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Nancy Gupton and Kitry Krause
Photograph by Magellan Project, JPL, NASA
Photograph by Mariner 10, NASA
Photograph by Corbis
Photograph by NASA
Photograph by NASA Great Images in Nasa Collection
Photograph by The Hubble Heritage Team
Photograph by NASA/JPL
Photograph by Kenneth Seidelmann, U.S. Naval Observatory, and NASA
Photograph by NASA
Photograph by NASA Jet Propulsion Laboratory
Photograph by NASA, JPL, Michael W. Carroll
Photograph by R. Hurt (SSC-Caltech), JPL-Caltech, NASA
Photograph by Thierry Lombry
Photograph by NASA, ESA, Southwest Research Institute, Cornell University, University of Maryland, College Park, and M. Mutchler and Z. Levay
Photograph by NASA/JPL-Caltech/S. J. U. Higdon (Cornell University)
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A thick, rapidly spinning atmosphere
The lack of moons
The planet's distance from the sun
Heavy volcanic activity
These two gases absorb infrared radiation, trapping heat from the sun on Venus's surface—temperatures can reach over 850 degrees Fahrenheit, hot enough to melt lead. The thick atmosphere also contributes to the intense pressure on Venus, the same pressure found at a depth of 2,953 feet in Earth's oceans.]]>
It virtually has no atmosphere, which allows heat to escape
Its thick atmosphere, which doesn't allow sunlight to reach the surface
The angle of its axis
Its iron core, 75 percent of the planet's radius
The similarities end there, since Venus's atmosphere makes its surface unsuitable for the life that Earth's combination of air, land, and water supports.]]>
The tallest volcanic mountain
The smallest moon
The largest impact crater
The most seasons
Located in the northern Tharsis region of Mars, Olympus Mons and other volcanoes are so huge they deform the roundness of the red planet.
Mars also boasts the solar system's largest rift valley, Valles Marineris, which on Earth would stretch from New York to Los Angeles.]]>
Phobos, the larger of Mars's moons, is identifiable by the six-mile crater that covers nearly half the moon's width. In its present orbit, it's spiraling inward toward Mars; in 50 million years it will either crash into the planet or break up, possibly leaving a ring around the planet.]]>
Twice its current size
Ten times larger
Eighty times larger
A hundred million times larger
Pieces of comets
Pieces of asteroids
All of the above
The seven dwarfs in "Snow White"
Characters in William Shakespeare's plays
Characters in Homer's "Iliad"
Characters from Walt Disney movies
A ring around Neptune
Six new moons
Water on Triton, Neptune's largest moon
All of the above
Voyager 2 also sent back images of Neptune's largest moon, Triton, and a Great Dark Spot, similar to the Great Red Spot on Jupiter.]]>
It can't clear other objects from its orbit.
It takes too long to orbit the sun.
It doesn't have enough gravity to keep it in a ball-like shape.
It orbits within the Kuiper belt.
Since Pluto can't clear other objects from its orbit, it now belongs to a new class of celestial bodies known as dwarf planets.]]>
3.7 billion miles
4.2 billion miles
6.4 billion miles
100 billion miles
Not all dwarf planets are plutoids, because a plutoid must orbit outside Neptune. Ceres isn't a plutoid, because it orbits inside Neptune, between Mars and Jupiter.]]>
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