Astronomy 113 Planetary Missions Tuesdays, Thursday 1 4 pm Kendade Hall 305 Tom Burbine tburbinemtho - PowerPoint PPT Presentation

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Astronomy 113 Planetary Missions Tuesdays, Thursday 1 4 pm Kendade Hall 305 Tom Burbine tburbinemtho

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NEAR-Shoemaker mission to 433 Eros. NEAR stands for Near-Earth Asteroid Rendezvous ... around Eros occurred on February 14, 2000. 13 13 33 km. 433 Eros ... – PowerPoint PPT presentation

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Title: Astronomy 113 Planetary Missions Tuesdays, Thursday 1 4 pm Kendade Hall 305 Tom Burbine tburbinemtho


1
Astronomy 113Planetary MissionsTuesdays,
Thursday 1 -4 pmKendade Hall 305Tom
Burbinetburbine_at_mtholyoke.edu
2
HW
  • 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

3
Whats the difference?
  • Asteroids
  • Comets
  • Meteorites

4
Whats 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

5
Why are these things important?
6
Why 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

7
Moon
8
Record 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

9
Resources
  • 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

10
Meaning of Asteroid
  • Asteroid means star-like
  • Called vermin of the sky by astronomers

11
When you observe an astronomical body
  • You measure intensity
  • Intensity amount of radiation

12
When 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

13
216 Kleopatra
14
Magnitude System
brightest asteroid
4 Vesta
  • Brighter lower number

http//www.astronomynotes.com/starprop/appmag.gif
15
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16
Asteroid 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

17
951 Gaspra
  • 20 x 12 x 11 km
  • Galileo spacecraft flew by this asteroid

18
243 Ida
  • 56 x 24 x 21 kilometers
  • Galileo spacecraft flew by this asteroid

19
Ida has a satellite Dactyl
20
NEAR-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

22
13 13 33 km
23
433 Eros
  • Surface of 433 Eros
  • Landing of NEAR-Shoemaker on Eros

24
Hubble Image of 4 Vesta
25
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26
Dawn 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
27
Basic 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

28
Differences between ellipses and circles
29
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30
Titius-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
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32
So
  • 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

33
But
  • 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.

34
Just numbered asteroids
35
all asteroids
36
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38
Asteroid Families
39
Asteroid Families
  • Clumpings of asteroids with similar orbital
    elements
  • Thought to be due to the breakup of a larger
    parent body

40
How 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

41
Half 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

42
Order 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

43
Asteroids 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

44
Asteroid Numbers and Names
  • When well-observed, asteroid is given a number
  • 5159 1977 RG
  • When was it discovered?

45
Asteroid Numbers
  • When well-observed, asteroid is given a number
  • 5159 1977 RG
  • When was it discovered?
  • 1977
  • R Sept.1-15
  • G 7th asteroid

46
Asteroid Names
  • Then the discover gets to name it for period of
    10 years or so
  • 5159 1977 RG
  • Was named

47
Asteroid Names
  • Then the discover gets to name it for period of
    10 years or so
  • 5159 1977 RG
  • Was named
  • 5159 Burbine

48
Everybody in the room reflects light differently
  • Different minerals also reflect light differently

49
When you look at an asteroid?
  • Where does the light from the asteroid come from?

50
  • Reflected from the Sun

51
Energy and wavelength
  • Energy h frequency
  • h Plancks constant 6.626 x 10-34 J-s
  • c frequency wavelength

52
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53
Wavelengths
  • Micron (µm) 1 x 10-6 meters
  • Nanometer (nm) - 1 x 10-9 meters
  • Angstrom (Å) - 1 x 10-10 meters

54
Water has a number of absorption features
55
Asteroid 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

56
When a photon strikes a grain
  • What happens?

57
The photon is either
  • Absorbed,
  • Passes through the grain, or
  • Reflected from a grain surface

58
Those 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

59
The photons you measure with a telescope from an
asteroid
  • Are those that have scattered away from the
    surface
  • Its called a Reflectance Spectrum

60
Albedo
  • 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

61
Albedo
  • Refers to the reflectance in the visible
    wavelength region
  • At a wavelength of 0.55 µm
  • Often called visual albedo

62
Asteroid 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
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64
Absorption Features
  • To determine the mineralogy of an asteroid, you
    use the presence or absence of specific
    absorption features

65
Mineral 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
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67
Since
  • Since different minerals have different
    chemistries and/or different crystal structures,
    they will tend to have different reflectance
    spectra

68
Absorption features due to the presence of Fe2
Splitting due to the application of a
non-spherical electrostatic field from
surrounding atoms
3d
69
Electrons
  • 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

70
Ca 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

71
Olivine
The M2 site is larger and much more distorted
than the M1 site.
72
Reflectance Spectrum
Fe2 in M2
Fe2 in M1
Fe2 in M1
EET 99402 Fa35
olivine
73
pyroxenes
Fe2 in M2
Bouvante eucrite Fs53Wo14
Fe2 in M2
Lodran lodranite Fs13Wo3
Band II
LAP 91900 diogenite Fs22Wo2
Band I
74
For 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

76
pyroxenes
Bouvante eucrite Fs53Wo14
Lodran lodranite Fs13Wo3
LAP 91900 diogenite Fs22Wo2
Band II
Band I
77
pyroxenes (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
78
Olivine (Sunshine and Pieters, 1998)
Fa
79
UV feature
  • UV (ultraviolet) feature
  • Electrons jump between cations or between cations
    and anions
  • Very strong absorptions

80
Reflectance Spectrum
UV feature
EET 99402 Fa35
olivine
81
pyroxenes
Bouvante eucrite Fs53Wo14
UV feature
Lodran lodranite Fs13Wo3
Band II
LAP 91900 diogenite Fs22Wo2
Band I
82
Olivine-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

83
LL4 Greenwell Springs 50 olivine, 25 pyroxene
Band II
Band I
H5 Allegan 30 olivine, 30 pyroxene
84
Predicting Ratios of Olivine to Pyroxene
pyroxene-dominated
olivine-dominated
85
Pyroxenes
  • Meteorites tend to be mixtures of a number of
    different types of pyroxenes
  • Orthopyroxenes
  • Clinopyroxenes pigeonite, augite, diopside

86
Howardite EET 87503 (Hiroi et al. 1994)
Average pyroxene En5217Fs4014Wo88 (Burbine et
al. 2001)
(Buchanan and Mittlefehldt, 2003)
87
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