Charged solar particles create an induced magnetosphere around Mars that does not have its own magnetic field.
The red planet does not have a powerful magnetic field of the terrestrial type, but its atmosphere is well protected from the influence of the solar wind, which causes leakage of ions. A new study was conducted using the Swedish device ASPERA-3 on the ship Mars Express.
Modern Mars is a cold desert with 1% of terrestrial atmospheric pressure on the surface. But many geological features hint that about 3-4 billion years ago the planet had an active hydrological cycle. However, it needs a warmer climate in early history, and therefore in a much more dense atmosphere that can create a greenhouse effect.
The generally accepted hypothesis states that the solar wind eventually destroyed the Martian atmosphere, causing a greenhouse effect and destroying the hydrological cycle. Unlike the Earth, the Red Planet is not endowed with a global magnetic field, but the stellar wind induces currents in the ionized upper atmosphere (ionosphere), creating an induced magnetosphere. It has long been believed that this is not enough to protect the Martian atmosphere. Since 2004, the Swedish ion analyzer on Mars Express has been measuring the leakage of ions from the planet. Scientists compared the figures for different solar wind conditions and levels of ionizing solar radiation. The analysis shows that the stellar wind has a small effect on the rate of outflow of ions.
Despite the powerful solar wind and levels of UV radiation from the early Sun, the leak is unable to account for more than 0.006 bar of atmospheric pressure lost over 3.9 billion years. The results show that a strong stellar wind accelerates particles, but does not increase the rate of outflow of ions.