Structure of the Frass Meteorite
The
very structure of the rock is evidence of its Martian origin. The rock is
made much like a space shuttle heat tile, in that it has very thin walls with
vesicles (holes) between the walls. This structure was made possible by
the low gravity, the thin atmosphere, and the cold temperatures on the Martian
surface. As the lava came forth from the volcano, the lower gravity of
Mars let the material form very thin walls. With less gravity, these walls
could form thinner than one would see on Earth. Many of the walls are only
as thick as a piece of paper.
The volcanoes near Los Alamos, New Mexico are very young
volcanoes and thus are
very similar in age to the lava flows of Mars that created the Frass
Meteorite.
The lava flows around here also have inclusions in them, where the lava flowed
around objects that were present on the surface when the lava flowed.
However, the larger gravity of Earth has caused the walls to be much thicker,
since they would have to support more weight to be stable. In this
picture, the thin walls are clearly visible.
Notice
how every surface has sand stuck to it. This is because the lava that
created the rock flowed through a bed of sand. Virtually every surface,
inside
or outside, of the Frass Meteorite is coated with this layer of sand.
In many places it appears to be "welded" to the rock, as the rock was probably
hot when it first touched the sand. Apparently the atmospheric temperature was very
low, because the lava appears to have cooled almost instantly. Thus many
of the inclusions in the rock are not melted. Most of the sand grains touching
the walls of the meteorite are stuck to the walls and cannot be easily
dislodged although the ones in the middle of each vesicle are easily detached by
the addition of water.
The overall shape of the meteorite is much like pillow
lava on Earth,
which forms when lava flows into ocean water, cooling rapidly and forming a
spherical shape with a crevice where the material parted the main flow.
The Frass Meteorite exhibits similar features, but was probably formed on the
surface of Mars, where the cold temperatures caused
rapid cooling resulting in
the spherical shape and the parting plane crevice. In this view one can
easily see the melting that occurred over the entire rock. The melted
surfaces tend to reflect the light and are thus the "shinny" pats of the
meteorite.
