Most earthlike exoplanet started out as a gas giant

Jan 06, 2010
This artist's impression shows sunrise over CoRoT-7b, the smallest-known exoplanet. The world is about 70 percent larger than Earth. Now, a team led by Brian Jackson at NASA's Goddard Space Flight Center finds that the planet may be the rocky remains of a gas giant planet whose atmosphere was evaporated by close proximity to the star. Credit: ESO/L. Calçada

The most earthlike planet yet found around another star may be the rocky remains of a Saturn-sized gas giant, according to research presented today at the American Astronomical Society meeting in Washington.

"The first planets detected outside our solar system 15 years ago turned out to be enormous gas-giants in very tight orbits around their stars. We call them 'hot Jupiters,' and they weren't what astronomers expected to find," said Brian Jackson at NASA's Goddard Space Flight Center in Greenbelt, Md. "Now, we're beginning to see Earth-sized objects in similar orbits. Could there be a connection?"

Jackson and his colleagues turned to CoRoT-7b, the smallest planet and the most like that astronomers have found to date. Discovered in February 2009 by the Convection, Rotation and Planetary Transits (CoRoT) satellite, a mission led by the French Space Agency, CoRoT-7b takes just 20.4 hours to circle its sunlike star, located 480 light-years away in the constellation Monoceros. Astronomers believe the star is about 1.5 billion years old, or about one-third the sun's age.

"CoRoT-7b is almost 60 times closer to its star than Earth, so the star appears almost 360 times larger than the sun does in our sky," Jackson said. As a consequence, the planet's surface experiences extreme heating that may reach 3,600 degrees Fahrenheit on the daylight side. CoRoT-7b's size (70 percent larger than Earth) and mass (4.8 times Earth's) indicate that the world is probably made of rocky materials.

"But with such a high dayside temperature, any rocky surface facing the star must be molten, and the planet cannot retain anything more than a tenuous , even one of vaporized rock," Jackson said. He estimates that solar heating may have already cooked off several Earth masses of material from CoRoT-7b.

With the help of computer models that track the planet's mass loss and orbital changes, the researchers have turned back the planet's clock.

"There's a complex interplay between the mass the planet loses and its gravitational pull, which raises tides on the star," Jackson explained. Those tides gradually change the planet's orbit, drawing it inward in a process called tidal migration. But closer proximity to the star then increases the mass loss, which in turn slows the rate of orbital change.

After accounting for the give-and-take of mass loss and tidal migration, the team finds that CoRot-7b could have weighed in at 100 Earth masses -- or about the heft of Saturn -- when it first formed. At that time, it orbited 50 percent farther from its star than it does now.

The researchers also show that regardless of whether CoRot-7b started life as a Saturn-like or as a rocky world, the planet has probably lost many Earth masses of material since its formation.

"You could say that, one way or the other, this planet is disappearing before our eyes," Jackson said.

He suggests that similar processes likely have influenced many other exoplanets that lie close to their . In fact, several recent studies suggest that many hot Jupiters have undergone similar mass loss and tidal evolution, perhaps leaving behind remnant cores similar to CoRoT-7b.

"CoRoT-7b may be the first in a new class of planet -- evaporated remnant cores," Jackson said. "Studying the coupled processes of mass loss and migration may be crucial to unraveling the origins of the hundreds of hot, earthlike space missions like CoRoT and NASA's Kepler will soon uncover."

Explore further: Image: Hubble sweeps a messy star factory

Related Stories

Team finds smallest transiting extrasolar planet ever

Feb 03, 2009

The CoRoT satellite has discovered a planet only twice as large as the Earth orbiting a star slightly smaller than the Sun. It is the smallest extrasolar planet (planet outside our solar system) whose radius ...

First Solid Evidence for a Rocky Exoplanet (w/ Video)

Sep 16, 2009

(PhysOrg.com) -- The longest set of HARPS measurements ever made has firmly established the nature of the smallest and fastest-orbiting exoplanet known, CoRoT-7b, revealing its mass as five times that of Earth's. ...

Mass Loss Leaves Close-In Exoplanets Exposed to the Core

Apr 21, 2009

(PhysOrg.com) -- An international team of scientists has found that giant exoplanets orbiting very close to their stars could lose a quarter of their mass during their lifetime. The team found that planets ...

COROT and the new chapter of planetary searches

Nov 14, 2006

The launch of COROT on 21 December 2006 is a long awaited event in the quest to find planets beyond our Solar System. Searching from above the Earth's atmosphere, COROT – the CNES project with ESA participation ...

Recommended for you

Image: Multicoloured view of supernova remnant

10 hours ago

Most celestial events unfold over thousands of years or more, making it impossible to follow their evolution on human timescales. Supernovas are notable exceptions, the powerful stellar explosions that make ...

Ultra-luminous X-ray sources in starburst galaxies

10 hours ago

Ultra-luminous X-ray sources (ULXs) are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. ULXs are rare. Most galaxies (including ...

When a bright light fades

10 hours ago

Astronomer Charles Telesco is primarily interested in the creation of planets and stars. So, when the University of Florida's giant telescope was pointed at a star undergoing a magnificent and explosive death, ...

Image: Horsehead nebula viewed in infrared

11 hours ago

Sometimes a horse of a different color hardly seems to be a horse at all, as, for example, in this newly released image from NASA's Spitzer Space Telescope. The famous Horsehead nebula makes a ghostly appearance ...

The Milky Way's new neighbour

11 hours ago

The Milky Way, the galaxy we live in, is part of a cluster of more than 50 galaxies that make up the 'Local Group', a collection that includes the famous Andromeda galaxy and many other far smaller objects. ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

austux
not rated yet Jan 06, 2010
A more interesting exoplanet is KOI 74b, which is 4x hotter than the star it orbits...
Rohitasch
1 / 5 (1) Jan 06, 2010
Since they've been finding gas giant after gas giant, I have had a feeling that most rocky planets should be left-over cores of gas planets.
omatumr
1 / 5 (3) Jan 06, 2010
No. This Earth-like planet formed out of elements near the core of the supernova that gave birth to the solar system [Science 195, 208-209 (1977); Nature 277, 615-620 (1979)].

With kind regards,
Oliver K. Manuel
Nik_2213
not rated yet Jan 07, 2010
Could Mercury be a 'Hot Jupiter' remnant, or does Venus' orbit suggest otherwise ??

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.