Download 28.2 – The Inner Planets

28.2 – THE INNER PLANETS
MAIN IDEA
•
Mercury, Venus, Earth, and marks have high densities and rocky surfaces
• Just as in a family in which brothers and sisters share a strong resemblance, the
inner planets share many characteristics
TERRESTRIAL PLANETS
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The four inner planets are called terrestrial planets because they are similar in density to
Earth
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They have solid rocky surfaces
•
Density is important because it indicates the internal conditions of these planets are
compressed
MERCURY
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Mercury is the closest planet to the sun, for this reason it
is difficult to see from Earth
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Is about 1/3 of the size of Earth
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Easily seen at sunrise and sunset
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Very slow spin – it takes 1407.6 hours to spin
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In one orbit, Mercury spins one and one-half times
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This means Mercury’s years equal three complete
Mercury days!
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No moons!
MERCURY’S ATMOSPHERE
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The atmosphere in Mercury is mostly made up of oxygen and sodium
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The daytime temperature is 427°C while temperatures at night fall to -173°C
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This is the largest day-night temperature difference among the planets
SURFACE OF MERCURY
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A U.S. space probe passed the surface of the moon in 1974 and 1975 and it found the
surface is similar to the moon with craters and plains
•
Maria on the surface formed like the ones on the moon
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The gravity of Mercury is much greater than the moon, resulting in small ejecta and rays
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Planetwide system of cliffs called scarps
INTERIOR OF MERCURY
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Has a high density made up of nickel-iron core
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Small magnetic field
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Core is molten
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Mercury’s size was much larger but outer layers may have been lost with a collision with
other celestial bodies early in history
VENUS
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Brightest planet in the sky – albedo is 0.75 therefore known as the bright ‘star’
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Aka ‘evening or morning star’
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Very thick clouds make it difficult to observe
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In 1989 Magellan spacecraft was able to map 98% of the surface using radio-telescopes
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In 2006 – Venus express gathered atmospheric data for 1.5 yrs
VENUS’ ROTATION
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Slow rotation – one day is equivalent to 243 Earth days
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Spins clockwise, unlike other planets which spin counter-clockwise
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Sunrise in the west and sets in the east
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Collision with another body may have caused this
VENUS’ ATMOSPHERE
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Most similar to the Earth
•
Physical properties like diameter, mass, and density
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Venus is 92 atmospheres (atm) – 915m of water
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Clouds of sulphuric acid
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Hottest planet because of high levels of carbon dioxide
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So hot (464°C) that liquid water cannot exist
SURFACE AND INTERIOR
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Venus has a smooth surface
from lava flow however no
crustal plates or impact
craters
•
Because of its size and
density, scientists believe
the internal structure is very
similar to that of Earth
• Liquid core
• No measurable
magnetic field because
of its slow rotation
EARTH
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Allows water to exist as solid, liquid and
gas
•
Dense atmosphere of nitrogen and
oxygen allows for life
•
Only planet where plate tectonics occurs
MARS
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The red planet
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Smaller and less dense than Earth
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Has two irregularly shaped moons – Phobos and Deimos
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Lots of exploration
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Historic Log at NASA
MARS’ ATMOSPHERE
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Mars is very similar to Venus
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Density and pressure is much lower, there greenhouse effect is not as strong
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Constant winds and dust storms can last for weeks because of thin atmosphere
MARS’ SURFACE
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Northern and southern hemisphere vary greatly
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Southern hemisphere is heavily cratered
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Lots of highlands
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Northern hemisphere has sparsely cratered plains
MARS’ SURFACE
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Four gigantic shield volcanoes are located near the equator called the Tharsis Plateau
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Largest volcano is called Olympic Mons
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3 times higher than Mount Everest
TECTONICS
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Valles Marineris is an enormous canyon
stretching 400km long
•
10 times longer than the grand canyon
and 3 times deeper
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Formed by a fracture 3 bya
EROSIONAL FEATURES
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Dried river and lake beds
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Outflow channels and runoff channels
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Astronomers think the atmosphere was once much warmer, thicker, and richer in carbon
dioxide allowing liquid water to flow on Mars
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Small amount of Ice at the poles
ICE CAPS
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Caps grow and shrink with the
seasons
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Seasons caused by tilt and orbit
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Carbon dioxide ice
•
Interior
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The interior remains unknown of
Mars as it is hypothsized that
there is a core of iron, nickel, and
sulfur
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No magnetic field
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Snow Falls