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Home , Comet tail, Neptune, Pluto

1 Lecture 16 Dwarf and January 8a, 2014 2 -- Basic Information

• Discovered by in 1930

• Period: Porb = 248 years • Distance: a = 39.5 AU • 3 (, , ) • Demoted to Dwarf in 2006

3 General Characteristics

• = 0.0025 times the – Determined by using General form of Kepler’s 3rd Law • Radius = 0.2 Earth – Determined from of Charon •  = 2300 kg/m3 ice and rock

• Little known due to its large distance from the . • Pluto is tilted on its side.

4 Spin and • Highly elliptical orbit (e = 0.25) – Pluto is sometimes closer to the Sun than – Orbit is tipped 17° from – Aphelion = 49.3 AU – Perihelion = 29.7 AU

• Both Pluto and Charon are tidally locked in synchronous .

– Pspin= 6.4 days (Pluto and Charon) – Porb = 6.4 days (Charon) 5

Surface Properties

• Planet predominantly ice • Frozen detected on surface • May have thin methane

• May be similar to 6 Surface Features

Pluto has never been visited by a (the probe is on its way and will arrive in 2015) so there are no clear images of its surface. At left are Hubble Space global maps of Pluto (smaller insets are actual images) that show bright and dark areas visible as the rotates. At right is a composite in true color that is derived from eclipses by Charon. 7 If Pluto is sometimes closer to the Sun than Neptune, why doesn’t it ever collide with Neptune?

A. They do collide every few thousand years. B. Neptune is primarily made of gases, so Pluto would pass right through it. C. Pluto’s orbit is steeply tilted with respect to Neptune’s, so they never actually cross. D. The synchronized timing of their orbit periods ensures a collision never occurs. 8 If Pluto is sometimes closer to the Sun than Neptune, why doesn’t it ever collide with Neptune?

A. They do collide every few thousand years. B. Neptune is primarily made of gases, so Pluto would pass right through it. C. Pluto’s orbit is steeply tilted with respect to Neptune’s, so they never actually cross. D. The synchronized timing of their orbit periods ensures a collision never occurs. 9 http://photojournal.jpl.nasa.gov/catalog/PIA05567 Origins of Pluto • Composition much more like a • Other objects similar to Pluto (such as Sedna, below) are being found in the

http://photojournal.jpl.nasa.gov/catalog/PIA05568 10 Comparison of distant planets

Object Year Diameter Perhelion Aphelion discovered (km) (AU) (AU) Pluto 1930 2380 29.7 49.4 Quaoar 2002 1250 41.9 44.9 Sedna 2003 1800 76.1 942 2005 2860 38.2 97.6

2005 FY9 2005 1400? 38.7 52.6

2003EL61 2005 1500? 35.2 51.5 11

Solar System Debris

• After formation of the , some material was left over. • , comets, and give clues to composition of early solar system. – Have undergone little processing (heating, weathering). 12 Comets • Made of ices and some rocky material • Travel in very elliptical about the Sun.

Comet McNaught, January 2007. Click here for more info. 13 • Long period comets – May orbit once every million years – Origin in Oort -- spherical cloud up to 100,000 AU from Sun • Short period comets – Periods < 200 years – Origin in Kuiper Belt -- disk shape 30-100 AU from Sun.

14 Anatomy of a • Nucleus – few km in diameter – ices and rocky material (“dirty ice ball”) – Only part of a comet that exists away from the Sun. • -- Gases evaporated off of surface of nucleus as Sun heats it. 15 • envelope • Tails -- Always point away from the Sun – Dust tail -- small dust particles, slightly curved in direction of orbit. – Ion tail -- ionized molecules pushed straight back by solar 16

Neither tail trails the comet like a jet contrail. In fact, the tail sometimes leads the comet! 17 Suppose the of a comet’s tail is 8.5×10−17 kg/m3 and it’s a cylinder 5×105 km in radius and 1.0 AU (1.5×108 km) long. What is the total mass of the tail ? A. 1.0×1013 kg B. 5.0×1010 kg C. 1.0×106 kg D. 20,000 kg 18 Suppose the density of a comet’s tail is 8.5×10−17 kg/m3 and it’s a cylinder 5×105 km in radius and 1.0 AU (1.5×108 km) long. What is the total mass of the tail ? 2 A. 1.0×1013 kg m V   r L 17 3 B. 5.0×1010 kg 8.5  10 kg/m   2 C. 1.0×106 kg 5.0 108 m  1.5 10 11 m D. 20,000 kg m 1.0 1013 kg 19 Comet NEAT 20 Comet –

http://www.nasa.gov/mission_pages/deepimpact/multimedia/HRI-937.html 21 Comet Tempel 1

• Deep Impact revealed the composition of the comet Tempel 1 • Some of the expected constituents: (sand), water ice • …and some surprises: – Clay, and carbonates (how did these form without liquid water?) – iron compounds – aromatic 22 Halley’s Comet •Nucleus almost completely dark •Period: 76 years •Next Visit: 2061 23

Halley’s Comet 24 Comet Shoemaker-Levy 9

• Comet struck in July 1994 • Original comet ~2-10 km in diameter • Before impact it broke into many small pieces 25 Astronomers think that most comets come from A. interstellar space. B. a region in the extreme outer parts of the Solar System. C. condensation of gas in the Sun’s hot outer atmosphere. D. material ejected by volcanic eruptions on the moons of the outer planets. 26 Astronomers think that most comets come from A. interstellar space. B. a region in the extreme outer parts of the Solar System. C. condensation of gas in the Sun’s hot outer atmosphere. D. material ejected by volcanic eruptions on the moons of the outer planets.