Discovery of coolest Earth-like planet

January 26, 2006

An international team of astrophysicists has discovered a new planet five times the size of Earth, the smallest extrasolar planet unearthed to date outside of our solar system.

Using a network of telescopes scattered across the globe, the group discovered the extrasolar planet is more Earth-like than any other planet found so far. It circles its parent star every 10 years. The discovery opens a new chapter in the search for planets that support life.

"That fact that we stumbled on one means there are thousands of them out there," said Kem Cook, an astronomer at the Lawrence Livermore National Laboratory who is also a member of PLANET, Probing Lensing Anomalies NETwork, a part of the group that made the discovery. "It's got a solid core. Its mass is low enough that it couldn't hold itself together if it were just gas."

The new planet and its red dwarf parent star lies in the constellation Sagittarius, not far from the central bulge of our galaxy.

To date, more than 200 planets within the Milky Way have been found. However, the majority of them are gas giants, close to the size of Jupiter or Saturn that orbit their parent star at distances much less than the distance from Earth to the sun. The new planet, made of rock and ice, orbits at three times the distance from Earth to the sun.

The team used a technique called microlensing, an idea that Albert Einstein came up with in 1936. By observing a particular star (A) on the sky, imagine another star (B) in the line of sight toward A. He showed that when A, B and the observer are exactly aligned, a ring-like image will be formed. Star B acts as a gravitational lens by bending the light of star A toward the observer. From there, objects, such as planets or white dwarfs, around A temporarily brighten star B.

In this case, star A causes a characteristic brightening in star B that lasts about a month. Any planets orbiting star A can produce an additional signal, lasting days for giant planets down to hours for Earth-mass planets. The planet is not directly 'seen,' or even the star that it's orbiting, but its presence can be deduced from the effect of its gravity. In the case of the newly found planet, the extra brightening lasted about 12 hours.

"There's a deviation of light when a planet is in the way," Cook said. "In this instance, there was a half-day brightening that was indicative of a planet."

The new planet - deemed OGLE-2005-BLG-290 Lb - orbits a red dwarf five times less massive than the sun. Its cool parent star and large orbit implies that the surface temperature is close to 428 degrees Fahrenheit below zero, much too cold for liquid water. Astronomers predict that its rocky surface is probably deeply buried beneath frozen oceans.

"There must be lots of these out there," Cook said. "The microlensing technique is not going to find nearby planets. We're not going to discover planets to which NASA can fly. Microlensing can tell us how common planets are in distant parts of the galaxy and probe details of planetary formation that other techniques cannot."

The discovery is the joint effort of three independent microlensing campaigns: PLANET/RoboNet, OGLE (Optical Gravitational Lensing Experiment), and MOA (Microlensing Observations in Astrophysics), involving a total of 73 collaborators affiliated with 32 institutions in 12 countries - France, the United Kingdom, Poland, Denmark, Germany, Austria, Chile, Australia, New Zealand, United States, South Africa and Japan.

In most cases, new planets have been found using a technique called the Doppler shift, in which the wavelength of light emitted by a moving object is shifted due to its motion. Radiation is red shifted when an object is moving away from us and blue shifted when the object is moving toward us. Astronomers use Doppler shifts to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. As a giant planet orbits a star, it tugs it back and forth, producing a very small (meters per second) Doppler shift. However, using the Doppler shift method, most planets found have been giant gas planets.

Microlensing is more sensitive to planets that orbit their star at distances that are in the range of the Earth sun separation. OGLE-2005-BLG-390Lb is only the third extra-solar planet discovered so far from microlensing searches.

The new planet and its red dwarf parent star lies in the constellation Sagittarius, not far from the central bulge of our galaxy.

The research appears in the Jan. 26 edition of the journal Nature.
Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.

Laboratory news releases and photos are also available at and on UC Newswire.

DOE/Lawrence Livermore National Laboratory

Related Planets Articles from Brightsurf:

Stars and planets grow up together as siblings
ALMA shows rings around the still-growing proto-star IRS 63

Two planets around a red dwarf
The 'SAINT-EX' Observatory, led by scientists from the National Centre of Competence in Research NCCR PlanetS of the University of Bern and the University of Geneva, has detected two exoplanets orbiting the star TOI-1266.

Some planets may be better for life than Earth
Researchers have identified two dozen planets outside our solar system that may have conditions more suitable for life than our own.

Fifty new planets confirmed in machine learning first
Fifty potential planets have had their existence confirmed by a new machine learning algorithm developed by University of Warwick scientists.

Rogue planets could outnumber the stars
An upcoming NASA mission could find that there are more rogue planets - planets that float in space without orbiting a sun - than there are stars in the Milky Way, a new study theorizes.

Could mini-Neptunes be irradiated ocean planets?
Many exoplanets known today are ''super-Earths'', with a radius 1.3 times that of Earth, and ''mini-Neptunes'', with 2.4 Earth radii.

As many as six billion Earth-like planets in our galaxy, according to new estimates
There may be as many as one Earth-like planet for every five Sun-like stars in the Milky way Galaxy, according to new estimates by University of British Columbia astronomers using data from NASA's Kepler mission.

How planets may form after dust sticks together
Scientists may have figured out how dust particles can stick together to form planets, according to a Rutgers co-authored study that may also help to improve industrial processes.

Planets around a black hole?
Theoreticians in two different fields defied the common knowledge that planets orbit stars like the Sun.

The rare molecule weighing in on the birth of planets
Astronomers using one of the most advanced radio telescopes have discovered a rare molecule in the dust and gas disc around a young star -- and it may provide an answer to one of the conundrums facing astronomers.

Read More: Planets News and Planets Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to