INTRODUCTION

Pegasia isn't an alien planet. It's a mere moon, orbiting a gas giant bigger than Jupiter (and much closer to its sun). Such giants are common--and this week's theory (the turnover's fast) says they're trouble. A hot Jupiter's not born close to the sun but spirals in, slowed by dust, swallowing any Earthlike worlds or flinging them out of the system. It even may have happened here. Look what lies between us and Jupiter! The asteroids, Mars? Mars is rubble! ONE NINTH Earth's mass--just a big rock. Jupiter may have suppressed planet-formation for hundreds of millions of kilometers around it.

So hot Jupiters are trouble--and they're everywhere. Bad news for life! Or is it? Many are bigger than Jupiter. Some of their moons will be oversize too--Martian, even Terran! Big enough for life. Gravity giveth, and gravity taketh away. Pegasia's such a moon, half the mass of Earth.

Pegasia looks Earthlike at first glance. Look again! Dense air, low gravity, jagged terrain, shallow seas, restless tectonics. And the skies! Zeus (its gas giant) looms overhead, causing bloody red eclipses every noon; rusty Tharn (a sister moon like a living Mars) grows and shrinks as it swings by; auroras crackle and shimmer even in the tropics; every 48-hour day, the weather swings like Terran seasons--frosty nights, balmy dawns, afternoon hurricanes!

And one more difference: Pegasia has many intelligent species. What kinds? You tell me. Pegasia is a contest for species-designers! See Creatures and Peoples for guidelines and sample entries, and Evolution for background. But first... just click somewhere on the map you'd like to go.

PEGASIA: BASICS

• Class = moon! Pegasia's not a planet--and that fact colors everything.
• Sun = smaller, redder, and cooler than Sol--and much commoner! Most exobiologists focus on sunlike stars. They assume Earths orbiting small stars will have to huddle so close for warmth that solar tides would slow their spin till they're locked facing the sun--burning dayside, freezing nightside. But not moons! Their planet, not the sun, dominates their tides, so they often end up facing their primary--and spinning relative to the sun, even if it's close. Pegasia and its sister Tharn both have tolerable 48-hour days--and they might not, if they were planets. Even if only a few red stars have viable moons, I suspect they outnumber the Earths out there! Because little red stars are common as dirt.
• Orbit = elliptical, from 0.4 to 0.7 AU. Pegasia's primary, Zeus, swings in and out, creating a short worldwide summer, then a long mild worldwide winter (the outer half of an elliptical orbit is slower--takes up more of the year). Why elliptical? Well, eccentric planets are commonly written off as unfriendly to life. But are they? Temperature swings can be good--some part of the cycle may be a growing season.
• Total annual insolation = only 85% of Earth's. Sounds chilly, but it's no Mars (44%). In fact, Pegasia's as warm as Earth, due to two mitigating factors:
  1. Better greenhousing than Earth or Mars. See CO2, Air Pressure and Temperature, below.
  2. A second source of heat: the surface of Zeus is nearly as hot as Venus--600 K. Its nightside doesn't glow visibly, but it's like a heat lamp in the sky. It's cooled slowly over the last few billion years; meanwhile the sun's slowly heated up, as stars usually do. This compensating pattern will be common--Pegasian moons orbiting hot giants have a slight advantage over Earthlike planets in long-term thermal stability.
• Axial tilt = only 3 degrees, relative to the sun. Though Pegasia doesn't have two poles, but six: north and south (cold), inner (hot days broken by a long noon eclipse, warm nights, with Zeus looming overhead like a bed of coals), outer (hot days, but cooler at night, without Zeus), front (warm days, nights crackling with auroras) and back (warm, mild).
• Ultraviolet = low. The cool red sun produces less and Pegasia's dense air blocks most of that.
• Radiation: varies regionally. The cooler sun produces much less, but the magnetic field of Zeus creates a loop like the one linking Io and Jupiter (though weaker); it funnels most charged particles onto the leading hemisphere. Pegasia's own weaker field steers them toward the north and south poles, resulting in an arc of auroras from north to front to south poles. The dense atmosphere keeps even this face livable, if a bit "hot." The trailing hemisphere has much lower levels.
• Solar year = 7 months? I'm being vague because I haven't looked up the curve for light vs mass of Pegasia's sun yet, and the mass determines the year-length. Just keeping some wiggle room!
• Seasons = planet-wide, caused by the eccentric orbit, not hemispheric seasons caused by axial tilt. The sun grows and shrinks visibly. The equatorial belt is warm but more seasonal than Terra's tropics. During global winter, "rainforests" are warm to mild with light rains; in the summer, hot and torrential. Quite monsoonish! High latitudes see little change in day-length, just brightness. Dense air, the lack of icecaps and the many inland seas generally keep winter temperatures milder than Earth.
• Mass = 0.5 Earths.
• Density = 3.9 gm/ml (like Mars; Earth=5.5). Pegasia's iron core is smaller than Earth's. Most solar systems are poorer in heavy elements than ours, AND cool, outer planets tend to be lightly built--and that's where Zeus and Pegasia came from. At least Pegasia has an iron core, and tidal stress keeps it molten, creating a magnetic field--a radiation shield. Many Pegasian moons will be largely silicon rock, carbon compounds and ice; even some with iron cores will be cold and shieldless.
• Diameter = 11,500 km (7,160 mi): 90% of Earth's, a bit smaller than Venus. Circumference is about 36,000 km (22,500 mi). One degree is 100 km (62 mi); the thirty-degree lines on the map are 3000 km apart. Convenient!
• Surface area = 415 million sq km (161 M sq mi); 82% of Earth.
• Gravity = only 0.63 G! (Earth=1, Venus 0.9, Mars 0.38).
• Primary (the gas giant Pegasia orbits) = Zeus, 200,000 km across (125,000 mi), nearly 50% wider than Jupiter and nearly twice its mass (600 Earths). Its heat puffs Zeus up to only 2/3 Jupiter's density.
• Pegasia orbits 570,000 km out; further than Luna, more like Europa orbiting Jupiter. Its sister moons on either side are much smaller than Europa's and orbital eccentricity is modest, but even so, tidal stress heats Pegasia's core and mantle and tidal drag has slowed its rotation. Fortunately! If Zeus moved across Pegasia's sky, the seas would follow, and huge tides would drown half the land twice a day. But Zeus just hovers--nutation ("nodding") is modest. Also, Pegasia's rock is warmer and more elastic than Earth's, so it bulges along with the seas. Tides are high, but not catastrophic.
• Day = 48 hours. This is also its month, the time it takes to orbit Zeus. One side always faces inward, like Luna, Io, or Titan. Tide-locked! The long day causes strong temperature swings. Mini-seasons! On the inner face, thermal radiation from the gas giant warms the long nights, and the noon eclipse cools the day, smoothing these swings. The outer face is harsher--hot days, cold nights. One last oddity: the dense atmosphere bends sunlight, lengthening dawn and dusk, so on average daylight lasts over 25 hours, nights less than 23. Sounds odd, but even on Earth the sun's refracted a degree or so.
• Water = 25% of Earth's--still plenty for a shallow worldwide sea. Why so much water on a low-grav world? Wrong question! You should be asking "Why so little?" Pegasia was born in the cold outer system, and most outer bodies are ice-rich--think of Europa! But...
  1. Not all outer worlds are wet. The probe into Jupiter's atmosphere found the Big Paisley surprisingly dry.
  2. Pegasia's mass and escape velocity are half Earth's, so air and water loss has been significant, ever since it warmed up...
  3. and that's been a while! Pegasia is old. It spiraled into the warm zone 7-8 billion years ago. (We forget how long-lived small suns are. Earth is doomed to a short life, as worlds go.)
  4. Jupiter's simultaneously cited as a comet-shield for Earth and as a comet-disturber, creating the rain of comets that showered our hot young world with outer-system ice. So does Jupiter decrease or increase total comet-strikes on Earth? It's not as clear as some authors would have you believe. We'll need to see cratering rates in a system with no Jupiter, and THAT'll be a while yet! Now Zeus is twice Jupiter's size, but it's closer to its sun; its gravity well moves much less, and disturbs the system less overall. Fewer comets! Though Pegasia may have started wetter than Earth, it's had fewer refills.
  5. Pegasia originally swung much closer to Zeus (tidal forces push moons slowly outward--Luna originally hugged Earth, too). Back then, Zeus still glowed red-hot! That steamed off a lot of ice. Only Pegasia's gravity (strong for a moon) saved it. Tharn, the other big moon, was smaller and lost much more--or perhaps never had it. Its mineralogy and more eccentric orbit suggest Tharn's a small, captured planet.
  
• Internal heat and volcanic potential = Earthlike and then some! Zeus, the sun, and the huge, distant outer moon Tharn all tug at Pegasia--tidal stresses heat its core and mantle warmer than Earth's.
• "Moonlight" = brilliant. Zeus looks huge--a garish, striped, swirling "moon" 20 degrees across, some 1500 times the area of our full moon, and 4000 times brighter!
• Other moons = 11, but only two are of interest. Tharn is bigger than Mars! Despite thin air (0.25 atmospheres) and only 0.1% of Earth's water, shallow lakes dot its basins, craters and trenches. Like an early Mars--or a very old Earth! Its orbit outside Pegasia swings as close as 600,000 km; it looms 55% wider than Luna. Naked-eye observers can see clouds, the gleam of seas, and a seasonal flush of green. Dry though it is, Tharn teems with life--intelligent life.
  Galilea, the size of Pluto, orbits close to Zeus, and resembles a dwarf Io--volcanic, violent.
• Sea = 65% of surface area, but over a third of this is continental shelf or shallow inland seas. Coral reefs and kelp forests cover nearly 20% of Pegasia (2-3% on Earth). Only 43% of the surface is deep sea basins--and "deep" means just a mile, not 3 or more, as on Earth. (The last few per cent are trenches.)
• Land = 35% of Pegasia's surface, or 145 million sq km (53 M sq mi) -- nearly 90% of Earth's land area! And Pegasia's in a warm, wet phase, with shallow inland seas. When Pegasia's poles glaciate and the sea level drops, the inland seas become plains--up to half the surface is land! 57% of Pegasia's surface is light continental rock (Earth: 30%). Pegasia creates such rock no faster than Earth, but it's had 8 billion years to accrete the stuff (which grows over time; even a billion years ago Earth had far less land). And in shallower seas, the light rock spreads further as it erodes from mountains into plains and deltas.
• Tectonic activity = higher than Earth. Radioactive heating is below Terran levels, but tidal stress is higher. The heat's dispersed both by volcanoes and many active spreading zones. The seas resemble our Atlantic--a sinuous rift zone flanked by low basins. And they're all similar widths--hence, probably similar ages. Did a big impact wake up the whole planet, a quarter of a billion years ago? Traces of previous rifts, ridges and sea-basins are now scrunched inside the new continental clusters, rather like the twisted undersea ridges of the Mediterranean or Indonesia. Pegasia doesn't experience much continental drift any more, for its copious continental rock's run out of places to drift to; Pegasia suffers continental crunch. Rather than carry continents peacefully along for the ride, like Australia, the expanding sea-floor slips under most coasts, building high coastal ranges... and volcanoes.
• Relief = rugged, helped by low gravity. Pegasia's vigorous plate-motions push up many Andean ranges at plate boundaries, and huge volcanoes rise over hot spots. The highest peaks rise 12 km above sea level (Earth: 8.8; Mars, 26); the deepest ocean trench is 6 km (Earth: 11; Mars, 8 (not an ocean trench, of course, but Hellas Basin)).
• Atmosphere = nitrogen 68%, oxygen 22%, argon 8%, neon 2%. Of course, it's no coincidence the air is fairly Earthlike on a living world. Life does that! I'm not pushing an extreme Gaia hypothesis, in which life deliberately generates an optimal envelope for itself (Earth's isn't optimal, after all--we have big dead zones.)
• Air pressure at sea level = about 1.2 bars, or 1.6 Earth atmospheres. I bet you thought it'd be well below Earth's--a bit Martian. But if tiny Titan's so air-rich, why not Pegasia? Air loss? Sure! It's lost, say, two-thirds of its air and water--from an original 5 atmospheres! (Air pressure's unpredictable, not a neat function of mass or surface gravity. Try charting Venus, Earth, Titan and Mars by mass and atmospheric density--Pegasia could plausibly have anything from 0.1 to 10 atmospheres!) The partial pressure of oxygen is 76% higher than on Earth, and native life takes full advantage of the supercharged air and low gravity: most Pegasian animals fly.
• CO2 = 400 parts per million at present, and Pegasia's dense air makes this comparable to 640 ppm on Earth. It fluctuates, of course, but Pegasia is always strongly greenhoused (and with its dimmer sun, it needs to be!) Volcanoes emit more CO2 than on Earth. The main feedback loop on land: as CO2 rises, the climate warms, and melting ice swells inland seas; coral reefs bloom. Continental interiors grow rainy, and forests spread. All this new life locks up CO2 again. Low CO2 chills the tropics and builds ice caps; inland seas dry to prairie and desert. With fewer plants to absorb CO2, levels rise again. On Earth, the loop's a bit different: during ice ages, forests do die and deserts increase, but dust and glacial silt fertilizes seas that are nutrient-starved in warmer eras. Basically, while land plants die back, releasing CO2, the seas bloom, sucking up CO2. Life's net effect is small, so on Earth inanimate factors dominate the CO2 feedback loop: shifting currents, precession, volcanoes, the weathering of new mountain ranges--and human meddling. But Pegasia's huge coral reefs in warm eras are just as fertile as the Ice Age seas. No CO2 sponge in the sea! The die-back on land is unopposed, releasing CO2--and the ice melts.
• Temperature = Currently around 5 degrees warmer than Earth's global average. But the warmth (and rainfall) is skewed--instead of neat lateral belts as on most worlds, Pegasia has blotches around hot, cold, wet and dry poles. Most importantly, the inner pole's wetter and milder.
• Sky color = variable. Sunlight's gold, but the denser air scatters not just blues but greens; this leaves the sun's disk looking distinctly orange. Over land the noon sky is pale cream, tinting to jade over rainforests and pale turquoise over seas. Sunsets are spectacular, as high-floating clouds often glow ruby-red, lit from the underside by refracted rays. Since the sun's image refracts several degrees around the planet in the dense air, nights are an hour shorter than you'd expect. And Zeus lights the inner face so brightly there is no real night--you'd still see full color at midnight, and the night sky's purple. Even the outer face is usually bright-lit by the other ten moons--Tharn alone sheds up to six times Luna's light!
• Cloud cover = A bit more than Earth's, on average.
• Albedo (reflectivity) = More clouds, but smaller deserts (which reflect a lot on Earth), so Pegasia's albedo is much like Earth's--in visible light. The strong greenhouse effect makes it darker in infrared, though the belt of equatorial rainforests shines out.
• Polar caps = variable over deep time. Currently under 1% of the surface is glaciated--and much of this is montane, not polar, for the high coastal mountains common on every continent tend to glaciate in the moist sea-winds. The north and south poles do have extensive sea-ice each winter, but without land, thick icecaps don't develop.
• Climate belts = Pegasia's belts are distorted by Zeus. The noon eclipse and "heatlamp" effect at night create a milder climate on the inner side, reducing evaporation. Raw rainfall and temperature figures are deceptive in this hemisphere. Essentially there's a huge, invisible bulge of tropicality. The outer hemisphere is harsher: more taiga, more tundra, more deserts. On the other hand, sharper temperature swings fuel more thunderstorms in some continental interiors, greening some areas that would otherwise be deserts.
• Air loss over time = sustantial. That's a virtue, not a problem! In Pegasia's early days, even after Zeus's orbit settled down, the sun was dim (most stars slowly brighten with age). The only ice-free seas were equatorial, plus a huge patch around the inner pole--like a wedding ring with a big diamond. Ice capped the land down to 30 north and south. Two factors kept the seas open: in those early days, Zeus was hotter--dim, red, but huge, a heatlamp in the sky--and the atmosphere was denser, perhaps 3-5 times Earth's, and rich in CO2. Life probably started in the deep rifts and crept up slowly to the unpromising surface, as the sun heated up and the seas fully thawed. The land took a billion years extra to conquer. But then, Pegasia has time: its sun will outlast Sol by 5-10 billion years!
• Age = 8 billion Earth years.
• Biomass = 160% of Earth's (average density = twice Earth's). Rainforests and coral reefs are much more extensive, accounting for most of the difference. In colder, drier times, total biomass drops as low as Earth's. Deserts where reefs flourished!
• Habitat diversity = moderate. In the current warm phase, most land is forest. Continental interiors are often deserts ringed by wide grasslands. Alpine meadows are far more extensive than Earth's; thick air and low gravity (making air pressure drop off slowly) moderate Pegasia's montane climates, so none of the highlands are as harsh as Tibet. The many coastal ranges create ecological islands and local rainshadows. These rugged, icy coastal ranges also fertilize the seas with more silt and volcanic ash than Earth's seas get; and those seas are far richer in shallows and coral reefs.
• Biodiversity = high. Not surprising, given nine continents with many rainforests--labs to cook up new species! However, this diversity may be just variations on a few themes, for the continents haven't been sundered long. In ice ages, when the sea level drops, there are only three supercontinents--a cluster round the inner pole, one around the outer, and a tongue of the outer cluster cut off by the south polar cap, extending nearly to the inner pole. Flora and fauna spread readily over land bridges at these times. And in the low gravity and thick air; many animals fly, so even in warmer times, a successful species can spread worldwide. Under the superficial fragmentation, Pegasian life has an unEarthly unity. For contrast, see a dry world like Serrana, where life from several puddle-like seas colonized land separately, with wildly diverse body plans and blood chemistries. While there's only a single worldwide "continent", it's a biological hodgepodge.
• Intelligent species = yes, yes, yes! But what? YOU TELL ME. Pegasia is open for reader entries. Design a species! See creatures and peoples for contest guidelines and samples. See Evolution on Pegasia for general principles.
• Nomenclature depends on what species will live on Pegasia, and where, and what their languages sound like. Invent a species yourself! See creatures and peoples. See the gazetteer for spelling and pronuciation guidelines and a list of tentative placenames; species designers should view these grouped by possible language, though you can also just send me your own along with your proposed species. Continents are temporarily numbered 1-9; islands and seas combine the digits of nearby continents. Continent 3 and eastern Continent 2 are the site of an experiment: I've added placenames to the tours, but still no physical descriptions of the locals. Invent people to fit the language!

The gazetteer will have a full index of native placenames, with descriptions--once the contests's over and we have natives to name them.

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