Slashdot Mirror

← Back to Stories (view on slashdot.org)

Mars Express Captures Phobos and Deimos

Posted by Soulskill on from the holding-for-ransom dept.

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. '"

21 of 84 comments (clear)

  1. Wow. by FlyingSquidStudios · · Score: 4, Funny

    It's so weird when reality looks like bad Photoshop.

    --
    http://twitter.com/OLDTELEGRAM
    1. Re:Wow. by Tablizer · · 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.

      --
      Table-ized A.I.
    2. Re:Wow. by DNS-and-BIND · · Score: 4, Informative

      Most "space images" are very heavily processed. If they took a normal picture it wouldn't look nearly as good. NASA learned a long time ago that its only reason for getting funded (besides being a jobs program) was making pretty pictures.

      --
      Shutting down free speech with violence isn't fighting fascism. It IS fascism!
    3. Re:Wow. by sznupi · · Score: 2, Informative

      Hm, at NASA...I don't know, perhaps.

      But Mars Express is ESA mission.

      --
      One that hath name thou can not otter
  2. Anyone noticed ... by PIBM · · Score: 2, Interesting

    That the jpg weight in at 666kb ?!!!?

  3. Ask slashdot by papabob · · Score: 2, Interesting

    Please, forgive my ignorance (physics is not my field): What orbit model is going to be refined? I've always thought that planetary movements were resolved centuries ago, and that modern cosmology studies the 'very big' things, portions of universe so massive that introduce glitches in relativistic theories, instead of moons' orbits.

    1. Re:Ask slashdot by Tablizer · · Score: 5, Informative

      Please, forgive my ignorance (physics is not my field): What orbit model is going to be refined? I've always thought that planetary movements were resolved centuries ago

      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.
           

      --
      Table-ized A.I.
    2. Re:Ask slashdot by sznupi · · Score: 2, Interesting

      Planetary models from centuries were basically an example of:
      a) idealized scenario (frictionless vacuum kind of stuff)
      b) based on Newtonian physics; which is not quite accurate...

      With the number of bodies and their interactions, Solar System is pretty much chaotic:

      http://en.wikipedia.org/wiki/N-body_problem
      http://en.wikipedia.org/wiki/Stability_of_the_Solar_System

      --
      One that hath name thou can not otter
    3. Re:Ask slashdot by Brett+Buck · · Score: 2, 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

    4. Re:Ask slashdot by mbone · · Score: 3, 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 - 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, 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 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 - 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.

    5. Re:Ask slashdot by mbone · · Score: 2, Interesting

      Well, if you pick times at random, we would say that a 1% chance of encountering something is fairly low. But, of course, 1% events happen all of the time, even in Astronomy.

      Here is a better way to look at probability in astrophysics and planetary physics - if you conclude that you just happened to observe something or catch some event at an unlikely point of its life-cycle, that may be a clue that you are calculating your probabilities wrong, i.e., that your theory is wrong or incomplete. So, improbable events tend to get the theorists interested. One obvious way to make Phobos less improbable is to see if the high dissipation could be intermittent.

      By the way, when the short lifetime for Phobos was first realized back in the 1950's, it was thought that the orbital decay was due to atmospheric drag, which required a lot of drag at a high altitude. One way to accomplish this would be to have a very low Phobos mass to area ratio, which lead to I.S. Shklovsky hypothesizing that Phobos was a hollow spacecraft. In that case, a short lifetime would not be surprising, as a spacecraft would presumably be a fairly recent addition to Mars's satellites. Alas, with a proper tidal model and data such as the OP, there is no more need for that hypothesis.

    6. Re:Ask slashdot by CecilPL · · Score: 2, 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.

  4. action films by f3r · · Score: 5, Insightful

    It's sad that we are so used to action and sci-fi films with amazing simulations of astonishing things, that when it comes to the real one (a piece of rock which really exists up there, and IS cool) we think we are seeing the intro for a 1985 asteroid game, and think for ourselves 'where are the explosions? I myself had to do an effort to rationally avoid that thinking and covince myself of the real coolness of the thing.

  5. That's odd... by jtownatpunk.net · · Score: 3, Funny

    I don't see any Leather Goddesses. Maybe I need to set the naughtiness level to "lewd".

  6. Nice mission overall by dragisha · · Score: 2, Interesting

    Movie is only one of mission returns, and it surely looks like a video game to many who don't think further than WoW when thinking about exploring unknown :).

    Mission itself is what is important here - being technologically advanced far more than Voyagers and giving us previews of what will come in future.... Better cameras and other instruments, better communications, faster spacecraft.... We are only beggining to see around solar system (Voyager is only 32 yrs old) and Mars Express is BIG THING.

    What is also expected is downplay of whole thing, not-invented-here syndrome... But it's ok and it's temporary - results will surely be used without discrimination in world's scientific communities.

    What I can't understand is why they're still inventing whole lander thing when technology for safe landing (and going back up) of people is tried FORTY years ago?!! One would expect it wil be everyday thing after so much time. Just think about how other technologies developed in 40 years span. Just compare already mentioned cameras and communications.... Weird.

    --
    http://opencm3.net, http://www.nongnu.org/gm2/
    1. Re:Nice mission overall by tftp · · Score: 4, Interesting

      What I can't understand is why they're still inventing whole lander thing when technology for safe landing (and going back up) of people is tried FORTY years ago?!!

      We know how to land in dense atmosphere (Earth, Venus) and in vacuum (the Moon). But there are no good solutions for landing in thin atmosphere (Mars). You can't use a parachute because there isn't enough atmosphere for it, and you can't use a rocket engine because incoming flow of atmospheric gases interferes with the engine (extinguishes flame and creates oscillations like in a whistle.) That's why robots are just dropped on Mars in a big airbag. But the deceleration is too high for a human.

    2. Re:Nice mission overall by sznupi · · Score: 2, 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.

      --
      One that hath name thou can not otter
    3. Re:Nice mission overall by Brett+Buck · · Score: 2, Interesting

      We know how to land in dense atmosphere (Earth, Venus) and in vacuum (the Moon). But there are no good solutions for landing in thin atmosphere (Mars). You can't use a parachute because there isn't enough atmosphere for it, and you can't use a rocket engine because incoming flow of atmospheric gases interferes with the engine (extinguishes flame and creates oscillations like in a whistle.) That's why robots are just dropped on Mars in a big airbag. But the deceleration is too high for a human.

                What in the world are you talking about? Both parachutes and rocket-braked landings have successfully been used, in combination on the same mission. Parachutes are marginal due to the thin air, so you use rocket engines to slow it down. There is no significant issue with firing engines in thin air, it's a non-issue - the bit about "atmospheric gasses interfering with the engine" is 99% nonsense. The only issue with doing it entirely with rocket engines is that it takes so much fuel that you would have trouble getting it there without a huge rocket. So you aerodynamically brake it to some reasonable velocity, then finish it off with rocket engines. It's a relatively simple problem that was solved and proven i 1976 and repeated many times since.

            Airbags are useful for smaller missions because it allows you to do less rocket-propelled braking and save fuel. But even the airbab missions used both parachutes and rocket braking. If you just let it fall at terminal velocity with no chute and no braking, no airbag is going to save it, you are going to dig a pretty deep hole.

                Brett

  7. No! Get away! by Windwraith · · Score: 2, Funny

    Or you might end knee-deep in the dead.

  8. Odd Phobos striations by macraig · · Score: 2, Interesting

    What's the deal with the curious striations running longitudinally across the whole surface? Notice, in particular, that they even continue down into and through craters! What could cause that?

    My first thought was that Phobos must have a fast spin in addition to its fast orbit, and that it was acquiring those gouges as it spins through clouds of debris. Then I read the notes and learned that the "N" marked the north pole of its axis, meaning that the striations are running perpendicular to its rotation!?

    Back to the drawing board....

    1. Re:Odd Phobos striations by macraig · · Score: 2, 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.