Astronomers estimate that our galaxy is teeming with around 50 billion exoplanets, but the number of alien worlds confirmed to exist has just passed the 700 mark.

One database keeping track of the growing number of exoplanet discoveries is the Extrasolar Planets Encyclopedia ( administered by astrobiologist Jean Schneider of the Paris-Meudon Observatory. On Friday news of this milestone was announced via the awesome (and free) the Exoplanet iPhone app:

There are now more than 700 confirmed exoplanets in the database. The latest addition is the planet

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Wait a minute. What was all that news in 2010 about NASA’s Kepler Space Telescope spotting over 1,200 candidate exoplanets? Why is this particular database reporting only 700 discoveries?

The key word here is “candidate.”

Kepler has spotted a slew of alien worlds, but many of these detections require follow-up observations to confirm whether or not they actually exist.

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For example, the recent controversy surrounding the potentially habitable exoplanet Gliese 581 g is a result of a follow-up observation of an exoplanet that Kepler (may have) detected, only for it not to be detected by another project — the European Southern Observatory’s (ESO) High Accuracy Radial Velocity for Planetary Searcher (HARPS). The scientific process continues in the aim of confirming — or denying — Gliese 581 g’s candidature.

The Extrasolar Planets Encyclopedia is reporting 700 confirmed exoplanets,* whereas other projects (such as Kepler) have detected signs of hundreds more that await confirmation — only then will they be added to the database.

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Launched in 2009, the Kepler mission has identified 25 confirmed exoplanets and mission scientists are confident that around 80 percent of the growing family of candidates will be proven to exist in the not-too-distant future.

Although 700 identified alien worlds may seem like a tiny number compared with the estimated 50 billion in the Milky Way, we’ve only just begun this profound journey of scientific discovery. We are only just glimpsing the tip of the proverbial exoplanetary iceberg.

Recent exoplanet discoveries include:

  • A newborn exoplanet

  • An exoplanet

  • A weird world

  • An exoplanet that is

  • An alien world that’s more alien than most:

*This number differs to NASA’s Jet Propulsion Laboratory’s “PlanetQuest: New Worlds Atlas” database that currently stands at an exoplanet count of 687. PlanetQuest has a more conservative approach when listing exoplanet discoveries — Schneider’s database displays the discoveries as soon as they are announced.

According to Wesley Traub, chief scientist of NASA’s Exoplanet Exploration Program at the Jet Propulsion Laboratory in Pasadena, Calif., in an interview with, PlanetQuest will list the discovery only when it has been validated, checked, and the study has been accepted for publication. This means the NASA database will always lag behind the European one.