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 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

Asteroid orbits objectapprox. a (AU)approx. e Main Belt asteroid Hilda, Thule3.9, asteroid Trojan5.2 (= Jupiter) NEA Asteroid orbits objectapprox. a (AU)approx. e Main Belt asteroid Hilda, Thule3.9, asteroid Trojan5.2 (= Jupiter) NEA NEAs derived from Main Belt by perturbations

Asteroid locations

3.2 AU 2.2 AU Main Selected NEA orbits

Asteroid semi-major axes Trojans Main Belt Hilda- group Thule- group Hungaria- group

Kirkwood gaps

Kirkwood gaps represent areas in asteroid belt relatively free of material form at locations (resonances) that experience repeated perturbations from Jupiter strong resonance locations include 1:3 & 2:5 material in gaps moved elsewhere, such as into planet-crossing orbits (e.g., NEAs)

Asteroids: spectra & albedos

Examples of asteroid spectral types

Asteroid spectral types albedomain type(%)location (a)mineralogyanalogue S AUpyroxeneO-chondrites? + - metalachondrites? + - olivinestony irons? M AUmetaliron meteorites C AUhydratedC-chondrites silicatesmany meteors? + carboncomets? D AUcarbon /none? Porganic-richcomets? silicates Asteroid spectral types albedomain type(%)location (a)mineralogyanalogue S AUpyroxeneO-chondrites? + - metalachondrites? + - olivinestony irons? M AUmetaliron meteorites C AUhydratedC-chondrites silicatesmany meteors? + carboncomets? D AUcarbon /none? Porganic-richcomets? silicates

Asteroids: different types in different locations

Asteroids: examples Gaspra Ida Mathilde Vesta Eros

Main Belt, S-type

Main Belt, S-type member of family

Main Belt, C-type

Many large craters !

NEA, possible chondrite parent body

Eros: up close & personal The ultimate “meteorite” collecting site!

Relative crater size- frequency diagram (“R plot”) Gaspra-- younger (recent collision?) Mathilde-- surplus of larger craters (how?)

Asteroids: Eros geology

Eros: the Saddle (Himeros)

Eros: grooves & troughs

Eros: ridges & grooves

Eros: mass wasting

Eros: ponds-- asteroidal sedimentary deposit

Asteroids: Landing the NEAR spacecraft on Eros (or how to make an asteroid landing, without designing for it)

Asteroids: Space weathering

Space weathering-- We have clear evidence for the importance of space weathering on all asteroids seen up close. On such asteroids, space weathering makes objects redder, darker, and less crystalline. Space weathering-- We have clear evidence for the importance of space weathering on all asteroids seen up close. On such asteroids, space weathering makes objects redder, darker, and less crystalline.

Color-exagerrated image

Eros spectral reflectance: mineralogy 2 micron band: Fe-bearing pyroxene micron band: Fe-bearing olivine, pyroxene

Eros: pyroxene signature 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 on Eros. Implies we can make sedimentary deposits on asteroids or small-gravity objects by space weathering. (Not seen on Moon.) Space weathering-- Has important implications for making links between asteroids and meteorites. Probably involved in “pond” formation on Eros. Implies we can make sedimentary deposits on asteroids or small-gravity objects by space weathering. (Not seen on Moon.)

Asteroids: NEAs

NEAs: the more we look, the more we find them

NEA asteroid 1999 JM8 diameter ~ 3.5 km a = 2.71 AU e = 0.65 i = 13.8 o 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 AU e = 0.63 i = 0.5 o q = 0.92 AU radar images

NEA asteroid 1999 KW4: binary asteroid diameter of primary object ~ 1.2 km diameter of secondary object ~0.4 km orbital period ~ 16 hrs a = 0.64 AU e = 0.69 i = 39 o q = 0.20 AU radar images

NEA asteroid 1950 D4 diameter ~1.1 km rot. period ~2.1 hrs a = 1.70 AU e = 0.51 i = 12.2 o q = 0.84 AU Target: Earth?