astro 2 Flashcards
describe radiometric dating
Careful measurement of proportions of various radioactive
isotopes = radioactive nuclei that undergo spontaneous
change –i.e. radioactive decay- due to breaking
apart/emission of nuclear particles or conversion of a
proton in a neutron.
describe the rate of radioactive decay
The rate at which this transformation occurs is characterized by
the parent isotope’s half-life = the time necessary to decay for
half of the number of initial parent nuclei.
Formation of terrestrial planets
Solid seeds of metal
& rock in the inner Solar nebula grew through the
accretion process.
Microscopic particles stick together through electrostatic forces
As they
grow larger, their surface area ↑ ↑
easier to make contact with others!
Particles grew in mass until they became planetesimals, where
gravity dominated in the accretion process
For larger planetismals, collisions were increasingly destructive
These planetesimals eventually assembled into terrestrial planets,
which are relatively small in size because rock & metal made up only a
small amount of the materials in the Solar nebula
Formation of Jovian planets
Accretion occurred similarly in the outer solar nebula.
The outer solar system included more abundant ices along with
metal/rock
The Jovian planets began as large icy planetesimals, which
captured H, He & other gases from the Solar nebula.
Their gravity grew stronger as they accumulated matter, allowing
them to capture even more matter (positive feedback)
Each Jovian planet became surrounded by its own
(micro)accretion disk of gas, spinning in the same
direction as the planet’s rotation.
Moons accreted from icy planetesimals within these disk ended up
with nearly circular orbits in the same direction as the planet’s
rotation and lying in (or close to) the planet’s equatorial plane
As the Jovian planets formed, they quickly cleared away their orbital
path inside the Solar nebula
How was the Solar system formed?
Solar nebula probably began as a large & roughly spherical cloud
(a few light-years diameter) of very cold & low-density gas.
Collapse may be triggered by:
Shock wave from the explosion of a nearby star.
Local densification of gas due to solar winds of new stars
Once started, gravity ensures that it would continue
What is the kant laplace theory
Nebular theory = Solar system formed from
the gravitational collapse of an interstellar cloud of gas
where are forming stars always found in the nebular theory
always found within interstellar clouds
where are stars formed
Interstellar clouds (where stars are formed) represent only a stage of a complex galactic recycling process
which planets rotate on their side and “backwards”
f Uranus & Venus
which moon of which planet is unusally large
the moon of earth
what are asteroids and coments
Swarms of smaller bodies populate the solar system:
Asteroids = small rocky bodies orbiting the Sun like planets, but
much smaller.
Comets = small icy bodies (water ice, NH3 ice, CH4 ice, but also N2
ice, CO & CO
2 ices, etc., & rock) orbiting the Sun.
Most asteroids are in the asteroid belt (between the orbits of Mars &
Jupiter).
Comets are found in 2 distinct regions: Kuiper belt & Oort cloud:
The great majority never visit the
inner solar system!
Kuiper belt contains >100,000 icy
objects, of which Pluto & Eris are
the largest known.
The Oort cloud is much more distant
and its comets have orbits randomly
inclined to the ecliptic plane
give
Oort’s cloud a spherical shape
briefly describe asteroids
small rocky bodies orbiting the Sun like planets, but
much smaller.
briefly describe comets
small icy bodies (water ice, NH3 ice, CH4 ice, but also N2
ice, CO & CO2 ices, etc., & rock) orbiting the Sun.
where are comets distinctly found
Kuiper belt & Oort cloud:
The great majority never visit the
inner solar system!
where are most asteroids formed
are in the asteroid belt (between the orbits of Mars &
Jupiter).
what the shape of oort’s cloud
spherical
what is the kuiper’s belt
contains >100,000 icy
objects, of which Pluto & Eris are
the largest known.
is the oort cloud much more distant than kuiper’s belt
yes
describe the oort cloud
The Oort cloud is much more distant
and its comets have orbits randomly
inclined to the ecliptic plane
what are the two major types of planets
terrestrial and jovian
briefly describe terrestrial planets
Earth-like. Smaller size & mass Solid rocky surface Closer to the Sun (and closer together) Made mostly of rock & metal and with abundant metals in their cores Few moons and no rings
briefly describe jovian planets
Jovian = Jupiter-like (gas giants). Large size & mass No solid surface Farther to the Sun (and farther together) Made mostly of H, He & hydrogen compounds (e.g. H2O, CH4, NH3) Numerous moons and have rings
who saw four moons orbiting Jupiter, proving that not all objects orbit the Earth
Galileo
who built the first reflecting telescope
newton
Tides rise & fall _ times a day
2
Orbital energy =
kinetic energy + gravitational potential energy = ct.!
“Kepler’s first two laws
apply to ____________”
“all orbiting objects,
not just planets”
However, because tidal forces stretch Earth itself, the process creates
friction, called tidal friction
describe the strength of earth’s tidal force on moon vs moon’s on earth
Earth’s tidal force
on the Moon has a much greater effect than the Moon’s tidal force on
Earth
What is synchronous rotation between the earth and the moon
The Moon rotates on its axis in exactly the same time period that it takes to orbit Earth
what gives the moon 2 bulges along the earth moon line
Earth’s tidal force
what slows down the moon’s rotation
Earth’s tidal force
on the Moon has a much greater effect than the Moon’s tidal force on
Earth
Earth’s tidal force gives the Moon 2 bulges along the EarthMoon line
The Moon’s gravity tries to keep the tidal bulge on the Earth-Moon line
The Earth’s rotation tries to pull the tidal bulges around with it
The resulting friction slows down Moon’s rotation
Why electrical repulsion doesn’t make the tightly bunched p + in the nucleus to fly apart?
Because an even stronger force, the strong (or nuclear) force, acts at subatomic scales and holds particles together, overcoming electrical repulsion.
Planck’s law
Planck’s law describes the EM radiation emitted by a blackbody in thermal equilibrium at a definite temperature:
Wien’s Displacement Law: λ
The peak wavelength of
a thermal radiation spectrum
changes as a function of temperature
Wien’s Law
explains the shift of the radiation curve’s peak to shorter wavelengths as T Hotter objects emit most of their radiation at shorter wavelengths
The Doppler effect refers to the
change in frequency of a
wave for an observer moving relative to the source of the wave.
The amount of shift is proportional to the relative velocit
Due to the Doppler effect:
The light (spectrum) of an object moving towards us is blueshifted The light (spectrum) of an object moving away from us is redshifted
what are the limitations of the Geocentric Model
Hard for the geocentric model to explain the
apparent retrograde motion of planets.
Kepler’s First Law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus. Nothing at the other focus
Kepler’s Second Law
As a planet moves around its orbit, it sweeps out equal areas in equal times. A planet travels faster when it is nearer to the Sun & slower when it is farther from the Sun It is actually an embodiment of the law of conservation of angular momentum L for the orbiting object of mass m
Kepler’s Third Law
“More distant planets
orbit the Sun at slower
average speeds, obeying
the relationship:
p2 =a3 p = Orbital period, in[years]
a= Average distance from Sun, in [AU] …”
what is the size of mars
About ½ Earth’s size: larger than Mercury & the Moon
does mars have a very thin atmosphere
yes
describe the atmosphere of mars
Only a very thin atmosphere:
95% CO2, but with extremely little O2, even fewer other greenhouse
gases & no O3 or H2O, at a pressure = ~0.01pEarth
describe the polar ice caps in mars
Polar ice caps consist primarily of H2O ice covered by CO
2 ice.
describe some cool features of mars
Has unique & impressive geological features: huge
ancient volcanoes, a great canyon ~20% its
circumference, polar ice caps of frozen CO2 & water.
what would happen if the martian ice caps melted
the water would be enough to cover the
whole planet to a depth of 35 m.
when were martian warm and we periods
2~3b years ago
when might Sporadic running water still occur on mars
very shortly during summer.
describe the tectonics on mars
No tectonics but some internal heat and even rare volcanism are
believed to still exist.
describe the magnetic field on mars
No generated magnetic field but has spots with residual surface
magnetisation
how did mars lose its magnetosphere
Lost its magnetosphere as it cooled (much faster than Earth since it was much
smaller and less massive), causing its dynamo effect to cease some 4.2 billion
years ago
(b y.a.)
how was the martian atmosphere slowly stripped away
its atmosphere was slowly stripped away (in several
hundreds of m y.) by the solar wind bombardment.
what’s jupiter mostly made of
Primarily composed of H & He
is jupiter’s orbit beyond the asteroid belt
orbit is beyond the asteroid belt.
what is the 3rd brightest object in the night sky after the moon and venus
jupiter
what are the first two brightest objects in the night sky
moon and venus
what are the 4 moons of jupiter
Io, Europa, Ganymede & Callisto
describe the outer atmosphere of jupiter
Outer atmosphere visibly segregated into several bands with storms along their interacting boundaries
give me one fact about io
Slightly larger than Earth’s Moon
give me another fact about io
Tidally locked
what is io mostly made out of
silicate rock surrounding a molten Fe or FeS2 core
describe io’s volcanoes
Its volcanoes eject hot plumes of sulfur and sulfur dioxide high above the surface
how does io orbit
within a belt of intense radiation known as the Io plasma torus, a doughnut-shaped ring originating from the ionization of the neutral atoms in the “cloud” surrounding Io by the strong Jovian magnetosphere
what does io feed
radiation & aurorae caused by Jupiter’s magnetosphere
what size is europa
90% of earth’s moon
is europa tidally heated
yes but much less than io
what type of crust does europa have
Icy crust with possibly subsurface ocean of liquid water One of the preferred targets for search of Life in the Solar system; At its center is thought to contain a rocky mantle and iron core
describe the europa core
rocky mantle and icy core
describe the size of ganymede
The largest moon in the Solar system (25% larger than Mercury!)
describe the surface of ganymede
Icy surface that may hide subsurface oceans.
which is the only moon with a hot core convection generated magnetic field
ganymede
what is ganymede’s core
fe-rich liquid
describe callisto
Almost the size of Mercury but only about ⅓ of its mass No tidal heating Large, heavily cratered “ice ball”, possibly with subsurface oceans.
what are jupiter’s moons
io europa ganymede callisto
what is the 2nd largest planet in the solar system
saturn
what is saturn made of
mostly of H & He
how far away from the sun is saturn
Twice as far from the Sun as Jupiter
what is saturn’s density
The only planet of the Solar system that is less dense than water!
what is the mass of saturn
Slightly smaller than Jupiter but ~⅓ of Jupiter’s mass because of its very low density
what is the shape of saturn
Flattened at the poles & bulges at the equator. Other gas planets are also oblate, but to a lesser extent
how many moons does saturn have
many
describe the rings of saturn
They are made of countless small chunks of ice & rock, from the size of a grain of sand to km-sized boulders, each orbiting like a tiny moon around Saturn
describe the size of uranus
Although much smaller than Jupiter or Saturn,
it still is more massive (14.5×) than Earth.
what are the compounds in uranus
Gas giant, but besides H & He also has hydrogen compounds (NH3, CH4, H2O, H2S)
what are the ice giant planets
neptune and uranus
which planet may rain diamonds
uranus
what is uranus’ colour
Pale blue-green colour due to CH4
what is the rotation of uranus
Has a retrograde rotation, turning on its axis in
the opposite direction to the rest of the planets
what is the axial tilt of uranus
axial tilt of 97.9
