TEXT: © Mark F Peoples 1999
  1
  NEW PLANETARY SYSTEM GENERATOR
  The Planetary System Generator presented in the Gamemaster Guide enables the GM to create
  solar systems similar to our own, with rocky planets close to the star, gas giants further out, and
  smaller giants further still, where the scarcity of planet-building material has arrested the growth
  of large worlds. Finally, there are the icy worldlets of the Kuiper belt, and beyond that the Oort
  comet cloud that delineates the Solar System.
  Until only a few years ago it was universally accepted that most, if not all, solar systems would
  follow this plan.  With only one example to work from, it is hardly surprising that formation theory
  predicted that other systems would be pretty much like our own.  The system generator in the
  GMG reflects this.
  The truth, however, is a little more complicated.
  Since the middle of the nineties, approximately twenty planets have been found orbiting a number
  of stars.  One star, Upsilon Andromedae (which is visible to the naked eye during autumn and
  winter - check a star map) is host to at least three giant planets (Jovian worlds like the four giants
  of our system are the only planets that can be detected so far).
  One of the first things noticed about these new worlds was that they don’t necessarily occupy
  nice, circular orbits about their primary.  Many of these worlds (including the Up. And. system)
  have distinctly elliptical orbits.
  If this were the only revelation to be had, a simple note at the bottom of the page could fix it.  But
  this wasn’t the only difference.  The first planet detected, back in 1995 by groundbreaking new
  methods, was a giant planet in orbit about the star 51 Pegasi.  It possessed a remarkable trait.
  This planet orbits 51 Peg at 0.05 AU, much closer than Mercury orbits the Sun.  At least six other
  systems (including Upsilon Andromedae) have similar planets, called epistellar planets, or “Hot
  Jupiters”.  These giant planets pose much more of a problem for the world generation system in
  the GMG, since it is simply incapable of producing planets like this.
  All of the above problems have prompted me to create the following revision to the System
  Generator.
  Revised Orbit Track
  A slight revision to the orbit track system is necessary because of the Hot Jupiter problem.
  When you run out of orbital rings but still have a planet left, test for planets at distances of 0.05
  and 0.1 AU (check at 0.3 and 0.4 for A-type stars, and check at 0.02 and 0.05 for red dwarfs).  If
  you achieve a positive result, a planet will occupy this “epistellar” orbit.  Note, only ONE planet
  can exist in ONE of these orbits per system.
  Binary and Multiple Systems
  While binaries (and other multiples) may appear a little daunting at first, they’re not actually
  difficult to generate.  First, roll a d8 and consult table 1 below to determine the distance between
  them.  Stable planetary orbits can exist up to thirty percent of the distance between the stars (the
  closest approach distance in stars with eccentric orbits), and at a distance of greater than twice
  the distance between them.  Each star may have its own worlds in close orbit (any leftovers from
  each star may orbit the pair from the safe outer distance, if there are any corresponding orbit
  rings available), and multiples with large separations will act almost like separate solar systems.
  
  © Mark F Peoples 1999
  2
  Brown Dwarfs
  A system may contain a brown dwarf companion.  Problematic as these objects are, I have
  chosen to treat them like planets, since they bear a much stronger resemblance to large Jovian
  planets than to red dwarf stars.  Massing anywhere from 10 to 50 Jupiter masses, a brown dwarf
  will appear in a system on a roll of 16 on 2d8.  Use table 1 to determine separation.  If this
  conflicts with stars in a multiple system, discount the presence of the brown dwarf.  The brown
  dwarf may have “moons” in the same way as a large Jovian planet.
  Planet Type
  System density decreases after a drop-off zone where beyond this point, planetesimals are
  scattered too far apart to coalesce easily into large planets. These figures are given in table 3.
  The Hot Jupiter problem raises its ugly head here, too.  Instead of using Table G62, Roll d20 and
  consult the two-part table below (table 2) to generate planet types:
  Since we no longer have an automatically generated Hot/Temperate/Cold rating, use table 3 to
  determine the relevant zones.  Note that each spectral type has been split into two (G0, G5, K0,
  K5 etc.).  This illustrates the range of luminosity within a spectral type.  Note also that the figures
  given for type M0 on the main sequence chart only apply to the very brightest M-types, which are
  very rare (1 in 20 or so).  All other red dwarfs’ cold zones extend from stellar orbit outwards.
  Planets orbiting giant stars are unlikely to have life–bearing planets of their own, but life-
  compatible planets would be suitable for terraforming and colonisation.
  Orbital Eccentricity
  As mentioned above, not all planets orbit their stars in neat, circular orbits.  Even in our own
  system, both Mercury and Pluto have eccentricities in excess of 0.2.  As far as is known,
  approximately 1 in 3 planets so far discovered have eccentricities that equal or exceed this figure.
  The most extreme case so far is the planet orbiting the star 16 Cygni B.  Massing at least 2.4
  times the mass of Jupiter, this planet has an eccentricity of 0.57, ranging in distance from its sun
  from 0.7 to 2.7 AU.  To determine eccentricity, roll on table 4 below.
  Now we have a number, but what does it mean in real terms? All planetary orbits are ellipses, not
  true circles.  Therefore, a planet has a nearest and furthest point in its orbit, referred to as
  perihelion and aphelion respectively.  These nearest and furthest distances can be worked out as
  follows:
  Perihelion = d x (1 – e)
  Where d is the average distance in (AU) and e is
  Aphelion = d x (1 + e)
  the eccentricity figure.
  The orbit of the planet dominates the entire distance from perihelion to aphelion.  It is entirely
  possible to create two orbits which actually cross.  In such a situation, the more massive planet
  will likely hurl the less massive planet into the sun or out of the system entirely.  The Hubble
  Space Telescope has taken an image of what is believed to be a planet that has been ejected
  from a binary system, together with a streamer of dust and gas.  Alternatively, you could rule that
  the less massive planet has a strong inclination to the ecliptic plane of your system.
  The Importance of Large Moons
  It has recently been theorised that the presence of our moon has helped to stabilise our planet’s
  axial tilt.  If this is correct, then planets otherwise suitable for life may have only the most basic
  microbial life, since more complex forms could not survive the pressure of a randomly changing
  seasonal pattern.  This would not preclude their suitability for colonisation, since their climates
  would change on timescales of millions of years.  However, this does mean that the homeworld of
  a civilisation (or any world harbouring multicellular life) must have a giant moon like our own, or
  else be in orbit about a more massive body itself.
  
  © Mark F Peoples 1999
  3
  A Brief Note Regarding Supergiants
  Supergiant stars are not believed to play host to planets, since the immense particle and radiation
  pressure produced at their ignition would quickly drive out any planet – forming material.  Also,
  the life spans of these stars are so short that planets would barely have time to form before being
  destroyed in a supernova.  Type O and B stars of any class have the same problem.
  Tables
  Table 1: Binary star separation
  d8 Roll:
  1:
  2d8 million kilometres apart, roll d20.  On a 20, system is a contact binary in which the
  stars are separated by less than a stellar diameter.  Intense radiation and particle winds
  render the system unsuitable for life or colonisation.
  2:
  1d12/10 AU apart
  4:
  1d12 AU apart
  5:
  1d12x10 AU apart
  6:
  1d12x100 AU apart
  7:
  1d12x1,000 AU apart
  8:
  1d6x10,000 AU apart
  In multiple systems, the separation of each binary pair and single straggler is at least one order of
  magnitude greater than the greatest separation of a binary pair.  For example, in a trinary system
  in which the binary pair is separated by 40AU (a roll of 5), the minimum separation between the
  pair and the single must be 100s of AU (roll 6 or greater).
  Table 2: Planetary Type
  Inner (Populous) System
  Roll (d20)
  Planet Type
  # of Moons
  Moon Modifier
  1-4
  Large Jovian
  2d12*
  0
  5-7
  Small Jovian
  2d8*
  -1
  8-10
  Super – Terran
  d8-3
  -2
  11-14
  Terran
  d6-3
  -3
  15-18
  Sub – Terran
  d6-4
  -5
  19-20
  Asteroid Belt
  -
  -
  Outer (Depopulated) System
  Roll (d20)
  Planet Type
  # of Moons
  Moon Modifier
  1-8
  Small Jovian
  2d8*
  -2
  9-12
  Terran
  d6-4
  -3
  13-16
  Sub – Terran
  d6-4
  -5
  17-20
  Comet Belt**
  -
  -
  * 1 in 2 of these moons are Tiny.  Check before rolling for moon size on table G63
  ** A comet belt can only exist in a star’s cold zone.  Otherwise, it will be an asteroid belt.
  
  © Mark F Peoples 1999
  4
  Table 3: Stellar temperature zones
  Main Sequence Stars
  Spectral Type
  Density Drop-Off
  Hot Zone
  Temperate Zone
  Cold Zone
  A0
  19AU
  0 – 7AU
  7 – 9AU
  9+ AU
  A5
  15AU
  0 – 3.7AU
  3.7 – 5AU
  5+ AU
  F0
  14AU
  0 – 2.8AU
  2.8 – 3.9AU
  3.9+ AU
  F5
  13AU
  0 – 2AU
  2 – 2.7AU
  2.7+ AU
  G0
  11AU
  0 – 1.2AU
  1.2 – 1.7AU
  1.7+ AU
  G5
  10AU
  0 – 0.9AU
  0.9 – 1.2AU
  1.2+ AU
  K0
  10AU
  0 – 0.6AU
  0.6 – 0.9AU
  0.9+ AU
  K5
  9AU
  0 – 0.3AU
  0.3 – 0.4AU
  0.4+ AU
  M0
  8AU
  0 – 0.1AU
  0.1 – 0.4AU
  0.4+ AU
  Giant Stars
  Spectral Type
  Density Drop-Off
  Hot Zone
  Temperate Zone
  Cold Zone
  A0
  22AU
  0 – 9AU
  9 – 13AU
  13+ AU
  A5
  19AU
  0 – 7AU
  7 – 10AU
  10+ AU
  F0
  15AU
  0 – 4.4AU
  4.4 – 6AU
  6+ AU
  F5
  15AU
  0 – 4.4AU
  4.4 – 6AU
  6+ AU
  G0
  13AU
  0 – 5AU
  5 – 8AU
  8+ AU
  G5
  15AU
  0 – 7AU
  7 – 10AU
  10+ AU
  K0
  13AU
  0 – 7.5AU
  7.5 – 11AU
  11+ AU
  K5
  13AU
  0 – 10AU
  10 – 14AU
  14+AU
  M0
  12AU
  0 – 11AU
  11 – 15AU
  15+AU
  M5
  12AU
  0 -  13AU
  13 – 19AU
  19+AU
  Table 4: Orbital eccentricity
  Eccentricity Class: (d6)
  1-4 Circular
  Roll d12 and divide by 100 to determine eccentricity
  5-6 Eccentric
  Roll 2d20+18 and divide by 100 to determine eccentricity
  
SOURCE: textdata/thevault/Deduped  Shit/3rd Party/Alternity New Planetary System Generator.pdf