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Halo Science 101


May 2, 2007 Article Start Previous Page 4 of 6 Next
 

The exception, of course, is Threshold’s lone enigmatic moon, named Basis. Basis is unusual by solar system standards. It’s a huge moon. With a radius of 11,924 kilometers, it is nearly twice the radius of the planet Earth and has over 6.5 times the volume! Just as there was a bit of a discrepancy with Threshold’s planet/brown dwarf duality, a similar statement can be made for Basis. Giant planets like Threshold radiate a lot of energy, especially infra-red energy. This means that although the light and heat from Soell is quite faint, it’s nevertheless quite toasty near a body like Threshold.

This would imply that Basis is composed primarily of rock, like Jupiter’s innermost large moon Io. Because of Threshold’s heat, icy satellites would not remain icy long. On the other hand, if we assume that Basis is, in fact, composed of rock, and if it had a density close to that of Io (which is still less than that for any of the terrestrial planets), then the gravity on the surface would be nearly 1.2 times that of Earth. Master Chief and his fellow marines might be moving a trifle slowly on Basis if this were the case. The gravity on Basis appears to be similar to that for Earth, however, and it would certainly be enough to hold an atmosphere. Further, the appearance of Basis is not dissimilar to Jupiter’s moon Europa. If we assume that Basis has a similar composition as Europa, and we assume the same density, then it has the same gravity as Earth (this, perhaps, is what the game designers had in mind). It seems, then, that Basis is a bit of a paradox. For gravity there to be the same as Earth, the moon would almost certainly have to be composed of a mixture of ice and rock, but since the surface seems to have a temperature comfortable to humans, then most of that ice should be in the liquid state.

A careful examination of the viewscreen on Pillar of Autumn shows that Installation 04 is halfway between Threshold and Basis. This is an untenable place to put a Halo for many reasons. More likely the Halo is situated near, or orbiting about, the L1 Lagrange point between Threshold and Basis, which would put it closer to Basis and not at the halfway point. In a system with two massive bodies (like Threshold and Basis, which we’ll call the primary and secondary bodies), there are five points where a third body of negligible mass, owing to a combination of gravitational attraction and orbital centrifugal force (understanding that “centrifugal force” is what physicists call a “fictitious force;” here, the more colloquial usage is adopted), would remain stationary with respect to the two massive bodies.

These are known as LaGrange points, and they are labeled L1 through L5. The L4 and L5 points, sixty degrees ahead and behind the smaller massive body in the same orbit, are stable. Objects placed in a co-planar orbit at either L4 or L5 will remain in roughly the same location relative to the two massive objects. The solar system is, in fact, full of examples. At the Sun/Jupiter L4 and L5 points are hundreds of asteroids, called the Trojan Asteroids, which co-orbit with Jupiter. The Saturnian moon Tethys even has smaller moons at its L4 (Telesto) and L5 (Calypso) points.

The L1, L2, and L3 points are called “meta-stable,” however. All three points orbit the primary at the same orbital rate as does the secondary body, and each maintains the same relative position between the two. L1 is along the line connecting the primary body to the secondary body and is situated at what a mathematician would call a “saddle point.” A ball bearing placed on a saddle would roll to the middle of the saddle from front to back but would have a tendency to roll off to one side or the other. The L1 point is “stable” in one direction (along the primary-secondary line), but unstable along its orbit, hence meta-stable. This implies that Installation 04 actively corrects its orbit to keep Threshold and Basis at the same relative locations. Though the L1 point is unstable, there exist trajectories that “orbit” the L1 point that are stable. The NASA Solar and Heliospheric Observatory (SOHO) and Genesis missions, both of which took data about the sun, were on such trajectories (which, ironically, are called “halo orbits”).

In placing a structure like a Halo so near a body like Threshold, other complications arise. One would be the radiation environment. The largest structure in the solar system is the magnetic environment around the planet Jupiter. If it could actually be seen, from Earth it would appear to be a few times larger than the full moon. Such a large and intense magnetic field traps charged subatomic particles like electrons, which spiral along the magnetic field lines. Some electrons can even be accelerated to relativistic speeds—a large fraction of the speed of light. This makes life near a jovian planet difficult at best. A human standing on Jupiter’s innermost large moon, Io, would receive a lethal dose of radiation from only a few minute’s worth of exposure. Surely the radiation environment surrounding a Halo in close orbit about a gas giant would be similar.

Earth is bathed in a stream of changed subatomic particles not dissimilar to those in close proximity to Jupiter: the solar wind. Earth is protected from charged particles where Io is not, owing to its magnetic field. Since electrons and other charged particles are deflected by magnetic fields, the solar wind flows around Earth, except at the poles. At Earth’s poles, there is a hole, or cusp, in the magnetic field where the solar wind can penetrate more deeply. The solar wind’s interaction with Earth’s upper atmosphere underneath the polar cusps is what creates the aurorae.

Certainly a Halo bathed in the radiation of a gas giant like Threshold would require shielding similar to that around Earth, and it turns out that to do this might be a fairly straightforward task. Magnetic fields are generated by moving charged particles like electrons, implying that any wire along which a current flows is surrounded by a magnetic field. It’s not inconceivable, then, that huge conductive cables could run the entire 31,416-kilometer circumference of a Halo, nestled within the ring structure itself. By creating electrical currents within these cables, the Forerunners could have easily created a protective magnetic environment that was strong enough to make a Halo inhabitable, but not so strong that it would interfere with the function of electronic equipment.


Article Start Previous Page 4 of 6 Next

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