Video: NASA discovers two Earth-sized planets

  1. Closed captioning of: NASA discovers two Earth-sized planets

    >>> a lot of discovering of new planets going on lately. they just discovered one a few days back, and now they found two more. the new ones are kepler 20-e and 20-f. both planets are close to earth's size. the bummer is the temperature. daytime highs averaging 800 and 1,400 degrees. it's a dry 800 and 1,400 degrees. while it would take any known spacecraft millions of years to get there, it's nice to know they're out there.

updated 12/20/2011 7:39:30 PM ET 2011-12-21T00:39:30

Two planets orbiting a star 950 light-years from Earth are the smallest alien worlds known, astronomers announced Tuesday. One of the planets is actually smaller than Earth, scientists say.

These planets, while roughly the size of our planet Earth, are circling very close to their star, giving them fiery temperatures that are most likely too hot to support life, researchers said. The discovery, however, brings scientists one step closer to finding a true twin of Earth that may be habitable.

"We've crossed a threshold: For the first time, we've been able to detect planets smaller than the Earth around another star," lead researcher François Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., told "We proved that Earth-size planets exist around other stars like the sun, and most importantly, we proved that humanity is able to detect them. It's the beginning of an era."

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To discover the new planets, Fressin and his colleagues used NASA's Kepler space telescope, which noticed the tiny dips in the parent star's brightness when the planets passed in front of it, blocking some of its light. This is called the transit method of planet detection. The researchers then used ground-based observatories to confirm that the planets actually exist by measuring minute wobbles in the star's position caused by gravitational tugs from its planets.

"These two new planets are the first genuinely Earth-sized worlds that have been found orbiting a sunlike star," Greg Laughlin, an astronomer at the University of California at Santa Cruz ho was not involved in the new study, said in an email to "For the past two decades, it has been clear that astronomers would eventually reach this goal, and so it's fantastic to learn that the detection has now been achieved." [Gallery: Smallest Alien Planets Ever Seen]

Chances for life
The two Earth-size planets are among five alien worlds orbiting a star called Kepler-20 that is of the same class (G-type) as our sun, and is slightly cooler.

Two of the star system's planets, Kepler-20e and Kepler-20f, are 0.87 times and 1.03 times the width of Earth, respectively, making them the smallest exoplanets yet known. They also appear to be rocky, and have masses less than 1.7 and 3 times Earth's mass, respectively.  Scientists think that they are composed mainly of silicates and iron, much like Earth, though they lack our planet's atmosphere.

Kepler-20e makes a circle around its star once every 6.1 days at a distance of 4.7 million miles (7.6 million kilometers) — almost 20 times closer than Earth, which orbits the sun at around 93 million miles (150 million kilometers).

The planet's sibling, Kepler-20f, makes a full orbit every 19.6 days, at a distance of 10.3 million miles (16.6 million kilometers). Both planets circle closer to their star than Mercury does to the sun. [Infographic: Earth-Size Alien Planets Explained]

These snuggly orbits around their star give the newfound planets steamy temperatures of about 1,400 degrees Fahrenheit (760 degrees Celsius) and 800 degrees F (430 degrees C) — way too warm to support liquid water, and probably too hot for life as we know it, researchers said.

Fressin said the chance of life on either of these planets is "negligible," though the researchers can't exclude the possibility that they used to be habitable in the past, when they might have been farther from their star. There is also a slim chance that there are habitable regions on the planets in spots between their day and night sides (the planets orbit with one half constantly facing their star and the other half always in dark). But astronomers aren't holding out hope.

Image: Planetary lineup
Tim Pyle / CfA
This planetary lineup displays two Earth-sized extrasolar planets, Kepler-20 e and Kepler-20 f, together with Earth and Venus, ranked by their size. Kepler-20 f is represented with an atmosphere, since it may possibly have one, while Kepler-20 e is entirely rocky, as it is likely too hot and would have lost its atmosphere to evaporation.

"The chances of liquid water and life as we know it on Kepler-20e and f are zero," Laughlin said.

Flip-flopped planets
The planetary system around Kepler-20 is an unusual one.

For one thing, scientists say the rocky planets can't have formed in their current locations.

"There's not enough rocky material that close to the host star to form five planets," Fressin said. "They didn't form here; they probably formed farther from their star and migrated in."

Furthermore, the five planets are in an odd order, with the rocky worlds alternating with their gaseous, Neptune-size siblings. That's quite different from most solar systems, including our own, which keeps the rocky terrestrial worlds in close to the sun and the gas giants farther out.

"The architecture of that solar system is crazy," science team member David Charbonneau of Harvard University said during a Tuesday teleconference about the finding. "This is the first time that we've seen anything like this."

Scientists will likely have to revise their theories of how planets form to fully understand the Kepler-20 system.

"How did that form?" Fressin said. "I think it's a puzzle the theorists will have to try to explain."

The star's other planets are called Kepler-20b, 20c, and 20d. Their diameters are 15,000 miles (24,000 kilometers), 24,600 miles (40,000 kilometers) and 22,000 miles (35,000 kilometers), respectively, and they orbit Kepler-20 once every 3.7, 10.9 and 77.6 days.

The largest of these, Kepler-20d, weighs a little less than 20 times Earth's mass, while Kepler-20c is 16.1 times as heavy as Earth, and Kepler-20b is 8.7 times our planet's mass.

Evolving effort
Scientists say finding the smallest exoplanets yet represents a significant milestone in the fast-evolving effort to learn about planets beyond the solar system.

The first alien planet was discovered in 1996, and the first planet found through the transit method came just 11 years ago. Both of those planets were roughly the size of Jupiter.

"I think we're living in special times," Fressin said. "This was unfeasible 10 years ago, and just with the quality of detectors and the quality of the treatment is it possible now."

The total tally of known alien planets is above 700. Kepler alone has discovered 28 definite alien planets, and 2,326 planet candidates, since its launch in March 2009.

Earlier this month, the Kepler team announced another landmark find, the first planet known to occupy the habitable zone around its star where liquid water, and perhaps life, could exist. That planet, called Kepler-22b, is about 2.4 times as wide as Earth.

The dream now is for astronomers to combine the two discoveries and find an Earth-size planet that's also orbiting its star in an Earthlike orbit that puts it in the habitable zone.

"The holy grail of the search for other worlds is to find an Earth analogue, a true Earth twin," Fressin said. "We just need to have these two pieces of the puzzle together."

While the newfound planets orbit with periods of 6.1 and 19.6 days, Fressin estimated the habitable zone around Kepler-20 begins at orbits that take roughly 100 days to make a circuit.

Astronomers think it's only a matter of time before they finally find one that's just right.

"These discoveries are a great technological step forward — to detect small planets, in size like Earth — but these planets are very hot and not in the habitable zone around their star," astronomer Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics wrote in an email. Kaltenegger, who studies the habitability of exoplanets, was not involved in the new study.

"If we can already find these small planets with radii around Earth's now, some future ones could be in the habitable zone of their stars and those future ones would be great targets to look for liquid water and signatures for life," Kaltenegger said.

A paper detailing the discovery was published online by the journal Nature on Tuesday.

You can follow assistant managing editor Clara Moskowitz on Twitter @ClaraMoskowitz. Follow for the latest in space science and exploration news on Twitter@Spacedotcom  and on Facebook.

Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Interactive: The search for extrasolar planets

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
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    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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