Mercury's magnetic field is nearly 4 billion years old, researchers have found.

A planet's magnetic field is generated by the flow of liquid iron deep in its core. While Earth's magnetic field helps shield life here from solar radiation, Mercury is unlikely to be harboring inhabitants that need protection.

Still, the information is useful because it "is dating processes in the interior of the planet, and it basically tells us something about Mercury's past," said Catherine Johnson, a geophysicist at the University of British Columbia and an author of the new study, published in the journal Science.

Mercury, like all of the planets in our solar system, is just over 4.5 billion years old.

The data were gathered by NASA's Messenger, a small spacecraft that orbited Mercury for four years before crashing into the planet on April 30. The spacecraft measured the magnetism of rocks on Mercury's surface.

Johnson and her colleagues will continue to analyze data from Messenger. They are also looking forward to a 2016 mission to Mercury known as BepiColombo.

U.S., Europe sign physics initiative

Laying the groundwork for what they said would be a new era of scientific cooperation, leaders of European and U.S. particle physics initiatives signed an agreement at a White House ceremony to share the spoils of their research in the coming decades.

Scientists and diplomats said the deal — signed by the Department of Energy, the National Science Foundation and CERN, the European Organization for Nuclear Research — allows the United States to continue to collaborate on the world's flagship experiment, CERN's Large Hadron Collider, where the long-sought Higgs boson was discovered three years ago. For the first time, CERN will now be able to collaborate on projects in the United States, a necessity in an age when big scientific experiments are too expensive for any one country or even one continent to foot on its own.

'Submarine' is 500 million years old

A 500-million-year-old fossilized arthropod found in the Burgess Shale, a fossil field in the Canadian Rockies, may provide clues to how heads evolved in early animals. The fossil is a submarine-shaped arthropod, Odaraia alata, of the Middle Cambrian Period. A paper in Current Biology reports that both Odaraia alata, originally found about 100 years ago, and another ancient arthropod have a hard plate, known as the anterior sclerite, and eye-like features that were connected by nerves to their brains. They may have controlled their vision in much the same way that modern insects, crustaceans and spiders do.

News services