Mars Express Captures Phobos and Deimos 84
westtxfun writes "The Mars Express Orbiter captured a very cool movie of Phobos and Deimos on Nov 5. Besides the 'wow factor,' the images will be used to refine models of the moons' orbits. The orbiter has also captured high resolution images of Phobos back in July. 'The images were acquired with the Super Resolution Channel (SRC) of the High Resolution Stereo Camera (HRSC). The camera took 130 images of the moons on 5 November at 9:14 CET in a span of 1.5 minutes at intervals of 1s, speeding up to 0.5-s intervals toward the end. The image resolution is 110 m/pixel for Phobos and 240 m/pixel for Deimos — Deimos was more than twice as far from the camera. '"
Re:Ask slashdot (Score:5, Informative)
Solar radiation and the solar "wind" has an effect on smaller bodies, such as those moons. The effects vary depending on the color, composition, and texture of the moons' surfaces. We need better models to know their impact on orbits. Relativity may also have a very minor impact on orbital changes.
Re:Wow. (Score:3, Informative)
It looks kind of fake because it was taken through a telescopic lens, and thus you don't see the perspective of movement. When photographers and artists want to exaggerate perspective, they do the opposite: use a wide-angle lens.
Re:Wow. (Score:5, Informative)
Re:Wow. (Score:3, Informative)
Hm, at NASA...I don't know, perhaps.
But Mars Express is ESA mission.
Re:Nice mission overall (Score:3, Informative)
Yes, it has been done, but only for objects with small mass; decelerating them fairly easy in comparison to what would be required from several-tonne lander capable of carrying humans.
Re:Ask slashdot (Score:3, Informative)
The theory behind orbits in general is a solved problem, for some limited specific condtions (i.e. gravity as a point source, two bodies, and stuff like that). But that doesn't mean you know the actual parameters of the orbit (inclination, semi-major axis (period), etc) of any particular body. Any orbit "fit" is alwasy being refined.
The other issue is that gravity actually isn't a point source with a simple inverse-square law nor are there only two bodies involved. The gravity of any real physical body is lumpy, other bodies pull on it, too, so the orbits are far from completely predictable and will never be perfectly well known.
Brett
Re:Ask slashdot (Score:4, Informative)
The orbit of Phobos, particularly, has an oddity that has attracted a lot of interest, and more data is always welcomed.
The orbit of Phobos is decaying, presumably due to tidal friction [cornell.edu] - the work required for Phobos to raise a small tidal bugle in the part of Mars below it. There is nothing surprising in that, per se (Moons inside a geostationary orbit will decay inwards due to tidal friction, Moons outside a geostationary orbit will "decay" outwards), but what is surprising is the "Q" required to match the observations. (The Q is total energy in the bulge divided by the rate of energy lost per orbit.) The Q inferred from observations of Phobos's orbital decay, and the rigidity of the Martian surface found from observations of the Martian Solar tide [berkeley.edu], is about 90. The corresponding Q for the Earth is about 12, but that is mostly due to ocean tides, and the Q inferred for the Earth's mantle is about 280.
So, the Mars-Phobos system has a higher solid-body dissipation [usra.edu] than the Earth-Moon system, which is surprising. In nailing this down, all sorts of data have been acquired for Phobos (including eclipse data from the Mars Rovers), but there is always room for more. What the current data should do is provide a tie for the relative longitudes of Phobos and Deimos which (especially if this can be repeated) will help make sure that there are no drifts between the orbits of the two Moons.
By the way, with the current orbital decay, the expected lifetime of the orbits is somewhere in the 20 to 40 million year range [arxiv.org] - it seems unlikely that we just happen to catch Phobos at its end-of-life, which has raised speculation about its decay being time variable.
Re:Ask slashdot (Score:3, Informative)
The North Pole for a body is the pole that lies in the Northern hemisphere.
That's tautologous. There are two common definitions of a body's North Pole. The first (and the International Astronomical Union's) is the pole of rotation that lies on the same side of the ecliptic plane as the Earth's north pole. This implies that Venus rotates "backwards".
The second definition is more local - it defines the North Pole as the pole around which the body rotates counterclockwise.
Re:Odd Phobos striations (Score:3, Informative)
After I commented, I found and read quite a few commentaries about them, none of which had an adequate explanation. The most curious aspect is how they continue THROUGH craters, even deep ones. It's almost as if something drove, or was dragged, across those areas. I'm having a hard time visualizing how any impactor could "slide" across the surface like that, even down into and then back out of craters and continuing. At first, second, and third glance they certainly appear to be unnatural.