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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.

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Presentation Transcript
slide2

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

slide3

Asteroid orbits

object approx. a (AU) approx. e

Main Belt 2.2 - 3.2 0 - 0.4

asteroid

Hilda, Thule 3.9, 4.3 0 - 0.2

asteroid

Trojan 5.2 (= Jupiter) 0 - 0.2

NEA 0.7 - 3 0.2 - 0.8

NEAs derived from Main Belt by perturbations

slide4

Asteroid

locations

slide5

2.2 AU

Main

Selected

NEA orbits

3.2 AU

slide6

Asteroid semi-major axes

Hungaria-

group

Hilda-

group

Main Belt

Trojans

Thule-

group

slide8

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)
slide9

Asteroids:

spectra & albedos

slide10

Examples

of asteroid

spectral types

slide12

Asteroid spectral types

albedo main

type (%) 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-chondrites

silicates many meteors?

+ carbon comets?

D + 2-6 3-5 AU carbon / none?

P organic-rich comets?

silicates

slide14

Asteroids: examples

Gaspra

Ida

Mathilde

Vesta

Eros

slide16

Main Belt, S-type

member of family

slide20

Many

large

craters !

slide22

NEA,

possible

chondrite

parent body

slide23

Eros: up close & personal

The ultimate “meteorite”

collecting site!

slide24

Relative

crater size-

frequency

diagram

(“R plot”)

Gaspra--

younger

(recent

collision?)

Mathilde--

surplus of

larger

craters (how?)

slide25

Asteroids:

Eros geology

slide26

Eros:

the Saddle

(Himeros)

slide27

Eros:

grooves & troughs

slide28

Eros:

ridges & grooves

slide29

Eros:

mass wasting

slide30

Eros:

ponds--

asteroidal

sedimentary

deposit

slide31

Asteroids:

Landing the NEAR spacecraft

on Eros

(or how to make an asteroid landing, without

designing for it)

slide34

Asteroids:

Space weathering

slide35

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.
slide38

Eros spectral reflectance: mineralogy

0.9 -1 micron band:

Fe-bearing olivine, pyroxene

2 micron band:

Fe-bearing pyroxene

slide39

Eros: pyroxene signature

Himeros

Himeros

Psyche

slide40

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
slide41

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.)
slide44

NEA asteroid

1999 JM8

diameter ~ 3.5 km

a = 2.71 AU

e = 0.65

i = 13.8o

q = 0.96 AU

radar images

slide45

NEA asteroid 4179 Toutatis:

“contact binary” or elongated asteroid?

radar images

diameter = 4.6 x 2.4 x 1.9 km

a = 2.51 AU

e = 0.63

i = 0.5o

q = 0.92 AU

slide46

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 = 39o

q = 0.20 AU

radar

images

slide47

Target: Earth?

NEA asteroid

1950 D4

diameter ~1.1 km

rot. period ~2.1 hrs

a = 1.70 AU

e = 0.51

i = 12.2o

q = 0.84 AU