Hour 5: Planets in Our Solar System --Histories Compared with Earth

• Information from Meteorites• Earth as a Planet• Venus and Mars: Good Planets Gone Bad• Tidal heating of Jovian moons - extending the Habitable Zone

Take-aways:• Meteorites: (1) give age of the solar system, (2) contain organic

molecules, and (3) show evidence the solar system formed soon after a nearby supernova explosion

• Earth is the largest and consequently the most geologically active of the 4 terrestrial planets; is that significant for biological environment ?

• Earth itself was not “Earth-like” until as recently as 1 Byr ago• Venus and Mars were both once more Earth-like, but “went bad”

-- Venus as “runaway greenhouse”--- Mars as “runaway refrigerator”

• Mars had substantial liquid water on its surface during its first billion years - the length of time in which life started on Earth

• Tidal (gravitational) heating of moons of large planets may extend the Habitable (liquid water) Zone across the solar system

Meteorites

• Chips of asteroids• Material for solar system radiometric age• Some carry organic matter• Some show evidence that formation of the

solar system was triggered by a supernova

Fig. 19-2d, p.455

Shocks Triggering Star Formation

Henize 206 (infrared)

Earth as a Planet

Fig. 17-1, p.380

Fig. 17-9, p.394

p.384a

p.384b

Venus and Mars:Good Planets Gone Bad

Celestial Profile, p.399

Fig. 17-12, p.398

Fig. 17-13, p.402

Fig. 17-14, p.403

Fig. 17-4, p.386

Venus• Planet originally in Habitable Zone --cool

enough for liquid water• “Runaway” greenhouse effect• Evidence that an entire ocean of water has

evaporated• Without water, CO2 cannot be removed into

crust sediments (Venus atmosphere has same amount of CO2 as Earth crust)

• This is the eventual fate of the Earth as the Sun’s luminosity continues to rise

Mars

Celestial Profile, p.405

p.401c

p.401d

p.401e

Fig. 17-18c, p.407

Fig. 17-20, p.408

Fig. 17-17, p.406

Fig. 17-16, p.406

Fig. 17-21, p.410

Mars• Planet originally in Habitable Zone -- warm

enough for liquid water• Low-mass planet with light gravity and little

geologic activity slowly lost its atmosphere (and greenhouse warming)

• Images showing effects of surface water in oldest terrain

• Rovers find evidence there was once significant amounts of standing water (e.g. lakes)

Moons of the Giant Planets -- Tidal Heating Extends

Habitable Zone ?

Fig. 18-1, p.420

Fig. 18-5, p.428

Tidal Heating

• Jupiter’s moons: Io, Europa (also Ganymede and Callisto?)

• Saturn’s moons Enceladus, Titan

Fig. 18-9, p.430

Fig. 18-8, p.429

Fig. 18-12c, p.436

18CO, p.418

Fig. 18-11a, p.432

Fig. 18-11b, p.432

Fig. 18-11c, p.432

Take-aways:• Meteorites: (1) give age of the solar system, (2) contain organic molecules,

and (3) show evidence the solar system formed soon after a nearby supernova explosion

• Earth is the largest and consequently the most geologically active of the 4 terrestrial planets; is that significant for biological environment ?

• Earth itself was not “Earth-like” until as recently as 1 Byr ago• Venus and Mars were both once more Earth-like, but “went bad”

-- Venus as “runaway greenhouse”--- Mars as “runaway refrigerator”

• Mars had substantial liquid water on its surface during its first billion years - the length of time in which life started on Earth

• Tidal (gravitational) heating of moons of large planets may extend the Habitable (liquid water) Zone across the solar system