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