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Martian Moons May Have Formed Like Earth's

Posted by Soulskill on from the carved-out-of-green-cheese dept.

sciencehabit writes: Astronomers have long believed that Mars snatched its two moons — Phobos and Deimos — from the asteroid belt. That would explain why the objects look like asteroids—dark, crater-pocked, and potato-shaped. But computer simulations by two independent teams of astronomers (abstract 1, abstract 2) indicated that Mars's moons formed much like ours did, after a giant space rock smashed into the planet and sprayed debris into orbit.

50 comments

  1. Wou would have thought. by nospam007 · · Score: 3, Funny

    "Mars snatched its two moons — Phobos and Deimos — from the asteroid belt."

    So there really _are_ (astronomical) body snatchers from outer space.

    1. Re:Wou would have thought. by Ken_g6 · · Score: 2

      Yeah, except TFA is about how Mars isn't (much of) one. Jupiter is a big body snatcher, and Neptune may have snatched a big body (Triton), but it looks like Mars is innocent.

      --
      (T>t && O(n)--) == sqrt(666)
    2. Re:Wou would have thought. by antiperimetaparalogo · · Score: 3, Informative

      "Mars snatched its two moons — Phobos and Deimos — from the asteroid belt."

      So there really _are_ (astronomical) body snatchers from outer space.

      I am full of Fear and Dread right now...

      --
      Antisthenes: "Wisdom begins by examining the words/names." - excuse my English, i am (slightly...) better with my Greek!
    3. Re:Wou would have thought. by michelcolman · · Score: 1

      But how exactly does a planet "snatch" another object? The smaller object starts out at a huge distance from the planet, falls towards it (increasing its kinetic energy), passes by the planet (if it doesn't crash into it), and then... converts its kinetic energy back to the amount of potential energy it started out with, right?

      Now if two different bodies would collide while close to the planet, some of the debris might just end up in orbit around the planet. But why would one small object not simply leave the planet again?

      (Just an honest question, not saying anyone is wrong, just wondering how it works)

    4. Re:Wou would have thought. by Rockoon · · Score: 1

      But why would one small object not simply leave the planet again?

      There is no reason that doesnt defy physics for stable orbits to form in the manner suggested for "capture" of single bodies. A force other than gravity needs to be applied.

      Not sure why it is so often suggested that "captures" work. They don't unless there is a 3rd body that can be given the energy difference. If this 3rd body then leaves the system then a stable orbit is possible for the "captured" object, but if it doesnt leave the system then its a 3 body problem where the initial conditions preclude the possibility of a stable orbit.

      --
      "His name was James Damore."
    5. Re:Wou would have thought. by Vulch · · Score: 3, Interesting

      Basically you need a third object to get involved, for instance it's thought that Triton was one of a pair of similar sized objects in orbit around each other. Triton was (relatively) going backwards at the time of a close approach so landed up in orbit around Neptune, it's partner got slung away. That also seems to explain why Triton is in a retrograde orbit.

    6. Re:Wou would have thought. by cusco · · Score: 1

      In the case of small bodies (such as spacecraft) the atmosphere can substitute for the third body. I would assume that if it is small enough a debris cloud like Saturn's rings could substitute over a long period of time, but the upper limit on that would have to be pretty low.

      --
      "Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
    7. Re:Wou would have thought. by Anonymous Coward · · Score: 0

      That is true of a two body system, but a planet+potential moon+the Sun is a three body system.

    8. Re:Wou would have thought. by Rockoon · · Score: 2

      In the case of small bodies (such as spacecraft) the atmosphere can substitute for the third body.

      No, it can't.

      You have found a way to lose enough energy for the object to remain in the system, but have not found a way to then add the energy necessary to put the object into a stable orbit (one that doesnt intersect your "solution" atmosphere.)

      To be quite clear: If the orbit intersects the atmosphere this time around, and you dont add energy at some point immediately after that, then it will again intersect the atmosphere the next time around, and the time after that.... it will only take a few orbits until your "captured" object slams into the planet/moon that you claim is "capturing" it.

      --
      "His name was James Damore."
    9. Re:Wou would have thought. by Anonymous Coward · · Score: 0

      BOOM BOOM!

  2. Aphelion vs Parhelion by TWX · · Score: 4, Informative

    Phobos and Deimos both have nearly circular orbits, with aphelions and parhelions that are not very far apart:

    Phobos:
    9,234 km min
    9,376 km average
    9,518 km max


    Deimos:
    23,453 km min
    23,458 km average
    23,463 km max


    Compared to our Moon:
    384,400 km min
    363,104 km average
    405,696 km max


    I can see how one could say that Phobos and Deimos, like our Moon, have extremely regular orbital distances, but given that the science that has stated that our Moon was caused by an impactor is still itself being both refined and challenged, I wonder if it's a little premature to conclude that based on orbital characteristics alone the two Martian moons derived from the same sort of event as our Moon. After all, many of the planets have orbits that are very near circular, but we do not interpret their existence in a similar fashion.

    --
    Do not look into laser with remaining eye.
    1. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      Refined, OK, but is the impactor theory actually being challenged? I mean, has anybody came up with something nearly as good?

      I recall, before the impactor theory became popular, scientists joking that the moon "shouldn't even be there", given its size relative to Earth. No theory at the time could explain why the Earth has such a big moon.

    2. Re:Aphelion vs Parhelion by aaron4801 · · Score: 1

      This is 2015, we don't need to have any better theories before we challenge science. America, FUCK YEAH!

    3. Re:Aphelion vs Parhelion by ebacon · · Score: 1

      Technically Aphelion and Perihelion refer to distance from the Sun for Sun-Orbiting bodies. I'm not sure what the term for min/max orbital distance for Mars orbits would be. Since greek for Mars is Ares, maybe aparion and periarion ?

    4. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      I wonder if it's a little premature to conclude that based on orbital characteristics alone the two Martian moons derived from the same sort of event as our Moon

      It's not based on that alone, the conclusion is also based on computer simulations of an impact. RTFS.

      384,400 km min
      363,104 km average

      So for our Moon the average is smaller than the min? That's rather unusual don't you think?

    5. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      the generic terms are 'periapsis' and 'apoapsis' or 'apsis'

    6. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      W00t!

      Here hold my Beer, while I burn this cross on some scientists lawn.

    7. Re:Aphelion vs Parhelion by Tablizer · · Score: 1

      Don't tidal forces eventually produce near-circular orbits? Thus, if they were captured asteroids, over time a "lopsided" orbit should grow circular and roughly equatorial.

      --
      Table-ized A.I.
    8. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      *WHOOSH*

    9. Re:Aphelion vs Parhelion by TWX · · Score: 1

      Thanks. Couldn't remember the generic terms. I guess you could blame the combination of video games use apogee and perigee, plus the use of perigee in that episode of Star Trek: The Next Generation where Q lost his powers while the ship was trying to save a planet from a natural satellite crashing down, so I picked the ones that I knew didn't specifically refer to Earth-orbiting satellites, though i guessed poorly...

      --
      Do not look into laser with remaining eye.
    10. Re:Aphelion vs Parhelion by ceoyoyo · · Score: 2

      "many of the planets have orbits that are very near circular, but we do not interpret their existence in a similar fashion."

      We do actually. It's pretty well accepted that the planets around the sun coalesced from a protoplanetary disc surrounding the young sun. The impact hypothesis for moon formation is similar: a big impact causes debris to be thrown into an orbiting disc around the planet and one or more moons then coalesce out of it. The alternative, capture of a separately orbiting body, isn't seriously considered for the origin of the planets.

    11. Re:Aphelion vs Parhelion by painandgreed · · Score: 3, Informative

      I can see how one could say that Phobos and Deimos, like our Moon, have extremely regular orbital distances, but given that the science that has stated that our Moon was caused by an impactor is still itself being both refined and challenged, I wonder if it's a little premature to conclude that based on orbital characteristics alone the two Martian moons derived from the same sort of event as our Moon. After all, many of the planets have orbits that are very near circular, but we do not interpret their existence in a similar fashion.

      The impactor theory for the origin of the moon is being refined, but AFAIK, it really hasn't been challenged seriously since the early 90's. Before that there were many competing theories for the origin of the moon from forming at the same time as the earth, captured by there earth, formed from impact, and a few others. Meanwhile there are various criteria such scenarios must meet dealing with angular velocity of the moon, composition, etc. In the early 90's computer modeling got to the point that they could do such for impactor theory and resulted with a model of an impact of another body of similar composition that would collide with the proto-Earth, split off a glob that would become the moon while leaving it's own iron core to explain the Earth's relative large one. At that point, while not perfect, the impactor theory was basically doing better over all in the criteria than the other options. I remember seeing the presentation and video of the computer simulation while an undergrad in physics in the early 90's. I've been keeping up with the subject when I see it, and it has been modified, mainly that two moons were formed and then they recombined in a rather low energy collision to form the moon. I have not heard any serious competition by the other theories since then.

    12. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      There was no "whoosh", you fucking idiot.

      GP was mocking people that hold to the actual scientific method as backwater "America! FUCK YEAH" types, thereby advocating that hypotheses shouldn't be challenged or tested.

      The "Whoosh" was the wind between your own ears.

    13. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      DOUBLE WOOSH...

    14. Re:Aphelion vs Parhelion by Anonymous Coward · · Score: 0

      I only know those words because of Kerbal Space Program

    15. Re:Aphelion vs Parhelion by painandgreed · · Score: 1

      More detailed info:

      https://www.psi.edu/epo/moon/moon.html

  3. Martians??? by Anonymous Coward · · Score: 0

    Isn't the bigger news here that we discovered Martians???

  4. Dumbing down by ArcadeMan · · Score: 1

    Mars's moons formed much like ours did, after a giant space rock smashed into the planet and sprayed debris into orbit.

    Is that the technical term?

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    1. Re:Dumbing down by Anonymous Coward · · Score: 0

      "Giant Flaming Meteorite" is the proper term. (Dave Lister)

    2. Re:Dumbing down by H0p313ss · · Score: 1

      I had the same reaction.

      I weep for my unborn grandchildren's generation.

      --
      XML is a known as a key material required to create SMD: Software of Mass Destruction
  5. cheese by tverbeek · · Score: 1

    You mean Phobos and Deimos are also made of cheese?

    --
    http://alternatives.rzero.com/
  6. Phobos and Deimos by Anonymous Coward · · Score: 1

    That also explains where the names of the characters came from in Quake 3 :)

  7. Surely a chemical analysis would reveal origin? by Anonymous Coward · · Score: 0

    Can't we do a chemical analysis of the composition of the moons and see if a) they are similar to each other, and b) they are similar to Mars, and c) they are similar to other asteroid belt bodies? Should be pretty straightforward.

    1. Re:Surely a chemical analysis would reveal origin? by prgrmr · · Score: 1

      We tried that, but it resulted in yet another failed mission to Mars: http://en.wikipedia.org/wiki/P...

    2. Re:Surely a chemical analysis would reveal origin? by ceoyoyo · · Score: 1

      The Russians tried to send a sample return mission to Phobos. It failed to get out of Earth orbit. Eventually we'll probably do that though.

  8. KISS by Anonymous Coward · · Score: 0

    I guess that it makes sense in one way -- it's rather unlikely for asteroids to happen to approach in a way that they'll get captured, but it is rather likely for big rocks to splat into a planet. If splats send debris out in many directions, it may be more likely for debris to end up in orbit than for asteroids to get captured.

  9. Computer Simulations by Rob+Riggs · · Score: 1

    Computer simulations would indicate that I can fly an X-wing fighter better than most Jedi, am an awesome mech warrior driver, and can land a spaceship on the moon with more finesse than Neil Armstrong.

    --
    the growth in cynicism and rebellion has not been without cause
  10. Density matches theory by Yergle143 · · Score: 3, Interesting

    Here are some relevant space object mean densities. Mars 3.93 g/cm3, Phobos 1.87 g/cm3, Deimos 1.47 g/cm3, Mercury 5.42 g/cm3, Luna 3.34 g/cm3, Earth 5.51 g/cm3, Ceres 2.07 g/cm3, Vesta 3.45 g/cm3, Europa 3.01 g/cm3, Comet 67P/Churyumov–Gerasimenko 0.47 g/cm3. If Phobos and Deimos formed from a violent collision it might be expected that they would be dense rocky objects like our moon or Vesta. However it seems that these moons more resemble the icy object end of the density spectrum. Did they form during a wetter Martian era?
    I think the take home message is that some exploring of the Martian moons is in order; a sample return mission would be much simpler than a Mars return with an interesting scientific purpose.
     

    1. Re:Density matches theory by ceoyoyo · · Score: 3, Interesting

      The impact hypothesis nicely explains why the moon is less dense than Earth: the impact preferentially threw up light elements from the crust and upper mantle, not heavy elements that would have sunk to the core. The densities of Phobos and Deimos are also less than that of Mars, but because they're so small, and are probably more like orbiting gravel piles, their densities are also consistent with small asteroids.

  11. Time to take some samples. by Anonymous Coward · · Score: 0

    Fortunately, such an event will leave behind evidence. Earth's moon has almost exactly the same material makeup and percentages of elements as the Earth itself. So, we can take samples of Mars and its moons to test TFA's hypothesis.

  12. How long ago? by Anonymous Coward · · Score: 0

    Phobos will crash into Mars 40 millions years from now. So how long ago was the impact with the large Ceres size body? If it was 4Byrs ago during the bombardment era I wouldn't sweat it. But if it was more recent I would start worrying.

  13. WTF by Anonymous Coward · · Score: 0

    Everybody including Barak Obama knows that Climate Change invented the TV in 1738.

    Dah.

  14. Re:Why should we allow Muslims into the country? by deodiaus2 · · Score: 0

    In the last 500 years of Western expansion, 75 Billion indigenous people were killed. The Arabs are mere amateurs at this compared to Christians.

  15. Re:Why should we allow Muslims into the country? by Hognoxious · · Score: 1

    Can you explain how they managed to kill people more than once?

    --
    Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  16. Re:Why should we allow Muslims into the country? by Anonymous Coward · · Score: 0

    That is an interesting figure, given that an estimated 100 billion people have ever died in human history, and more than about 40 billion of those would have been before Christianity even existed, and 80 billion would have died more than 500 years ago.