# Is it possible to know if a planet is located in the Habitable Zone knowing it's properties?

Is there an equation that can give me the possibile distance of the planet from his star knowing planet's temperature (or other datas)?

I found this method for calculating the Habitable Zone but it's based only on star's properties.

• The planet temperature depends on it's atmosphere and the properties of the star and the distance to the star. – ProfRob Mar 19 '16 at 12:56
• Venus is hotter than Mercury, so, atmosphere obviously matters. Jupiter emits more heat than it receives from the sun, so, heat of formation matters, especially for larger planets. There's a variety of factors, the planet's color being another important factor. How much water, CO2/CH4 vs O2 ratios. There's quite a few moving parts to planetary temperature, so I don't think you'll find a straight forward formula anywhere. That said, I think the method for calculating habitable ZONE that you posted isn't bad. The zone is fairly large, our solar system's zone probably extends past mars. – userLTK Mar 19 '16 at 21:44

The habitable zone is, roughly, defined as the region around a star in which a planet could have liquid surface water. So if the surface temperature of the planet is between 0 and 100*C then the planet is in the habitable zone. The converse, however, is not true.

The reason for this definition is that the sort of chemical reactions that are needed for life work best when there are complex molecules dissolved in some kind of solvent, and the best polar solvent is H2O.

If you know the distance a planet is from its star, the temperature can be estimated from the properties of the star and the atmosphere of the planet. Not every planet in the habitable zone actually has liquid water. Venus, Earth and Mars are all in the Habitable zone of the sun, since they could all have liquid water if they had the right atmosphere. But of course only Earth actually does have liquid water in any substantial amounts.

So just being in the habitable zone, doesn't make a planet certainly suitable for life, and even if water does exist on the surface, it does not mean that humans could inhabit the planet.

• Of course! rephrased to make this obvious. – James K Mar 19 '16 at 21:59
• So is there an equation that can give me the habitable zone based on the properties you wrote? – astronomy-domine Mar 20 '16 at 15:31
• $0<T<100$ Habitable zone really just mean it is possible that there might be liquid water. – James K Mar 20 '16 at 15:41
• I guess what I mean is that if you know the planet's properties, like its surface temperature, you don't need to know if it is in the habitable zone or not. The purpose of finding if the planet is in the habitable zone is to get some idea of what the surface temperatures of the planet might be. Analogy if you have a meat thermometer, you don't need to time your roast. But if you don't then knowing how long your joint has been in the oven allows you to estimate if it has been cooked properly. – James K Mar 20 '16 at 16:08
• Oh I see. In fact i need this to build a little exoplanet data simulator so if i can decide the temperature i won't need to know if it's in the habitable zone or not. – astronomy-domine Mar 20 '16 at 17:43