Mercury, the closest planet to the sun, has a 4 billion year-old magnetic field that was once as strong as that of Earth's.
NASA's Messenger craft's discovery is instrumental in fully understanding how mercury evolved all these years. Messenger studied Merucry for a length of four years before it crashed into the surface of the planet a week ago.
As the journal Science published, the discovery has proven that Mercury is the only other planet in the system, aside from the Earth, which possesses a magnetic field brought about by a moving molten core composed of liquid iron.
Previously, scientists have detected evidences which suggest that Mars, once upon a time, had a global magnetic field; however, it disappeared 3 billion years ago. Venus, on the other hand, never had this characteristic.
"This means Mercury's core has to be at least [still] partially liquid," Space quoted Catherine Johnson, lead author and planetary geophysicist from British Columbia University, as saying.
The finding is surprising according to Johnson since Mercury's actual size suggests that it would have quickly cooled after forming and becoming compact.
Johnson added, "If we did not have these recent data and observations, we will never have detected how Mercury's magnetic field slowly evolved through time. It is just waiting for us to reveal its story."
Messenger's data were gathered in 2014 and the first quarter of the present year as it was approaching Mercury's surface. Within 90 miles distance, signs of magnetization from the planet's crust were detected.
Mercury came about 3.9 million years ago and remains detectable until today. Its magnetic field might be the longest living in the inner solar system's planet, researchers said.