Repurposing Kepler

One of my favorite telescopes has to be Kepler. Kepler has been orbiting the Sun, much like Earth does, since its launch in 2009. Its primary mission was to discover Earth-like planets orbiting other stars, called exoplanets. And since its launch in 2009, Kepler spent some four years staring at one region of the sky, unblinking, carefully monitoring how thousands of stars’ brightnesses change with time, with insane precision.

Kepler finds planets orbiting other stars using a technique called the transit method. That’s really just a fancy way of saying, “if a dark thing passes in front of a bright thing, we see less light.” Consider planet = “dark thing” and star = “bright thing”… and that’s it! Kepler isn’t fancy; rather, it takes a simple idea and milks it for all it’s worth. Bigger planet? More starlight blocked. Slow-moving planet? Starlight blocked for longer.

Artist's impression of the Kepler Space Telescope. An example of the transit method Kepler uses to detect planets is in the upper left corner. Note, however, that Kepler can't actually take a picture like this - it just records how a star's brightness seems to change over time. Image from http://www.stsci.edu.
Artist’s impression of the Kepler Space Telescope. An example of the transit method Kepler uses to detect planets is in the upper left corner. Note, however, that Kepler can’t actually take a picture like this – it just records how a star’s brightness seems to change over time. Image from http://www.stsci.edu.

While exoplanets are Kepler’s specialty (and it has found hundreds!), Kepler has somewhat unintentionally revolutionized stellar astrophysics, too. Planets getting in the way isn’t the only thing that can make a star’s brightness change. Scientists studying exoplanets have to deal with many other brightness-changing effects to properly characterize the planets they discover. As we say, though, one astronomer’s noise is another’s data: the “annoyance” of seeing so many rotating stars, pulsating stars, spotted stars, and even stars orbiting other stars, is my personal favorite of Kepler’s many successes.

Unfortunately, a critical part of Kepler broke recently, and there is no way to fix it. One of Kepler’s specialties is pointing ever-so-carefully at one part of the sky. To accomplish this, it needs a good sense of balance in three dimensions. This was provided by a set of “reaction wheels,” which are basically gyroscopes that spin to keep Kepler oriented in the right direction. Three dimensions of space means you need three wheels. Kepler actually has four, so one is redundant – we intentionally built Kepler with an extra reaction wheel in case one broke. As luck would have it, one stopped working shortly after launch. “No problem!” said scientists back on Earth. “We still have three wheels!” Or rather, we did. Until last spring, when a second one bit the dust.

And that is the sad story of how NASA wound up with a crippled telescope that can no longer search for Earth-like planets.

Thankfully, though, Kepler’s story doesn’t end there.

After a series of thorough tests to be sure two wheels really were broken, the folks at NASA put out a call to astronomers everywhere. They provided technical details about Kepler’s capabilities and limitations, and asked, “What should we do with Kepler now?”

More than 40 proposals flooded in to answer that question. See them here.

Most of these are full-fledged papers, representing hours of work for each author (and most of them have many, many authors!). Teams of astronomers from all over the world collaborated to come up with countless ideas for putting Kepler back to work. From those ideas, they fleshed out the most promising ones, and did extensive research to present science goals that are both realistic given Kepler’s current state and important to advance astronomy.

Just to put this in perspective: hundreds of astronomers spent countless hours to come up with creative, robust ideas for a telescope that doesn’t work properly anymore. Nobody paid them to write these proposals. Realistically, only one from a multitude of ideas will be able to happen, because we only have one Kepler. And it is broken!

I can’t help but imagine the science astronomers could accomplish if we had access to multiple, UN-broken space telescopes like Kepler. Even so, it is heartening to know that Kepler will have some scientific purpose, going forward. Long live Kepler!

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