Stuart Littlefair/Univ. of Sheffield
This artist's concept shows two newly discovered planets orbiting the binary star NN Serpentis.
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updated 10/27/2010 11:29:17 AM ET 2010-10-27T15:29:17

Two massive Jupiter-like planets were recently discovered orbiting around two extremely close sister stars an unexpected find, given the disturbing gravitational effects within most binary star systems that usually disrupt planets from forming.

The alien planets were found to orbit around the binary star system NN Serpentis, which is located about 1,670 light-years from Earth.

The more massive of the two stars is a very small white dwarf the burnt-out remnant that is left over when a sun-like star dies. The star is 2.3 times the diameter of Earth, but has a temperature of more than 89,500 degrees Fahrenheit (49,700 degrees Celsius) almost nine times hotter than the surface of the sun.

The other star in the pair is a larger but cooler star, with a mass only one-tenth that of the sun. The two stars are joined in a very tight mutual orbit.

Lucky break
The astronomers caught a lucky break in observing this binary star system because it happens to lie in the same plane as Earth, creating an eclipse every 3 hours and 7 minutes when the larger star moves in front of the smaller one. [ Gallery: The Strangest Alien Planets.]

The resulting change in the brightness of the system acts like a highly precise clock. By monitoring the eclipses, the team of astronomers was able to detect small changes in the timing caused by the gravitational pull of two planets orbiting the stellar pair and tugging them out of whack, altering the eclipse schedule.

The larger planet in the system is about 5.9 times more massive than Jupiter. It orbits the binary stars every 15.5 Earth years at a staggering distance of roughly 558 million miles. Closer in, the second planet orbits every the binary pair every 7.75 Earth years, and is about 1.6 times more massive than Jupiter.

An international team of astronomers detected the planetary system using a wide variety of observations taken over two decades from several ground-based telescopes.

Binary parents
While the discovery of planets outside our solar system is becoming more common, only a tiny fraction of these planets have been found to orbit stars which themselves are in binary or multiple systems. This is simply because in these systems, there is little room between the stars for planets to form.

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The two planets in NN Serpentis do not orbit very close to the binary stars, but the double star system was not always as tight as it is now. Back when the present white dwarf star was a normal star, twice as massive as the sun, the two stars were separated by a much greater distance such that the observable eclipses would have happened about once every two years.

When the more massive star ended its normal life of burning hydrogen in its core, it bloated itself into a red giant star and engulfed the second star in its diffuse outer envelope. The friction of the companion star moving within the red giant's envelope eventually caused the red giant to lose 75 percent of its mass.

This left only the intensely hot core of the original star, and a relatively unscathed companion star that now orbits extremely close to the newly created white dwarf.

The turbulent change from a normal double star system to a tight binary containing a hot white dwarf would have been even more dramatic for any planets present beforehand: The 75 percent loss of the original star's mass would also equal a 75 percent loss in the star's gravitational force.

This could easily result in the release of planets, sending them careening off into space. Or, it may simply have resulted in a dramatic change in the planets' orbits.

Second option
In a separate scenario, the planets around NN Serpentis could have also been created only a million years ago, when large amounts of gas and dust were cast off from the main star to form a more massive version of a proto-planetary disk. From this material, planets might have formed. If this is the case, then it is possible that these massive planets were, in fact, born after the death of the star that enabled their creation.

The results of the study are published online in recent issue of the journal Astronomy & Astrophysics.

In a separate discovery, a Jupiter-sized alien planet was recently found orbiting the star HR 7162, which is a binary star system located 49 light-years away, in the constellation Lyra. These recent findings are forcing astronomers to rethink their theories about how gas giant planets form.

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Photos: Month in space: September 2010

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  1. Martian sea of sand

    Near Mars' north pole, the landscape is dominated by sand dunes forming a massive erg, or sand sea, much like parts of the Sahara Desert on Earth. In parts of the erg, sand is abundant and covers the entire surface. Here, near the edge, sand is in shorter supply and the dunes are separated by areas of lighter-toned soil. This color-coded image from NASA's Mars Reconnaissance Orbiter was captured in July and published on Sept. 1. (NASA /JPL/ University of Arizona) Back to slideshow navigation
  2. Dance of the galaxies

    NGC 5426 and NGC 5427 are two spiral galaxies of similar sizes engaged in a dramatic dance. It is not certain that this interaction will end in a collision and ultimately a merging of the two galaxies, although the galaxies have already been affected. Together known as Arp 271, this dance will last for tens of millions of years. This image, released Aug. 30, was taken with the EFOSC instrument attached to the New Technology Telescope at the European Southern Observatory's La Silla facility in Chile. (ESO) Back to slideshow navigation
  3. Crazy cones on Mars

    These Martian volcanic cones are similar in size and shape to cones found in Iceland, where hot lava has run over wet ground. The heat from the lava boils the water, which bursts through the lava flow. These steam-driven exploding bubbles of lava throw chunks of molten and solid lava into the air. A long series of such explosions is needed to build up one of the large cones. This image, released Sept. 1, was taken by a high-resolution camera on NASA's Mars Reconnaissance Orbiter. (NASA via AP) Back to slideshow navigation
  4. Creating Curiosity

    Engineers work on the Curiosity rover at NASA's Jet Propulsion Laboratory in Pasadena, Calif., on Sept. 16. Curiosity, also known as the Mars Science Laboratory, is due to be launched to the Red Planet from Cape Canaveral Air Force Station in Florida in late 2011. (Jae C. Hong / AP) Back to slideshow navigation
  5. Igor the Terrible

    A photo taken from the International Space Station on Sept. 15 shows Hurricane Igor whirling through the Atlantic Ocean hundreds of miles below. In the foreground you can see a Russian spacecraft docked to the space station. (NASA via AFP - Getty Images) Back to slideshow navigation
  6. Dodging a bullet

    An extreme ultraviolet image from NASA's Solar Dynamics Observatory shows an exceptionally heavy plasma eruption on the surface of the sun on Sept. 8. Not to worry, though: The resulting blast of electrically charged particles missed Earth. (NASA/SDA via EPA) Back to slideshow navigation
  7. Bull's-eye on the moon

    A color-coded topographic map based on data from NASA's Lunar Reconnaissance Orbiter shows the 580-mile-wide Mare Orientale, the largest young impact basin on the moon. This basin formed when a projectile hit the moon about 3.8 billion years ago and penetrated deeply into the lunar crust, ejecting huge amounts of material. The image was released Sept. 16 to coincide with the publication of scientific papers about LRO's mission. (NASA / Goddard / MIT / Brown) Back to slideshow navigation
  8. Two flashes from Jupiter

    A fleeting bright dot on each of these images of Jupiter marks a small comet or asteroid burning up in the atmosphere. The image on the left was taken on June 3 by Australian amateur astronomer Anthony Wesley, with a fireball appearing on the right side. The image on the right was taken by Japanese amateur astronomer Masayuki Tachikawa on Aug. 20, with a fireball appearing at upper right. In a report published Sept. 9, NASA said neither event left a lasting mark on the planet. (NASA via Reuters) Back to slideshow navigation
  9. Spiral in space

    A picture from the Hubble Space Telescope, published Sept. 7, shows an unusual spiral nebula around the star LL Pegasi, 3,000 light-years from Earth. Astronomers say the spiral shape was created by material swirling out from one of the stars in a binary-star system. (ESA / NASA) Back to slideshow navigation
  10. Bootprint on Mars?

    Orcus Patera is an enigmatic elliptical depression near Mars' equator, in the eastern hemisphere of the planet. Located between the volcanoes of Elysium Mons and Olympus Mons, its formation remains a mystery. The favored theory is that the feature was created when a comet or asteroid hit the Red Planet at a shallow angle. This picture of Orcus Patera, released Aug. 27, was taken by the European Space Agency's Mars Express orbiter. (ESA) Back to slideshow navigation
  11. NASA's six-legged robot

    The All-Terrain Hex-Limbed Extra-Terrestrial Explorer, or ATHLETE, is a prototype heavy-lift utility vehicle designed to support future human exploration of extraterrestrial surfaces. ATHLETE got a chance to flex its limbs on Sept. 15 in northern Arizona during NASA's Desert RATS field tests. (Robyn Beck / AFP - Getty Images) Back to slideshow navigation
  12. Practicing for Mars

    Geologists Jacob Bleacher and Jim Rice take a close look at a rock formation in northern Arizona before collecting samples on Sept. 5. The geologists took part in NASA's Desert RATS exercise, which is aimed at trying out the equipment and procedures that could come into play during a mission to Mars or other interplanetary destinations. The "RATS" in the name stands for "Research and Technology Studies." (NASA Desert RATS) Back to slideshow navigation
  13. Ice sculptures in space

    Clouds of gas and dust in the Carina Nebula are sculpted into bizarre shapes by stellar radiation, as seen in this image captured by the Hubble Space Telescope and unveiled on Sept. 16. The Hubble team compares the pillars to "cosmic ice sculptures." (NASA, ESA, and the Hubble Heritage Project) Back to slideshow navigation
  14. New York at night

    New York City is ablaze in an image sent by NASA astronaut Doug Wheelock from the International Space Station on Aug. 28. "The City That Never Sleeps," he wrote in a Twitter tweet. "New York, New York on a clear summer night." (Doug Wheelock / NASA via AP) Back to slideshow navigation
  15. Shooting a laser at the sky

    This image, released on Sept. 6, shows a laser beam shooting up from the European Southern Observatory’s Paranal Observatory in Chile. The laser beam is used as a guide for the observatory's adaptive-optics system, which compensates for unsteadiness in the atmosphere to produce sharper astronomical images. (Y. Beletsky / ESO) Back to slideshow navigation
  16. Thar she blows!

    A solid rocket motor that could be used on future NASA launch vehicles is tested Aug. 31 at ATK Aerospace Systems' test site in Promontory, Utah. The rocket motor burned for just over two minutes during the successful static test, producing about 3.6 million pounds of thrust. (ATK) Back to slideshow navigation
  17. The road ahead

    NASA's Opportunity rover looks across a series of sand ripples and bedrock outcrops toward the rim of Endeavour Crater on the horizon on Sept. 6. Opportunity has just crossed the halfway mark in its trip from Victoria Crater to Endeavour. The rover headed out from Victoria in September 2008. (NASA / JPL-Caltech) Back to slideshow navigation
  18. Saturn and its children

    Four of Saturn's moons join the planet for a well-balanced portrait, released by the Cassini orbiter's imaging team on Sept. 10. Saturn's largest moon, Titan, is at lower left. Tethys is at upper right. Two much smaller moons, Pandora and Epimetheus, are barely visible near the rings. (NASA/JPL/Space Science Institute) Back to slideshow navigation
  19. Moon and Earthglow

    A crescent moon is just about to set below Earth's glowing horizon in a picture taken Sept. 4 from the International Space Station. The glow is sunlight scattered by Earth's atmosphere. (NASA via Reuters) Back to slideshow navigation
  20. Twilight of the shuttle

    Photographers gather early on the morning of Sept. 21 to take pictures of the space shuttle Discovery, just after its arrival at the launch pad. Discovery is scheduled to embark on the shuttle fleet's penultimate mission on Nov. 1. The final shuttle flight, involving Endeavour, is set for launch in February - although there's a chance that one additional mission will be flown. (Scott Audette / Reuters) Back to slideshow navigation
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