Evening Mercury

Car wrecks aren’t all alike, so there’s a wide range in the results.

The same principle may apply to the bodies of the early solar system, when the planets were taking shape. In fact, a recent study says the modern appearance of the planet Mercury could be explained by a glancing blow between two bodies of similar size.

Mercury is an oddball among the rocky planets of the inner solar system. Its metallic core accounts for about 70 percent of its mass – a far higher ratio than for Earth or the other planets. And the core is surrounded by a fairly thin mantle – a layer of lighter-weight rocks.

Some simulations have suggested that was the result of a giant impact – a massive collision between bodies of much different sizes. Such impacts were common in the early solar system; one of them might have led to the creation of the Moon.

But the recent study suggested something else. It found that a glancing blow between Mercury and a similar-sized planet could have stripped away much of Mercury’s mantle. But the research doesn’t tell us what happened to the other planet, or the debris from the impact. So scientists will ponder the possible collision a little longer to understand the planet Mercury.

Mercury is peeking into view in the early evening. It looks like a bright star, but it’s quite low in the west during twilight, so it can be hard to spot. The Moon will join it tomorrow night; more about that tomorrow.

Script by Damond Benningfield