New data from NASA’s MESSENGER orbiter suggest that Mercury’s magnetic field is 3.7 – 3.9 billion years old.
This image was taken on January 14, 2008, when the MESSENGER spacecraft was moving from a distance of roughly 12,800 to 16,700 km from the surface of Mercury. Image credit: NASA / JPL.
MESSENGER probe was launched on August 3, 2004, by a Delta II rocket from Cape Canaveral, Florida.
It reached Mercury in 2008 and has orbited the planet March 18, 2011, sending valuable data back to researchers.
“The mission was originally planned to last one year; no one expected it to go for four,” said Dr Catherine Johnson of the University of British Columbia, who is the first author on the study published in the journal Science Express.
The spacecraft crashed onto Mercury last week after running out of fuel, but the mission provided a trove of new information on the planet closest to the Sun.
Dr Johnson and her colleagues used data obtained by MESSENGER in the fall of 2014 and 2015 when the spacecraft flew close to the planet’s surface – at altitudes as low as 15 km.
When the orbiter flew close to the planet, its magnetometer collected data on the magnetism of rocks on the planet’s surface. 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 Earth, over 4.5 billion years ago.
“The science from these recent observations is really interesting and what we’ve learned about the magnetic field is just the first part of it,” Dr Johnson said.
Planetary researchers have known for some time that Mercury has a magnetic field similar to Earth’s, but much weaker.
According to the team, Mercury is the only inner Solar System body other than Earth that currently possesses a magnetic field generated by a dynamo in a fluid metallic outer core. There is evidence that Mars once had a magnetic field but it disappeared at some point over 3 billion years ago.
“Magnetized rocks record the history of the magnetic field of a planet, a key ingredient in understanding its evolution,” Dr Johnson said.
“We already know that around 3.7 to 3.9 billion years ago Mercury was volcanically and tectonically active. We now know that it had a magnetic field at around that time.”
“If we didn’t have the recent very low-altitude observations, we would never have been able to discover these signals. Mercury has just been waiting to tell us its story.”
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Catherine L. Johnson et al. Low-altitude magnetic field measurements by MESSENGER reveal Mercury’s ancient crustal field. Science, published online May 07, 2015; doi: 10.1126/science.aaa8720
