Now that were in the midst of the showing the first batch of science grade data from the K2 mission, I thought I’d give some more details about the K2 light curves and how K2 mission works.
Planet transits are small changes in the star’s light, a Jupiter-sized object produces only a 1% drop in the brightness of a Sun-like star and Earth-sized planets generate even smaller dips at the 0.01 % level. Kepler needs the stars to be precisely positioned on its imaging plane in order to achieve the photometric accuracy required to detect these drops in light. To do this the stars have been positioned and kept at the same location with millipixel precision. Kepler was able to achieve this during it’s primary mission and the first half of its extended mission To do this Kepler used three reaction wheels (one for x, y, and z directions) with one backup spare to finely nudge the spacecraft to keep the target stars positioned during a Quarter. Kepler suffered two reaction wheel failures and can no longer operate in this mode. This effectively ended the monitoring of the Kepler field, that Kepler was staring at for 4 years. The drift of the spacecraft was too large that the photometric precision was sufficient enough for a transiting planet search.
This is where K2 comes in. The K2 mission repurposes the Kepler spacecraft. Kepler has thrusters but they are used for coarser pointing corrections, they can’t be used to be the fine adjustments that used to be achieved with the third reaction wheel, but you can use the Sun in a way to be that reaction wheel. This is how K2 works. If Kepler is pointed observing fields that are along the plane of the Solar System, than the two working reaction wheels are used to maintain the x-y locations of the stars on the focal plane with the Sun and thrusters taking care of the rest. Kepler is positioned such that the irradiation of the Sun is balanced which basically keeps the spacecraft from rotating. This is a quasi-stable and every 6 hours or so the spacecraft will start to roll. The thrusters can then be used to roll the spacecraft back to it’s original orientation. (You can see this in the raw light curves just plotted. You can see a Nike check-like feature that dips slowly and rapidly goes up.The light curve processing Andrew does tries to remove as many of those artifacts and others as possible. It does a pretty good job, though occasionally there may be an artifact that remains. ) This scheme works pretty well at keeping the stars on Kepler’s focal view located on the same pixels and achieves photometric precision about 3x time worse than what the original Kepler mission was achieving. With this, we can still find planets around other stars, especially smaller cooler stars.
The K2 light curves we’re currently showing on Planet Hunters come from Campaign 0. Campaign 0 is the first full science grade test field data for the K2 mission. Kepler was staring at a field centered around see a region of the sky plotted in the star chart below. The observations commenced on March 12 and the campaign was completed on March 27th of this year. Campaign 0 serves as a full shake down of the performance of the spacecraft in this new mode of operating. The specific targets Kepler monitored in the Campaign 0 were community driven with astronomer putting proposals for what they wanted to be observed, and were decided by a Time Allocation Committee (TAC) organized by the Kepler team. You can learn more about the observing proposals and selected targets for Campaign 0 here.
On the site we’re only showing roughly 30 days worth of data, that’s because the light curves derived from the second half of Campaign 0 are more indicative of what the rest of the K2 mission will be like, so we’re only looking at that data. The observations at the start of the Campaign 0 were taken with Kepler not in fine pointing mode with a guide star and thus the positional consistency of the target stars over time on the imager is lower, causing a decrease in the photometric accuracy. Therefore we’re focusing on the better quality second half data. Future K2 Campaigns will have the full ~75 days worth of data in fine point mode, and we plan on showing all of the observations on the Planet Hunters website in the future.
We are showing light curves from the Kepler 2-wheel mission for Campaign 0 (a.k.a. “K2 C-0″) now and wanted to explain some issues that you may notice with these data. The K2 C-0 data are poorer quality than what you are used to seeing. The Kepler team is still working optimize the light curves, and this has been made more difficult by instabilities in the pointing control of the spacecraft. You can expect to see more trends and glitches. Furthermore, the first few weeks of K2 C-0 data were not useable so the length of the light curve (in days) is shorter than what you might have expected. All of this should improve for the next campaign, C-1.
A second issue with the K2 C-0 data is that we don’t have access to information about the stars. We know the EPIC numbers, coordinates, brightness of the stars, and the program numbers (telling us who requested observation of the stars). Postdoctoral Fellow Ji Wang has been an enormous help – he wrote a program to filter the published 2MASS and Sloan catalogs and to search for stars within a small radius about the EPIC coordinates. Ji then used the stellar brightness to obtain an unambiguous identification. This helps, but we still don’t know the stellar gravities (radii), masses or spectral types. Therefore, the information we can display for each of the K2 C-0 stars is much more limited than what you are used to seeing.
Since we don’t know the stellar radii, we are not able to make up accurate simulations for the K2 C0 data. To compensate we will show these light curves to more people than usual to build up consensus about the presence of transits.
The K2 data have many more selection effects than the original Kepler data because the targets are drawn from several guest observer programs. However, this is part of the fun – scavenger hunting for planets among the K2 stars is sure to be an adventure!
We are also trying to improve our turn-around time for PH results. Instead of waiting until we obtain telescope time to carry out follow-up data and publish a paper (sometimes a year later!) we will put the high probability transit candidates that you identify on the “Planet Hunters Object of Interest” (or PHOI – which I think is pronounced something like “fooey”). This is supposed to be a fun home-grown analog of the “Kepler Objects of Interest.”
Thanks to Andrew Vanderburg at Harvard University who has extracted these K2 C-0 light curves for Planet Hunters.
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?
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.
As part of the new Planet Hunters classification interface, the Summary page (see below) suggests some hashtags you could use to label the light curves you’re seeing in Talk and in the Talk comment area on the Summary page. A few people on Talk have asked for a full list, so here’s a handy list of the first set of hashtags suggested by the science team at launch of the new Planet Hunters.
RR Lyrae Star - Pulsating star with periods ~1/2 day
Pulsating star with periods >1 day.
Pulsators – Rapid up and down changes in brightness on the order of a few hours
Eclipsing binary - A star transits another star, often exhibiting V-shape and uneven transit depth
Cataclysmic variable - Cataclysmic variables (cv’s) are a class of stars where the sudden ignition of material on the surface of a white dwarf results in gigantic increase in brightness for several days before returning to natural quiescent state.
Variable star – Change in brightness on timescales greater than 1 day. May be periodic or non-periodic.
Heartbeat star – Two stars get very close together but avoid collision. Their structure changes, and the light curve exhibits a shape like a cadiogram.
glitch – Occasional malfunction of data reduction pipeline.
Planet transit - A planet goes in front of a star and blocks a portion of the star light
Stellar flare – Sudden brightening of a star, often associated with massive material ejection. duration of a few hours. Typically non-periodic.
These listed above are suggested hashtags the science team has come up with. A light curve can definitely be described by more than one hashtag. Also do feel free to use your own hashtags too. There are many more ways to describe and sort the light curves and stars. You can see the most frequent hashtags being used by the Planet Hunters community on the left side of Talk under ‘popular hashtags’
Today we have a post from Joey Schmitt, a graduate student in the Astronomy department at Yale University, where he is working with the exoplanet group led by Debra Fischer, and in particular he has been working on the follow-up of Planet Hunters planet candidates.
We’re happy to announce the discovery of a new planet discovered by Planet Hunters volunteers, which is now published in The Astrophysical Journal. You can read the article for free on the arXiv here.
The star (PH3/Kepler-289/KOI-1353/KIC 7303287) is young and Sun-like. Two planets in the system, with periods of 35 and 126 days, had been previously validated statistically, the outer planet being a gas giant. However, Planet Hunters volunteers discovered a third transit signal between these two planets at a period of 66 days (PH3 c).
A quirk in the system allowed us to actually measure the mass of all the planets using only the exact times that each planet transited. The outer two planets, PH3 c and d, do not have a constant period like most planets do. Instead, it oscillates around an average value in a regular manner, which meant that it had been missed by computer algorithms but was easy to find for human eyes. In particular, the period of PH3 c changes by 10.5 hours in just 10 orbits due to the gravitational influence of the outer gas giant tugging on the middle planet. If Earth experienced such large changes, then if 2014 were 365 days long, 2024 would be 367.4 days long, almost two and a half days longer than 2014.
The new planet is about 2.7 times the radius of Earth and 4 times as massive. Its low density means that, despite its low mass, a large chunk of the planet must be composed of hydrogen and helium: 2% by mass and 50% by radius. The outer planet, on the other hand, is like a warm version of our Saturn, while the inner planet’s mass is poorly known. It could be mostly rocky, watery, or gassy.
We would like to thank all of the people involved in the project and all of the Planet Hunters volunteers for making this possible. We hope to find more gems like this in the future.
There were some big changes to the Planet Hunters website and our Talk discussion tool yesterday. Along with the main Planet Hunters website and classification interface being completely rebuilt, we are now pairing the main Planet Hunters website with the latest version of the Zooniverse’s Talk discussion tool. Now when you go to http://talk.planethunters.org it will take you to Planet Hunters Talk 2.0. In this blog, I’ll give you a brief overview and introduction to the new features added into Planet Hunters Talk.
What happened to the original Planet Hunters Talk?
Before I introduce the new features of Planet Hunters Talk 2.0, I wanted to give an update of what happened to the original Planet Hunters Talk. The original Planet Hunters talk is still online at http://oldtalk.planethunters.org, and you’ll find a link to it on the navigation bar of the New Talk. The original Talk is a repository of discussions and discoveries, and we’re not taking it offline or shutting it down. You can still log in and post there. The differences in how stars are treated between the two versions and the sheer volume of interconnected discussions and comments makes it very difficult and time consuming to attempt to migrate that content to Talk 2.0. There’s a very real chance we could do this incorrectly, so we thought the safest option was to leave the original Planet Hunters Talk online as resource and with all light curves shown from Planet Hunters 2.0 going to the new Talk.
Starcentric versus light curve chunk-centric
There are a few key differences between new Planet Hunters Talk and the original version. Firstly how we treat the stars is different. On the original Planet Hunters Talk, we treated each 30-day light curve section shown in the classification interface as a different entry in Talk with its own page, where people could leave 140 character comments and start side conversations. So a single star would have many discussions spread across different light curve Talk pages with no easy way to tell that someone had posted a comment about a different quarter. In the new version of Talk, we give each star a Talk page (with the APH ID representing the Planet Hunters ID for the star) so comments and conversations are grouped together from people who see the different light curves chunks from the star.
Overview of Planet Hunters Talk 2.0
Talk Subject Page
Below is an example of a Talk page for star APH0000622 (http://talk.planethunters.org/#/subjects/APH0000622). Here you’ll be presented with a light curve viewer for the star with all available quarters of Kepler data for this star to peruse through (if you enter this page from the main classification interface the light curve chunk you reviewed in the classification interface will be automatically loaded in the light curve window). Later in the future, we plan to add scrolling and zooming capability to the light curve viewer. In addition we list the Kepler id for the star, and any other information we have for the star (like radius and temperature) and some useful links which we’ll describe in more detail in another blog post.Like original Talk, you can make collections, write 140 character comments, add hashtags, and have longer side discussions about the star and the light curve you reviewed.
Just like old Talk, if you have more to say than 140 characters there’s the ability in New Talk to start and have longer side discussions about the star. The difference is that now you have to select which topic, Help, Science or Chat your discussion will be about it and then click on the Post button to start the discussion. this is because the discussion is also linked and archived for easy access on the Discussion Boards (more about this in the next section).
New Talk has discussion boards (which you can navigate to with the top bar by clicking on Discussion Boards) like original Talk in three categories: Help, Science, and Chat. The main difference is there are now subboards under each of these three headings where you can post and start discussion threads.
You’ll notice that each of the three board categories has an ‘The Objects’ subboard. This is where you can also access the side discussions you make on the star Talk pages. They get linked and archived here for so they’re easy to find by the Planet Hunters community and the science team. In the old version of Talk a side discussions were often buried and hard to get to. Now you can quickly check out each ‘The Objects” board and see what longer discussions people were having about a given star.
Front Page/Recent Page
The font page of Talk accessible when you go directly to http://talk.planethunters.org ( or by clicking on the Recent tab in Talk) lists the most recent 140 character comments made on Talk as well as displays the latest comments in the discussion board threads for easy access. By clicking on the comment, you’ll get taken to the Talk page for the given star. By clicking on the discussion board post, will take you to directly to that thread.
You can either go directly to the Talk website by url – http://talk.planethunters.org or you can access Talk through the main Planet Hunters classification interface. Once your classification for a light curve is submitted in the main interface, a summary page appears (see below). Here you can directly write a 140 character comment about the light curve you saw (that will appear on the star’s Talk page) without leaving the classification interface. If you click ‘Discuss on Talk’ you’ll be brought to the Talk page for the star with the light curve chunk you reviewed queued up in the light curve viewer.
Direct/private messages on New Talk are a little different that has been done in the past for Planet Hunters. You won’t get an email when someone sends you a private message, instead the envelope icon on the top right of the navigation bar (by the return to classifying button) will tell if you have any unread messages. If you have an new unread message, the envelope will brighten and the number of unread messages will be listed. Clicking on the envelope or the Profile tab will take you to your list of messages.
More Features and Upgrades to Come
We wanted to get to the new interface out to you as fast as we could so that we’ll be ready for the K2 data which we’re currently processing and placing in a format the new interface can read in. There are some small finishing touches the Zooniverse developers will be adding in the coming days to new Planet Hunters Talk. Thanks for your patience as we go through these small growing pains with the project. If you have suggestions of features you would like to see in Talk, please post your ideas in this thread, and we’ll try our best to accommodate those requests.
Need Help? Ask the Planet Hunters Talk Moderators
The Planet Hunters Talk moderators (TonyJHoffman, constovich, and echo-lily-mai) are standing by ready and willing to help. So if you’ve got a question about the new Planet Hunters or Talk don’t hesitate to ask them.
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?
By Joey Schmitt (Planet Hunter team)
Planet Hunters will soon start work on a new, important question in the field of exoplanets: how common are planets around other stars? This question has become a hot topic in exoplanets, but Planet Hunters has one major, unique advantage. Planet Hunters are sensitive to planets with just one or two transits. The automated computer algorithms require three or more transits; otherwise, they would be overloaded with spurious signals. This allows Planet Hunters to explore much longer periods than the rest of the field.
Until now, Planet Hunters have been looking for planets one quarter at a time. This has been successful in discovering more than 60 new planet candidates and two new confirmed planets (and counting). However, this one-quarter-at-a-time method doesn’t let us figure out how common planets truly are.
Planet Hunters will be moving from this quarter-focused method to a star-focused method with Planet Hunters 2.0. Instead of showing a few quarters of data for all Kepler stars, we will be showing all quarters of data for some stars. This will allow us to determine how common planets really are around these stars. (But don’t worry. Whenever we get a download of fresh data from the new K2 mission, these new light curves will take priority.)
The Planet Hunters team has decided to first show all the light curves for all the red dwarf stars. These stars are much smaller than the Sun, live for tens of billions of years or more, and have habitable zones very close to the star. They’re the best chance to find habitable, Earth-like worlds. Red dwarfs are also the most common type of star in the universe, making up about 70% of all stars. Kepler has only observed about 4,000 red dwarfs consistently, so we hope to finish this project over the course of just a few months (but keep in mind that the peer-review process can take longer). If we’re successful, we will do the same thing for the tens of thousands of Sun-like stars.
The biggest challenge in exoplanet statistics is to know how many planets we’re missing. However, we can actually figure this out by creating “synthetic data”. To non-scientists, this might sound like nonsense, but this is an extremely important tool that scientists use all the time. We must “inject” synthetic transits of planets of various sizes and periods into real light curves and let the Planet Hunters users classify them. This allows us to know how effective we are at finding these planets and correct for how many we’re missing.
For example, if Planet Hunter volunteers detect 50 of 100 synthetic Earth-size planets at a period of 300 days, then we know that if we detect 5 true Earth-like, 300-day planets, there are actually about 10 of them. Unfortunately, in order to correct (with any sort of scientific certainty) for the number of planets that we all may miss, we must inject a large number of synthetic planets into the real data.
This project will roll out with the release of our new site. The Planet Hunters team is excited about this new project and wants you to know that you will be helping answer one of the most important questions in astronomy: how common are planets in the Milky Way?
Yesterday marks the start of a new era for the Kepler spacecraft with the public release of the first observations from K2, the two-wheeled Kepler mission.
After four years of staring at the same field and the failure of 2 reaction wheels on the Kepler spacecraft, Kepler is now observing ever changing fields on the ecliptic, plane of the Solar System, for periods of ~75 days. From March to May of this year, Kepler stared at the same patch of sky monitoring stars nearly continuously for planet transits, supernovae, among other reasons. You can find more details about Campaign 0 here and the K2 mission here. Now there’s a new set of stars never before looked at, that may be harboring unknown and undiscovered planets. The Planet Hunters science team and Zooniverse team are working hard to getting the K2 data prepared and ready for showing on the Planet Hunters website.
There are some new challenges to overcome in order to get the K2 data ready, but we’re working on making it possible in the near future to view K2 data Thanks to funding from JPL PlanetQuest, we’ve been able to rebuild the Planet Hunters website to make Planet Hunters 2.0. These past many months the Zooniverse development team and the science team have been working to make Planet Hunters 2 easier to use as well as faster and more efficient for searching for exoplanet transits in Kepler field data and especially with the K2 mission in mind. We’ve incorporated much of the feedback we’ve gotten from you over the past 3 years into the rebuild. The site is not quite ready from prime time, but will be very soon. Stay tuned to this space for more updates on Planet Hunters 2 and the K2 data. In the meantime if you have questions about the rebuild we’ll try to answer them on Talk here.