Transcript Moreover atmosphere

The Solar System:
An Insider’s Guide
Wednesday!
Inner Terrestrial Planets:
Mercury, Venus, Earth and Mars
Day
Wednesday
Content
The Inner Terrestrial Planets
Activities
Cratering
Phases of Venus
Solar Observing
Habitable Zone
Come and Visit Mars
Music
News
Grand Return of Mars
Mercury—The Hot Spot
Cratered Surface, Smallish, Super-hot, not much air, very dense,
large core. The Moon’s big brother?
Mariner 10 launched in
1973, encountered Venus
and then went into orbit
around Mercury.
Mariner Spacecraft orbit
was twice Mercury’s
orbit, but it only mapped
one side. Why?
Mercury Day/Year
Mercurian Year: A year on Mercury takes 87.97 Earth days; it takes 87.97 Earth days for Mercury to
orbit the sun once.
Mercurian Sidereal Day: Each sidereal day on Mercury takes 58.65 Earth days; it takes Mercury 58.65
days (2/3's of its year) to rotate around its axis once. One day on Mercury seems to last two Mercurian years
(or 176 Earth days), i.e., sunrise to sunrise. It is daytime for one Mercurian year, and nighttime for one
Mercurian year. (It used to be thought that Mercury always kept the same side side towards the sun, but this
is not true.)
Mercury’s Hidden Side
Mercury at a glance
Densest planet.
Smallest Terrestrial Planet.
Surface very similar to the Moon (cratering, no evidence of
present techtonic or volcanic activity.
Tides with Sun forced it into a 3:2 spin:orbit resonance with no
axial tilt, similar to the effects Earth—Moon tides have had on
the Moon’s spin:orbit.
At this point in time, the least studied of the Terrestrial Planets,
but the MESSENGER project hopes to change all that...
Venus-An important stop on our modern
view of the Universe, and it’s right next door!
Galileo could not ignore his incredible discovery— the planet Venus,
long known to be different in kind from the fixed stars, actually
undergoes orbital phases, similar to those of Earth’s Moon, but with an
important difference. The *size* of the planet also changes in step with
the phase. This could only be explained if Venus actually orbits the Sun
(and not the Earth). Galileo had observed the birth of a new view of the
Universe.
Transits of Venus: rare minieclipses, one coming soon!
Several times a millennium, the orbits
of the Earth and Venus line up so that from
Earth we can watch Venus pass right in front of
the Sun’s disk! There are always two transits
separated by eight years. Since the time of
Galileo, transits have given us a rare
opportunity to learn about the scale of the solar
system. The atmosphere of Venus was
discovered during one of the 18th century
transits. The next transit happens in June 2004.
Appearance of Venus
in front of the Sun.
More on Venus
Venus rotates in the opposite direction of the Earth (and the other planets, except possibly Uranus).
Looking from the north, Venus rotates clockwise, while the other planets rotate counterclockwise. From
Venus, the Sun would seem to rise in the west and set in the east (the opposite of Earth). No one knows
why Venus has this unusual rotation.
Images of
Venus
Venus has no water, no ice—not even at the poles—, lots of volcanic activity, no plate
tectonics, and a dense carbon dioxide atmosphere. The abundant CO2 sets up a strong
greenhouse effect that works to keep the surface temperature above 700F.
Mars
Mars has two small moons, Phobos
and Deimos (“Fear” and “Terror”).
The huge feature across the globe is
a giant canyon on Mars that puts the
Grand Canyon to shame, and is
evidence of early geologic activity.
Water exists only as “permafrost” and in
large and variable plar caps.
Mars: So long our mental playground for
life beyond Earth
Olympus Mons—the Solar
System’s largest Volcano
Ancient dry riverbeds.
Yogi.
Another Face on Mars!
More on Mars
Ancient Life on Mars?
It’s clear that Mars did have significant
liquid water flowing on its surface long ago,
and probably a more substantial
atmosphere. The meteor at right is believed
to come from Mars because the abundance
of elements found as gas pockets within it
match the Mars atmosphere, while they are
a very poor match for Earth’s atmosphere.
The conclusion drawn is that these pockets
of gas collected in the rock as it was
forming, on the surface of Mars. It reveals
tantalizing, though not conclusive, evidence
that bacteria existed there billions of years
ago.
Earth in Context
Earth as seen
from Apollo 13
Earth’s Ozone
layer absorbs
much damaging
UV radiation
from the Sun
GOES-8 Infrared channel
showing water vapor
global circulation
Earth’s volcanic and tectonic
processes are still at work
reshaping our land forms and
the face of the planet.
Unlike Earth, Mercury and
Venus have no Moon. This
view taken by the Galileo
Spacecraft as it left orbit.
All terrestrial planets have
metal cores, an abundance of
heavier metals, are similar in
size, and once had gaseous
atmospheres. Of these four
planets, it appears only the
Earth is in the right place at
the right time. Moreover, our
large Moon has helped to
regulate our spin and keep the
planet habitable.
Terrestrial Planets, family portrait