Guest post by Sarah Pearson, Columbia Astronomy Graduate student and creator of the Space with Sarah YouTube channel (www.youtube.com/spacewithsarah). Today Sarah is describing her latest YouTube episode.
Within the last couple of decades, humans have detected thousands of planets around stars other than our own Sun (exoplanets). The enormous number of galaxies each with billions of stars which statistically all have a planet orbiting them, makes it weird to think that life here on Earth should be the only life that exists in the entire Universe.
A question which hasn’t received that much attention yet is: how old could the oldest planetary system be?
We know that our own solar system is roughly 4.6 billion years old, which is actually quite young compared to the whole Universe which is ~13.8 billion years old. The Big Bang, mostly produced Hydrogen and Helium, while Earth’s crust consists mostly of oxygen, silicon and iron. This means Earth couldn’t have formed right after the Big Bang. But for how long would we need to wait?
To create the elements that rocky planets like Earth consist of, stars in the Universe actually need to first be created and then die to spread elements heavier than Hydrogen and Helium into space. Heavier elements are mostly produced in stellar interiors through fusion and when the stars eventually explode and shed their layers to their surroundings. It takes hundreds of thousands of years for the stars’ material to fully mix into nearby space, and subsequently this material needs to collapse and form new stars and planets.
While there’s definitely an observed correlation between the amount of time passed since the Big Bang and the amount of heavier elements in the Universe, astronomers are still having a hard time creating a precise timeline for the amount of heavy elements created at what time. But we do know that something like Earth could not have formed until enough stars in the Universe had exploded, and we also know that this could have happened a lot earlier than when our own solar system formed.
One of the most interesting planetary systems astronomers have found in our own Galaxy is Kepler-444 (Campante et al. 2015, ApJ) which consists of five rocky planets orbiting a star which is 6.6 billions years older than our own solar system, meaning that it formed only 2.6 billion years after the Big Bang! While this system probably doesn’t harbor life (the planets are too close to their star to have liquid water), its existence demonstrates that planetary systems could have formed a lot earlier in the history of the Universe than our solar system. This begs the question: how intelligent would alien civilization be if they have evolved for billions of years longer than life here on earth?
On the Space with Sarah YouTube channel (www.youtube.com/spacewithsarah), astrophysicist Sarah Pearson answers frequently asked space related questions in 3-6 minute videos.
By Yale grad student, Joey Schmitt
In the 10th paper(!) from the Planet Hunters citizen science program, a stupendously great number, we independently discovered 10 new planet candidates in the K2 *Kepler* data (Campaigns 1 and 3). However, simply discovering them was not the main goal of the new paper. We wanted to explore their neighborhoods.
The environment in which a star is created has a large and enduring impact on how planets form. Under standard planet formation theory, when a star collapses, it forms a disk, called a protoplanetary disk, due to the conservation of angular momentum. It is in this disk of material orbiting the infant star that planets are formed. Solid material clumps together and forms planets. In the inner disk, the material is hotter, so the only solid material is metallic or rocky. In the outer disk, the material is cooler, which allows molecules like ice and frozen ammonia to clump together as well. This extra solid mass in the outer solar system allows the outer planet to grow bigger and eventually capture gas. Interactions between all these planets can then jumble them around.
However, most stars are not born alone. They more often come in pairs or triplets or even larger clusters. If two stars are forming too close together, each star could disrupt or even completely destroy the other’s
protoplanetary disk, making one or both stars devoid of planets. Conversely, it’s at least hypothetically possible that, at certain distances, a star could funnel its protoplanetary disk material into the protoplanetary disk of a neighboring star, giving the star more material to make planets out of. Current research has suggested that the destructive effect dominates. We aimed to test this suggestion and to further examine the potential effects of stellar neighbors to planetary systems. There are similarly interesting questions exploring the effect of a third star in eclipsing binary (EB) systems.
In this paper, we made a selection of many planet candidates, several from Planet Hunters and several others from previously published journal articles, and also many EB candidates, all of which were discovered through Planet Hunters volunteers, for a total of 75 targets. In order to find nearby stellar companions to these planet or EB systems, one has to take very high resolution images. Typically, this is impossible due to atmospheric turbulence blurring the starlight (seeing). To get around this,
we used two telescopes, SOAR in Chile and Keck in Hawaii, that get around this problem. The SOAR telescope uses speckle imaging, which takes hundreds images so quickly that the air doesn’t have time to move around and blur the image and then combines them. The Keck telescope, on the other hand, uses lasers to measure the air turbulence and then deforms its mirrors many times per second to correct the light before it reaches the camera.
With these techniques, we were able to find three stellar companions to our planet-host stars and six companions to our EBs. While we did not have a large enough set of targets to definitively measure the overall effect of nearby neighbors on planetary and EB formation, the results were suggestive
of two things. First, we found just one very close companion to a planet-host, strengthening the hypothesis that nearby stars are in fact destructive to planet formation. Secondly, we discovered several new stars
near very short-period EBs, implying that the shortest period EBs necessarily need a third star in the system. The third star steals energy from the close pair, which pushes those two stars on a shorter and shorter orbit.
The six companion stars found by the SOAR telescope are shown in the image below:
In the meantime, we are continuing to show data from the original *Kepler* set of stars. This current project will allow us to calculate the frequency of planets in long-period orbits around *Kepler *stars, something
that no other research project is yet capable of doing. An integral part of this is displaying synthetic (or “fake”) planets in the data. The synthetic transits allow us to measure how good Planet Hunters are at
finding planets of different sizes and periods around different kinds of stars. This knowledge is *required* to know how frequent planets occur because it allows us to correct for the planets that are there but *not*
We would like to thank everyone involved in this program! The volunteers here at Planet Hunters are simply wonderful. This is one of the most popular *and scientifically productive* of the Zooniverse projects. We’re
also looking into if and how we can reincorporate K2 data and, in the future, TESS data. We hope that you continue to contribute to astronomical research.
The (not *quite* final) public version of this paper is here.
Please join me in congratulating one of our prolific Planet Hunters, Daryll LaCourse (aka Nighthawk Black), who received the Chambliss Prize for Amateur Astronomy. Woo-hoo! The award was announced at the American Association of Astronomy meeting on January 6th 2016.
Daryll is the second Planet Hunter to receive the Chambliss Amateur Achievement award, which goes to a person not employed in the field of astronomy in a professional capacity, who is resident in North America. The key factor in judging nominations is that the work contributes to the advancement of the science of astronomy.
The citation reads: Daryll LaCourse is a dedicated and talented amateur astronomer who has made significant contributions to exoplanet research as a leading member of the Zooniverse Planet Hunters program. Through painstaking examination and independent reanalysis of Kepler data, he has discovered several new exoplanet candidates, more than 100 previously unknown eclipsing binary systems, and other notable, enigmatic variable stars. He is an energetic and productive collaborator with many professional astronomers. He has coauthored several scientific publications and was lead author on a paper with more than a dozen professional astronomers as co-authors. To quote from one of his letters of support, “If Daryll were a professional astronomer, I would be impressed by the quantity, quality, and creative insight of his work. He is an extraordinary citizen scientist — and highly deserving of the Chambliss award for scientific contributions from amateur astronomers.”
Today’s blog post is from Dr. Michelle Collins, a Hubble Fellow working at Yale.
After 9 years, 3 billion miles, a Jupiter fly by, and some of the most complex route calculations ever implemented, New Horizons reached its destination a couple of weeks ago on July 14th. This NASA probe went whizzing by our distant, dwarf planet neighbour Pluto at a dizzying speed of 31,000 mph, and has already provided us with a wealth of spectacular images, data and science. It will continue to spew out incredible discoveries about Pluto over the coming 16 months or so, as the flyby data trickles back to us.
To say that this space probe has revolutionized our view of this failed planet is a giant understatement. Pluto has long been an elusive, poorly understood system, hovering on the periphery of our solar system. It was discovered back in 1930 by Clyde Tombaugh, an American working at the Lowell Observatory in Flagstaff Arizona. Due to some miscalculations of the mass of Neptune, it was initially believed that Pluto was a massive planet, at least as big as the Earth, and possibly up to 4 times the size of our home planet. So naturally, it was classified as a planet. However, as the decades wore on, the mass of Pluto was revised downwards, finally lurching to a halt at a mass of only ~0.2% the mass of the Earth in 1978, much lighter than originally thought. With this extreme weight loss, and the discovery of similar size – and even more massive – dwarf planets in the solar system (particularly Eris, discovered in 2005), Pluto’s status as a planet was starting to raise some eyebrows. And so, in 2006, when the International Astronomical Union met to decide what the lower bound on a planet should be defined as, Pluto didn’t make the cut, and was relegated to a dwarf planet.
But, aside from it’s low mass, and controversial status as the only de-throned planet in the Solar System, what else did we know about Pluto, pre-New Horizons? Well, not very much, really. Given it’s huge distance (it’s orbit takes it anywhere between 2.7-4.8 billions miles from the Earth during a single Pluto year), it was hard for us to study Pluto in detail, or take a decent image of it, even with the Hubble Space Telescope. We knew it was an icy world, probably with a rocky core, and maybe underground oceans. It is mostly composed of Nitrogen, with some methane and carbon monoxide. It has an extended, tenuous atmosphere and 5 moons – Charon, Nix, Hydra, Kerberos and Styx. It is locked in a binary orbit with the largest of these, Charon. But the other, smaller moons appeared to us a little more than points of light in Hubble images. If we wanted to learn more about their composition, and that of Pluto itself, we’d need to get A LOT closer to Pluto. And so, New Horizons was constructed and launched on a mammoth journey on 19th January 2006 to our favorite minor planet to get a better look. It was the fastest spacecraft ever launched from Earth, and even managed to image Jupiter and its moons as a bonus science project on its way out to Pluto.
Much of New Horizons journey was spent in hibernation (roughly 7 years), and it was finally awoken on December 6th 2014. From then on, it began imaging Pluto with its onboard cameras, LORRI (a high resolution reflection imager) and Ralph (a multi-filter, lower resolution camera and spectrograph). The combination of these two instruments provided us with incredibly detailed, color images of the surfaces of Pluto and Charon, that got clearer and clearer the closer they got to Pluto. In the weeks before the flyby, we could see that Pluto is a red world, with complex geology. A huge, heart shaped ice plain could be seen on its surface (informally named Tombaugh Reggio after the man who discovered Pluto), and evenly spaced dark spots located on the opposite side of Pluto, which are the size of Missouri, surprised astronomers. Huge craters could also be seen, and regions that seemed surprisingly crater-free too. We also learned that Pluto is a little bigger than we thought, with a radius of 1473 miles, making it larger (though still less massive) than Eris. The sheer variety of surface features, not only on Pluto, but on Charon also, increased the anticipation of the New Horizons team as their target drew nearer, as it was clear that the high resolution flyby would provide them with a treasure trove of answers to the questions already forming.
Tensions were probably pretty high on the day of the flyby itself. After traveling 3 billion miles over 9 years, New Horizons needed to hit a window in space that was only 60×90 miles in size within 100 seconds of its predicted arrival time, otherwise it would miss Pluto. But the orbital calculations were bang on, and New Horizons was able to complete its full range of observations of Pluto and Charon, as well as taking detailed images of Pluto’s 4 other moons. Over the course of a few hours, New Horizons made high resolution maps of segments of both Pluto and Charon, with a maximum resolution of 60 meters per pixel. With that level of detail, you’d be able to count the ponds in central park! In addition to these maps, New Horizons also used several instruments – Alice, REX, PEPSSI and SWAP – to study the atmosphere of Pluto.
So, what else do we know about Pluto now? TONS! For example, the high resolution mapping of Pluto has shown us ice flows on the surface, and evidence for recent geological activity, such as cryovolcanism, which is completely unexpected for such a low mass object that isn’t orbiting a more massive planet. It also has huge mountains ranges, that tower up to 11,000 ft above the surrounding plains. These are most likely composed of water ice.
We also know more about Pluto’s atmosphere. For one thing, the solar wind appears to be stripping it away from Pluto, resulting in a cometary tail-like feature. It also has a hazy quality, where gaseous methane molecules are irradiated by UV light, causing them to condense into complex hydrocarbon molecules known as tholins, which are responsible for the reddish color of Pluto. Its atmosphere also seems to have a lower pressure than previously measured, and could imply that half of it is freezing out and condensing back onto the surface as Pluto segues into its colder season.
We also have high resolution maps of Charon, Pluto’s binary companion. It too, has a geologically young surface, which is totally unexpected for such a small moon. It has a complex set of cliffs, troughs and canyons whose sizes eclipse the Grand Canyon here on Earth. These are thought to be signs of fractured crust on the moon, caused by internal processes. It also has an extended, diffuse dark spot at its pole, informally named ‘Mordor’.
Speaking of moons, we’ve also received the most detailed images of Nix and Hydra from New Horizons. Nix is jelly bean-shaped, approximately 22×26 miles in size, and seems to have a large red spot on one of its faces which may be a crater. Hydra has an irregular shape, that has been compared to the state of Michigan and is about 34 miles in length. It too shows signs of cratering.
And this is only the beginning. There’s much more to come over the next year, and we’re highly anticipating the first ever images of the other 2 Pluto moons, Styx and Kerberos, which should be downloaded in October. There’s more to learn about the surfaces of both Pluto and Charon, with detailed spectroscopy coming in from the Ralph instrument, and more to come on the atmosphere too. So stay tuned to NASA for updates. New Horizons and Pluto have plenty more surprises in store for us, as we learn just how complex and awesome dwarf planets can be.
Today’s guest blogger, Jay Pasachoff, gives us an update (as of July 1, 2015) on his exciting occultation program, first described on May 26, 2015. This is the wild west of astronomy!
Observations of the occultation of June 29, 2015, were very successful both from the ground and from the air. My team has a wonderful light curve from the Mt. John University Observatory in New Zealand; we were close enough to the center of the path that the light curve showed a central peak (a “central flash”), a focusing of starlight as it passed around Pluto, that allowed probing very low in Pluto’s atmosphere. Other teams had light curves from elsewhere in New Zealand and from Tasmania. NASA’s instrumented SOFIA (Stratospheric Observatory for Infrared Astronomy), with its 2.5-m telescope mirror, recorded excellent light curves from high altitude above New Zealand. The views of this occultation will provide excellent comparisons with the ultraviolet and radio occultation results that should be provided by NASA’s New Horizons spacecraft about two weeks later. Further, the long-term run of occultation studies should provide context for the high-quality snapshot view of Pluto’s atmosphere that New Horizons should provide.
Today’s blog is by guest blogger Dr. Jay Pasachoff. Jay is Chair of the International Astronomical Union’s Working Group on Eclipses and is Field Memorial Professor of Astronomy at Williams College. He has viewed 61 solar eclipses, and is an expert on both their use for scientific observations and their use for public education. Jay has has written several astronomy books including the Field Guide to the Stars and Planets and the textbook The Cosmos: Astronomy in the New Millennium. He last provided a blog post about occultations of stars by Pluto in 2011, about a different way of planetary bodies blocking out star light that’s a little closer to home than the exoplanet transits normally discussed in this blog. He’ll be discussing what we can learn from studying dwarf-planet Pluto blocking out (or occulting) the light from distant background stars and relating it to the forthcoming flyby of Pluto by a NASA spacecraft.
As I write, NASA’s New Horizons spacecraft gets closer to Pluto after a 9 year journey. Soon it will give images BTH: Better than Hubble. Already, it is imaging all five known moons of Pluto (http://pluto.jhuapl.edu).
For the last dozen years, my colleagues, students, and I from Williams College have been working with MIT colleagues to observe Neptune’s moon Triton, Pluto, and Charon occult stars–usually stars ranging from 14th to 17th magnitude. The starlight comes into the solar system as parallel light, so the path on Earth from which the occultation is visible is the same width as the occulting object: about 2400 km wide for Pluto and half that for Charon. Our various occultations observed are discussed at a website I set up at http://stellaroccultations.info.
Our group now extends to include Bryce Babcock and me at Williams College; Michael Person, Amanda Bosh, and Carlos Zuluaga at MIT; Amanda Gulbis at the South African Astronomical Observatory; and Stephen Levine at Lowell Observatory, as well as students and others. Carlos posts the MIT group’s latest predictions at http://occult.mit.edu.
I last blogged about our work at the time of a double Pluto/Charon occultation in 2011, which our group observed from several telescopes in Hawaii as well as from the SOFIA aircraft. Our recently published papers that resulted are as follows:
Person, M. J., E. W. Dunham, A. S. Bosh, S. E. Levine, A. A. S. Gulbis, A. M. Zangari, C. A. Zuluaga, J. M. Pasachoff, B. A. Babcock, S. Pandey, D. Amrhein, S. Sallum, D. J. Tholen, P. Collins, T. Bida, B. Taylor, J. Wolf, A. Meyer, E. Pfueller, M. Wiedemann, H.-P. Roeser, R. Lucas, M. Kakkala, J. Ciotti, S. Plunkett, N. Hiraoka, W. Best, E. J. Pilger, M. Miceli, A. Springmann, M. Hicks, B. Thackeray, J. Emery, S. Rapoport, I. Ritchie, M. Pearson, A. Mattingly, J. Brimacombe, D. Gault, R. Jones, R. Nolthenius, J. Broughton, T. Barry, 2013, “The 2011 June 23 Stellar Occultation by Pluto: Airborne and Ground Observations,” Astron. J. 146, 83 (15pp), October, doi:10.1088/0004-6256/146/4/83.
Gulbis, A. A. S., J. P. Emery, M. J. Person, A. S. Bosh, C. A. Zuluaga, J. M. Pasachoff, and B. A. Babcock, 2015, “Observations of the same-day 2011 stellar occultation by Charon and graze by Pluto,” Icarus 246, 226-236. DOI: 10.1016/j.icarus.2014.05.014
Bosh, A. S., M. J. Person, S. E. Levine, C. A. Zuluaga, A. M. Zangari, A. A. S. Gulbis, G. Schaefer, E. W. Dunham, B. A. Babcock, A. B. Davis, J. M. Pasachoff, P. Rojo, E. Servajean, F. Förster, T. Oswalt, D. Batcheldor, D. Bell, P. Bird, D. Fey, T. Fulwider, E. Geisert, D. Hastings, C. Keuhler, T. Mizusawa, P. Solenski, B. Watson, 2015, “The State of Pluto’s Atmosphere in 2013,” Icarus 246, 237-246. http://dx.doi.org/10.1016/j.icarus.2014.03.048
For the ten minutes or so nearest to the occultation for ground-based telescopes, the object and the star appear merged, and we detect the occultation by the light curve. For Charon, with no atmosphere (and our occultation method is very sensitive), the starlight disappears abruptly. If the star is brighter than the occulting object, the occultation is quite noticeable; if the star is fainter, then just a percentage is subtracted from the total. For Pluto (and, earlier, for Triton), its atmosphere bends and distorts the starlight, and the ingress and egress are slanted on the light curve. These ingresses and egresses can last a minute or so with a central occultation of five minutes or so, depending on the relative speed of Pluto with respect to the star.
Astronomical circumstances currently put most of the occultations visible mainly in the southern hemisphere. Last year, in late July 2014, my student Adam Schiff ’15 (Keck Northeast Astronomy Consortium, from Middlebury College), Robert Lucas from Sydney, and I observed from the Mt. John University Observatory of Canterbury University, New Zealand. The observatory is about a 3-hour drive west of Christchurch. We were helped especially by the observatory’s superintendent, Alan Gilmore. Even though the UCAC star catalogue’s values of 15th magnitude for the occulted stars were high by about two magnitudes, we succeeded in observing two occultations by Pluto out of the three we tried. While we were there, we had heard from Wes Fraser of the Herzberg Institute of Astrophysics, Canada (who I knew from when we were both in Mike Brown’s group at Caltech a few years ago) about a prospective occultation by the KBO Quaoar, and also from NZ occultation coordinator David Herald about a prospective occultation by Pluto’s tiny moon Nix; we have flat light curves for both of them–that is, no occultation shadow passed over our site. One needs a dense picket fence of telescopes plus a lot of luck to capture occultations of such small objects. While we were there, we had coordinated observations from Amanda Gulbis with the 4-m telescope on Siding Spring, Australia, and with David Osip on the 6.5-m Clay, Stephen Levine on the 4.1-m SOAR, and Mike Person on the 2.5-m DuPont telescopes in Chile but they, unfortunately, had clouds for the most part.
After our observing run was over in New Zealand, there was another event in Chile, with an especially bright star for us, 12th magnitude. But clouds came in 90 seconds before the predicted ingress. Still, our colleagues noted on the light curve a 2% dip just before the clouds came. Was it from a ring around Pluto? Was it from a hitherto unknown moon of Pluto? It turned out that it was from a previously unknown 15th magnitude star lurking in the Airy disk of the 12th magnitude star, as our colleagues soon confirmed with Keck AO. It was clearly much less exciting to discover a 15th magnitude star than to find a ring around Pluto or to discover a moon. Anyway, we have the light curve of an occultation by that 15th magnitude star, which was the typical brightness of our occultation stars that we were observing anyway. We are about to submit a paper to the Astronomical Journal about our results.
It is important to search in the Pluto system ahead of and behind Pluto itself, since the New Horizons spacecraft’s radio signals are so weak that it will take 18 months or so after the July 14, 2015, flyby to send back all the data (from about 40 au; at 8 light minutes per au, it takes over 5 hours to get signals back at all). So if the spacecraft is killed at flyby by running into a ring particle or other dust, then most of the data–even from closest approach–would be lost. Our earlier occultation observations provided some limits on the dust content, and were among many pieces of evidence considered by the New Horizons team at Southwest Research Institute, headed by Alan Stern, in targeting their spacecraft.
We actually don’t know exactly how big Pluto is, because its lower atmosphere is opaque to starlight during occultations. It could be from haze in the lower atmosphere or thermal inversion. Eris, on the other hand, is so far out that its atmosphere has frozen and snowed onto the surface. We therefore now know from occultation studies by the Bruno Sicardy group from Paris just how big Eris is, and it turns out to be near the lower end of the possible range of Pluto’s size. Would the IAU have reclassified Pluto as a dwarf planet in 2006 if Pluto hadn’t been thought to be smaller than Eris? (It is certainly less massive, since each has at least one moon that has provided an accurate mass value.) Would NASA have launched a spacecraft to Pluto if it hadn’t been thought to be the 9th, and the only unvisited, planet?
We have a prediction this year for the occultation of a 12th magnitude star from the region of New Zealand, and perhaps the lower half of Australia. (http://occult.mit.edu/research/occultations/Pluto/P20150629) If you can observe from the centerline, you might get a central flash from focusing of the starlight all around Pluto–as we once got (with much luck) from Hubble. With this desirable possibility in mind, NASA’s SOFIA (Stratospheric Observatory for Infrared Astronomy) will fly out of Christchurch, with Mike Person from our group on board. Amanda Bosh will be in Flagstaff, coordinating last-minute updates to the astrometry. Bryce Babcock and I will be at Mt. John, with our Williams College undergraduates Rebecca Durst ’17 and Christina Seeger ’16; Alan Gilmore will continue to assist us, even though he has retired. This time, we have not only the 1-m telescope but also an adjacent 0.6-m telescope, for which Stephen Levine will bring down an infrared camera from our Williams College alumnus Henry Roe who is now at the Lowell Observatory. We even have arranged with a Japanese group who use a second 0.6-m telescope to get three-color photometry from it, unless they have an urgent need for it as part of their gravitational-lensing program. Amanda Gulbis will be observing from a different location in New Zealand, to give us a different chord. The Southwest Research Institute (SwRI), especially Leslie Young and Eliot Young, have also arranged observations from telescopes around Australia and New Zealand, just as we are coordinating with other telescopes besides those at Mt. John. The Bruno Sicardy group from Paris also has its own prediction.
It could be particularly important and interesting to be observing so close to the July 14 flyby by New Horizons, since then we can compare results taken at a comparable state of Pluto’s atmosphere. The atmosphere of Pluto, far from snowing out by now even though it passed perihelion in 1989, had warmed slightly and had increased pressure by the time of our 2002 observations, and has since leveled off. There will certainly be enough atmosphere for New Horizons to observe, which had not been clear a dozen years ago. It must start cooling at some point, as Pluto recedes from the Sun. We hope to calibrate our atmospheric models with the new size of Pluto we will get from New Horizons, and to follow Pluto’s atmosphere as it continues to evolve.
Our occultation work at Williams College has been sponsored by grants from NASA’s Planetary Sciences Division, most recently NNX12AJ29G.
13 May 2015
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.
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?