PlanetQuest Background

The Challenges

PlanetQuest started in 2000 as a response to two important problems.

© Lynette Cook,
The giant planets in our Solar System all have rings and fairly large moons. Some of the recently discovered planets, such as in this beautiful artist's conception, could also have rings and moons, perhaps some large enough to be habitable. Unlike any other planet detection method, the transit method can potentially detect both rings and moons around giant transiting planets.

Education in math and the sciences is generally lacking the world over—particularly in North America—and astronomy can combine both of these fields in a thought-expanding way. We believe that educating the world's next generation of deep thinkers is a top priority. PlanetQuest draws on world-renowned expertise to offer a variety of ways to learn about astronomy and other natural sciences, mathematics, the history of science, and other topics in a way that allows you to measure your progress. We also offer free lesson plans to schools and suggestions on how to introduce the PlanetQuest Collaboratory into curricula from the primary to the college level. For undergraduate and graduate students, we offer a wide variety of exciting internships—the ultimate hands-on learning opportunity! We are educators first and foremost here at PlanetQuest, regardless of the other hats we wear.

There are few astronomical data sets available that include large-scale imaging of millions of stars over long periods of time—and this is the optimum method for the detection of extrasolar planets (planets around other stars) by photometric transit. To find an extrasolar planetary transit in a huge data set requires that millions of models of possible transits be compared with the actual light variations of each star over a period of time. We saw great potential in distributed computing, which creates large virtual networks by using the spare computational power of simple desktop computers connected to the Internet. Our goal is to include everyone in the thrill of discovery by taking distributed computing and astronomical research to new levels by using our expertise to build the world's largest astronomical observatory—exciting people about science and astronomy by allowing them to participate and learn.

Cutting-edge Science

PlanetQuest is a direct outgrowth of our pioneering work in the field of planet detection over the last fifteen years. (Combined, the scientists working with PlanetQuest have published over 100 extrasolar planetary detection papers in the refereed technical scientific literature over the past ten years.)

The photometric transit method, used by PlanetQuest for finding planets around other stars, measures a drop in the brightness of the star as a planet crosses (or "transits") in front of it. The planet's orbit has to be very nearly edge-on to our line of sight for this to be detectable, since the planet in effect must cast its shadow upon the Earth. Between 0.5% and 10% of planetary orbits should be situated thus, depending on the size of the planetary orbit and the size of the parent star itself.

A great advantage of this method is that instead of trying to detect planets around only one star at a time (as in, for example, the successful radial velocity method, which has resulted in the discovery of most extrasolar planets to date), literally tens of thousands of stars can be observed simultaneously. This can be done by imaging (taking photographic images of) densely crowded star regions, such as those that exist in the direction of the plane of our Milky Way Galaxy. Images are recorded by a large CCD camera mounted on a wide-angle meter-class telescope.

Densely crowded star field in the galactic plane. Taken by PlanetQuest astronomers (Baade's Window 3rd region). We have measured the light curves of over 64,000 stars in this image.

Each exposure of these regions produces an image with many tens of thousands of stars. By analyzing all of the images together, the brightness variation of each star over time (the star's "light curve") can be examined in detail, in three steps. This is the task of the transit detection algorithm (TDA) in the PQ Collaboratory that will be downloadable from the website, and that will employ the computers of PlanetQuesters.

  1. The first step is to isolate a star's brightness from that of nearby stars. This is done by computing an aperture around each star and adding up the brightness within that aperture. This works well if the star is fairly well isolated visually from other stars and the atmospheric conditions over the observatory are fairly stable throughout the night. Otherwise the star must be fit with what is known as a "point spread function" ("psf"), where the centroid of the star's psf is calculated, allowing it to be isolated from stars that appear to be very nearby and then measuring the psf brightness. Although pretty much all but the closest stars are points, the atmosphere of Earth spreads them out—hence the psf of the star is a measure of the stability of that night's atmosphere over the observatory.

  2. The second step is to make a detailed examination of each brightness variation of each star (the star's light curve) to ascertain if it is a variable star and, if so, what type of variable it is. This is important, as it allows both the classification of the star's variability type (if it is an eclipsing binary, for example) and the diffentiation of any intrinsic periodic brightness variations from brightness variations caused by planetary transits. There are about 200 well-known variable star types, and the discovery by a PlanetQuester of any of these types will be a scientific contribution—their name and their discovery will be recorded in the PlanetQuest Discoveries Catalog and become part of astronomical research history. Stable stars will also be important as standard brightness references and as potential targets for SETI (search for extraterrestrial intelligence) because of their stable circumstellar habitable zones (CHZs).

  3. The third step is to match models of different
    Actual dip in a light curve indicating a transit of a giant planet around the star HD209458 (HST STIS photometry). Data are from Brown et al. 2000. The depth of a theoretical terrestrial-type planet is shown for comparison.
    possible planetary orbital periods and locales to the much-smaller-scale brightness variations in the light curve that could be caused by a planet blocking out a small part of the star's light as the planet transits across the stellar disk. As there will be many different "twinkles"of the star (variations in the light curve) due to the Earth's atmosphere, variations in the observatory cameras, and stellar variability itself, to find a planet one must test, or match, millions of planetary transit models against the star's light curve to learn whether a particular dip in the brightness was indeed due to the transit of a planet. Using this technique provides information on the planet's orbital period, size, and epoch (starting location in its orbit). The transit models all imitate dips of different sizes and shapes in the light curve, and the TDA finds the one that fits the best. If the fit is really good, then a planet candidate has been detected and the PlanetQuester is notified that they have a potential planet detection. Their computer will then contact PlanetQuest headquarters and they will be given credit for that discovery (as a collaborator) when the planet is confirmed.

The PlanetQuest Approach

All three of these steps can significantly benefit from a distributed computing application that exploits underused CPU cycles on networked computers to create a virtual supercomputer. The resulting computing platform is many times more powerful than any conventional supercomputer, handling an exponentially greater number of complex calculations per second. Other computationally complex scientific projects have successfully used this approach, including SETI@home, Genome@home, and Folding@home.

Over the past three years, the technologies behind distributed computing have advanced, producing more efficient communications and tools. PlanetQuest fully makes use of these opportunities and the experiences of other distributed computing projects. But PlanetQuesters do not just help others with discovery; PlanetQuesters become explorers and discoverers themselves! The PlanetQuest Collaboratory will help you understand what you have discovered, and what others have discovered, as well.

Here is how the Collaboratory works. You download a small program from the PlanetQuest website that, when installed, runs as a "background" or shadow process on your computer. As a background process, the PlanetQuest browser lies idle and unobtrusive until it detects that your computer is no longer in use. At that point, the PlanetQuest program retrieves a small packet of sequential planetary imaging data from the central PlanetQuest server. Your computer then begins to work on analyzing the data—again, only when either you tell PlanetQuest to begin or when PlanetQuest detects that the computer is no longer in use. The PlanetQuest Collaboratory will display the characteristics of the star you're working on, along with an image of the star's region, and can include information on the star, such as its color, size, distance, spectral type, variable type, and so on.  You can find out more about your star and its neighborhood by using the Collaboratory's built-in tools.

Web links allow you to dig even deeper into the background of the stars in the sky field you're examining, as well as to explore related astrophysics at many educational levels—from very elementary text to copies of technical papers in professional journals. Whether you are in grammar school or a postdoc, you will find something to satisfy your curiosity. You'll also be able to subscribe to additional premium content by joining the PlanetQuest Academy. This will include video and audio lectures streamed over the Web, Proceedings of the PlanetQuest Academy, certificates of discovery, special astronomical and scientific travel opportunities, and special rates on our PlanetQuest clothing and caps. We will offer special gifts of PlanetQuest memberships, as well, so you don't have to quest alone! Bring a friend along for the adventure!