Most meteorites that fall on Earth are fragments of broken-up asteroids which orbit the
Sun mostly between the orbits of Mars and Jupiter. This is indicated by photography of
meteorite fire balls as they enter Earth’s atmosphere, and extrapolation of the orbits which
reach into the Asteroid Belt.
Photograph of the bolide
resulting from the entry of
the Lost City, Oklahoma,
stone meteorite (ordinary
chondrite) on January 3,
1970.
The Lost City, Oklahoma, stone meteorite, recovered based on the triangulation of
the place of fall from the photographs of the associated bolide
Telescopically measured
optical reflectance spectra
of asteroids (points, with
error bars) with the
spectra of powders of
various types of meteorites
(solid lines). Conclusion:
The meteorite spectra
match the asteroid spectra
and, hence, the meteorites
come from asteroids
A = Comet Toit-Hartley; B = Asteroid 1982 DB
The Galileo spacecraft, on its way to Jupiter, was the first to obtain close-up pictures of
asteroids
The complex
orbit of the
Galileo spacecraft
The Galileo
spacecraft
during
construction
Launch of the
Galileo
spacecraft from
the Shuttle
Galileo Spacecraft after launch from the Shuttle
The Galileo spacecraft imaged the asteroids Gaspra and Ida.
Mathilde was imaged by the NEAR spacecraft.
Asteroids are highly irregular in shape, and some may have
moons too! Ida and its moon Dactyl, imaged by the Galileo
spacecraft
Dactyl
Asteroid Mathilde, imaged by the NEAR Spacecraft on its way to Asteroid Eros
Asteroid Eros – Orbited by NEAR* spacecraft in 2000
* NEAR = Near Earth Asteroid Rendezvous mission
Asteroid Eros and landing site of NEAR Spacecraft
Landing site
NEAR Spacecraft approaching Asteroid Eros
NEAR Spacecraft approaches the landing site on Asteroid
Eros
Landing site of the NEAR Spacecraft on Asteroid Eros, February 12th, 2001
Topography of Asteroid Eros, based on the NEAR mission
How many asteroids are there and where are they?
Number of asteroids as a function of their
distance from the Sun (in AU). The
Kirkwood Gaps are apparent, and the
resonances with Jupiter are also indicated
Inclination of orbits of asteroids
as a function of distance from
the Sun (in AU)
Orbits of some major asteroids
Summary
Chondrites are meteorites from broken-up primitive,
undifferentiated asteroids that never melted. Thus, the properties of
their constituents [calcium-aluminum-rich inclusions (CAIs),
chondrules, matrix, and metallic Fe,Ni] are today as they were when
the Solar System formed
Chondrite NWA 5028
Polished slice of an ordinary chondrite. White = metallic Fe,Ni; brown = silicates.
Handspecimen of an ordinary chondrite with a large chondrule
Thin section photomicrograph of an ordinary chondrite. Chondrules are ~ 1 - 5
mm in diameter
Chondrule consisting of glass (pink) and olivine (Fe-Mg- silicate) crystals (white)
Barred chondrule consisting of parallel bars of olivine (Fe-Mg
silicate) crystals (white) and silicate glass (pink-brown)
When a chondritic asteroid melts, it differentiates, i.e., the dense metallic Fe,Ni sinks and forms the
core, and the rocky material forms the mantel (e.g., ureilite) and crust (e.g., basalt) of the asteroid.
These rocks are collectively called achondrites, because they do not contain chondrules.
Minute diamonds (bright) in a ureilite. They formed from carbon by
high-pressure shock when asteroids collided.
Basaltic meteorite (eucrite), most likely from the crust of the asteroid Vesta
Pallasite – possibly fragment from the core/mantle boundary of a broken-up
asteroid.
Shiny = metallic Fe,Ni; brown = olivine, an Fe-Mg-silicate.
When a chondritic asteroid melts, it differentiates, i.e., the dense
metallic Fe,Ni sinks and forms the core, and the rocky material
forms the mantel (e.g., ureilite) and crust (e.g., basalt)
of the asteroid (just like in case of Earth).
Handspecimen of an iron meteorite – a fragment of the
core of a broken-up asteroid
How many meteorites, and of what types? Early observations of
“Falls” and “Finds”, excluding those from Antarctica and hot deserts.