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Moon Earth

Earth Gets Another Quasi-Moon 54

The Bad Astronomer writes Astronomers have found a new asteroid, 2014 OL339, that is a quasi-moon of the Earth. Discovered accidentally earlier this year, the 150-meter asteroid has an orbit that is more elliptical than Earth's, but has a period of almost exactly one year. It isn't bound to Earth like a real moon, but displays apparent motion as if it did, making it one of several known quasi-moons.
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Earth Gets Another Quasi-Moon

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  • Poor Alan (Score:5, Funny)

    by kruach aum ( 1934852 ) on Wednesday October 01, 2014 @01:50PM (#48039175)
  • by wisnoskij ( 1206448 ) on Wednesday October 01, 2014 @01:57PM (#48039277) Homepage
    Obligatory quote.
    • by fyngyrz ( 762201 )

      There's no dark side of the moon. It's all dark, really...

      • Quote triple play.

        It can be either all dark or all light at certain locations...

        The Moon's axial tilt with respect to the ecliptic is only 1.5424 degrees, much less than the 23.44 degrees of Earth. Because of this, the Moon's solar illumination varies much less with season, and topographical details play a crucial role in seasonal effects. From images taken by Clementine in 1994, it appears that four mountainous regions on the rim of Peary crater at the Moon's north pole may remain illuminated for the entire lunar day, creating peaks of eternal light. No such regions exist at the south pole. Similarly, there are places that remain in permanent shadow at the bottoms of many polar craters, and these dark craters are extremely cold: Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (238 C) and just 26 K close to the winter solstice in north polar Hermite Crater. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto.

        • by dkman ( 863999 )
          That is an odd quote. 238 Celsius in 511 Kelvin. 35 Kelvin is -238 Celsius. I know parenthesis are used to represent negatives in excel, but I don't think that was the intention here, nor does that get communicated.
        • ...it appears that four mountainous regions on the rim of Peary crater at the Moon's north pole may remain illuminated for the entire lunar day, creating peaks of eternal light.

          Not quite. Unless I'm more mistaken than usual, even those peaks go dark during a total eclipse of the Moon.
      • by osu-neko ( 2604 )

        There's no dark side of the moon. It's all dark, really...

        Well, there is a darker side. It's just not always the same side.

  • So in other words...aliens.
  • Is a quasi-moon like a quasi -planet (i.e., Pluto)?
    • by gstoddart ( 321705 ) on Wednesday October 01, 2014 @02:21PM (#48039541) Homepage

      Sort of. ;-)

      The quasi-moons are more moon-like than planet like, because the quasi-moons orbit planets and quasi-planets orbit the sun, so in that regard they're almost entirely different, except for how they're not. =)

      If the quasi-moon orbited the sun it would be quasi-planet, but then it's too small, so then it just becomes another piece of space debris with an orbit around the sun. And then it's probably an asteroid. Unless it's a really big asteroid, then it's kind of like a planet. Or possibly a quasi-planet.

      It's all very complicated. :-P

    • by radtea ( 464814 ) on Wednesday October 01, 2014 @02:37PM (#48039695)

      Is a quasi-moon like a quasi -planet (i.e., Pluto)?

      Nope. Pluto's designation is based on it's size, mostly. The category "planet", like all categories, is made by humans to conveniently describe the universe to ourselves, and the precise boundaries are constrained (but not determined) by how the universe actually is and how we actually are. Within those constraints we can put the boundary where we like, and in the case of planets, smaller bodies that don't dominate their gravitational neighbourhood have been deemed to fall outside the human-created category we use the word "planet" to label.

      Quasi-moons are bodies in solar orbits that have interacted with their quasi-primary such that they are "station keeping" with it. A body like this one will wander around in the general vicinity of Earth as both Earth and quasi-moon travel around the sun together. So from the perspective of an observer on Earth, the quasi-moon executes periodic but non-orbital motion: it wanders in a closed configuration that does not describe a path that goes around the Earth.

      This is, like many such distinctions, fairly arbitrary: the sun's gravity at the orbit of the Moon is a good deal stronger than the Earth's gravity at the orbit of the Moon, so one could describe the Moon as being in orbit about the sun, with it's orbit perturbed into a wobble by the nearby Earth. That is, from an outside observer's perspective, the Moon's motion is never retrograde with respect to it's mutual orbit with Earth around the sun.

      Consider the view:

      O o .

      where the O is the sun, the o is the Earth and the . is the Moon. In the configuration shown (with the Moon on the outer wobble of its orbit about the Sun) it is moving faster than average (imagine the Earth and Moon both rotation clockwise around the Sun, and the Moon moving clock-wise around the Earth, so when in the image above it is moving "down" on the page).

      But in the situation that obtains two weeks later:

      O . o

      where the Moon on the inner wobble of its orbit about the Sun, it is still moving "down" on the page relative to the Sun even though it is moving "up" on the page from the perspective of an observer on Earth.

      Another way to see this is to consider that the Moon executes a wobble like this once a month, traveling 2*pi*0.25 million miles (lunar orbit is about 250 thousand miles), but at the same time moves 2*pi*96/12 million miles in its orbit around the Sun (which is 96 million miles from Earth), and since 96/12 > 0.25 it should be clear that the Moon's orbital velocity around the Sun is higher than it's orbital velocity around the Earth. Ergo: no retrograde motion for the Moon!

      All of this is a very long-winded way of saying: how we classify Moons vs quasi-moons is useful, but--as with all the ways we as knowing subjects classify the objectively real universe we live in--somewhat arbitrary. We could--but don't, so far as I know--have a name for the class of moon-like objects that have orbital velocities around their primary that are greater than their orbital velocity around their primary's primary (most Earth-orbiting satellites fall into this category.) Instead, we have a name for objects that don't execute motions relative to their (quasi-)primary that look like a loop around it from the perspective of an observer on the primary's surface.

      • Pluto's designation is based on it's size, mostly

        I thought that it had more to do with 2 factors: 1. Its composition (mostly ice) and 2: Its highly eccentric orbit.

        There is a name for bodies which are mostly ice and have very eccentric orbits: "asteroid".

        • At this point, also massive enough to be quasi spherical and having cleared its orbit of debris
        • by hawk ( 1151 )

          Nah, it's just inflation.

          Kind of like how a buck used to get you a great burger, but now only the dregs of the menu.

          Two enormous rocky-ice things in orbit around one another used to be enough to get you a planet, but no longer . . .

          hawk, pretty sure that it's not about a disney trademark . . .

      • by Anonymous Coward

        Sure, but by that token, the moon doesn't orbit the sun either, but the supermassive black hole at the center of the Milky Way. It probably stops there, but you could still claim that its motion is more influenced by the expansion of the universe resulting from the Big Bang. The point is, describing the Moon as orbiting around the Earth is useful - it's true in the reference frame of the Earth. But this quasi-moon doesn't orbit the Earth, not even in the reference frame of the Earth.

    • A quasi-moon is more like an object trapped in an orbital resonance [wikipedia.org]

      And are you still pining for 9 planets? Forget about Pluto, there's much more interesting possibilities out there! [wikipedia.org]

      What we learned in elementary school is not the be-all, end-all of information. :)

      • Yet most people stop learning once they get out of school, knowing all they need to know and surprised that they really don't know anything.
  • Hmmm ... (Score:5, Funny)

    by gstoddart ( 321705 ) on Wednesday October 01, 2014 @02:12PM (#48039467) Homepage

    2014 OL339 is awkward. It sounds like it needs a proper name.

    How about Quasimoondo?

  • Would this one be easier to fully chrome?

  • Capture it (Score:4, Insightful)

    by Spy Handler ( 822350 ) on Wednesday October 01, 2014 @02:16PM (#48039503) Homepage Journal

    1. bring it into true earth orbit
    2. ???
    3. Profit!

    • 2. Fill it full of extreme high definition satellite cameras and sell it to NSA.
    • Act quick. From TFA: Earths gravity is pushing it away. Within 200 years it'll be just another asteroid.
      • by arth1 ( 260657 )

        Earths gravity is pushing it away.

        So it's an antimatter quasi-moon, then?
        Otherwise, Earth's gravity would be pulling it away.

        • Otherwise, Earth's gravity would be pulling it away.

          Orbital mechanics is fun. Pretend you're in a spacecraft in the exact same orbit as the ISS, except offset such that it is always 100 meters in front of you. What happens when you apply an instantaneous delta-v directly toward it? Answer: you will now be orbiting slower than the ISS, and after you get a little closer, the ISS will pull away from you.

          What we're probably looking at here (I don't know, I haven't checked) is more like a slow gravity assist maneuver. The Earth's gravity is changing the angul

        • Not this again.

          I'm assuming you're just trying to be funny, but the usual formulas for gravity as a strictly attractive force apply only in an inertial frame. But it's possible, using calculus, to change the co-ordinate system to derive comparable laws of physics for a system which follows the Earth. In this frame of reference, gravity is much more interesting [mrreid.org]. So it's entirely possible, that from the point of view of an observer on the Earth, Earth's gravity is pushing this asteroid away.

          And for what it

  • For sure. They are watching us.

All laws are simulations of reality. -- John C. Lilly

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