REPORTS of the death of our principal planet hunter have been greatly exaggerated. The prolific Kepler space telescope may yet be able to keep seeking out planets, this time with a gravitational magnifying glass.
Since its launch in 2009, NASA’s Kepler mission has discovered 132 exoplanets and thousands of other possible worlds, making it one of the most celebrated exoplanet missions.
To catch sight of far-off worlds, Kepler must stare at stars with an unwavering eye, looking for tiny dips in starlight when a planet transits, or crosses in front of its host star. To do this, the craft needs at least three orientation-controlling reaction wheels to stabilise its vision. Two of its four wheels have now failed.
Shaky eyesight doesn’t have to mean curtains for Kepler, says Keith Horne of the University of St Andrews, UK. He and Andrew Gould at Ohio State University in Columbus suggest that the hobbled telescope can use its gear to take up microlensing, an alternative way to spot planets (arxiv.org/abs/1306.2308).
When two stars align in our line of sight, the gravitational pull of the closer star bends and magnifies the light of the further star. If the nearer star has orbiting planets, their gravity provides added magnification.
“The signals from planets are quite large in this case, sometimes even a 100 per cent change of brightness of the star, so it’s relatively easy to see these things,” says Horne.
The pair estimates that Kepler could find a few dozen exoplanets a year with microlensing. These would be very different from its previous quarry. With transits, it is easier to spot planets that orbit close to their stars – crucial for finding worlds warm enough to host liquid water, and maybe life.
Even with shaky eyesight, Kepler could spot new exoplanets with a method called microlensing
Microlensing is better for finding planets further from their stars, which would be too cold for liquid water. Studying both extremes would help us understand the borders of the habitable “Goldilocks” zone in between, says Horne.
Although ground-based observatories can use microlensing to discover planets, Kepler is in a unique position. It orbits the sun, trailing Earth by millions of kilometres, so it can watch for stellar alignments that we can’t see from our angle and it could spot previously undetectable exoplanets.
Kepler was not designed for microlensing though, so it might be more cost-effective to use funds for a dedicated mission, says Geoff Marcy of the University of California, Berkeley. NASA is considering one such proposal called the Wide Field Infrared Survey Telescope (WFIRST).
WFIRST isn’t due to launch for at least a decade, says Horne, and getting Kepler to do microlensing now would add to our planetary roster faster and might even improve WFIRST.
Meanwhile, NASA engineers are still trying to coax one of Kepler’s reaction wheels back into service, letting it continue its original mission. “They’re working on the patient, not planting tulips on its grave,” says Marcy.
This article appeared in print under the headline “Planet seeker might live to hunt again”