spacerocks

Space Rocks !: 

Space Rocks ! John Curchin, USGS, Denver

Questions to be Considered : 

Questions to be Considered What are asteroids and how are they classified (Astronomy)? Are they a threat to Earth (Geology)? Do we already have samples (Meteoritics)? The answers to all three have origins with the ‘state of science’ in 1804.

Astronomy in 1804 (and 2004): 

Astronomy in 1804 (and 2004) Uranus is discovered in 1781 by the English musician, William Herschel using a home-built telescope The first 3 asteroids Ceres, Pallas, and Juno are discovered between 1801 and1804 ‘Bode’s Law’ holds up; nature seems to be deterministic and predictable 1 Ceres 3 Juno

Asteroid Belt as viewed from Above: 

Asteroid Belt as viewed from Above Over 100,000 objects greater than 10 km. now identified in the Main Belt Total mass less than 1% of moon’s mass Over 100 NEAs greater than 1 km. across are being tracked; probably part of a population of about 2000 Kirkwood gap (and others) occur in the belt where there are orbital resonances with Jupiter Asteroids classified by ‘spectral group

How to Classify Asteroids: 

How to Classify Asteroids Glass (or a fine mist of water droplets) separates lignt into separate wavelengths due to ‘differential refraction’ Eyes are sensitive to brightness variations (rod cells) and 3 colors (R, G, B cone cells)

Spectral Identification of Minerals: 

Spectral Identification of Minerals

S Asteroids (‘silicaceous’): 

S Asteroids (‘silicaceous’) 951 Gaspra 433 Eros (true color) Ida (and Dactyl) 19 x 12 x 11 km 33 x 13 x13 km 58 x 23 km (1km) Galileo flyby, 199 NEAR orbit/landing Galileo flyby, 1993 Grooves, curved near-Earth asteroid, member of Koronis depressions, ridges space weathering family, first ID of (Phobos-like) effects documented asteroid ‘moons’

C Asteroids (‘carbonaceous’): 

C Asteroids (‘carbonaceous’) 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker Surface as dark as charcoal; typical outer belt asteroid

Comets: 

Comets Comet Borrelly, visited by Deep Space 1, 1999 8 x 3 x 3 km (bowling pin) Variety of surface terrains, albedos (craters?) Comet Wild 2, visited by Stardust in January, 2004 5.5 x 4 x 3.3 km (hamburger) Craters may be due to impact or outflow jets of gases; indicate cohesive strength of nucleus

Comet Shoemaker-Levy 9 fragments impact Jupiter, July 16-22, 1994: 

Comet Shoemaker-Levy 9 fragments impact Jupiter, July 16-22, 1994 ‘Bull’s eye’ on Jupiter larger than Earth; first evidence of water in the jovian atmospher

What is the Asteroid Threat ? ‘Can’ they strike Earth and how often?: 

What is the Asteroid Threat ? ‘Can’ they strike Earth and how often? Controversial until late 20th century; few NEAs were known, spectral matches between asteroids and meteorites were poor, and no known mechanism could account for their delivery from the asteroid belt Recognition of ‘chaos’, extreme sensitivity to initial conditions, as fundamental to most natural processes, especially for orbital dynamics (Comet SL 9, 1994) Collisional (orbital) and radiation (space weathering, Yarkovsky effect) processes become important to objects in asteroid belt over billions of years Combination of processes provides a ‘conveyer belt’ of (reddened) material to Earth orbit Must look to geology for ‘ground truth’ – what is the evidence for impact, size-frequency distribution of impacting bodies?

Geology in 1804: 

Geology in 1804 “Theory of the Earth” by James Hutton, establishes geology as a science, with the its primary doctrine of uniformitarianism (explained by Lyell) Application of this doctrine to the stratigraphy and structure of terrestrial rocks suggests an ancient Earth Georges Cuvier, a French paleontologist, recognizes that fossils are ancient life forms, these forms change through time, and that most fossils are of forms now extinct

Slide13: 

Full Moon (telescope view) with lighter highlands and darker basalt plains, filling multi-ringed basins Apollo 16 view of Descartes Highlands, with impact craters at all scales

Meteor Crater: 

Meteor Crater Owned by Barringer family since 1903; 1.2 km Formed ~50,000 years ago from 50m impactor Origin established by Gene Shoemaker in 1950s Associated with Canyon Diablo meteorite field

Wolfe Creek: 

Wolfe Creek ~1/2 mile across; 300,000 years old, W. Australia Also associated with many small iron meteorites

Simple vs. Complex Craters: 

Simple bowl structure Diameter is 15-20 times diameter of impacting object All less than 1-2 miles across on Earth Complex structure with central peak, peak ring, or multiple rings Melt sheet generated and thick breccia lens Terraced, collapsed walls; about 10x impactor diameter Simple vs. Complex Craters

Clearwater Lakes: 

Clearwater Lakes 14 and 20 miles wide; 290 million years old Located near Hudson Bay, Quebec Submerged central peak in smaller lake

Manicouagan, Ontario: 

Manicouagan, Ontario 60+ miles across; including annular melt sheet Approx. 212 million years old Extensive shock features in crystalline rocks

Chixulub, Yucatan penninsula, Mexico: 

Chixulub, Yucatan penninsula, Mexico Gravity map of buried structure 180 miles across; 65 millions years old Identified in early 1990s with seismic data, after 10 year ‘search’

Other Impact-related Features: 

Other Impact-related Features a) Shatter cones b) Planar deform-ation featrures c) Vitrified (and high pressure) mineral phases d) Impact melt lens

Tektite buttons: 

Tektite buttons Moldavite A tektite from Czechoslovakia

Tunguska, Siberia, June 30, 1908: 

Tunguska, Siberia, June 30, 1908 Black and white photos taken during field expedition in 1927; color photo taken in 1990

Jackson Hole Fireball, August 10, 1972: 

Jackson Hole Fireball, August 10, 1972

Potentially Hazardous Asteroid ThreatSize-frequency diagram for impacting objects: 

Potentially Hazardous Asteroid Threat Size-frequency diagram for impacting objects ~100 tons of meteroritic dust falls each day 50 m impactor once per 1000 yr (local effects) 500 m impactor once per million years (regional effects) 5 km. impactor once per 100 million years (global effects)

Meteoritics in 1804: 

Meteoritics in 1804 Ernst Chladni, a German physicist, proposes an extraterrestrial origin for meteorites in 1794 Numerous witnessed meteorite falls occur in the 1790s, especially at Siena, Italy in 1794 and at Wold Cottage, England, in 1795 Chemical analysis on many ‘fallen stones’ during 1802-1803, establishes their chemical similarity to each other, and distinctive differences from terrestrial rocks

Hoba Iron: 

Hoba Iron 3m x 2m x 1m; 60+ tons Found 1920, Namibia No crater, classified ataxite

Gibeon Iron: 

Gibeon Iron 3000+ gm full slice Distinctive Widmanstatten pattern of intergrown iron-nickel alloys Found Namibia, 1836 Strewn field with over 50 tons of ‘irons’ Available on E-bay for $1995.00

Ordinary Chondrites (S Asteroids?): 

Ordinary Chondrites (S Asteroids?)

Stereoscope adapted for Polarized Light Viewing: 

Stereoscope adapted for Polarized Light Viewing Thin sections are wafer thin slices of rock (.03 mm) glued to a standard glass slide For geologic purposes, standard (‘biologic’) microscopes are adapted with two polarizers and a rotating stage The unique optical properties of different mineral crystals affect polarized light differently

Chondrites in Thin Section: 

Chondrites in Thin Section Tuxtuac, Mexico; fall 1975 Lost Creek, Kansas classified LL5 classified H3.8 ‘barred’ olivine chondrule radial pyroxene (~ 1 mm diameter) chondrule

Allende (C asteroid?) Fell in Mexico, Feb, 1969: 

Allende (C asteroid?) Fell in Mexico, Feb, 1969 Carbonaceous, subclass of the stony chondrites Primitive composition (solar, minus lightest elements) Contains abundant chondrules and CAIs, calcium-aluminum inclusions, dated at 4.567 billion years old

Glorietta Mountain New MexicoPallasite (full slice): 

Glorietta Mountain New Mexico Pallasite (full slice) Stony-iron meteorite Olivine suspended in an iron matrix Etched iron shows Widmanstatten pattern Olivines with very uniform composition Likely source: core-mantle boundary region of a once differentiated and since-shattered asteroid

Howardites, Eucrites and Diogenites : 

Howardites, Eucrites and Diogenites ‘Achondrites’ – meteorites without chondrules; from differentiated objects that have melted inside Eucrites similar to terresrial basalts Diogenites, of almost pure pyroxene, resemble terrestrial ‘cumulates’ Howardites are breccias of other two Spectral similarities with V asteroid class

Three Views of Vesta: 

Three Views of Vesta Hubble image, model and color-shaded topography Largest member of V class of asteroids (vestoids) Spectral variations consistent with HEDs

Differentiated Worlds: 

Differentiated Worlds Terrestrial basalt, Mt. Holyoke flow, Connecticut Martian basalt, zagami meteorite Vestan basalt Lunar low Ti basalt

But how do we know?!: 

But how do we know?! Oxygen isotope ratios distinguish among solar system materials chemically; Earth and Moon plot together Planetary processes ‘smear’ O isotopes along a trend within one world; different initial ratios for each world

What were the processes and products in the early Solar System (Meteoritics, 2004): 

What were the processes and products in the early Solar System (Meteoritics, 2004) Impact features on all planetary surfaces; planets formed by accretion of planetesimals from a turbulent solar nebula Much mixing of components; completed in 5-10 million years ‘Residual’ debris forms asteroid belt; Kuiper belt, Oort cloud

Star-forming region in Large Magellenic Cloud, Hubble, 2003: 

Star-forming region in Large Magellenic Cloud, Hubble, 2003

Cassini approaching Saturn March 27, 2004 : 

Cassini approaching Saturn March 27, 2004

Closing in on Phoebe: 

Closing in on Phoebe Phoebe is an outer moon of Satrurn, 220 km. in diameter, and a retrograde orbit Top 3 images taken between June 4th and 7th Discovered in 1898, it has an albedo of 6% and a density of 1.6 gm/cc. June 10th image shows craters, peaks and bright- ness variations

Phoebe : 

Phoebe High resolution mosaic taken at closest approach on June 11, 2004 Contrast is highly ‘stretched’ in this image to show icy areas (bright streaks on crater walls) Craters visible at all scales; ancient surface Probably a remnant from an early, icy outer population of planetes- imals now in the Kuiper Belt beyond Neptune

Phoebe Mineral Maps: 

Phoebe Mineral Maps Images taken at visible and infrared wavelengths Red, green and blue are assigned to different IR wavelengths representing different materials Composite image shows mineral distribution of ferrous (+2) iron, water ice and unidentified ‘dirt’ component

Titan in Natural Colors: 

Titan in Natural Colors Atmosphere thicker than Earth’s; composed of nitrogen and methane Reactions with sun- light in the upper atmosphere generate a rich organic smog Conditions at surface (low temp.; high pressure) suggest possible lakes and/or oceans of complex hydrocarbons at surface May be similar to conditions on early Earth; Huygen’s probe to enters Titan’s atmosphere Jan. 14, 2005

Titan at Different Wavelengths : 

Titan at Different Wavelengths ‘Pictures’ of Titan taken at three different wavelengths (2 of which actually ‘saw’ the surface) Brightness variations in each image are scaled to either red, green or blue RBG composite yields ‘surface composition’ map

Rings of Saturn: 

Rings of Saturn Visible rings 99%+ water ice particles A ring: ice mountains Cassini division: ice cubes B ring: ice boulders C ring: snowflakes

Saturn’s Rings at Different Wavelengths: 

Saturn’s Rings at Different Wavelengths Image taken above rings with transmitted light at closest approach June 25 IR reflectance shows thickness; ice concentrated in outer A ring Cassini division shows both ice and the ‘dirt’ signature seen at Phoebe

Saturn’s Rings in Ultraviolet Light: 

Saturn’s Rings in Ultraviolet Light C ring B ring transition Trend from ‘dirty’ outer C ring on left to ‘icier’ B ring Cassini Division and entire A ring; 15,000 km wide A ring increasingly icy to outside; Encke gap‘dirty’?

Target Earth : 

Target Earth