[meteorite-list] Mystery of Planet-forming Disks Explained by Magnetism (Spitzer)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 7 Mar 2014 13:26:58 -0800 (PST)
Message-ID: <201403072126.s27LQw2G014674_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2014-071

Mystery of Planet-forming Disks Explained by Magnetism
Jet Propulsion Laboratory
March 06, 2014

Astronomers say that magnetic storms in the gas orbiting young stars may
explain a mystery that has persisted since before 2006.

Researchers using NASA's Spitzer Space Telescope to study developing
stars have had a hard time figuring out why the stars give off more
infrared light than expected. The planet-forming disks that circle the
young stars are heated by starlight and glow with infrared light, but
Spitzer detected additional infrared light coming from an unknown source.

A new theory, based on three-dimensional models of planet-forming disks,
suggests the answer: Gas and dust suspended above the disks on gigantic
magnetic loops like those seen on the sun absorb the starlight and glow
with infrared light.

"If you could somehow stand on one of these planet-forming disks and
look at the star in the center through the disk atmosphere, you would
see what looks like a sunset," said Neal Turner of NASA's Jet Propulsion
Laboratory, Pasadena, Calif.

The new models better describe how planet-forming material around stars
is stirred up, making its way into future planets, asteroids and comets.

While the idea of magnetic atmospheres on planet-forming disks is not
new, this is the first time they have been linked to the mystery of the
observed excess infrared light. According to Turner and colleagues, the
magnetic atmospheres are similar to what takes place on the surface of
our sun, where moving magnetic field lines spur tremendous solar
prominences to flare up in big loops.

Stars are born out of collapsing pockets in enormous clouds of gas and
dust, rotating as they shrink down under the pull of gravity. As a star
grows in size, more material rains down toward it from the cloud, and
the rotation flattens this material out into a turbulent disk.
Ultimately, planets clump together out of the disk material.

In the 1980s, the Infrared Astronomical Satellite mission, a joint
project that included NASA, began finding more infrared light than
expected around young stars. Using data from other telescopes,
astronomers pieced together the presence of dusty disks of
planet-forming material. But eventually it became clear the disks alone
weren't enough to account for the extra infrared light -- especially in
the case of stars a few times the mass of the sun.

One theory introduced the idea that instead of a disk, the stars were
surrounded by a giant dusty halo, which intercepted the star's visible
light and re-radiated it at infrared wavelengths. Then, recent
observations from ground-based telescopes suggested that both a disk and
a halo were needed. Finally, three-dimensional computer modeling of the
turbulence in the disks showed the disks ought to have fuzzy surfaces,
with layers of low-density gas supported by magnetic fields, similar to
the way solar prominences are supported by the sun's magnetic field.

The new work brings these pieces together by calculating how the
starlight falls across the disk and its fuzzy atmosphere. The result is
that the atmosphere absorbs and re-radiates enough to account for all
the extra infrared light.

"The starlight-intercepting material lies not in a halo, and not in a
traditional disk either, but in a disk atmosphere supported by magnetic
fields," said Turner. "Such magnetized atmospheres were predicted to
form as the disk drives gas inward to crash onto the growing star."

Over the next few years, astronomers will further test these ideas about
the structure of the disk atmospheres by using giant ground-based
telescopes linked together as interferometers. An interferometer
combines and processes data from multiple telescopes to show details
finer than each telescope can see alone. Spectra of the turbulent gas in
the disks will also come from NASA's SOFIA telescope, the Atacama Large
Millimeter/submillimeter Array (ALMA) telescope in Chile, and from
NASA's James Webb Space Telescope after its launch in 2018.

JPL manages the Spitzer Space Telescope mission for NASA's Science
Mission Directorate, Washington. Science operations are conducted at the
Spitzer Science Center at the California Institute of Technology in
Pasadena. Spacecraft operations are based at Lockheed Martin Space
Systems Company, Littleton, Colo. Data are archived at the Infrared
Science Archive housed at the Infrared Processing and Analysis Center at
Caltech. Caltech manages JPL for NASA. For more information about
Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin at jpl.nasa.gov

2014-071
Received on Fri 07 Mar 2014 04:26:58 PM PST