Originaly posted on the TSR online message board (www.tsr.com) by Bruce Heard. (July 1998)
Prior to AC1016, outer space was roughly comparable to real world space with a cold vacuum and weightless conditions. During AC1016, however, a group of Alphatian mages recovered ancient parchments that described how their ancestors had filled space around their native world with breathable air.
The scrolls were very old and partially damaged, and these Alphatian wizards failed to fully comprehend what they were dealing with. They attempted to test the ancient spell which they thought would draw from the Plane of Air enough of an atmosphere to fill the inner void inside the Hollow World. The Spell of Preservation governing the Hollow World conflicted with their newfound magic, and caused its center to shift from the inside of the Hollow World to a fair distance outside Mystara.
It took the wizards many weeks to discover where the spell was centered and put an end to it. By then, vast expanses of outer space surrounding Mystara, its two moons, and much of its solar system was filled with air. Much worse, the Alphatian spell was powerful enough to alter some of the laws of physics. It made it possible to stabilize such a huge expanse of gas, normal planetary gravity and movement in space.
Although dismayed at first, some of the wizards were overjoyed that their spell did work, even if outside the Hollow World only. Whether this had forever altered their world was of no concern at all to them. Their interest was for the spell itself, and for them it remained almost a purely academic experiment. Satisfied that Alphatian arcane know-how hadn't lost its edge, these scholars went on with other projects. They were satisfied that the Alphatians had finally left a lasting mark on this world, in letting this good, wholesome air vent away all the "festering miasma and unhealthy vapors exhaled from human civilization and choking so fine a world"!" From their point of view, outer world travel would also be so much easier. At least that's what they thought then.
The remainder of these Alphatians did not share their colleagues' jubilation. For them, the spell had indeed run amuck. But worse, as it presumably made space travel easier it also made Mystara more vulnerable to possible incursions from other worlds. Virtually nothing was known of what lay in the distant worlds of the firmament. Empress Eriadna of Alphatia was the most eminent and vocal of the spell effect's detractors. She ordered that the spell be undone at once, but to no avail. The wizards did not know how to reverse such a powerful enchantment. The entire group was subsequently condemned to live on an asteroid past Matera's far side, there to pursue their research for a counter-spell. Only then would they be permitted to return from their place of exile. Fortunately, the Hollow World remained unaffected and ever so difficult to reach without Immortal-magic.
Objects of ten tons or more, like a ship for example, exert their own gravity. Gravity is comparable to normal Mystaran gravity, except it extends to a much shorter range (no more than 100ft from edges of the hull). The ship's gravity centers on its heaviest, single part, which has prompted some space explorers to fit a mast underneath their ship, ending with a very dense, heavy object. This gives the illusion of vertical gravity that is roughly perpendicular to the ship's decks. Naturally, this counterweight is removed or jettisoned before crossing into a planet's Skyshield.
Should a larger object, like a planet for example, be close enough, it would affect the smaller object as a whole, single object. The latter means that a ship's own gravity does not change when cruising near a planet, causing passengers to suddenly lose their footing and fall off their ship. The rule of thumb is that a ship and its passengers would be attracted by a planet as if they were one single object until they crossed its Skyshield, at which point normal laws of physic apply.
This is where things get really wierd. Feel free to jump in and suggest different approaches for this. I'm just putting down some ideas -- this isn't a final contribution, naturally.
Planets hurtle through space at high speeds, however, their Skyshields prevent air friction from interfering with their course to some degree. Mystara's moon, Matera, is an airless satellite by design. It has its own Skyshield to prevent air from reaching it. Vast quantities of air filling Mystara's outer-space move along with the planets and their moons. The further one travels from a planet's orbital path, the more turbulence, until reaching another air current. "Cosmic turbulence" is more than enough to rip apart any ship attempting to cross through without protection.
Magic can be used to avoid some of the effects of cosmic turbulence. Find the Path not only allows a traveling ship to target the appropriate spot to reach a planet, but if cast at sufficient level, enables the ship to accelerate to planetary speeds (the "warp* speed described in Champions of Mystara). The spell causes the ship and its passengers to become partly incorporeal, thereby avoiding the problem of air resistence, cosmic turbulence, and intervening obstacles in the ship's path. Crossing regions of cosmic turbulence remains a rough ride nevertheless. The experience level needed to cast the spell amounts to one level for 10 tons of material to be displaced (ship, cargo, and passengers for example).
Travelling ships also have to contend with pockets of rarefied air and varying temperatures. So far, no humidity has slipped into the breathable space, so no earthlike storms should be expected. There could be pockets of other gases and electrical phenomena affect Mystara space.