November 9, Imaging Foundations with Richard Wright. October 19, By: Monica Young September 28, Solar System. By: Jure Japelj September 21, September 16, August 16, July 15, Its atmosphere consists mostly of hydrogen, helium, ammonia and methane.
Saturn is about nine times Earth's radius and is characterized by large rings; how they formed is unknown. It has 53 known moons and nine more awaiting confirmation, according to NASA.
Like Jupiter, it is mostly made up of hydrogen and helium that surround a dense core and was also tracked by ancient cultures. Its atmosphere is similar to Jupiter's. Uranus has a radius about four times that of Earth's. It is the only planet tilted on its side, and it also rotates backward relative to every planet but Venus, implying a huge collision disrupted it long ago.
The planet has 27 moons, and its atmosphere is made up of hydrogen, helium and methane, according to NASA. It was discovered by William Herschel in Neptune also has a radius about four times that of Earth's. Like Uranus, its atmosphere is mostly made up of hydrogen, helium and methane.
It has 13 confirmed moons and an additional one awaiting confirmation, according to NASA. It was discovered by several people in Super-Earths: Scientists have found a multitude of "super-Earths" planets between the size of Earth and Neptune in other solar systems. There are no known super-Earths in our own solar system, although some scientists speculate there may be a "Planet Nine" lurking in the outer reaches of our solar system.
Scientists are studying this category of planets to learn whether super-Earths are more like small giant planets or big terrestrial planets. Astronomers think the giants first formed as rocky and icy planets similar to terrestrial planets. However, the size of the cores allowed these planets particularly Jupiter and Saturn to grab hydrogen and helium out of the gas cloud from which the sun was condensing, before the sun formed and blew most of the gas away.
Since Uranus and Neptune are smaller and have bigger orbits, it was harder for them to collect hydrogen and helium as efficiently as Jupiter and Saturn. This likely explains why they are smaller than those two planets. On a percentage basis, their atmospheres are more "polluted" with heavier elements such as methane and ammonia because they are so much smaller. Scientists have discovered thousands of exoplanets. The collision of more than 20 large pieces of Comet Shoemaker—Levy 9 with Jupiter in the summer of see Figure 3 is one dramatic example of this process.
Figure 3: Comet Shoemaker—Levy 9. The comet was approximately million kilometers from Earth, heading on a collision course with Jupiter. Weaver STScl , E. Smith STScl. Figure 4: Jupiter with Huge Dust Clouds. The Hubble Space Telescope took this sequence of images of Jupiter in summer , when fragments of Comet Shoemaker—Levy 9 collided with the giant planet. Here we see the site hit by fragment G, from five minutes to five days after impact.
Several of the dust clouds generated by the collisions became larger than Earth. Hammel, NASA. During the time all the planets have been subject to such impacts, internal forces on the terrestrial planets have buckled and twisted their crusts, built up mountain ranges, erupted as volcanoes, and generally reshaped the surfaces in what we call geological activity.
Among the terrestrial planets, Earth and Venus have experienced the most geological activity over their histories, although some of the moons in the outer solar system are also surprisingly active. In contrast, our own Moon is a dead world where geological activity ceased billions of years ago. Geological activity on a planet is the result of a hot interior.
The forces of volcanism and mountain building are driven by heat escaping from the interiors of planets. As we will see, each of the planets was heated at the time of its birth, and this primordial heat initially powered extensive volcanic activity, even on our Moon. But, small objects such as the Moon soon cooled off. The larger the planet or moon, the longer it retains its internal heat, and therefore the more we expect to see surface evidence of continuing geological activity.
The effect is similar to our own experience with a hot baked potato: the larger the potato, the more slowly it cools.
If we want a potato to cool quickly, we cut it into small pieces. For the most part, the history of volcanic activity on the terrestrial planets conforms to the predictions of this simple theory. The Moon, the smallest of these objects, is a geologically dead world. Although we know less about Mercury, it seems likely that this planet, too, ceased most volcanic activity about the same time the Moon did.
Mars represents an intermediate case. It has been much more active than the Moon, but less so than Earth. Earth and Venus, the largest terrestrial planets, still have molten interiors even today, some 4. The giant planets have dense cores roughly 10 times the mass of Earth, surrounded by layers of hydrogen and helium.
The terrestrial planets consist mostly of rocks and metals. They were once molten, which allowed their structures to differentiate that is, their denser materials sank to the center.
The Moon resembles the terrestrial planets in composition, but most of the other moons—which orbit the giant planets—have larger quantities of frozen ice within them. In general, worlds closer to the Sun have higher surface temperatures. The surfaces of terrestrial planets have been modified by impacts from space and by varying degrees of geological activity. Skip to main content.
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