NJIT Physics 320: Astronomy and Astrophysics – Lecture XIV Carsten Denker Physics Department Center for Solar–Terrestrial Research

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


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


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.


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.


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


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


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!)


Hale-Bopp


Halley’s Comet


Sungrazer (SoHO/LASCO)Sungrazer (SoHO/LASCO)


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


Asteroids (cont.)


Orbital Resonances and Trojans


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.

Documents

NJIT Physics 320: Astronomy and Astrophysics – Lecture XIV Carsten Denker Physics Department Center for Solar–Terrestrial Research