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Welcome to the Era of K2
Image Credit: NASA Ames/ W Stenzel
Last August, I wrote about the end of Kepler's original mission as it had been operating for the past 4 years. Kepler was launched in 2009 with a goal for providing a census for planets around Sun-like stars and helping us understand the frequencies of rocky planets. Kepler stared at the same field monitoring 160,000 stars nearly continuously for those 4 years. To achieve the precision pointing to obtain precise enough measurements to detect rocky terrestrial planets, Kepler had to point with extreme precision with the stars moving very little on the camera. To do this Kepler had three reaction wheels (and one spare) that would help nudge the spacecraft slightly one way or another. Last year, Kepler suffered a second reaction wheel failure that prevents it from continuing with its mission of monitoring the Kepler field. Pointing at the Kepler field, the spacecraft moves too much, and this effectively ended the Kepler mission as is. Kepler had taken its last observations of the Kepler field.
The Kepler team devised a new way of observing with Kepler using solar irradiation to help stabilize the spacecraft and act as the third reaction wheel. They set out to test it and prove this was a viable mission (which they dubbed 'K2') that would return interesting science and discoveries worthy of NASA funding. Back in December, NASA gave the go ahead for K2 to compete with other viable missions in the Senior Review. Well, what is this Senior Review? Space missions cost money. You have to pay for the engineers that keep the spacecraft happy and running, pay the project managers and support staff and scientists, have funds if there are guest observer programs, as well as it costs money to use time on the Deep Space Network to send commands to and receive the data from your favorite telescope. The NASA Senior Review is NASA's way of prioritizing and deciding which already existing missions will continue on and receive funding from the limited amount of funds available to spend while building and launching new spacecraft. Ben Montet from Astrobites has a nice summary description of the competing missions from this year's Senior Review. Funding is tight and although these missions and spacecraft have all produced interesting science and capable of continuing to do that, not every mission that was on the chopping block is guaranteed to get money to pay for its operating costs. There simply isn't enough to go around.
Officially today, NASA has announced the results from the Senior Review. You can read the full report from the panel here and the response from NASA. The verdict from the panel for Kepler/K2: "This is an outstanding mission and we look forward to the results from the program. K2 uniquely addresses a range of observational goals and is expected to engage a broad community of scientists." K2 has been recommended by the review to continue with the extended K2 mission, and NASA has agreed to provide funding. The Kepler team didn't get all the money they asked for, but 90% of the requested budget more than enough for the K2 mission to officially start science operations in June. K2 is a go! There will be new light curves from never before seen stars coming from Kepler over the next 2 years!
Congratulations to everyone involved in the Kepler project who made this happen. They put in lots of tireless effort to find a way to use Kepler in a novel observing scheme and prove that it could deliver interesting science worthy of continuing on. The Senior Review specifically about the science goals and case for K2: "K2 will allow exoplanet surveys of all stellar classes,O-M, giants-dwarfs, and white dwarfs as well as the asteroseismology of late stars, studies of nearby open clusters for the fundamental properties of pre-main sequence (PMS) and zero age main sequence (ZAMS) stars, and explore supernovae and accretion physics in AGNs. These are but a small sample of what can be achieved with the study of precise photometric long term continuous data" .
This is exciting times for the study of extrasolar planets, as Kepler is now primed to deliver a whole new crop of planets and other astrophysical discoveries and results. The Planet Hunters science team and the Zooniverse are working on preparing the site to be able to ingest and serve the K2 data to you all in a fast and efficient way. Stay tuned to this space as we get closer to August when the first science grade K2 data is released.
You can learn more about the K2 mission at http://keplerscience.arc.nasa.gov/K2/
in K2, Kepler Mission
K2 – Kepler's (Proposed) 2nd Exoplanet Mission
K2 mountain, the 2nd highest peak in the world Image credit: Wikipedia (http://en.wikipedia.org/wiki/File:K2_2006b.jpg)
In May, Kepler lost its 2nd reaction wheel halting continuing observations of the Kepler field and its original exoplanet mission. Later this summer, NASA announced that attempts to revive the broken reaction wheels had failed, and that was the official end to the observations of the Kepler field with the 30 ppm (parts per million) precision obtained with the 3-wheel pointing. Other than the bum leg, the spacecraft and imager were in good condition. NASA issued a call for white papers soliciting ideas for potential use cases for a 2-wheeled Kepler.
It was announced two weeks ago at the 2nd Kepler Science Conference, that the Kepler team has a plan to return Kepler to exoplanet hunting that they will be proposing to NASA to give the go ahead and fund. They are dubbing this new 2-wheeled mission for Kepler 'K2'. You might be inclined to call 'K2' Zombie Kepler, but in reality Kepler hasn't gone anywhere. After the 2nd reaction wheel failure, the spacecraft has just been resting while NASA and Ball Aerospace engineers have been working on ways they could use the remaining two reaction wheels and thrusters to do exoplanet science. In the past few weeks Kepler has been taking engineering data to test stability and photometric precision in this K2 pointing/observing scheme.
Here's how K2 works. With the loss of the 3rd reaction wheel, Kepler lost fine tuning in one of three spatial directions. If Kepler is pointed keeping the Sun in the X-Y plane, there's a pointing ridge where they can balance the spacecraft and use the remaining wheels and thrusters to keep pointing. That means fields have to be in the ecliptic (plane of the Earth's orbit). With that pointing very little changes to the current Kepler team data pipeline are needed to produce light curves with the same 29.4 minute cadence. The photometric precision is predicted to be better than 300 ppm (measured from preliminary engineering runs and testing). So there is a loss of sensitivity, 3-wheeled Kepler had 30 ppm photometric precision. Still Kepler can detect giant planets and for both bright and small stars, Kepler can detect rocky planets.
Kepler will not be able to stare at any one field for very long. The fields on the ecliptic would change as the Kepler orbits the Sun. Each field would get ~40 days worth of observations with some craft pointings able to extend the baseline to ~70-80 days. Also the number of pixels per star needs to be increased significantly, and since Kepler has a limited memory on board to store all of this data, the number of stars observed needs to significantly decreased from the over 160,000 stars monitored when observing the Kepler field. 10,000-20,000 stars would be monitored in K2. The K2 data, like that in the Kepler extended mission, would be available to the public and scientific community after it was downloaded and reduced.
The exciting prospect is that Kepler would observe different populations of stars than the Kepler field, which will be interesting to see how the frequencies of planets compares to the Kepler field. Not to forget, the prospect of having many many more new planets/planet candidates to characterize and study. There will be also be observing of cooler M dwarf stars where the habitable zone (the goldilocks region where water might exist on a rocky planet's surface) is close to the star, and thus Kepler will find many more rocky planets in the habitable zone to further study. Also bright stars will be targeted which will enable ground-based follow-up with the radial velocity technique, which for gas giant planets can actually measure masses and confirm these planets. Also there's a wealth of stellar astrophysics (and even potentially microlensing monitoring ) that could be done with K2, including observing stars in open clusters (conglomeration of stars loosely bound together that were all formed from the same molecular cloud) where we know their ages.
K2 is a mission concept at this point. The Kepler team is working hard, and has achieved or on track to finish software upgrades needed to enable Kepler to point and track on ecliptic fields for K2. Test data is starting to coming down from the spacecraft. The Kepler scientists and engineers are analyzing the data and assessing the data quality from K2-like observing. In the next few weeks the Kepler team will propose K2 to NASA, in December NASA will decide if K2 is viable and then give the go ahead for the Kepler team to propose for K2 in the senior review in April, where Kepler as well as other NASA missions will be examined and funding will be decided. Let us hope that K2 gets the full go ahead with (cross our fingers) observations starting some time in 2014.
The prospects for K2 are exciting, and I hope the missions gets the green light. I think the place for Planet Hunters in the K2 era is interesting. I think there will be a niche for Planet Hunters, especially with the short time span on each field, identifying single transits will be important for follow-up of the planetary systems discovered. There will be new eclipsing binaries monitored, and the prospect for more circumbinary planets which is also where I can see Planet Hunters contributing. Plus don't forget the unexpected discoveries waiting to be found, as we've learned from the Kepler field data. So bring on K2!
Want to know more about the proposed K2 mission? Watch the 2nd Kepler Science Conference talks by Charlie Sobeck and Steve Howell detailing the specifics about K2.