Featured Research

from universities, journals, and other organizations

Some orbits more popular than others in planetary systems

Date:
March 19, 2012
Source:
University of Leicester
Summary:
Computer simulations have revealed a plausible explanation for a phenomenon that has puzzled astronomers: Rather than occupying orbits at regular distances from a star, giant gas planets similar to Jupiter and Saturn appear to prefer to occupy certain regions in mature solar systems while staying clear of others.

Computer simulations suggest high-energy radiation from baby sun-like stars are likely to create gaps in young solar systems, leading to pile-ups of giant planets in certain orbits.
Credit: NASA/JPL-Caltech

Computer simulations have revealed a plausible explanation for a phenomenon that has puzzled astronomers: Rather than occupying orbits at regular distances from a star, giant gas planets similar to Jupiter and Saturn appear to prefer to occupy certain regions in mature solar systems while staying clear of others.

"Our results show that the final distribution of planets does not vary smoothly with distance from the star, but instead has clear 'deserts' -- deficits of planets -- and 'pile-ups' of planets at particular locations," said Ilaria Pascucci, an assistant professor at the University of Arizona's Lunar and Planetary Laboratory.

"Our models offer a plausible explanation for the pile-ups of giant planets observed recently detected in exoplanet surveys," said Richard Alexander of the University of Leicester in the United Kingdom.

Alexander and Pascucci identified high-energy radiation from baby sun-like stars as the likely force that carves gaps in protoplanetary disks, the clouds of gas and dust that swirl around young stars and provide the raw materials for planets. The gaps then act as barricades, corralling planets into certain orbits.

The exact locations of those gaps depend on the planets' mass, but they generally occur in an area between 1 and 2 astronomical units from the star. One astronomical unit, or AU, marks the average distance from Earth to the sun. The findings are to be published in the journal Monthly Notices of the Royal Astronomical Society.

According to conventional wisdom, a solar system starts out from a cloud of gas and dust. At the center of the prospective solar system, material clumps together, forming a young star. As the baby star grows, its gravitational force grows as well, and it attracts dust and gas from the surrounding cloud.

Accelerated by the growing gravitation of its star, the cloud spins faster and faster, and eventually flattens into what is called a protoplanetary disk. Once the bulk of the star's mass has formed, it is still fed material by its protoplanetary disk, but at a much lower rate.

"For a long time, it was assumed that the process of accreting material from the disk onto the star was enough to explain the thinning of the protoplanetary disk over time," Pascucci explained. "Our new results suggest that there is another process at work that takes material out of the disk."

Pascucci presented the findings at the 43rd Lunar and Planetary Science Conference in The Woodlands, Texas on March 19.

That process, called photo-evaporation, works by high-energy photons streaming out of the star and heating the dust and gas on the surface of the protoplanetary disk.

"The disk material that is very close to the star is very hot, but it is held in place by the star's strong gravity," Alexander said. "Further out in the disk where gravity is much weaker, the heated gas evaporates into space."

Even further out in the disk, the radiation emanating from the star is not intense enough to heat the gas sufficiently to cause much evaporation. But at a distance between 1 and 2 AU, the balancing effects of gravitation and heat clear a gap, the researchers found.

While studying protoplanetary disks, Pascucci found that gas on the surface of the disk was gravitationally unbound and leaving the disk system via photoevaporation, as Alexander had previously predicted. "These were the first observations proving that photoevaporation does occur in real systems," she said.

Encouraged by those findings, Alexander and Pascucci then used the ALICE High Performance Computing Facility at the University of Leicester to simulate protoplanetary discs undergoing accretion of material to the central star that took the effects of photo-evaporation into account.

"We don't yet know exactly where and when planets form around young stars, so our models considered developing solar systems with various combinations of giant planets at different locations and different stages in time," Alexander said.

The experiments revealed that just as observations of real solar systems have shown, giant planets migrate inward before they finally settle on a stable orbit around their star. This happens because as the star draws in material from the protoplanetary disk, the planets are dragged along, like a celebrity caught in a crowd of fans.

However, the researchers discovered that once a giant planet encounters a gap cleared by photo-evaporation, it stays put.

"The planets either stop right before or behind the gap, creating a pile-up," Pascucci said. "The local concentration of planets leaves behind regions elsewhere in the disk that are devoid of any planets. This uneven distribution is exactly what we see in many newly discovered solar systems."

Once surveys for discovering extrasolar planet systems such as the Kepler Space Telescope project become more sensitive to outer giant planets, Alexander and Pascucci expect to find more and more evidence for the pileup of giant planets around 1 AU.

Pascucci said. "As we discover more exoplanets, we will be able to test these predictions in detail and learn more about the conditions under which planets form."

The research was funded by the National Science Foundation and the UK's Science & Technology Facilities Council.


Story Source:

The above story is based on materials provided by University of Leicester. Note: Materials may be edited for content and length.


Journal Reference:

  1. R.D.Alexander, I.Pascucci. Deserts and pile-ups in the distribution of exoplanets due to photoevaporative disc clearing. Monthly Notices of the Royal Astronomical Society, 2012 [link]

Cite This Page:

University of Leicester. "Some orbits more popular than others in planetary systems." ScienceDaily. ScienceDaily, 19 March 2012. <www.sciencedaily.com/releases/2012/03/120319111601.htm>.
University of Leicester. (2012, March 19). Some orbits more popular than others in planetary systems. ScienceDaily. Retrieved September 17, 2014 from www.sciencedaily.com/releases/2012/03/120319111601.htm
University of Leicester. "Some orbits more popular than others in planetary systems." ScienceDaily. www.sciencedaily.com/releases/2012/03/120319111601.htm (accessed September 17, 2014).

Share This



More Space & Time News

Wednesday, September 17, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Boeing, SpaceX to Send Astronauts to Space Station

Boeing, SpaceX to Send Astronauts to Space Station

AFP (Sep. 17, 2014) — NASA selected Boeing and SpaceX on Tuesday to build America's next spacecraft to carry astronauts to the International Space Station (ISS) by 2017, opening the way to a new chapter in human spaceflight. Duration: 01:13 Video provided by AFP
Powered by NewsLook.com
East Coast Treated To Rare Meteor Sighting

East Coast Treated To Rare Meteor Sighting

Newsy (Sep. 16, 2014) — Numerous residents along the East Coast reported seeing a bright meteor flash through the sky Sunday night. Video provided by Newsy
Powered by NewsLook.com
Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) — Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
NASA Picks Boeing and SpaceX to Ferry Astronauts

NASA Picks Boeing and SpaceX to Ferry Astronauts

AP (Sep. 16, 2014) — NASA is a giant step closer to launching Americans again from U.S. soil. It has announced it has picked Boeing and SpaceX to transport astronauts to the International Space Station in the next few years. (Sept. 16) Video provided by AP
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