3D models indicate that about 3.7 billion years ago, a much stronger dynamo operated on Mercury than today. The finding narrows down possible explanations for the origin of the ancient field and points to intense convection in the planet's core.
Mercury It is the smallest of the planets inSolar System and closest to the Sun, but inside it is still operating today a dynamo mechanism that creates magnetic field Global. New research shows that in the distant past this field was much stronger: probably 50–100 times its current strength.
Next to the Earth, Mercury It is the only rocky planet in the solar system that currently has an internal dynamo. Its current field is very weak – about 200 nanotesla at the equator – but measurements by the spacecraft Messenger Discovered that ancient parts of the planet's crust carry Magnetization Strong residual.
The magnetized crust formed about 3.9–3.7 billion years ago. The magnetic signal measured above it reaches about ten nanoteslas even at an altitude of about 30 kilometers, evidence that a significant global field was active on Mercury at the time of its formation.
Reconstructing a field that cannot be measured directly
Isaac Nart, Benjamin Weiss, Sarah Steele, and John Bierstaker sought to calculate what ancient field strength was required to leave the magnetization observed today in the crust.
The researchers combined 3D magnetohydrodynamic simulations of the interaction between the wind of the sun and the planetary field with models that describe the cooling of the crust and the acquisition of magnetization by rocks.
The result is a range, not a single number. According to the study, the field strength on the surface of Mercury was at least about 2,000 nanotesla – ten times the current field. However, more likely scenarios point to more than 10,000 nanotesla, meaning a field 50–100 times stronger than the one operating today.
Dynamo is strong at its core
magnetic field A planetary nebula is formed when liquid, electrically conductive material moves within the planet's core. The movement creates electric currents, which generate the magnetic field in a process known as a dynamo.
The intensities obtained in the study make it difficult to explain the ancient dynamo by solar wind feedback or thermoelectric currents alone. According to the researchers, a more plausible scenario is that at that time an increased energy flow drove strong convection in the metallic core.
The conclusion changes the picture of young Mercury. The weak field we see today is not necessarily a permanent feature of the planet, but a late result of its thermal evolution and the weakening of motions within the core.
It's still a restoration.
The researchers do not directly measure a field that was active billions of years ago. The reconstruction depends on assumptions about the thickness of the magnetized layer, the minerals that carry the signal, the rate of cooling of the crust, and the strength of the early solar wind. Therefore, they emphasize a possible range rather than an exact value.
Despite its limitations, the result provides a new constraint for models of the interior of Mercury. It also provides a basis for comparison with future studies and with measurements from the Mars Reconnaissance Orbiter mission. In Colombo.
Questions and Answers
what is Planetary dynamo? A mechanism in which the movement of a liquid and electrically conductive material inthe core of a planet Creates electric currents and a magnetic field.
How do we know that Mercury had an ancient magnetic field? Rocks in the crust that are approximately 3.9–3.7 billion years old retain residual magnetization, which the Messenger spacecraft measured above the surface.
How strong was the ancient field? According to the models, at least ten times the current field, and probably 50–100 times.
Is this a direct measurement? No. This is a reconstruction based on measurements from the spacecraft, the age of the crust, and models of cooling, magnetization, and interaction with the solar wind.
For the scientific article: The study in PNAS
