We don’t often think about magnets when we talk about objects in our Solar System. Large celestial objects like Earth have magnetic fields that help us sustain life. The Moon certainly appears dormant now, but let’s take a look at how magnetic fields have played a role in making the Moon what it is today.
What Is a Magnetic Field?
In a very general sense, a magnetic field causes electrical charges to move along invisible lines. These lines start at a south pole and travel to a north pole in an oval or circular shape around the magnetic object. They can be caused by a magnet, electric current, or a changing electric field.
Magnetic fields are stronger the closer they are to the source object. Field lines never cross each other and follow the circular pattern from the south pole to the north pole.
When it comes to our Earth, we have a magnetic field that is caused by currents of electricity that flow through the iron in our molten core. These currents are so big and travel so fast that they generate a powerful magnetic field that passes from our planet out into space. This sphere of magnetic protection is also known as the magnetosphere.
A Look at the Earth’s Magnetosphere
The magnetic field generated by our Earth puts up a shield that protects all of us from most of the Sun’s solar winds and cancer-causing ultraviolet particles. While a few particles do get through, most of them are reflected back out into space thanks to our magnetic field.
We also use our magnetic field for navigation. Compasses used for nearly one thousand years rely on the Earth’s magnetic field to keep ships, planes, and even us pointed in the right direction.
At times, the Sun can cause minor disturbances to the Earth’s magnetic field. These disturbances are sometimes made visible in certain parts of the world, particularly near the poles. This phenomenon is known as an aurora and often looks like a green curtain of light draped in the sky.
The Earth’s magnetic field has gone through periods of strengthening and weakening throughout history. It’s even flipped its poles a few times, with the last known event happening some 78,000 years ago. Still, the magnetic field has never disappeared, and we’ve always been able to rely on it for protection.
What if Our Magnetic Field Ceased to Be?
Without our magnetic field, the Sun would bombard the Earth with solar particles, damaging the ozone layer and subjecting us to further ultraviolet radiation. Compasses would stop working, and everything that uses one for guidance would be lost.
While we probably wouldn’t immediately die from these effects, the increase in solar activity would leave us at great risk for untold problems.
Does the Moon Have a Magnetosphere?
At present, the Moon does not have a magnetosphere that encompasses the satellite. Interestingly enough, the Moon is believed to have at least a thin layer of molten iron in its core. This molten iron is likely not big enough or flows fast enough to generate a magnetic field any longer.
Scientists know from careful analysis of Moon rocks brought back from Apollo missions that areas on the Moon show magnetic properties. In fact, there are localized regions hundreds of miles in size that see a great deal of magnetic influence.
No one understands how these pockets of magnetic field formed or why they remain. They do prove that the Moon once had a significant magnetic field of its own.
Did the Moon Have a Magnetic Field in the Past?
It’s believed that, as the Earth and Moon formed, the Moon was much closer to the Earth than it is now. The two incredibly hot objects both had large amounts of molten iron churning in their cores. As a result, the Earth and the Moon shared a magnetic field that helped protect life as it formed on our planet.
Obviously, the Moon’s magnetic field did not survive the test of time, as its core has cooled almost completely solid. The lack of a magnetosphere allowed the Sun to tear away all but the tiniest atmosphere that the Moon had. This rendered it inhospitable and susceptible to impact from orbital debris.
Can You Use a Compass on the Moon?
If you found yourself lost on the Lunar surface, pulling out a traditional compass would, unfortunately, do you little good. The small magnetic pockets that the Moon has may even make things more difficult for you, as they are located in different areas of the Moon, and each have a north and south pole.
Astronauts on the later Apollo missions took lunar rovers out on the Moon’s surface and needed to be able to find their way back to the lunar module. Since a magnetic compass was out of the question, they used a gyroscopic device to get back to base safely. A gyroscope is simply a free-spinning disc set to point at a particular object.
Before using their rover for the first time, the astronauts had to calibrate their gyroscope. They used the angle of the Sun as a reference point, given that the Sun was low and to the east during their excursions.
What Other Objects in the Solar System Have Magnetic Fields?
While all of the gas giant planets have strong magnetic fields, we have yet to discover what causes them or how they exist. Scientists have had no way of seeing the composition of each gas giant’s core. As a result, it’s unknown if they are formed by molten iron like on Earth or something else entirely.
There are only three known rocky planetary objects in the Solar System that have a magnetic field. There’s the Earth, of course, but Mercury has a hot core that is able to generate a magnetosphere. That being said, it’s only 1.1% the strength of Earth’s.
The only other rocky object confirmed to have a magnetosphere in our Solar System is the largest of its moons, Ganymede. Ganymede’s magnetosphere exists entirely under the umbrella of Jupiter’s but is distinct. Plasma from Jupiter forces the moon’s magnetic field into wide circles emanating away from Jupiter.
The Moon may no longer have a magnetosphere, but it certainly did at one point. We likely have the Moon’s magnetic field to thank for at least some of the protection our planet received as it was forming billions of years ago. Even so, it’s easy to marvel at the relationship we have with our celestial neighbor – and where we might be without it.