Introduction to the Solar System

Why do we have tides twice a day, instead of once? Why not just the side facing the moon. It works like this:
Moon pulls on the whole Earth
The pull is actually 'felt' by the Earth at its center
Water on the Moon side is actually pulled more than average
Water on the side facing away from the moon actually is pulled less than the average--The water can flow, so it bulges away.

Half the size of Earth
24 hour day, same as Earth
23 deg axial tilt, same as Earth --which means it has seasons just like Earth
Half as much sunlight as Earth
Very cold, -50 F on average
But in the summer on the equator, it can get room temperature
Has a thin CO2 atmosphere, 1/100th of the Earth's.
Almost same composition as Venus', but 10,000 times thinner
Has polar caps, made of water ice and dry ice (CO2)
It has weather, with morning clouds, snow, storms, dust storms
But no evidence for running water recently (recall surface dating with crater counting). It's all frozen out.

Most of what we know about comes from an incredible mission: The Viking Missions to Mars in 1976
Two spacecraft, with two orbiters and two landers
Perhaps the pinnacle of human exploration of the planets
Orbiters mapped the planet, looking at some areas with 20 m resolution
Landers photographed the surface, studied the chemistry of the soil, and also performed as weather stations measuring winds, temperatures, and atmospheric pressures
They also had a complex set of biological experiments to look for life
Details in the Mars Quest show in the planetarium on Monday.

Here's what Viking saw
Mars has two kinds of terrain, roughly divided between the Northern hemisphere and Southern hemisphere
The northern hemisphere, which we are looking at here is smooth, relatively crater free
It has huge shield volcanoes, sitting on a huge bump on the surface, as well as other places.
It also has an enormous crack, the size of the US, splitting down the side of the bump
The northern hemisphere has relatively few craters, probably wiped out by the volcanism--it is a relatively young surface, maybe 1 by old
Notice the clouds on the morning terminator--morning fog surrounding three enormous volcanoes on the Tharsis bulge
Light is where windblown dust has settled -- dark areas may be bedrock
Mars is red because it the surface has oxidized iron -- rust, just like volcanic red dirt on the Earth

The southern hemisphere is much, much older, as evidenced by a lot of craters
The entire south is higher than the volcanic plains, and we call it the highlands, just like on the moon

The southern portion looks just like the moon, like a dead planet
This is a huge basin and numerous other craters in the south
When we sent Mariner 9 there in 1971, it flew under the south pole, and we thought Mars was just like the Moon. It was very disappointing
But Viking changed all that

Since we didn't know what to expect, we surveyed possible landing sites for several months before deploying the landers
The lander used parachute and rockets, and used the orbiter as a relay

Landers were semiautonomous, and bristling with instruments

You can imagine the anticipation we felt, wondering what this new place, new world looked like.
Far more Earth like, this is even a place that could be home to humanity
Here's what it saw
Rock strewn desert, light sky
The rocks are probably strewn from some distant impact crater or volcano
If you look at the rock on the lower right, it looks vesicular
That means it has evidence of bubbles that came out as the rock cooled
Probably volcanic in origin

Viking scooped up soil with a shovel, and put it in various chambers for testing
They tested what elements the rocks were made of -- Fe, Mg, Al --basalts
They looked for water (1%)
I know a researcher who discovered you can retrieve the water from this kind of soil with a microwave oven

One of the most incredible things the Viking Landers did was search for evidence of life
They tried to stimulate microorganisms to do photosynthesis
They looked for evidence that carbon was used up in metabolic activity
And they directly measured the organic content of the soil
What they found was that there were no organic molecules at all
But they also found that gases were given off by the soil violently
The soil is very chemically reactive
But there was no life
Later, we came to realize that the experiments were a bit naive, too restricted in what we expect from life
Also, we may have to dig in different places to look for fossil remains of life

One lander landed N, about 50 deg latitude, and one landed nearer the equator
The northern one saw dramatic seasons.
This is a shot of the area around lander 2 during the morning
A thin CO2 frost has condensed out of the atmosphere during the night
During the day, it will quickly sublimate --directly from frost to gas

While the lander is doing its complex experiments, up in orbit, the orbiter is mapping the planet
The most striking features are volcanoes, much, much bigger than Earth volcanoes
Here are the three Tharsis volcanoes, on the big bump, shrouded in clouds
You can see that they have calderas, or volcanic craters on the tops
Notice the cracks, the beginning of the huge crack going SE from the Tharsis Bulge

The biggest volcano in the solar system
80,000 feet high, 500 miles across
Called Olympus Mons
Enormous pit in the center
Calderas are formed when the volcano finished erupting, and the magma from below withdraws. The ground collapses at the top

Stereo images were taken by Viking that allows us to reconstruct the 3-D nature of the surface.
Here you can see the miles high scarp, or cliff that surrounds Olympus Mons
Caused by the falling away of material
This mountain is almost exactly like the large Hawaiian shield volcanoes
It was probably created by a huge plume of hot material from the depths of Mars

Because it is so high, Olympus Mons strongly influences the weather on Mars, just like mountains do here
Here is an oblique view of the summit, encircled by clouds

Because Viking orbited for 3 years, it was able to take very close looks at certain portions of the planet
So we looked closely at the volcanoes
Here's a volcano with a huge caldera, and some impact craters
By counting craters around the volcanoes, we find that some may be as little as 100 my.
If Mars is a dead planet, then the corpse is still warm
Maybe even some hydrothermal activity (hot vents of gas) still left
This is exciting, because there is life in hydrothermal systems on the Earth, and it looks like a good place to evolve

Some of these calderas are very complex, showing evidence for multiple eruption events -- volcanoes may have lasted for a long time
Therefore, hydrothermal systems may have lasted for a long time, allowing life to evolve
Bu see the bottom left--evidence for something flowing

In fact everywhere we look, in both the old (South) and new (north) areas of Mars, we see evidence for running water in the past
Here is a very, very old valley network
The valleys are more common in the old regions, but there is also evidence for a large system of drainage networks from older region to newer regions

Some of the river systems clearly look like rivers, and must have carried enormous amounts of water
We interpret this to mean that Mars was warmer in the past
It has almost no greenhouse effect now, because the air is so thin
But it may have had a much thicker CO2 atmosphere in the past, now sequestered at the poles or escaped from the planet
Mars has a lower gravity, and light gases can escape easily
Higher pressure, more greenhouse, liquid water
Now the water is probably frozen as permafrost, or under the ground
There is other evidence for massive climate change as well

But most of the intricate river networks are ancient -- 3.5 B years ago
Recall that the solar system is 4.5 billion years old
But there is more recent evidence of flowing water
This is the result of a series of great floods
You can tell that the water has moved fast, cutting deep channels
These may have been much more recent -- maybe 1 by ago

There are places where it looks like huge amounts of ice melted suddenly and flowed out. The land collapsed in these places, creating chaotic terrain
There are places like this on the Earth -- badlands of Eastern Washington

But there is other evidence for flowing water
Here, you see a teardrop shape around a crater. Somehow when the crater formed (before the flood) it sort of cemented the ground, making it more resistant to erosion as the water flowed

Some craters have funny impact ejecta, called lobate ejecta
It looks like the impactor hit where there was subsurface ice
The ice melted on impact, made mud, which was flung out in these patterns

Some people have even suggested that Mars may have had oceans, and that there are ancient shorelines
This is the scarp that makes a boundary between the south and north
you can see a crater with lobate ejecta in the center right
Channels ending between s and n
Sand dune fields

VIDEO: CLIPS OF FLYING OVER MARS FROM 'FLYING BY THE PLANETS'

6/14/96