The habitat of the planet depends on many factors. One of them is the existence of a strong and durable magnetic field. These fields are generated thousands of kilometers below the planet’s surface in its liquid core and propagate far into space, protecting the atmosphere from harmful solar radiation.
Without a strong magnetic field, the planet is trying to hang a breathing atmosphere – which is bad news for life, as we know it. A new study published in Science Advances suggests that the extinct magnetic field of the moon may have helped protect our planet̵7;s atmosphere when life formed about 4 billion years ago.
Today, the Earth has a strong global magnetic field that protects the atmosphere and low-orbit satellites from harsh solar radiation. In contrast, the Moon has neither a breathing atmosphere nor a global magnetic field.
Global magnetic fields are generated by the motion of molten iron in the nuclei of planets and moons. Energy, such as heat entering the core, is needed to keep fluid moving. When there is not enough energy, the field dies.
Without a global magnetic field, charged particles of the solar wind (solar radiation) passing close to the planet generate electric fields that can accelerate charged atoms, known as ions, from the atmosphere. This process takes place on Mars today, and as a result it loses oxygen – something that was directly measured by the atmosphere of Mars and the changing evolution (Maven). The solar wind can also collide with the atmosphere and knock molecules into space.
According to the Maven team, the amount of oxygen lost from the atmosphere of Mars in its history is equivalent to the amount contained in the global water layer, 23 meters thick.
[Read: The Moon’s surface is rusting — and Earth may be to blame]
Probing of ancient magnetic fields
A new study examines how the early fields of the Earth and the Moon may have interacted. But exploring these ancient fields is not easy. Scientists rely on ancient rocks that contain small grains that have been magnetized as rocks are formed, maintaining the direction and strength of the magnetic field at the time and place. Such rocks are rare, and careful and delicate laboratory measurements are required to obtain a magnetic signal.
However, such studies have shown that the Earth has generated a magnetic field for at least the last 3.5 billion years and possibly another 4.2 billion years, with an average strength of just over half its current value. We don’t know much about how the field behaved before that.
In contrast, the lunar field was perhaps even stronger than the Earth’s, about 4 billion years ago, before rapidly declining to a weak field 3.2 billion years ago. Little is currently known about the structure or time variability of these ancient fields.
Another complication is the interaction between the early lunar and geomagnetic fields. A new paper that simulates the interaction of two magnetic fields with north poles, aligned or opposite, shows that this interaction extends the area of near-Earth space between our planet and the Sun that is protected from the solar wind.
The new study is an interesting first step in understanding how important such effects will be if averaged over a lunar orbit or over hundreds of millions of years, which are important for assessing planetary suitability. But to know for sure, we need further modeling and more measurements of the Earth’s strength and the Moon’s early magnetic fields.
Moreover, a strong magnetic field does not guarantee the constant suitability of the planet’s atmosphere – its surface and deep internal environments are just as important as the effects of space. For example, the brightness and activity of the Sun have evolved over billions of years, and hence the ability of the solar wind to capture the atmosphere.
How each of these factors contributes to the development of planetary adaptation, and hence life, is still not fully understood. Their nature and how they interact with each other are also likely to change on a geological scale. But fortunately, the latest study has added another piece to an already addictive puzzle.
This article was published in an interview with Christopher Davis, an associate professor of theoretical geophysics at the University of Leeds, and John Mound, an associate professor of geophysics at the University of Leeds under a Creative Commons license. Read the original article.
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