Introduction to the Solar System

Viking Biology experiments, 1976
Did 4 tests for life
1. Directly measured for carbon molecules.
assumption: life is carbon based
2. Tested for the incorporation of CO2 in chemical/life reactions
If we incubate the soil, do we see metabolic activity, the use of C to build organic molecules? -- Pyrolitic Release Experiment
3. Look for the generation or uptake of other gases, some kind of unusual chemistry. If we incubate the soil, are gases exchanged between an organism and its environment? -- Gas Exchange Experiment
4. Feed the soil 'nutrient' and see if it uses it by breaking it down and eating it. Labeled Release Experiment

1. No carbon molecules
2. Some CO2 went into organics (probably just some unknown chemical reaction)
3. Lots of gases exchanged, but it looks like just reactive soil
4. Nutrient broke down, but best explanation is the reactivity of the soil
No carbon-based life that uses its environment to feed and grow

Black smokers
Hydrothermal systems -- volcanism + water
sulfur bacteria that don't use the sun
They get energy from sulfur minerals and gases coming out of the vents
Anaerobic -- they don't use O2
Life originally must have been anaerobic

Endolithic organisms
Things that live in rocks --fungi
Photosynthetic, but very very slow
Antarctica dry valleys -- a lot like Mars
But biomass of organisms beneath the surface may exceed what is at the surface!

Early Mars was wetter and warmer
Record indicates that life on the Earth evolved very rapidly after impacts slowed down -- perhaps only in a few 100,000 years (Christian De Duve)
Could life have evolved on Mars, and then retreated to comfortable niches as the climate got colder and dryer?
Look for geothermal systems, old lake beds for fossil evidence, sedimentary layers
Maybe polar ice cap frosts and rocks (endolithic organism)

We know that impacts are common other planets -- SL-9 on Jupiter 2 years ago
W tend not to think of impacts as important events, because historically, impacts haven't happened
Human history -- 4000 years, 1 millionth of the history of the Earth
Over the geologic history of the Earth, impacts are important
Helped bring water to the Earth, and liberate it from existing rocks
Probably brought organic molecules -- maybe most of all organics from impacts
Impact frustration of life
Mass extinctions 3 - 10 in the 600 My we've had fossils
Last major mass extinction -- killed the dinosaurs -- 10 km object struck the Yucatan 65 My ago
Note: Current rate of species extinctions due to human activity is several times that caused by an asteroid impact!
25,000 years ago -- 100 m metal object made Meteor Crater in Arizona
90 years ago -- huge explosion in Siberia that flattened trees for 100's km
Every year, one atomic-bomb sized explosion in the atmosphere
About 1/2 ton a day of stuff from outer space comes to Earth

1. Meteroids 1 mm to 100m, carbonaceous, rocks, metals.
broken bits of asteroids and comets
2. Asteroids 100 m to 1000 km, rocks and metal, little ice, no frozen gases. Most are in orbit between Mars and Jupiter, but we are also in a mini-belt, with 2000 asteroids near Earth
3. Comets 1 - 100 km. Dirty snowballs that inhabit the outer solar system in two distinct places -- Oort Cloud, Kuiper belt
Occasionally, a comet gets perturbed from its outer orbit due to Neptune or a passing star, and comes hurtling in to the inner solar system. These are the ones we see
4. Dust grains less than 1 mm. Most from dust given off in the tails of comets, but some may be from asteroid collisions. By far, most of the mass of interplanetary stuff we get is dust.
The bigger ones we see as meteors as they enter and burn up in the atmosphere (60 km up)
We get meteor showers after the close passage of a comet. Dust stays in orbit around the sun, and every year in our orbit we cross the dust stream
Best meteor shower -- Perseids, Aug 12, due to a comet that passed on Aug 12, 1862

Meteorites are rocks that are big enough not to completely burn up when they enter the Earth's atmosphere
1. Carbonaceous Chondrites -- directly condensed from the solar nebula -- oldest meteorites
Chondrules ('seed grains'), molten droplets that formed during collisions between planetesimals, the solidified into glass
Lots of black, carbon rich stuff, and water
Maybe like the dirt part of the comet dirty snowball
2. Stony meteorites (achondrites) -- rocks, much like basalts (like crust or mantle of Earth)
3. Stony-iron -- mixture of basalt like rock and Fe-Ni alloy
4. Iron -- Fe-Ni alloy, just like the core of the Earth
The different types probably exist because planets as large as 1000 km formed in the asteroid belt, and differentiated. They then broke up because of collisions
So we see the core and mantle of some long past differentiated planets

Can be seen in telescope photos as streaks against the stars, because they move around the sun like planets
Rocks or rocks+metal, little or no ice and frozen gases
About 100,000 between Jupiter and Mars
6,000 have been observed, just the largest. We estimate from that
Size-frequency curve of craters on the moon -- tells us how many small ones there are relative to big ones
Ceres is the largest -- 1000 km. 1/3 size of Moon. Probably differentiated
But the size of the asteroids goes all the way down to dust size grains
We can see the dust of the asteroid belt in the late twilight after sunset.
Zodiacal light, a thin band extending upwards from where the sun set, along the ecliptic
There are also 2000 Earth Crossing asteroids, or Apollo asteroids
Trojan asteroids, rocks trapped at Jupiter's Lagrange points
Lagrange points are gravitationally stable points 60 deg ahead of and behind Jupiter's orbit
Chiron 1977, between Uranus and Saturn -- 200 km giant comet
Pholus -- very red, lots of organics--comet, carbonaceous chondrite?
elliptical orbit Saturn Neptune

Large dirty snowballs left over from the formation of the solar system
They are just round snowballs until they get near the sun
Then the frozen gases sublimate off the surface, from jets, pulling gas and dust off the body of the comet, called the nucleus
Makes a temporary atmosphere around the nucleus called the coma
When we see comets far away in the telescope, they look like fuzzy balls
Since all kinds of things in the Universe look like fuzzy balls in the telescope, we can't be sure it's a comet until we see it move from night to night and calculate its orbit
Comets have come from a long way --from the outer solar system. So they are coming in fast on elliptical orbits
When the comet gets closer, it develops a distinctive tail, always pushing away from the sun
Two tails can develop -- plasma (gas) tail straight and dust tail, pushed by solar wind
Comets may be loose aggregates of several smaller dirty iceballs -- theory

Long period comets -- take centuries to go around the sun
Often on highly inclined orbits (not restricted to the ecliptic)
Some go out to hundreds of times further than Pluto
Short period comets -- take a century or less, and stay within the planets roughly. Halley's comet is an example, 76 year period
Short period comets tend to move along closer to the ecliptic

Comets seem to inhabit two different parts of the solar system
Oort cloud spherical shell around the solar system 100 billion same as the number of stars in the Milky Way
50,000 - 100,000 AU -- part way to the nearest star
Originally formed near Saturn, Uranus, Neptune, and ejected way out into the oort cloud by gravity
Long period comet come from the Oort cloud, which explains why they don't usually travel in the plane of the solar system
Kuiper belt -- flattened disk just beyond Pluto, 30 - 100 AU
These were comets that formed there and stayed -- no large planets around to throw them around
This was theory until 5 years ago, when the first Kuiper belt object was discovered at Mauna Kea observatory
Since the, 32 have been discovered 10's of thousands, at least
Short period comets come from the Kuiper belt, which explains why they are found on the ecliptic

They contain H2O, CO, CO2, NH3, and organic molecules
Main organic molecules -- H2CO formaldehyde (precursor of sugars)
HCN hydrogen cyanide -- precursor of amino acids and nucleotides
Halley 40% water, 30% organics

Comet are large, and go very fast because they come from far away
They can do tremendous damage
1 km comet could destroy civilization (much smaller than Halley 10 km)
Cause 500 ft tidal wave if drops in ocean
Throw a sheet of melted magma into the sky, globally
Global forest fires
Block the sun for 6 months after impact because of dust thrown up
Even though it's never happened, the chances of getting killed by a comet or asteroid impact are about equal to your chances of getting killed in an airplane accident 1/25,000
SL-9 comet broke up due to tidal forces of Jupiter -- more gravity on one side than on the other ripped it apart
Shows the comet wasn't very strong, supports the multiple snowball idea
Each piece of SL-9 was 0.5 to 1 km and caused huge explosions which rose above Jupiter's cloud decks
There is evidence on Jupiter's moons of tidally broken up objects hitting -- crater chains

VIDEO: THE THIRD PLANET, MIRACLE PLANET SERIES (Second Half)

6/19/96