trans-neptunian objects and pluto astronomy 311 professor lee carkner lecture 21
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Trans-Neptunian Objects and Pluto
Astronomy 311Professor Lee
CarknerLecture 21
Trans-Neptunian Region
Beyond Neptune is the region of small, icy, Trans-Neptunian Objects
The region is populated by icy planetesimals that either formed at the edge of the solar system or were ejected out by the planets
Pluto -- God of the Underworld
Pluto is the God of the Dead in Roman mythology
The Discovery of Pluto In the late 1800’s it was believed that
Neptune’s orbit was being perturbed by a 9th planet
In 1930 a young astronomer named Clyde
Tombaugh found a very faint planet near Lowell’s predicted position
The Discovery of Pluto
Observing Pluto
Through most telescopes Pluto simply appears as a faint star
Recent attempts to develop a
spacecraft have been curtailed
Pluto Facts
Size: 2300 km
Orbit: 39.5 AU
Description:
Pluto’s Orbit Pluto has the most eccentric and most
inclined orbit in the solar system
Pluto’s orbit carries it inside the orbit of Neptune
Pluto is tipped on its side like Uranus
Composition of Pluto Pluto has a density of 2000 kg/m3
Pluto is probably composed of ice and rock Spectra of Pluto reveal the presence of
methane, nitrogen and carbon monoxide
HST Images Pluto
Features of Pluto
The other bright regions may be areas where impacts have gouged out fresh ice
Pluto and Charon
Charon Pluto’s moon Charon was discovered as a
small bulge in a high resolution image (1978)
Pluto and Charon are in a close, tidally locked orbit
Where Do Comets Come From?
Comets are small (few km) icy bodies that sometimes come in to the inner solar system on highly elliptical orbits
Short period comets
Long period comets
The Kuiper Belt
Around 1950 Kuiper and Edgeworth proposed a belt of comets out beyond Neptune
In 1992 the first (besides Pluto) Kuiper belt object was discovered (QB1)
The Kuiper Belt
Discovering Kuiper Belt
Objects
The Known Kuiper Belt There are now hundreds of known Kuiper Belt
Objects (KBOs)
Total population of large KBO’s may be 70000 (larger than 100 km)
Kuiper belt seems to end at about 50 AU
Larger and larger KBO’s being detected
Larger than Pluto
Large KBO Sizes
Known KBOs as of 10/2003
Plutinos and Plutos
These orbits tend to minimize perturbations from Neptune
Some KBO’s have fairly large sizes
2003 UB313 is probably larger than Pluto
Some may have dark surfaces and be hard to see
Is Pluto a Planet?
Pro
Con
What Makes Something a Planet?
Planets used to be obvious
Needed new definition when rest of solar system was discovered with telescopes
The International Astronomical Union (which has authority over these things) calls Pluto a planet
The Oort Cloud In 1950 Dutch astronomer Jan Oort
postulated a spherical shell of comets surrounding the solar system at about 50,000 AU
Population of the Oort Cloud
The Oort cloud is the source of the long period comets
They are too far away to see, so
we only have indirect methods of studying them
Diagram of the Oort Cloud
Summary Past the orbit of Neptune the solar system
is made up of many small icy bodies Kuiper Belt
extends from 30-500 AU formed from left over planetesimals at the
edge of the solar system Oort Cloud
extends from 1000-100,000 AU formed from ejected icy planetesimals
Summary: Pluto Description: small, cold , distant Pluto resembles a large Kuiper belt object
more than a planet Has a closely orbiting large moon Charon Properties
Thin atmosphere Very cold (~50 K) Bright surface features possibly composed of
fresher ice
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