Astronomy 1 - Lecture Notes - Nov 30, 1998

Meteor and Comets

Notices: Final Exam - Thursday, Dec 17 at 9 am
New Location: Room 206 Huggins Science Hall 

Deep Space Picture by Hubble Space Telescope (November 23)
Taken in Tucana (Southern Skies) over a 10 day period (Galaxies 12 billion ly away)
High Resolution (5.8 Mbyte) Image
  1. Asteroids
  2. Comets
  3. Meteoroids, Meteors, and Meteroids 
ASTEROIDS (NEO)

Kirkwood Gap's in Distribution of Semimajor axes of Asteroid Orbits
(See Figure 14.6 in Chaisson)

Toutatis near approach in 1992-3
(4179) Toutatis 1989 AC
In 1999 Jan 22 approach 0.006 AU   (perihelion =  0.919 AU)
Period = 1.85 years
a = 2.511	i = 0.5o 	e = 0.634
M = 198.5 	Peri. = 274.7		Node = 128.3
   
Close Approach to the Earth of 1996 JA1 on  1996 May  19.7
Minimum Distance = 0.0030(AU) 
                     
1996 JA1
Epoch 1996 Apr. 27.0 TT = JDT 2450200.5       
M 344.09901              (2000.0)          
n   0.24592611     Peri.  245.94759   
a   2.5230912      Node    58.76165
e   0.6960932      Incl.   22.16223   
P   4.01years

List of Hazardous Asteroids (MPC)

COMETS:
(SEDS WWW Page on Comets)
Orbits: 
	Parabolic or elliptical with eccentricity near 1
	Very large semi-major axis 
	Perihelion about or less than 1 AU

Types:
	Periodic = period < 200 years
		Shortest = 3.3 year (Comet Encke)
		Halley = 76 years (e = 0.97)
	Long Period = period > 200 years
		Hale-Bopp = 3400 years
		Hyakutaki (DIAGRAM of it ORBIT)

Origins:
	Kuiper Belt: 
		> 50 AU disk of comet nucleii revolving in the same counter 
			clockwise revolution at the planets .
		Source of Short Period Comets with obits prograde orbits and 
			low inclinations


	Oort Cloud: 50,000 AU-100,000AU 
		1 light-year = 63,400 AU
		Nearest Star distance = 4.3 ly = 207,000 AU
		 (within the gravitation sphere of influence of the Sun)
		Source of long period comets with high inclination 
			and retrograde orbits.
		Spherical cloud of comet nucleii
		Oort estimated 100 billion comets in the sphere
		Orbits perturbed by other objects to drop into the inner solar system.
		(Halos have been seen around other stars that could be 
			Oort clouds there)

Physical Properties:

   IMAGE of Comet Hale-Bopp

	Nucleus (solid, usually invisible) = real body that produce 
	the atmosphere and tail
		First studied when Giotto flew past Comet Halley, 1986)
			8km x 13 km
			density ~ 1000 kg/m3 (water density)
			mass ~ 6x1014kg = 10-10 mass of earth
			Composition of a dirty snowball (ices and dust) 
			very low albedo
			kilometres size 
			rotates (effected by jets of material that occur near perihelion)

	Coma or Head (bright center) = atmosphere around the nucleus
		Dense gas/dust ejecta from heating by the Sun
		Mostly H2O ~79%; with H2CO2, CO2, CO~ 13%: CH4 etc ~ 2.5%
		ejecta ~ 1 km/s because no gravity of significance 
		Provide a rocket-like action that effects orbit motion!!!!

	Tail: Streaming atmosphere of gas and dust
		Dust Tail: Solar Radiation Pressure pushes away from Sun
			Small micrometre size dust grains
		Plasma or Gas Tail: Solar Winds pushes away from the Sun
			Ions of gases in coma CO+, H2O+, N2+
			Changes in solar winds appear as changes in plasma tail

	Halo: Invisible Hydrogen envelope
		Size ~ 10 million kilometres in size
	
	STARDUST MISSION by JPL/NASA
	to observe the Comet Wild2 in 2004.

Historic Comets:
	1577 Great Comet - Tycho Brahe determined to be beyond the Moon
	1811 Great Comet - Largest Head > 2 million km diameter
	1843 Great Comet - Brightest  - visible in daylight
	1970 Bennet - Similar to Hale-Bopp
	1976 West - Best Recent Comet until Hyakutake, Hale-Bopp
		nucleus broke into four pieces
	Halley (1531, 1607, 1682, 1758, 1834, 1910, 1986, 2061)
		Actually has been observed and recorded every passage since 239 BC
		Predicted to return in 1758 by Halley
		Famous periodic comet (76 year period) poor postion in 1986, plasma tail
		Studied in detail by space craft in 1986 (Giotto)
	Shoemaker-Levy 9 - Hit Jupiter in 1994 (discovered in 1992)
		Not visible without a very large telescope (orbit about Jupiter)
	Hyakutake (1996)	
		Small comet with orbit near the Earth, Mostly Plasma Tail
	Hale-Bopp (1997)
		Larger Comet (10 times size Hyakutake) with large dust tail

MPC Orbit Plots of Comets and Asteroids

Fate of Comets:
	1. Eroded away by solar heat, and winds
	2. Breakup and Collision with Jupiter (Shoemaker-Levy 9)
	3. Breakup by tidal forces of Sun 
	4. Small perihelion, drop into the Sun
		(Recently SOHO has obseved many sun grazing comets)

Small Comet Controversy (Dr. Frank)
	Holes seen in the UV emissions from the atmosphere = water vapor
	Small comets hitting atomsphere
	Imaged from military satellites many years ago - now declassified 

METEOROIDS, METEORS, METEORITES
(meteoroids in space, hit the the earth atmosphere and appear as meteors, 
and if they don't burn up, they land and become meteroites)
Meteroids:
	Interplanetary dust
	Cometary dust
Meteors:
	~ 1 every 5 minutes sporadics (random direction but most visible in morning)
	Visible ones ~ 1 gram (< peas size)
	Bright Fireball ~ 100 grams ~ marble size
	~100 km up in atmosphere
	visible 200 km away
	25 million/day on the Earth
	~ 100 tons/day
Showers 
	Radiant = the point of convergence of the trails (all meteroids coming from that direction)
	Time = same each year as Earth passes the same point in its orbit.
	Meteroid swarm from Comet passage leaving debris.
	Showers of Note:  (see table 14.1 of Chaisson)
			Date		Comet			ZHR	speed	duration
									(km/s)	(days)
	Quadrantids	Jan 3		-???			85	42 	0.8
	Lyrids		April 21	Thatcher		15	48	6
	Eta Aquarids	May 4		Comet Halley		30	65	14
	Perseid		Aug 12		Swift-Tuttle		100	60	5
	Orionids	Oct 20		Comet Halley		20	66	8
	Leonids		Nov 16		Tempel-Tuttle		60	71	4
	Geminids	Dec 14		Phaethon 		95	35	3
					(NEO Asteroid)

The Geminds 1998


(3200)Phaethon
Epoch 1999 Jan. 22.0 TT = JDT 2451200.5             
M 265.73112              (2000.0)        
n   0.68760924     Peri.  321.84396  
a   1.2712811      Node   265.55801    
e   0.8901089      Incl.   22.11218  
P = 1.43 years

DIAGRAM of (3200)Phaethon's Orbit
			
			1/4 pk	Moon's	Zenith	Population 	velocity
Date	time	Solar	Duratn	Illum	Hourly	Index		km/s
	UT	Long	(days)		(%)	Rate		per mag
Dec 14	12h	262o	3	17	95	2.6		35	
	8h AST

ZHR is for meteors at the zenith with 6.5 mag stars visible
If you can only see magnitude 4.5 then you must reduce the rate 
corresponding to two magnitudes or to 95/2.6/2.6 = 14 per hour = 

Counts can be reported to the International Meteor Organization

ZHR OF LEONIDS 1998
This graph shows ZHR versus Solar Longitude (1o ~ 1 day)

Meteorites:
Types:
Primitive Stones = material from solar nebula not modified by heat or pressure
		= chrondrites with chondrules = round granules 
			+ dark carbonaceous meteorites
	Differentiated Stones = stones subject to heat and pressure
	Irons = iron, nickle (differentiated core of body) subject to heat and pressure
	Stoney-irons = mixture of material subject to heat and pressure: core interface

Occurances:			Finds		Falls		Antarctic
	Primitive Stones	51%		87%		85%
	Differentiated Stones	  1%		  8%		12%
	Irons			42%		  3%		  2%
	Stony-irons		  5%		  1%		  1%

Recent 'Fall' in Turkey in June 1998
A Carbonaceous Meteorite was found after a 'Daytime' Fireball 
left dark smoke across the sky.
	meteorited size: 0.81 m long
	mass: 850 kg
	Crater: 6 m diameter and 4 m deep