Unit 4 Flashcards
Mercury (brief)
Terrestrial planet
more typical of the inner planets than watery surface of earth
No atmosphere
Dangerous place
There is a lot of cratering records in our solar system
on planets and moons (natural satellites)
Terrestrial planets
when these planets formed they were hot and molten (liquid rock)
Differentiation acured
Differentiation
As planets cool the denser material sinks towards the center of the planet and forces lighter materials to float to the surface
The outer solar system
4 giant planets
* Jupiter
* Saturn
* Uranus
* Neptune
While harder to reach still the subject of many successful missions
Planet Types
Terrestrial
* small and rocky
* orbit close to the sun
Jovian
* much larger and gaseous
* orbit much further out
Jovian Worlds
Mostly made of hydrogen and helium, gases we see in the sun
when we see these planet it is their atmosphere we observe
Many hydrogen compounds in the atmosphere
Ganymede
Jupiters Moon
Largest satellite
Jovian vs Terrestrial planets
A big difference between Jovian and Terrestrial planets is the number of natural satellites
Jovian worlds have lots more satellites Jupiter has 95 orbiting around it
The terrestrial planets have few if any satellites
Impact today
In 1994 Jupiter sustained impacts from over 20, 1km size rocks
* moving at over 60 km/s from gravitationally disrupted comet
If any were to hit Earth, significant devastation would occur
Dwarf planet
Pluto First discovered as a planet
* Then late was proven to be considered a Dwarf planet (Smaller than our moon)
* Has active ice volcanoes
Unlike planets we are not sure how many dwarf planets exist
this is a new category of objects (2006)
Rings
All 4 Jovian worlds possess rings
* some better developed (brighter and larger)
Made up of rock and since, normally only a few centimeters in size but can range up to meters
Asteroids (Minor planets)
Are everywhere
Number in the millions
some are 100 Km in diameter
small pieces of rock that do not become part of planet during the solar system formation 4.5 billion years ago
Comets
Also leftover materials from the formation of the solar system
only a few kilometers in diameter
different from asteroids
* they contain a lot more volatile materials (water, ice, methane, carbon dioxide)
* when heated they generate very bright and long tails
Age determination
Determined by counting the number of creates in a given area
* More means older
* Only works if the surface is not geologically active
Using radioactive dating
* Every radioactive element has a half-life
* Original material is often called the parent, and what it decays into is the daughter
Solar system formation
Our solar system is formed from a large cloud of dust and gas (giant molecular cloud (GMC))
* As it began to spin, it flattened into think disk (Pancake)
* in the center the acceleration was fast forming our proto-star
Planetesimals
* smaller pieces of rock began to collide and grow larger forming protoplanets
Inner solar system was warming up forcing gasses towards the outer solar system beyond the ice-line (Asteroid belt today)
the Jovian planets grew larger form accretion and the abundant supply of volatiles
the terrestrial plants remained small(ish) and were comprised of refractory elements (higher melting points)
when the sun started nuclear fusion in tits core, solar system formation stopped
Our moon
very similar to mercury
* Almost the same size
* physical appearance
No atmosphere because of low gravity (1% Earth mass)
lacking dense metals and no appreciable core
overall density similar to Earth’s crust
“Dead” world
Lunar exploration
ALSEP (Apollo Lunar Science Experiment Packages) operated for many years
Many countries have also focuses on the moon
* Japan, India, China, ESA have all sent probes to the moon
Our moons appearance
moon formed as the solar system was forming ~4.5 billion years ago
83% Lunar highlands
* composed of low density anothrosites
17% Flat Maria
* very powdery because of years of impacts
* dust is one of the biggest concerns for astronauts as they are sharp
Our moon Origin
Fission theory
* The moon was once part of Earth, but somehow separated from it early in their history
Sister theory
* The moon formed together with (but independent of) Earth, as we believe many moons of the outer planets formed
Capture Theory
* The moon formed elsewhere in the solar system and was captured by Earth
Giant impact hypothesis (Probably correct)
* In essence, a large shearing impact removed a substantial portion of earth’s crust that then colled to form our moon
Mercury
Its proximity to the sun makes mercury very hot
Its small size means it cannot maintain an atmosphere
Density suggests a composition similar to Earth with a much larger core relative to its size
weak but significant magnetic field
dominated by a metallic core same size as our moon
orbital period of 3:2
* spins on its axis 3 times for every 2 orbital periods around the sun
Mercury’s Appearance
Heavily cratered with water ice, high cliffs and plains of dried lava
No Natural satellites
Mercury formation
Formed in a similar way to Earth (Venus and Mars too)
lack of crustal material suggest dramatic collision early on, ripping away material
Venus
Apart from the sun and the moon Venus is the brightest
called the Morning Star or Evening Star
its perineal cloud gives its brightness
* makes surface feature identification impossible from Earth
Rotates East to West
* not the usual west-to-east
Takes 243 days to complete a rotation
A year on Venus is 225 days long
Dense atmosphere (90 * Earths)
Surface temp of 450C
Acid Rain
Venus Surface
Thousands of volcanoes
* some may be active
75% of the surface is a lowland plain of lava
Venus atmosphere
Dominated by carbon dioxide (96%) with some nitrogen (3.5%)
Clouds of sulphuric acid persist between 30 and 60km above the surface
Venus Evolution/History
Earth-like early in its history with water on the surface
Closer to the sun and thus a modest increase in temperature resulted in evaporation
leading to a runaway greenhouse effect and the current environment
The outer planets
The 2 gas giants, 2 ice giants
Colder region of the solar system
composition includes hydrogen and helium (dominant) but also ice (water, methane, ammonia) and rocks (silicate metals, etc. )
Elements formed preferentially with hydrogen
These 4 planets are much more massive than terrestrial planets
The clouds are what we see when observing the outer planets
Lots of ammonia crystals in Jupiter and Saturn clouds, and more methane for Neptune
Seasons on these worlds vary from extreme on Uranus to non-existent on Jupiter
Uranus
* Rotates on its side
Jovian planet interiors
The interior structure of Jupiter and Saturn are similar
Uranus and Neptune being less massive
the cores are small and not easily defined by Uranus and Neptune’s cores are larger than Jupiter and Saturn
All 4 have leftover heat from the formation
* Lots of insulation to trap heat
* some heat from contractions as well
All 4 planets rotate very quickly (Jupiter in 10 hours)
Cloud top Appearance
Internal heat sources, rapid rotation, convection, and mixing of a lot of chemical interactions occur giving rise to the carried and colorful appearances
Jovain versus terrestrial planets
Density, composition, size, location, etc.
All outer solar system planets have numerous satellites orbiting around them
each possesses a ring system.
Moons (Satellites)
over 200 are currently known to orbit the 4 outer planets
Highlights
* Ganymede is the largest satellite in the solar system
* Io is the most volcanic object in the solar system\
* Europa has a sub-surface ocean of warm water (surface organic material)
* Titan orbiting Saturn has a denser atmosphere than Earth and has liquid methane on its surface
* The Triton (Neptune’s largest moon)
Pluto
The size of pluto was not established until 1978
its mass was found to be .2% of Earth
it’s so little its a different category of object than a planet
* it’s a Dwarf planet
its a rocky icy mix similar to many solar system satellites
its reflective surface has frozen methane, nitrogen, and carbon monoxide gases it
* has a very thing atmosphere
Planet definition
Orbit the sun
Be round
Have cleared out (Dominates) its orbit
Rings
Another obvious distinction between the terrestrial and jovian worlds is the presence of a ring system
the ring’s systems are quite different from each other with Saturn being the brightest and most extensive and Jupiter being the least developed
Ring Composition
Made of rock and icy particles by the billion
* they orbit in the planet’s equatorial plane
Did they originate as a breakup of an asteroid or small or are the ring’s leftover material unable to form a satellite?
All are very thine compared to their diameters
large and smaller “shepeherding” satellites gravitationally manage the motion of the ring particles
