Science for your Game - The Habitable Exoplanets Catalog

The University of Puerto Rico at Arecibo hosts the  Habitable Planets Catalog, a graphical resource on the nearly 1000 exoplanets so far discovered. They include a Primer on Habitable Planets. Traveller players or referees who want exploration missions on 'strange new worlds' will find useful and interesting information.
 
The Catalog offers basic astronomical data, such as temperature zone, mass, radius and orbital period.  "Warm" planets are those planets in the Habitable Zone where the surface temperature is above the freezing point of water, at least for part of its orbital cycle. "Cold" planets, mostly beyond the habitable zone are below the freezing point of water for the entire cycle. "Hot" planets are nearer to their parent star than the habitable zone. 

From the data in the table, the referee can easily calculate the UWP size code, the surface gravity, and make an educated guess about the Atmosphere and Hydrosphere code. Fill in the Population, Government, Law and Tech levels as you wish.

We are still looking for a planet of similar size, atmosphere and temperature to Earth, like what we see on Star Trek, but the search for exoplanets is a very young branch of astronomy, and even in the last decade or less, the number of confirmed exoplanet findings has grown tremendously.

In Traveller, explorers have access to technology from vacc suits to sealed structures that could allow for colonization of worlds far less habitable than Earth. So the occasional "Earth-like" planet is good and reasonable, but so are all of the inhospitable ones that the world generation tables in Bk 3 produce.