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Friday, June 21, 2013

Is this the end of the line for the Kepler Space Telescope?

The Kepler Space Telescope has been orbiting the sun since 2009, finding exoplanets at a surprising rate. During those 14 years, the Kepler has been responsible for confirming the existence of 132 planets and for discovering over three thousand possible exoplanet candidates. It has shown us that just about every star we see in the sky has planets, many of them potentially Earth-like.


Position of the Kepler space telescope. Note, objects in this video are not to scale. 

Unfortunately, the Kepler’s planet-hunting days may be behind it.

The Kepler uses the ‘transit method’ to find exoplanets. As a planet passes in front of its star from our vantage point, we see a slight dimming of the light coming from that star. If that dimming follows a regular pattern, we have a strong suspicion that an object is orbiting the star and that the object is most likely a planet. 

The Kepler telescope monitors a single patch of sky, continuously observing the same 100,000 plus stars. In order to do that job, the Kepler is kept in position by four reaction wheels. Three wheels are necessary to control orientation in each of the three dimensions and the fourth is a redundant spare. Last month, two of the wheels failed, leaving the telescope unable to maintain its precise orientation.

All may not be lost, however. Jacob Aron, writing at New Scientist suggests that the Kepler switch to another planet finding method, known as ‘gravitational microlensing’. This method relies on the fact that the gravitational pull of an object will bend and magnify the light coming from more distant stars. On the plus side, this type of detection does not require the tight spacial positioning that the transit method demands. On the minus side, microlensing is best suited for finding planets outside the habitable zone of their stars rather than for detecting Earth-like planets, which was Kepler’s original mission.


Gravitational microlensing schematic

An illustration of the gravitational microlensing technique, showing an Einstein ring
Credit: Timberlake Studios.

This week’s episode of the excellent Big Picture Science podcast discusses the Kepler in detail.