Eyes on Exoplanets

• Why does NASA's planet count differ from other databases?

  Different online databases of exoplanet discoveries have varying criteria for what they count as an exoplanet discovery, and some are more lenient than others. There's no universally accepted 'official' count. NASA's Exoplanet Archive, the database this visualization uses for its exoplanet count, requires that planets be documented in a published scientific paper that's been reviewed and approved by other astronomers. It's more strict than some other online databases.

• I heard about a new exoplanet that isn't listed under 'latest discoveries' in this visualization. Why isn't it listed there?

  A new exoplanet will appear in this visualization once the discovery has been published in a refereed scientific journal and vetted by scientists at the NASA Exoplanet science Institute (NExScI). Otherwise, it will not be shown, even though the discovery may have been announced in a news release or in media reports.

• Why is 2015 considered the 20th anniversary of exoplanet discoveries?

  The year 2015 marks the 20th anniversary of the discovery of 51 Pegasi b, which is widely acknowledged as the first true exoplanet to be identified in orbit around a normal star. However, other planetary bodies outside our solar system were detected earlier than this, including HD 1147672 b (or Latham's Planet) which was initially thought to be a brown dwarf and was only later confirmed to be a planet. Additionally, the existence of so-called 'pulsar planets,' rocky worlds orbiting the stellar remnant of a supernova, were confirmed as early as 1992.

• Why do the planet counts displayed for some planet types in “Eyes on Exoplanets” differ slightly from the counts shown on the Exoplanet Exploration website?

  In some cases, there is insufficient data to visualize either the planet’s orbit, radius, or mass, and these planets are omitted from “Eyes on Exoplanets.” If future astronomical observations fill in the missing gaps, these planets will be included.