Subscribe free to our newsletters via your
. 24/7 Space News .




EXO WORLDS
Rocky Planets Could Have Been Born as Gas Giants
by Nola Taylor Redd for Astrobiology Magazine
Moffett Field CA (SPX) Sep 21, 2011


Nayakshin determined that Super-Earths and other terrestrial planets could, in fact, be the cores of more massive proto-planets that did not have time to mature and were instead robbed of most of their gas by their parent stars. Rocky cores and close atmospheres could survive this disruption process because they are much denser.

When NASA announced the discovery of over 1,200 new potential planets spotted by the Kepler Space Telescope, almost a quarter of them were thought to be Super-Earths. Now, new research suggests that these massive rocky planets may be the result of the failed creation of Jupiter-sized gas giants.

Most astronomers currently believe planets are created by a method known as core accretion. Giant disks of gas circle newborn stars. Grains in these disks bond together to form larger objects known as planetesimals, which collide, creating larger and larger clumps of material. When the clumps reach a critical mass, their gravity pulls in gas from the disk around them.

But last summer, Sergei Nayakshin of the University of Leicester in the United Kingdom proposed a new theory for planetary formation. Known as "tidal downsizing," it works at a faster pace.

In tidal downsizing, a gas disk first forms massive gas clumps farther out in space than where most of the planets discovered so far reside in their solar systems. Left to their own devices, these clumps would cool and contract into very massive (~10 Jupiter mass) planets.

Nayakshin showed that during this contraction dust grains grow to large sizes and then fall to the center of the gas clump, forming a massive solid core there - the proto-rocky planet within the much more massive gas cocoon.

"Once you have a core, it may build up an atmosphere around it," Nayakshin explained. "The atmosphere is dominated by hydrogen, but it is much more chemically-rich than the primordial dust material."

The more massive the rocky core, the more massive the atmosphere around it, and it grows with time. Given time, such a mix would result in a giant gas planet with a solid core inside, for example, a super-Jupiter.

However, the surrounding disk pushes the planet in, closer to the star, and there the outer layers of the gas envelope start to be disrupted and actually consumed by the star.

Building on this theory, Nayakshin determined that Super-Earths and other terrestrial planets could, in fact, be the cores of more massive proto-planets that did not have time to mature and were instead robbed of most of their gas by their parent stars.

Rocky cores and close atmospheres could survive this disruption process because they are much denser. His paper describing this mechanism appeared in the August edition of the Monthly Notices of the Royal Astronomical Society.

"The remaining core is pretty much a rocky planet, with a mass anywhere from almost zero to ten or so Earth masses," Nayakshin said.

This means the resulting planet could wind up close to their parent star - or farther away, in the area known to astronomers as the habitable zone.

Differing from star to star, the "habitable zone" is the area where water can exist as a liquid on the surface of a rocky world. Planets orbiting within this range are considered the most likely to host life.

In this respect, Aaron Boley of the University of Florida says that if planets do form as described by the tidal disruption theory, then planets may be able to form in systems that are unfavorable to the core accretion mechanism, such as in disks with little dust. Although he did not work with Nayakshin, he explored a similar theory early last year.

"I like to think of the mechanisms as opposites," he said. "One is bottom up - core accretion - and the other is top down - tidal disruption."

Boley, who has done extensive research on the formation of gas giant planets and the evolution of planet-forming disks, believes that tidal disruption makes it more likely for life to evolve in a wider variety of stellar systems.

"It is another way Nature can make planets," Boley said.

And more planets mean more chances at life.

As a new theory, Nayakshin admits that there are many detailed calculations left to perform. He expressed hope that other scientists would help him put his theory to the test.

In last year's paper, Nayakshin expressed the idea that tidal downsizing capitalized on the best of the core accretion model and competing (though more often challenged) model of gravitational instability, while neutralizing the problems in both.

Gravitational instability allows for the rapid creation of planetesimals at a distance from the star, but it doesn't allow them to migrate inward. As such, it can't account for many of the closer planets seen today.

"Tidal downsizing and core accretion are both mechanisms that can form a wide range of planets," Boley said. "They occur during different stages of a proto-planetary disk's lifetime, and are not mutually exclusive."

Core accretion has a difficult time forming planets in more distant orbits over a long period of time. Gravitational instability quickly forms them farther out, where they remain unless they can migrate inward. Tidal downsizing requires that they migrate inward fast enough to have their envelopes removed by tides from their star.

Nayakshin noted that the models contain similar physical steps, but in different proportions.

"In this sense, the final model is likely to be a composite."

Boley expressed interest in watching the new theory develop, and seeing how well it stood against up to the more popular model of core accretion.

"Progress is made in science by taking testable ideas and trying to use them until they are proved wrong," he said.

.


Related Links
University of Leicester
Lands Beyond Beyond - extra solar planets - news and science
Life Beyond Earth






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








EXO WORLDS
From Star Wars to Science Fact: Tatooine-Like Planet Discovered
Cambridge, MA (SPX) Sep 20, 2011
Although cold and gaseous rather than a desert world, the newfound planet Kepler-16b is still the closest astronomers have come to discovering Luke Skywalker's home world of Tatooine. Like Tatooine, Kepler-16b enjoys a double sunset as it circles a pair of stars approximately 200 light-years from Earth. It's not thought to harbor life, but its discovery demonstrates the diversity of planets in o ... read more


EXO WORLDS
United Launch Alliance Launches GRAIL Spacecrafts To Moon

NASA launches twin spacecraft to study Moon's core

Second bid to launch NASA's Moon-bound spacecraft

NASA to launch Moon-bound twin spacecraft

EXO WORLDS
Young Clays on Mars Could Have Been Habitable Regions

Opportunity on verge of new discovery

Opportunity Studies Chester Lake Rock Outcrop

Opportunity Inspects Next Rock at Endeavour

EXO WORLDS
Spaceship factory opens in California

What did we get from the US space program

NASA Announces Two Game-Changing Space Technology Projects

Iowa State chemists help astronauts make sure their drinking water is clean

EXO WORLDS
Tiangong-1 launch will pave way for China's first space station

China to launch unmanned space module by Sept 30

China to launch space station's first module

China launches new communication satellite

EXO WORLDS
Private US capsule not to dock with ISS

Crew safely returns to Earth after crash

Russia postpones next manned launch to ISS

Russia announces launch of 2 spacecraft in Oct-Nov

EXO WORLDS
Countdown to first Soyuz launch at Kourou under way

Ariane rocket launches satellites after strike delay

Double prime for Astrium on next Ariane launch

Strike delays Ariane-5 launch: official

EXO WORLDS
Rocky Planets Could Have Been Born as Gas Giants

How Common Are Earth-Moon Planetary Systems

From Star Wars to Science Fact: Tatooine-Like Planet Discovered

Astronomers confirm first planet orbiting two stars

EXO WORLDS
Maxwell Technologies launch UK division to target European space market

Did chemical reactions cause Twin Towers collapse?

Apple to unveil iPhone 5 on October 4: report

Saab wins U.S. Navy radar contract




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement