New data from NASA's MESSENGER spacecraft, which orbited Mercury for four years before it crashed into the surface of the planet a week ago, suggests that Mercury's liquid metal core had spawned a magnetic field nearly 4 billion years ago.

Months before MESSENGER ran out of fuel and plunged into demise, it provided scientists with unprecedented images and data about the closest planet to the sun.

Mercury is characterized by frigidly cold and scorchingly hot temperatures and proved to be an odd world. In the solar system, Mercury is also the only other planet besides Earth that has a global magnetic field produced by the movement of metallic fluids in its core albeit Mercury has a much weaker magnetic field.

By looking at the number of impact craters shown in images sent by the MESSENGER, scientists said that the magnetic field of the planet first formed between 3.7 billion to 3.9 billion years ago, suggesting that Mercury's magnetic field started about 700 million years after the formation of the planet. Counting the crater is a commonly used technique for estimating the age of the surface of the planet, with the younger areas characterized by fewer impacts compared with older areas. It isn't yet clear, though, if the planet's magnetic field has continuously operated since then.

Data collected by MESSENGER's magnetometer also suggest that Mercury formed about the same time as our planet more than 4.5 billion years ago. The mission likewise revealed that Mercury had a magnetic field that rivaled that of our planet, although it is about 100 times weaker.

"The strength of Mercury's magnetic field may have ranged anywhere from its strength today to something about 100 times stronger, comparable to the strength of Earth's magnetic field at Earth's surface today," said University of British Columbia planetary geophysicist Catherine Johnson.

The findings, which were reported in the journal Science on May 7, suggest that the evolution of Mercury's magnetic field took place over a long time, shedding light on the structure and composition of the planet and how it may have cooled and evolved.

Johnson said that being able to determine how long Mercury has had its magnetic field can help scientists narrow down scenarios of the planet's history and how Mercury changed over time. She added that this gives scientists a better understanding about planetary evolution in general.

"Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data," the researchers reported.

Photo: NASA Goddard Space Flight Center | Flickr