Ask most people to name a space telescope and they’ll probably tell you Hubble. While that telescope’s name is certainly
worthy of its fame, there’s another that, arguably, has done as much to broaden our cosmological horizons as its more famous sibling: the Kepler space telescope.
There’s a precedent for naming space hardware after historic astronomers, and the Kepler space telescope is no exception. Johannes Kepler was a German astronomer who lived in the late 16th and early 17th century. Most famously, he discovered the laws of planetary motion that have since allowed us to accurately predict the positions of the planets for almost any time in history.
Four hundred years later, in the early 1990s, NASA proposed a series of unmanned missions – some to investigate our solar system and others to search for other planets orbiting other stars. It would be almost another ten years and four rejected proposals before the telescope was finally approved, in December of 2001.
Given that its mission was to discover potentially habitable Earth-sized planets, and that those discoveries relied upon the laws of planetary motion, it seemed only appropriate that the telescope is named after Kepler.
When was the Telescope First Launched?
The telescope itself comprised of a primary mirror 1.4 meters (55 inches) in diameter – the largest of its kind at its launch. Also, on-board were 42 CCD cameras, each with a resolution of 2,200 x 1,024 pixels, giving a total resolution of nearly 95 megapixels. The cameras were designed to detect the brightness changes of stars as planets appeared to transit across them.
It was finally launched on March 7th, 2009, aboard a Delta II rocket from Cape Canaveral, Florida. At the time, some 350 exoplanets were known to exist and it was hoped the telescope would discover thousands more during the course of its three and a half year mission. Scientists also hoped to discover dozens of Earth-sized worlds, but only time would tell if the telescope would be successful.
Continuously pointed toward the same area of sky, around the constellations of Cygnus and Lyra, the telescope studied approximately 150,000 stars in an area containing 4.5 million stars over 115 square degrees (or roughly a 0.25% of the entire night sky.) Hold your fist out at arm’s length and it would cover about the same area!
After a month in orbit, its cover was discarded and the first test images were taken on April 8th. The mission began properly on May 12th and scientists would spend the next two months calibrating its systems by studying five previously known exoplanets.
Ten days were spent studying HAT-P-7b, a “hot Jupiter” world some 1,000 light years away that orbits its parent star in just 2.2 days. The telescope was able to successfully detect its atmosphere and its changes in brightness as it orbited the planet.
HAT-P-7b wasn’t the only exoplanet studied during that initial two month period. Others included Kepler-1b and TrES-2b, the darkest known exoplanet. Kepler discovered this gas giant reflects less than 1% of the light it receives, making it darker than acrylic black paint and giving rise to the planet’s nickname: the Coal Planet.
What Were Some of Kepler’s First Discoveries?
- January 4th, 2010. During a meeting of the American Astronomical Society in Washington, scientists announce the first exoplanets discovered by Kepler. In all, there are five new worlds, called Kepler-4b, 5b, 6b, 7b, and 8b. Neptune-sized 4b
is the smallest while the others are all about the size of Jupiter.
- February 2nd, 2011. Astronomers announce the discovery of six planets orbiting a single star some 2,150 light years away. What makes this system so special is that five of the planets have orbits smaller than Mercury’s, making it one of the most compact systems known. The star, Kepler-11, is Sun-like so the worlds are too hot to support life.
- September 15th, 2011. Star Wars fans rejoice as the first exoplanet found orbiting a double star system is announced. Unlike the fictional planet of Tatooine in the famous movies, Kepler-16b is a cold Saturn-sized gas giant.
- December 20th, 2011. Astronomers announce the discovery of the first Earth-sized planets orbiting a Sun-like star. The star, Kepler-20, lies some 929 light years away and has five exoplanets in orbit. One, Kepler-20f, was the first exoplanet discovered to be smaller than the Earth. Unfortunately, neither of those two worlds lay within the habitable zone.
How Did Kepler’s Primary Mission Come to an End?
By the end of 2011, there were 2,326 exoplanet candidates. Of those, 207 were Earth-sized, 680 were about twice the size of the Earth, 1,181 were the size of Neptune, 203 were Jupiter-sized and 55 were thought to be larger than Jupiter.
The implications were staggering. Based on the data, scientists estimated there could be as many as fifty billion planets in the Milky Way, including about two billion Earth-sized worlds with at least half a billion in the habitable zone. Of those, some 30,000 were thought to lie within a thousand light-years of the Earth.
Other discoveries include:
- May 18th, 2012. The discovery of a super-Mercury is announced, but this planet is not like any other. Some 1,500 light years from Earth, this planet is slowly disintegrating as it orbits its parent star and could be gone in as little as 200 million years.
- June 21st, 2012. A celestial pair of planetary twins is announced. The two worlds, Kepler-36b and 36c are only 1.2 million miles apart at their closest – about 20 times closer than any two planets within our own solar system. The planets would be easily visible as spheres within each others’ skies.
Despite these successes, the telescope suffered the first of several setbacks in July 2012 when one of its four reaction wheels failed. Used to keep the telescope pointing in the right direction, the telescope required three of the four wheels to be functioning and, fortunately, the telescope was able to continue its work.
- August 26th, 2012. The discoveries continued with the announcement of Kepler-47, the first multi-planet system orbiting a binary star system some 5,000 light years away.
- February 20th, 2013. The discovery of Kepler-37b is announced. The smallest known exoplanet, it’s only slightly larger than our own Moon. It orbits its parent star at less than one-third of Mercury’s distance from the Sun. At that distance, it seems highly unlikely to support any kind of life.
On May 15th, 2013. NASA holds a press conference to announce the failure of a second reaction wheel. With only two of the four wheels functioning, the program risks cancellation. The telescope can no longer point at the designated area of sky with the accuracy required for its primary mission and NASA begins to consider other options. One such option is to find new ways for the telescope to perform astronomical studies.
- September 30th, 2013. The first cloud map of an exoplanet, Kepler-7b, based upon data from Kepler, is made public.
- October 15th, 2013. Using data from Kepler, civilian volunteers and astronomers from Yale lead to the discovery of exoplanet PH1, the first world found to be orbiting a quadruple star system.
- October 30th, 2013. The discovery of Kepler-78b is announced. The first Earth-sized planet confirmed to be rocky and with a density the same as Earth’s, it whizzes about its parent star in just 8.5 hours. It is totally inhospitable to life as we know it.
What Were Some of the Highlights of K2, Kepler’s “Second Light” Mission?
On November 26th, 2013, K2, also known as “Second Light”, the second major Kepler mission, is unveiled. It’s proposed that the telescope should continue to search for exoplanets but also expand its targets to include supernovae, star formation, asteroids, and comets.
- April 17th, 2014. The discovery of Kepler-186f is announced. The first Earth-sized world found within the habitable zone, it orbits a star half the size of the Sun once every 130 days with four other planets within the same system. Although there might be liquid water on its surface, the planet only receives about a third of the energy the Earth receives from the Sun. Even at high noon, its parent star would only appear as bright as our Sun close to sunset.
- December 18th, 2014. The discovery of HIP 116454b, the first exoplanet found during the “Second Light” mission, is announced. A super-Earth some 180 light years away, it orbits too close to its parent star to be habitable.
- January 28th, 2015. The discovery of five exoplanets orbiting Kepler-444 is announced. The solar system is estimated to be some 11.2 billion years old, making it the old known planetary system in existence. None of the worlds are Earth-sized or within the habitable zone.
- July 23rd, 2015. Astronomers announce the discovery of 12 potentially Earth-sized exoplanets, all within the habitable zones of their parent stars. One of these, Kepler-452b, is the first Earth-sized world discovered within a habitable zone. Its parent star is a type G2 star, the same as the Sun.
- September 11th, 2015. KIC 8462852, popularly known as Tabby’s Star, hits the headlines when it’s announced that data
from Kepler, gathered over four years, shows an unexplained dip in the star’s brightness. Explanations ranged from huge alien megastructures to a more plausible cloud of dust surrounding the star.
- March 21st, 2016. Kepler’s observations of two stars exploding result in the first optical measurements of a “shock breakout” – the brilliant flash of an exploding stars’ shockwave.
- June 13th, 2016. Kepler-1647b becomes the largest exoplanet discovered orbiting a double star system. The planet is thought to be similar in size to Jupiter.
- June 20th, 2016. The discovery of the youngest known exoplanet is announced. K2-33b is a Neptune-sized world just 5 to 10 million years old that orbits its parent star in just five days.
From this point on, Kepler was involved in a large number of projects – called campaigns – that took its focus away from the hunt for exoplanets. These campaigns included studying over 36,000 galaxies, the center of our own Milky Way galaxy, the planets Mars and Neptune, comets and asteroids within our own solar system, star-forming regions in Taurus, supernovae, variable stars, the Praesepe, and M67 star clusters, and the red dwarf star Wolf 359, as made famous by the television series Star Trek: The Next Generation.
The Legacy of the Kepler Space Telescope
Campaign 19 was to be it’s last. On October 30th, 2018, NASA announced that the telescope had run out of fuel and that, after nine years, its mission would come to an end. The telescope was deactivated with a “goodnight” command on November 15th – the anniversary of Johannes Kepler’s death in 1630.
It’s hard to underestimate the role the Kepler space telescope has played in the history of astronomy. As of the time of writing (June 2019) the telescope is credited with 2,343 confirmed exoplanet discoveries with another 2,421 yet to be confirmed. When the mission was first proposed, back in the early 1990s, none were known to exist.
And if the astronomer Johannes Kepler could know of his namesake and the worlds it had discovered, what would he think? When he was born, people still believed that everything in the universe orbited about the Earth. When he died, the idea that the planets orbited the Sun instead was just beginning to take hold. Both the astronomer and the telescope existed at a time when our view of the universe was evolving – and they both played an enormous role in expanding it.
For a more complete timeline and list of discoveries, click here.