Why did Venus turn itself inside-out?
Why did Venus turn itself inside-out?
Years ago, planetary scientists thought of Venus as Earth's sister planet. Similar in size, both close to the Sun, both rocky bodies, Earth and Venus were practically considered
two of a kind. That abruptly changed, however, when astronomers got their first close- up look at Venus. The moment arrived in 1962, when Mariner 2 flew by the planet, and far more forcefully in 1970, when Venera 7 touched down on the hellishly hot surface. Not only do surface temperatures on our sister planet exceed 750° F (400° C), but Venus'thick carbon- dioxide atmosphere produces a greenhouse effect that hosts sulfur- dioxide and sulfuric-acid clouds. It's not a friendly environment for living things of any sort.
VOLCANIC VENUS. Volcanoes in a region on Venus called Guinevere Planitia lowland suggest thick, sticky lava oozed from a point at the surface here. The center volcano spans 31 miles (50 km).
Scientists'understanding of Venus and its geology catapulted forward with the most significant mission thus far, the Magellan spacecraft. It arrived in venusian orbit in 1990 and continued to collect data through 1994.
Magellan mapped 98 percent of the planet's surface and returned thousands of spectacular views of Venus'geological features. Almost one-quarter of the images returned by Magellan became com
Surface
temperatures on our sister planet exceed 750° F (400° C).
puterized, 3-D images of regions with altitude effects exaggerated by the image processors. For the first time, humans had a good look at what Venus is really like.
There were surprises. The most amazing was the relative lack of craters compared with other inner solar system bodies like the Moon, Mars, and Mercury. Water, wind, volcanoes, and tectonic shifts constantly resurface our planet. Venus must be hiding many old craters, too. Astronomers wondered what resurfacing forces could keep Venus'surface looking so young. Astronomers observed other weird artifacts on the planet's surface, in addition to many substantial volcanoes
NASA/JPL
Color shows radius (km)
6,048 6,050 6,052 6,054 6,058 6,060 6,062
that suggest an active geology in the recent past. These include coronae (crown-shaped surface features), tesserae (crunched features where the planet's crust is pushed together and buckles), and arachnoids (circular or oval features filled with concentric rings) — so named because they are spiderlike in appearance. Moreover, scientists found trace signs of erosion and tectonic shifts on our sister planet.
As scientists looked more carefully at the body of data returned from Magellan, it became clearer that this was a planet that had, somehow, turned itself inside-out. Dating various features on the planet's surface
subsequently revealed Venus must have undergone a cataclysmic upheaval about 300 to 500 million years ago, very recently in geologic terms. At about that time, Venus' surface seems to have been wiped clean.
Planetary scientists believe strongly in the gradual, slow, methodical workings of
HELLISH WORLD. Scientists created this hemispheric view of Venus using Magellan spacecraft data. The image is color-coded to elevation and reveals features as small as 2 miles across, nasa/jpl
nature. Venus'geology placed them in an awkward position, because a huge, catastrophic event apparently attacked the planet suddenly.
Nonetheless, in 1992, Gerald Schaber of the U.S. Geological Survey wrote that what was observed on the planet may have resulted from a "global resurfacing event or events." Don Turcotte of Cornell University followed a year later, proposing the venu- sian crust may have grown so thick over time that it trapped the planet's heat inside, which eventually flooded the planet with molten lava. Turcotte described the process as cyclical, suggesting that the event of several hundred million years ago may have been just one in a series.
Others have suggested that low-level volcanism may be responsible for coating the planet's surface over time without a need for any global catastrophes. But the current thinking seems to favor the huge maelstrom."All the geologists agree," says Schaber,"Something very strange happened." Scientists have yet to determine exactly why the planet resurfaced globally and what mechanisms were involved. With the European Venus Express mission inserted into orbit in 2006, further clues will continue to roll in.EE
HILLY LAVA Three thick dome-like hills dominate the center of this 3-D Venus image made using Magellan data. The hills, on the eastern edge of Alpha Regio, were formed by thick eruptions of lava that solidified on level ground.
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Years ago, planetary scientists thought of Venus as Earth's sister planet. Similar in size, both close to the Sun, both rocky bodies, Earth and Venus were practically considered
two of a kind. That abruptly changed, however, when astronomers got their first close- up look at Venus. The moment arrived in 1962, when Mariner 2 flew by the planet, and far more forcefully in 1970, when Venera 7 touched down on the hellishly hot surface. Not only do surface temperatures on our sister planet exceed 750° F (400° C), but Venus'thick carbon- dioxide atmosphere produces a greenhouse effect that hosts sulfur- dioxide and sulfuric-acid clouds. It's not a friendly environment for living things of any sort.
VOLCANIC VENUS. Volcanoes in a region on Venus called Guinevere Planitia lowland suggest thick, sticky lava oozed from a point at the surface here. The center volcano spans 31 miles (50 km).
Scientists'understanding of Venus and its geology catapulted forward with the most significant mission thus far, the Magellan spacecraft. It arrived in venusian orbit in 1990 and continued to collect data through 1994.
Magellan mapped 98 percent of the planet's surface and returned thousands of spectacular views of Venus'geological features. Almost one-quarter of the images returned by Magellan became com
Surface
temperatures on our sister planet exceed 750° F (400° C).
puterized, 3-D images of regions with altitude effects exaggerated by the image processors. For the first time, humans had a good look at what Venus is really like.
There were surprises. The most amazing was the relative lack of craters compared with other inner solar system bodies like the Moon, Mars, and Mercury. Water, wind, volcanoes, and tectonic shifts constantly resurface our planet. Venus must be hiding many old craters, too. Astronomers wondered what resurfacing forces could keep Venus'surface looking so young. Astronomers observed other weird artifacts on the planet's surface, in addition to many substantial volcanoes
NASA/JPL
Color shows radius (km)
6,048 6,050 6,052 6,054 6,058 6,060 6,062
that suggest an active geology in the recent past. These include coronae (crown-shaped surface features), tesserae (crunched features where the planet's crust is pushed together and buckles), and arachnoids (circular or oval features filled with concentric rings) — so named because they are spiderlike in appearance. Moreover, scientists found trace signs of erosion and tectonic shifts on our sister planet.
As scientists looked more carefully at the body of data returned from Magellan, it became clearer that this was a planet that had, somehow, turned itself inside-out. Dating various features on the planet's surface
subsequently revealed Venus must have undergone a cataclysmic upheaval about 300 to 500 million years ago, very recently in geologic terms. At about that time, Venus' surface seems to have been wiped clean.
Planetary scientists believe strongly in the gradual, slow, methodical workings of
HELLISH WORLD. Scientists created this hemispheric view of Venus using Magellan spacecraft data. The image is color-coded to elevation and reveals features as small as 2 miles across, nasa/jpl
nature. Venus'geology placed them in an awkward position, because a huge, catastrophic event apparently attacked the planet suddenly.
Nonetheless, in 1992, Gerald Schaber of the U.S. Geological Survey wrote that what was observed on the planet may have resulted from a "global resurfacing event or events." Don Turcotte of Cornell University followed a year later, proposing the venu- sian crust may have grown so thick over time that it trapped the planet's heat inside, which eventually flooded the planet with molten lava. Turcotte described the process as cyclical, suggesting that the event of several hundred million years ago may have been just one in a series.
Others have suggested that low-level volcanism may be responsible for coating the planet's surface over time without a need for any global catastrophes. But the current thinking seems to favor the huge maelstrom."All the geologists agree," says Schaber,"Something very strange happened." Scientists have yet to determine exactly why the planet resurfaced globally and what mechanisms were involved. With the European Venus Express mission inserted into orbit in 2006, further clues will continue to roll in.EE
HILLY LAVA Three thick dome-like hills dominate the center of this 3-D Venus image made using Magellan data. The hills, on the eastern edge of Alpha Regio, were formed by thick eruptions of lava that solidified on level ground.
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