WASHINGTON -- New data from the U.S. MESSENGER spacecraft, which crash-landed into Mercury just a week ago, showed that the planet's magnetic field is almost 4 billion years old, researchers said Thursday.
The discovery, published in the U.S. journal Science, provided "critical information on Mercury's interior thermal and dynamic evolution," wrote the researchers led by Catherine Johnson of the University of British Columbia.
Scientists have known for some time that Mercury, the closest planet to the Sun, has a magnetic field similar to the Earth's, but much weaker. The motion of liquid iron deep inside the planet' s core generates the field. The MESSENGER probe left the Earth in 2004, reached Mercury in 2008 and had orbited the planet since 2011, sending valuable data back to the Earth. In recent months, it flew incredibly close to the planet's surface -- at altitudes as low as 15 kilometers, before crashing into its surface on April 30.
When MESSENGER flew close to the planet, its magnetometer collected data on the magnetism of rocks in Mercury's surface, the researchers said.
Those tiny signals revealed that Mercury's magnetic field is very ancient, between 3.7 and 3.9 billion years old. The planet itself formed around the same time as the Earth, just over 4.5 billion years ago.
"If we didn't have these recent observations, we would never have known how Mercury's magnetic field evolved over time," said Johnson, also a scientist at the U.S.-based Planetary Science Institute. "It's just been waiting to tell us its story."
Mercury is the only other planet besides the Earth in the inner solar system with such a magnetic field. There is evidence that Mars once had a magnetic field but it disappeared at some point over 3 billion years ago.
