Messenger, NASA’s spacecraft, offered scientists precious data about the planet’s magnetic field which formed 1.9 billion years ago. Messenger has circled Mercury for four years until it crashed into the planet’s surface last week because it ran out of fuel. This data is very valuable since it enables researchers understand more about how the closest planet to the Sun formed. More details about the discovery can be found in the journal Science.
The space probe had circled at less than ten miles above the surface of Mercury. This discovery makes Mercury the second planet after Earth in the inner solar system which has a magnetic field. Indeed there is Mars which it is also believed to have had a magnetic field in the past, but evidence indicates that it disappeared more than three billion years ago.
It seems that although Mercury’s magnetic field is 100 times weaker it is similar to the one which the Earth has. The liquid metal existing deep inside Mercury’s core moves and it generates the magnetic field of the planet. This is similar to how the Earth’s magnetic field was formed.
The lead author of the study, planetary geophysicist Catherine Johnson of the University of British Columbia in Vancouver said that this indicates that at least some part of Mercury’s core is liquid. She remarked:
“This was a surprise at first, because Mercury is very small, so you would expect it to cool quickly after it formed a non-metallic stuff in Mercury’s core, that’d lower its freezing point and make it hard to be completely solid.”
According to Johnson if researchers had not possessed the data from Messenger they would not have known how Mercury’s magnetic field evolved in time. The data indicates that the magnetic field is very old. It formed just after 700 million years after the planet came into being, at least 3.7 to 3.9 billion years ago. The strength of the field may have ranged from today’s strength. According to Johnson it could have been 100 times stronger than Earth’s magnetic field of today.
Researchers are still not certain if Mercury’s magnetic field has existed all the time. The simplest explanation is that the magnetic field was switched on and continued to exist until the present day, but Johnson says that there could also be the possibility that the field was switched on and off. Further research is needed in order to find out more. Until then the data which the scientists have now sheds light on how the planet cooled down over time and also about Mercury’s structure and composition.
Image Source: Space.com