MESSENGER’s four-year mission at Mercury ended last week with the spacecraft, out of fuel to raise its orbit, crashing into the planet’s surface. But for months before its demise, MESSENGER gave scientists a parting gift: unprecedented, close-up images and data about the solar system’s innermost planet.
Mercury, situated just 36 million miles from the sun (compared to Earth’s 93 million-mile roost) has proven to be an odd world, both scorchingly hot and frigidly cold, and the only planet in the solar system besides Earth that has a global magnetic field generated by a dynamo – motions of metallic fluids in the core.
MESSENGER’s close-ups allowed scientists to pick up trace signals of magnetization in Mercury’s crust. Based on the number of impact craters, the magnetized regions are very old, dating back 3.7 billion to 3.9 billion years. (Counting craters is a common technique to approximate the age of a planet’s surface, with younger areas showing fewer impacts than older ones.)
The findings push back the clock for the start of Mercury’s magnetic field to about 700 million years after the planet’s formation. Researchers, however, cannot yet say if Mercury’s magnetic field has been operating continuously since then.
“The simplest possible explanation is that you switched a magnetic field on and then it just continued to the present day … but it may turn out that it would have been easier for that field to have switched on and off,” MESSENGER guest investigator Catherine Johnson, a geophysicist with the University of British Columbia in Vancouver, told Discovery News.
“At the moment we don’t know anything about (the magnetic field) between 4 billion years ago and today. Obviously, that’s something that we’re going to be looking at,” she added.
Read more at Discovery News
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