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Hot Friends of Hot Jupiters: The WASP-47 system

Ever since a mechanical failure caused the end of the original Kepler mission in 2013, the Kepler spacecraft has been conducting a survey of new stars, searching for planets across the ecliptic plane in its new K2 mission (https://blog.planethunters.org/2014/12/12/more-about-the-k2-campaign-0/). The K2 dataset is a goldmine of fascinating science results. One such result is the recent discovery of two new planets in the WASP-47 system.

Until a few months ago, everyone knew that hot Jupiter planets don’t have “friends”, or nearby small planets in close orbits to the host star. These other planets had been searched for extensively, through radial velocity measurements, analysis of the transit times of the hot Jupiters, and even through transits by Kepler during its original mission. All of these searches turned up nothing.

This all changed one day last July, when Hans Martin Schwengeler, a Planet Hunter who enjoys poring over Kepler and K2 data searching for new transiting planets by eye, came across the telltale signatures of two extra transiting planets in the hot Jupiter system WASP-47. WASP 47b was, by all indications, a perfectly normal hot Jupiter — in the discovery paper, Coel Hellier wrote “With an orbital period of 4.16 days, a mass of 1.14 Jupiter masses, and a radius of 1.15 Jupiter radii, WASP-47b is an entirely typical hot Jupiter”. The discovery of additional transiting planets dramatically changed the narrative.

When Hans came across the planets, he posted them to the Planet Hunters forum, where he and other citizen scientists discuss their findings. Andrew Vanderburg came across the post suggesting that a known hot Jupiter had planetary companions. Using his K2 data reduction pipeline (https://blog.planethunters.org/2015/01/08/a-recipe-for-making-a-k2-light-curve/), he analyzed the light curve and confirmed Hans’s discovery – there were additional planets in the system, a super-Earth at a 0.8 day period and a Neptune at a 9 day period!

Andrew emailed me, and at first I hardly believed that the lightcurve was real. How could a hot Jupiter have close-in planetary companions? I knew people had been looking for this type of companion for years via both photometry and transit timing variations, but the lack of discoveries indicated that they might not exist. I performed some numerical stability simulations (because it seemed at first like this system could not be dynamically stable!) and sure enough, the N-body simulations showed that the system was likely stable on timescales of 10 million years.

At that point, we formed a team with Hans, Andrew, MIT Professor Saul Rappaport, University of Michigan Professor Fred Adams (my advisor!), and me. Once this team was formed, we devoted ourselves to understanding as much about the systems as we could. Some work by Saul and Andrew confirmed that the planets were all orbiting the same star, Andrew fit the lightcurve to get the planet properties, and I ran more stability simulations. Soon enough, Fred suggested that I look at what transit timing variations (or TTVs, which happen when transits come late or early because of the gravity of other planets in the system) we would theoretically expect to see from the system – and I found that for the outer two planets, the TTVs should be observable.

I then measured the TTVs from the lightcurve, and sure enough – there was something there. After some discussion, we realized we could measure the masses of the planets from those TTVs! Though I had never done dynamical fits before, I wrote the code to utilize Kat Deck’s TTVFAST code in a Markov Chain Monte Carlo fit. With some advice from Kat and help from Fred, I eventually got the fits working and we were able to measure or put limits on the masses of each planet.

In a little less than two weeks, we had put together a paper deriving planet properties from the lightcurve, mass limits from the TTVs, and showing that you CAN detect companions to hot Jupiters using TTVs!

This result is exciting because it is the very first time a hot Jupiter has been found to have such close-in other planets. Before this discovery, it was unclear if hot Jupiter could have nearby friends, as they might destabilize the friends’ orbits during migration. This discovery opens up new questions about how these systems form – it is possible that there is more than one migration mechanism for hot Jupiters.

The paper on WASP-47 and its new companions, which was published earlier this week in ApJ Letters and is available at http://arxiv.org/abs/1508.02411, was a collaboration between myself (Juliette Becker, a graduate student at the University of Michigan), graduate student Andrew Vanderburg (Harvard CfA), Professor Fred Adams (the University of Michigan), Professor Saul Rappaport (MIT), and Hans Schwengeler (a citizen scientist).

 

Comets or Aliens?

Let’s deal with the big question first. Has Planet Hunters discovered aliens?

The answer is no. But that doesn’t mean that all of the press who have written about us in the last 48 hours, sending a flood of volunteers to the site, are completely misguided. Let me backtrack…

A few weeks ago we submitted the ninth planet hunters paper to the journal, and that paper is now available on the arXiv service. Led by Tabetha Boyajian at Yale, it describes a rather unusual system (what the Atlantic called the most interesting star in the Galaxy), which was identified by Planet Hunters, four of whom (Daryll, Kian, Abe, Sam) are named on the paper*. They spotted a series of transits – which is normally what signifies the presence of a planet – but these were unusual.

The star’s light dimmed for a long period of time, loosing a fifth of its brightness for days or even months at a time. More mysteriously, the duration of the dips was not always the same, so this couldn’t possibly be a planet. This behaviour is unique amongst the more than a hundred thousand stars studied by Kepler – we have a bone fide mystery on our hands.I think the team’s immediate thoughts were that it must be the star itself that’s misbehaving, but stars aren’t known to behave like this and some careful follow up reveals it to be nothing more than a normal F-type star, slightly hotter and more massive than the Sun. So it’s not the star, and we’re sure too that it’s not Kepler itself misbehaving; something is really blocking the light from this star.One option is a disk of dust around the star. It’s from such disks that planets form (see DiskDetectives.org for more on this!) and so that wouldn’t be too surprising. Yet enough dust to cause the deep eclipses we see would glow brightly in the infrared, and there’s no sign of a strong infrared source around this star.

You can read the paper to find out what else we considered, but we think the best explanation is that there is a group of exocomets in orbit around the star. Comets are an appealing scenario to invoke because they would be faint in the infrared, and because they move on elliptical orbits, accounting for the random timing of the transits and their different lengths. Such a group of comets could have come from the breakup of a larger object, leaving a cloud of smaller remnants in similar orbits behind.

Much detailed work is needed to flesh out the details of this (pleasingly outlandish!) scenario. One possibility is that the recent passage of a nearby star triggered the cometary bombardment whose effects we’re seeing. The paper is currently in the peer review process and there is – of course – the possibility that there is a perfectly sensible solution we haven’t yet considered. However, so  far over 100 professional scientists have had a look at the lightcurves and not managed to come up with a working solution.

One other proposed theory is that this pattern of behaviour is due to a fleet of alien spaceships in orbit around a star, a possibility considered by Jason Wright and collaborators here. Jason and co were tipped off about our discovery by the team, and it’s included in their paper as an object with ‘a bizarre light curve consistent with a “swarm” of megastructures’, much to the excitement of much of the internet. ‘Consistent with’ isn’t the same as ‘definitely is’, of course – and personally, my money is very firmly on the comet theory with a side bet on weird stellar behaviour – but until those models are properly investigated alien spaceships remain a possibility. The Wright paper points out this star is now a supremely interesting target for SETI (the search for extraterrestrial intelligence), and we agree – I hope radio astronomers will go and listen for signals. We need more observations of transits in action, too, and will be trying to follow-up to try and work out what’s actually going on.In the meantime, who knows what else is lurking in the Kepler data? Planet Hunters is about finding planets, but this ability to identify the weird and unusual is one of the project’s great advantages. Get clicking at www.planethunters.org, and let us know through Talk if you find anything a little odd.

Chris

* – This isn’t the final version of the paper, and we have more names to mention too before we’re done.

Extracted Lightcurves From Vanderburg & Johnson (2014) Now Available at MAST

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A new MAST High Level Science Product from K2 has been delivered that includes extracted lightcurves. Courtesy of Vanderburg & Johnson (2014), long-cadence targets from Campaigns 0 and 1 now have detrended, extracted lightcurves available at MAST, including 20 different photometric apertures. There’s a MAST Classic Search Interface so you can get lightcurves based on target IDs, coordinates, EPIC catalog fluxes, etc. You can also use our interactive plotter to explore the lightcurves using any of the photometric apertures before downloading the FITS files. Check out all the details here: http://archive.stsci.edu/prepds/k2sff/

Kepler 2.0

It’s up!

The first science data from the new Kepler K2 mission is up on Planet Hunters just waiting to be looked at for new planets, eclipsing binaries, and whatever else lies in the data. This is a set of completely new stars! (Check out the K2 page for more information about the K2 mission.)

This data may go fast, so get classifying now! But don’t worry, there will be more K2 data when the next quarter is released. And when each K2 quarter is finished, keep classifying stars from the four-year Kepler mission to help solve one of the biggest mysteries in astronomy: how common are planets?

– Joey

Blurry Eyes and Stellar Contamination in the Kepler Light curves

The light curves you see on Planet Hunters are not always the light of a single star. Kepler has very very precise but blurry vision. The CCD pixels on Kepler’s focal plane are very big, four arcseconds to be exact. The light measured at each observation from several of these pixels are added together to create the light curve you see on Planet Hunters. So what does this exactly mean? In some cases the Kepler stars are pretty isolated, but in others there are fainter background stars that appear nearby in the sky can get blended with the light from the Kepler target star. It turns out you can hide a lot within 4 arcseconds.

This stellar contamination can impact what we see in the final light curve. If the main Kepler star has a transiting planet, the contaminating star can dilute the transits. The transits will look shallower than they really are, and you’ll estimate a small planet radius. Sometimes the fainter contaminating star is an eclipsing binary. Combined with the light from the brighter Kepler target star, the stellar eclipses from the eclipsing binary are diluted. The secondary eclipse (when the fainter cooler star goes behind the larger brighter star and the smaller cooler star’s light is blocked out) can be diluted such that it’s not seen and the primary stellar eclipse (when the smaller cooler star transits in front of the larger brighter star and blocks out a portion of the brighter star’s light) get shallower, looking like a planet transit. Other times depending on the brightness of the eclipsing binary, it will look like the main Kepler target is the eclipsing binary when it’s not.

This is something the Kepler mission always had to deal with and there are some observational checks and data tests that can help determine whether the transit-like signal is likely coming from the actual Kepler target star. You can take follow-up observations like we did for PH1 b and PH2 b using telescopes with adaptive optics that minimize the blurring effects of the Earth’s atmosphere to zoom in around the Kepler target star to look for contaminating stars. Also you can look for shifts in the position of the brightest pixel during and before and after a transit which signals the transit signal isn’t coming from the primary Kepler target star.  Also you can look at the individual pixel by pixel light curves from Kepler  (Kepler reads out a subimage around each target star and a small number of those pixels get added together to make the Kepler light curve)and see if the transit signal or eclipsing binary signal is present in every pixel or if you see say an eclipsing binary signal in one pixel making the light curve and in pixels near by around a different star. Here’s an example from some of the Planet Hunters volunteers who examined to see if an eclipsing binary was contaminating a light curve.

Despite Kepler’s slightly blurry eyes, we can use a host of techniques to try and rule out false positives, identify where there is stellar contamination, and still find planets. So bear this in mind when you see the light curves, that although it’s likely most of the star’s light is from the Kepler target star, a tiny portion (in most cases) is contributed by neighboring stars.

Source contaminating the main Kepler target that confirmed circumbinary planet PH1 b orbits (the contaminating source itself happens to be a visual binary)

 

A Brand New Planet Hunters

On December 16, 2010, the Zooniverse launched Planet Hunters to enlist the public’s help to search for extrasolar planets (exoplanets) in the data from NASA’s Kepler spacecraft. Back then we didn’t know what we would find. It may have been the case that no new planets were discovered and that computers had the job down to a fine art. The project was a gamble on the ability of human pattern recognition to beat machines just occasionally and spot the telltale dip in a star’s brightness due to a transiting planet that was missed by automated routines looking for repeating patterns.

Nearly four years later, Planet Hunters has become a success beyond anyone’s expectation. To date 8 published scientific papers have resulted from the efforts of nearly 300,000 volunteers worldwide. Planet Hunters has discovered 9 planet candidate co-discoveries with the Kepler effort, over 30 unknown planet candidates not previously identified by the Kepler team, a confirmed transiting circumbinary planet in a quadruple star system  (PH1b), a confirmed Jupiter-sized planet in the habitable zone of a Sun-like star (PH2b), and identified the 7th planet candidate of a 7 planet star system.

Today in collaboration with JPL’s PlanetQuest, the Planet Hunters science team and the Zooniverse are proud to announce the launch of Planet Hunters version 2.0. We’ve taken your feedback and the lessons learned over the past 3.5 years to build a fast new interface that we think will take the project to the next stage. Using the Zooniverse’s latest technology, Planet Hunters 2.0 is built specifically with the next generation of transiting exoplanet surveys in mind, including the new K2 mission, which repurposes the Kepler spacecraft.

Kepler had been monitoring ~170,000 stars for the signatures of transiting exoplanets over the past 4 years in the Kepler field located in the constellations of Cygnus and Lyra. The new-two wheel Kepler mission dubbed ‘K2‘ will have Kepler observing brand new sets of 10,000-20,000 stars every 75 days. These stars are different from the sources that Kepler had been monitoring in the past. Your eyes will be one of the first to gaze upon these observations. Most of the K2 target stars will have never before been searched for planets, providing a new opportunity to find distant worlds. K2 observations will be made available by NASA and the Kepler team to the entire astronomical community and the public shortly after being transmitted to Earth and processed. We aim to get them on Planet Hunters 2.0 as fast as we can.

We think that Planet Hunters 2.0 will play a key role for finding extrasolar planets in the age of K2, and we have built a site we think can deliver the best science and find interesting planets with your help. We aim for rapid identification and dissemination of planet candidates discovered by Planet Hunters in the K2 era. You’ll hear more about additional new features and tools built into Planet Hunters 2.0 for analyzing K2 light curves closer to the release of the first K2 engineering observations sometime this month.

We also know there is much interesting and valuable science left to do with the Kepler field data. Much of the four years of Kepler field data has not been searched by the original Planet Hunters, and there may very likely be planets lurking in the light curves missed by the computers waiting for you discover. The new Planet Hunters will start by focusing all 17 quarters of observations on a subset of the Kepler field stars starting with cool M dwarf stars, the most common star in the Galaxy. We’ll use the classifications from these select set of stars from the original Kepler mission as well the new K2 observations to study the variety of planetary systems and their frequencies.

You’ll hear more about the science goals of Planet Hunters 2.0 and new functionality, tools, and guides built into the website in the coming days and weeks. We’re excited about this new phase of the project, and we hope you are as well. We don’t know what we’ll find, but with your help, we can’t wait to find out! Whether you’re new to the project or a seasoned veteran, with the new and improved Planet Hunters you can search for planets around other stars like never before.

It’s just possible that you might be the first to know that a star somewhere out there in the Milky Way has a companion, just as our Sun does.

Fancy giving it’s a try?

An Introduction to MAST

Today we have a guest post from Scott Fleming. Scott is a scientist at the Space Telescope Science Institute, located in Baltimore, MD, USA, where he works on the data archives.  His research interests include eclipsing binaries, stellar astrophysics, brown dwarfs, and extrasolar planets. Today Scott is here to tell you a more about MAST, the online public data archive where the Planet Hunters team obtain the Kepler light curves that are processed and eventually show up on the Planet Hunters site for you to classify.

The Mikulski Archive for Space Telescopes (MAST) is the official archive of data from NASA-funded space telescopes.  We primarily house data from ultraviolet and optical space telescopes.  Some of the missions we support include GALEX, the Hubble Space Telescope, the James Webb Space Telescope (after it launches), and of course, Kepler.  We also archive, and plan to archive, data from many other missions that have launched over the past 40 years, ranging from the 1970’s to future space and ground-based telescopes.

 Our role in the Kepler mission is to serve as the Data Management Center.  This means that, in addition to some data processing, we archive the lightcurve data itself (the timestamps, fluxes, flux uncertainties), as well as information related to each observation that’s required for calibration purposes, and catalog information that contains data on the host stars (their brightness in different wavelengths, estimates of their temperatures and sizes, etc).  We primarily serve professional researchers by facilitating access to the data, enabling powerful search capabilities so they can locate the data they need for their research, and providing tools that allow the scientists to preview and visualize the data before they download it to their machines for further analysis.  However, we do have some online tools that are used by educators and amateur astronomers as well.

Our newest tool is the MAST Discovery Portal.  This online search interface allows users to enter coordinates or target names and do a search for data across many missions all at once.  This is kind of like a “Google” for astronomical data, where users can discover observations that may have been taken on their objects, even if they weren’t aware of its existence beforehand.   You can enter the coordinates or name of a Kepler star, for example, and discover what other data exist by searching “All MAST Observations” or the “All Virtual Observatory Collections” in the top-left menu.  The Virtual Observatory is an online service that provides access to data from other astronomical archives around the world.  This allows users to search not only the ultraviolet and optical data at MAST, but also data in the radio, infrared, x-ray, and gamma-ray.

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MAST Discovery Portal Astroviewer (image credit: Scott Fleming)

The Discovery Portal includes an AstroViewer.  Using background images of the sky created from ground-based surveys, users can see the “footprints” (i.e., the field-of-view) of a given piece of data, and see exactly where your objects lie inside.  If you’d like to try it out, do a search on “Kepler 2”.  In the AstroViewer on the right-hand-side of the screen you will see lots of footprints appear.  The small squares around stars in the field are from Kepler; they show which stars Kepler looked at in the field.  Our target, Kepler 2, is automatically centered in the AstroViewer.  You will notice larger squares around it, which are the footprints of data observed with the Hubble Space Telescope.  If you zoom out to larger scales using the “minus” button on the lower-left corner of the AstroViewer, you will start to see very large squares and circles.  The biggest squares come from the Swift space telescope, while the large circle is an observation from the ultraviolet GALEX space telescope.  You can see how this visualization of data from many missions allows users to discover new data on their targets, and look for cross-mission overlap that can enable new kinds of science when multiple instruments observe the same target.

 Feel free to try out the Discovery Portal for yourself.  There is no registration or login required.  You can follow MAST online on Facebook and follow us on Twitter @MAST_News.  Although our posts are directed at professional astronomers to alert them when new data and tools are available at MAST, it’s still a way to keep up-to-tabs on what new projects are happening in the professional astronomy circles.

K2 – Kepler’s (Proposed) 2nd Exoplanet Mission

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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.

What to do with a 2-wheeled Kepler?

Now that Kepler is officially 2-wheeled,  NASA and the Kepler team are looking at what Kepler could be re-purposed to do. Except for having a bum leg, the rest of Kepler is in good shape. NASA put out a call for white papers, detailed proposals for ideas  for what to potentially do next with Kepler. There was no shortage of ideas. In total there were 42 white papers.  The proposed ideas ranged from studying the photometric variability of Active Galactic Nuclei (AGN) to a microlensing planet search. There is even a white paper from Kepler’s Principal Investigator (PI) Bill Borucki on how Kepler could continue exoplanet observations (though perhaps not at the same precision before the wheel failure). There are also other proposed options to do an exoplanet transit search by targeting new fields where the Kepler pointing would be better than going back to the the current Kepler field, though likely the observation span would be different from that before the reaction wheel failure. There are even proposals to stay the course and continue to follow-up the Kepler field even with the reduced sensitivity to transit depth with the aim of monitoring known Kepler planetary systems for transit timing variations (TTVs) and also look for long period giant planets.

If you’re interested in reading about all the proposed ideas in gory detail, all the white papers are online and freely available on the Kepler Guest Observer website. If you’re interested in the abridged version, Astrobites has an excellent summary by Nick Ballering highlighting the main categories of use cases proposed.

Some time in the Spring of 2014, NASA will  decide on an alternative plan for Kepler and hopefully if there is funding, Kepler will be taking data in the Fall of 2014 whether it’s looking for exoplanets, searching for Near Earth Asteroids, or something else.

Thoughts on the (possible) death of Kepler

Today brought some incredibly sad news to planet hunters everywhere. The Kepler satellite, which has provided all the data which has fed our site since the beginning, has probably reached the end of its useful life, at least as far as hunting for planets goes.

Kepler team members (& friends of Planet Hunters) Jon Jenkins, Natalie Batalha and Bill Borucki look at Kepler data in an artful press shot. They’re just three of the team who have devoted such care to Kepler.

Facts first. As reported elsewhere, Kepler’s fourth reaction wheel seems to have failed. The reaction wheels are what the spacecraft uses to point accurately, and with this failure Kepler’s down to only two, not the three needed to point precisely at its targets. Without three functioning reaction wheels, Kepler won’t be able to hold its gaze on the part of the sky that hold the stars that we’ve all become so familiar with over the last few years. There are still things to be tried – most of them variants on the tried and trusted ‘turn off and turn back on again’ methods – but the participants in today’s press conference didn’t seem very confident. The likely best case scenario involves Kepler being placed into a stable mode while those of us left on Earth spend the next few months contemplating what else it might be used for (budgets notwithstanding).

So where does this leave Planet Hunters? Bill Borucki – Kepler’s indefatigable principal investigator – was at pains during the press conference to stress that there is plenty of science left in the data that the spacecraft has already sent to Earth. He believes (and who are we to doubt) that Kepler already has enough information on hand to satisfy the critical science goal of determining what the odds of an Earth-sized planet are. There is a year or so of data that hasn’t been seriously reviewed by anyone, and much less than half of the data supplied has ever been viewed by Planet Hunters. In the long run, there are other data sets (the European COROT mission might be worth a look) and future missions (NASA’s TESS will follow where Kepler led, but looking for nearby planets).

Those discussions are for the days to come, though. For now, I want to pay tribute to the people behind the spacecraft. There’s a temptation at times like this to anthropomorize, to feel sorry for our plucky little planet hunter way up in space. Yet the truth is a mission like Kepler is what it is because of the blood, sweat and tears of hundreds of people, many of whom have dedicated literally years of their lives. I don’t know Bill Borucki well, but I first met him when I interviewed him for the BBC’s Sky at Night program. What struck me then, apart from his relaxed humility, was the tale he spun of year after year pitching what was to become Kepler only to be told that his ideas were unrealistic. Most people would have given up, but Bill and his team pressed on and as a result of that dedication were in the right place at the right time when the time came for an exoplanet mission to be picked.

The Kepler team are scattered across the US, and indeed across the world this evening. I hope many of them will be raising a glass to (what seems to be) the end of a job well done. Before we join them, the least we can do is go and look at some of their data they collected – after all, we still don’t know what’s lurking in the Kepler data displayed at Planet Hunters.

Chris