Comment from the discussion thread at the mineralcollectors subreddit:
To be clear, large crystals can and do form on Earth, most are much larger than those in these structures. There are stable places in the earth crust where this can happen - but the cooling rates required for this iron-nickel pattern is what makes them unique.These interlocking structures are like a fingerprint for iron-nickel meteorites. They can only form only in space, where asteroid cores cool at an incredibly slow and stable rate—about 1 to 100°C per million years. That kind of slow cooling doesn’t happen on Earth.Edit: Had to look up the name. They’re called Widmanstätten patterns.
So molten metal gets ejected into space from some collision, and then in a vacuum there is nothing to conduct the heat away, so it cools only by radiation and only a couple degrees per million years. You learn something every day.
More info on Widmanstätten patterns.
If the slow cooling rate is true, then would it not stand to reason that if your body temperature was at, say, 96 degrees, and you went for a spacewalk in deep space, that you wouldn't necessarily need to wear thermal clothing? That is, all the movies that show someone freezing in space (e.g., the last Guardians of the Galaxy) are not factually correct?
ReplyDeleteI think you're right. I hope someone else will chime in.
DeleteI also came here for this discussion, because that bit makes no sense to me. There are three ways to transmit heat - conduction and convection don't work in space (materially), it's true, due to lack of mass / air. But radation works fine. Any object in space emits heat in the form of radiation (see black-body radiation). And that can be pretty significant, certainly not limited like described above. So something else must be going on here.
DeleteMust be about being at the centre of a very large asteroid, and cooling slowly because of the insulation of the rest of the asteroid itself? Earth creates heat at the centre because of fusion. Perhaps an asteroid large enough creates less heat than is lost in space, or creates no heat but is insulated by kilometres of rock so as to slow the cooling rate to extreme extents?
DeleteThanks for the reminder re radiation; I've amended the post's text accordingly.
DeleteLetter to one's true love "My ardour for you my dear, cools no faster than an iron-nickel alloy does to form Widmanstãtten patterns, in effect basically always molten"
ReplyDeleteA good post. It is thought (but obviously not proven) that these nickel iron meteorites were in the center of large asteroid. In the early solar system things were much more radioactive (supernova star stuff) and smaller asteroids could melt. The result is similar to the earth, iron core, silicate covering, but on a much smaller scale. The silicate covering insulated the iron core, causing the slow cooling rate. Later impacts broke up the parent body producing silicate meteorites (achondrites) and NiFe metal like this sample.
ReplyDeleteMore briefly, the silicate blanket is what kept the iron cooling slowly.
Cheers.
?the silicate blanket is more consequential than the nonconductive vacuum?
DeleteI am on less solid ground* with this but vacuum still allows radiative cooling. In other words a glowing ball of metal/silicate can still be seen in a vacuum and thus is radiating energy (photons) into space. A thermos bottle works because it does not allow conductive heat transfer.
ReplyDeleteCheers.
* I just know that the current theory in meteoritics explains the slow cooling rate by the insulation effect of the silicates. In addition, the radioactive elements continue to heat the whole mess over a long time (time depending on the isotope, Aluminum 26 is a favorite heating element with a half life of about a million years).