Image: Exoplanets
PHL @ UPR Arecibo, ESA/Hubble, NASA
There are 27 candidate planets waiting for inclusion in the the Habitable Exoplanets Catalog.
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updated 12/6/2012 8:20:31 PM ET 2012-12-07T01:20:31

A new catalog aims to list all the known planets in the galaxy that could potentially be habitable to life. The count is at seven so far, with many more to come, researchers said.

The online listing, called the Habitable Exoplanets Catalog, celebrated its first anniversary this week. When it was first released last year, it had two potential habitable planets to its name. According to lead researcher Abel Mendez, the team expected to add maybe one or two more in the catalog's first year. The addition of five suspected new planets was wholly beyond anyone's expectations.

"The main purpose is for research, but then I realized that also for the public, it was very important," said Mendez, director of the University of Puerto Rico at Arecibo's Planetary Habitability Laboratory.

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"There are many press releases announcing discoveries of habitable planets ... and that is confusing," Mendez told SPACE.com. "So having a catalog that everyone can check what is available right now is useful."

Mendez also said scientists are getting smarter about finding exoplanets, and the pace of discovery is increasing. [ Gallery: 7 Habitable Exoplanets ]

There are 27 candidate planets waiting for inclusion in the habitable portion of the catalog. Meanwhile, the HARPS (High Accuracy Radial Velocity Planet Searcher) instrument in Chile and orbiting Kepler Space Telescope, among others, are quickly finding new exoplanets every month.

Preliminary parameters for life
Mendez's team principally assesses the potential of life on a planet using three metrics: the variability of energy from the host star that the planet receives, the mass of the planet and the planet's size. Simplistically, bigger gas giants orbiting variable stars are less likely to host life than smaller, rocky planets near stable stars.

Much of the catalog's data come directly from the research teams involved in an exoplanet's discovery. The catalog also includes information from the Extrasolar Planets Encyclopaedia and the NASA Exoplanet Archive.

Mendez cautions that the information is preliminary. So far, most of what we know about exoplanets comes from a simple physical assessment. Much less is known about chemical and biological information.

Also, sometimes a planet is found that can't be confirmed through independent observation. One famous example is Gliese 581g, which was discovered by one team but could not be found by another team using a different instrument. New datasets have been released, but there still is a debate. Mendez calls these situations "tricky."

"There are two versions of the story, and the two versions can be supported by data," he said. "But because we think that there's still the sense that planet could exist, we are including it [as a candidate]."

Public support
Mendez initially created the database to help with his research. He says he was honored by the reaction from the public and research community in the months after its release.

In the first two days of its existence, the catalog attracted 100,000 views — "for a research page, that's good," Mendez joked. It now consistently garners 10,000 to 30,000 views a month.

He's been approached at conferences and praised for his work, and the NASA Astrobiology Institute has told him the catalog is a useful tool. "It was more than I expected," he said.

Mendez has been aggressive with public outreach, with his team building mobile phone apps as well as a "periodic table" of exoplanets to drum up interest.

Meanwhile, more work on the catalog beckons. The team expects to add new models in the coming year, which will affect the measurements on objects already in the catalog.

But it will be discoveries, rather than mathematics, that will drive the pace of change, the team added in a statement.

"A true Earth analog or a potentially habitable exomoon would be big discoveries," it read. "Certainly, this was the right time to start mapping the habitable universe around us."

Follow Elizabeth Howell @howellspace, or SPACE.com @Spacedotcom. We're also on Facebook and Google+.

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Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
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  5. Accidental art

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  6. Supersonic test flight

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    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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