Image: HIP 13044b
L. Calcada / ESO
This artist’s impression shows HIP 13044b, an exoplanet orbiting a star that entered the Milky Way from another galaxy.
By Senior writer
updated 11/18/2010 3:54:28 PM ET 2010-11-18T20:54:28

Astronomers have confirmed the first discovery of an alien planet in our Milky Way that came from another galaxy.

The Jupiterlike planet orbits a star that was born in another galaxy and later captured by our own Milky Way, sometime between 6 billion and 9 billion years ago, researchers said Thursday. A side effect of the galactic cannibalism brought a faraway planet within astronomers' reach for the first time ever.

"This is very exciting," said study co-author Rainer Klement, an astronomer at Germany's Max-Planck-Institut fur Astronomie, or MPIA. "We have no ability to directly observe stars in foreign galaxies for planets and confirm them."

Stars currently residing in other galaxies are simply too far away, Klement added.

The find may also force astronomers to rethink their ideas about planet formation and survival, researchers said, since it's the first planet ever discovered to be circling a star that is both very old and extremely metal-poor. Metal-poor stars are lacking in typically lack elements heavier than hydrogen and helium.

The newfound planet, called HIP 13044b, survived through its star's red-giant phase, which our own sun will enter in about 5 billion years. So studying it could offer clues about the fate of our solar system as well, researchers said.

HIP 13044b sits extremely close to its parent star, which has now contracted again. The planet completes an orbit every 16.2 days, and it comes within about 5 million miles (8 million kilometers) of its parent star at closest approach — just 5.5 percent of the distance between Earth and the sun.

Searching for telltale tugs
The newly discovered alien planet is at least 25 percent more massive than Jupiter, researchers said. It orbits the star HIP 13044 about 2,000 light-years from Earth in the constellation Fornax.

HIP 13044 is about as massive as the sun, and it is nearing the end of its life. The star has already gone through its red giant phase — when sunlike stars bloat enormously after exhausting the hydrogen fuel in their cores.

The star is also composed almost entirely of hydrogen and helium. It is less than only 1 percent as metal-rich as our sun, making it the most metal-poor star known to host a planet, researchers said.

  1. Space news from
    1. KARE
      Teen's space mission fueled by social media

      Science editor Alan Boyle's blog: "Astronaut Abby" is at the controls of a social-media machine that is launching the 15-year-old from Minnesota to Kazakhstan this month for the liftoff of the International Space Station's next crew.

    2. Buzz Aldrin's vision for journey to Mars
    3. Giant black hole may be cooking up meals
    4. Watch a 'ring of fire' solar eclipse online

The research team scrutinized HIP 13044's movement using a telescope at the European Southern Observatory's La Silla Observatory in Chile. After six months of observing, they detected tiny movements that betrayed the gravitational tug of an orbiting planet.

"For me, it was a big surprise," said study lead author Johny Setiawan, also of MPIA. "I was not expecting it in the beginning."

Setiawan, Klement and their colleagues reported their results in a paper published online Thursday by the journal Science.

An extragalactic origin
Last year, another research team announced that it may have detected a planet in the Andromeda Galaxy. However, that faraway find will be nearly impossible to confirm.

The astronomers performing that previous study used a method called gravitational microlensing, which only works when a planet-hosting star happens to line up with another star. Such events happen very rarely.

HIP 13044, on the other hand, belongs to the Helmi stream of stars that were once part of a nearby dwarf galaxy. Astronomers believe our own Milky Way gobbled up the Helmi stream between 6 billion and 9 billion years ago.

While it's technically possible that the planet was born in the Milky Way and then stripped from its parent star by the interloping HIP 13044, the odds of that happening are minuscule, researchers said.

So HIP 13044 almost certainly has an extragalactic origin.

"We can be pretty sure about that," Klement told "Stellar encounters in the Milky Way essentially don't occur. The chance that the star captured the planet from another star by an encounter is very, very unlikely."

Rethinking theories of planet formation
Most of the nearly 500 alien planets discovered so far orbit metal-rich stars, researchers said. And a metal-rich star is fundamental to the dominant theory explaining how giant planets form — the core-accretion model.

This model posits that dust and gas particles circling a young star cling together and gradually become larger, forming rocks, boulders and eventually the stony cores of giant, gassy planets like HIP 13044b.

  1. Most popular

Because its parent star is so metal-poor, HIP 13044b may have formed in a different way, researchers said. The planet may have arisen via the gravitational attraction between gas molecules, through a process termed the disk-instability model. So it may not have a rocky core at all.

"You are able to form pure gas planets by this method," Klement said.

The fact that such a metal-poor star can host planets should inspire astronomers to look at other stars like it, Klement added. Astronomers haven't examined many up to this point, so they don't have a good handle on how frequently planets might pop up around low-metal stars.

The discovery also hints that planets may have studded the cosmos from the universe's early days — back when pretty much all stars were metal-poor.

"You can think of the very first stars in the universe, or the second or third generation of stars," Klement said. "Could they already have been able to form planets? That's a very fascinating question."

Vision of our solar system's fate?
Our own sun is on the same stellar-evolution track as HIP 13044; scientists predict it will bloat into a red giant in 5 billion years or so. So astronomers may be able to learn something about the fate of our solar system by studying HIP 10344b and its parent star, researchers said.

That fate would not be pretty for Earth. HIP 13044b likely once orbited much farther away from its star but spiraled closer and closer during the red giant phase due to friction with the swollen star's envelope, researchers said. Any more interior planets would have been destroyed during this process.

When our own sun enters its red giant phase, Earth will likely get cooked.

"The inner planets, including Earth, maybe will not survive," Setiawan told "But Jupiter, Saturn and the outer planets might move to closer-in orbits, exactly like we detected."

HIP 13044b is a survivor, but it won't live forever. Its parent star is due to expand again in the next phase of its stellar evolution, researchers said, and this time the planet will almost certainly be engulfed.

© 2013 All rights reserved. More from

Interactive: The search for extrasolar planets

Video: New frontiers in planetary science

Photos: Month in Space: January 2014

loading photos...
  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
  1. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  2. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  3. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  4. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.


Discussion comments


Most active discussions

  1. votes comments
  2. votes comments
  3. votes comments
  4. votes comments