Join Donate

Bruce BettsJanuary 4, 2010

Kepler discovers its first five exoplanets

Congratulations to NASA's Kepler mission team on their announcement of the discovery of its first five exoplanets (planets around other stars). All five are "hot Jupiters," meaning that they are the sizes of the gas giants in our solar system, but are extremely close to their parent stars. These are the easiest for Kepler to discover, so not surprisingly the first to be announced. The discoveries are based on about six weeks worth of data.

Kepler uses the transit method of planet detection. The spacecraft stares at the same 150,000 stars over and over and looks for tiny dips in light that would indicate a transit of a planet in front of the parent star, blocking out some of the starlight. Science operations started in May 2009.

Transit light curves for Kepler's first five exoplanets


Transit light curves for Kepler's first five exoplanets
Kepler uses the transit photometry method to discover planets orbiting other stars.

The new exoplanets, named Kepler 4b, 5b, 6b, 7b and 8b, range in size from similar to Neptune to larger than Jupiter, and have orbits ("year" lengths) ranging from 3.3 to 4.9 Earth days. Estimated temperatures of the planets range from 1,200 to 16,00 degrees Celsius (2,200 to 3,000 degrees Fahrenheit). All five of the exoplanets orbit stars hotter and larger than Earth's Sun. All have been confirmed as exoplanets by ground-based observatories.

Sizes and Temperatures of Kepler's first five exoplanets


Sizes and Temperatures of Kepler's first five exoplanets
On January 4, 2010, the Kepler mission announced its first five planet discoveries. All are hot Jupiters, gas-giant-sized planets orbiting very close to their host stars.

Kepler's true goal is to find Earth-size planets in the habitable zone of Sun-like stars. That will take three years of data, and lots of Earth-based follow-up from projects like FINDS Exo-Earths. In the meantime, Kepler should continue to produce a multitude of discoveries of larger planets orbiting closer to their parent stars. For information on the previous 300+ exoplanets discovered by all methods, see The Planetary Society's Catalog of Exoplanets.

First Light for Kepler


First Light for Kepler
Taken on April 8, 2009, these are the first images taken by the planet-hunting mission Kepler. The large image in the center shows a 100 degree square patch of sky containing an estimated 14 million stars. Kepler will observe this region continuously for more than 3 years, searching for signs of transiting planets in a group 100,000 pre-selected stars. The dark lines crisscrossing the image indicate the arrangement of the charged coupled devices (CCD's) in Kepler's powerful camera). The top left image is of a region 1000 times smaller than the full field, which contains the known transiting planet TrES-2. The image on the top right includes star cluster NGC 6791, at a distance of 13,000 lightyears from Earth.

Read more: pretty pictures, Kepler, mission status, extrasolar planets, explaining science, many worlds

You are here:
Bruce Betts Head Shot 2015
Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society
Read more articles by Bruce Betts

Comments & Sharing
Bill Nye and people
Let's Change the World

Become a member of The Planetary Society and together we will create the future of space exploration.

Join Today

The Planetary Fund

Help advance robotic and human space exploration, defend our planet, and search for life.


"We're changing the world. Are you in?"
- CEO Bill Nye

Sign Up for Email Updates