Astronomy Pic of the Day

The Solar System Ingredients?

The Solar System Ingredients? 1 Star: the Sun 8 Planets + a few “minor planets” 126 moons around these planets Asteroids, meteoroids, comets A lot of nearly empty space

Questions What percentage of the total mass of the solar system does the Sun contribute? How is the solar system laid out in space? Spacing between planets? Orbital directions?

Sun, Planets and Moon to scale Sun accounts for 99.9% of solar system mass!

An Easy Mnemonic Mother Very Easily Made a Jam Sandwich Using Nectarines Mercury Venus Earth Mars asteroid belt Jupiter Saturn Uranus Neptune

Solar System Perspective ● Spacing between adjacent planets roughly doubles. Most orbits are roughly circular. ● Distance from Sun to Pluto: 40AU or about 1/1000 of a light year. ● All orbit in same direction. Most in same plane.

Two Kinds of Planets "Terrestrial" Mercury, Venus, Earth, Mars "Jovian" Jupiter, Saturn, Uranus, Neptune Distance from Sun? Size? Composition? Density? Rotation Rate? Number of moons? Rings? Heavy or light Elements?

Two Kinds of Planets "Terrestrial" Mercury, Venus, Earth, Mars "Jovian" Jupiter, Saturn, Uranus, Neptune Close to the Sun Small Mostly Rocky High Density Slow Rotation ( days)‏ Few Moons No Rings Heavier Elements Far from the Sun Large Mostly Gaseous Low Density Fast Rotation ( days)‏ Many Moons Rings Main Elements H, He

Origin of Pluto Large member of a class of objects in the outer reaches of the Solar System: The Kuiper (pronounced K-eye-per) Belt Objects 100's found since Orbits tend to be more tilted, like Pluto's. Leftover planetesimals from Solar System formation?

Questions What are some of the smaller objects (or debris) found in the solar system? What information do they contain that the planets and moons do not?  (Hint: What effects do erosion, geological activity, vulcanism, etc. have on a planet?)‏

Questions What are some of the smaller objects (or debris) found in the solar system?  Comets, asteroids, meteoroids What information do they contain that the planets and moons do not?  Solar system debris is unevolved => gives direct evidence of conditions during solar system formation!

Solar System Debris Comets Comet Halley (1986)‏ Comet Hale-Bopp (1997)‏ Short Period Comets Long Period Comets year orbits Orbits prograde, close to plane of Solar System Originate in Kuiper Belt Few times 10 5 or 10 6 year orbits Orbits have random orientations and large ellipticities Originate in Oort Cloud

Oort Cloud is a huge, roughly spherical reservoir of comets surrounding the Solar System. ~10 8 objects? A passing star may redirect Oort cloud objects, creating long period comets. Kuiper Belt object can be redirected by Neptune, creating a short- period comet.

Question What causes the tail of a comet?  (Hint: The tail always points directly away from the sun.)‏

Nucleus: ~ km ball of ice, dust Coma: cloud of gas and dust around nucleus (~10 6 km across)‏ Tail: Always points away from Sun. Comet Structure Coma and tail due to gas, dust, and ice warming up and being removed from nucleus by the Solar Wind. Far from Sun, comet is a nucleus only. Highly Elliptical Orbits, exhibiting all inclinations. Periods from hunderds to millions of years.

Comet Trajectory

Meteor Showers Comets break up when near Sun - solar wind, evaporation, tidal force. e.g. Halley loses 10 tons/sec when near Sun. Will be destroyed in 40,000 years. Debris spreads out along comet orbit. Intersection of orbits => meteor shower

Asteroids Most in Asteroid Belt, between Mars and Jupiter. Predominently rocky. Typically smaller than comets and larger than meteoroids. Largest are spherical (gravity dominates) but smaller can be irregularly shaped. If a potato represents an asteroid in the asteroid belt how far away on average (using the same scale) is the next nearest potato?

How did the Solar System Form? What must be explained? ● Solar system is very flat. ● Planetary orbits are nearly circular. ● Almost all moons and planets (and Sun) rotate and revolve (orbit) in the same direction. ● Planets are isolated in space. ● Terrestrial - Jovian planet distinction. ● Leftover junk (comets and asteroids). (Website Animation)‏

Nebular Theory Nebula: Cloud of interstellar dust and gas about a light-year across Condensing (due to external perturbation) cloud heats up - star forms at center But why is solar system rotating and flat?

Nebular Theory Nebula: Cloud of interstellar dust and gas about a light-year across Condensing cloud heats up - star forms at center But why is solar system flat? Conservation of Angular Momentum + Centrifugal Force  Ang. Mom. ≈ mass x rotation speed x radius^2 Nebula collapses most rapidly along its axis of rotation flattens into a disk!

Conservation of angular momentum‏

So, as nebula contracted it rotated faster. It became a flattened disk, like a pizza crust. (Centrifugal hoops demo)‏

But, clumps in rotating gas tend to disperse! Need modified theory. Solar Nebula: 98% of mass is gas 2% in dust grains Condensation theory: 1) Dust grains act as "condensation nuclei” - microscopic platforms to which other atoms can attach, forming larger and larger balls of matter. Also radiate heat => help to cool gas => faster gravitational collapse. 2) Accretion: Clumps collide and stick 3) Gravity-enhanced accretion: objects now have significant gravity => faster growth

Asteroid Belt Perhaps a planet was going to form there. But Jupiter's strong gravity disrupted the planetesimals' orbits, ejecting them out of Solar System. The Belt is the few left behind. And Finally... Remaining gas swept out by intense period of solar wind activity.

Planetary Ejection