The tragedy of the failure of Russia's Phobos-Gunt mission to explore Mar's largest moon is that we may never solve some enduring and fasinating mysteries about this stange object. The window to contact the stranded space probe and send it on its mission to the Martian moon has officially closed. Although the spacecraft could still fly by the Red Planet, but it will no longer be able to complete its exploration of the moon Phobos and return to Earth, space industry sources told Russian state news agency RIA Novosti.
Over the last two weeks, there was no clear response from attempts to get in contact with the Mars probe, which got stuck in Earth's orbit when its engines failed to fire and send it on its way to the Red Planet.
One of the least reflective bodies in the solar system, Phobos, orbits the planet below the synchronous orbit radius (it moves around Mars faster than the planet itself rotates).
In a recent development, scientists say they have uncovered firm evidence that Phobos, is made from rocks blasted off the Martian surface in a catastrophic event, solving a long-standing puzzle. It has been suggested that both Phobos and Deimos could be asteroids that formed in the main asteroid belt and were then "captured" by Mars's gravity.
An alternative theory suggests that 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.
Previous 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. This 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.
Data from the European Space Agency's Mars Express spacecraft appears to make the asteroid-capture scenario look less likely. Recent 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 -- 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.
"We 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. These phyllosilicate rocks are thought to form in the presence of water, and have been found previously on Mars.
"This is very intriguing as it implies the interaction of silicate materials with liquid water on the parent body prior to incorporation into Phobos," said Dr Giuranna. "Alternatively, phyllosilicates may have formed in situ, but this would mean that Phobos required sufficient internal heating to enable liquid water to remain stable."
Other observations from Phobos appear to match the types of minerals identified on the surface of Mars. Thus, the make-up of Phobos appears more closely related to Mars than to asteroids from the main belt, say the researchers. In addition, said Pascal Rosenblatt of the Royal Observatory of Belgium, "the asteroid-capture scenarios also have difficulties in explaining the current near-circular and near-equatorial orbit of both Martian moons (Phobos and Deimos)".
The researchers also used Mars Express to obtain the most precise measurement yet of Phobos' density."This number is significantly lower than the density of meteoritic material associated with asteroids. It implies a sponge-like structure with voids making up 25%-45% in Phobos's interior," said Dr Rosenblatt. A highly porous asteroid would have probably not survived if captured by Mars. Alternatively, such a highly porous structure on Phobos could have resulted from the re-accretion of rocky blocks in Mars's orbit.
In describing the internal geometric structure of this "moon" as revealed by MARSIS, European Space Agency (ESA) sources emphasized that "several of these interior Phobos compartments also appear to still be holding some kind of atmosphere ... " which has given birth to wild speculation that Phobos could prove to be an artificial satellite of some sort."
Like our Moon, Phobos always shows the same side to the planet, so it is only by flying outside the orbit that it becomes possible to observe the far side. Mars Express did just this on 7, 10 and 13 March 2010. Mars Express also collected data with other instruments.
The failed 2011 Russian Phobos–Grunt (meaning Phobos Soil) mission to land on the martian moon was to make in-situ observations with an important payload that would operate on the surface for one year. Moreover, it will collect samples which will be sent back on Earth for precise analyses.
The mission main objectives were solve the following :
-the origin of Phobos in relation with the study of the primitive matter,
-its evolution in relation with Mars,
-the role of the asteroids impacts in the formation of the planets and in the evolution of their atmosphere, their crust and in the inventory of the volatile elements.
In the late 1950s and 1960s, the unusual orbital characteristics of Phobos led to speculations that it might be hollow. Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky, studying the secular acceleration of Phobos' orbital motion, suggested a "thin sheet metal" structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin. Shklovsky based his analysis on estimates of the upper Martian atmosphere's density, and deduced that for the weak braking effect to be able to account for the secular acceleration, Phobos had to be very light.
The density of Phobos has now been directly measured by spacecraft to be 1.887 g/cm³, which is inconsistent with a hollow shell. In addition, images obtained by the Viking probes in the 1970s clearly showed a natural object, not an artificial one, and the "hollow Phobos" speculations have been relegated to the status of a historical curiosity
However, mapping by the Mars Express probe and subsequent volume calculations do suggest the possible presence of vast caverns within the moon and indicate that it is not a solid chunk of rock but a porous body instead. The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third of the moon being hollow, likely in the form of large voids.
In a July 22, 2009 interview with C-Span U.S. astronaut Buzz Aldrin said: "We should go boldly where man has not gone before. Fly by the comets, visit asteroids, visit Phobos, a moon of Mars. There’s a monolith there. A very unusual structure on this potato shaped object that goes around Mars once in seven hours. When people find out about that they’re going to say ‘Who put that there? Who put that there?’ The universe put it there."
The Daily Galaxy via via ESA
The Daily Galaxy via dailymail.co/uk
Image shows Planned landing site of the Russian Phobos-Grunt mission
Image Credits: ESA/DLR/FU Berlin (G. Neukum)