Econintersect: It has been only 18 years since the first planet outside our own solar system (an exoplanet) was discovered. Since then more almost 1,000 exoplanets have been added to the inventory, and suspects number a couple of thousand more.
Video from MSN follows the Read more >> jump.
It has been estimated that there could be more than a sextillion planets in the 'observable universe' (that is 10 to the 21th power) and that up to 0.1% might exist in what is known at the 'habitable zone' for earth-like life. That would be as many as a quintillion (10 to the 18th power) potentially habitable exoplanets.
As far as our own galaxy is concerned, there may be as many as 50 million potentially habitable planets. Most of the much smaller number located to date have been found by NASA's Kepler mission and are all in the regions of our galaxy closest to the solar system.
The 44 green data points in the excerpted box define the planets in the Kepler inventory (976 as this is written) with the gravity and temperature characteristics compatible with conditions on earth. So these are the potentially habitable planets identified thus far. There are a potential 49,999,956 (approximately) left to locate in our own galaxy. And still 10 to the 18th to go in the known universe.
We have no idea how much more potential lies beyond the known universe, so 10 to the 18th could be a very small number.
Note: Not all exoplanets have been discovered by the Kepler mission. Some are visible from earth's surface. See for example this infographic.
- Space's 10 Most Amazing Exoplanets (Maker Studios, MSN)
- 50 Million More Earths in the Milky Way? (GEI News, 18 January 2012)
- Observable Universe (Wikipedia)
- Kepler, A Search for Habitable Planets (NASA, Ames Research Center)
- Infographic of the Day: Four Giant Exoplanets of Star HR 8799 (GEI News, 23 March 2013)