Cultivating a Planetary Garden: How Long Does It Take?

According to the most popular theory of planet formation, planets are akin to redwood trees, growing in size very gradually. Rocky planets like Earth develop over millions of years, followed by gas giants like Jupiter, which build upon rocky cores. But new evidence from NASA's Spitzer Space Telescope suggests that some gas giants may sprout in less than one million years, more like planetary wildflowers than trees.

Image: An artist's conception of planets clearing a gap in a stellar disk. NASA/JPL-Caltech/T. Pyle (SSC)

The evidence comes in the form of gaps and holes. Planets are born out of flat disks of dust and gas that spin around young stars. As a burgeoning planet circles around its star, it is thought to cut through the disk, leaving an empty gap or doughnut-like hole.

Spitzer is acquiring data on more and more of these disk clearings around stars that are surprisingly young. Though some of the clearings were seen before, Spitzer's highly sensitive infrared eyes are providing new, detailed information that indicates gas giant planets may be the cause. Because the stars are only about one million years old, relatively young in cosmic terms, the putative planets would have sprung up quickly.

"The results pose a challenge to existing theories of giant planet formation, especially those in which planets build up gradually over millions of years," said Dr. Nuria Calvet of the University of Michigan, Ann Arbor. "Studies like this one will ultimately help us better understand how our outer planets, as well as others in the universe, form."

A new paper from Calvet and her team, appearing in the Sept. 10 issue of the Astrophysical Journal Letters, presents further evidence for fast-track planets. They report the most detailed models yet of two known clearings around young stars- a gap in the disk of GM Aurigae, and a hole in the disk of DM Tauri.

Last year, the team found similar results on a third clearing, a hole in the disk of an equally young star called CoKuTau4. That study was led by team member Dr. Dan Watson of the University of Rochester, N.Y.

In all three cases, the Spitzer data reveal that the clearings have sculpted outer walls, a strong indicator that bodies are sweeping through the dust, leaving empty trails. The bodies would most likely be gas giants because rocky planets would be too small to produce the clearings. These observations were made with Spitzer's infrared spectrograph.

"Before we had only a fuzzy knowledge of the holes and the gap," said Calvet. "Spitzer's infrared spectrograph doesn't give us a picture, but provides detailed information about the structure of the clearings. The structure suggests that planets may be present."

GM Aurigae, DM Tauri and CoKuTau4 are all sibling stars living in the same youthful stellar neighborhood in the Taurus constellation, 420 light-years from Earth. GM Aurigae is about the same size as our Sun, while the two siblings are smaller.

If DM Tauri's hole existed in our own solar system, it would encompass Mercury, Venus, Earth and Mars; CoKuTau4's hole would expand out to the orbit of Saturn, and GM Aurigae's gap would span the space between the orbits of Jupiter and Uranus.

"GM Aurigae is essentially a much younger version our Sun," said Watson. "Looking at it is like looking at baby pictures of our Sun and outer solar system."

Future Spitzer observations of similarly young stars and their disks will help astronomers determine if planets are indeed making their way through the dust. Ultimately, this information will help astronomers better understand the roots of our own planetary garden.

Copyright 2005 by Space Daily, Distributed United Press International

Related stories:

Rapid-born planets present 'baby picture' of our early solar system
Using NASA's Spitzer Space Telescope, a team of astronomers led by the University of Rochester has detected gaps ringing the dusty disks around two very young stars, which suggests that gas-giant planets have formed there. A year ago, these same researchers found evidence of the first "baby planet" around a young star, challenging most astrophysicists's models of giant-planet formation.
Beta Pictoris planet finally imaged?
(PhysOrg.com) -- The hot star Beta Pictoris is one of the best-known examples of stars surrounded by a dusty 'debris' disc. Debris discs are composed of dust resulting from collisions among larger bodies like planetary embryos or asteroids. They are a bigger version of the zodiacal dust in our Solar System. Its disc was the first to be imaged — as early as 1984 — and remains the best-studied system. Earlier observations showed a warp of the disc, a secondary inclined disc and infalling comets onto the star. "These are indirect, but tell-tale signs that strongly suggest the presence of a massive planet lying between 5 and 10 times the mean Earth-Sun distance from its host star," says team leader Anne-Marie Lagrange. "However, probing the very inner region of the disc, so close to the glowing star, is a most challenging task."
Submillimeter Eagle Eyes on Mauna Kea
(PhysOrg.com) -- Three observatories on Mauna Kea have come together to form the world's most powerful facility for detailed submillimeter imaging. An exploratory project, the Extended Submillimeter Array (eSMA) will explore the Universe using light that the human eye cannot see, at wavelengths around 0.8 millimeter. There are many objects in the sky that emit radiation in this submillimeter range, especially the dusty regions in which new stars, planets and even entire galaxies are being born. These clouds of gas and tiny dust particles are completely dark in visible light, but submillimeter waves can penetrate them.
Hubble directly observes planet orbiting Fomalhaut
(PhysOrg.com) -- Estimated to be no more than three times Jupiter's mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Austrinus (the Southern Fish).
First fuzzy photos of planets outside solar system
(PhysOrg.com) -- Astronomers using the Gemini North telescope and W.M. Keck Observatory on Hawaii's Mauna Kea have obtained the first-ever direct images identifying a multi-planet system around a normal star.
Dusty Shock Waves Generate Planet Ingredients
(PhysOrg.com) -- Shock waves around dusty, young stars might be creating the raw materials for planets, according to new observations from NASA's Spitzer Space Telescope.
Magnetic fields record the early histories of planets
(PhysOrg.com) -- Meteorites that are among the oldest rocks ever found have provided new clues about the conditions that existed at the beginning of the solar system, solving a longstanding mystery and overturning some accepted ideas about the way planets form.
Worlds in collision
Two terrestrial planets orbiting a mature sun-like star some 300 light-years from Earth recently suffered a violent collision, astronomers at UCLA, Tennessee State University and the California Institute of Technology will report in a December issue of the Astrophysical Journal, the premier journal of astronomy and astrophysics.

News discussion:

Space & Earth science news