a double planet at the edge of our solar system
| Lecture | |
| Pluto and Charon
a double planet at the edge of our solar system |
After listening to the lecture and reading these on-line notes, you should be able to
List the primary surface composition of Pluto and Charon.
Explain how Pluto and Charon develop and lose their atmospheres during their orbit.
Describe the characteristics of the tidal locking between this double planet.
Describe what the Kuiper Belt is and how it is thought to have formed.
List two reasons why Pluto and Charon (and Neptune's moon Triton) could be considered members of the Kuiper Belt rather than planets or moons.
Take the Quiz!
The surface of Pluto is primarily ices: frozen nitrogen, carbon monoxide, and
methane. The dark contrasts may be due to rock, exposed by winds on Pluto.
Pluto and Charon are small, comet-like bodies, approximately 40 AU's from our
Sun. Because of their eccentric orbit, they spend part of the time inside of
Neptune's orbit. This slight warming of this double planet creates a tenuous,
temporary atmosphere. Because Pluto and Charon are so close to each other
(a mere 19,800 km or about 12,200 miles), when the surface ices of Pluto start to
sublimate part of its atmosphere may be transferred to Charon.
Pluto was discovered in 1930 by Clyde Tombaugh; its moon, Charon, in 1978. Charon
is about half the size of Pluto.
Pluto and Charon, by
Hubble Space Telescope.
Pluto and Charon are so close to each other that they are in synchronous rotation, with a period of 6.387 days (a true tidal lock!). If you were on the moon-side of Pluto, you would always see Charon; never if you were on the opposite side. Charon would go through phases. If you were on the planet side of Charon, you would always see Pluto; never if you were on the opposite side. Pluto would go through phases. (The bulges are exaggerated in this image from "The Cosmic Perspective," (Addison & Wesley).)
Pluto shares one thing in common with another outer planet, Uranus. Pluto is also tipped with respect to the orbital plane, by 122 degrees. Pluto also has a lot in common with Neptune's moon Triton, being nearly the same size and probably of similar composition.
GRAVITY OF THE PLANETS acted during the early stages of the solar system to sweep away small bodies within the orbit of Neptune. Some of these objects plummeted toward the sun; others sped outward toward the distant Oort cloud (From Scientific American -- see link below) The first of the group of objects that have become known as the Kuiper belt was discovered in 1992, after years of fruitless search, by Jane Luu and Doug Jewitt. The presence of these objects was predicted by Dutch-American astronomer Gerard P. Kuiper:
Kuiper and others reasoned that the disk of the solar system should not end abruptly at Neptune or Pluto (which vie with each other for the distinction of being the planet most distant from the sun). He envisioned instead a belt beyond Neptune and Pluto consisting of residual material left over from the formation of the planets. The density of matter in this outer region would be so low that large planets could not have accreted there, but smaller objects, perhaps of asteroidal dimensions, might exist. Because these scattered remnants of primordial material were so far from the sun, they would maintain low surface temperatures. It thus seemed likely that these distant objects would be composed of water ice and various frozen gases-making them quite similar (if not identical) to the nuclei of comets. (Scientific American, May 1996)
Planet or King of the Kuiper Belt
Well, those who cry "planet" at the moment are ahead, with official recognition that Pluto remains a planet by the IAU (International Astronomical Union), the official naming body. But, stay tuned. Some astronomers believe it is just a matter of time before we find another object out there by Pluto that may be larger than Pluto. For example, take a look at these trans-Neptunian objects and note that Pluto is the largest, but not by much:
So, for now Planet!
[but, also a famous puppy]
Inside the Solar Nebula:
Inside the solar nebula. This view shows the scene in the region of the Earth less than a
million years after the sun formed. Small grains of dust are aggregating into "planetesimals."
Planets grew by collisional aggregation of these objects.
Painting copyright William K. Hartmann.
Except for addressing the possibility of life on other planets and the new science known as astrobiology, this lecture concludes our study of the planets. With Pluto, Charon, Triton and the other trans-Neptunian (Kuiper Belt) objects, we have a complete picture of our solar system, and a coherent picture of why our solar system looks, acts, and is as it is.
What Lurks in the Outer Reaches of the Solar System?
The Kuiper Belt from Scientific American
Read about Plutinos, small orbiting bodies that share a 3:2 resonance with Neptune just like Pluto.
