23.2 Note Guide
The Terrestrial Planets
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In January ____________________, the space rover, _______________________________, bounced onto the
rock littered surface of Mars, known as the Red Planet
Spirit and its companion rover, __________________________________, were on the Red Planet to study
_______________________________________________________________ processes, both past and present
They also searched for signs of ______________________________________________—such as eroded rocks
or dry stream channels on Mar’s surface
For the next few months, the rovers sent back to Earth numerous ________________________________ and
___________________________________ analysis of Mars’s surface
Much of what we learn about the planets has been gathered by rovers, such as ____________________________,
or space probes that travel to the far reaches of the solar system, such as ________________________________
In this section, we’ll explore three terrestrial planets –________________________________________________
____________________________—and see how they compare with the fourth terrestrial planet—Earth
Mercury: The Innermost Planet
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Mercury, the _______________________________ and _____________________________________________
planet, is hardly larger than Earth’s moon and is smaller than three other moons in the solar system
Like our own moon, it absorbs most of the sunlight that strikes it and reflects only _______________ of sunlight
back into space
This low percentage of reflection is characteristic of terrestrial bodies that have no _________________________
Earth, on the other hand, reflects about _______________ of the light that strikes it
Most of this reflection is from ________________________________
Surface Features
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Mercury has cratered _________________________________, much like the moon, and vast smooth terrains that
resemble ____________________________
Unlike the moon, however, Mercury is a very _____________________________ planet, which implies that it
contains a large ___________________________ core for its size
Mercury also has very long ________________________________ (deep slopes) that cut across the plains and
craters alike
These scarps may have resulted from crustal changes as the planet ______________________________________
____________________________
Surface Temperature
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Mercury revolves around the sun ___________________________, but it rotates __________________________
On Mercury, one rotation requires __________________ Earth-days
Thus, a night on Mercury lasts for about ______________________________________ and is followed by
_________________________________________ of daylight
Nighttime temperatures drop as low as ___________________, and noontime temperatures exceed
__________________—hot enough to melt lead
Mercury has the greatest __________________________________ extremes of any planet
The odds of life as we know it existing on Mercury are _______________________________________________
Venus: The Veiled Planet
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Venus, second only to the __________________________ in brilliance in the night sky, is named for the goddess
of __________________________________________________
It orbits the sun in a nearly perfect ________________________________ once every ____________________
Earth-days
Venus is similar to _____________________________ in size, density, mass, and location in the solar system
Thus, it has been referred to as “_____________________________________________”
Because of these _____________________________________, it is hoped that a detailed study of Venus will
provide geologists with a better understanding of Earth’s history
Surface Features
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Venus is covered in thick ________________________________ that visible light cannot penetrate
Nevertheless, ________________________________________________ by the uncrewed Magellan spacecraft
and by instruments on Earth have revealed a varied topography with features somewhat between those of Earth
and Mars
To map Venus, _____________________________________________ are sent toward the planet’s surface, and
the heights of plateaus and mountains are measured by timing the return of the radar echo
These data have confirmed that __________________________________ volcanism and tectonic activity shape
Venus’s surface
Based on the density of ___________________________________________________, these forces must have
been very active during the recent geologic past
About _________________ of Venus’s surface consists of plains covered by volcanic flows
Some ________________________________________________ extend hundreds of kilometers—one is 6800
kilometers long
Scientists have identified __________________________________ of volcanic structures
Most are small _______________________________ volcanoes, although more than ______________ volcanoes
greater than _____________ kilometers across have been mapped
One of these volcanoes is ________________________________________, which is 400 kilometers across and
1.5 kilometers high
Flows from this volcano mostly erupted from its _____________________________________ rather than its
_______________________________, in the manner of Hawaiian shield volcanoes
Only ________________ of Venus’s surface consists of highlands that may be similar to continental area on
Earth
Tectonic activity on Venus seems to be driven by ___________________________________________________
_____________________________________ of material in the planet’s interior
The processes of _____________________________________________________ do not appear to have
contributed to Venus’s present topography
Surface Temperature
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Before the advent of s_________________________________, Venus was considered to be a possible habitat for
living things
However, evidence from ____________________________________________________ indicates otherwise
The surface temperature of Venus reaches _______________________, and its atmosphere is 97%
__________________________________________
Only small amounts of ___________________________ vapor and _______________________________ have
been detected
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Venus’s atmosphere contains a cloud layer about ________________ kilometers thick
The atmospheric pressure is ________________ times that at Earth’s surface
This _______________________________ environment makes it unlikely that life as we know it exists on Venus
Mars: the Red Planet
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Mars has evoked greater _________________________________ than any other planet
Mars is easy to __________________________________, which may explain why so many people are fascinated
by it
The surfaces of all other planets within telescopic range are hidden by __________________________—except
for ________________________________, whose nearness to the sun makes viewing it difficult
Mars is known as the _______________________________________ because it appears as a reddish ball when
viewed through a telescope
Mars also has some ___________________________ regions that change intensity during the Martian year
The most prominent telescopic features of Mars are its brilliant white ___________________________________
The Martian Atmosphere
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The Martian atmosphere has only ____________ the density of Earth’s
It is made up primarily of _______________________________________________ with tiny amounts of water
vapor
Data from Mars probes confirm that the polar caps of Mars are made of _________________________________,
covered by a thin layer of frozen carbon dioxide
As ____________________________ nears in either hemisphere, temperatures drop to ____________________,
and additional carbon dioxide is deposited
Although the atmosphere of Mars is very thin, extensive __________________________ storms occur and may
cause the ___________________________ changes observed from Earth
The ______________________________________________ winds up to _________________ kilometers per
hour can persist for weeks
Images from _____________________________ reveal a Martian landscape remarkably similar to a rocky
______________________________ on Earth, with abundant ________________________________________
and impact craters partially filled with dust
Surface Features
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___________________________________, the first spacecraft to orbit another planet, reached Mars in
_______________ amid a raging dust storm
When the dust cleared, images of Mars’ northern hemisphere revealed numerous large
________________________________
The biggest, ___________________________________________, is the size of Ohio and is __________
kilometers high—over two and a half times higher than ______________________________________________
This gigantic volcano and others resemble ____________________________________ shield volcanoes on Earth
Most Martian surface features are ________________________ by Earth standards
The highly cratered southern hemisphere is probably _____________ billion to ____________ billion years old
Even the relatively “___________________________” volcanic features of the ___________________________
hemisphere may be older than 1 billion years
Another surprising find made by Mariner 9 was the existence of several ________________________________
that are much larger than Earth’s _______________________________________________
One of the largest is _________________________________________________
It is thought to have formed by slippage of material along huge _________________________ in the crustal layer
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In respect, it would be comparable to the rift valleys of ___________________________
Water on Mars
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Some areas of Mars exhibit ____________________________________________________ similar to those
created by streams on Earth
The rover _____________________________________, for example, found evidence of evaporite minerals and
geologic formations associated with liquid water
______________________________ images have revealed ancient island sin what is now a dry streambed
When these _____________________________________ channels were first discovered, some observers
speculated that a thick water-laden atmosphere capable of generating torrential downpours once existed on Mars
The _______________________________ Martian atmosphere contains only traces of water
Images from the ___________________________________________________________ indicate that
groundwater has recently migrated to the surface
These ____________________________________ seeps have created gullies where they emerge from valley and
crater walls
Some of the escaping water may have initially frozen due to the average Martian temperatures that range between
___________________________________
Eventually, however, it seeped out as a slurry of ______________________________, ___________________,
and ___________________________ that formed the gullies
Many scientists do not accept the ________________________________ that Mars once had an active water
cycle similar to Earth’s
Rather, they believe that most of the large stream-like valleys were created by the _________________________
of surface material caused by the slow melting of subsurface ice
Data from Opportunity, however, indicates that some areas were “________________________________” in
water
It will take scientists many ___________________________, if not _______________________, to analyze the
data gathered by the latest Mars mission
Because water is an _________________________________________________________ for life, scientists and
nonscientists alike are enthusiastic about exploring this phenomenon