Planet Hunter enters Hibernation

NASA has put its planet hunting  Kepler space telescope  into hibernation because it is running low on fuel. Kepler has discovered over 2,500 exoplanets by monitoring more than 150,000 stars for slight dips in brightness that might be caused by an exoplanet passing in front of the star.

Artistic rendition of NASA’s planet-hunting Kepler spacecraft operating in a new mission profile called K2.

NASA made the move to ensure that Kepler has enough fuel left to beam its latest data haul to its handlers early next month. Kepler has been on its 18th observation campaign since May 2018. It has been pointing at a patch of sky towards the constellation of Cancer that it previously studied in 2015. This second look will provide data that helps astronomers  confirm previous exoplanet candidates. Returning the data back to Earth is the highest priority for the remaining fuel. On August 2, the team will command the spacecraft to awaken from its hibernation state, maneuver the spacecraft to point its large antenna back toward earth, and transmit the data over the Deep Space Network.

The Kepler mission launched in March 2009, with the goal of helping astronomers determine just how common Earth-like planets are throughout the Milky Way galaxy. Kepler has been tremendously successful by any measure. A key finding from he spacecraft’s observations suggest that about 20 percent of sunlike stars host a roughly Earth-size planet in the habitable zone (where liquid water could exist on a world’s surface).

Kepler’s primary mission  ran through May 2013, when the second of the spacecraft’s four orientation-maintaining reaction wheels failed. The K2 mission  was developed  in the months following the failure with the novel concept of using sunlight pressure to help stabilize the spacecraft. K2 became fully operational in May 2014 allowing Kepler to  continue making scientific observations.

The transit method of detecting exoplanets looks for slight dips in the brightness of a star when a planet passes in front of a it as viewed from Earth. We can observe an occasional transit of Venus or Mercury when they pass in front of the Sun and appear as a small black dot creeping across the Sun’s surface as seen from Earth.

Kepler Habitable-zone exoplanet hall of fame

After  several transits are detected, the planet’s orbital radius can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star. The size of the planet is found from the depth of the transit (how much the brightness of the star drops) and the size of the star. From the orbital size and the temperature of the star, the planet’s characteristic temperature can be calculated. From this the question of whether or not the planet is habitable (not necessarily inhabited) can be answered.