Without a strong magnetic field, a planet struggles to rotate on a breathless atmosphere – which is bad news for life as we know it. A new study published in Science Advance suggests that the now extinct magnetic field of the Moon may have helped protect our planet’s atmosphere as life was formed around 4 billion years ago.
Today, the Earth has a strong global magnetic field that protects the atmosphere and low-orbiting satellites from harsh solar radiation. In contrast, the Moon does not have either a breathless atmosphere or a global magnetic field.
Global magnetic fields are generated by the motion of molten iron in the cores of planets and moons. The fluid needs energy to keep moving, such as the heat trapped within the core. When there is insufficient energy, the field dies.
Without a global magnetic field, charged particles of the solar wind (radiation from the Sun) passing close to a planet generate electric fields that can accelerate charged atoms, called ions, out of the atmosphere. This process is occurring on Mars today and is resulting in a lack of oxygen – something that has been directly measured by Mars’ atmosphere and the Unstable Evolution (Maven) mission. Solar wind can also hit the atmosphere and knock molecules into space.
The Maven team estimates that throughout its history the amount of oxygen lost from the Martian atmosphere is contained in a global layer of water 23 meters thick.
[Read: The Moon’s surface is rusting — and Earth may be to blame]
Ancient magnetic fields test
New research shows how the early regions of the Earth and Moon would have interacted. But examining these ancient areas is not easy. Scientists rely on ancient rocks that have small grains that are magnetized as rocks, saving the direction and strength of the magnetic field at that time and place. Such rocks are rare and require careful and delicate laboratory measurements to extract their magnetic signal.
However, such studies suggest that the Earth has generated a magnetic field for at least the last 3.5 billion years, and possibly return to 4.2 billion years, which is more than half of its current time value. We do not know much about how this area was behaving compared to before.
In contrast, the lunar field was probably stronger than the Earth at about 4 billion years ago, before the state of the weak zone declined 3.2 billion years ago. At present, very little is known about the structure or time-variability of these ancient regions.
Another complication is the interaction between early lunar and geomagnetic fields. The new paper, which showed the interaction of two magnetic fields with the north poles either aligning or vice versa, shows that this interaction extends the area of Earth’s space between our planet and the Sun that is shielded by solar wind. .
The new study is an interesting first step towards understanding how important such effects will be in a lunar orbit or averaged over hundreds of millions of years that are important for the assessment of planetary habits. But to ensure that we need further modeling and more measurements of the strength of the initial magnetic fields of the Earth and Moon.
What’s more, a strong magnetic field does not guarantee the continuity of a planet’s atmosphere – its surface and deep internal environments also matter, as do the effects from space. For example, the brightness and activity of the sun has evolved over billions of years and therefore the ability of solar wind to strip the atmosphere.
Each of these factors contributes to the development of the planet’s habit, and therefore life, is still not fully understood. Their nature and how they interact with each other is also likely to change with geological time. But thankfully, the latest study has added another piece to an already fascinating puzzle.
This article is republished from a conversation by Christopher Davis, Associate Professor in Theoretical Geophysics, University of Leeds, and John Mound, Associate Professor at the University of Leeds under a Creative Commons license. Read the original article.
Why training neural networks comes with a heavy price tag