We started with just two planets in our Habitable Exoplanets Catalog almost two years ago on December 2011. At that time having a catalog for just two planets was overkill and we were not expecting much change anyway until many years, but we were surprised. We ended the first years with seven and now we have twelve, and the year is not over yet. That certainly exceeded our expectations. The exoplanets field was moving much faster toward the detection of smaller Earth-size planets by both the radial velocity and transit methods. A catalog is now a necessary tool to track these discoveries.
The 2010's is the decade when we finally started to discover potentially habitable worlds (the exception is Gliese 581d discovered on 2007). We have enough data now to give some preliminary prediction on the expected number of habitable exoplanets to be discovered in the next years. If we follow the present trend (Figure 1) there could be a total of 21 by 2014 and 38 by 2015. That still sounds like too many for just two years but there are 36 waiting for confirmation from the NASA Kepler mission alone. Similar predictions can be derived for the total number of confirmed exoplanets (Figure 2). Lets wait and see what happens.
Figure 1. Cumulative number of potentially habitable exoplanets detected in the last four years (red dots). The data was fitted with an exponential function (blue line) included at the top of the plot. The fit predicts reaching about 21 exoplanets by 2014 and 38 by 2015. Predictions for longer periods are much more uncertain. Data source is available in Table 1.
Figure 2. Cumulative number of confirmed exoplanets detected in the last 22 years (red dots). The data was fitted with an exponential function (blue line) included at the top of the plot. The fit predicts reaching over 1,000 exoplanets by the end of 2013 and over 1,500 by 2015. Predictions for longer periods are much more uncertain. Data source is available in Table 1.
Table 1. Number per year and cumulative (total from all previous years) of discovered confirmed exoplanets and those potentially habitable. Data from the PHL's Exoplanet Catalog. The year 2011 was a good year for exoplanet discoveries. Figures 1 and 2 show the cumulative data plotted.