Solar System Planets: Venus

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Solar System Planets Venus
I. Venus - atmosphere - surface features -
interior
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Evolution of Atmospheres Earth vs. Venus

• because water can exist in liquid form on Earth
  oceans
• original CO2 has dissolved into oceans, rocks
  (carbonates)
• which keeps levels of CO2 just balanced in
  atmosphere
• keeps planet WARM but not HOT
• if planet were hotter, CO2, H2O would be boiled
  out of oceans
• and baked out of rocks ? more CO2, H2O enter
  atmosphere

• water may have existed early in Venus history
  but more
• vaporized into atmosphere T was hotter on Venus
• H2O vapor is a greenhouse gas and would trap
  energy
• making planet hotter eventually T so high that
  water boils
• runaway because more H20 into atmosphere as
  evaporates
• no water left on planet to dissolve CO2 out of
  balance!
• eventually stabilized when H20 broken down by UV
  sunlight
• and no further CO2 to bake out of the Venus
  surface

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Evolution of Atmospheres Earth vs. Venus

• important role of the oceans on Earth which keep
  the CO2 levels
• balanced and not runaway

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Revealing the surface of Venus with Magellan

• a few large highland regions
• volcanoes, smooth plains
• channels, craters and folding crust
• And trying to determine interior
• no magnetic field possibly
• planet rotates too slowly to generate
• a current to drive magnetic field
• do surface volcanoes indicates molten
• interior ?? on the Earth they do
• 60 of surface is within 500 m of
• the highest, lowest point little variation
• 80 of surface is smooth (lava flows)
• no seismic information
• molten interior ? plate tectonics

radar observations Magellan (1989-1994)
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Little surface evidence for plate tectonics on
Venus

• Volcanic mountains do not appear in chains on
  surface
• Lack of fault-like features
• not as much difference in altitude across the
  planet as on Earth

Magellan radar image
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Based on carefully radar imaging of the surface
of Venus, astronomers have also made progress on
understanding the interior of this planet

• very similar to Earths
• - iron core (based on density)
• - mantle, crust layers
• volcanoes indicate magma
• upwelling from some source
• lack of magnetic field,
• plate tectonics indicate that
• there is little or no liquid/molten
• core but the mantle must be
• somewhat pliable/flexible
• not very well determined
• a topic of current study

cartoon of Venus proposed interior
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Cratering and the age of Venus surface

• not nearly as many craters on Venus surface as
  on the Moon, Mercury, Mars
• surface has been almost uniformly resurfaced by
  lava flows during the last few 100 million years
• 1. equilibrium resurfacing ? rate of impact
  craters rate of lava resurfacing
• 2. global catastrophe hypothesis intense period
  of eruptions 100 million yrs. ago

reconstructed image from Magellan showing a large
impact crater in foreground, but relatively
crater-free surface compared with the Moon or
Mercury
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• The outer planets a new region of the Solar
  System
• beyond the asteroid belt (well come back to
  that)
• Earth distance from Sun 1 AU 150 million km
• Mars distance from Sun 1.5 AU 230 million km
• Jupiter distance from Sun 5.2 AU 780 million
  km
• Uranus distance from Sun 19 AU 2880 million
  km
• Neptune distance from Sun 30 AU 4500
  million km
• nearest star distance from Sun 4.3 ly
  37,000 billion km
• our Galaxy has 100 billion stars in it!

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• ? The most notable thing about the Jovian planets
  is that they have very large masses and sizes
  compared to terrestrial planets.
• Why?
• Jovian planets formed in the cold outer solar
  system
• Jupiters composition 71 Hydrogen, 24 Helium
  5 other heavier elements (almost identical
  to the Suns makeup)
• H-rich gases (methane, ammonia, and water) could
  condense. Since these materials were/are far
  more abundant than Si- or Fe, Ni-rich material,
  planets in the outer solar system had more
  material available for growth and H, He would not
  vaporize or escape!!
• Much like the Suns formation, actually, more so
  than the terrestrial, inner planets
  (conglomeration, accretion of little rocks)

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• Fast Facts on Jupiter
• distance 5.3 AU (average)
• eccentricity of orbit 0.05 (like Earths)
• diameter 142, 984 km (equatorial)
• 133, 708 km (polar)
• 11 x Earth diameter
• mass 1.9 x 1027 kg 318x Earth
• (more massive than all the other planets
• combined!!)
• average density 1326 kg/m3
• orbital period 12 years
• rotation period 10 hours (!)
• average temperature -125 K (-165 F)
• albedo 0.44

Jupiter biggest, most massive planet
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Lord of the Solar System named for the King of
the Gods Jupiter Roman and Zeus Greek
SIZE use distance to Jupiter and its angular
size (50!) to determine physical diameter 11x
Earth size! MASS use observations of
Jupiters four satellites (Galileos
original) - from the perspective of nearby
stars Jupiter and the Sun are probably the only
bodies that are discernable in our Solar System
from an outside observer (this is important when
we talk about detecting other planet systems
around other stars)
Jupiter biggest, most massive planet
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As for all the OUTER planets, Jupiter is best
viewed during opposition

• Jupiter is three times brighter
• than Sirius (brightest star)
• Only Moon and Venus
• outshine Jupiter
• Oppositions of Jupiter
• occur every 13 months
• Next Opposition
• - 4 March 2004
• - Jupiter should be visible in
• the spring night sky

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Spacecraft view of Jupiter
Earth-based view of Jupiter
Zones
Belts
From Earth, it is possible to see belts and
zones as easily as from space Also possible to
see - Great Red Spot (first discovered in
1664!) - rotation of Jupiters atmosphere - 9
hours 50 minutes 28 seconds - Cassini (1690)
discovered that poles rotate more slowly than
equator