Planet Occurrence Rates

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?

Coming soon…..

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.

PH2_frontpage

A sneek peak of the new Planet Hunters front page

 

Naming Exoplanets

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)

The Kepler in TESS

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.

Expected TESS sky coverage from Ricker et al. (2014)

 

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.

TESS_full_frame_simulation

Simulation of a portion of a TESS full frame engineering image – Image credit: TESS Team take from George Ricker’s January 2014 NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG) presentation

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.

Your Chance to Feature Planet Hunters on the Daily Zooniverse

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 :

Image Credit: Sean63/Planet Hunters  http://talk.planethunters.org/discussions/DPH100suo7?page=54&per_page=10

Image Credit: Sean63/Planet Hunters

Studying the Chemistry in Protoplanetary Disks (Part 2)

Today we have a guest post from Colette Salyk. Colette is the Leo Goldberg Postdoctoral Fellow at the National Optical Astronomy Observatory in Tucson, Arizona. She studies the evolution and chemistry of protoplanetary disks (the birthplace of planets) using a variety of ground and space-based telescopes.

Welcome to Part II of my three-part post about studying the chemistry in protoplanetary disks!  (You can find Part I here.) In the last post I talked about techniques for detecting molecules. But once we detect them, what do we do with these detections? Ultimately, we want to make chemical “maps” of the protoplanetary disks, so we can understand what kinds of environments planets are forming in at different distances from their host star. In this post I’ll explain how we use the Doppler shift (yet again!) plus Kepler’s law to locate molecules in protoplanetary disks. (In Part III, I’ll discuss some of the connections between disk chemistry and the formation of planets.)
In the figure below, I’ve reproduced the observed water emission line that I discussed in my first post, but have converted wavelength to velocity using the Doppler shift equation, (λ−λ0)/λ0 = v/c , and centered the line at zero velocity. Note that in the first post, I focused on the shift of the entire line relative to the theoretical line center; here I am repositioning the line to account for this new center, and we’ll be discussing Doppler shifts relative to this new center.
emission_plotAlthough molecules emit/absorb at very specific wavelengths, the water vapor emission line we observed is clearly not thin and pointy. Instead, it has a rounded shape — something we refer to as “line broadening.” This broadening occurs for all spectra, due to two reasons. One reason is that the instrument optics always blur out the signal somewhat — this is called the “instrument response function.” The other reason is that the molecules themselves are always moving, and the motion of each molecule produces a Doppler shift. Collectively, they produce emission at a range of wavelengths. In our case, the instrument response function (plotted in the figure) is much narrower than our line. Therefore, the broadening is dominated by the motion of the molecules.

The molecules are moving around due to a variety of reasons, including bouncing around due to their temperature, being kicked around by turbulence, and being in orbit around the star. The last effect dominates in our case, and I’m going to focus on that motion in this post. A simple example that may help you picture how orbital motion broadens the emission line is to consider a thin ring of molecules orbiting a star, oriented edge-on to our view. The molecules on one side of the star are moving away from us, and are redshifted; the molecules on the other side are moving towards us and are blueshifted. The amount of Doppler shift also depends on the orientation of the motion — as we examine parts of the ring that appear “closer” to the star from our point of view, we see progressively more transerve motion, and progressively less radial (and therefore Doppler shift-producing) motion. This collection of Doppler shifts turns a thin theoretical emission line into something broader, with symmetric blueshifted and redshifted components.

How fast are the molecules moving in the disk as they orbit their host star? If you’ve taken Astronomy 101, you’ve probably heard of Kepler’s laws — they are a set of relatively simple rules that dictate how the planets of the solar system orbit around the sun. Kepler’s third law relates the period (P) and semi-major axis (a) of planetary orbits, stating that P^2 ∝ a^3. Alternatively, astronomers often convert period to velocity (using v = 2πa/P), and put in the correct constants so that the law applies to stars of all masses (not just ones like the sun), to obtain: v = sqrt(GM⋆/a), where G is the gravitational constant and M⋆ is the mass of the star. This is a very powerful statement, because it means that we can directly relate velocity (v) to distance from the star (a). Since we can use the Doppler shift to measure velocity, we can therefore use the line broadening to measure the location of the molecules.

In contrast to the simple ring example I gave above, real emission lines originate from a range of disk radii, and the amount of light emitted at each radius also depends on the temperature and density of molecules. Also, the line width depends on how inclined the disk is with respect to our view. The figure below shows example emission lines originating from a disk where I’ve assumed the molecules are located between two radii, Rin and Rout, and that the disk is inclined by 30°. Have a look at the plots to see how the line shape depends on both Rin and Rout.

model_plotWhat I find especially cool about this technique is that it works especially well when the molecules are at small radii. For example, it’s really easy to tell the difference between molecules located at 0.1 AU vs. molecules located at 1 AU! It’s not currently possible to obtain this kind of detailed spatial information through imaging alone, and so we sometimes say that we’re achieving “super-resolution”. I think this is a neat parallel to the Kepler mission, in which the transit observations are used to obtain detailed information about the sizes and orbital radii of planets, even though we cannot directly image the planets.

Now some questions for you. Have a look at the detected water emission line in the first figure. Assuming this disk is inclined by 30°, as I assumed in my models, where do you think the molecules are located in this disk?

Latest Science Paper Accepted for Publication: The First Kepler Seven Planet Candidate System and 13 Other Planet Candidates from the Kepler Archival Data

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 at Planet Hunters are happy to announce the acceptance of the PHVI paper to the Astronomical Journal, in which 14 new planet candidates were discovered. All of these new planet candidates are located far from their host stars. In fact, seven of them lie in their host star’s habitable zone. Unfortunately, all of these planets are too large to be Earth-like.

Two of the new planet candidates are in multiple candidate systems. One of them, the new candidate orbiting KOI-351, is the seventh planet candidate orbiting its host star. Planet Hunters actually detected three new candidates around this star when KOI-351 was only known to have three candidates, showing how great the Planet Hunters can be in discovering multiple planet systems. The planets in KOI-351 also show strong gravitational interactions between the planets, which helps to confirm them as true planets. The gravity from some planets in the system causes other planets to transit before or after what we would otherwise expect, called transit timing variations. In fact, the second-to-last planet transited a full day after we expected it would. Others in the exoplanet field have been working for over a year to determine the masses of these planets.

The new candidate in KOI-351 makes it the only star with seven known transiting planets. After our submission in October, two other teams claimed confirmation of the seven signals to various levels of certainty. Look forward to the brand new stars in the K2 campaign, changes to the Planet Hunters strategy, and new papers of the latest planets and candidates discovered by Planet Hunters.

You can read the revised accepted version of the paper here. The Planet Hunters volunteers who participated in identifying and analyzing the candidates presented in this paper are acknowledged  at http://www.planethunters.org/PH6, and the contributions of the entire Planet Hunters community are individually acknowledged at http://www.planethunters.org/authors.

K2 keeps on rolling – the start of Campaign 1 observations

NASA has recently approved funding for the two-wheeled Kepler mission dubbed ‘K2.’ Field 0 was an engineering field that Kepler started monitoring before the senior review decision. The data will be science quality with Kepler monitoring about ~8000 sources, which includes open cluster M35. Observations started on March 8th and were recently completed on May 30th. You can see the proposals astronomers put in requesting targets for Kepler to monitor and the final selected target list here.

With the Senior Review decision and the funding, the K2 mission officially starts with observations of Campaign 1. On May 30th, Field 1 observations officially commenced and should last for roughly 75 days. You can find out which targets Kepler is observing in Field 1 here.

The engineering data of Field 0 should now have been downloaded to the ground and is likely  undergoing processing at NASA. The preliminary data products should be ready hopefully sometime in August. With new stars there will be chances to find new undiscovered planets. The  Planet Hunters team and Zooniverse team are working on ways to have the data ready and accessible on the website soon after it is released by NASA and the Kepler team to the astronomical community and the public. Stay tuned to the blog as we get closer to August.

Credit: ESO/S. Brunier/NASA Kepler Mission/Wendy Stenzel.

Credit: ESO/S. Brunier/NASA Kepler Mission/Wendy Stenzel.

Exploring Planetary Dynamics with Super Planet Crash

Today we have a guest post from Stefano Meschiari. Stefano is a postdoctoral researcher at the University of Texas at Austin. He works on planet formation in binary environments and planet detection through radial velocities and transits. He developed the Systemic software as a tool for scientists and citizens to analyze radial velocity data, and he is also the creator of Super Planet Crash. His hobbies include cooking, clumsy puppeteering and all things pop culture. You can read more about his research here. Today he’s going to tell us a bit more about Super Planet Crash

Screen Shot 2014-04-07 at 11.25.49 AM

Since Newton’s law became the accepted model for gravitation, physicists, mathematicians and astronomers have been preoccupied with a simple question: is the Solar System stable? Planets weakly perturb each other through gravity, and over time, these perturbation can add up in an unpredictable (chaotic) way. This can even result in planets colliding or being expelled from the system. For exoplanetary systems, a common criterion to validate a set of orbital parameters is to check that the system is stable on scales of billions of years — if the system is unstable, we would not be observing it today!

Super Planet Crash is a simple online game that lets you design exoplanetary systems and drive them to instability. It is a digital orrery that evolves a planetary system according to Newton’s law of gravity in your browser. You can add up to 12 bodies of preset mass in initially circular orbits. Your score is calculated based on how close your system is to instability — more massive planets will yield more points, but your system may go unstable more quickly! It’s a delicate balancing act.

Design your exoplanetary system and watch it go BOOM at http://www.stefanom.org/spc.

Welcome to the Era of K2

k2_graphic_sm_0

Image Credit: NASA Ames/ W Stenzel

Last August, I wrote about the end of Kepler’s original mission as it had been operating for the past 4 years. Kepler was launched in 2009 with a goal for providing a census for planets around Sun-like stars and helping us understand the frequencies of rocky planets. Kepler stared at the same field monitoring 160,000 stars nearly continuously for those 4 years. To achieve the precision pointing to obtain precise enough measurements to detect rocky terrestrial planets, Kepler had to point with extreme precision with the stars moving very little on the camera. To do this Kepler had three reaction wheels (and one spare) that would help nudge the spacecraft slightly one way or another. Last year, Kepler suffered a second reaction wheel failure that prevents it from continuing with its mission of monitoring the Kepler field. Pointing at the Kepler field, the spacecraft moves too much, and this effectively ended the Kepler mission as is. Kepler had taken its last observations of the Kepler field.

The  Kepler team devised a new way of observing with Kepler using solar irradiation to help stabilize the spacecraft and act as the third reaction wheel. They set out to test it and prove this was a viable mission (which they dubbed ‘K2‘) that would return interesting science and discoveries worthy of NASA funding. Back in December, NASA gave the go ahead for K2  to compete with other viable missions in the Senior Review. Well, what is this Senior Review? Space missions cost money. You have to pay for the engineers that keep the spacecraft happy and running, pay the project managers and support staff and scientists, have funds if there are guest observer programs, as well as it costs money to use time on the Deep Space Network to send commands to and receive the data from your favorite telescope. The NASA Senior Review is NASA’s way of prioritizing and deciding which already existing  missions will continue on and receive funding from the limited amount of funds available to spend while building and launching new spacecraft. Ben Montet from Astrobites has a nice summary description of the competing missions from this year’s Senior Review.  Funding is tight and although these missions and spacecraft have all produced interesting science and capable of continuing to do that, not every mission that was on the chopping block is guaranteed to get money to pay for its operating costs. There simply isn’t enough to go around.

Officially today, NASA has announced the results from the Senior Review. You can read the full report from the panel here and the response from NASA. The verdict from the panel for Kepler/K2: “This is an outstanding mission and we look forward to the results from the program. K2 uniquely addresses a range of observational goals and is expected to engage a broad community of scientists.” K2 has been recommended by the review to continue with the extended K2 mission, and NASA has agreed to provide funding.  The Kepler team didn’t get all the money they asked for, but 90% of the requested budget more than enough for the K2 mission to officially start science operations in June. K2 is a go! There will be new light curves from never before seen stars coming from Kepler over the next 2 years!

Congratulations to everyone involved in the Kepler project who made this happen. They put in lots of tireless effort to find a way to use Kepler in a novel observing scheme and prove that it could deliver interesting science worthy of continuing on. The Senior Review specifically about the science goals and case for K2: “K2 will allow exoplanet surveys of all stellar classes,O-M, giants-dwarfs, and white dwarfs as well as the asteroseismology of late stars, studies of nearby open clusters for the fundamental properties of pre-main sequence (PMS) and zero age main sequence (ZAMS) stars, and explore supernovae and accretion physics in AGNs. These are but a small sample of what can be achieved with the study of precise photometric long term continuous data .

This is exciting times for the study of extrasolar planets, as Kepler is now primed to deliver a whole new  crop of planets and other astrophysical discoveries and results. The Planet Hunters science team and the Zooniverse are working on preparing the site to be able to ingest and serve the K2 data to you all in a fast and efficient way.  Stay tuned to this space as we get closer to August when the first science grade K2 data is released.

You can learn more about the K2 mission at http://keplerscience.arc.nasa.gov/K2/

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