# What temperature do small meteorites have on impact

A question which has haunted me for years. What temperature do small meteorites (which don't evaporate on impact) have if you find them immediately after they hit the surface. I understand that the outer parts are heated by atmospheric friction, but what about the inside? Can the inside keep its low temperature that it inherits from space?

There are some stories on the internet about meteorites that were so cold, that the moisture of the air froze on the surface of the meteorite. Can this really happen?

Subquestion:

• Are there numerical simulations that can prove this?

Some of the rumours are summed up here: "Frosty" meteorite (Wikipedia).

• Since it's the surface of the meterorite that the myth talks about, and it's the friction on the surface that causes the heat, that seems a bit farcical, doesn't it? Unless it was a really slow meteorite... The Skeptics.SE site usually requires an example of the claim in question for myth-busting/proving exercises like these. I would think that that might be a good practice to follow for this site as well. Do you have a link to an example? Apr 16 '14 at 12:19
• @naught101 Somewhat of an explanation would be: If only the surface is heated (a few Millimeters depth with lets say 500 Kelvin) and the meteorite has a diameter of 0.5 Meter at lets say 100 Kelvin. Then the heat of the surface would be relatively small compared to the volume. The surface heat could dissipate into the air and the inside of the meteorite, but the total system would be below freezing. The question is, does this simple thought experiment occur in nature? Apr 16 '14 at 15:02

Love & Brownlee (1991) put together numerical models for the experiences of micrometeorites entering the atmosphere. They say:

The peak temperatures experienced by submillimeter micrometeoroids rarely exceed 1700°C. Maximum temperature and mass loss rate generally occur at altitudes between 85 and 90 km during ∼1 sec of peak heating. A typical melted particle spends ∼2 sec at temperatures above the melting point.

Flynn (1989) discusses interplanetary dust, with figures for peak temperatures given in the abstract.

But I think that what you really want is Sears (1975), Temperature gradients in meteorites produced by atmospheric passage:

Temperatures in the order of 200°C have usually penetrated no further than 5-10mm, which is consistent with a luminous flight time of the order of 10s.

Using the geologists' rule of thumb for timescales of cooling (I believe $\tau^2 = \ell/\kappa$, where $\tau$ is the timescale, $\ell$ is the thickness of the cooling body, and $\kappa$ is the thermal conductivity - though it's a while since I've had to do this so I may be misremembering...), the information above about the height above the surface at which peak temperature is commonly reached, and an estimate of particle velocity, you can probably back-of-envelope a temperature for a meteorite on impact!

When meteorites are found, they are cold, much like it is in deep space. The meteor body may be warm to the touch (has been reported, whether or not it is true is another thing) but it is important to know that it is the air around the meteor which is emulating visible light, not the rock itself. Light flight: what we see (the fireball), which occurs from approx 80km altitude and continues to approx 20km altitude. Dark flight: From 20 km altitude to surface. The rock is now falling at terminal velocity and would not retain any heat from the heated luminescent air during it's light flight. The end result: meteorites are cold to the touch upon impact. The proof: meteorites found on snowy surfaces or grassy surfaces. The snow isn't melted and grass isn't burnt. Sure is fun reading some eye witness accounts stories though lol. They are most certainly fabricated to cause shock value. The science doesn't lie.