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The Neighborhood: A Halo’s Place in Space
Though it is likely that Halos heretofore unseen may exist in different environments, Installations 04 and 05 were both in orbit around jovian planets. In Halo: Combat Evolved, Installation 04 orbits the superjovian gas planet Threshold (Earth Survey Catalog B1008-AG), which, in turn, orbits the star Soell. Like Jupiter, Threshold is a gas giant with clouds of ammonia (white) and ammonium hydrosulfide (reddish brown) crystals. Unlike Jupiter, though, the diameter of Threshold is given at 214,604 kilometers, exactly half again as large as Jupiter (it is unlikely this is a coincidence, more likely a conscious choice on the part of the game designers).
The Halo game designers have exhibited an amazing attention to detail throughout the games. It is therefore likely that this is a result of recent astronomical discoveries more than any other reason, but jovian planets like Threshold are unlikely to exist in the real universe. Jupiter is about as large as a jovian planet can be. If increasingly more mass were added to Jupiter, it would begin to contract, collapsing under its own weight—becoming smaller even as it increased in mass. If a gas planet the size of Threshold did exist, and it had approximately Jupiter’s density, it would “weigh in” at a bit less than 3.8 Jupiter masses, or around 1,070 Earth masses. In reality, though, an object of 3.8 Jupiter masses would be smaller than Jupiter, while an object the radius of Threshold would be a medium-sized brown dwarf.
The debate of the late 1990s and early 2000s regarding Pluto’s status as a planet was less about Pluto than it was the definition of the cut-off point of what defines a planet at the low-mass end of the spectrum. A cut-off for the high-mass end of the spectrum has been in existence for quite some time, however. Large planets, like stars, tend to be composed largely of hydrogen. If an object has enough mass to sustain the nuclear fusion of hydrogen, thus generating its own light and heat, it is considered a star. To sustain hydrogen fusion and become a star, a body has to have roughly eighty-four Jupiter masses or more.
Objects between twelve and eighty-four Jupiter masses have properties that are intermediate between jovian planets and the smallest red dwarf stars and are called brown dwarfs. Although theoretically predicted to exist back in the 1960s, the first confirmed brown dwarf was viewed in 1995 and is 400 light years away from Earth in the Pleiades (a.k.a Subaru) open star cluster. Known as Teide 1, it is roughly twice the diameter of Jupiter, yet has fifty-five times Jupiter’s mass. For Threshold’s rasois to be 1.5 Jupiter radii, it would likely have at least twenty Jupiter masses of material and would appear quite differently— it would be more uniform in appearance than a jovian planet, as opposed to having multi-colored cloud bands.
Installation 05, or the Delta Halo from Halo 2, orbits the gas giant planet Substance. Less information is given about Substance than for Threshold, but based on its color, it is likely more Uranus- or Neptune-like than Jupiter-like. Uranus and Neptune are both blue, or bluish-green, in color, suggesting the presence of methane in their atmospheres. Methane absorbs the red light from the sun, and the resultant reflected light appears blue. So, we can make a logical deduction regarding the substance of Substance simply by its color.
Not only is Threshold unusual in that it appears to have properties of both a jovian planet and a small star, it is also unusual in that it has only one moon, and a very large one at that. Known gas giants have numerous moons, most of them small. By way of example, at present count, Jupiter has sixty-three moons, and Saturn has forty-eight. Even if some, even most, of the moons of Threshold had been used as construction materials for Installation 04, it is unlikely they all would have been suitable.
Most natural satellites of jovian planets, especially those as distant from their sun as Threshold appears to be, are composed of a mixture of ice and rock. In fact, it is normally so cold where the gas giants live that planetary scientists consider ice to be a rock—because ice is a main component of many of the solid objects in the outer solar system, and at the temperatures that exist in the outer solar system, ice is normally as hard as granite. Given that metals are comparatively rare around gas giants, it is unlikely that all of the moons would have been used as Halo construction materials. Perhaps some were melted for lakes, and some processed for atmosphere, but this still does not entirely explain the dearth of moons around such a large planet.
A likely explanation is that the region around Threshold was cleared on purpose. Alpha Halo monitor 343 Guilty Spark claims that Installation 04 is at least 101,217 years old. While that represents the blink of an eye in the cosmic timescale, it is still enough time for the Halo to have accumulated numerous impact scars, a few quite large. While the bulk of material in a planetary system is swept up and accreted as part of the planet-formation process, there are still countless small—and not-so-small—particles careening through the system. When the Hubble Space Telescope (HST) was serviced by the space shuttle Atlantis in 2002, it had literally hundreds of micrometeoroid impacts. In fact, it has been estimated that every square meter of HST receives five impacts from sand-grain-sized particles every year.
Most impactors are small, some aren’t: there was a three-quarter-inch hole in HST as well. After a span of 100,000 years, a megastructure the size of a Halo would be scoured and likely would have suffered a major impact event or two. This would be catastrophic, since a major impact would likely release as much energy as was released at the end of the game by the fusion drive on Pillar of Autumn, and we know what happened there. Even the claim that the Halo had some sort of force field is inconsistent with what we’ve seen: human and Covenant spacecraft seemed to have no resistance in coming (both landing and crashing) and going. Given all that we’ve seen, then, it may very well be that the Forerunners found a way to clear the Threshold system of debris to ensure the safety of Installation 04 and its research.