flashcards
What is in our solar system?
Early astronomers knew Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors. Now: ● 1 star ● 8 planets (add Uranus & Neptune) ● 166 moons ● >660,000 asteroids ● comets, meteoroids ● ~50 dwarf planets, ● Kuiper Belt objects
What are terrestrial planets?
Close to the Sun. Made of rocks (silicon) and iron.
High density
Small (10000 km in diameter)
What are Jovian Planets?
Farther from the Sun. Made of gases (H, He, methane, water, ammonia), lower density, large
How do the planets orbit the Sun?
The planets orbit the sun from W to E along the plane of the ecliptic – looking down from the Earth’s North pole, planets orbit counterclockwise
Can we develop a model for the formation of the solar system that explains these properties?
The nebular hypothesis suggests that the planets formed from a gas cloud which collapsed into a disk.
This gas cloud has roughly the same composition as the Sun (mostly hydrogen, helium, + a trace of carbon, oxygen, nitrogen, iron etc)
The idea that the planets form from a disk is called
The nebular hypothesis.
This idea was proposed by
many people, one of which
was Pierre Simon Laplace, a mathematician in 18th century France
However, this was not the only idea
Alternatives to the nebular hypotheses
Tidal model: a passing star ripped material from the Sun and that material collapsed to form the planets
Capture model: The sun and planets formed separately, but the planets were captured later by the Sun
Accretion model: The sun moved through a gas cloud, got some gas and that gas formed the planets
What should we remember about the mass of our solar system?
Remember that most of the mass of the solar system is in the Sun. So the formation of the solar system is a footnote to the formation of the Sun.
Recall that stars form from molecular clouds.
What is a protostar
The collapse of a molecular cloud from a star forms a protostar and the disk of gas that surrounds it
What is Disk Formation
As the cloud collapses, the angular momentum in the gas makes it spin faster and faster until the the gas moves fast enough to orbit the protostar.
This is a general principle in astronomy. Collapse of stuff leads to the formation of a disk due to angular momentum
What is the concept of angular Momentum?
Hint: think of an ice skater
Angular momentum: spinning things keep spinning, and in the same direction Conservation of angular momentum says that product of radius and rotation rate must be constant.
→ Therefore, as a dust cloud collapses, its rate of
rotation will increase.
What is the condensation of the planets?
● Gas does not condense (because it remains gas), but dust can gather – tiny chunks of rocky and icy matter, with sizes of about 10-5 m
● Dust grains form in cool atmospheres of old stars, are ejected, grow by accumulating molecules from interstellar gas
● Dust collects into larger bodies: dust bunnies!
What is the process of clumps of dust growing larger?
accretion
What is happens when objects get large enough to create gravity strong enough to affect their neighbors?
Planetesimals
Eventually nearly all material is wept up into ________?
Protoplanets
What happens to the stuff that escapes capture and is left over?
Asteroids and Comets
How did the Moon form
During the formation of the Earth, the young Earth suffered a collision with a Mars-sized body that threw up material into orbit that condensed to form the Moon.
This is a rare event, and Earth is the only terrestrial planet with a large moon
How are Jovians formed?
To form the Jovian planets, we need one more stage of planet formation in which the gas accretes onto these rocky cores
However, to accrete gas we need a big core!
Bigger cores are possible if you can gather more material. In regions where the gas is so cold that ices form – beyond the snow line or frost line – we have the extra stuff to make this possible.
What is Scattering and Ejection
The larger pieces of this debris in the early solar system are called planetesimals. The ejection and scattering of planetesimals allowed the planets to change their orbits.
Generally Neptune, Uranus and Saturn move outward at the expense of Jupiter, which moves inward.
Jupiter being the biggest planet tends to fling stuff out of the solar system, causing it to move inward, while the other three planets tend to move planetesimals inward – so they move outward.
The Nebular Hypothesis and the Solar System
● Planets form in a rotating disk
○ Planets are all (nearly) in a plane to about 1%
○ All orbit in a counterclockwise direction and nearly all
rotate in the same direction as well.
○ Orbits are nearly circular
● Planets are relatively isolated – far away from their neighbors
○ Planets accrete all the material in their neighboring orbits
What are good indicators of the past composition?
The small bodies that have the best clues are asteroids, comets, meteoroids (coming from asteroids and comets) and plutoids.
The age and chemical composition of these things can tell us about the early solar system
What are Asteroids?
● Rocky bodies that are held together by gravity and internal forces
● Most live in a belt between Mars and Jupiter at 2.8 A.U. called the asteroid belt
● about 100,000 rocky objects bigger than 1 km exist
● Ceres is the largest asteroid with a diameter of ~1000 km
● A few thousand have orbits that cross Earth’s orbit –
called near-Earth asteroids (NEAs)
● Some are near Jupiter (60 degrees ahead and behind)
and are called Trojans
Why do we care about Asteroids?
● Asteroids are left-over material from formation of the solar system
→ ideal laboratory to study formation of earth and other planets
● Potential source of water on earth
What are Meteors, Meteorids, and Meteorites
Although these terms sounds very similar, they describe different phenomena that can be arranged by time:
A meteoroid is a piece of interplanetary matter that is smaller than a kilometer and frequently only millimeters in size.
Most meteoroids that enter the Earth’s atmosphere are so small that they vaporize completely and never reach the planet’s surface.
The flash of light we see while they burn up in the atmosphere is what we call a meteor (or fireball, for the brightest ones)
Whatever is left once it hits the ground (anywhere between the size of a sand grain to a giant boulder) is a meteorite.
What is a widely accepted hypothesis about the dinosaurs?
A widely accepted hypothesis is that an impact of a 10 km asteroid hit the Earth 65 million years ago and killed off the dinosaurs.
What are Comets?
● Icy bodies – called “dirty snowballs” – made of rocks, water ice, frozen methane, frozen ammonia, and frozen carbon dioxide
● ~1 – 10 km in size.
● When they pass close to the sun, the ices sublimate: solid
→ gas. Blows out a halo of gas and rocks (pebbles),
which is called a coma
● Sunlight and the solar wind push on the gas and dust
blowing the tail away from the sun
● Comet tails point away from the sun, NOT opposite of
direction of motion
What is the diffuse halo of gas and dust around the nucleus of the comet
coma
How do comet’s tail point?
Comet tails point away from the sun due to the solar wind and the light from the Sun.
What are meteor showers
Meteor showers are associated with comets – they are the debris left over when a comet breaks up.
What are defining factors of EARTH?
Radius is 6400 km
Density ~ 5000 kg/m3 – five times density of water
● Has a thick atmosphere of mostly nitrogen and oxygen
● Has active volcanoes
● Has a magnetic field
● Has known life
What are defining factors of MERCURY?
Radius ~ 2400 km
mass ~ 5% of Earth Density 5400 kg/m3 – about the same as Earth No atmosphere
No volcanoes
Has a magnetic field Covered in craters similar to Earth’s moon
What is the temperature on Mercury?
Temperature on Mercury varies drastically! On the day side it is hot, 700K, but on the night side it is cold, 100 K (-200 F)
● Wide variation in temperature because there is no atmosphere to trap heat and moderate temperatures
● Because Mercury has no atmosphere and no water, there is no erosion, so the surface is heavily cratered like the Moon
What does Mercury have that the Moon doesn’t?
Mercury has one feature unique to it and not found on the Moon. It has scarps or cliffs.
These scarps result from the cooling (and shrinking) of Mercury, which resulted in compression and cracking of the surface.
What are the defining factors of Venus?
● Radius ~ 6100 km
● Mass ~ 82% of Earth
Density ~ 5300 kg/m3 – about the same as Earth
● Very thick atmosphere
● Many volcanic features, indirect evidence of current volcanic activity
● No magnetic field
What type of atmosphere does Venus have?
Venus has a large, thick atmosphere which covers the entire surface with clouds of sulfuric acid.
Its atmosphere is 90x thicker than the Earth’s: pressure on the surface is 90 times higher than on Earth
What is the temperature on Venus?
Venus is HOT! Its average temperature is 730 K – hotter than Mercury and hot enough to melt lead.
● This is because the atmosphere traps heat via the greenhouse effect
● Sunlight strikes surface and is converted to heat, which is absorbed and re-radiated by carbon dioxide in the atmosphere instead of radiating out into space
What is the greenhouse effect on Earth?
Greenhouses gases (carbon dioxide, water vapor, methane) in the atmosphere trap heat Sunlight strikes surface and is converted to heat, which is absorbed and re-radiated in the atmosphere instead of radiating out into space An increase in the amount of greenhouse gases in the atmosphere increases the heat trapped
Why is Mars red?
Called the red planet because of its red color – due to rust, iron oxide
● Has nearly a 24 hour day – very similar to earth
● Atmosphere is made mainly of carbon dioxide, but it is very thin – 1/150 that of earth. Remember Venus is 90x that of earth
Does Mars have seasons?
Mars has seasons – the tilt of Mars is close to that of earth.
What is the Atmosphere of Mars?
Atmosphere is mainly CO2 (carbon dioxide) with some nitrogen and argon.
It is so cold that the atmosphere freezes onto the poles as frozen CO2 depending on the season
What are the bands and what is the that prominent feature on Jupiter?
Multicolored bands in atmosphere
● Bands are caused by convective cells that are stretched by rotation
● Most prominent feature is the Great Red Spot – a hurricane that has persisted for at least 300 years
Why do Jupiters belts stretch around Jupiter?
These belts are high and low pressure regions, as we also have on Earth
However, because of the Jupiter’s rapid rotation and thick atmosphere, these belts stretch around the planet rather than being localized
What is the structure of Jupiter?
Inner core rocky, like Earth Mantle is liquid metallic hydrogen: under very high pressures, hydrogen becomes liquid and acts like a metal – able to conduct electricity
Outer mantle is molecular hydrogen
Atmosphere very convective with large, persistent weather features
What is Europa?
It is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei[1] and was named after Europa, the Phoenician mother of King Minos of Crete and lover of Zeus (the Greek equivalent of the Roman god Jupiter).
What are defining factors of SATURN?
Radius ~ 10 times Earth, mass ~ 100 times Earth
Density ~ 700 kg/m3 – less than water, Saturn would float!
● Composed of mainly hydrogen and helium
● No surface - Strong magnetic field
What are Saturns Rings made of?
Made of icy particles from 1 cm to a few meters in size
The many divisions in the rings are due to tiny moons between the divisions known as shepherd moons
What is Titan?
Saturn’s largest moon – 2nd largest in solar system (Jupiter’s Ganymede is largest)
● Only other body in solar system with stable surface liquid: seas and lakes of methane
● Nitrogen-rich (98%) atmosphere, thicker and denser than Earth’s
Evidence for methane rain
What are the defining factors of URANUS?
Radius
~ 4 times Earth Mass
~ 15 times Earth Nearly featureless
Rotation axis is tilted 98 degrees!
The tilt may be result of a giant impact (?)
What are the defining factors of NEPTUNE?
Radius ~ 4x bigger than Earth.
Mass ~ 17x Earth Has bands of clouds unlike Uranus
Has a large storm on it called the Great Dark Spot.
What can fit inbetween our Earth and Moon?
The distance between earth and moon is large enough to fit all planets in the solar system between them.
What is NOT a characteristic of the early solar system, based on current observations?
The initial composition of the solar nebula varied between its inner and outer regions
What is a planetesimal
Bodies of ice and rock 100 meters or more in diameter
Whether or not a planet is composed mostly of rock or gas is set by
its mass
its temperature
its distance from the star when it formed
random chance
a combination of A, B, and C
a combination of A, B, and C
What is the best description of a moon
Any natural satellite of a planet or asteroid
Why do the outer giant planets have massive gaseous atmospheres of hydrogen and helium whereas the inner planets do not?
The outer planets grew massive quickly enough to gravitationally hold on to these gases before the solar wind dispersed the accretion disk
What are Asteroids and comets?
material left over from the formation of the planets
The moon probably formed
out of the collision between Earth and a Mars-sized object
Which of the following is NOT considered evidence of cataclysmic impacts in the history of our Solar System?
Uranus is “tipped over” so that it rotates on its side
Correct!
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the circumference of the planet
Mercury has a crust that has buckled on the opposite side of an impact crater
Mimas has a crated whose diameter is roughly one-third size on the Moon’s size
Mercury, Earth’s Moon, and many other small bodies are covered with many impact craters
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the circumference of the planet
Was it ever possible (or is it currently possible) for Jupiter to become a star?
No, it would have to be at least 13 times more massive
Why do the terrestrial planets have a much higher fraction of their mass in heavy chemical elements (as opposed to lighter chemical elements) than the giant planets?
Terrestrial planets are low in mass and high in temperature, thus their lighter chemical elements eventually escaped to the outer reaches of the Solar System
Because of the greenhouse effect, this planet has the hottest surface temperature in the Solar System
Venus
What are pulsar planets?
The first planets that were found using pulsar PSR
They found 3 planets from looking at the timeing irregularities of the pulsar.
As planets orbit the pulsar, they exert tiny tugs on the pulsar which move it slightly out of place.
What is the first technique for finding planets?
Technique 1: Radial Velocity
So as you look at a star which has an orbiting planet, the light of the star is redshifted as it moves away from you and blue-shifted as it moves toward you
This reveals the presence of a hidden body that pulls on the star, i.e., the planet
Instead of looking for the planet directly, we look for the wobble it causes in the star
What is technique 2 - transits
Watching for eclipses, when planets pass in front of their parent star.
Look for a very small drop in the amount of light received.
This can tell us the radius of the planet, since we know how uch of the light of the star is blocked.
Technique 3 is direct imaging
This is done by blocking out the light of a star using a coronagraph
This has been done for the Sun for years in order to study the corona – hence the name coronagraph
But stars are so small
that it is very hard to block out their light
Technique 4: Microlensing
The curvature of space-time bends both matter and light
So light will bend as it moves around a massive ody like a star or galaxy.
What are the four ways of finding planets
●Radial velocity – gives mass
● Transits – gives size
● Direct imaging – it might give size, but it’s always good to actually see the planet
● Microlensing – gives mass, and for a long time was the only way to detect Earth-mass planets
What is the most powerful technique?
The combination of radial velocity and transits is the most powerful technique now
What are 3-day orbits and what size are the planets in 3 day orbits?
When astronomers began look for extrasolar planets, they found many planets with about 3-day orbits. This is called the 3-day pileup.
For the most part, these planets are all Jupiter-mass or bigger.
So these are known as the hot Jupiters