say they have uncovered firm evidence that Mars’s biggest moon, Phobos, is made
from rocks blasted off the Martian surface in a catastrophic event.
origin of Mars’s satellites Phobos and Deimos is a long-standing puzzle.
has been suggested that both moons could be asteroids that formed in the main
asteroid belt and were then “captured” by Mars’s gravity.
latest evidence has been presented at a major conference in Rome.
new work supports other scenarios. Material blasted off Mars’s surface by a
colliding space rock could have clumped together to form the Phobos moon.
Phobos could have been formed from the remnants of an earlier moon destroyed by
Mars’s gravitational forces. However, this moon might itself have originated
from material thrown into orbit from the Martian surface.
observations of Phobos at visible and near-infrared wavelengths have been
interpreted to suggest the possible presence of carbonaceous chondrites, found
in meteorites that have crashed to Earth.
carbon-rich, rocky material, left over from the formation of the Solar System,
is thought to originate in asteroids from the so-called “main belt”
between Mars and Jupiter.
now, data from the European Space Agency’s Mars Express spacecraft appear to
make the asteroid capture scenario look less likely.
observations as thermal infrared wavelengths using the Planetary Fourier
Spectrometer (PFS) instrument on Mars Express show a poor match between the
rocks on Phobos and any class of chondritic meteorite known from Earth.
would seem to support the “re-accretion” models for the formation of
Phobos, in which rocks from the surface of the Red Planet are blasted into
Martian orbit to later clump and form Phobos.
detected for the first time a type of mineral called phyllosilicates on the
surface of Phobos, particularly in the areas northeast of Stickney, its largest
impact crater,” said co-author Dr Marco Giuranna, from the Italian National
Institute for Astrophysics in Rome.
phyllosilicate rocks are thought to form in the presence of water, and have
been found previously on Mars.