Topic 12 Flashcards
Define the Goldilocks zone
region around star where liquid water might be found on surface of planet
where is the goldilocks zone on smaller and more massive stars?
-further out from star (more massive stars)
-closer to star (smaller stars)
planets here are exposed to high x-ray levels
What does SETI stand for
Search for Extra-Terrestrial Intelligence
What kind of wave does SETI use
Radio-wave
Define Exoplanet
a planet that orbits another star
Name 4 methods of discovering exoplanets
1.The Transit Method
2.Astrometry
3.Radial Velocity Method
4.(Direct Imaging)
Describe the transit method
-method used to discover exoplanets
-“wink”
-planet passes infront of star and blocks the light
-causes a dip in star’s brightness
Disadvantage: planet must orbit aligned with earth so that we can see its transit
Describe Astrometry
-method used to discover exoplanets
-“wobble”
-planet’s gravity pulls star, causing it to wobble
-this method detects the wobble
Example:ESA’s Gaia Satellite
Describe the Radial Velocity Method
-method used to discover exoplanets
-“wobble”
-planet’s gravity pulls star, causing it to wobble
-it’s red-shifted when it moves towards earth
-it’s blue-shifted when it moves away from earth
Describe Direct Imaging
looks at the infrared radiation reflecting off the exoplanet
When did most collisions occur
heavy bombardment period
Give 4 pieces of evidence of collisions
1.Earth’s axial tilt (theia->moon)
2.Venus’ retrograde spin (not all scientists agree with this)
3.Uranus’ orbital tilt (80 degrees)
4.Impact craters on surface of moon (and earth) -(mimas which looks like death star)
Define solar wind
-constant flow of charged protons & electrons from sun travelling at high speed (up to 400km/s)
-They escape gravity of sun because they have too much energy
Give 1st effect of solar wind-a
1.aurora
-when particles that get caught in the Van Allen Belts caused by the Magnetosphere then move along these field lines toward the magnetic north and south poles and observers in these location witness aurorae.
Give 2nd effect of solar wind-c
2.comets have tails
-As comets move nearer the sun the sun’s radiation is responsible for heating a comet and the solar wind particles will interact with the comet and form an ion tail which points away from the Sun.
Give 3rd effect of solar wind-h
3.heliosphere
-cigar-shaped bubble surrounding solar system caused by solar wind. (cigar shaped because sun is orbiting galactic centre) 80-100 AU from sun
Describe the composition of a gas giant
-thick hydrogen and helium atmosphere
-rocky core
-largest gas giants have an outer core of liquid metallic hydrogen which creates a strong magnetic field
-smallest gas giants have an outer core of molecular hydrogen and water-ammonia
-jupiter and saturn have clouds at the top of their atmosphere
How did the gas giants form?
-formed quickly in early few million years of solar system
-sun heated up+started nuclear fusion
-solar wind evaporated gas from planetary disc
-gas clumped together due to gravity
-swept up by gas giants
-rocky material would not be evaporated
What are the 3 conditions which determine whether a planet will have an atmosphere or not
-high enough gravitational field strength
-not too hot for gas to escape into space
-not exposed to strong solar wind (magnetic field strength)
What 2 forces determine if an object is spherical?
elastic forces
vs
gravitational forces
How does an object become spherical?
high gravitational forces means that (object has enough mass) so bits of surface fracture and flow round to be more round
-not enough mass= grav forces too low to be spherical
Define Roche Limit
The distance from a planet where an orbiting object will be broken apart by tidal forces which overcome gravitational forces of object
-these remnants are thought to have created ring systems
How far away is the roche limit from a planet
~2.5x the planets radius
Define barycentre
centre of mass of both/all bodies in orbiting system (which those bodies orbit)
Define orbital resonance
where two or more bodies orbiting another larger body have orbital periods that have a gravitational effect on one another so their orbital periods use a time ratio.
Give 2/3 examples of orbital resonance:
- Jupiter’s moons
-Ganymede, Europa, Io in 4:2:1 ratio
2.Neptune and Pluto
-in 3:2 ratio
-stops them colliding?
(3.) Jupiter and saturn
-5:2
What are langrangian points?
locations relative to two bodies where a smaller object can maintain a position in orbit.
What and where are each lagrangian point (on earth)?
L1- between earth and sun
-good for viewing sun
-SOHO satellite
L2- other side of planet than L1
-good for viewing galaxy
-james webb telescope, GAIA
L3- other side of sun to earth
-no communication with earth
L4&5- little bit ahead/behind earth’s orbit
-jupiter’s trojan asteroids are here
-most stable lagrangian points
-STEREO observatories
Why is the moon’s orbit getting 4cm farther every year?
The effects of tides is causing Earth to slow down which in turn causes the Moon to lose momentum and slow down, moving it further away.
-moves away because it conserves angular momentum
Why hasn’t the asteroid belt formed a planet?
-Although it has enough material to make a small terrestrial planet:
-tidal effects of mars’ and jupiter’s orbits prevented anything larger than ceres forming
How is internal heating caused?
moon gets stretched and squashed as it rotates causing the inside to heat
-may cause moons to be volcanically active (for example Io of jupiter)
What effect do tidal forces have on moon’s rotation
slowing down moon’s rotation (synchronous rotation where orbital period=rotational period)
Describe composition of inner planets’ atmospheres +titan & pluto
MERCURY-Small, close to the Sun and so likely not to have been able to form an atmosphere
VENUS-Closer to the Sun than Earth but maintains a thick carbon dioxide atmosphere.
EARTH- Nitrogen/oxygen atmosphere. Within the habitable zone, magnetosphere protects against the solar wind.
MARS-Further away, smaller body than Earth/Venus, thinner carbon dioxide atmosphere, no magnetosphere.
TITAN-Nitrogen/methane atmosphere, one and a half times ticker than Earths. Thought to be produced by internal heating.
PLUTO-Past the main planets it keeps a very thin nitrogen atmosphere despite being smaller than Mercury. Thought to be produced by internal heating.
What does solar wind do to planets
-it strips off planets’ atmosphere if planet does not have a strong enough magnetic field (magnetosphere) and/or gravitational field
