We used to have a magnetic moon
The point on the studies is related to the magnetic field of the Moon, at least up to about 3.3 billion years ago and now extinct. The researchers publish Benjamin Weiss (Massachusetts Institute of Technology) and Sonia Tikoo (University of California and Berkeley Geochronology Center) in the latest issue of the journal Science.
The Moon, now, doesn’t have a magnetic field, but it should not have been the case in the past. A very remote past, which is placed between approximately just over 4 and about 3.5 billion years ago, a time when the rocks and lunar crust still bear the traces of a magnetic field significantly. However, the origin, the intensity and the duration of this field are very uncertain. What has generated magnetism on our satellite is still a matter of debate. A sort of dynamo present in its metallic core fluid, in analogy to what happens on Earth and on other planets or bodies in the Solar System? Or external magnetic fields to the Moon itself? Understanding in particular, if the Moon has had in the past or not an intrinsic magnetic generator would be important for other aspects, such as the study of its formation and evolution and, more in general, the physics of the formation of planetary magnetic fields.
On this subject, the journal Science publishes an article in the latest issue in which Benjamin Weiss (Massachusetts Institute of Technology) and Sonia Tikoo (University of California and Berkeley Geochronology Center) take stock of the situation. The researchers point out the first great leap in studies of lunar geology permitted by the Apollo missions, thanks to which nearly four hundred pounds of moon rocks were collected and returned to Earth.
Recent laboratory studies of these samples, combined with in situ measurements of the present magnetic field, conducted through the Lunar Prospector mission, have helped to improve our view of the geological past of our natural satellite. These studies have confirmed that in ancient times the magnetic field must have really existed in the core, at least between 4 and 3.5 billion years ago, with intensity comparable to that of the magnetic field on the Earth’s surface. Value which then began weakening, until reduced by at least ten times after 3.3 billion years.
For the two scientists, the confirmation of a primordial active dynamo in the core of the Moon, which has produced a magnetic field so intense and prolonged, it is a surprising result. It will be necessary in the coming years to get even more accurate measurements from the rocks, together with the development of theoretical models more refined, more precisely to reconstruct the inside story of our satellite. And then of its ancient magnetism.
“This study confirms the existence of a primordial dynamo inside the moon as well as with the Earth and other planets in the solar system, such as Jupiter or Mars, or for smaller bodies, like Vesta, one of the largest asteroids in the Main Belt object of study of the Dawn mission, proving once time as this mechanism is widespread among the bodies of our solar system to explain the existence of the corresponding magnetic fields, “says Michelangelo Formisano, a researcher at the Institute of Astrophysics and Space Planetology INAF in Rome. “The presence of a dynamo is very important because it allows understanding if the body (in this case the Moon) is differentiated or not, i.e. whether it has a layered structure (essentially composed of the core, mantle, and crust) as was the case for the earth. This is because, in order to have a dynamo, there is need first of all an iron core which is formed during the process of differentiation (“ferrous” materials tend to aggregate toward the center of the body). But not enough.
The core must also meet certain requirements to ensure that the development of a dynamo. Future studies on the Moon will undoubtedly help us to better constrain certain geophysical parameters of our satellite and then to improve our knowledge of its magnetic field, through theoretical models gradually more and more accurate. “