Discovery Of Mercury’s Fluid Core
Researchers have been stufying the planet Mercury for quite some time and have finally discovered that there is molten fluid inside this tiny planet. This has helped researchers to understand why Mercury has small magnetic field surrounding it.
The magnetic field, which was discovered a few years ago by the Mariner 10 spacecraft, had scientists confused. At that time they were under the impression that the core of the planet had solidified a long time ago. Probably the most common explanation for a magnetic field is a molten interior, such as on Earth.
The Moon and Mars, for example, show evidence only of ancient magnetic fields. The Messenger spacecraft is on its way to Mercury and is expected to arrive next year, but in the meantime researchers led by Jean-Luc Margot, an assistant professor of astronomy at Cornell University, launched their own attempt to learn about the planet’s core.
Scientists discovered this unusual finding by closely studying its movements using telescopes in California, Puerto Rico and West Virginia. They sent powerful radar signals at the planet, then received the echo, which appeared as a unique pattern of speckles reflecting the roughness of the planet’s surface, at widely separated locations.
By measuring how long it took for a particular speckle pattern to reproduce at different locations they were able to calculate Mercury’s spin rate with an accuracy of one part in 100,000. The observations, conducted over five years, allowed the scientists to calculate twists in Mercury’s spin, called librations, caused by the effect of the sun’s gravity.
The magnitude of the librations was twice what would be expected for a completely solid body, they concluded. But it matched what would be expected for an object whose outer core is molten and not forced to rotate along with its shell.
Sean C. Solomon of the Carnegie Institution of Washington, who was not part of the research team, said in a commentary that the measurements “constitute a triumph” of theoretical ideas developed in the past. Margot’s research was supported by NASA.