New Delhi: Venus, Earth and Mars all started out as similar terrestrial worlds assembled around a newborn star about 4.5 billion years ago. However, the three planets went down very different evolutionary trajectories, even though all three were believed to be habitable in the infancy of the Solar System. Venus is a hothouse with a runaway greenhouse gas effect, Earth has an oxygen-rich atmosphere, a protective geomagnetic field, and liquid water on the surface, while Mars is an arid and cold desert. In the past, scientists believe Mars was habitable too, and also had liquid water flowing on the surface, with any potential organisms on the surface protected from the harsh radiation from the Sun, by a magnetic field that new research reveals lasted longer than previous estimates.
The new findings indicate that the magnetic field of Mars could have survived till 3.9 billion years ago, which is a revision of the previous estimate of 4.1 billion years. Mars was habitable for hundreds of millions of years longer than scientists previously believed. The researchers used sophisticated computer modelling to estimate the age of the Martian geodynamo, or the iron-rich planetary core that was responsible for producing the global Martian magnetic field. The researchers simulated cooling and magnetisation cycles of well-studied impact basins on Mars, that researchers believed formed only after the geodynamo shut down.
Impact basins as fossils for magnetism
Following a major impact event, the rock is heated up, with the ferromagnetic minerals aligning with the surrounding magnetic fields, that get solidified in place once the rock cools down. The minerals essentially act as fossilised magnetic fields. The researchers now believe that some of the impact basins formed when the geodynamo was undergoing a polarity reversal, which can explain why these impact basins have weak magnetic fields today. A paper describing the findings has been published in Nature Communications.
