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IMAGES OF ASTEROID GASPRA
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This montage of 11 images taken by the Galileo spacecraft as it flew by the
asteroid Gaspra on October 29, 1991, shows Gaspra growing progressively
larger in the field of view of Galileo's solid-state imaging camera as the
spacecraft approached the asteroid.
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Gaspra Approach Sequence
October 29, 1991
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Sunlight is coming from the right.
Gaspra is roughly 17 kilometers (10 miles) long, 10 kilometers (6 miles)
wide. The earliest view (upper left) was taken 5 3/4 hours before closest
approach when the spacecraft was 164,000 kilometers (102,000 miles) from
Gaspra, the last (lower right)at a range of 16,000 kilometers (10,000
miles), 30 minutes before closest approach. Gaspra spins once in roughly 7
hours, so these images capture almost one full rotation of the asteroid.
Gaspra spins counterclockwise; its north pole is to the upper left, and the
'nose' which points upward in the first image, is seen rotating back into
shadow, emerging at lower left, and rotating to upper right. Several craters
are visible on the newly seen sides of Gaspra, but none approaches the scale
of the asteroid's radius. Evidently, Gaspra lacks the large craters common
on the surfaces of many planetary satellites, consistent with Gaspra's
comparatively recent origin from the collisional breakup of a larger body.
The Galileo project, whose primary mission is the exploration of the Jupiter
system in 1995-97, is managed for NASA's Office of Space Science and
Applications by the Jet Propulsion Laboratory.
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This picture of asteroid 951 Gaspra is a mosaic of two images taken by the
Galileo spacecraft from a range of 5,300 kilometers (3,300 miles), some 10
minutes before closest approach on October 29, 1991.
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Gaspra - Highest Resolution Mosaic
October 29, 1991
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The Sun is shining from
the right; phase angle is 50 degrees. The resolution, about 54 meters/pixel,
is the highest for the Gaspra encounter and is about three times better than
that in the view released in November 1991. Additional images of Gaspra
remain stored on Galileo's tape recorder, awaiting playback in November.
Gaspra is an irregular body with dimensions about 19 x 12 x 11 kilometers
(12 x 7.5 x 7 miles). The portion illuminated in this view is about 18
kilometers (11 miles) from lower left to upper right. The north pole is
located at upper left; Gaspra rotates counterclockwise every 7 hours. The
large concavity on the lower right limb is about 6 kilometers (3.7 miles)
across, the prominent crater on the terminator, center left, about 1.5
kilometers (1 mile). A striking feature of Gaspra's surface is the abundance
of small craters. More than 600 craters, 100-500 meters (330-1650 feet) in
diameter are visible here. The number of such small craters compared to
larger ones is much greater for Gaspra than for previously studied bodies of
comparable size such as the satellites of Mars. Gaspra's very irregular
shape suggests that the asteroid was derived from a larger body by nearly
catastrophic collisions. Consistent with such a history is the prominence of
groove-like linear features, believed to be related to fractures. These
linear depressions, 100-300 meters wide and tens of meters deep, are in two
crossing groups with slightly different morphology, one group wider and more
pitted than the other. Grooves had previously been seen only on Mars's moon
Phobos, but were predicted for asteroids as well. Gaspra also shows a
variety of enigmatic curved depressions and ridges in the terminator region
at left. The Galileo project, whose primary mission is the exploration of
the Jupiter system in 1995-97, is managed for NASA's Office of Space Science
and Applications by the Jet Propulsion Laboratory.
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This picture of asteroid 951 Gaspra is a mosaic of two images taken by the
Galileo spacecraft from a range of 5,300 kilometers (3,300 miles), some 10
minutes before closest approach on October 29, 1991.
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Gaspra - Highest Resolution Mosaic
(False Color)
October 29, 1991
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The Sun is shining from
the right; phase angle is 50 degrees. The resolution, about 54 meters/pixel,
is the highest for the Gaspra encounter and is about three times better than
that in the view released in November 1991. Additional images of Gaspra
remain stored on Galileo's tape recorder, awaiting playback in November.
Gaspra is an irregular body with dimensions about 19 x 12 x 11 kilometers
(12 x 7.5 x 7 miles). The portion illuminated in this view is about 18
kilometers (11 miles) from lower left to upper right. The north pole is
located at upper left; Gaspra rotates counterclockwise every 7 hours. The
large concavity on the lower right limb is about 6 kilometers (3.7 miles)
across, the prominent crater on the terminator, center left, about 1.5
kilometers (1 mile). A striking feature of Gaspra's surface is the abundance
of small craters. More than 600 craters, 100-500 meters (330-1650 feet) in
diameter are visible here. The number of such small craters compared to
larger ones is much greater for Gaspra than for previously studied bodies of
comparable size such as the satellites of Mars. Gaspra's very irregular
shape suggests that the asteroid was derived from a larger body by nearly
catastrophic collisions. Consistent with such a history is the prominence of
groove-like linear features, believed to be related to fractures. These
linear depressions, 100-300 meters wide and tens of meters deep, are in two
crossing groups with slightly different morphology, one group wider and more
pitted than the other. Grooves had previously been seen only on Mars's moon
Phobos, but were predicted for asteroids as well. Gaspra also shows a
variety of enigmatic curved depressions and ridges in the terminator region
at left. The Galileo project, whose primary mission is the exploration of
the Jupiter system in 1995-97, is managed for NASA's Office of Space Science
and Applications by the Jet Propulsion Laboratory.
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This montage shows asteroid 951 Gaspra (top) compared with Deimos (lower
left) and Phobos (lower right), the moons of Mars. The three bodies are
shown at the same scale and nearly the same lighting conditions.
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Gaspra, Deimos, and Phobos
Comparison
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Gaspra is
about 17 kilometers (10 miles) long. All three bodies have irregular shapes,
due to past catastrophic conditions. However their surfaces appear
remarkably different, possibly because of differences in composition but
most likely because of very different impact histories. The Phobos and
Deimos images were obtained by the Viking Orbiter spacecraft in 1977; the
Gaspra image is the best of a series obtained by the Galileo spacecraft on
October 29, 1991. Galileo is scheduled to add the detailed view of another
asteroid when it flies by Ida in August 1993. The Galileo project, whose
primary mission is the exploration of the Jupiter system in 1995-97, is
managed for NASA's Office of Space Science and Applications by the Jet
Propulsion Laboratory.
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Mathilde, Gaspra, Ida
Comparison
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These are views of the three asteroids that have been
imaged at close range by spacecraft. The image of
Mathilde (left) was taken by the NEAR spacecraft on June
27, 1997. Images of the asteroids Gaspra (middle) and
Ida (right) were taken by the Galileo spacecraft in 1991
and 1993, respectively. All three objects are presented
at the same scale. The visible part of Mathilde is 59 km
wide x 47 km high (37 x 29 miles). Mathilde has more
large craters than the other two asteroids. The relative
brightness has been made similar for easy viewing;
Mathilde is actually much darker than either Ida or
Gaspra.
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