A new and exciting field in astronomy to study exoplanets and gauge whether they possess conditions that will favour the presence and sustainability of life. In this quest, an important part is looking at our own celestial backyard to gain insights – hence the many missions to Mars and Venus probing for signs of past life. One thing that astronomers search for in exoplanets, in the so-called Goldilocks zone of habitability, is the existence of liquid water and an atmosphere like that on Earth. In this context it is believed by many that Mars once had such an atmosphere. The mechanism as to why it lost its atmosphere has remained in doubt. Scientists from Indian Institution for Science Education and Research (IISER) Kolkata suggest that it was the planet’s intrinsic magnetic dynamo which, by shielding its atmosphere from the sun’s solar wind, protected its atmosphere. When the magnetic dynamo switched off, the atmosphere slowly was eroded by the solar wind and eventually vanished, leaving the thin remnant we see today. These results have been published in the journal Monthly Notices of the Royal Astronomical Society.

Two scenarios

In the simulation, the researchers build a computer model of a Mars-like planet interacting with the plasma wind from a Sun-like star. They study two scenarios. In the first one, the planet has a magnetic dynamo and an intrinsic magnetosphere surrounding it. The physics is described by Maxwell’s equations – which describe electro-magnetic fields and their interactions with matter – in the presence of plasma. In a simulation, they mimic the Mars model with an intrinsic magnetosphere and allow a solar-wind like plasma to fall on the dayside of the planet. They run the model to simulate the interactions between the magnetized solar wind and Mars.

In the second scenario, they modelled the same system but with no intrinsic magnetic field.

The right track

To ascertain that they are indeed on the right track, the researchers modelled the present day Mars, with no intrinsic magnetosphere. “We perform a simulation for present day Mars based on which we generate the magnetic environment around the planet. We find that this has good correspondence with observations from NASA Mars Global Surveyor and NASA Maven missions,” says Dibyendu Nandi from Center of Excellence in Space Sciences India (CESSI), in IISER Kolkata, in an email to The Hindu.

From the study, the scientists infer that when Mars had an intrinsic magnetosphere, it enveloped the planet like a shroud and shielded its atmosphere from the stripping effect of the solar wind. When the planet lost its intrinsic magnetosphere, only the imposed one due to the pileup of the solar wind remained. “This imposed magnetosphere was made of the Sun’s magnetic fields which slips past Mars when the solar wind flows past it after impacting the day side,” explains Prof. Nandi. “So, there is a continuous slippage of magnetised plasma from the day-side to the night-side of Mars which also strips away the atmosphere of Mars slowly.”

The computational models being developed in CESSI, in IISER Kolkata can be used to simulate and predict the space environment around planets, according to Prof. Nandi.

“Thus these are particularly important to complement and aid in the interpretation of data from planetary space missions,” he says. “These simulations can also help in understanding how astrophysical space environments determine atmospheric evolution and thus habitability of planets and exoplanets,” he adds.