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

• The four inner planets are called terrestrial planets because they are similar in density to

Earth

• They have solid rocky surfaces

• Density is important because it indicates the internal conditions of these planets are

compressed

MERCURY

• Mercury is the closest planet to the sun, for this reason it

is difficult to see from Earth

• Is about 1/3 of the size of Earth

• Easily seen at sunrise and sunset

• Very slow spin – it takes 1407.6 hours to spin

• In one orbit, Mercury spins one and one-half times

• This means Mercury’s years equal three complete

Mercury days!

• No moons!

MERCURY’S ATMOSPHERE

• The atmosphere in Mercury is mostly made up of oxygen and sodium

• The daytime temperature is 427°C while temperatures at night fall to -173°C

• This is the largest day-night temperature difference among the planets

SURFACE OF MERCURY

• 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

• The gravity of Mercury is much greater than the moon, resulting in small ejecta and rays

• Planetwide system of cliffs called scarps

INTERIOR OF MERCURY

• Has a high density made up of nickel-iron core

• Small magnetic field

• Core is molten

• Mercury’s size was much larger but outer layers may have been lost with a collision with

other celestial bodies early in history

VENUS

• Brightest planet in the sky – albedo is 0.75 therefore known as the bright ‘star’

• Aka ‘evening or morning star’

• Very thick clouds make it difficult to observe

• In 1989 Magellan spacecraft was able to map 98% of the surface using radio-telescopes

• In 2006 – Venus express gathered atmospheric data for 1.5 yrs

VENUS’ ROTATION

• Slow rotation – one day is equivalent to 243 Earth days

• Spins clockwise, unlike other planets which spin counter-clockwise

• Sunrise in the west and sets in the east

• Collision with another body may have caused this

VENUS’ ATMOSPHERE

• Most similar to the Earth

• Physical properties like diameter, mass, and density

• Venus is 92 atmospheres (atm) – 915m of water

• Clouds of sulphuric acid

• Hottest planet because of high levels of carbon dioxide

• So hot (464°C) that liquid water cannot exist

SURFACE AND INTERIOR

• 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

• 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

• The red planet

• Smaller and less dense than Earth

• Has two irregularly shaped moons – Phobos and Deimos

• Lots of exploration

• Historic Log at NASA

MARS’ ATMOSPHERE

• Mars is very similar to Venus

• Density and pressure is much lower, there greenhouse effect is not as strong

• Constant winds and dust storms can last for weeks because of thin atmosphere

MARS’ SURFACE

• Northern and southern hemisphere vary greatly

• Southern hemisphere is heavily cratered

• Lots of highlands

• Northern hemisphere has sparsely cratered plains

MARS’ SURFACE

• Four gigantic shield volcanoes are located near the equator called the Tharsis Plateau

• Largest volcano is called Olympic Mons

• 3 times higher than Mount Everest

TECTONICS

• Valles Marineris is an enormous canyon

stretching 400km long

• 10 times longer than the grand canyon

and 3 times deeper

• Formed by a fracture 3 bya

EROSIONAL FEATURES

• Dried river and lake beds

• Outflow channels and runoff channels

• Astronomers think the atmosphere was once much warmer, thicker, and richer in carbon

dioxide allowing liquid water to flow on Mars

• Small amount of Ice at the poles

ICE CAPS

• Caps grow and shrink with the

seasons

• Seasons caused by tilt and orbit

• Carbon dioxide ice

• Interior

• The interior remains unknown of

Mars as it is hypothsized that

there is a core of iron, nickel, and

sulfur

• No magnetic field

• Snow Falls