Mercury is shrinking

[grace55]

Patterns of scalloped-edged cliffs or lobate scarps on Mercury's surface are thrust faults that are consistent with the planet shrinking and cooling with time. However, compression occurred in the planet's early history and Mariner 10 images revealed decades ago that lobate scarps are among the youngest' features on Mercury.

[Friendz]

Messenger Probe Reveals That Mercury Planet Is Shrinking
The scientists at NASA revealed, on Saturday, that Mercury, the nearest planet to the sun and the smallest in the solar system, is shrinking.


An image of the planet Mercury, made during the January 2008 fly-by of the planet by the Messenger space probe

[Royaldoa]

wow, i never knew that and im a science wiz :P

[grace55]

The incredible shrinking planet

The idea that Mercury's surface was somehow shrinking arose when Mariner 10 returned images of great scarps biting deep into the planet's surface. One such scarp, Discovery Rupes, cuts a mile (1.6-kilometer) into Mercury's crust as it snakes across the surface.

On Earth, such scarps could resemble tectonic features like the fault lines running parallel to the coastal U.S., researchers said. But on Mercury, the formations are randomly distributed. The scarps also don't appear to have formed by the in-filling processes that led to similar features on Earth's moon due to their length, which can stretch hundreds of kilometers across the surface.

Under the shrinking surface theory, researchers believe that Mercury's crust first formed over a gigantic molten core. As that core cooled, it led to a volume change causing the surface to buckle and break.

Unlike water, which actually expands as it cools, most materials tend to contract and the same goes for Mercury's rocky crust, Robinson said. Based on observations of the planet's known hemisphere, scientists estimate the planet's surface has shrunk inward between less than one kilometer and three kilometers in all, he added.

"It's not something insignificant," Robinson said.

But since much of the mystery surrounding Mercury's surface stems from its poorly understood core, researchers have their work cut out for them.

"Our understanding [of the core] is very rudimentary," Robinson said. "It's just based on the fact that Mercury has this very high uncompressed density."

Because Mercury is extremely dense for its size -- it's comparable to Earth -- researchers believe it has a large metallic, most likely iron core. But exactly how large the core is, whether its outer regions are molten, and whether it rotates to power the planet's strong magnetic field, are still unknown.

"Mercury is a small enough planet that its core should have frozen about 2.2 billion years ago," said MESSENGER payload manager Robert Gold, of the Johns Hopkins University Applied Physics Laboratory.

Mercury is 3,031 miles (4,878 kilometers) in diameter, a bit larger than Earth's moon.

[Friendz]

SEE SOME PICS

Scarps that cut across the surface of Mercury suggest the planet has been shrinking (Image: Science/AAAS)