New Images Reveal That This Asteroid Is Actually Two Conjoined Space Rocks. They Form a Peanut-Shaped Object Called a 'Contact Binary'
www.smithsonianmag.com
A flyby conducted by the Japanese spacecraft Hayabusa2 uncovered the asteroid's strange shape. Data gathered by the probe will also help defend the planet against potentially threatening space rocks
        • Buddahriffic@lemmy.world
          2·
          4 days ago

          Eventually all orbiting bodies will meet because they lose energy to gravity waves they send off into space.

          Unless the larger body is spinning faster than the smaller body, in which case tidal forces will give it energy (unless the larger body is perfectly uniform and solid enough that it lacks fluid tides) which causes its orbit to rise and can lead to orbital escape, especially if there’s other bodies to pull on it in the vicinity.

          Our moon is an example of that exception. We were once joined, some 4.5 billion years ago or so, but never will be again, other than rocks carried by visitors and the low chance we end up impacting the sun in the same place when it expands past earth’s orbit (assuming the moon is even still there, though iirc the timeline for its escape is a bit longer than the sun’s timeline for swallowing earth).

    • OwOarchist@pawb.socialEnglish
      3·
      5 days ago

      Well, it’s part of the process sometimes, surely.

      Planets (usually) form from a protoplanetary disc around a young star, mostly made up of star formation material that had too much orbital momentum for it to fall inward and become part of the star itself. But a flat spinning disc is only semi-stable in orbit. Its spin prevents it from falling inward toward the star, but there’s nothing to counteract the gravitational attraction of itself pulling on itself. So, gradually the homogeneous disc becomes more like a banded series of rings, starting off from random variations that happened to have a little more mass and gravitational pull than the surrounding regions of the disc. The same thing happens along the path of the orbit as well – a section that’s even slightly more massive than the rest will attract more material to itself, grow even more massive, and begin a feedback loop that results in it growing more and more, drawing more and more of the material from its ring into itself, until finally the entire ring coalesces into a single point, which forms a planet (or smaller body, if there’s not enough material).

      However, while that’s the idealized version, it’s usually not such a smooth process. There are always random variations in distribution, sometimes multiple masses within one orbit that are growing at the same time, sometimes things getting disturbed by random debris from outside the star system, etc. So that all means that there will sometimes be collisions occurring. If two large proto-planets collide (large enough to already be spherical), they will probably tear each other apart gravitationally as they reach the roche limit, and the resultant debris will quickly (relatively quickly) coalesce into a single larger spherical object (or maybe two spherical objects with one orbiting the other, which is how Earth is theorized to have acquired the moon.) But if the two colliding objects haven’t grown to that scale yet, they may very well directly collide without the roche limit being involved. And if their collision speed is low enough to not destroy them both, they may form a contact binary like this asteroid pair. However, if they’re still within a planet-forming disc, that will be only temporary. As the pair gravitationally attracts and accumulates more material, they will eventually become massive enough that the gravitational force overwhelms their structural rigidity, which means that they will collapse into a single spherical shape.