It all started back in the olden-days of mid-2007 with GalaxyZoo: the ultimate in online, interactive citizen science where anyone with eyes, an Internet connection, patience, and an appreciation for beautiful galactic images from the Sloan Digital Sky Survey could make a reasonably important contribution to astrophysical scientific research. Driven by the initial success of this project, including an in-press research paper featuring the discovery of an ionisation nebula coined “Hanny’s Voorwerp” from a GalaxyZoo user, the supporting researchers of GalaxyZoo and the Citizen Science Alliance are rapidly developing new research interfaces based on the original GalaxyZoo model under a canopy program call “Zooinverse.”

From mapping the surface of the Moon, watching for solar flares, identifying merging galaxies, sorting and mapping our Milky Way … and more … the Zooinverse program offers wonderful opportunities for anyone at home to interact with our amazingly expansive universe and help better understand what is out there. All of these projects are important for keeping an eye on our local galactic neighborhood and mapping the greater cosmos.

Now, launched just earlier this month, the most critical and valuable Zooniverse project has begun: Planet Hunters.

We live on an amazing planet. It has perfect habitats for our species and human being continue to thrive on Earth. However, 2011 marks a predicted global population of 7 billion with a rapid rise to 9 billion in 2045 (read the current feature in National Geographic, January 2011). Earth is a very big place, and people are very little inhabitants. So, this planet really can handle quite a bit of our exponentially-increasing consumption, and it will successfully deal with our ways for millennia. However, humanity does like to take up a lot of space, and the long term dilemma might be that we as a species won’t be able to handle ourselves in such large numbers.

Just like the development of simple tools and all subsequent technology is a defining and fundamental evolutionary advantage of homo sapiens, one of the next big leaps using our technology will be discovering, traveling to, and inhabiting another home in the Universe. The goal should not be to find a replacement homestead (unless an asteroid places us in its gravitationally-driven cross-hairs — keep an eye out yourself for close approaches), but rather just a galactic expansion plan for human beings.

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“… And then, the earth being small, mankind will migrate into space, and will cross the airless Saharas which separate planet from planet, and sun from sun. The earth will become a Holy Land which will be visited by pilgrims from all quarters of the universe.” – Winwood Reade, The Martyrdom of Man, page 515 (1872).

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Any possible home away from home, however, will be in a neighborhood far from our spot in the Milky Way. The nearest star to Earth — Proxima Centauri — is 4.2 light years, or nearly 25 trillion miles (40 trillion km) away. That’s a long trip no matter what units you use! And, unfortunately for us there doesn’t seem to be a pale blue dot orbiting Proxima Centauri. So, without a doubt, an impressive technological advancement in human transportation must be developed before any upward and outward expansion launches. And before we can even set our sights onto another inhabitable planet, we, of course, need to actually find one — if one even exists!

If planets orbiting stars throughout our galaxy and others have not been an assumed notion for at least the duration of what current history labels “modern science,” then their existence certainly has been imagined, anticipated, and thoroughly written about. We just have to find them.

The two key planet hunting techniques successfully used over the past two decades to reign in a host of extrasolar planetary systems were initially suggested in 1952 by Otto Struve (1897-1963) while at the University of California, Berkeley. Struve suggested that it should not be unreasonable that Jupiter-sized objects might be orbiting very close to its host star, in contrast to our own system. Finding a large planetary mass together with a small orbit radius and high orbital frequency would make it possible to detect the gravitationally-induced spatial oscillations of the host star due to the planet.

Struve offered the important caveat that this approach — called the “wobble method” — which would be most reasonable with orbiting systems that are aligned with a line of sight toward an observer on Earth near a 90° inclination; i.e., so that the orbit crosses an observer’s view point perpendicularly rather than straight on and the reactive motion of the star would face “toward Earth”.

He also suggested a second method — the “wink method” — currently used today for detecting decreases in starlight intensity as an orbiting object passes directly between its host star and an Earth observer’s line of sight.

Struve, O. “Proposal for a project of high-precision stellar radial velocity work.” The Observatory, vol. 72, pp. 199-200 (1952). [download the original paper]

With technological advances in instrumentation sensitivity since Struve’s proposal, these very methods, along with additional new ideas, have been used with great success in discovering and measuring basic physical properties of extrasolar planets. For a more detailed review of the “wobble,” “wink,” and other methods, including direct imaging, please read the DPR review article on Extrasolar Planet Discovery Techniques.

It wasn’t until 1992 that human beings finally discovered an extrasolar planet so long envisioned. Today, there is a rapidly increasing list of extrasolar, or “exoplanets”, on the record books with many teams around the world working at a feverish pace to find more and discover weird, new behaviors in our Universe. One official count maintained by Jean Schneider of the Paris Observatory and the Extrasolar Planets Encyclopedia sets the total discoveries at 515 identified exoplanets as of December 25, 2010. A previous check of this catalog by DPR — on June 27, 2005 — found only 160 planets identified, so the discovery rate is certainly impressive.

The mission of discovering planets in other solar systems is so exciting, and yet so grueling that professional astronomers formally opened up the hunt to the avid amateur community. There is a great deal of grunt work and extensive measurement time involved with systematically searching the countless visible stars in the sky for the off-chance that a planetary orbit may be observed; and time is expensive when big telescopes and federal grants are required to make progress. Planet hunter and professor at University of California, Santa Cruz, Gregory Laughlin, established to guide amateur astronomers with a good telescope and a lot of patience in searching for likely candidate stars as hosts for planets. Bruce Gary has written the detailed, 253-page guide “Exoplanet Observing for Amateurs, Second Edition,” which he has made available as a free PDF e-book [ download now ]. Amateurs may learn from this valuable resource on how to take your backyard telescope and transform it into an optimal planet-hunting machine.

Kepler Spacecraft and Photometer. Courtesy NASA.

On March 6, 2009, NASA launched its tenth Discovery Mission called Kepler, which is designed to directly monitor the brightness of 100,000 sun-like stars in our neck-of-the-woods of the Milky Way. Using the “wink method,” the light curves fed to Earth from Kepler can be analyzed to look for signatures of transiting bodies. If the measured light intensity from a star drops, there might be a transiting body. If the intensity drops again, and again — in a stable, periodic way — then there just might be an orbiting planet.

Once an orbit is identified, then a great deal of information can be calculated, including a reasonable prediction if the planet might be habitable based on our human standards of what makes a nice home. Using the period of the orbit calculated from the observed repetition of the drop in star brightness, the orbit size can be determined. And, along with the observed temperature of the star, a characteristic temperature of the planet can be estimated. (Read more about the Kepler mission and learn more about NASA’s Center for Exoplanet Science.)

So far, researchers have confirmed eight planets from the light curves provided by Kepler. Each of these eight rocks seem to be very hot, very big, and very close to their host star. In other words, not so pleasant.

But this is only the beginning of the search! Kepler is continuously scanning thousands of stars, and there are many light curves to individually review. All of the data is being made available to the public for download and review through an online archive funded by NASA, but the interface is rather cumbersome for the interested amateur. So, this is where the team at Zooinverse enters into the game…

The creators of Galaxy Zoo have developed their latest interface that takes the raw light curve data from the public Kepler database and presents it to users in a scalable graph. After presenting a particular data set, the interface asks you a few simple questions about what you see. The questions are relatively trivial for a human observer with our extremely efficient pattern recognition abilities, but extraordinarily difficult for an automated computer program scanning the data points. It is this fundamental advantage over artificial intelligence code that offers not only the beauty of the Planet Hunters project, but also is the essence for why citizen scientists can be so crucial to important scientific pursuits.

A screenshot of the Planet Hunters interface from Zooinverse.

Many of the measured stars look like the data set presented above: the brightness measured from the star varies somewhat randomly over a period of time, but maintains a simple average level with the variation due to white noise or random behavior in the star’s activity. Other data might show a clearly periodic or cyclical pattern to the brightness, which represents a pulsating star, or it might have a very irregular brightness pattern, but the variation occurs over a smooth, continuous curve.

If a star has another massive orbiting body pass directly through the line-of-sight of the Kepler telescope toward the star, then a sudden dip in the brightness will be measured. This rapid dip is due to the orbiting body — most likely a planet! — blocking some of the light radiating from the star. If this extreme dip is seen periodically, then the full orbit of the planet can be measured.

Possibly two transiting planets classified by Dynamic Patterns Research on Planet Hunters.

On December 27, 2010, Dynamic Patterns Research was fortunate enough to help classify a very clear example of a light curve that might represent two separate orbiting planets around SPH10122348, a dwarf star with apparent visual magnitude of 12.9, a temperature of 5,625 K, and a radius of about 1.7 times that of the Sun (view the light curve with a Google star map).

The data interface for SPH10122348 presents a “quiet” star with apparently constant brightness, within some random variation, but it has four extremely dramatic dips in brightness. Two of the dips are relatively shallow — representing a smaller orbiting planet that only covers a small fraction of the star, and the other two dips are particularly deep — possibly showing a very large planet that obscures a larger portion of the star, at least from the view of Kepler.

The four blue outlined boxes are part of the intuitive interface, which are movable and scalable boxes that the user may manipulate to identify potential transit data. Here, we placed two shorter boxes over the “small” transiting body, and two long boxes over the “larger” transit. The classification is saved and reported into the researchers at Zooinverse to review, further analyze and send back through the system to allow other users to make independent confirming classifications of the same data.

Once a light curve has been identified and vetted as a potential candidate for an exoplanet, the research team will identify which users were involved in the classification and post the results on their candidate page (view current list). Further review will check to make sure the star is not already on a previously identified list from either Kepler or older observations. If the data appears to be a new discovery, then the research team will follow up with spectroscopic data from the Keck telescope in Hawaii, and if further screening tests are passed, then the result will be submitted for publication. Citizen scientists who participated in identifying the transiting planets will be included as co-authors on all published research papers.

Scientists around the world are looking for planets around other stars, and with the power of citizen science you can now play an integral role in this critical research. This is a prime moment for citizen scientists to prove their value in professional scientific work, and this opportunity is extremely easy to dive into. Unleash your citizen scientist and start hunting planets now…



  1. […] Recently, Dynamic Patterns Research featured a review of the important citizen science project of Planet Hunters where anyone can sign up to visually analyze light curves obtained from NASA’s Kepler Discovery Mission (read more). […]

Last updated July 10, 2017