Frequently Asked Questions
What is an exoplanet?
An exoplanet is defined as a planet that orbits a star outside of our solar system. This includes any planet that orbits one of the estimated 100-400 billion other stars in our Milky Way Galaxy.
Why does NASA's planet count differ from other databases?
Different online databases of expoplanet 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 Expolanet 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 Expoplanet sicence 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.