Why are there no known meteorites from Mercury or Venus?

We have meteorites from the Moon, Mars and asteroids, but none confirmed from Mercury or Venus. Physics explains why.

Venus. Venus is almost Earth's size, so its escape velocity is high, about 10.4 kilometres per second. Its atmosphere is about 90 times as dense as Earth's at the surface. For a rock to escape, an impact would have to throw it upwards faster than escape velocity and through that thick atmosphere, which would slow it down and heat it. Models suggest this is extremely difficult, though a very large impact might occasionally launch some material. Even then, Venus's rocks might be highly altered by the planet's harsh surface conditions.

Mercury. Mercury has no significant atmosphere and lower gravity, with an escape velocity of about 4.3 kilometres per second, so impacts can launch rocks into space. However, Mercury is deep in the Sun's gravity well. Rocks leaving Mercury tend to orbit close to the Sun and are more likely to fall into it or hit Venus than to reach Earth. Models suggest a small number could reach Earth, perhaps a fraction of the rate for Martian meteorites.

Candidates. Some researchers have proposed that certain unusual meteorites could come from Mercury, such as aubrite-like rocks or the ungrouped achondrite NWA 7325, because Mercury's surface is low in iron. None has been accepted. The BepiColombo mission, due to orbit Mercury from late 2026, will measure its surface composition, which may help test these ideas.

More about the science of meteorites

• What is the most common type of meteorite to fall?
• Do meteorites contain sugars or DNA building blocks?
• How do scientists stop meteorites being contaminated?
• Why are witnessed falls more useful to science than finds?
• What happens to a meteorite as it weathers on Earth?
• Can micrometeorites tell us about Earth's ancient atmosphere?

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