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.
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?
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.
With next year being the 20th anniversary of the discovery of the first planet orbiting a main-sequence star outside our Solar System, it’s exciting to think that the official naming of extrasolar planets (exoplanets) and their host stars is becoming a reality.
The International Astronomical Union’s (IAU) Exoplanets for the Public Working Group, which includes astronomers Alain Lecavelier des Etangs, Chris Lintott (Zooniverse founder and PI ), Geoff Marcy, Andrew Cameron, Eric Mamajek, and Didier Queloz, have come up with a process approved by the IAU that will be implemented to allow the public to join in the naming of these distant worlds. The first set of 20-30 exoplanets and their host stars will be formally bestowed names in July 2015, just months before the October anniversary of 51 Pegasi b’s discovery.
Back in July the IAU announced the naming process and how the public will take center stage. Here’s a brief overview of what will happen over the next year. In September astronomy clubs and astronomy-related non-profit organizations will be able to register to take part in the naming process. These groups in October-December 2014 will vote to pick the first set of 20-30 exoplanets to be named from a list of 305 planets discovered before December 31, 2008. Then in December 2014, these clubs, groups, and organizations will submit naming proposals for the planetary systems (both the planets in them and the host star). Valid proposals will then be subject to a public vote in March of 2015. Anyone can vote at that point, and the most popular name will be bestowed as the formal name during the IAU General Assembly meeting in August 2015 in Honolulu, Hawaii. Like named minor planets in our Solar System, these exoplanets will still keep their license plate identifiers (like GJ 436 b) given at discovery as alternate designators , but their formal names will be the ones from the public vote.
One day in the future PH1b and PH2b will likely be offered a similar opportunity to be named. I fully expect when that happens that the Planet Hunters community will submit a proposal for their names. At this point, the Planet Hunters science team is fairly confident that Planet Hunters counts as an online non-profit astronomy organization and will be able to take part in voting on which systems should be named and submitting a naming proposal. Watch this space over the coming months for updates and further news as the IAU naming process gets underway.
You can learn more on the specifics and the rules and regulations of the exoplanet naming process at the IAU and Zooniverse’s NameExoWorlds website: http://www.nameexoworlds.org
(Full disclosure- I’m on the science teams for two astronomy/planetary science-based Zooniverse projects. I’m not involved in any way with creation or implementation of this IAU initiative, but I work with collaborators who are)
By the end of September, the first science grade K2 observations from Campaign 0 should be made available to the astronomical community and the public. Stayed tuned to this space for updates on the data release and how we’re making Planet Hunters ready to accommodate the K2 observations. While we eagerly await the public release of the first full science grade data from K2, I’ve been thinking about how K2 serves as a stepping stone to TESS, which is expected to launch in 3 years from now.
Over its 2 year mission, TESS is going to monitor ~200,000 of the brightest stars across the sky for the signs of exoplanet transits by taking measurements of the stars’ brightness every 2 minutes. Most of these stars will be observed for only 27 days in total (though some patches of sky will be observed longer – see the expected sky coverage plot below) , but the worlds discovered around these bright stars, unlike most of the Kepler planet candidates and confirmed planets, will be able to be followed-up using ground-based techniques and technology as well as from the space-based James Webb Space Telescope (JWST). This will enable astronomers to probe the composition and structure of these planets’ atmospheres as well as their bulk composition.
One thing that I hadn’t appreciated from TESS was the engineering images it will take in addition to the 2 minute light curves. TESS will target a small number of bright stars at a 2 minute cadence, but every 30 minutes TESS will take the equivalent of a full frame engineering image across its roughly 2000 square degree field-of-view. These means we basically get the equivalent of Kepler observations but with blurrier vision (Kepler had pixels that covered 4 arcseconds per pixel. TESS’s are much larger covering 21 arcseconds) and 20x more area. Below is a simulation generated of what a subsection of one of these engineering images might look like from a presentation by TESS principal investigator George Ricker at NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG) meeting back in January.
We know from Kepler that it is possible to detect a plethora of exoplanet transits with 30 minute observations, so there is an exciting prospect of mining the engineering images. With the science that has already been done with Kepler both in the field of exoplanets and other astrophysics, the TESS engineering images will no doubt be a treasure trove of data waiting to be tapped into.Before Kepler the only star that had been monitored to such precision and cadence was the Sun. Kepler has changed that, but TESS will take it to the next level. With the Kepler-like quality of the engineering data, it means that if you don’t like the stars the TESS team decided to target, anyone can do an exoplanet search on other stars in the TESS field among other searches and studies like looking for supernovae or cataclysmic variables. There is a wealth of science to be mined out of the TESS full frame images, and I think there is a potential for citizen science (and likely Planet Hunters) to play a role in utilizing these observations to their fullest.
If you’re interested in learning more about the TESS spacecraft , camera design, and mission goals you can check out this paper by the TESS Team which is where I got the information for this post.
Each day something new from across all the Zooniverse projects is featured on the Daily Zooniverse blog organized by the Zooniverse’s Grant Miller. Have you classified a weird light curve or participated in an interesting discussion on Talk? Now’s the chance to have that highlighted on the Daily Zooniverse. Grant and the Daily Zoonvierse team are looking for contributions from the volunteers of Zooniverse projects (including Planet Hunters) to feature. Just add the hashtag #dailyzoo to a light curve or discussion page on Talk to nominate it.
If you want to also share your nominations with the rest of the Planet Hunters community, there is a thread started on Talk where you can can list your finds for everyone to see (do make sure to include the hashtag). If you’re looking for inspiration Echo-lily-mai, one of our Planet Hunters Talk moderators, has nominated this folded light curve plot of a candidate heartbeat star made by volunteer Sean63 :