Snippet: Can Pieces of Mercury be Found on Earth?

A meteorite on the surface of Mars. Image credit: NASA/JPL

This is an interesting thought. We know that rocks from space can fall through the atmosphere and hit the ground as meteorites. But where do these rocks come from? Some come from old remnants of the early solar system, floating through space until they are captured by the Earth’s gravitational pull. Other meteorites come from other planets, ejected pieces of the planet crust (caused itself by a meteorite impact), escaping from the planets gravity by achieving “escape velocity”. We have found samples known to come from the Moon and Mars, but what about the other planets? Venus’ atmosphere is too thick to allow pieces of its surface to fly into space, but what about the first planet from the Sun, Mercury? Can bits of Mercury travel through space and land on Earth?

New research suggests that finding a piece of Mercury on Earth may not be such a silly idea. The planet Mercury is the closest orbiting plant to the Sun in our solar system. It is an extreme place, enduring a temperature range of between 90 to 700 K (−180 to 430 °C) with very little atmosphere. As the planet is tiny (5.5% that of Earth’s mass), it also has a low gravitational pull (roughly a third of the Earth). These factors coupled with the fact that average impact velocities of meteorites on the planet are routinely 5 to 20 times the escape velocity (i.e. the velocity for an object to escape the gravitational pull of a body), we could be looking at a significant source of space rock debris. Mercury experiences the most violent impacts out of any planet in the solar system.

Cumulative percentage of test particles ejected from Mercury impacting Earth, as a function of time. Credit: Brett Gladman and Jaime Coffey.

This new research comes from Brett Gladman and Jaime Coffey at the University of British Columbia, Canada, and they calculate that roughly 5% of ejected rocks from Mercury impacts will have the necessary 9 km/s to reach the Earth within 30 million years (after all, it’s a long way!). Even more surprising is that statistical analysis results seem to indicate that 50% as many Mercury meteorites will hit the Earth as Mars rocks. This finding would suggest that many pieces of Mercury may be sitting in meteorite collections, but due to the unlikely thought that a piece of a planet so close to the Sun could reach us in Earth orbit, they have been overlooked and disregarded.



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