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I was wondering if any of the asteroids we have ever seen has a hot core like Earth's.

I'm thinking that Earth has a strong gravitational field and so formation would have involved a lot of gravitational energy being converted to heat, but not so much for the asteroids.

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    $\begingroup$ Most asteroids will not have hot cores, the've long-since equilibrated. But I don't know about the biggest, and I guess those are suddenly no longer classified as asteroids, but as dwarf planets. I think a good answer would include them as well. $\endgroup$
    – uhoh
    Commented Apr 7, 2019 at 23:58

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See Could a planet form without a molten state?, where Anders Sandberg calculates that a body with radius ~ 1000 km would melt from the heat of formation.

The largest asteroid, Ceres, has a radius of 473 km, so it's a bit too small to have totally melted just from gravitational accretion, but it may have picked up a little more energy from impacts that were faster than freefall. It could also generate some internal heat from radioactive decay, but it's not expected to contain a significant percentage of radioactive material.

Presumably, Ceres was plastic to some degree during formation, since it's (almost) spherical (and it's the only asteroid large enough for gravity to make it spherical). But that wouldn't have required a very high temperature, since Ceres contains a lot of water ice.

But even if it did totally melt when it formed, it's had over 4 billion years to cool down, so it's extremely unlikely to still have a hot core. However, it does emit more water vapour than expected, and it may be warm enough to contain some liquid water below the surface.

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As far as is known no asteroid currently has a hot core. Things were probably a bit different in the past. The asteroid Vesta is differentiated: it has a silicate mantle surrounding an iron core. This implies that during its formation Vesta did get hot enough that the materials separated. Ceres is also differentiated and may have a small metallic core, again implying an early hot interior state.

There are also iron asteroids, the largest of which is Psyche. These are probably remnants of differentiated objects (either fully or partially-differentiated) that got broken up: the iron asteroids are fragments of the metallic core.

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'll explain, the asteroids are small rocky objects that orbit the sun. Although asteroids orbit the sun like planets, they are much smaller than planets. Remember that most of them live in the asteroid belt that is that region between the orbits of Mars and Jupiter. Additionally some asteroids are in the orbital trajectory of the planets. This means that the asteroid and the planet follow the same path around the sun. You should also consider that these asteroids were usually all formed at the same time and that most of them are located at the furthest distances from the Kuipier belt that is closer to the 100UA. The fact is that due to their size and their physical characteristics, these objects can not have active nuclei.

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    $\begingroup$ You may want to expand your last sentence into an answer (why does their size not allow active nuclei?); the rest of the answer as written does not address the actual question. $\endgroup$
    – Anders Sandberg
    Commented Apr 8, 2019 at 18:22
  • $\begingroup$ there are no asteroids with active nuclei $\endgroup$
    – jormansandoval
    Commented Apr 12, 2019 at 14:19

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