TransNeptunian Objects and Pluto

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Trans-Neptunian Objects and Pluto

• Astronomy 311
• Professor Lee Carkner
• Lecture 21

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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

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Pluto -- God of the Underworld

• Pluto is the God of the Dead in Roman mythology

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The Discovery of Pluto

• In the late 1800s it was believed that Neptunes
  orbit was being perturbed by a 9th planet
• In 1930 a young astronomer named Clyde Tombaugh
  found a very faint planet near Lowells predicted
  position

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The Discovery of Pluto
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Observing Pluto

• Through most telescopes Pluto simply appears as a
  faint star
• Recent attempts to develop a spacecraft have been
  curtailed

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Pluto Facts

• Size 2300 km
• Orbit 39.5 AU
• Description

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Plutos Orbit

• Pluto has the most eccentric and most inclined
  orbit in the solar system
• Plutos orbit carries it inside the orbit of
  Neptune
• Pluto is tipped on its side like Uranus

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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

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HST Images Pluto
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Features of Pluto

• The other bright regions may be areas where
  impacts have gouged out fresh ice

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Pluto and Charon
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Charon

• Plutos moon Charon was discovered as a small
  bulge in a high resolution image (1978)
• Pluto and Charon are in a close, tidally locked
  orbit

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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

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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)

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The Kuiper Belt
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Discovering Kuiper Belt Objects
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The Known Kuiper Belt

• There are now hundreds of known Kuiper Belt
  Objects (KBOs)
• Total population of large KBOs may be 70000
  (larger than 100 km)
• Kuiper belt seems to end at about 50 AU
• Larger and larger KBOs being detected
• Larger than Pluto

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Large KBO Sizes
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Known KBOs as of 10/2003
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Plutinos and Plutos

• These orbits tend to minimize perturbations from
  Neptune
• Some KBOs have fairly large sizes
• 2003 UB313 is probably larger than Pluto
• Some may have dark surfaces and be hard to see

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Is Pluto a Planet?

• Pro

• Con

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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

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The Oort Cloud

• In 1950 Dutch astronomer Jan Oort postulated a
  spherical shell of comets surrounding the solar
  system at about 50,000 AU

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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

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Diagram of the Oort Cloud
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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

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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