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?