This program calculates the average surface temperature of a planet. You will choose values that describe how massive the nearest star is, how far away that star is from your planet, how much of the incoming starlight is reflected off the atmosphere and surface of your planet, and how much greenhouse effect is produced by your planet's atmosphere. The program will then use these values to calculate the average surface temperature of your planet.
Tap the "Build" button above to begin.
The first step is to enter the MASS of the star that your planet is orbiting. Our Sun has a "solar" mass of 1.0. Below 0.08 solar masses, a celestial object cannot initiate nuclear fusion and is not considered to be a star. Above 100 solar masses, the object is unstable, and so stars of such high masses probably do not form. The mass of your central star should be somewhere between 0.08 and 100 times the mass of our Sun.
Enter a value for the star's MASS between 0.08 and 100 (Earth's Sun = 1)
Next, decide how far away from your star your planet will be. The Earth is 1 Astronomical Unit (AU) away from the Sun. Mercury is a little under 0.4 AU away from the Sun. Pluto is around 39.5 AU from the Sun.
Less than 0.01 from a star a planet would likely be so hot that any solid surface would be molten. More than 1000 AU from a star and a planet would receive little, if any, heat from it. You should choose a distance somewhere between 0.01 AU and 1000 AU for your planet.
Enter a value for DISTANCE from 0.01 and 1000 (Earth's distance = 1)
Next you have to decide how much of the solar energy that reaches your planet gets reflected back into space. Energy reflected back into space does not heat your planet. The amount of energy a planet reflects depends on the composition of its atmosphere (if it has one) and whether it has a mostly rocky, watery or icy surface.
Dark rocks reflect very little energy, around 3% of the total energy they receive. Ice reflects a lot back, usually over 50%. Water reflects about 25%. Altogether, the Earth's surface and clouds reflect about 29% of the incoming sunlight back into space. This is called "BOND ALBEDO." The higher the Bond albedo, the more starlight is reflected by the planet. You need to decide the percent of starlight that your planet reflects back into space. Since this is a percent, you should choose a number between 0 (no starlight reflected) and 100 (all of the starlight reflected). You do not need to enter the percent sign.
Enter a value for BOND ALBEDO between 0 and 100 (Earth=29)
Finally, you have to decide how much infrared radiation, what you experience as "heat" when you warm your hands by a fire, is absorbed by the greenhouse gases in your planet's atmosphere. The more greenhouse gases in your atmosphere, the more the temperature of your planet will increase. If we say that Earth has a GREENHOUSE EFFECT factor of 1, then Venus would have a factor of around 200. A planet without any atmosphere would have a greenhouse factor of 0, meaning that there is no greenhouse effect. In theory, there is no upper limit, but it is hard to imagine a planet with a greenhouse factor much above 500. You should choose a number from 0 to 500 to represent how much heat is trapped in your planet's atmosphere by greenhouse gases.
(The greenhouse factor is how many times larger the effective column density of IR absorbing gas is than it is for the Earth.)
Enter a value for GREENHOUSE EFFECT between 0 and 500 (Earth=1)
If any of your entries are missing a value then you may have entered a non-number. Please change those entries before moving on to the results page by pressing the Results button at the top right.