MESSENGER left Earth in 2004, flew by Mercury for the first time in 2008, and had orbited the planet since 2011. MESSENGER was the first spacecraft ever to orbit the planet Mercury, and data from the spacecraft’s seven scientific instruments continue to help scientists unravel the history and evolution of the closest planet to the Sun.
Researchers used data obtained by MESSENGER in the fall of 2014 and early 2015 when the probe flew incredibly close to the planet’s surface – at altitudes as low as 15 kilometers. In the years prior, MESSENGER’s lowest altitudes were between 200 and 500 kilometers.
“The mission was originally planned to last one year; no one expected it to go for four,” said Catherine Johnson, a University of British Columbia planetary scientist and lead author of the study. “If we didn’t have these recent observations, we would never have known how Mercury’s magnetic field evolved over time.”
Mercury is the only other planet besides Earth in the inner solar system with such a magnetic field. Scientists have known for some time that Mercury has a magnetic field similar to Earth’s, but much weaker. The motion of liquid iron deep inside the planet’s core generates the field.
There is evidence that Mars once had a magnetic field – but it disappeared at some point more than 3 billion years ago.