Mirach (Beta Andromedae)

~ 200 light-years distant red giant star cooler than the Sun much larger than Sun

therefore, intrinsically much brighter than the Sun.

faint, fuzzy galaxy lies along same line of sight, but much more distant

diffraction spikes visible

diffraction spikes: optical aberration caused by light diffracting around the support vanes of the secondary mirror.

Primary mirror

Secondary mirror

Homework #7

Due next Monday, 10:00 pm

Exam #2: Thursday, Nov. 4

Review Session Tuesday evening

Room & time to be announced

The “Cambrian Explosion”Began: ~ 545 million Yr ago Duration: ~ 40 million years

Explosion of life forms

Animal branch of the tree of life came into being

All known body plans made appearance in fossil

record in a time span of 40 million years

Colonization of LandLife flourished where liquid water existed

Life on land was more complicated

Had to develop means of collecting solar energy above ground and nutrients below

Life in shallow ponds or edges of lakes

Water evaporates

Natural selection favored that which could withstand periods of drought

DNA evidence suggests that plants evolved from an

algae

It took only 75 million Yrs for animals to follow plants

out of water

Mass Extinctions

Mass Extinctions● Possible Causes

– Impacts● Impact sites found for K-T boundary● Suspected for Permian extinction 245 mill yr ago

– Active volcanism● Climate change

– External influence for copying errors● Increase in solar particles or radiation hitting surface● Local supernova

Primate Evolution

● Monkeys, apes, lemurs and humans have common ancestor that lived in trees

● Tree life– Limber arms for swinging between branches– Eyes in front of head for depth perception– Offspring would be born more helpless than other

animals

Emergence of Humans● Did NOT evolve from gorillas or monkeys● Share a common ancestor that lived just a few

million years ago● 98% of human genome is identical to genome of

the chimpanzee● 2% difference in genome separates the success of

humans verses chimps– Also indicates evolution of intelligence is complex

Emergence of Humans● After hominids diverged from chimps and gorillas,

evolution has followed a complex path

● Numerous hominids species existed, some during the same time period– All humans are the same species

● First skull fossils that are identical to modern human skulls dates to 100,000 yr old

● Our ancestors shared the Earth with Neanderthals– Went extinct 35,000 years ago

Cultural and Technological Evolution● Humans have not undergone biological evolution in

40,000 years– Mutation rates are slow

● Dramatic cultural changes– Transmission of knowledge between generations

● Spoken to written word, thousands of years● agriculture

● Technological evolution– Result of coupling between science and technology

– About 100 years between industrial revolution to landing on the Moon and generating weapons of mass destruction

Life in the Solar System?

Essentials for life

Chemicals / NutrientsEnergyLiquid solvent

• Chemical components of cells:– Oxygen– Carbon– Nitrogen– Hydrogen

These elements make up 96% of the mass of living organisms on Earth.

Where can we expect to find the necessary ingredients/chemicals for life?

• These elements are abundant in the Universe, except in older star systems

• As long as condensation and accretion occur during a star system’s formation, we can expect these elements to be present

• Organic molecules (building blocks for amino acids) have been found in asteroids and comets

What are the energy requirements for life?

• Sunlight (photosynthesis)

• Consuming organic molecules (ex. eating plants)

• Chemical reactions with inorganic compounds of iron, sulfur, or hydrogen

Sunlight?

Light most intense near the sun (or another star)

Light intensity falls off with distance from the Sun/star, going as 1/(distance)2

Inefficient far from a star

Where can we expect to find energy for life?

• Chemical Energy requires a means for chemicals to mix & interact

• Atmospheres and/or bodies of liquids can provide this means

What to use as a solvent?

Liquids exist only in specific temperature and pressure ranges. On the surface of a planet or moon, temperature

alone is insufficient for the presence of liquids.

• On Earth, all life requires water:

Water dissolves organic molecules so they can be used for chemical reactions in cells

Water transports chemicals into and out of cells

Water is directly involved in many metabolic reactions within cells

On Earth, the only other common liquid is molten rock (too hot)!

Alternative Liquids for Life(under 1 atmosphere pressure)

Substance Freezing

Temperature

Boiling Temperature

Width of Liquid Range

Water (H2O) 0 C 100 C 100 C

Ammonia (NH3) -78 C -33 C 45 C

Methane (CH4) -182 C -164 C 18 C

Ethane (C2H6) -183 C -89 C 94 C

Water remains liquid over broader and higher range of temperatures

The higher temperature range for liquid water allows faster rates of chemical reactions

On colder worlds (e.g., Titan), other liquids may be more common, such as Ammonia NH3

Methane CH4

Ethane C2H6

Chemical reactions are highly temperature sensitive, so on colder worlds with other liquids, reaction rates may be too slow for life.

ethane/methane lakes on Titan

• Advantages of water:1. Water remains liquid over the widest range of

temperatures2. Water is liquid at a higher temperature than the others.

High temp makes chemical reactions easier.3. Water is less dense when it freezes (ice floats),

allowing life to survive in the water under the ice

4. Ice insulates the water underneath, making it less likely to freeze all the way, promoting greater climate stability

5. Water is POLAR. Many substances can dissolve in water, but many do not. Cell membranes do not dissolve in water. Earth-like cells can only survive in water.

Water is the most likely candidate liquid for life.

Searching for liquid water may be the best

approach to searching for life.

We do not know if other liquids can support life.

Time to begin the search!

Is life possible on Mercury or the Moon ?

• Small (weak gravity)

• Airless

• Heavily cratered

• No significant tectonic activity

• No volcanic gases to form an atmosphere

• No liquids likely anywhere

Is Life Possible on Venus?

• Runaway greenhouse effect: too

hot!

• High Pressure

• Life might be possible in upper

clouds (though very acidic)

• Conditions better in early times

when the Sun was not as bright

Is life possible on Mars?

Is Life Possible On Mars?

Once had a thicker and warmer atmosphere and liquid water

Liquid water may stillexist underground

Mars: A home to life?

For a good and wide-ranging discussion of Mars, check out www.spacetoday.org/SolSys/Mars/Mars.html

The Canals of Mars

• In 1877, the Italian astronomer Giovanni Schiaparelli announced that he saw canali on Mars.

• Canali means "channels" (a natural waterway) in Italian, but was promptly mistranslated into English as "canals" (a constructed waterway)

The most famous proponent of the Martian canals was the American Percival Lowell (1855-1916), who took up astronomy after reading Schiaparelli, and founded an observatory in Flagstaff, AZ to study the canals.

Lowell reported seeing a great many canals, intersecting at junctions he referred to as ‘oases’.

He published 3 famous & well read books describing the canals and arguing for life on Mars.

• Mars (1895)• Mars and its Canals (1906)• Mars as the Abode of Life (1908)

The works of Schiaparelli & Lowell formed the basis of the popular view of life on Mars. This was carried over into the popular literature (e.g., War of the Worlds by H.G. Wells and many subsequent works.

Unfortunately, Lowell was wrong. • Very few other astronomers reported seeing these

canals.

• Those that did were inevitably using small telescopes and/or observing under adverse atmospheric conditions.

• Mars was is cold and has too little atmophere for canals to work.

• Long after most astronomers ceased to believe in canals, popular media continued to speculate about the canals.

• Much of current knowledge stems from robotic missions to Mars:– Viking (1976-78): 2 landers and 2 orbiters– Mars Pathfinder (1997): lander & rover– Mars Global Surveyor (1997 - ): orbiter– Mars Explorer rovers (Jan. 2004 - ):

• Spirit• Opportunity

– Mars ReconnaissanceOrbiter (Jan. 2007 - ): orbiter

– Human mission (2025)?

An overview of what we know today…

– Two major terrains• Southern Hemisphere: Ancient, heavily cratered highlands, ~ 4km

higher than northern hemisphere• Northern hemisphere: younger, lightly cratered volcanic plains

– Surface Features• Craters, impact basins, uplifted

regions, volcanoes, mountains, canyons, polar ice caps, river beds, flood plains

The Tharsis Bulge is a massive uplifted region the size of North America, right between the northern plains and southern uplands.

The Tharsis area bulges 10 km above its surroundings and is one of the least cratered (youngest) terrains on Mars. Surface less than 1 Byr old.

Three of Mars’ four great volcanoes are located here and the forth, Olympus Mons, is offset on the NW slope.

What is the cause of the Tharsis bulge?

1.A bulge of the crust due to a mantle plume, and a build-up of layers of lava.

1. We believe that the uplift began about 3 billion years (Gyr) ago, and continued to 1 Gyr ago, before the formation of the actual volcanoes.

2. On Earth and Venus, compressional forces produce uplifted terrain, such as Tibet and Lakshmi, with high mountains.

3.On Mars however, the highest features are volcanic, not compressional in origin.

• Volcanoes Including the tallest volcano in the solar system– Olympus Mons: 24 km tall, 500 km wide, a 6 km cliff at its base

Scale of Terrain on MarsThe figure below compares Olympus Mons with Everest (fold mountain) and Mauna Loa (shield volcano) on Earth.

Calculations show that on Earth, and Venus, mountains can only rise 10-15 km before the rock begins to deform under its own weight.

Mountains on Mars can get so big because the Martian gravity is only 40% that of the Earth.

• Cracks & Canyons– Valles Marineris: 3000 mi long, 60 mi wide, 4 mi deep– Origin - not running water but vertical tectonics

• The only ‘canal’of Lowell’s to exist.