An interview with PH Tom Jacobs, by Rebekah and Jennifer Kahn
Thomas Lee Jacobs is a long-time Planet Hunters member who recently coauthored “Likely Transiting Exocomets Detected by Kepler,” a paper in which the first exocomets were discovered by the transit method through his persevering efforts in reviewing over 200,000 light curves. Published in Monthly Notices of the Royal Astronomical Society, you can read that paper here: https://arxiv.org/pdf/1708.06069v2 . This is not Tom’s first scholarly paper, having previously been listed as coauthor of nine other papers, in which he explored eclipsing binaries, long period exoplanet orbits, and Jupiter size exoplanets in the Habitable Zone. And he tells us “there are more in the works.” With such a record of scholarly accomplishments as a citizen scientist, we thought his views of the past, present and future of PH would be worth listening to. And yes, he is a real citizen scientist; having graduated with a non-science degree from the University of Washington in Business Administration, his rewarding day job is working as an employment consultant for workers with intellectual disabilities.
PH: Could you tell us what attracted you to Planet Hunters when it was founded seven years ago? Were you already an amateur astronomer? Had you already been involved in exoplanets, and what other astronomy interests did you have then or now?
TJ: I originally was drawn to citizen science projects created by the Zooniverse Citizen Science Alliance at MoonZoo and moved over to Planet Hunters when it was launched in December of 2010. The idea of looking for planets outside of our solar system when there was only a handful of known exoplanet discoveries at the time was intriguing. We all know now that the NASA Kepler space telescope has revolutionized astronomy and astrophysics, but at the launch of Planet Hunters there were many unknowns. I think back to that period of time as being similar to the “Wild West”, as everything was fresh and uncharted and little was known about what we would find together as Planet Hunters members. For me, I started at ground zero with no background in astronomy and my college major was in business not science.
PH: What has been your experience with Planet Hunters, then and now?
TJ: As mentioned, I became a member of Planet Hunters around 2010 and attended the first Kepler Science Conference in 2011. At Planet Hunters “Talk” I began learning from other members with more experience and insight into the light curves. Kian Jek (kianjin) was one of the most respected members at the time. There were many stalwart surveyors and contributors and I list only a few- Gerald Green, Hans Martin Schwengeler, Daryll LaCourse, Alan Schmitt, Troy Winarski, Mark Omohundro, Johann Sejpka, Ivan Terentev and Robert Gagliano. What they all have in common is dedication, perseverance and a great love for finding new and unusual events in the light curves. Kian, Daryll and I attended the first Kepler Science Conference in 2011. At that time, Planet Hunters was very novel to the astronomical community. Non-science folks, making meaningful discoveries by visual survey of the Kepler data, still had a ways to go to being acceptable in science papers. Of course, this has all changed as we fast forward to today and Planet Hunters has made significant discoveries. It is safe to say that without Planet Hunters coming on to the scene, some of the more unusual astrophysical discoveries would still remain dormant in the Kepler data. Just think of Boyajian’s star, KIC 8462852.
If you do not have an advanced mathematical and science background do not worry. I do not have one either and can only perform the most basic analysis of the Kepler light curves. What I do have is the treasure hunter zeal and a practiced eye that lends well for surveying and looking for unusual patterns in the data. Currently, I survey the Kepler K2 data using Alan Schmitt’s LcTools light curve viewer and work in collaboration with Daryll and two veteran astronomers, Saul Rappaport and Andrew Vanderburg. Daryll and I perform the initial identification and screening and Saul and Andrew do all the heavy lifting (analysis). I have since been a coauthor on 10 Kepler science papers with more in the works.
PH: What were some of the early obstacles that PH had to overcome?
TJ: I think you both will agree that the original concept and design for Planet Hunters using crowd-sourcing techniques to identify interesting events quickly became obsolete. Some obstacles for analysis were not having access to the real KIC nomenclature, access to the Kepler data and having a fast, high resolution light curve viewer showing the entire observation period. This resulted in an independent subsystem of light curve analysis and sharing in the Planet Hunters “Talk” section.
PH: Well, we can remember that, at the time, things were moving along rather rapidly and everyone in the exoplanet community was learning on the fly.
TJ: One has to also acknowledge that in 2010 this was all new territory and the learning curve evolved over time. Without Planet Hunters, none of the subsequent discoveries would have been possible.
PH: And individual Planet Hunters not only made these discoveries, but also developed the analytical tools that enabled them. Can you tell us about that?
TJ: Yes. As you know, Alan Schmitt’s LcTools program was created to address the shortfall I mentioned of not having a fast, high resolution light curve viewer. His programs now provide a complete set of analytical tools. One can quickly scan individual light curves in ten seconds or less (actually an almost instantaneous scrolling feature) with excellent light curve resolution.
This year, I generated the Kepler DR25 long cadence light curves and they are available on his site, linked to my Gmail Google Drive as zip files for the LcTools viewer.
PH: Well, we hope to interview Mr. Schmitt for PH in the future and learn more from his perspective also. Now, you have been a significant force in making many PH discoveries. What particular outlook do you bring to the search for other worlds and how does this align with the PH mission and exoplanetary discovery as a whole?
TJ: I would consider myself more of a Kepler pattern recognition treasure hunter veteran and an individual who can perform only the most basic light curve analysis. I leave the heavy lifting to the skilled veterans.
PH: But you have been a coauthor on several important papers and part of so many exoplanet discoveries. Surely there is a bit more to it?
TJ: There are some tools available online for a more detailed look and many planet hunters are adept in doing so. I am not one of them. What I have found is over the course of many years one can develop an eye for what is an interesting event and what may be simply noise or artifacts in the light curves. Though periodicity is a key tell for real astrophysical events, machine searches are well suited to beat the trained citizen scientist making visual surveys. However, single (less so now), aperiodic and new light curve patterns of real astrophysical events give the visual surveyor a real edge in this area.
PH: So, even in these new days of neural networks and machine ‘deep learning’ that characterize light curves with great accuracy, there is still a place for citizen scientists and Planet Hunters?
TJ: A machine will only find known patterns. The visual surveyor travels into uncharted areas finding new and unusual events.
PH: Such as your recent exocomets find, for sure! Well, what is your process for finding and analyzing light curves and what resources do you use?
TJ: When I survey a light curve, the first thing I do is look for unusual or known light curve patterns. Depending on how they appear will give the surveyor an idea if the events are real, the star owns the events, if there are third body events and/or if there is contamination. The next thing to check is the actual FOV. PanSTARRS is relatively new site though there are others:
I will not list all the K2 and Kepler main field online archives search sites as they are well known. The IRSA/WISE site is also a great resource of looking for WISE band 4 IR that is a great tell for “Dippers.” Of course, Andrew Vanderburg’s site is a must see for K2. He has a page for each K2 light curve that shows background contamination such as BGEBs:
PH: What future projects do you think PH should pursue? And what are some suggestions for improvement?
TJ: I would be interested in learning more about how Planet Hunters will be working with the new TESS data when it becomes operational later this year (hopefully). Educating and training its members to work more independently and developing close relationships with veteran science team members with timely feedback would be of significant help. There will be quite a bit of excellent data to analyze and citizen scientists will need strong advocates in the professional astronomical community to ensure the data is accessible to the public similar to the Kepler data, though I have been told that the data will be accessible similar to K2.
PH: Can you point to any particular discoveries or experiences over the last seven years that you particularly enjoyed or are especially proud of?
In January of last year, I took on a very large project of downloading and visually surveying all 201,250 light curves of the Kepler prime-field stars in Ames Data Release 25. Alan Schmitt and I collaborated in downloading the stars. This was a dream that I had envisioned while surveying at Planet Hunters. What until January was not in place to do this was the technology, team, experience and time. The survey took five months and I kind of went off the charts devoting most of my free time to visually surveying before and after my day job working as a Special Projects manager for AtWork! in Bellevue, Washington helping people with intellectual disabilities find paid employment in their community. I have been doing this rewarding work for over 21 years. The visual survey was completed in May and a rich harvest of interesting finds was discovered. The discovery that stands out and is likely my high-water mark for surveying is the exocomet paper recently published last fall. These are the first exocomet candidates ever discovered using transit photometry. Without the team effort, the comets would still be lurking in the Kepler data. That is the power of visually surveying, team effort and a love of finding new and usual things in the light curves. Thank you Planet Hunters and Happy Hunting!
Thank you, Tom. We appreciate your work, explanation of your outlook and methods, and recommendations for the future. In particular, we hope that your thoughts might stimulate some further discussion on this blog. Reminiscences of our successful past are welcome, but practical suggestions for our future would be truly exciting.
Here is a great Planet Hunters story from Rebekah and Jennifer Kahn.
My sister and I are spending an entire week listening to and speaking with some of the top researchers of exoplanets. There, among the names of such renowned scientists as Batalha, Borucki, and Charbonneau from NASA and large universities, are Jennifer and Rebekah Kahn, undergraduates from small, all-women’s Smith College – registered participants! And as we take part in the international Kepler & K2 Science Conference, we think about how we got here and know that it all began with Planet Hunters.
Twin sisters born in China, we came to America when we were adopted at one year old, growing up on our eastern Connecticut farm, loving baseball, decorating the Revolutionary War graves just beyond our stone walls, and learning the constellations so brightly visible in our beautifully dark night sky. We were normal, healthy kids, except for our teeth. We each had two major dental operations in our very first years’ home and probably hold a world’s record in orthodontics, wearing braces from age 8 to age 17. All this required very frequent trips to specialized dentists in New Haven and Yale. Our dad, trying to make those visits educational if not enjoyable, each time took us to another Yale museum, library, or exhibit. The planetarium and observatory were our favorites (or second favorites, next to the collection of harpsichords that we were actually allowed to play). We became regulars there, looking through the telescopes, seeing each new show and exhibit, and gratefully receiving gift books from Heidi, the administrator.
It was a cold, clear January night in 2011 when the Yale astronomer assisting in observing asked us if we would be interested in becoming part of a new research project called Planet Hunters. A research project? Open to kids? We were ready the moment he asked. The chance to do “real” science and not just study it was exactly what we wanted – but of course, as we learned, first we had to do a bit more studying. You see, at age 14, like so many other people, we had never heard of exoplanets. While we had read science fiction stories, we did not know that 51 Pegasi B had made them a reality. So, Planet Hunters taught us about transits and light curves, and that led to transit depths, which then led to M dwarfs and the different star types, which in turn led to the Hertzsprung-Russell diagram, and then the effects of starspots and even eclipsing binaries. Taking part in Planet Hunters was not just our first chance to be “real” scientists (who were convinced that we would be the first to find another Earth), but also an immensely instructive project that made our education as painlessly distracting as our father had hoped our Yale visits would be. While we were too shy to participate in the on-line discussions, we read them avidly and learned much. Two years went by and, as home-schooled high schoolers still entranced by exoplanets, we were accepted into a distance learning “Computational Astrophysics” course from Dr. Laura Trouille (now a co-PI of Zooniverse) of Northwestern University, which published our term project Towards Eta sub Earth. Then as college freshman we spent the summer working on the Wesleyan Transiting Exoplanet Project for Prof. Seth Redfield, resulting in a paper on exoplanet light curves from white dwarfs, published by the Keck Astronomy Consortium.
And now, as undergraduate sophomores, here we are at NASA Ames Research Center. Jennifer is working with Dr. Jack Lissauer on discovering how varying the eccentricity of uniformly-spaced earth-sized planets in a Hamiltonian system affects the long-term stability of a planetary system, using the symplectic integrator REBOUND. The aim is to examine the nature of planetary system formation over long periods of time. Rebekah is working with Dr. Mark Marley looking at simulated data sets of exoplanet brightness to be obtained by the WFIRST Space Telescope with filter photometry; analyzing the brightness of each planet, and determining how much can be learned from photometry without spectra. The goal is to enable successful exoplanet characterization without a spectrometer flying on WFIRST, due to budget constraints. We are both exercising our programming knowledge at the moment, modeling the processes and then varying the inputs to better understand the results. We will be developing posters for later presentation and possibly short papers. It is challenging and interesting work and we are doing a lot of late night reading to make sure we get it right.
Back at the conference we note that there are a significant number of talks discussing the pipeline and processing of Kepler data. Basic difficulties of SNR and PSF have led to applying advanced methods such as MCMC and ROBOVET. Yet all of these are simply designed to improve the extraction of light curves with less error; all are attempting to decide whether the data indicates an exoplanet or an artifact. That is exactly what we were, and are, all trying to do at Planet Hunters.
If imitation is the sincerest form of flattery, then the talk by Prof. Ian Crossfield on crowd-sourcing K2 data interpretation through his “Exoplanet Explorers” project is very high praise for Planet Hunters, which it so closely resembles. While we ourselves have not been active Hunters for a while, we are proud to be part of a project which has enabled citizens to make important discoveries with published papers, two Chambliss Award winners (we haven’t run into Daryll LaCourse who is supposed to be at this conference), and even gained some popular fame (or perhaps notoriety) through the possibility of aliens revealed in Tabby’s Star.
To be honest, we are not “natural” STEM scholars and sometimes think we should be pursuing our harpsichord studies rather than exoplanet research. We struggle with the concepts and work long hours to make clear our research goals, but the importance of the quest outweighs our challenges in pursuing it. While we didn’t discover Earth 2.0 when we were 14, we truly believe that we will be part of that discovery in our lifetime. And, for us, it all began with Planet Hunters.
Dear Planet Hunters,
I am sorry to report that Gerald Green passed away on Wednesday Aug 16th. He was an active contributor to the Planet Hunter project and a co-author on two key papers (Boyajian et al. 2016, Wang et al. 2015). Our thoughts and condolences go to his wife, Barbara, and to his family.
For those who knew Jerry, I have pasted his obituary below, written by his youngest son.
Gerald Richard Green, 66, passed away on August 16, 2017. Survived by wife Barbara, sons Will (Patty), Steven (Sara) and Tom; grandsons Toby, Cormick and Sam; brothers Ray Green and Michael Green (Donna); brother in-law Richard Weiss (Patricia Davis) and sister in-law Giudi Weiss.
He married his high school sweetheart and loved her for 50 years. He gave Barbara everything good and beautiful in her life, including their children, their home, and a love of plants and animals; key deer and Key West. For her 50th birthday, he gave her butterflies that have maintained a presence in their lovely yard for the last 16 years.
He took care of the people he loved, and he taught his family that you don’t just tell the people you love that you love them; you show them. He taught them not to be afraid and to follow their dreams.
Jerry told his boys that if they found something they love to do, they would never work a day in their lives. Will became a software architect; Steven, an ecologist and wetland scientist; and Tom an award-winning sports journalist
He was devoted to his three boys, encouraging them in everything they pursued. He nurtured their curiosities and cultivated their passions. He taught them all to sail and drove them all over the country for regattas, and he never missed a basketball game. He bought one of the first home computers, a TRS-80, when Will was born, and he was determined to make sure he knew how to use it. He gave Steven his love of the outdoors, plants and wildlife. He took baby Tom to his advertising office and took care of his “Itty Bitty Buddy” there.
A loving grandfather to his three grandsons, Jerry sent them science kits, flew balsa wood planes with them, did armpit farts and taught them about trains.
He was a true renaissance man. Jerry taught himself the nuances of countless topics and skills. He was a sailor, a pilot, a flyfisher, a musician, an astronomer, a computer genius, an award-winning advertiser, an antique car collector, a botanist and a wildlife expert.
A past Commodore of the Coconut Grove Sailing Club in 1994, he also ran the club’s sailing program. He taught his children and many others to sail, instilling in them confidence, independence and judgment. As Rear Commodore in 1992, he helped bring CGSC through the aftermath of Hurricane Andrew; during the cleanup, he was elbow-deep in the seaweed that had filled the club’s toilets.
He sailed Biscayne Bay with his family on their 30-foot Catalina, Advocation. He skippered them to The Bahamas and single-handedly sailed Advocation from Miami to Key Largo, just to know he could do it.
After earning a degree from the University of Florida School of Journalism and Communications, Jerry began his career in advertising as a copywriter and won several ADDY Awards. He then taught himself all about computers and began his second career as a computer consultant, a venture that included support for the Ryan White Program in Miami-Dade County, which helped improve the lives of more than 10,000 people with HIV/AIDS every year.
In the mid 1980s, Jerry earned his pilot’s license. In his Beechcraft Musketeer, he flew his family to The Bahamas, the Keys, and the Everglades Seafood Festival.
A citizen scientist for the Planet Hunters project, he coauthored more than a dozen published scientific papers, including the two most important papers to come from that endeavor.
He was a civic activist and served eight years on the Coral Gables Board of Adjustment; he was instrumental in getting city ordinances passed that improved the quality of living in the Gables.
Steadfast in his beliefs, he was an avid critic of politicians whose policies he found cruel and uncaring. He hated bullies and never punched down.
A man of few words but many (silly) faces, Jerry’s dry wit, sarcasm and love of corny jokes and puns highlighted his rich sense of humor, which he passed down to his sons.
A fighter until the very end, he adopted the motto, “Never give up! Never surrender!”
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.