Title: Astronomy 113 Planetary Missions Tuesdays, Thursday 1 4 pm Kendade Hall 305 Tom Burbine tburbinemtho
1Astronomy 113Planetary MissionsTuesdays,
Thursday 1 -4 pmKendade Hall 305Tom
Burbinetburbine_at_mtholyoke.edu
2HW
- HW 1 done last class (people who didnt do it
then can do it at noon on Thursday in this
classroom) - HW 2 HW is online on syllabus part of website
- HW 3 computer exercise during last hour of
class
3Whats the difference?
- Asteroids
- Comets
- Meteorites
4Whats the difference?
- Asteroids - small, solid objects in the Solar
System - Comets - small bodies in the Solar System that
(at least occasionally) exhibit a coma (or
atmosphere) and/or a tail - Meteorites - small extraterrestrial body that
reaches the Earth's surface
5Why are these things important?
6Why are these things important?
- These things can hit us (and possibly kill us)
- They are records of the early solar system
- They could be sources of material for mining
7Moon
8Record of Early Solar System
- Meteorites usually have ages of 4.6 billion
years - Asteroids and comets are thought to be the
building blocks of the terrestrial planets
9Resources
- In outer space, it may be easier (and less
expensive) to extract raw materials from
asteroids or comets then to bring them from Earth - Raw materials include water, iron, aluminum,
chromium
10Meaning of Asteroid
- Asteroid means star-like
- Called vermin of the sky by astronomers
11When you observe an astronomical body
- You measure intensity
- Intensity amount of radiation
12When you see an object in the sky
- You measure its brightness
- Its brightness is a function of its
- Distance from Earth (can be calculated from
orbit) - Albedo
- Size
13216 Kleopatra
14Magnitude System
brightest asteroid
4 Vesta
http//www.astronomynotes.com/starprop/appmag.gif
15(No Transcript)
16Asteroid Flyby
- Movie
- Images of 2002 NY40 on August 15-16
- Asteroid has diameter of 700 meters
- 524,000 kilometers from Earth (1.3 times the
distance of the Earth to the Moon) - Movie over 2 hour time period
17951 Gaspra
- 20 x 12 x 11 km
- Galileo spacecraft flew by this asteroid
18243 Ida
- 56 x 24 x 21 kilometers
- Galileo spacecraft flew by this asteroid
19Ida has a satellite Dactyl
20NEAR-Shoemaker mission to 433 Eros
- NEAR stands for Near-Earth Asteroid Rendezvous
- Shoemaker is for Gene Shoemaker
21- Launch date Feb. 17, 1996
- The first of four scheduled rendezvous burns on
December 20, 1998 aborted due to a software
problem - Rendezvous delayed for a year
- Orbital insertion around Eros occurred on
February 14, 2000
2213 13 33 km
23433 Eros
- Surface of 433 Eros
- Landing of NEAR-Shoemaker on Eros
24Hubble Image of 4 Vesta
25(No Transcript)
26Dawn Spacecraft will visit 4 Vesta and 1 Ceres
- Will be launched September 26, 2007
- Will orbit Vesta in 2011-2012
- Will orbit Ceres in 2015
http//en.wikipedia.org/wiki/ImageDawn_Flight_Con
figuration_2.jpg
27Basic orbital elements
- a semi-major axis average distance of the
body to the sun - i inclination of orbit to the ecliptic
- e eccentricity of the orbit
28Differences between ellipses and circles
29(No Transcript)
30Titius-Bode Law
- The mean distance a (AU) of the planet from the
Sun - a 0.4 0.3 x k
- where k0,1,2,4,8,16,32,64,128 (0 followed by the
powers of two) - 1 astronomical unit (AU) is the average distance
from the Earth to the Sun
31(No Transcript)
32So
- Baron Franz Xaver von Zach organized a group of
24 astronomers to search the sky for the "missing
planet" - But the first asteroid, 1 Ceres, was not
discovered by a member of the group, but rather
by accident in 1801 by Giuseppe Piazzi
33But
- Three other asteroids (2 Pallas, 3 Juno, 4 Vesta)
were discovered over the next few years
(1802-1807) - After eight more years of fruitless searches,
most astronomers assumed that there were no more - However, Karl Ludwig Hencke persisted, and began
searching for more asteroids in 1830. - Fifteen years later, he found 5 Astraea, the
first new asteroid in 38 years. He also found 6
Hebe less than two years later.
34Just numbered asteroids
35all asteroids
36(No Transcript)
37(No Transcript)
38Asteroid Families
39Asteroid Families
- Clumpings of asteroids with similar orbital
elements - Thought to be due to the breakup of a larger
parent body
40How are these objects named?
- Asteroids
- After being observed on two consecutive nights,
the object is given a provisional designation - a 4-digit number indicating the year
- a space
- a letter to show the half-month
- another letter to show the order within the
half-month - And an optional number to indicate the number of
times the second letter has been repeated in that
half-month period. - For example, 1977 RG
41Half Month Discovery
- Letter Dates Letter Dates
- A Jan. 1-15 B Jan. 16-31
- C Feb. 1-15 D Feb. 16-29
- E Mar. 1-15 F Mar. 16-31
- G Apr. 1-15 H Apr. 16-30
- J May 1-15 K May 16-31
- L June 1-15 M June 16-30
- N July 1-15 O July 16-31
- P Aug. 1-15 Q Aug. 16-31
- R Sept.1-15 S Sept.16-30
- T Oct. 1-15 U Oct. 16-31
- V Nov. 1-15 W Nov. 16-30
- X Dec. 1-15 Y Dec. 16-31
- I is omitted and Z is unused
42Order within Month
- A 1st B 2nd C 3rd D 4th E 5th
- F 6th G 7th H 8th J 9th K 10th
- L 11th M 12th N 13th O 14th P 15th
- Q 16th R 17th S 18th T 19th U 20th
- V 21st W 22nd X 23rd Y 24th Z 25th
- I is omitted
43Asteroids discovered between Sept 16-30 of 1995
- 1995 SA 1
- 1995 SB 2
- ...
- 1995 SY 24
- 1995 SZ 25
- 1995 SA1 26
-
- 1995 SZ1 50
- 1995 SA2 51
- ...
- 1995 SZ9 250
- 1995 SA10 251
44Asteroid Numbers and Names
- When well-observed, asteroid is given a number
- 5159 1977 RG
- When was it discovered?
45Asteroid Numbers
- When well-observed, asteroid is given a number
- 5159 1977 RG
- When was it discovered?
- 1977
- R Sept.1-15
- G 7th asteroid
46Asteroid Names
- Then the discover gets to name it for period of
10 years or so - 5159 1977 RG
- Was named
47Asteroid Names
- Then the discover gets to name it for period of
10 years or so - 5159 1977 RG
- Was named
- 5159 Burbine
48Everybody in the room reflects light differently
- Different minerals also reflect light differently
49When you look at an asteroid?
- Where does the light from the asteroid come from?
50 51Energy and wavelength
- Energy h frequency
- h Plancks constant 6.626 x 10-34 J-s
- c frequency wavelength
52(No Transcript)
53Wavelengths
- Micron (µm) 1 x 10-6 meters
- Nanometer (nm) - 1 x 10-9 meters
- Angstrom (Å) - 1 x 10-10 meters
54Water has a number of absorption features
55Asteroid Spectrum
- Asteroid Asteroid x Standard Star
- Sun Standard Star Sun
- A Standard Star is a G2 class star with a
spectrum similar to the Sun - You cant observe the Sun, but you can observe a
star similar to the Sun - Also, takes out absorption features in the
atmosphere
56When a photon strikes a grain
57The photon is either
- Absorbed,
- Passes through the grain, or
- Reflected from a grain surface
58Those that are scattered
- The photons that are scattered
- (reflected from a grain surface or refracted
through the grain) - may either encounter another grain or be
scattered away from the surface
59The photons you measure with a telescope from an
asteroid
- Are those that have scattered away from the
surface - Its called a Reflectance Spectrum
60Albedo
- Is a measure of the reflectivity of a surface or
body - Usually expressed as a percentage from 0 to 100
- 50 would be a high albedo for an asteroid
- Very white surface
- 5 would be a low albedo for an asteroid
- Very dark surface
61Albedo
- Refers to the reflectance in the visible
wavelength region - At a wavelength of 0.55 µm
- Often called visual albedo
62Asteroid Albedos
- Are difficult to measure from Earth
- The brightness of an asteroid is a function of
its size, distance from Earth, and albedo - So you need to know one to determine the other
63(No Transcript)
64Absorption Features
- To determine the mineralogy of an asteroid, you
use the presence or absence of specific
absorption features
65Mineral Spectra
- A number of minerals abundant in meteorites have
very distinctive absorption features - For example,
- Olivine
- Pyroxene
- These absorption features are also present in the
reflectance spectra of asteroids
66(No Transcript)
67Since
- Since different minerals have different
chemistries and/or different crystal structures,
they will tend to have different reflectance
spectra
68Absorption features due to the presence of Fe2
Splitting due to the application of a
non-spherical electrostatic field from
surrounding atoms
3d
69Electrons
- Electrons can absorb photons at specific energies
to go from one energy level to another - The energies of these photons correspond to
visible and near-infrared wavelengths
70Ca and Mg
- Ca and Mg do not have incompletely filled 3d
orbitals - Do not have absorption features in the visible
and near-infrared - Pure enstatite has no absorption features
- But their presence affects the position of the
absorption features due to Fe
71Olivine
The M2 site is larger and much more distorted
than the M1 site.
72Reflectance Spectrum
Fe2 in M2
Fe2 in M1
Fe2 in M1
EET 99402 Fa35
olivine
73pyroxenes
Fe2 in M2
Bouvante eucrite Fs53Wo14
Fe2 in M2
Lodran lodranite Fs13Wo3
Band II
LAP 91900 diogenite Fs22Wo2
Band I
74For pyroxenes
- Fe2 in the M1 site in pyroxenes tends to have
weaker features than those in the M2 site - Band I is called the 1 µm feature
- Band I is called the 2 µm feature
75- When you substitute Fe and/or Ca for Mg in the
crystal structure - The crystal structure expands and/or distorts
- The band positions move to longer wavelengths
76pyroxenes
Bouvante eucrite Fs53Wo14
Lodran lodranite Fs13Wo3
LAP 91900 diogenite Fs22Wo2
Band II
Band I
77pyroxenes (Adams, 1974 Cloutis and Gaffey,
1991) From Clark (1999)
Ca
Band I center
Fe
Open circles have 11 wollastonite and solid
symbols Band II center
78Olivine (Sunshine and Pieters, 1998)
Fa
79UV feature
- UV (ultraviolet) feature
- Electrons jump between cations or between cations
and anions - Very strong absorptions
80Reflectance Spectrum
UV feature
EET 99402 Fa35
olivine
81pyroxenes
Bouvante eucrite Fs53Wo14
UV feature
Lodran lodranite Fs13Wo3
Band II
LAP 91900 diogenite Fs22Wo2
Band I
82Olivine-Pyroxene Mixtures
- Most meteorites are a mixture of olivine and
pyroxene - Olivines absorption bands overlap the Band I
feature of the pyroxene - Pyroxene is more absorbing so it tends to
dominate the spectrum
83LL4 Greenwell Springs 50 olivine, 25 pyroxene
Band II
Band I
H5 Allegan 30 olivine, 30 pyroxene
84Predicting Ratios of Olivine to Pyroxene
pyroxene-dominated
olivine-dominated
85Pyroxenes
- Meteorites tend to be mixtures of a number of
different types of pyroxenes - Orthopyroxenes
- Clinopyroxenes pigeonite, augite, diopside
86Howardite EET 87503 (Hiroi et al. 1994)
Average pyroxene En5217Fs4014Wo88 (Burbine et
al. 2001)
(Buchanan and Mittlefehldt, 2003)
87Any Questions?