Astronomy 10: Chapters 5-8 (final)

the overall process of the creation of stars and planets

nebula → molecular cloud → molecular core → solar nebula → protostellar disk →protoplanetary disk → sun, planets

Interstellar medium

materials in space between stars

protostars

formed in molecular core; has protostellar disk and then this disk is called a protoplanetary disks when planets start forming

thermal energy

The energy that resides in the random motion of atoms, molecules, and particles, by which we measure their temperature; pushes outwards after cloud contacts and heats up

magnetic fields

A field that is able to exert a force on a moving electric charge. Occurs when object has molten interior and rotates at a moderately rapid speed; collapses with turbulence as collapsing cloud resists gravity

Importance of a magnetic field

Protects the Earth from harmful solar wind and cosmic radiation by deflecting charged particles away from the planet.

Nebula Theory

explains process from Nebula to Solar System formation

protostellar disk

the solar nebula settles into a protosun in the center and a disk

protoplanetary disk

forms planets (core accretion model)

exoplanets

planets orbiting around stars other than the Sun

Conservation of angular momentum

The physical law stating that the amount of angular momentum of an isolated system does not change over time; as cloud contracts, rotation increases

after conservation of angular momentum…

* Collisions between particles in the cloud caused flatten into a disk (gas particles colliding reduce up & down motions)
* Spinning cloud flattens as it shrinks
* Grains in the disk accrete into planetesimals that eventually form into planets

Conservation of energy

The physical law stating that the amount of energy of an isolated, closed system does not change over time; Gravity causes cloud to contract and heat up

planetary systems consist of…

* a star
* planets/dwarf planets
* moons
* asteroids
* comets

our solar system consists of…

* Terrestrial planets
* Asteroid Belt
* Jovian (gas giants) planets


* KBO (Kuiper Belt object)
* Oort Cloud

Oort Cloud

A spherical distribution of comet nuclei stretching from beyond the Kuiper Belt to more than 50,000 astronomical units (AU) from the Sun

General characteristics of a solar system we have accepted from our Solar System

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Thermal profile of a solar system and observations

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Thermal profile of a solar system that is hot and cools further away from the Sun

* Frost line/snow line: \n - Inside: Too hot for hydrogen compounds to form ices \n - Outside: Cold enough for ices to form
* Refractory: do not melt at high temps
* Volatile: melt or evaporate ate moderate temps

frost line

* giants formed outside of it
* terrestrials formed inside of it

Solar system observations to be explained

* The large bodies orbit in same direction and plane
* There are two types of planets: terrestrial and jovian (giant planets)
* There are smaller bodies: asteroids and comets
* Notable exceptions to usual patterns:( Most likely due to bombardment/collision) odd tilt of Uranus and Venus’ retrograde rotation

2 scenarios planet formation theories

1. gravitational collapse (like stars) - doesn’t explain the whole process
2. core accretion (the more acceptable theory)

* The core of planets form by planetesimal accretion; then gas is accreted
* Gas giants must form before the solar nebula dissipates (less than 10 Mys)

core accretion

Gas giant planet forms from dust and gas. Dust sticks together to form planetesimals, which grow by accreting more material. Once they reach critical mass, they attract gas and rapidly increase in size.

gravitational collapse

when the astronomical object no longer has the interior pressure to counter the gravity, so it contracts

planet formation ends when…

solar wind blew solar nebula away

A glowing, rapidly moving knot of gas and dust that is excited by bipolar outflows in very young stars.

Herbig-Haro (HH) objects

T Tauri variables

T Tauri variables are young stars that vary in brightness due to changes in their accretion rate. They have protoplanetary disks and are important for studying early star and planet formation.

asteroids

left over after accretion process; A primitive rocky or metallic body (planetesimal) that has survived planetary accretion. Also are the parent bodies of meteoroids.

comets

left over after accretion process; A complex object consisting of a small, solid, icy nucleus; an atmospheric halo; and a tail of gas and dust.

exo-planetary solar systems

* not all look like our solar system
* have many Jupiter sized planets really close to their star
* have other planets also really close to their star

2 major detection methods

radical velocity and transmit method

radical

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The speed at which an object is moving in a circular path is called __________ velocity. It is perpendicular to the tangential velocity and is dependent on the radius of the circle.

Doppler effect

The change in wavelength of sound or light that is due to the relative motion of the source toward or away from the observer.

* Red shift: The shift toward longer wavelengths of light by any of several effects, including Doppler shift, gravitational redshift, or cosmological redshift.
* Blue shift: The Doppler shift toward shorter wavelengths of light from an approaching object.

Wobble method

Transit Method

Method used to detect exoplanets by measuring the periodic dimming of a star's brightness as a planet passes in front of it; used by Kepler Mission

formation history

Earth formed 4.6 billion years ago from the inner solar nebula.

Interior parts of Earth

Core: Highest density; nickel and iron \n Mantle: Moderate density; silicon, oxygen, etc. \n Crust: Lowest density; granite, basalt, etc.

Interior Differentiation

Gravity pulls high-density material to center

lower-density material rises to surface \n Material ends up separated by density

Heating of Interior

early Earth: accretion & differentiation \n Current Earth : radioactive decay

Cooling of Interior (how HOT goes to COLD)

* Convection: transports heat as hot material rises and cool material falls
* Conduction: transfers heat from hot material to cool material
* Radiation: sends energy into space

Geological activity that shapes the Earth’s surface

* Impact cratering
* from asteroids and comets
* Volcanism
* eruption of molten rock onto surface
* Tectonics
* Disruption of a planet’s surface by internal stresses
* Earth is only terrestrial with plate tectonics
* Erosion
* Surface changes made by wind, water, ice or debris

Greenhouse Effect

Generally a good thing when occurring naturally. But when the process is sped up through human activity, it is not good

Planetary sizes

small planets cool faster than large planets → heating/cooling of interior atmosphere (to have or not to have)→ erosion (water, ice, wind, debris)

Habitual zone

the region around a star in which planets could potentially have surface temperatures at which liquid water could exist

Moon

* Lowlands (Maria) à basins flooded by lava flows \n Moon formation/history (Earth was hit by Mars-sized object and ejected
* material into space, eventually accreting into our Moon
* Moon rock composition similar to that found on Earth

Mercury

* Closest to the Sun
* No tilt
* Very slight ionic atmospherescarps
* Caloris Basin and “Rocky Road” feature just on the opposite side of Mercury from Caloris Basin→ something big hit Mercury !!! ?
* large core most likely due to massive impacts that blew away the mantle during formation

Venus

* not as mountainous and not as rugged as Earth; just nasty terrain
* the surface is mainly gently rolling plains;
* Only Venus has: “pancakes”/Coronae craters, shield volcanoes
* acid rain
* extremely high atmospheric pressure (92 atm) Greenhouse Effect went into “overdrive”
* Rotates cw (clockwise) → (planet knocked over upside down?)
* Very slow rotator → longer rotation time than orbit time
* Atmosphere rotates very quickly → once in 4 days
* One hot planet: 900F everywhere
* We can see phases, like the Moon

Mars

* rotates just 40 mins longer than Earth
* tenth of Earth’s mass
* half Earth’s radius
* shield volcanoes:
* Olympus Mons → highest & largest in the Solar System
* Tharis range
* Vallis Marineris
* Hellas & Argyre basins
* Many features believed to be caused by water flows
* Thin atmosphere mostly CO2
* Has a tilt (about 25O) → has seasons
* Has been explored by orbiting and roving probes, A LOT!
* Life on Mars? Still searching and hoping.

Formation history for giant planets

Giants formed 4.6 billion years ago → core accretion

Gas planets

Jupiter and Saturn

Water/icy planets

Uranus and Neptune

General knowledge for Jovians (giant planets)

* are made of mostly gases (H, He, H2 O, CH4 (methane), NH3 (ammonia) )
* have rock/ice cores
* do not have solid surfaces: gases --> liquid & solid at high pressure
* have ring systems and many moons
* formed faster than terrestrials (less than 3 – 5 Myrs)
* large because they accumulated gas directly from the solar nebula (true for Jupiter and Saturn)
* are far from the Sun

Jupiter

* largest and contains ¾ of total Solar System planetary mass
* Red Eye storm


* core is liquid rock and water
* very strong magnetic field
* rotation period of 9.94 hours
* magnetic field aligned with axis

Saturn

* has the largest set of rings
* core is liquid rock and water
* is a gas planet
* rotation period of 10.56
* magnetic field aligned with axis

Uranus

* axis of rotation is in the plane of the Solar System
* 98° tilt (maybe due to collision)
* there’s weather change
* alike to Neptune
* has liquid core
* rotation period of 17.23 hours
* magnetic field is upside down

Neptune

* \
* crosses orbits with Pluto but will never collide
* has a liquid core
* is alike to Uranus
* rotation period of 16.10 hours
* magnetic field is off center from axis

Roche limit

distance from object where another smaller object can broken apart because of gravity 

* closer object gets to bigger object, the more the smaller object will stretch until it breaks
* Ex.: Saturn’s rings