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Ames to pitch NASA on value of 'new' Kepler mission

Posted: November 15, 2013

Managers in charge of the Kepler telescope have identified a way of salvaging the crippled observatory for a modified, less-sensitive cosmic survey for alien worlds, but NASA may not have the money to pay for the mission.

Artist's concept of the Kepler spacecraft. Credit: NASA/Ames
Since Kepler was knocked offline in May, officials at NASA's Ames Research Center in California have considered and analyzed new missions for the telescope.

And they think they have found a concept that is both feasible and scientifically intriguing.

The new mission scenario, dubbed "K2," calls for pointing Kepler across a swath of sky known as the ecliptic plane, or the plane where all the solar system's planets orbit the sun.

If approved by NASA Headquarters, the renewed Kepler campaign would be a shift from looking at stars like the sun to observing smaller, cooler stars that may harbor rocky planets close in, meaning they would be easier to detect.

"This is science that Kepler can do, and the K2 mission can do this uniquely, so this is really a selling point," said Steve Howell, Kepler's project scientist, during a Nov. 4 presentation at the second Kepler Science Conference held at Ames.

Plagued by reaction wheel failures and unable to adequately control its roll motion, Kepler can no longer hold its gaze toward a field of more than 150,000 stars in the constellations Cygnus and Lyra. Kepler's optical detectors kept up a near-contant stare at the star field, which was selected because it was representative of the rest of the Milky Way, allowing scientists to extend their findings predict what may lie elsewhere in the sky.

"That means it needs to do some alternate science," said William Borucki, Kepler's principal investigator from Ames. "Right now, what would be very intriguing is to have it look within the ecliptic plane of our solar system and look at smaller stars [than the sun]."

Kepler officials at Ames gave a high-level overview of the K2 proposal Nov. 4, but the Kepler team planned to submit a formal report to NASA Headquarters by the end of November detailing its technical viability, scientific utility and financial cost.

Paul Hertz, director of NASA's astrophysics division at NASA Headquarters, said the agency would put the proposal under the microscope of two independent review boards to ensure the K2 mission meets technical, scientific and financial criteria.

First, reviewers will decide whether the K2 proposal is competitive enough to even be considered in a fight for scarce funding alongside other NASA missions.

"If it passes [that] filter, we'll send it to the senior review," Hertz told a National Research Council panel. "Then it will have to compete against all the other missions in the senior review for some of the operating money we have, and we don't have a lot."

A view of Kepler's original field-of-view in the constellations Cygnus and Lyra. Credit: NASA/Ames
The senior review is a regularly scheduled event every two years where researchers selected to represent the science community rank the value of all of NASA's operating space missions as they seek funds for an extension.

Missions rated highly almost always receive approval to continue their work, while missions at the bottom of the pile could receive only partial funding or be deactivated.

K2 would compete for money against proposed extensions of NASA's Spitzer infrared observatory and the Fermi Gamma-ray Space Telescope, among other missions. NASA's two most costly astrophysics missions, the Hubble Space Telescope and Chandra X-ray Observatory, are also up for review, but they will be considered separately, according to Hertz.

If the federal government is hit with a new round of automatic across-the-board spending cuts, which will happen Jan. 1 if Congress does not reach a bipartisan budget agreement, Hertz said something will have to be turned off.

"If we keep sequestration, we don't have enough money to keep everything going," Hertz said, adding he expected to receive the outcome of the senior review in April 2014.

But Kepler officials say they have a strong case for the K2 mission.

"We believe that there are cases ... where we can deliver small exoplanets, so don't believe everything you read on the Internet," Howell said. "There is a viable exoplanet mission here to find rocky planets around small stars, and some of them in the habitable zone."

Viewing stars in the ecliptic plane will require repointing of the spacecraft to a new star field every 40 to 80 days to keep bright sunlight from damaging Kepler's 95-megapixel camera, according to Charlie Sobeck, Kepler's deputy project manager.

Project scientist Howell said each star field would include between 10,000 and 20,000 stars, and K2 would observe four-to-six fields per year, moving on to a new section of the sky every two or three months. Over three years of K2 operations, the telescope would end up observing roughly the same number of stars as originally planned for Kepler.

The K2 concept would look at stars in the ecliptic plane because such a pointing orientation limits the effect of solar forces causing the telescope to drift away from its astronomical targets, Sobeck said.

For now, the Kepler ground team is using already-approved funding to test out the spacecraft's precise pointing ability with two reaction wheels, with an eye toward starting an abbreviated science campaign in early 2014 to prove the scheme works.

Sobeck said the K2 mission would cost the same or less to operate than the original Kepler mission, and it has enough chemical propellant on-board to last between seven and 10 years.

Kepler's growing planet catalog

Kepler's vast data catalog holds 3,538 planet candidates, including 647 that are twice the size of Earth or smaller and 24 worlds of that size where temperatures are just right to support liquid water, and potentially life.

Artist's representation of the "habitable zone," the range of orbits where liquid water is permitted on the surface of a planet. Credit: UC Berkeley
Data collected by Kepler have led to the confirmed discovery of 167 planets, and scientists expect the majority of the candidate planets will turn out to be real upon further analysis.

Kepler's camera registers tiny blips in starlight that indicate a planet is passing between its host star and the telescope. Complex computer algorithms crunch Kepler data on the subtle dimming of a star to find out the size and orbital characteristics of the planet.

That was Kepler's observing method before the reaction wheels, which generate momentum to point the spacecraft toward star fields, succumbed to high friction levels.

The spacecraft stayed healthy long enough for Kepler to complete its primary science mission, which ended in November 2012 after three-and-a-half years of observations. NASA awarded funding to extend Kepler operations through 2016 to allow more time to validate the existence of the smaller, Earth-sized worlds in the mission's listing of candidate planets.

Six months into the extended mission, and after desperate tries to resolve high friction afflicting a troubled reaction wheel, Kepler lost the ability to do what it was was designed to do.

The mission was originally tasked not to just look for the massive, Jupiter-sized planets that scientists already knew populated the galaxy, but for modest worlds the size of Earth that reside around stars like the sun. And Kepler was designed to distinguish which of those Earth-sized planets could be habitable.

Borucki said the mission's four-year data archive likely contains the mission's Holy Grail - an Earth-sized planet in the habitable zone of a star like the sun.

Only three years of data have been run through software designed to pick out the signatures of planets, so one-quarter of Kepler's entire data haul remains a mystery. Scientists expect many of the candidates announced so far to move into the confirmed column once astronomers see more data.

The Kepler science team wants to see three or four transits of a potential planet to weed out false positives, and that translates into three or four years for a star like the sun. A faraway telescope looking at the sun would likely need that long to confirm the discovery of Earth.

"We hoped at this point to have already found many more Earth-sized planets in the habitable zone," Borucki said. "This last year of data, I believe, will help us find those planets that we were expecting."

Follow Stephen Clark on Twitter: @StephenClark1.