Section 2: Planetary Systems Flashcards
Name 3 dwarf planets
Ceres, Pluto, Eris
How many known moons?
160
Where’s the asteroid/main belt
Between Mars and Jupiter
Avg. size of asteroid?
10m-100km
Name 2 asteroids in the asteroid belt
Vesta (brightest), Pallas
What’s an asteroid
Small solid body
What’s a comet
Nuclei of ice, dust and rock; develops gaseous coma and tails when relatively close to the sun
What’s a centaur
Show similarities to both asteroids and comets
Where do centaurs orbit
Between Jupiter and Neptune
Name 3 centaurs
Chiron, Hidalgo, Asbolus
What’s a TNO
Trans-Neptunian object; orbits sun from beyond Neptune
International Astronomical Union (IAU) definition of a planet:
- Is in orbit round the sun
- Is large enough to be spherical
- Has “cleared its orbit” of other objects
1 AU
Mean distance from Earth to Sun = 150 million km
Features of Mercury
Heavily cratered; lava filled basins; appears similar to moon
Features of Venus
Spins backwards; similar size to Earth; clouds of sulphuric acid; surface pressure 90x on Earth; dense atmosphere containing carbon dioxide (prevents infra red escaping so v. hot)
Features of Mars
Iron rich rocks; seasonal ice caps; 450 km “Valles Marineris” canyon; highest volcano “Olympus Mons” in solar system; violent dust storms
Features of Jupiter
Equatorial bulge; dynamic wind system; anticyclone weather system “Great Red Spot”
Features of Saturn
Gas giant like Jupiter; rings
Where has info about solar system come from
Scientific instruments on unmanned space probes
Similarities in Neptune and Uranus
Similar size; gas giants; atmosphere of hydrogen, helium, methane, ammonia
Differences between Uranus and Neptune
Uranus spins on side, featureless surface; Neptune heavily marked incl. Great Dark Spot
Problems with manned space missions
- Space Adaptation Syndrome and other physiological problems (brittle bones; muscle fatigue)
- Communication delays
- Radiation from sun
- Psychological problems (fatigue, low motivation)
- Time
- Cost
Name Mars’ moons
- Deimos
- Phobos
Irregular shape; ~10km; heavily cratered; half density of Mars; captured from Asteroid belt
Name Neptune’s moons and where they came from
- Triton - captured body from collision
- Dark Proteus - formed at same time
- Nereid - captured from Kuiper belt
Ecliptic
Plane of Earth’s orbit
Describe orbit of planets
Elliptical orbits slightly inclined to the ecliptic
Where do the planets appear to move through
Zodiacal band - a narrow region of sky
Inferior planets vs. superior planets
Inner vs. outer
Inferior = Mercury and Venus
Superior = Mars to Neptune
Direct motion
Planets generally move from West to East
Retrograde motion
Planets appear to move from East to West
- Planets orbit at diff. speeds
- Therefore we see planets from diff. viewpoints as we overtake or undertake them -> they appear to move backwards
Greatest elongation
Furthest from the sun in the sky - angle between planet-Earth and planet-sun is a right angle
Inferior planets
Inferior conjunction
Inferior planets: angle of elongation is 0 -> lies directly between earth and sun
Superior conjunction
Inferior planets: sun lies directly between earth and planet w. angle of elongation 0
Conjunction
Superior planets: sun lies directly between earth and planet
Transit
An inferior planet passes in front of the solar disc
Occultation
An astronomical body passes behind another and is temporarily hidden from view
Which planets atmosphere illustrates global warming
Venus: dense atmosphere of carbon dioxide; lower atmosphere 470 avg.
Composition of planetary rings
Particles of ice, rock and dust
Cometary orbits
- Much more elliptical and originate at vast distances from sun
- Can be either clockwise or anticlockwise
- Highly inclined to the ecliptic
Location and nature of Kuiper belt
Thick disc shaped region of icy bodies; lies beyond Neptune at 30-50 AU from sun
Location and nature of Oort Cloud
Spherical distribution of cometary nuclei; 50000 AU from sun
Short period comets origins
Kuiper Belt
Long period comet origins
Oort Cloud
Evidence for Oort Cloud
From long period comets:
- Orbits either direction
- Highly inclined to ecliptic
- High percentage originate at 50000 AU from sun
Coma of comet
Gas and dust up to 100000 km across
Ion tail
Blue coloured; molecules of gas; ionised by solar wind; atoms de-excite and fluoresce
Dust tail
Lighter colour, shorter broader than ion; radiation pressure pushes particles out of nucleus; shines by reflecting sun; curved as individual particles follow own orbit
When do comet tails form
When relatively close to sun from high temp
Nature of meteoroids
Small rocky irregular lumps of debris; micrometres to 10 m; orbit sun ~ 40 km/s
Origin of meteoroids
Broken fragments of asteroids; impacts with surface of moon/mars
Nature of Meteorites
Surviving part of meteoroid when it passes through earths atmosphere and lands on surface
Meteor
Friction causes air around meteoroid to heat up when passing through earths atmosphere
Fireballs
Meteors with magnitude of -3 or brighter
Meteor showers
Earth passes through meteoroid stream - meteoroids originating from dust tails of comets
Radiant
Where dust particles from meteor shower appear to diverge from
Orbits of PHOs
Bring objects closer than 0.05 AU to us
Consequences of PHO collisions with Earth
- Craters e.g. on moon
- Backwards rotation e.g. Venus
- Land destruction
- Tsunamis
- Global climatic change
Copernicus discoveries
- Heliocentric model of solar system (i.e. Orbit sun)
2. Retrograde motion of Mars, Jupiter and Saturn
Discoveries of Tycho
- Meticulously observed sky to work out actual positions of planets
- Tried to find evidence Earth orbited sun
Discoveries of Kepler
- Used Tycho’s observations to formulate “Laws of Planetary Motion”
Kepler’s second law
“An imaginary line from a planet to the sun sweeps out equal areas in equal intervals of time”
Kepler’s first law
Planets move in elliptical orbit with sun at one focus
Discoveries of Galileo
- Moon not spherical - contained craters and mountains
- Venus exhibited phases and it’s apparent size changed
- Four satellites orbit Jupiter: Callisto, Europa, Ganymede, Io
Discovery of Uranus
1781 by William Herschel
- Looking at faint naked-eye stars with telescope
Discovery of Ceres
1801 by Giuseppe Piazza
- Predicted there would be a planet between orbits of Mars and Jupiter
Discovery of Neptune
1846 by Galle and D’Arrest
- Predicted planet beyond Uranus due to wobbles in its motion
Discovery of Pluto
1930 by Clyde Tombaugh
- Uranus underwent further irregularities in orbit, predicted another planet lay beyond Uranus
Exoplanet
Planet not in solar system
Techniques for discovering exoplanets
- Astrometry - star wobbles in small orbit pulled by large exoplanet
- Transit method - exoplanets move across disc of host star cause drop in brightness
- Radial velocity method - wobbling of star causes wavelengths of star to be shifted regularly detected by spectroscopy
Difficulties with current methods for discovery of exoplanets
Can only discover large planets close to sun - “hot Jupiters”
Atmospheric turbulence can interfere with measurements
Essential chemicals for life
- Carbon - create organic compounds
2. Liquid water - solvent and transport mechanism for nutrients, photosynthesis, hydrolysis
Origin of water on Earth
- Out gassing of hydrogen and oxygen from volcanoes combining to steam condensing to water
- Deposited by ice containing comets striking Earth
Analysis of water by Rosetta probe
Drop small lander onto comet; see if it has same relative abundance of isotopes as water on Earth
“Goldilocks zone”
Also known as habitable zone, range of distances from star where temperature allows liquid water to exist
Drake equation
Estimates number of civilisations able to communicate with us
Factors:
1. Number of stars in galaxy
2. Fraction of stars with planetary systems
3. Number of planets capable of sustaining life
4. Fraction of life forms that are intelligent
5. Fraction of these that can and wish to communicate
Methods of obtaining evidence for life
- Space probes
- Spectral analysis of atmospheres above rocky exoplanets
- Analysis of radio waves possibly from extra-terrestrial intelligent life forms
