AST101 everything after midterm 2

asteroids

• orbits the sun

• made mainly of rock and metal

• there are 600 asteroids larger than 50 KM diameter

• there are 25 million asteroids larger than 100 m diameter

• most of them between mars and jupiter

orbit of asteroid

• orbits according to Keplers laws

  • objects orbit in ellipses

  • the time of an orbit depends on the semi-major axis

    • from centre of orbit to the edge

Kirkwood gap

• a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids

• 3:1 orbital resonance with Jupiter

• 5:2 orbital resonance

orbital resonance

3:1 orbital resonance means that the asteroid goes around 3 times exactly when Jupiter goes around once

• no asteroids going around more than 3 times when Jupiter is going once

5:2 orbital resonance

• very few to no asteroids that go around more then 5 times when Jupiter goes around twice

orbits in exact resonance with Jupiter get displaced

most of the asteroids in the orbits above get knocked out from Jupiters orbit into another orbit

Ceres

• the largest object in the asteroid belt

• has bright spots

  • salt deposits from a cryo-volcano

  • still active after a metro strike

• Ahuna Mons: a 4KM tall mountain

layers of ____

• rocky center (not iron core!!)

• liquid brine

• icy crust

• dark dust on surface

____ is spherical because it is large enough so the strength of gravity is stronger than the strength of the rock/ice it is made of

dwarf planets

• orbits the sun

• massive enough that gravity has made it roughly spherical

• it is not massive enough that it (mostly) clears out its orbit

vesta

• largest asteroid is _____

• it is around half the size of ceres

• it is not really round, so it is not a dwarf planet

layers of _____

• nickel/iron core

• mantle

• crust

at one point, _____ was hot enough for the interior to become liquid, consequently, _____ experiences differentiation

Bennu’s orbit

• _____ orbit crosses the earth’s

• it’s orbit is continuously perturbed by the planets and is not stable

• it has a 1 in 2700 chance of striking the earth before 2199

Kuiper Belt

• 20-200 times more massive than the asteroid belt

• includes several known planets, including Pluto

• formed outside the frost line

charon - pluto’s moon

• compared to Pluto, ____ is a very large for a moon

• the surface has more craters than pluto

• the surface is mainly water ice

Pluto

_____ is very distant

• the orbital period is 248 years

• its orbit is inclined (not in the ecliptic)

• it crosses Neptune’s orbit

• is is in a 3:2 resonance with Neptune, so they never collide

comets

• appear (rarely) in the sky

• visible for days

• have tails pointing roughly away from the sun

• often come back on a fixed period (decades to millennia)

comet orbit

• warmer close to the sun

• the sun heats up the comet, and the ice melts and boils away

• dust tail- accelerates by light form the sun, so it points a little behind the gas tail

• gas tail- gas/plasma is pushed directly away from the sun by high energy particles called the solar wind

the Oort cloud

• outside the kuiper is a huge spherical cloud of comets called the Oort cloud

• the comets in the Oort cloud were formed near Jupiter, but were kicked out by gravitational interactions

• there are trillions of objects in the Oort cloud

meteorites

when meteors hit earth, they are called meteorites

large ones can be destructive

jupiter’s atmosphere

• complex clouds and stable storms

• winds of up to 500km/hr

• bands and storms stable over decades

• wind bands are up to 3000 km thick

• reasons for bands is not fully understood

Jupiter’s clouds

• the temperature and pressure varies as you enter jupiter

• different molecules form clouds at different temperatures

• ammonia clouds are white

• ammonium hydrosulfide clouds are orange

Jupiter

• largest planet in the solar system

• mass is 317.8 times that of earth

• thick gaseous atmosphere surrounds a giant ball of liquid hydrogen

• density increases towards the centre.

• has very faint rings

• many moons: 79 detected so far. Callisto, Ganymede(further from Jupiter, less tidal heating), europa, io (closer to Jupiter, more tidal heating)

• orbits around 5AU from the sun

saturn

• second largest planet in the solar system

• 3.3 times less massive than juptier

• structure is much like jupiter

• has rings

  • diameter is the rings is over 260,000 km but they are less than 100 meters thick

• many moons: 82 have names

uranus

• coldest planet

• small rocky core (maybe)

• thick water + ammonia + methane mantle

• thick h2/He atmosphere

• rotation axis tilted 98 degrees

• thin rings and lots of moons

neptune

• furthest jovian planet from the sun

• structure similar to uranus

• rotation axis is tilted 28 degrees

• more surface features than uranus

• strongest winds in the solar system: up to 2,100 km/h

Europa: a moon of jupiter

• surface covers either un-cratered ice

• smaller than earth’s moon

• there may be a huge ocean beneath the surface

  • the smoothness of _____, the young age of the surface, the cracks on the surface, and magnetic field measurements suggest that _____ is covered by a huge ocean under the ice

why is the ocean under the surface of Europa not frozen?

• when farther from Jupiter, tidal forces are less.

• when closer to Jupiter, tidal forces are greater.

• this changing force distorting the moon, heats up

structure in the rings is caused by:

• gravitational interactions with moons

• varying particle properties

atmospheric absorption

• atmosphere absorbs and scatters light

• not all wavelengths of light can travel through the atmosphere

• the atmosphere is opaque at some wavelengths

astronomical seeing

• turbulence in the earth’s atmosphere distorts images

• for long exposures and large telescopes (required for dim objects) this blurs the image

• without corrective measures, resolution for ground based telescopes is limited

voyager probes

• in 1977, the alignment of planets was just right to visit all 4 jovian planets with one probe

• it used each planet’s gravity to accelerate and change direction to the next planet (slingshot)

• two were launched - voyager 1 and voyager 2

• they are still operating, 20 light-hours from earth

gravity assist (slingshot manoeuvre)

• when probe flies by a planet, gravity changes the probe’s speed and direction

• passing behind speeds it up

• passing ahead slows it down

transfer orbit - how to move from one orbit to another

1. start in the inner orbit

2. engine burn to speed up

3. now in the transfer orbit

4. do a 2nd burn to speed up

5. end in the outer orbit

mars global surveyor

• in orbit around mars

• made high resolution images of mars

• from 1999 until 2006

Juno mission to jupiter

• launched: August 5, 2011

• used both gravity assist (from earth) and a transfer obit to get to jupiter

• Arrived: July 5, 2016

• has 9 different instruments, including a camera. it measures gravity, magnetic fields, radiation, infrared and UV spectra, and radio emissions

• end of mission: July, 2021

Venera 13: mission to venus

launched: Oct 30, 1981

landed: March 1, 1982

parachute landing

temperature: 457 C

pressure: 89 atmosphere

survived 127 minutes

first colour image from venus

fist sound recording from another planet

analyzed rock types

Mars Rovers

• NASA has sent 4 rovers to mars

• sojourner (1997), spirit and opportunity (2004), and curiosity (2012)

• opportunity lasted 15 years and travelled 45 KM

• curiosity is still running and has travelled 32.4 km

Apollo program: people on the moon

6 moon landings between 1969 and 1972

in 1969, first time in space and sending people

power in space

• inner solar system: solar panels

• outer solar system: radioisotopes thermoelectric generator

  • uses radioactive plutonium to generate electricity

communication in space

• spacecraft communicate with earth using radio, large dishes are used to focus the very weak signals

• data rates tend to be very low: it took more than a year for new horizons to send back its images

• light travel times makes for long delays.

how can we find around other stars: direct imaging

1. take a picture of a nearby star

2. look for planets around it

• take an image of the nearest sun-like star to the earth - 4.34 light years away

• all we see is the bright diffraction spikes from the mirror supports

• block the light from the star(s) with a “chronograph” in the telescope

best for planets where:

• the system is near to the sun

• the planet is far from its star

how can we find around other stars: radial velocity method

planets DO NOT actually orbit around their star

both orbit around the “centre of mass” of the system

this means that the star will be moving back and forth along the line of sight

• measure the redshift and blueshift of the star as it and the planet around their centre of mass

• the amount of motion depends on the man (and the angle)

• the frequency of motion depends on the distance from the star

if we are in the same plane as the planet’s orbit, we see all of the motion

• if the orbit is “face on”, 90 degrees from us, we see no motion

• if the orbit is tilted, we see some of the motion

the velocity change we see depends on the mass and the angle

we cannot tell the angle this was, so we only know the minimum mass

doppler effect

• sound is a pressure wave

• pitch is frequency

• when the source of a wave is coming towards you, the pitch is higher

• when the source of the wave is going away from you, the pitch is lower

same thing happens with light

• if the source is moving closer, the light shifts to higher frequency (blue shifted)

• if the source is moving away, the light shifts to lower frequency (redshifted)

hot Jupiters

• we see lots of massive stars close to their stars (so they are hot)

• most planets found are this because they are easy to detect

• but: according to the nebular theory, they shouldn’t exist

planetary migration

how to explain the existence of hot Jupiters?

• one model: they formed outside the frost line, and migrated in

how?

1. friction from the protoplanetary disk slowed them down

2. interactions with some other massive object slowed them down

   • not fully understood

how can we find around other stars: the transit method

look at a star with a planet orbiting it

• you cannot see the planet because of the star

• but you can measure the total brightness

• when the planet passes infant of the star, it blocks some of the star’s light

• the signal stays lower for as long as the planet stays in front of the star

• the signal goes back up when the planet is not in front of the star

• from the depth of the dip, you can determine the size of the planet

  • bigger planets block more light

• the period between dips depends on the distance form the planet tot the star

• only works if the angle is right

• only works if the telescope is in the plane of the planet’s orbit

the habitable zone

• the habitable zone is the range of distances from the star where liquid water can exist

• if the planet orbits too close to the star, it is too hot

• if the planet orbits too far from the star it is too cold

• in the habitable zone, liquid water can exist, so maybe life can too

• small, low mass stars are much less bright

• therefore the habitable zone is much closer to the star

• the orbital period is much shorter

• the probability of detection is much higher

what can the transit method tell us

1. the distance from the star to the planet

2. the radius of the planet

3. the orbital inclination

what can radial velocity method tell us

1. the distance from the star to the planet

2. if we know the orbital inclination, it can tell us the mass

what can radial velocity and transit method tell us

1. the distance from the star to the planet

2. the radius of the planet

3. the orbital inclination

4. the mass of the planet

5. the density of the planet

measuring atmospheres

planets also glow from their own thermal radiation

• it is combined with the star’s spectrum

• when it goes behind the star, it disappears

• subtracting spectra gives the planet’s spectra

• measuring a planet’s spectra tells you about its atmosphere