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Planets: First 100 Lessons
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No commitment, cancel at any time. Home Dmca Privacy Contact. Even after this discovery, though, astronomers felt that perturbations in the orbits of Uranus and Neptune meant that another planet must still exist beyond Neptune. Based on these predictions, Clyde Tombaugh carefully studied photographs of the sky and found a faint object that was moving compared to the background stars. The object discovered was not massive enough to perturb the orbit of Neptune, so its discovery appears to have been accidental!
This object was named Pluto and was determined to be the ninth planet in the Solar System. However, as we have learned more and more about Pluto since its discovery, it appears to be different from our expectations in a number of ways.
Planet Maths - FolensOnline
The story of the discovery of Pluto and the controversy over its current status is summarized very well in the book, Is Pluto a Planet? This is my personal favorite astronomy book, and I recommend it highly. First of all, you should realize that Pluto is, by far, the most difficult of the nine historical planets to study. It is very distant and very faint, and so, prior to July , no satellite had visited Pluto. The Hubble Space Telescope is not powerful enough to reveal much about the planet Pluto.
Compare these Hubble Space Telescope images of Mars top image and Pluto bottom two images to see the difference in the quality of data on the two planets. Now that New Horizons has provided us with much higher resolution images of Pluto and Charon, it is clear how fascinating these worlds are. The scientific work in analyzing these images is not yet done as of your time working on this course, however, many surprises have already been discussed by the New Horizons team.
- Lead Generation Machine!
- Planetary Size and Distance Comparison.
In particular, Pluto's surface appears to be much more active than was expected. Prior to New Horizons study of Pluto, we discovered from the ground that Pluto has one large moon, called Charon pictured above , which is roughly half the size of Pluto. Pluto is approximately kilometers in diameter and Charon is approximately kilometers in diameter. By observing the two objects orbit each other, we can also calculate their masses using Kepler's laws.
The orbital properties of Pluto and its largest moon are also peculiar. Like Uranus, Pluto appears to have its rotational axis almost perpendicular to its orbital axis. That is, it is orbiting on its side compared to most of the planets in our Solar System.
Charon's orbit around Pluto is aligned with Pluto's rotation axis, so, from our point of view on Earth, Charon appears to orbit Pluto perpendicularly to the path Pluto takes around the Sun. Perhaps the most peculiar aspect of Pluto's orbit is its inclination compared to the Earth's orbit around the Sun.
If you define a plane containing the Sun and the Earth, you can measure the angle that each other planet's orbital plane makes with the Earth's orbital plane. Most of the other planets have orbital inclinations of less than 3. Mercury is inclined by more than 7 degrees, but Pluto's orbit is inclined by almost 20 degrees. So, compared to the planets, Pluto's path takes it from a point high above the Earth's orbital plane to another point below the Earth's orbital plane. See the below image captured from Starry Night. In recent years, there has been some controversy over the classification of Pluto as a planet.
It is much smaller than the outer planets, and in fact, it is smaller than many moons, including Io, Europa, Ganymede, Callisto, Titan, and Triton.
Its peculiar orbit also suggests that it may have had a different origin than the planets. Some astronomers suggest that perhaps Pluto is not a planet after all, but a different class of object. Recent discoveries of other, similar objects suggest that Pluto may be just one of a family of objects outside the orbit of Neptune. Beyond Neptune, astronomers have discovered a large population of objects with sizes of about kilometers or so up to more than kilometers. There is some controversy about whether or not Kuiper predicted the existence of the objects that are named after him, so sometimes the class of objects are more simply referred to as trans-Neptunian objects or TNOs.
The Kuiper Belt is a region of space in the Solar System that is donut-shaped. Its inner radius is just past the orbit of Neptune at 30 AU, and it extends out to perhaps 50 AU or farther. The thickness of the Kuiper Belt is approximately 10 AU. Inside of this region perhaps up to , KBOs orbit the Sun! Recently, several large objects have been discovered in the Kuiper Belt that has sizes similar to Pluto's moon, Charon.
Some have formal, approved names, and others have informal names. There is an excellent, well-maintained image of these objects to scale at Wikimedia Commons.
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To get a general idea of the properties of this class of objects, you can investigate further Quaoar as an example. The discovery of these objects in the Kuiper Belt with sizes comparable to Charon suggests that there are more large KBOs left to be discovered. Because these objects are small and extremely distant, they are difficult to observe. The brightness of many of them is comparable to some of the faintest stars in the Milky Way and to some of the faint galaxies in the Hubble Deep Field.