Featured Research

from universities, journals, and other organizations

Disks don't need planets to make patterns, NASA study shows

Date:
July 13, 2013
Source:
NASA/Goddard Space Flight Center
Summary:
Many young stars known to host planets also possess disks containing dust and icy grains, particles produced by collisions among asteroids and comets also orbiting the star. These debris disks often show sharply defined rings or spiral patterns, features that could signal the presence of orbiting planets. Astronomers study the disk features as a way to better understand the physical properties of known planets and possibly uncover new ones.

This chart compares the gas mass for several debris disk systems and shows where the photoelectric instability is most important. Systems like TW Hydrae contain so much gas that the instability is suppressed, but it could arise in relatively gas-free regions near the center of the disk.
Credit: NASA's Goddard Space Flight Center

Many young stars known to host planets also possess disks containing dust and icy grains, particles produced by collisions among asteroids and comets also orbiting the star. These debris disks often show sharply defined rings or spiral patterns, features that could signal the presence of orbiting planets. Astronomers study the disk features as a way to better understand the physical properties of known planets and possibly uncover new ones.

But a new study by NASA scientists sounds a cautionary note in interpreting rings and spiral arms as signposts for new planets. Thanks to interactions between gas and dust, a debris disk may, under the right conditions, produce narrow rings on its own, no planets needed.

Watch the changing dust density and the growth of structure in this simulated debris disk, which extends about 100 times farther from its star than Earth's orbit around the sun. At left, the disk is seen from a 24-degree angle; at right, it's face-on. Lighter colors show higher dust density.

"When the mass of gas is roughly equal to the mass of dust, the two interact in a way that leads to clumping in the dust and the formation of patterns," said lead researcher Wladimir Lyra, a Sagan Fellow at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "In essence, the gas shepherds the dust into the kinds of structures we would expect to be see if a planet were present."

A paper describing the findings was published in the July 11 issue of Nature.

The warm dust in debris disks is easy to detect at infrared wavelengths, but estimating the gas content of disks is a much greater challenge. As a result, theoretical studies tend to focus on the role of dust and ice particles, paying relatively little attention to the gas component. Yet icy grains evaporate and collisions produce both gas and dust, so at some level all debris disks must contain some amount of gas.

"All we need to produce narrow rings and other structures in our models of debris disks is a bit of gas, too little for us to detect today in most actual systems," said co-author Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md.

Here's how it works. When high-energy ultraviolet light from the central star strikes a clump of dust and ice grains, it drives electrons off the particles. These high-speed electrons then collide with and heat nearby gas.

The rising gas pressure changes the drag force on the orbiting dust, causing the clump to grow and better heat the gas. This interaction, which the astronomers refer to as the photoelectric instability, continues to cascade. Clumps grow into arcs, rings, and oval features in tens of thousands of years, a relatively short time compared to other forces at work in a young solar system.

A model developed by Lyra and Kuchner shows the process at work.

"We were fascinated to watch this structure form in the simulations," Lyra said. "Some of the rings begin to oscillate, and at any moment they have the offset appearance of dust rings we see around many stars, such as Fomalhaut."

In addition, dense clumps with many times the dust density elsewhere in the disk also form during the simulation. When a clump in a ring grows too dense, the ring breaks into arcs and the arcs gradually shrink until only a single compact clump remains. In actual debris disks, some of these dense clumps could reflect enough light to be directly observable.

"We would detect these clumps as bright moving sources of light, which is just what we're looking for when we search for planets," adds Kuchner.

The researchers conclude that the photoelectric instability provides a simple and plausible explanation for many of the features found in debris disks, making the job of planet-hunting astronomers just a little bit harder.


Story Source:

The above story is based on materials provided by NASA/Goddard Space Flight Center. Note: Materials may be edited for content and length.


Cite This Page:

NASA/Goddard Space Flight Center. "Disks don't need planets to make patterns, NASA study shows." ScienceDaily. ScienceDaily, 13 July 2013. <www.sciencedaily.com/releases/2013/07/130713095250.htm>.
NASA/Goddard Space Flight Center. (2013, July 13). Disks don't need planets to make patterns, NASA study shows. ScienceDaily. Retrieved August 29, 2014 from www.sciencedaily.com/releases/2013/07/130713095250.htm
NASA/Goddard Space Flight Center. "Disks don't need planets to make patterns, NASA study shows." ScienceDaily. www.sciencedaily.com/releases/2013/07/130713095250.htm (accessed August 29, 2014).

Share This




More Space & Time News

Friday, August 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Experiment Tests Whether Universe Is Actually A Hologram

Experiment Tests Whether Universe Is Actually A Hologram

Newsy (Aug. 27, 2014) Researchers at Fermilab are using a device called "The Holometer" to test whether our universe is actually a 2-D hologram that just seems 3-D. Video provided by Newsy
Powered by NewsLook.com
SpaceX’s Falcon 9 Rocket Explodes After Liftoff

SpaceX’s Falcon 9 Rocket Explodes After Liftoff

Newsy (Aug. 23, 2014) The private spaceflight company says it is preparing a thorough investigation into Friday's mishap. Video provided by Newsy
Powered by NewsLook.com
Did Russia Really Find Plankton On The ISS? NASA Not So Sure

Did Russia Really Find Plankton On The ISS? NASA Not So Sure

Newsy (Aug. 21, 2014) Russian cosmonauts say they've found evidence of sea plankton on the International Space Station's windows. NASA is a little more skeptical. Video provided by Newsy
Powered by NewsLook.com
Space to Ground: Hello Georges

Space to Ground: Hello Georges

NASA (Aug. 18, 2014) Europe's ATV-5 delivers new science and the crew tests smart SPHERES. Questions or comments? Use #spacetoground to talk to us. Video provided by NASA
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins