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

Progressive Character Generation

In books and movies, it’s rare to know the entire history of a character before the actual plot begins. In fact, in many books and movies, the only backstory you ever get occurs in flashbacks, after you’re familiar with the character on a more pedestrian level. The...

read more

March goes out like a rain of Falling Spaceship Parts

As we approach the final release version of the DayTrippers GameMasters Guide, little mechanical bits are falling off like parts from the Serenity! Members of the As If Collective via Patreon have been sprinkled in DayTrippers subsystems lately, from alien...

read more