DayTrippers Planet Generation System

Apr 17, 2025

The interstellar destination below was created using the DayTrippers Planet Generation rules (now in beta testing). Click here to generate another one.

0) {
$planetCount += rand(1,6);
$planetCountDice–;
}
return $planetCount;
}

function planetSize($planetMod) {
$planetSizeArray = array(“”, “”, “Small Rock Planet”, “Small Rock Planet”, “Asteroid”, “Moon”, “Artificial Satellite”, “Medium Rock Planet”, “Large Rock Planet”, “Gas Giant”, “Gas Giant”, “Gas Giant”, “Rogue Planet”);
$gravityModArray = array(0, 0, -3, -3, -3, -5, -2, -1, 0, 5, 5, 5, -3);
$planetSizeRoll = rand(1,6) + rand(1,6) + $planetMod;
if($planetSizeRoll < 2) { $planetSizeRoll = 2; } if($planetSizeRoll > 12) {
$planetSizeRoll = 12;
}
$planetSize = $planetSizeArray[$planetSizeRoll];
$gravityMod = $gravityModArray[$planetSizeRoll];
return array($planetSize, $gravityMod);
}

function gravity($gravityMod) {
$gravityBase = 0;
$divide = 0;
$gravityArray = array(“”, “”, “12”, “12”, “12”, “11”, “11”, “1”, “2”, “2”, “2”, “4”, “4”, “4”, “6”);
$atmoModArray = array(0, 0, -2, -2, -2, -1, -1, 0, 3, 3, 3, 5, 5, 5, 6);
$gravityRoll = rand(1,6) + rand(1,6) + $gravityMod;
if($gravityRoll < 2) { $gravityRoll = 2; } if($gravityRoll > 14) {
$gravityRoll = 14;
}
$gravityVal = $gravityArray[$gravityRoll];
if($gravityVal > 10) {
$gravityVal -= 10;
$divide = 1;
}
while($gravityVal > 0) {
$gravityBase += rand(1,6);
$gravityVal–;
}
if($divide) {
$gravity = number_format(1 / $gravityBase, 2);
} else {
$gravity = $gravityBase;
}
$atmoMod = $atmoModArray[$gravityRoll];
return array($gravity, $atmoMod);
}

function atmosphere($atmoMod, $gravity = 1) {
$atmoArray = array(“”, “”, “Atmosphere is escaping the planet”, “Atmosphere is escaping the planet”, “Atmosphere is escaping the planet”, “Extremely thin, no Oxygen”, “Chlorine”, “Carbon Dioxide”, “Nitrogen/Oxygen with heavy gases, Propane, Butane”, “Dense Air (Nitrogen/Oxygen)”, “Nitrogen/Oxygen with Ozone in Stratosphere”, “Nitrogen/Oxygen with trace toxins”, “Ammonia & Methane”, “Hydrogen & Helium”, “Exotic toxic gases”);
$waterModArray = array(0, 0, -6, -6, -6, -6, -4, -3, -2, -1, 1, 0, -4, -5, -6);
$atmosphereRoll = rand(1,6) + rand(1,6) + $atmoMod;
if($atmosphereRoll < 2) { $atmosphereRoll = 2; } if($atmosphereRoll > 14) {
$atmosphereRoll = 14;
}
$atmosphere = $atmoArray[$atmosphereRoll];
$waterMod = $waterModArray[$atmosphereRoll];
$pressure = $atmosphereRoll * $gravity;
return array($atmosphere, $waterMod, $pressure);
}

function water($waterMod) {
$waterArray = array(“”, “”, “No standing water”, “Arid rock/desert world, very little standing water”, “Arid rock/desert world, very little standing water”, “Arid rock/desert world, very little standing water”, “Semi-Arid world, water frozen or beneath surface”, “land”, “land”, “Ocean world”, “Water vapor makes up most of the atmosphere”);
$waterRoll = rand(1,6) + rand(1,6) + $waterMod;
if($waterRoll < 2) { $waterRoll = 2; } if($waterRoll > 10) {
$waterRoll = 10;
}
$water = $waterArray[$waterRoll];
return $water;
}

function climate() {
$climateArray = array(“”, “”, “Frozen solid; ice & rock”, “Frozen solid; ice & rock”, “Arctic conditions”, “Arctic conditions”, “Cold”, “Temperate”, “Hot”, “Greenhouse conditions”, “Greenhouse conditions”, “Wildly variable”, “Hellish”);
$precipDLArray = array(0, 0, 0, 0, 5, 5, 6, 7, 9, 8, 8, 5, 10);
$climateRoll = rand(1,6) + rand(1,6);
if($climateRoll < 2) { $climateRoll = 2; } if($climateRoll > 12) {
$climateRoll = 12;
}
$climate = $climateArray[$climateRoll];
$precipDL = $precipDLArray[$climateRoll];
return array($climate, $precipDL);
}

function biosphere() {
$biosphereArray = array(“”, “”, “Biotoxins in atmosphere”, “Biotoxins in atmosphere”, “No life”, “No life”, “Proto-organisms in suspension”, “Proto-organisms and non-mobile lifeforms”, “Non-sentient lower lifeforms”, “Sentient lifeforms”, “Sentient lifeforms”, “Highly evolved lifeforms”, “Highly evolved lifeforms”);
$biosphereRoll = rand(1,6) + rand(1,6);
$biosphere = $biosphereArray[$biosphereRoll];
return $biosphere;
}

/* BIDNEZ */

$starIndex = 0;
$starType = ‘Star’;
$stars = array();
$planetName = planetName();

$starSizeData = starSize();
/*
$stars[0][‘starSize’] = $starSizeData[0];
$stars[0][‘colorMod’] = $starSizeData[1];
$stars[0][‘planetMod’] = $starSizeData[2];
*/
$starSize = $starSizeData[0];
$colorMod = $starSizeData[1];
$planetMod = $starSizeData[2];

$starColorData = starColor($colorMod, 0); // 1=forcespecial 0=dont
$starColor = $starColorData[0];
$planetCountDice = $starColorData[1];
if($starColor == ‘Special’) {
$starSpecial = specialStar();
$starType = $starSpecial;
switch($starSpecial) {
case ‘Dwarf’ :
$starSize = ‘less than 0.1 times ‘;
$starType = ‘Dwarf Star’;
$starColorData = starColor(0);
$starColor = $starColorData[0];
if($starColor == ‘Special’) {
$starColor = ‘Black’;
}
break;
case ‘Cluster’ :
$starType = ‘Star’;
$starIndex++;
$starColorData = starColor(0);
$starColor = $starColorData[0];
if($starColor == ‘Special’) {
$starSize = ‘- tiny compared to ‘;
$starType = ‘Neutron Star’;
$starColor = ”;
}
break;
case ‘Nova’ :
$starSize = (rand(1,6) * rand(1,6) * 10) . ‘ light-years across’;
$starColor = ”;
break;
case ‘Brown Dwarf Star’ :
case ‘Pulsar’ :
case ‘Quasar’ :
case ‘Black Hole’ :
$starSize = ‘- tiny compared to ‘;
$starColor = ”;
break;
default :
$starType = ‘Star’;
break;
}
}
$stars[0][‘starSize’] = $starSize;
$stars[0][‘starType’] = $starType;
$stars[0][‘starColor’] = $starColor;

if($starIndex) {
while($starIndex > 0) {
$starSizeData = starSize();
$starSize = $starSizeData[0];
$colorMod = $starSizeData[1];
$planetMod = $starSizeData[2];
$starColorData = starColor($colorMod);
$starColor = $starColorData[0];
// $planetCountDice = $starColorData[1];
if($starColor == ‘Special’) {
$starSpecial = specialStar();
$starType = $starSpecial;
switch($starSpecial) {
case ‘Dwarf’ :
$starSize = ‘less than 0.1 times ‘;
$starType = ‘Dwarf Star’;
$starColorData = starColor(0);
$starColor = $starColorData[0];
if($starColor == ‘Special’) {
$starColor = ‘Black’;
}
break;
case ‘Cluster’ :
$starType = ‘Star’;
$starIndex++;
$starColorData = starColor(0);
$starColor = $starColorData[0];
if($starColor == ‘Special’) {
$starSize = ‘- tiny compared to ‘;
$starType = ‘Neutron Star’;
$starColor = ”;
}
break;
case ‘Nova’ :
$starSize = (rand(1,6) * rand(1,6) * 10) . ‘ light-years across’;
$starColor = ”;
break;
case ‘Brown Dwarf Star’ :
case ‘Pulsar’ :
case ‘Quasar’ :
case ‘Black Hole’ :
$starSize = ‘- tiny compared to ‘;
$starColor = ”;
break;
default :
$starType = ‘Star’;
break;
}
}
$stars[$starIndex][‘starSize’] = $starSize;
$stars[$starIndex][‘starType’] = $starType;
$stars[$starIndex][‘starColor’] = $starColor;
$starIndex–;
}
}

$planetCount = planetCount($planetCountDice);
$romanArray = array(”, ‘I’, ‘II’, ‘III’, ‘IV’, ‘V’, ‘VI’, ‘VII’, ‘VIII’, ‘IX’, ‘X’, ‘XI’, ‘XII’, ‘XIII’, ‘XIV’, ‘XV’, ‘XVI’, ‘XVII’, ‘XVIII’);
$planetNumber = rand(1,$planetCount);
$romanNumber = $romanArray[$planetNumber];

$planetSizeData = planetSize($planetMod);
$planetSize = $planetSizeData[0];
$gravityMod = $planetSizeData[1];

$gravityData = gravity($gravityMod);
$gravity = $gravityData[0];
$atmoMod = $gravityData[1];

$atmosphereData = atmosphere($atmoMod, $gravity);
$atmosphere = $atmosphereData[0];
$waterMod = $atmosphereData[1];
$pressure = $atmosphereData[2];

$water = water($waterMod);
if($water == ‘land’) {
$watercover = (rand(1,6)+3)*10;
$landcover = 100 – $watercover;
$water = $landcover . ‘% land, ‘ . $watercover . ‘% water’;
}

$climateData = climate();
$climate = $climateData[0];
$precipDL = $climateData[1];

$biosphere = biosphere();

/* DISPLAY */

echo ‘STELLAR SYSTEM ‘ . strtoupper($planetName) . ‘
‘;
$i = 1;
switch(count($stars)) {
case 5 :
echo ‘Pentary System:’;
break;
case 4 :
echo ‘Quadrary System:’;
break;
case 3 :
echo ‘Trinary System:’;
break;
case 2 :
echo ‘Binary System:’;
break;
default :
break;
}
foreach($stars AS $thing) {
if(count($stars) > 1) {
echo ‘
‘ . $i . ‘. ‘;
}
if($thing[‘starColor’] AND $thing[‘starColor’] == ‘Orange’) {
echo ‘An ‘;
} else {
echo ‘A ‘;
}
if($thing[‘starColor’]) {
echo $thing[‘starColor’] . ‘ ‘;
}
echo $thing[‘starType’] . ‘ ‘;
echo $thing[‘starSize’];
if($thing[‘starType’] != ‘Nova’) {
echo ‘the size of Sol’;
}
$i++;
}
echo ‘
‘;
echo ‘with ‘ . $planetCount;
if($planetCount == 1) {
echo ‘ planet in orbit.
‘;
} else {
echo ‘ planets in orbit.
‘;
}
echo ‘
‘ . strtoupper($planetName) . ‘ ‘ . $romanNumber . ‘
‘;
echo ‘TYPE: ‘ . $planetSize . ‘
‘;
echo ‘GRAVITY: ‘ . $gravity . ‘ G
‘;
echo ‘ATMOSPHERE: ‘ . $atmosphere . ‘
‘;
echo ‘PRESSURE: ‘ . $pressure . ‘ Earth atmospheres
‘;
if($planetSize != ‘Gas Giant’) {
echo ‘WATER: ‘ . $water . ‘
‘;
}
echo ‘CLIMATE: ‘ . $climate . ‘
‘;
echo ‘PRECIP DL: ‘ . $precipDL . ‘
‘;
echo ‘BIOSPHERE: ‘ . $biosphere . ‘
‘;

?>


‘;
?>

DayTrippers is a Surreal Science Fiction Reality-Hopping OSR RPG. Now available at RPGnow.com.

Explore More Insights

DayTrippers Core Rules Update

Version 1.3 of the DayTrippers Core Rules is now available in PDF. This version includes new rules for collaborative "GM-Lite" play, as well as new information on SlipShips, Technology and Companies in the world of DayTrippers. Designed for full compatibility with the...

read more

DayTrippers GameMasters Guide Now Available

IT'S OUT IN THE WILD! The DayTrippers GameMasters Guide is available now in PDF format. Get ready for the next level of Auteur GameMastering: an infinite variety of surreal science fiction tales are waiting to emerge at your table. Psychic Content. Oracular Prep....

read more