Frequently Asked Questions

Here's a list of questions we frequently get, along with our answers.

When can I download the Collaboratory?
How does PlanetQuest find planets?
How many stars have planets around them?
What makes a habitable planet?
Can I discover a planet?
Can I name a planet if I discover it?
Can PlanetQuest detect other "Earths"?
Where do the star pictures come from?
What is a light curve?
What is optical SETI?
What is a variable star?
What is the transit detection algorithm?
What is the PlanetQuest star catalog?
Where is PlanetQuest headquarters?
Who are the people of PlanetQuest?
How can I send questions in to PlanetQuest?

How can I stay informed about progress at PlanetQuest?
Will PlanetQuest run out of stars?

When can I download the Collaboratory?
We are currently working hard to develop the Collaboratory and have begun internal alpha testing. We plan to release a limited alpha version in 2007 and to go live by the end of the year with a full beta version. You can help us launch by making a donation!

How does PlanetQuest find planets?
When the orbit of a planet is aligned with our line-of-sight toward the star, we can detect the "transit" of the planet as it crosses the star’s disc. Thus we are actually detecting the shadow the planet casts onto Earth, which causes a slight drop in the brightness of the star. We then need to make sure it is a planet and not any of the other things (Earth’s atmosphere, starspots, noise from the electronic cameras, etc.) that can cause drops in brightness also, and this statistical check we call the "transit detection algorithm" or TDA for short. We will soon be adding three more detection algorithms—a double-star transit planet detection algorithm, an eclipsing binary timing planet detection algorithm, and a gravitational lens planet detection algorithm. In addition, we are developing a new SETI detection algorithm based on information theory that will complement existing SETI searches like SETI@home.

How many stars have planets around them?
A little less than 1% of the stable sunlike stars in the solar neighborhood have giant inner planets orbiting them. This statistic is the result primarily of the survey done by the radial velocity method of detecting extrasolar planets. The statistics of outer giant planets (like Jupiter) around other stars have yet to be constrained, and no-one has found a terrestrial-sized planet around another sunlike (dwarf) star yet (although large-terrestrial-mass planets have been found around pulsars, which are exploded giant stars). So about one in 100 stars have giant inner planets, and about 7% of these will be orbiting edge-on (in the line-of-sight between the star and Earth) so that we can detect a transit. The smaller the star, the larger the transit, so if smaller planets exist, we should be able to detect them as well around the smallest stars. And it looks like there could be many more smaller than larger planets around other stars.

What makes a habitable planet?
A planet is considered habitable (note that this does not mean inhabited, but that it has the potential of being inhabited) when liquid water can persist for long periods of time on the surface, organic material is readily available, and there is a dependable source of energy. Dwarf stars have good circumstellar habitable zones (CHZs) or places where water can exist for a long time because they are pretty stable stars. Giant and supergiant stars change brightness too quickly to have good CHZs. A planet also has to have an orbit the right distance from the star (together with atmospheric blanket warming—known as the "greenhouse effect") to be large enough to recycle its atmosphere (otherwise the gases in the atmosphere wind up as chemicals in the rocks), and small enough not to have amassed a huge atmosphere (like Jupiter, Saturn, Uranus, or Neptune in our solar system). There are many other factors but these three—a good star, a planet of the right size and distance from the star, and an atmosphere of the right composition—are the major considerations.

Can I discover a planet?

Yes. This is the main point of PlanetQuest, to bring the thrill of actual discovery to as many people as possible. This is quite different from your helping us to do science—we want you to be the scientist-astronomer!

Can I name a planet if I discover it?

The International Astronomical Union assigns official names to stars and planets; however, your name will be entered into the PlanetQuest Discoveries Catalog available on the Web as a classifier of the star and/or codiscoverer of a new planet.

Can PlanetQuest detect other "Earths"?

This depends on what one means by "other Earths." An Earth-sized planet around a Sunlike star is (at present) only detectable from space, and the transit method is the way that the upcoming NASA Kepler spacecraft mission will detect such planets. However, the PlanetQuest telescopes (2.0-meters) will be large enough to detect the light from many faint stars. (These faint stars are small—about 1/100th the brightness of our Sun—and are called "red-dwarfs" or "M-dwarfs.") These faint stars are smaller than the Sun—some less than 1/20th the size-area of the solar disc. If a moth flies in front of a searchlight, the relative dimming is quite small. But if it flies in front of a flashlight, the relative dimming is much larger. So, when a planet of a given size (moth) transits (flies in front of) a solar-sized star (searchlight), it takes much more precision to see a change than if it transits (flies in front of) an M-dwarf star (flashlight). So, we will be able to detect the larger of the terrestrial-sized planets around the smallest stars we can see. If these planets are discovered within the circumstellar habitable zone (which is much closer than the Earth-Sun distance), then we—actually you, the discoverer—will have an exciting prospect indeed: a potentially habitable planet!

Where do the star pictures come from?
We use a large electronic camera (a CCD—similar to the ones in digital cameras except with more precise ability to record light) at the focus of our telescopes to record incoming light that has traveled from between 4 and 30,000 light years so that we can record a change in the brightness due to any planetary transits. We must correct each star image for Earth’s atmospheric effects, and electronic effects caused by our equipment, and convert the time the image was taken to the time in the center of the Sun (this is called the heliocentric julian time or HJD) so that we can compare the times of transits taken at different points in Earth’s orbit around the Sun (without this correction, one could be almost 17 minutes off).

What is a light curve?
The light curve of a star is a plot of its brightness against the time it has that brightness. Most of the time this is given in "differential magnitudes" or the brightness variation of a given star compared with other stable (or "standard") stars in the same star field and so imaged (electronically photographed) at the same time. The light curve is corrected for star color differences, precise time, and all instrumental effects so that any remaining brightness variations are intrinsic to the star itself—or to a planet orbiting that star.

What is optical SETI?
Radio SETI (Search for Extraterrestrial Intelligence) is the effort to detect narrow-band radio signals. Nothing known other than technology (i.e., a radio station) can make narrow-band signals—that is, signals that you can tune into and out of with just a turn or two of the radio dial. Optical SETI uses the same reasoning, but here again apparently only technology can produce light pulses that last a billionth (nano) of a second (although stars can collapse to make a millisecond pulsar that can pulse a thousand times per second). Since PlanetQuest will be using only the red part of the star’s light to detect the transits of planets across their stars, we plan to "beam-split" (divide off) the blue light and send it to our nano-second diode detectors to see at the same time if any of those stars are sending billionth-of-a-second pulses toward us, as well. Thus you, the PlanetQuester, will be looking for planets and extraterrestrial technology at the same time!

What is the transit detection algorithm?
The transit detection algorithm (or TDA) is a statistical test of the presence of a planet in the light curve of a star (the light curve is a plot of the brightness of the star with time). It uses models of variable star types and compares them with the light curve of the unclassified star to see which one matches the best. It then proceeds to compare models of possible planet transits (varying the planet size, orbital period, and orbital phase—where it started in its orbit compared with when we started to observe it, sometimes called the orbital "epoch") to see which one of these matches the best, if any. Thus, when we have a candidate planet we can say with what dependability we know it is a planet (called the "confidence" level). The complementary way of looking at this is that we will also know what is called the "false alarm" rate—that is, at what level we are being fooled into thinking it is a planet when it is not. This number should be as small as possible and the confidence limit should be as high as possible. This is what takes so much computational time.

What is the PlanetQuest star catalog?
The PlanetQuest star catalog is where you go down in history as a true astronomical discoverer. Astronomers, astrophysicists, astrobiologists, and historians of science will know that you were the first to explore and classify a particular star. Also, that some of you will be discoverers of whole new worlds yourself. The Star Catalog will record all discoveries so that not just the professional astronomical community will know who made these discoveries but also you will find out how your friends are doing with their discoveries. Many many of the discoveries will be most important to the scientific community for centuries to come.

Where is PlanetQuest headquarters?
PlanetQuest is headquartered in the San Francisco Bay Area. Our telescope network at present includes the oldest professional reflecting telescope in the world (the Crossley 0.9-meter at Lick Observatory), a 1-meter at Siding Spring Australia (summer 2005), the PASS array in the Canary Islands, and the Vulcan South telescope at the South Pole. We have also been invited to join an observing consortium at the Calar Alto Observatory in southern Spain and to have two PlanetQuest telescopes at Cerro Tololo Inter-American Observatory in Chile.

Who are the people of PlanetQuest?
See the "People" section. The main people are astronomers whose expertise is extrasolar planet detection, engineers whose expertise is signal detection statistics, computer scientists whose expertise is distributed computing, educators whose expertise is fun in science learning, and business people whose expertise is creative support of a worldwide observatory and educational system.

How can I send questions in to PlanetQuest?
Just send your questions to info@planetquest.org and we will answer them in our Frequently Asked Questions section. They will be listed here and searchable by keyword.

How can I stay infomed about progress at PlanetQuest?
Sign up for our Friends of PlanetQuest newsletter! We send the latest news and up-to-date information to our supporters in this way, as well as on our News page right on this website.

Will PlanetQuest run out of stars?
PlanetQuest will only run out of stars if we run out of enthusiasm for looking at the heavens—not likely! We plan to add as many telescopes as needed to keep PlanetQuest going for everyone on Earth who would like to participate in this exploration of the heavens. And there are enough stars to vastly outdistance even the growing population of Earth; we will just need the telescopes to reach enough of them to continue the adventure. Email us at donate@planetquest.org for more information and see our Missions in Need page under Donate.