The Kepler Space Telescope has found over 1,000 confirmed exoplanets. I've said it before and I'll say it again: Kepler is a planet-hunting powerhouse. Even more impressive? Kepler is already finding new candidates after whirling around to its new view for the continuing mission last month.

Artist's concept of Kepler 64. Credit: D. Terrell

Between March 2009 and May 2013, Kepler monitored over 156,000 stars with a photometer, monitoring any change in brightness. A periodic dimming might be caused by a transiting planet, identifying a candidate planet for confirmation. When monitoring just 1/400th of the sky, the telescope found literally thousands of potential planets. With the advent of batch-confirmation, 715 exoplanets were confirmed in just 305 systems. The science of discovery was going fantastic, until disaster struck the telescope.

Periodic dimming of a star can be a signature of an exoplanet.

The space telescope had already lost one reaction wheel early in the mission, but in May 2013, the second wheel died and crippled its capacity to stay pointed in one direction. With a bit of finagling and a whole lot of cleverness, a solution was found by turning about to leaning the remaining wheels against the pressure of the solar wind for the telescope to survey a whole new patch of sky.

Kepler's original perspective overset on a painting of the Milky Way. Image credit: NASA/Jon Lomberg


Kepler orbits the sun to avoid Earth blocking out patches of sky, trailing behind our home planet. It points out into the ecliptic plane to avoid sunshine sneaking into the photometer, watching all the stars within 3,000 light-years. The original field of view was out towards Cygnus, Lyra, and Draco, checking out systems the same distance from the center of the Milky Way as for us. Since December, the telescope has reoriented to Sagittarius, continuing the campaign of planet-hunting.

Kepler's new point of view for the K2 mission. Image credit: NASA

By December 16, 2014, Kepler found its first exoplanet in the new stage of its mission: HIP 116454b. A super-Earth tucked in close to its sun, it's a large, hot rocky ball with no real chance for oceans or life.


Artist's concept of the first planet discovered by Kepler's K2 mission, HIP 116454b. Image credit: David A. Aguilar (CfA)

But it brought the telescope one planet closer to an outrageous milestone: over 1,000 confirmed exoplanet discoveries! Some planets are substantially cooler than others: not every planet gets to be a pit of darkness or experience sunsets from four different stars.

As the new year sorts itself out, the Kepler Space Telescope is the proud discoverer 1,004 planets, with another 3,171 exoplanet candidates yet to be verified. Eight confirmed planets are potentially Earth-like, rocky planets in the habitable zones of their stars, and of the most recent 554 unconfirmed candidates, another six fit the criteria. Just remember to take "Earth-like" with a grain of salt: these aren't perfect worlds all ready to colonize, but instead ones that are a lot closer to looking like our home planet than the hot gas-giants crammed into orbits smaller than Mercury's.

The eight confirmed rocky planets discovered by Kepler that fit that the Goldilocks criteria of neither too hot nor too cold, rocky with the potential for a long-lasting ocean are: Kepler-186f, Kepler-62e and Kepler-62f, Kepler-296e and Kepler-296f, and the newly-confirmed Kepler-438b, Kepler-442b, and Kepler-440b. Two of the new three planets are bigger than Earth, tucked in closer around smaller, cooler stars. Kepler-438b is 475 light-years away, 12% larger than Earth, and orbits its start ever 35.2 days. Kepler-442b is farther and bigger at 1,100 light-years away and 33% larger than Earth, orbiting its star ever 112 days. Less information has been released on Kepler-440b: it has an orbital period of just over 101 days, and may not even be a rocky planet.

Artist's concept of Kepler-62f. Image credit: NASA/Ames/JPL-Caltech

Here's the truly mind-blowing part: for all its relentless planet-discovering, Kepler is not the only telescope in the planet-hunting game. We've found literally hundreds and hundreds of alien worlds: 1,789 confirmed planets discovered by telescopes combined, with more added to the list every month. Only a handful of them could support life, but we've looked at such a tiny fraction of the sky that we know that more must exist in even just our galaxy. We're living in amazing times, where when we look up at the stars, we can imagine with confidence the planets waiting to be discovered whirling around all of them.

Just imagine what we're going to discover when the next generation of planet-hunting telescopes come online!