The innermost planet shriveled up more than researchers anticipated

Dec 11, 2013 07:49 GMT  ·  By

New data from the NASA MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) space probe suggest that Mercury, the innermost planet in our solar system, shrank by about 11 kilometers (6.8 miles) since it formed, some 4.5 billion years ago.

This level of shrinkage is considerably higher than what planetary scientists were expecting to find. Previous investigations of the scorched world suggested that only 2 or 3 kilometers (1.24 to 1.86 miles) of shrinkage had occurred as the world cooled down following the formation of the solar system.

All rocky planets in the solar system – Mercury, Venus, Earth and Mars – cooled and contracted after they formed from the debris disk that remained around the Sun after the star formed. This is estimated to have occurred around 4.6 billion years ago. The planets formed within a few hundred million years.

The new research is based on a census and analysis of lobate scarps, which are long curved ridges very similar in appearance to the wrinkles you would find on a rotting apple. The probe recently revealed that these structures were far more numerous on the surface of Mercury than previously thought.

Additionally, these lobate scarps were found to have much steeper faces than researchers had established. This suggests that the planet itself contract a lot more than usual. Details of the work were presented at the American Geophysical Union meeting, held in San Francisco.

The research was led by planetary scientist Paul Byrne, from the Carnegie Institution for Science in Washington. “We are resolving a four-decades-old conflict here,” he told attendants at the meeting.

Theoretical studies suggested a long time ago that Mercury must have shrunk a lot more than other worlds, in order to explain why its metallic core cooled the way it did. This investigation is the first to provide accurate evidences to support this claim.

Data collected in 1974 and 1975 by the Mariner 10 space probe suggested that Mercury shrank by 2 or 3 kilometers since its formation, but the new models based on MESSENGER data suggest the world may have shriveled up by anywhere between 10 to 20 kilometers (6.2 to 12.4 miles), Nature reports.

Even the new values may underestimate the amount of shrinkage Mercury went through over the past 4.5 billion years, some researchers comment. It could be that a lot more lobate scarps are lurking in various areas of the planet, and have yet to be discovered.

The NASA MESSENGER space probe has been studying Mercury since achieving orbital insertion around the planet, on March 18, 2011.The spacecraft was launched on August 3, 2004, but carried out one flyby of Earth, two of Venus and three of Mercury before finally reaching its destination.