Not A Review: Impact (2008)

While editing episode 141 of the podcast, I watched the film Impact on the Syfy Channel. And some of the things that were said in it were just....oh, I wanted to yell at the television. I mean, seriously, if you're going to write a movie about something like the Moon being driven into the Earth by the impact of a near-Earth object (NEO), then you should first at least try to UNDERSTAND some of the things you're having your scientist characters say.

These are just a few items that should either have been learned in a basic physics or earth science class or else just quickly checked out on Wikipedia or other online sources.

Does the Moon have a magnetic field?

Living on Earth, we tend to take the concept of magnets and the north and south poles for granted. The reason we are able to use a compass here on Earth is due to our planet having a large metallic core. Without going into a HUGE explanation, the simple version is this: the Earth's inner core is a giant ball of mostly iron surrounded by a liquid outer layer of molten metals. Since the core rotates at a different rate than the liquid shell around, friction generates an electric field between the two layers, and the motion of the core through that field creates a moving electric field which produces a magnetic field (Ampere's Law). This is the source of the Earth's magnetic field. ^[1][2]

The Moon, however, does have a magnetic field, but it is extremely weak. It's core is small at less than 25% of the Moon's radius (the Earth's core is 50% of the Earth's radius), and does not project a field.

Would the Moon falling towards the Earth create electricity?

Given that the Moon is actually a magnet, then it would generate an electric field while moving. A simple way to explain it is to use the Right Hand Rule for magnets in motion. When a magnet moves it creates an circular electric field around itself. If you point the thumb of your right hand and then curl your fingers (like you're gripping a can sideways)  then you can see what the field would look like. The thumb points in the direction of the change in the magnetic field (the motion) and the fingers point in the direction of the electric field being generated. This is the science behind generators, which use spinning magnets to generate electricity.^[3]

This effect was experience when, as the Moon fell towards the Earth, people on the surface of the Earth began experiencing electric surges. The problems lies not with the effect itself but with how the lead characters, who are scientists, react to it.

They say they have no idea what is causing the surges! Which is sad since Faraday's law is something taught in any basic physics course. Anybody who was an astrophysicist, cosmologist or similar discipline would know these things. It would be a part of their basic training at university.

Would objects on Earth suddenly float up towards the Moon?

No, they wouldn't. As the Moon moves towards the Earth, the pull of gravity by the Earth would slowly be counteracted by the gravitational pull of the Moon.^[4] You would gradually feel lighter, but never so light that you would float. The only way you would feel that light would be if you were on the object of less mass (the Moon), and even then it would be so close to impact between the two objects that your floating would really just be you falling off of the Moon onto the Earth.

The tides are caused by the Moon's gravity pull on the bodies of water on the side of the Earth facing the Moon, and on the crust on the far side of the Earth from the Moon. If anything would be affected by the Moon coming towards the Earth it would be a significant increase in both tidal activity as well as tectonic activity. The Moon would wreak havoc with the Earth's crust and with coastal regions as higher tides and flexing plates would cause the surface to violently shake and fracture.

To go further with this, if you DID suddenly become weightless or float away, there's no reason why you would then fall back to Earth again. In the film, a father and son as well as a commuter train experienced this floating and then both were cast back down to Earth violently some time after. But the gravitational force is a constant force at a distance. You wouldn't have a surge that would then evaporate and cause such an event. And it would have at least balanced that out if they had shown objects on the far side of the Earth suddenly being crushed under the same gravitational fluctuations.

If anything, the surface of the Moon would be experiencing a huge bit of electrical activity. Especially since, in reality, as the Moon moves through the Earth's magnetotail particles on the Lunar surface will actually rise up off of the surface and float!

But it is funny to see a grandfather and his two grandkids fly up into the air in their car, but the grandfather's hat and the girl's pig tails are unaffected by the reverse gravity that they're experiencing...

Conclusions

Sure, this film wasn't meant to be a serious scientifically based story. But to have a scientist say something as ridiculous as "The Moon is not capable of manipulating gravity itself" or for scientists to say, on one hand, that the Moon's magnetic field has changed and then say they don't know what is causing electrical surges on the Earth's surface is just ridiculous and shows sloppy writing and no interest in validating even simple science for the story. I wrote this opinion in less than 15 minutes with just a few google searches for references. I'm sure the writers had more time than that to work some real information into their story...

[1] - http://en.wikipedia.org/wiki/Earth's_magnetic_field#Earth.27s_core_and_the_geodynamo
[2] - http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law
[3] - http://en.wikipedia.org/wiki/Faraday's_law_of_induction
[4] - http://en.wikipedia.org/wiki/Gravitation