NJIT
Physics 320: Astronomy and Astrophysics – Lecture XIV
Carsten Denker
Physics DepartmentCenter for Solar–Terrestrial Research
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Pluto, Solar System Debris, and Formation
The Pluto-Charon SystemCometsAsteroidsMeteoritesThe Formation of the Solar System
December 10th, 2003NJIT Center for Solar-Terrestrial Research
The Pluto-Charon System Pluto discovered by
Clyde W. Tombaugh in 1930 (15th magnitude)
248.5 yr orbital period Eccentricity 0.25 29.7 AU perihelion
(closer than Neptune) 49.3 AU aphelion 17° inclination to
ecliptic 3-2 orbital resonance
with Neptune (no danger of collsions)
Radius 1160 km Its moon Charon
discovered in 1978 Orbit around common
center of mass in 6.4 d Separation 19640 km (1/20
Earth-Moon distance) Reduced mass is 0.24%
mass of Earth MCharon / MPluto = 0.09 to 0.16 Orbital plane of Pluto-
Charon system is inclined 122.5° with respect to their orbit around the Sun
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Pluto
Pluto is mostly brown. No spacecraft has yet visited this most distant planet in our Solar System. The map was created by tracking brightness changes from Earth of Pluto during times when it was being partially eclipsed by its moon Charon. Pluto's brown color is thought dominated by frozen methane deposits metamorphosed by faint but energetic sunlight.
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Pluto-Charon
Pluto is the only planet in our Solar System remaining unphotographed by a passing spacecraft. These maps depict the face of Pluto (left) that always faces Charon, and the face of Charon that always faces away from Pluto. The Pluto-Kuiper Express mission is tentatively planned for launch in 2004 and might encounter Pluto as early as 2012.
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Comets Halley’s comet
(observed since 240 B.C., 76 yr orbital period)
Nucleus: “dirty snowball” or “snowy dirtball”?
Size: 10 km Coma: cloud of gas and
dust, sublimated ice Interaction with sunlight
and solar wind creates dust (radiation pressure) and ion (magnetic field) tail up to 1 AU length
A hydrogen gas halo envelopes the coma
Tails are always directed away from the Sun (ion trails are straight, dust tails are curved)
Dust grains scatter light, tail appears white/yellow
Blue ion tail: CO+ ions absorb UV radiation and reradiate at 420 nm
Composition: 80% H2O, 10% CO, 3.5% CO2, few % (H2CO)n, 1% CH3OH
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Comets (cont.) Disconnection events Water on terrestrial
planets from comet impacts?
Halley: Suisei, Sakigake, Vega 1/2, Giotto (closest approach 600 km), Cometary Explorer
Halley’s size 15 km 7.2 km 7.2 km
Mass: 5 1013 kg to 1014 kg
Halley is a short-period comet < 200yr (Kuiper belt objects 30 AU to 100 AU)
Long-period comets 100,000 to 1 million yr
Long-period comets originate in the Oort cloud
Inner cloud in ecliptic 3,000 AU to 20,000 AU
Outer cloud has spherical distribution 20,000 AU to 100,000 AU
Planetesimals “catapulted” from Jovian planets to Oort cloud
Random motion
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Dust Tail
rad (radiation pressuco res )S A
Fc
2
rad 24
L RSF
c r c
3grain 3
grain2 2
4 4 with
3 3g
GM m GM RF m R
r r
critrad
16 3
3 16gF GM R c L
RF L GM c
3crit3000 kg/cm 191 nmR
R < Rcrit: net outward force, spiral away from Sun
R > Rcrit: continue to orbit Sun (Poynting-Robertson effect!)
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Sungrazer (SoHO/LASCO)Sungrazer (SoHO/LASCO)
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Asteroids Minor planets mostly
between Mars and Jupiter
Discovery of Ceres in 1801 by Piazzi
Combined mass of all asteroids 5 104 M
Orbital resonances with Jupiter
Kirkwood gaps Trojan asteroids
(1:1 resonance group, Lagrange points L4 and L5)
Hirayama families (originally single asteroid that suffered a catastrophic collision)
Collision speeds of up to 5 km/s
Composition is a function of the distance from the Sun (volatiles (water) vs. refractory compounds (silicon))
Metal rich asteroids from larger parent asteroids with chemical differentiation
December 10th, 2003NJIT Center for Solar-Terrestrial Research
Lagrange Points
The Italian-French mathematician Lagrange discovered five special points in the vicinity of two orbiting masses where a third, smaller mass can orbit at a fixed distance from the larger masses. The Lagrange Points mark positions where the gravitational pull of two large masses precisely equals the centripetal force required to rotate with them.