Minor Worlds

Dwarf Planets

Pluto, Ceres, Eris, Haumea, Makemake

Pluto

40 AU

Highly elliptical orbit (most others are nearly circular) and greatly inclined to ecliptic

5 moons:  Charon (1978), Nix (2005), Hydra (2005), Kerberos and Styx (2011/12)

Largely, Pluto and Charon are a double-dwarf system (tidally locked)

Atmosphere – Nitrogen, Carbon Monoxide, Methane

2 g/cc density - ice and rock – about twice the density of water

If we were standing on Pluto, sun would appear over a 1000 times fainter

Clyde Tombaugh, discover (in 1930) died in 1997

249 year period

Sometimes within Neptune’s orbit (20 years out of every Pluto spin around the Sun)

Frozen planet:  -391 F

Mountains, 2-3 km high

Chaotic orbit

Possibly from Kuiper belt in outer solar system

New Horizons (fastest spacecraft ever launched) did a fly-by in 2015

Roughly magnitude 13.5

Very hard to deduce basic info about Pluto – some is done by effects on Uranus

Roughly 1/500 Earth mass

From albedo, bright polar caps were discovered; dark band near equator

Low atmospheric pressure (1/100,000 Earth’s) – layered atmosphere - some methane, and a gas heavier than methane - carbon monoxide or nitrogen

Highly eccentric orbit, highly inclined to ecliptic

I love this quote from NASA:  “The New Horizons mission is one of the great explorations of our time; there's so much we don't know, not just about Pluto, but about similar worlds as well. Scientists won't be rewriting textbooks with this historic mission - they'll be writing them from scratch.”

Asteroids

Asteroid belt between Mars and Jupiter

Assigned a number in order of discovery:  1 Ceres, 16 Psyche, 433 Eros

Rarely come within a million km of each other, though there are occasional collisions

Larger asteroids are the same size (roughly) as some of the minor moons

Saturn’s outermost moon, Phoebe, is probably a captured asteroid

Mostly stony, though some are high in carbon

Not the result of a destroyed planet between Mars and Jupiter - old theory

There may be millions of asteroids

Some orbit each other, apparently – Ida and Dactyl

Hayabusa (Japan) landed on Itokaka, sampled it, and returned to Earth in 2010

Named in honor of people, alive or dead

Meteoroids

Small chunks of matter in interplanetary space - up to 10’s of meters across

When one hits the atmosphere, it heats up – meteor (shooting star); around 100 km up, 30 km/s or so

If a part hits the earth, we call it a meteorite

We are bombarded ALL the time - usually these disintegrate, but we’re still hit by tons of stuff per day (micrometeroites).  We can actually sample stuff in the upper atmosphere.

Barringer Meteor Crater in Arizona, formed 25,000 years ago or so

On occasion, we’re hit - once in a while by a meteoroid from Mars or the moon

Most meteorites originate from asteroids

Large asteroid impact, some 65 million years ago, is thought to have created the huge crater on the Yucatan Peninsula, and eliminated much life on Eaerth

Meteor Showers - when we pass through comet debris

Regular showers:

Perseids ~ August 12 (Swift-Tuttle)

Leonids ~ November 17 (Tempel-Tuttle)

Geminids ~ December 14 (Phaethon)

Orionids ~ October 21 (Halley)

Kuiper Belt

30-50 AU

KBO = Kuiper Belt Object

The probable home of short-period comets

Predicted in 1951

Several found so far, but there may be as many as 70,000 over 100  km in diameter, between 30 and 50 AU from sun

KBOs:  Quaoar, Sedna, Makemake (“Easterbunny”), Haumea (“Santa”)

These may give clues to the history of our solar system, since they are among the oldest objects in it

Oort Cloud

Proposed by Jan Oort, 1950

Comprised of trillions of comets (formed or forming)

A sphere some 100,000 AU in diameter!

On occasion, comets break free of the cloud and orbit the Sun (or elsewhere)

Huge cloud, but again – hypothetical, used to explain long-period comets

Comets

Appartently from Oort Cloud

Periods vary widely (a few years to thousands of years and more)

Tail directed away from Sun

~ 1 dozen discovered each year; most are new, and only

A few are naked eye

Nucleus

Dirty snowball (Whipple theory)

Few km wide

H20, CO2, NH3, CH4, Dust

Hale-Bopp, the most viewed comet of all time, was 40 km wide

Nucleus rotates

Coma

The rest of the comet’s head

~million km across

Surrounded by H-cloud (breakup of water molecules by UV)

Tails can be > 1 AU

Dust Tail - dust particles vaporized from nucleus, left behind, blown slightly away from Sun

Gas Tail - ions fairly straight behind comet

The tail can be sampled

Total mass of comet < 1 billionth Earth mass

Originates from Oort Cloud (probably the long-term comets, at least)

Famous comets:  Halley (76 year period), Hyakutake, Kohotek, Shoemaker-Levy 9, Hale-Bopp