1,235 Kepler mission

planet candidates, as

shown in transit with

their parent stars

ordered by size from

top left to bottom right.

Simulated stellar disks

and the silhouettes of

transiting planets are

all shown at the same

relative scale, with

saturated star colors.

Some stars show more

than one planet in

transit.

Homework #6

Due 6:00 pm, Monday, Oct. 31

Exam #2

Wednesday, November 2

Life in the Solar System?Life in the Solar System?

Essentials for Essentials for lifelife

Chemicals / NutrientsChemicals / NutrientsEnergyEnergyLiquid solventLiquid solvent

•Chemical components of cells:Chemical components of cells:– OxygenOxygen– CarbonCarbon– NitrogenNitrogen– HydrogenHydrogen

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

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

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

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

What are energy sources are What are energy sources are available?available?

• SunlightSunlight (photosynthesis)(photosynthesis)

• Consuming organic molecules (ex. eating Consuming organic molecules (ex. eating plants)plants)

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

Sunlight?Sunlight?Light is most intense Light is most intense

near the sun (or near the sun (or another star)another star)

Light intensity falls Light intensity falls off with distance off with distance from the Sun/star, from the Sun/star, going as going as 1/(distance)1/(distance)22

Inefficient far from a Inefficient far from a starstar

Where can we expect to find energy for Where can we expect to find energy for life?life?

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

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

What to use as a solvent?

Liquids exist only in specific temperature and pressure Liquids exist only in specific temperature and pressure ranges. ranges.

On the surface of a planet or moon, temperature alone On the surface of a planet or moon, temperature alone is insufficient for the presence of liquids.is insufficient for the presence of liquids.

• On Earth, all life requires water:On Earth, all life requires water:

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

Water transports chemicals into and out of cellsWater transports chemicals into and out of cells

Water is directly involved in many metabolic Water is directly involved in many metabolic reactions within cellsreactions within cells

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

Alternative Liquids for LifeAlternative Liquids for Life(under 1 atmosphere pressure)(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 On colder worlds (e.g., Titan), other (e.g., Titan), other liquids may be liquids may be more common, more common, such assuch as Ammonia NHAmmonia NH33

Methane CHMethane CH44

Ethane CEthane C22HH66

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

ethane/methane lakes on Titan

• Advantages of water:Advantages of water:1.1. Water remains liquid over the widest range Water remains liquid over the widest range

of temperaturesof temperatures2.2. Water is liquid at a higher temperature than Water is liquid at a higher temperature than

the others. High temp makes chemical the others. High temp makes chemical reactions easier.reactions easier.

3.3. Water is less dense when it freezes (ice Water is less dense when it freezes (ice floats), allowing life to survive in the water floats), allowing life to survive in the water under the iceunder the ice

4.4. Ice insulates the water Ice insulates the water underneath it, making underneath it, making it less likely to totally it less likely to totally freeze, promoting freeze, promoting greater climate greater climate stabilitystability

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

Water is the most likely candidate Water is the most likely candidate

liquid as a solvent in life.liquid as a solvent in life.

Searching for liquid water may be the Searching for liquid water may be the

best approach to searching for life. best approach to searching for life.

We do not know if other liquids can We do not know if other liquids can

support life.support life.

Time to begin the search!Time to begin the search!

Is life possible on Mercury or Is life possible on Mercury or the Moon ?the Moon ?

• Small (weak gravity)Small (weak gravity)

• AirlessAirless

• Heavily crateredHeavily cratered

• No significant tectonic activityNo significant tectonic activity

• No volcanic gases to form an No volcanic gases to form an atmosphereatmosphere

• No liquids likely anywhereNo 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 were better in early

times when the Sun was not as

bright

Is life possible on Mars?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?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 MarsThe “Canals” of Mars• In 1877, the Italian astronomer Giovanni Schiaparelli In 1877, the Italian astronomer Giovanni Schiaparelli

announced that he saw announced that he saw canali canali on Mars.on Mars.

• CanaliCanali means "channels" (a natural waterway) in Italian, but means "channels" (a natural waterway) in Italian, but was promptly mistranslated into English as "canals" (a was promptly mistranslated into English as "canals" (a constructed waterway)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 works of Schiaparelli & Lowell formed the basis of the popular view of life on Mars. This was carried over the popular view of life on Mars. This was carried over into the popular literature, e.g., War of the Worlds by into the popular literature, e.g., War of the Worlds by H.G. Wells and many subsequent worksH.G. Wells and many subsequent works. .

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

these canals.these canals.

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

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

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

• Much of current knowledge stems from Much of current knowledge stems from robotic missions to Mars (partial list):robotic missions to Mars (partial list):– Viking (1976-78): 2 landers and 2 orbitersViking (1976-78): 2 landers and 2 orbiters– Mars Pathfinder (1997): lander & roverMars Pathfinder (1997): lander & rover– Mars Global Surveyor (1997 - ): orbiterMars Global Surveyor (1997 - ): orbiter– Mars Express (2003 - ): orbiter & landerMars Express (2003 - ): orbiter & lander– Mars Explorer rovers (Jan. 2004 - ):Mars Explorer rovers (Jan. 2004 - ):

•SpiritSpirit•OpportunityOpportunity

– Mars ReconnaissanceMars ReconnaissanceOrbiter (Jan. 2007 - ): Orbiter (Jan. 2007 - ): orbiterorbiter

– Phoenix (2008): landerPhoenix (2008): lander– Human mission (2025)?Human mission (2025)?

An overview of what we know today…An overview of what we know today…

– Two major terrainsTwo major terrains• Southern Hemisphere: Ancient, Southern Hemisphere: Ancient,

heavily cratered highlands, ~ 4km heavily cratered highlands, ~ 4km higher than northern hemispherehigher than northern hemisphere

• Northern hemisphere: younger, Northern hemisphere: younger, lightly cratered volcanic plainslightly cratered volcanic plains

• Wide variety of 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 fourth, Olympus Mons, is offset on its NW slope.

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

• Cracks & CanyonsCracks & Canyons– Valles Marineris: 3000 mi long, 60 mi wide, 4 mi Valles Marineris: 3000 mi long, 60 mi wide, 4 mi

deepdeep– Origin - not running water but vertical tectonicsOrigin - not running water but vertical tectonics

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

• Surface:Surface: soil, rockssoil, rocks– Rocks - typically Rocks - typically

volcanic in originvolcanic in origin– Red color - iron oxidesRed color - iron oxides

What What are are they?they?

• Dark streaks, everywhere! Many satellite Dark streaks, everywhere! Many satellite images of the middle latitudes of the northern images of the middle latitudes of the northern & southern hemispheres of Mars show wild & southern hemispheres of Mars show wild patterns of criss-crossing dark streaks. patterns of criss-crossing dark streaks.

Dust devils! Those seen by Spirit & Opportunity are about the same size as those that whip up desert dust and sand in the southwestern United States (few hundred feet).

Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. Orbital images of Mars have detected dust devils that are up to several kilometers (a few miles) tall.

Ice CapsIce Caps

• Tiny compared Tiny compared to Earth.to Earth.

• They are a mix They are a mix of water ice + of water ice + frozen carbon frozen carbon dioxide (“dry dioxide (“dry ice”).ice”).

Ice caps show seasonal changes

North Pole

Frozen carbon dioxide (“dry ice” covering frozen water

frozen water

Spring at one pole: CO2 sublimates at that pole, thereby increasing the local atmospheric pressure.

Fall at opposite pole: CO2 condenses out of the atmosphere, thereby decreasing the local atmospheric pressure.

Winds flow from high pressure areas to low pressure areas, picking up dust along the way

– Windy, dusty placeWindy, dusty place During summer, a lot of frozen CODuring summer, a lot of frozen CO22 in the summer in the summer

hemisphere’s ice cap sublimates, increasing the local hemisphere’s ice cap sublimates, increasing the local atmospheric pressureatmospheric pressure

COCO2 2 freezes out of the atmosphere in the opposite pole, freezes out of the atmosphere in the opposite pole, decreasing atmospheric pressure theredecreasing atmospheric pressure there

The change in pressure leads to strong winds blowing from The change in pressure leads to strong winds blowing from one hemisphere to the other, picking up dust as it blowsone hemisphere to the other, picking up dust as it blows

– Really COLD place!Really COLD place!

Current Mars AtmosphereCurrent Mars Atmosphere

• Predominantly COPredominantly CO2 2 (~95%)(~95%)

– minor contributions from Nminor contributions from N22, Ar, H, Ar, H22O, OO, O22, CO, CO

• Global mean temperature = 220 K (brrr!!)Global mean temperature = 220 K (brrr!!)

• Atmospheric pressure = 0.6% Earth (6 Atmospheric pressure = 0.6% Earth (6 millibars)millibars)– this means that water isn’t stable; even in this means that water isn’t stable; even in

places where the temp gets greater than the places where the temp gets greater than the freezing pointfreezing point

Now for the good stuff: Now for the good stuff:

could Mars once have been warm and soggy?could Mars once have been warm and soggy?

And could Mars have/had life?

Early Mars was similar to Early Mars was similar to EarthEarth