Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. 24/7 Space News .




EXO WORLDS
'Neapolitan' exoplanets come in three flavors
by Staff Writers
Boston MA (SPX) Jun 03, 2014


New research finds that exoplanets can be divided into three groups - terrestrials, gas giants, and mid-sized "gas dwarfs" - based on how their host stars tend to fall into three distinct groups defined by their compositions. All three are portrayed in this artist's conception. Image courtesy J. Jauch.

The planets of our solar system come in two basic flavors, like vanilla and chocolate ice cream. We have small, rocky terrestrials like Earth and Mars, and large gas giants like Neptune and Jupiter. We're missing the astronomical equivalent of strawberry ice cream - planets between about one and four times the size of Earth. NASA's Kepler mission has discovered that these types of planets are very common around other stars.

New research following up on the Kepler discoveries shows that alien worlds, or exoplanets, can be divided into three groups - terrestrials, gas giants, and mid-sized "gas dwarfs" - based on how their host stars tend to fall into three distinct groups defined by their compositions.

"We were particularly interested in probing the planetary regime smaller than four times the size of Earth, because it includes three-fourths of the planets found by Kepler. That's where you'll find rocky worlds, which are the only kind that we would consider potentially habitable," says lead author Lars A. Buchhave of the Harvard-Smithsonian Center for Astrophysics (CfA).

Buchhave presented his research at a meeting of the American Astronomical Society.

Kepler finds exoplanets using the transit method, looking for a star that dims as a planet passes in front of it from our point of view. We can learn the planet's size from how much starlight it blocks.

However, to determine the planet's composition we need to measure its mass, so its density can be calculated. A rocky planet will be much denser than a gas giant. Unfortunately, the smaller a planet, the harder it is to measure its mass, especially for the dim and distant stars examined by Kepler.

Buchhave and his colleagues took a different approach. They measured the amount of elements heavier than hydrogen and helium, which astronomers collectively call metals, in stars with exoplanet candidates. Since a star and its planets form from the same disk of material, the metallicity of a star reflects the composition of the protoplanetary disk.

The team took follow-up spectra of more than 400 stars hosting over 600 exoplanets. Then, they conducted a statistical test to see if the sizes of the planets fell into natural groups, along with the stellar metallicities.

They found two clear dividing lines - one at a size 1.7 times as large as Earth and the other at a size 3.9 times larger than Earth. They infer that these boundaries also mark changes in composition. Planets smaller than 1.7 Earths are likely to be completely rocky, while those larger than 3.9 Earths are probably gas giants.

Planets between 1.7 and 3.9 times the size of Earth were dubbed gas dwarfs since they have thick atmospheres of hydrogen and helium. The rocky cores of gas dwarfs formed early enough to accrete some gas, although they did not grow as large as gas giants like Jupiter.

In addition, Buchhave and his collaborators discovered that the size of the largest rocky world isn't fixed. The farther a planet is from its star, the larger it can grow before accumulating a thick atmosphere and turning into a gas dwarf. This suggests that some super-Earths can grow into true monsters.

Finally, the team found that stars with small, terrestrial worlds tended to have metallicities similar to the Sun. Stars hosting gas dwarfs tended to be slightly more metal-rich. Stars with gas giants contained the most metals - about 50 percent more than our Sun.

"It seems that there is a 'sweet spot' of metallicity to get Earth-size planets, and it's about the same as the Sun. That makes sense because at lower metallicities you have fewer of the building blocks for planets, and at higher metallicities you tend to make gas giants instead," explains Buchhave.

He emphasizes that metallicity is only one of many factors determining what kinds of planets will form around a given star. Also, their study was limited to relatively close-in planets since those were the easiest for Kepler to spot. They plan to extend their study to planets in wider orbits as that data becomes available.

.


Related Links
Harvard-Smithsonian Center for Astrophysics
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




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





EXO WORLDS
'Godzilla' of Earths circles distant star
Washington (AFP) June 02, 2014
Astronomers have spotted the "Godzilla" of all Earths, a huge rocky planet orbiting a star 560 light years away that is changing scientists' understanding of the origins of the universe. This new mega-Earth weighs 17 times as much as our planet, and was found by NASA's Kepler mission, experts said at a meeting in Boston of the American Astronomical Society. The new discovery, named Keple ... read more


EXO WORLDS
Earth's gravitational pull stretches moon surface

NASA Missions Let Scientists See Moon's Dancing Tide From Orbit

Water in moon rocks provides clues and questions about lunar history

NASA Invites Public to Select Favorite Moon Image for Lunar Orbiter Anniversary Collection

EXO WORLDS
LDSD Testing for Large Payloads to Mars

New Mars Lander to Probe Interior of Red Planet

A habitable environment on Martian volcano

Mars Curiosity rover may have transported Earth bacteria to Mars

EXO WORLDS
SpaceX founder unveils his 'future of space travel' capsule

First Phase To Certify New US Space Transport System Completed

NASA faces identity crisis, funding battle

US may lose 'star wars' to Russia

EXO WORLDS
Chinese lunar rover alive but weak

China's Jade Rabbit moon rover 'alive but struggling'

Chinese space team survives on worm diet for 105 days

Moon rover Yutu comes closer to public

EXO WORLDS
Russian Soyuz with New Crew Docks at ISS in Automatic Mode

Russian, German and US astronauts dock with ISS

Six-Person Station Crew Enjoys Day Off Following Docking

ESA astronaut Alexander Gerst arrives at ISS

EXO WORLDS
SpaceX unveils capsule to ferry astronauts to space

Roscosmos Scolded for 'Pestering Society' with Proton Crash Theories

Elon Musk to present manned DragonV2 spacecraft on May 29

Russia puts satellite in orbit from sea platform after 2013 flop

EXO WORLDS
'Godzilla' of Earths circles distant star

Astronomers find a new type of planet: The 'mega-Earth'

Because you can't eat just one: Star will swallow two planets

'Neapolitan' exoplanets come in three flavors

EXO WORLDS
Russia preparing to launch Okno space surveillance system at full capacity

Citizen Scientists Contact Vintage Spacecraft

New Method of Wormlike Motion Lets Gels Wiggle through Water

Stronger than steel




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news 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 All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.