14 DAY TRIAL // Mercury is the smallest planet in the solar system, but one thing is certain: it wasn't always this small. At least, that's what the data collected by NASA's MESSENGER spacecraft during the beginning of this year reveals. In the early history of the solar system, when Mercury was much warmer than it is today, it could have had a diameter bigger by at least 1.6 kilometers. Now, scientists say that the same cooling effect which is thought responsible for the shrinking of Mercury can account for its mysterious magnetic field.
"Cooling of the planet's core not only fueled the magnetic dynamo, it also led to contraction of the entire planet. And the data from the flyby indicate that the total contraction is at least one-third greater than we previously thought," said Principal Investigator Sean Solomon of the Carnegie Institution of Washington.
The Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft if the first mission to visit Mercury since the Mariner 10 mission more than three decades ago. In January this year, it completed the first of the three scheduled fly-bys around the planet, which will eventually result in inserting the spacecraft in a permanent orbit around Mercury, passing at only 200 kilometers above the surface.
This first approach allowed it to take multiple measurements of the planet, and revealed that Mercury had an active volcanic surface in the past, filling impact craters up to 2.7 kilometers deep with massive amounts of lava. "That's a lot of lava. It shows the planet was really active in its early history," said Dr James Head of Brown University.
Alternatively, MESSENGER detected silicon, sodium and water ions in Mercury's weak atmosphere, which were probably created as solar wind blowing from the Sun reaches the surface of Mercury and blasts ions into space, which are then captured by the planet's magnetic field. "The Mercury magnetosphere is full of many ionic species, both atomic and molecular," said Dr Thomas Zurbuchen of the University of Michigan.
Albeit, the magnetic field of the planet doesn't only form the magnetosphere, it also exerts a great deal of influence on the surface structures. "The dominant tectonic landforms on Mercury, including areas imaged for the first time by Messenger, are features called lobate scarps, huge cliffs that mark the tops of crustal faults that formed during the contraction of the surrounding area. They tell us how important the cooling core has been to the evolution of the surface," said Dr Solomon.