While NASA's Messenger Probe may be gone, having crashed into the surface of Mercury, the data it collected is still providing scientists with a wealth of knowledge on the planet that is closest to our Sun.  According to data sent back from Messenger, the magnetic field of the little planet is almost four billion years old.

The discovery has helped scientists piece together the history of Mercury, a planet that up until now we knew very little about.

"The science from these recent observations is really interesting and what we have learned about the magnetic field is just the first part of it," said Catherine Johnson, planetary scientist from University of British Columbia and lead author of the study.

Scientists have known for some time that the magnetic field of Mercury is very similar to the magnetic field here on Earth, only weaker.  Mercury is the only planet besides Earth in the inner solar system with such a magnetic field.  There is evidence that Mars once had a magnetic field but it vanished at some point over three billion years ago.

When Messenger flew close to the planet, its magnetometer collected data on the magnetism of rocks on Mercury's surface.  The signals revealed that Mercury's magnetic field is very ancient, between 3.7 and 3.9 billion years old.  The planet itself formed at around the same time of the Earth, just over 4.5 billion years ago.

"If we did not have these recent observations, we would never have known how Mercury's magnetic field evolved over time," Johnson added.

NASA's Messenger probe originally left Earth in 2004 and first reached Mercury in 2008.  In 2011, the probe moved in orbit and remained there for four years sending back valuable data to scientists before the mission finally came to end when Messenger ran out of fuel and crashed onto the surface.

To learn about Mercury's magnetic field, scientists used data obtained by Messenger in the fall of 2014 and 2015 when the probe flew incredibly close to the planet's surface, at altitudes as low as 15 kilometers. 

"It's quite a risky thing to do because if you get it wrong, you wind up in the planet a little too early," said study lead author Catherine Johnson, a geophysicist at the University of British Columbia in Vancouver, Canada.

The Earth also has a liquid outer core that powers its magnetic field -- which is roughly 100 times stronger than Mercury's -- so teasing apart the story of Mercury's magnetic field could help shed more light on our own, Johnson said.

The paper presenting the findings was published in the journal Science Express.