interplanetary bodies: asteroids asteroid-- rocky object in orbit around the sun includes:
DESCRIPTION
Interplanetary bodies: asteroids asteroid-- rocky object in orbit around the sun includes: Main Belt asteroid Hilda and Thule asteroid near-Earth asteroid (NEA) Trojan asteroid origin: rocky material that never accreted into a larger object; survivors of the planetary sweep-up process. - PowerPoint PPT PresentationTRANSCRIPT
Interplanetary bodies: asteroids
asteroid-- rocky object in orbit around the sun
includes:Main Belt asteroidHilda and Thule asteroidnear-Earth asteroid (NEA)Trojan asteroid
origin: rocky material that never accreted into a largerobject; survivors of the planetary sweep-up process
Interplanetary bodies: asteroids
asteroid-- rocky object in orbit around the sun
includes:Main Belt asteroidHilda and Thule asteroidnear-Earth asteroid (NEA)Trojan asteroid
origin: rocky material that never accreted into a largerobject; survivors of the planetary sweep-up process
Asteroid orbits
object approx. a (AU) approx. e
Main Belt 2.2 - 3.2 0 - 0.4asteroid
Hilda, Thule 3.9, 4.3 0 - 0.2asteroid
Trojan 5.2 (= Jupiter) 0 - 0.2
NEA 0.7 - 3 0.2 - 0.8
Asteroid orbits
object approx. a (AU) approx. e
Main Belt 2.2 - 3.2 0 - 0.4asteroid
Hilda, Thule 3.9, 4.3 0 - 0.2asteroid
Trojan 5.2 (= Jupiter) 0 - 0.2
NEA 0.7 - 3 0.2 - 0.8
NEAs derived from Main Belt by perturbations
Asteroidlocations
3.2 AU
2.2 AU
MainSelectedNEA orbits
Asteroid semi-major axes
TrojansMain Belt Hilda-group
Thule-group
Hungaria-group
Kirkwoodgaps
Kirkwood gaps
• represent areas in asteroid belt relativelyfree of material
• form at locations (resonances) that experiencerepeated perturbations from Jupiter
• strong resonance locations include 1:3 & 2:5
• material in gaps moved elsewhere, such as intoplanet-crossing orbits (e.g., NEAs)
Asteroids:
spectra & albedos
Examplesof asteroidspectral types
Asteroid spectral types
albedo maintype (%) location (a) mineralogy analogue
S 10-22 1.8-3.5 AU pyroxene O-chondrites? + - metal achondrites?
+ - olivine stony irons?
M 10-20 2.3-3.2 AU metal iron meteorites
C 3-7 2-4 AU hydrated C-chondritessilicates many meteors?+ carbon comets?
D + 2-6 3-5 AU carbon / none?P organic-rich comets?
silicates
Asteroid spectral types
albedo maintype (%) location (a) mineralogy analogue
S 10-22 1.8-3.5 AU pyroxene O-chondrites? + - metal achondrites?
+ - olivine stony irons?
M 10-20 2.3-3.2 AU metal iron meteorites
C 3-7 2-4 AU hydrated C-chondritessilicates many meteors?+ carbon comets?
D + 2-6 3-5 AU carbon / none?P organic-rich comets?
silicates
Asteroids: different types indifferent locations
Asteroids: examples
GaspraIdaMathildeVestaEros
Main Belt,S-type
Main Belt, S-typemember of family
Main Belt,C-type
Manylargecraters !
NEA,possiblechondriteparent body
Eros: up close & personal
The ultimate “meteorite”collecting site!
Relativecrater size-frequencydiagram(“R plot”)
Gaspra--younger(recentcollision?)
Mathilde--surplus oflargercraters (how?)
Asteroids:
Eros geology
Eros:the Saddle(Himeros)
Eros:grooves & troughs
Eros:ridges & grooves
Eros:mass wasting
Eros:
ponds--asteroidal
sedimentarydeposit
Asteroids:
Landing the NEAR spacecrafton Eros
(or how to make an asteroid landing, without
designing for it)
Asteroids:
Space weathering
Space weathering--
• We have clear evidence for the importanceof space weathering on all asteroids seen up close.
• On such asteroids, space weathering makesobjects redder, darker, and less crystalline.
Space weathering--
• We have clear evidence for the importanceof space weathering on all asteroids seen up close.
• On such asteroids, space weathering makesobjects redder, darker, and less crystalline.
Color-exagerratedimage
Eros spectral reflectance: mineralogy
2 micron band:Fe-bearing pyroxene
0.9 -1 micron band:Fe-bearing olivine, pyroxene
Eros: pyroxene signature
Himeros
Himeros
Psyche
Space weathering--
A common process on asteroids
• Color variations on Gaspra & Ida: “redder” color = more weathered
• Albedo variations on Eros: darker = more weathered
• Spectral variations on Eros: weaker pyroxene signature = more weathered
Space weathering--
A common process on asteroids
• Color variations on Gaspra & Ida: “redder” color = more weathered
• Albedo variations on Eros: darker = more weathered
• Spectral variations on Eros: weaker pyroxene signature = more weathered
Space weathering--
• Has important implications for making
links between asteroids and meteorites.
• Probably involved in “pond” formation onEros.
• Implies we can make sedimentary deposits onasteroids or small-gravity objects byspace weathering. (Not seen on Moon.)
Space weathering--
• Has important implications for making
links between asteroids and meteorites.
• Probably involved in “pond” formation onEros.
• Implies we can make sedimentary deposits onasteroids or small-gravity objects byspace weathering. (Not seen on Moon.)
Asteroids:
NEAs
NEAs: the more we look, the more we find them
NEA asteroid1999 JM8
diameter ~ 3.5 km
a = 2.71 AUe = 0.65i = 13.8o
q = 0.96 AU
radar images
NEA asteroid 4179 Toutatis:“contact binary” or elongated asteroid?
diameter = 4.6 x 2.4 x 1.9 km
a = 2.51 AUe = 0.63i = 0.5o
q = 0.92 AU
radar images
NEA asteroid 1999 KW4: binary asteroid
diameter of primary object ~ 1.2 kmdiameter of secondary object ~0.4 kmorbital period ~ 16 hrs
a = 0.64 AUe = 0.69i = 39o
q = 0.20 AU
radarimages
NEA asteroid1950 D4
diameter ~1.1 kmrot. period ~2.1 hrs
a = 1.70 AUe = 0.51i = 12.2o
q = 0.84 AU
Target: Earth?