Astronomers have discovered hundreds of Jupiter-like planets in our galaxy. However, a handful of the planets found orbiting distant stars are more Earth-sized. This gives hope to astrobiologists, who think we are more likely to find life on rocky planets with liquid water.The rocky planets found so far are actually more massive than our own. Dimitar Sasselov, professor of astronomy at Harvard University, coined the term "Super-Earths" to reflect their mass rather than any superior qualities. But Sasselov says that these planets - which range from about 2 to 10 Earth masses - could be superior to the Earth when it comes to sustaining life.
On Shaky Ground
It is said that 99 percent of all species that ever lived have gone extinct. Earth, it seems, is a tough place to call home. Our planet has gone through Ice Ages and global warming trends, it has been hit by comets and asteroids (leading, in one case, to a mass extinction that felled the mighty dinosaurs), and the amount of oxygen in the atmosphere has risen and fallen over time. Our planet is always in a state of flux, and life must adapt to these changes or die.
The shifting of tectonic plates is another example of Earth's restless nature. Continents bang together, forming mountains, only to be later torn apart. Islands grow from underwater volcanoes, and elements are liberated from rocks when they are melted beneath the crust.
While all this geologic activity makes us literally stand on shaky ground, scientists have come to believe that tectonics is one of the key features of our planet which makes life possible. If not for tectonics, carbon needed by life would stay locked within rocks.
The fear today is that too much carbon dioxide in the atmosphere will lead to global warming. Yet too little carbon dioxide in the atmosphere would make Earth a much colder place, and the photosynthetic plants and algae that rely on CO2 would perish. The demise of these oxygen-producing organisms would leave us all gasping for breath.
According to Sasselov, Earth's mass helps keeps tectonics in action. The more massive a planet, the hotter its interior. Tectonic plates slide on a layer of molten rock beneath the crust called the mantle. Convective currents within the mantle push the plates around.
For smaller planets like Mars, the interior is not hot enough to drive tectonics. Super Earths, with a larger and hotter interior, would have a thinner planetary crust placed under more stress.
This probably would result in faster tectonics, as well as more earthquakes, volcanism, and other geologic upheavals. In fact, Sasselov says the plate tectonics on Super Earths may be so rapid that mountains and ocean trenches wouldn't have much time to develop before the surface was again recycled.
Venus, only slightly less massive than Earth, has had a great deal of volcanic activity, but it does not appear to have tectonics. This may be because low mass planets need water to lubricate the process, and Venus lost its water long ago through evaporation. Sasselov says Earth has just enough water for tectonics to work. Tectonics on Super Earths might be so efficient that water isn't even needed.
On the other hand, it's possible that a SuperEarth could be entirely covered by water. Sasselov says that in the case of such an ocean world, most of the water will be in an exotic state known as iceVII - a very compressed, hard ice with a melting point above 212 degrees Fahrenheit (100 degrees Celsius).
Whether made of rock or ice, Sasselov says Super Earths will be only 1 or 2 times the actual size of Earth because they become densely compressed as they gain mass. This higher density will result in greater gravity. Sasselov says the most massive Super Earth would have about 3 times the gravity of Earth.
Tests of human resistance to vertical G-force, where the blood is pulled down to the legs, have found the typical person can tolerate up to 5 Gs before losing consciousness. So while you might feel much heavier walking on a Super Earth, the extra gravity wouldn't be beyond what human explorers could endure. Of course, any life that evolved on a Super Earth would be adapted to the greater gravity, just as a human feels comfortable on the 1 G surface of Earth.
On Shaky Ground
It is said that 99 percent of all species that ever lived have gone extinct. Earth, it seems, is a tough place to call home. Our planet has gone through Ice Ages and global warming trends, it has been hit by comets and asteroids (leading, in one case, to a mass extinction that felled the mighty dinosaurs), and the amount of oxygen in the atmosphere has risen and fallen over time. Our planet is always in a state of flux, and life must adapt to these changes or die.
The shifting of tectonic plates is another example of Earth's restless nature. Continents bang together, forming mountains, only to be later torn apart. Islands grow from underwater volcanoes, and elements are liberated from rocks when they are melted beneath the crust.
While all this geologic activity makes us literally stand on shaky ground, scientists have come to believe that tectonics is one of the key features of our planet which makes life possible. If not for tectonics, carbon needed by life would stay locked within rocks.
The fear today is that too much carbon dioxide in the atmosphere will lead to global warming. Yet too little carbon dioxide in the atmosphere would make Earth a much colder place, and the photosynthetic plants and algae that rely on CO2 would perish. The demise of these oxygen-producing organisms would leave us all gasping for breath.
According to Sasselov, Earth's mass helps keeps tectonics in action. The more massive a planet, the hotter its interior. Tectonic plates slide on a layer of molten rock beneath the crust called the mantle. Convective currents within the mantle push the plates around.
For smaller planets like Mars, the interior is not hot enough to drive tectonics. Super Earths, with a larger and hotter interior, would have a thinner planetary crust placed under more stress.
This probably would result in faster tectonics, as well as more earthquakes, volcanism, and other geologic upheavals. In fact, Sasselov says the plate tectonics on Super Earths may be so rapid that mountains and ocean trenches wouldn't have much time to develop before the surface was again recycled.
Venus, only slightly less massive than Earth, has had a great deal of volcanic activity, but it does not appear to have tectonics. This may be because low mass planets need water to lubricate the process, and Venus lost its water long ago through evaporation. Sasselov says Earth has just enough water for tectonics to work. Tectonics on Super Earths might be so efficient that water isn't even needed.
On the other hand, it's possible that a SuperEarth could be entirely covered by water. Sasselov says that in the case of such an ocean world, most of the water will be in an exotic state known as iceVII - a very compressed, hard ice with a melting point above 212 degrees Fahrenheit (100 degrees Celsius).
Whether made of rock or ice, Sasselov says Super Earths will be only 1 or 2 times the actual size of Earth because they become densely compressed as they gain mass. This higher density will result in greater gravity. Sasselov says the most massive Super Earth would have about 3 times the gravity of Earth.
Tests of human resistance to vertical G-force, where the blood is pulled down to the legs, have found the typical person can tolerate up to 5 Gs before losing consciousness. So while you might feel much heavier walking on a Super Earth, the extra gravity wouldn't be beyond what human explorers could endure. Of course, any life that evolved on a Super Earth would be adapted to the greater gravity, just as a human feels comfortable on the 1 G surface of Earth.
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