Science and Progress: Short Period Planets in Q1
Chris Lintott (Zookeeper Chris) and I wanted to give an update on what the team is working on and some of the changes made to the PH site to help us answer the question we are tackling right now. We used very simple cuts and visual inspection to come up with a preliminary list of planet candidates that John has discussed in an earlier post. We’ve been brainstorming on how to combine the results from all the multiple user classifications (about 10 users looking at each lightcurve) to tease out every transit in the database of over 2.0 million classifications. We are working hard on more sophisticated algorithms and techniques to take all your Q1 classifications and transit boxes and extract transits and planet candidates.
After starting to look at your classifications and results from the simulated transits, Chris and I think an interesting question to look at is what are the abundances of planets on short period orbits (less than 15 days ) in the Q1 data. The Kepler team is doing something similar and it will be very interesting to compare the two results. As an initial step we are only looking at planets bigger than 2 Earth radii so only gas and ice giants because the transits are more pronounced than the smaller rocky planets. Less than 2 Earth radii will be much harder to detect, so we first we want to develop the analysis tools and then we’ll come back to the less than 2 Earth radii planets later.
With just the transit discoveries alone we can’t answer this question. This is because we don’t know how complete the sample is. If we found 120 Neptune-sized planets for example, we can’t say anything about their abundance compared to Jupiter-sized planets, since we don’t know how many we might have missed in the data set. This is where the synthetic transits we insert into the interface play an important role. If users flag 100% of the Jupiter-sized simulations with orbital periods shorter than 15 days, but only 50% of the Neptune-sized synthetic transits, then we know that the number of transiting Neptunes in the real light curves is a factor of two larger than what we found. With this completeness estimate we can debias our sample and begin to understand the spectrum of solar systems providing crucial context for own solar system.
We find that we need higher numbers and finer resolution in period and radii for the synthetic lightcurves to do this analysis. Starting today, mixed in with the Q2 data, we will be showing newly generated synthetic Q1 lightcurves specifically made for this task. As always with the simulated transits ,we will identify the simulated transit points in red after you’ve classified the star and will mark the lightcurve as simulated data in Talk . With the results from these synthetics we can better tweak our analysis tools for extracting transits from your classifications as well as get sufficient numbers to calculate the short period planet detection efficiency for Planet Hunters. The new synthetics won’t be the only non-Q2 lightcurves you see. We also have about 5800 additional lightcurves from Q1 that were released by the Kepler team on Feb 1st,. Now that the Q2 data upload is complete, these have now been introduced into the database and we’ll be showing these mixed in the classify interface as well as a small subset of the Q1 data previously looked at to examine how classifications have changed over time since December.
Chris and I have are aiming to have the bulk of the analysis complete before October, so we can present the results at the joint meeting of the European Planetary Science Congress (EPSC) and the American Astronomical Society Division for Planetary Sciences (DPS) meeting being held in Nantes, France, in October. We will keep you posted on our progress and results as time goes on. Abstracts are due in May, and so we need to start work now to be able to have results for the Nantes meeting. With your help, we think this will lead to a very interesting paper.
Cheers,
Q2 Data now fully online!
Hi all –
The Q2 data (chopped up into Q2.1, Q2.2 and Q2.3) are now fully online. Since these data cover a much longer time frame than just the Q1 data, we can now start looking for planets with longer periods. If you spot a single transit in a light curve that you think looks good, why not check all the other data (bot Q1 and Q2) for similar transits; it may be a long period planet.
Why is this so interesting? A planet around a star like our sun that is far enough away not to be fried by the star takes about one year to go around the star once. So you’d see one transit every year. Like our own earth. Around a dimmer star than our sun, the habitable zone is closer in, but still long. So happy hunting, especially for long period transits!
A word from the Kepler Team
Dear Planet Hunters: Dr. Natalie Batalha, Deputy Science Team Lead for the Kepler Mission, asked us to post the following message:
Welcome! We are so glad you’re here!
I’m sure I speak for the entire Kepler team when I say how happy we are that Zooniverse is being applied to the Kepler data. For some time now, I’ve watched the public actively work with archived data from other missions. The folks at Unmanned Spaceflight, for example, regularly share the latest images they’ve doctored up from Solar System missions like MER and Cassini. And the SOHO mission recently hit a milestone, discovering its 2000th comet on December 26th, 2010. The discoverer was not part of any formal SOHO science team but rather an astronomy student at Jagiellonian University in Krakow, Poland. I’ve added “Citizen Scientist” to my urban dictionary and appreciate its tremendous potential.
That’s all well and fine when it comes to Martian landscapes, comets, and sunlight glinting off the surface of methane lakes millions of miles away. But how in the world could we entice the public to look at boring old lightcurves? PlanetHunters.org has done exactly that. Not only are thousands of people looking at light curves, they are getting just as hooked on their variety as we are! Welcome to the ranks of those who love light curves.
The Kepler spacecraft is a new piece of technology. Never before have humans stared at stars with such unwavering precision and patience. And whenever humanity does something new, there are sure to be surprises. One of the biggest surprises to me so far is the impact that Kepler is having on stellar astrophysics. Who knew, for example, that a star like RR Lyrae — one of the brightest and well-studied objects in the sky — would blow the dust off textbooks written on this class of star? Who knew we’d see such a symphony of variability occurring just below the noise levels typical of ground-based telescopes?
But the name of the game here is planet hunting. I’ve heard people wonder why they should bother to hunt for planets when the Kepler team has spent years designing savvy computer algorithms to do exactly that — algorithms that can tease signals out of the noise that the human eyes cannot even see. The answer is simple.
Kepler relies, in large part, on automation. We are a relatively small team. There are currently less than 15 scientists working in the Kepler Science Office here at Ames. In the early days, there were only 5 of us! Let’s say we divided up the 150,000 stars we are monitoring amongst the 15 scientists at Ames. We’d each be responsible for 10,000 stars. If we spent only 60 seconds looking at each star, it’d take us over 160 hours to finish out allotment. That’s a solid month of doing nothing else but looking at light curves. Just in time since more data comes down from the spacecraft each month and the process would have to start all over again. Such a plan would never have earned taxpayer dollars. We need our scientists doing other things — like monitoring the instrument and optimizing the software and vetting out the false positives and interpreting the results. And so we write computer software that combs through the data searching for transit-like features.
It’s a challenge to design a one-size-fits-all approach to transit detection. The transit are buried in the light curves of stars with widely different properties and behaviors. You’d build one kind of tool for finding a needle in a haystack but a different kind of tool for finding a needle in a swamp. We don’t even yet know what all the possibilities are because we’ve never looked at stars with this kind of precision.
Another consideration is that the software pipeline requires 3 transits for complete modeling and pipeline generation of they key statistics that are used to vet out the false positives — astrophysical signals masquerading as planet transits. It’s certainly true that we’ve gone back and cherry-picked some of the more compelling light curves displaying less than 3 transits — especially those of the brightest stars. However, many such signals are still lurking in the archive.
So what else did our algorithms miss? Ah, let’s find out, shall we? We’re here with you, ready to help. Come stand here in the crow’s nest and experience the thrill of discovery with us. We welcome your keen eyes!
A huge thank you to the folks at planethunters.org for putting this together.
Natalie Batalha
Deputy Science Team Lead
Kepler Mission
Transits (examples)
The Kepler team recently announced the detection of five stars, each with multiple transiting planets (Steffen et al, 2010). The left Figure below shows the Quarter 1 (Q1) light curve for the star SPH10102031 (Kepler ID 10723750) with two transit dips from two different planets. The transits do not repeat because the orbital periods are longer than the time baseline. The first transit dip is from a planet that is about the size of Jupiter. To highlight the typical boxy shape of a planet transit curve, we have zoomed in on the second transit event in the Figure below and on the right. The depth of the transit is about 0.25% and given the assumed radius of the star, the planet radius is about 7.6 times the radius of the Earth (larger than Neptune, but smaller than Jupiter).
Light curves for two other stars in the Steffen et al 2010 paper are shown below. The Figure on the left is the Q1 light curve for SPH10120491 (Kepler ID 8394721). This light curve contains transit dips from three different planets! One of these is very obvious and is caused by a planet that is 6.5 times the radius of Earth that only transits once during the 35-day light curve. However, there are two other transiting planets that are harder to see with radii of just a few times that of the Earth. One of these planets transits every 13.5 days and the other transits every 27.4 days.
The Figure above and to the right shows the light curve for SPH10017624 (Kepler 5972334). There are three transit dips from a Jupiter-sized planet that orbits every 15.4 days. In this Figure, it is virtually impossible to see the second planet, which has a radius just twice that of the Earth and transits every 2.4 days.
To get a better look and some practice (you won’t be able to save these), pull up these amazing light curves and use the zoom tool to identify the transits.
Eclipsing binaries vs transits
It’s Christmas Eve and I’m starting a five-night observing run at the Keck Telescope using a high-resolution spectrograph (HIRES) to search for exoplanets. In the photo here, I am communicating with the telescope operator, Terry, by polycom. He is on the summit of Mauna Kea at 14,000 ft where the air is thin and I see that he has oxygen flowing. I’m glad that I’m working in comfort at Keck HQ in Waimea.
Tonight, I’m using the Doppler technique to measure the velocities of stars. Orbiting planets tug their host stars around a common center of mass. This reflex stellar velocity is largest for massive planets.
When small stars eclipse larger stars, the brightness dip can be virtually the same as those for transiting gas giant planets. To confirm a transit candidate as a planet, Doppler measurements are needed to determine the mass of the transiting object. The Kepler team has a massive follow-up campaign (led by Dr. Geoff Marcy at UC Berkeley) using the same setup that I’m using now. Dr. Natalie Batalha (Deputy Scientist for the Kepler project) explains that the team is also eager to have others helping and to have Planet Hunters combing through the data. Watch for a blog post by Dr. Batalha here soon!
Some of you have asked how many consecutive low points you should see during a transit. That depends on how close the planet is to the star. Close planets orbit faster and transit in a few hours while more distant planets take several hours to transit. You should look for more than one low point. Since the brightness measurements are taken every 30 minutes, a 3 hour transit would consist of just 6 low points. However the ingress, or first transit point, might be transitional and not reach the transit floor. Ditto for the egress, or last transit point).
The light curves for eclipsing binary stars are quite spectacular – they remind me of sketches I used to make with a “spirograph” toy I had as a kid. Some of the planet hunters have called this a shutter effect and I’ve written a quick program to demonstrate what is happening. In the Figure below, I created a theoretical light curve for a contact eclipsing binary with an orbital period of just 6 hours. If we had observations of this star every few minutes, then the light curve would look similar to a sine wave (left plot). However, if we observe this star less frequently (a slow “shutter speed”), then some interesting patterns emerge. The plot on the right in the Figure below shows an under-sampling of the light curve over 30 days. The pattern is similar to what appears in some of the eclipsing binary curves you are finding in the Kepler data.
Planety w tranzycie
Cześć, mam na imię Matt i jestem doktorantem na Uniwersytecie Yale oraz członkiem Zespołu Naukowego. Jesteśmy pod ogromnym wrażeniem dotychczasowego ruchu na planethunters.org. Niektórym użytkownikom już udało się zauważyć naprawdę niezwykłe obiekty! Ponieważ kilka osób prosiło o dodatkowe wyjaśnienia dotyczące wyglądu tranzytów, w tym poście postaram się rozwiać Wasze wątpliwości.
Zdjęcie powyżej przedstawia krzywą blasku gwiazdy zbliżonej rozmiarem do naszego Słońca. Na wykresie dokonaliśmy symulacji efektów, które zostałyby wywołałane przez tranzyty różnych typów planet.
Białe kropki oznaczają ilość światła gwiazdy, jaką rejestruje teleskop Keplera, kiedy nie dochodzi do żadnych tranzytów. Niebieskie kropki pokazują, jak wyglądałby wykres w przypadku tranzytu planety wielkości Jowisza. Ta konkretna planeta, o wielkości ok. 11,2 razy większej od Ziemi i ok. 10 razy mniejszej od gwiazdy, pokazana jest (z zachowaniem skali) w niebieskiej ramce po lewej.
Zielone kropki pokazują, jak wyglądałby na wykresie tranzyt planety wielkości Neptuna. Ponieważ planeta ta jest znacznie bardziej oddalona od gwiazdy niż Jowisz, miałaby mniejszą prędkość orbitalną, a co za tym idzie, okrążenie przez nią gwiazdy trwałoby dłużej, stąd dłuższy czas – czyli większa szerokość – tranzytu na wykresie. Ponieważ Neptun jest o wiele mniejszy od Jowisza (jego promień jest 3,9 razy większy od promienia Ziemi), blokuje mniej światła, dlatego głębokość tranzytu jest mniejsza.
Oba te przypadki tranzytów są bardzo wyraźne w porównaniu do efektów, jakie miałby tranzyt planety wielkości Ziemi. Niewielki punkcik widoczny na tle gwiazdy w czerwonej ramce po prawej pokazuje, jak – w skali – wyglądałby tranzyt takiej planety. Teraz widzicie, jak trudnym zadaniem jest wykrywanie planet wielkości Ziemi! Jeśli okres orbitalny tej planety trwałby 1 rok, jak w przypadku naszej Ziemi, to spadek jasności gwiazdy podczas tranzytu wyglądałby mniej więcej tak, jak zbiór czerwonych punktów zaznaczony na wykresie. Ziemia położona jest o wiele bliżej gwiazdy, więc jej prędkość orbitalna jest o wiele większa, a długość tranzytu – o wiele krósza niż w przypadku Jowisza czy Neptuna. Ponieważ planeta wielkości Ziemi jest o wiele mniejsza od Jowisza i Neptuna, blokuje również o wiele mniej światła, tak że spadek jasności dostrzegany przez nas jest ledwie zauważalny.
Nie oczekujemy, że zauważąycie wszystkie te zdarzenia, więc nie martwcie się tym, że możecie je przegapić. Właśnie po to wprowadziliśmy do wykresów “fałszywe” planety. Są to symulacje, które pomagają nam określić skuteczność działania Planet Hunters, czyli prawdopodobieństwo wykrycia planet o różnych rozmiarach i różnych okresach orbitalnych.
Transiting Planets
Hi I’m Matt, a graduate student at Yale University and a member of the Science Team. We’re really impressed with the turnout so far on planethunters.org and users have already pointed out some really amazing objects! Quite a few people have asked for some clarification on what transits look like, so I’ll address that in this post.
In the figure above, we’ve taken a Kepler light curve from a star that’s about the same size as the Sun and have simulated what the effects would be if a few different types of planets were to transit.
The white dots show the amount of light from the star measured with Kepler with no planets transiting. The blue points show what we would see if a planet just like Jupiter orbiting this star were to transit. This Jupiter-size planet, at about 11.2 times the size of the Earth and one tenth the size of the star, is shown to scale transiting its parent star in the top left blue box.
The green dots show what a planet just like Neptune would look like transiting. Since it is much further away from the star than Jupiter, it would have a slower orbital speed so it would take longer to transit the disk of its parent star, which is what explains the longer duration, or wider width, of the transit event. With Neptune’s much smaller size than Jupiter, at 3.9 times the radius of the Earth, it doesn’t block out as much light, which is why the depth is much shallower.
Both of these events are very noticeable, compared to the effects of an Earth-size planet. The tiny speck on the star in the far right red box shows, to scale, what a transiting Earth-size planet would look like if we could see it. Now you get an idea of how difficult finding Earth-size planets is going to be! If that transiting planet had an orbital period of 1 year just like the Earth, then the dip in light observed from the parent star as the planet transits would be similar to the red points in the light curve. Since the Earth is much closer to the star, it has a much faster orbital speed, which then makes the duration of transit much shorter than the duration of either Jupiter or Neptune. Because the Earth-size planet is much smaller than either Jupiter or Neptune, it also blocks out less light making the dip in light we receive here on Earth barely discernible from no transit at all.
We don’t expect people to see these events all the time, so don’t worry about missing them. That’s why we’ve introduced fake planets into the mix. The fake, or synthetic, planets will help us determine the completeness of Planet Hunters, or how likely we are to detect planets of different sizes and with different orbital periods if they exist.
Planet Hunters Introduction
Hi, I’m Meg Schwamb a postdoctoral fellow at Yale University and member of the Planet Hunters Team. Welcome to Planet Hunters! We’ve been working hard, and we are excited to finally show you the finished product!
In the last decade, we have seen an explosion in the number of known planets orbiting stars beyond our own solar system. With ground based transit searches, stellar radial-velocity observations, and microlensing detections, over 500 extrasolar planets (exoplanets) have been discovered to date. Studying the physical and dynamical properties of each of these new worlds has revolutionized our understanding of planetary formation and the evolution of planetary systems. But we have just barely scratched the surface in understanding the diversity of planetary systems and planet formation pathways.The current inventory of known exoplanets has been limited to mostly Jupiter-sized or larger gas-rich planets, most orbiting extremely close to their parent stars. The current inventory of known exoplanets has been limited to mostly Jupiter-sized or larger gas-rich planets, most orbiting extremely close to their parent stars. While these planets have provided great insight into the formation of giant planets, beyond Mercury, Venus, Earth, and Mars, in our own solar system, little is known about the formation and prevalence of rocky terrestrial planets in the universe.
Finding Earth-size planets is a difficult task because the transit-signals, the dimming of the star’s light caused be a planet moving in front of the star, are so shallow. For a Jupiter-size planet, the transit depth is ~1% of the star’s brightness. For an Earth-size planet transiting a Sun-like star the decrease in brightness is less than .001%. Ground-based surveys have not reached the sensitivity to detect such planets around stars similar to our Sun, but with NASA’s space-based Kepler mission, launched in March 2009, astronomers are primed to start a new era in the study of exoplanets. Even with the exceptional data from the Kepler telescope, finding these Earth-sized planets will be extremely difficult, but in the age of Kepler, the first rocky planets will likely be detected including the potential to find Earth-like planets residing in the habitable zone, warm enough to harbor liquid water and potentially life on their surfaces.
NASA’s Kepler spacecraft is one of the most powerful tools in the hunt for extrasolar planets. The Kepler data set is unprecedented, both in observing cadence and in the photometric precision. Before Kepler, the only star monitored this precisely was our own Sun. The lightcurves reveal subtle variability that has never before been documented. The Kepler data set is a unique reservoir waiting to be tapped. Kepler lightcurves are now publicly available with the first data release this past June and the next release scheduled for February 2011.
The Kepler Team computers are sifting through the data, but we at Planet Hunters are betting that there will be transit signals which can only be found via the remarkable human ability for pattern recognition. Computers are only good at finding what they’ve been taught to look for. Whereas the human brain has the uncanny ability to recognize patterns and immediately pick out what is strange or unique, far beyond what we can teach machines to do. With Planet Hunters we are looking for the needle in the haystack, and ask you to help us search for planets.
This is a gamble, a bet, if you will, on the ability of humans to beat machines just occasionally. It may be that no new planets are found or that computers have the job down to a fine art. That’s ok. For science to progress sometimes we have to do experiments, and although it may not seem like it at the time negative results are as valuable as positive ones. Most of the lightcurves will be flat devoid of transit signals but yet, 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 a try?
Planet Hunters 