Good Night, Dear Kepler — Planet-Hunting Telescope Sends Last Images to Earth; Is That Tetris?

The last images ever from the Kepler Space Telescope show the galaxy around us buzzing with stars and planets, while conveying a call to deeper explore the mysteries of the Cosmos. Many people, however, are comparing a new mosaic of the final images from the Kepler spacecraft to a game of Tetris.

The Kepler space telescope was launched on March 6, 2009, on a mission to study a single field of 150,000 stars in the constellation Cygnus. Instead, the orbiting observatory went on to scan the galaxy, discovering thousands of worlds now waiting to be explored.

“Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate in Washington.

Kepler final images
The final images from Kepler, arranged in a mosaic. Image credit: NASA/Ames Research Center

Four years after its 2009 launch, the loss of gyroscopes critical to aiming the spacecraft failed, ending its initial mission in May 2013. In an effort to save the spacecraft, engineers soon unveiled the K2 mission. During this phase of the life of the Kepler spacecraft, researchers realigned the vehicle just once every three months. This second phase of observations doubled the lifespan of the mission.

GJ 9827 from Kepler. Image credit: NASA/Ames Research Center
TRAPPIST 1
The last view of TRAPPIST-1 from Kepler. Image credit: NASA/Ames Research Center

As recently as January 2019, citizen scientists using data from the Kepler spacecraft discovered a super-Earth, roughly twice the size of our home planet. This exoplanet, K2–288Bb, orbits in the “habitable zone” around its parent star, where temperatures are warm enough for liquid water to exist on a planet (but not so hot that it boils away). However, astronomers do not yet know whether K2–288Bb is rocky or composed largely of gas.

Thanks to the science which came out of Kepler, astronomers now believe that between 20 and 50 percent of the stars around us possess planets that are small and rocky, like the Earth, placed at just the right distance to Earth for liquid water to pool on their surface.

Our Solar System is composed of four small, rocky planets — Mercury, Venus, Earth, and Mars, and four gas giants — Jupiter, Saturn, Uranus, and Neptune. However, the most common type of planets seen by Kepler are mid-sized, larger than Earth, but smaller than Neptune. This means that our Solar System does not contain the most common type of planet in our region of the Milky Way!

For its final observations, mission engineers pointed Kepler to a number of intriguing targets for extra-solar planet hunters. One of these, TRAPPIST-1, is known to have at least seven rocky planets, three of which are placed at a distance from its sun where liquid water might collect on their surface. Another target was the GJ 9827 system, containing a planet with an atmosphere that astronomers might study from Earth.

NASA retired the Kepler mission as the vehicle ran out of fuel on October 30, 2018, after assuring the vehicle was in a safe orbit. But, even then, Kepler kept carrying out its duty to science.

“In addition to the static snapshots Kepler routinely took of its full field of view, the telescope’s camera also recorded selected targets at 30-minute increments. These continued for another several hours after the “last light” image before data collection ceased,” NASA reports.

During its lifetime, Kepler studied over 500,000 stars, discovering more than 2,600 planets beyond our solar system. Although these photos are the last full set of images to ever come from Kepler, researchers are still poring through data from the mission, which could yield new discoveries for years to come.

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