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




EXO WORLDS
Chemical Clues Point To Dusty Origin For Earth-Like Planets
by Staff Writers
Washington DC (SPX) Jun 23, 2008


The researchers determined that in order for the molten droplets that formed the chondrules to remain as closed systems and retain constant levels of sodium, the initial dust cloud must have been far denser than previously supposed.

Higher than expected levels of sodium found in a 4.6 billion-year-old meteorite suggest that the dust clouds from which the building blocks of the Earth and neighboring planets formed were much denser than previously supposed. The study, by scientists from the Carnegie Institution, American Museum of Natural History, and U.S. Geological Survey, is published in the June 20 issue of Science.

Conel Alexander and Fred Ciesla of the Carnegie Institution's Department of Terrestrial Magnetism, with colleagues Jeffrey Grossman of the U.S. Geological Survey and Denton Ebel of the American Museum of Natural History, analyzed the sodium content of grains in objects called "chondrules" from the Semarkona meteorite, which fell in India in 1940.

The Semarkona meteorite, like all other chondrule-bearing meteorites (known as chondrites), dates from the early stages of the solar system's formation. Unlike most others, however, its constituents have been relatively unaltered by heat and chemical changes over the more than four billion years since its origin, making it an important window into the early history of the solar system.

Chondrules, which make up 20 to 80% of the volume of chondrites, are round, roughly millimeter-sized objects made of glass and crystals. Chondrules are thought to have formed by flash heating of dust in the primordial solar system. From the types of minerals found in chondrules, scientists have determined that they formed at temperatures of up to nearly 2,000 degrees C (3600 degrees F).

The source of this high heat, which would have affected vast areas of dust, is unknown. The heat would also be expected to have boiled off many of the volatile chemical elements, such as sodium, leaving the chondrules depleted in these elements.

But the chemical analyses by the research team found that the Semarkona chondrules had surprisingly high sodium abundances when they formed, indicating that sodium was not driven off. Rather, it remained at nearly constant levels during chondrule formation.

"Chondrules formed as molten droplets produced by what was probably one of the most energetic processes that operated in the early solar system," says Alexander.

"You would expect all the sodium to evaporate and be lost from the chondrules under such conditions. Instead, the sodium was retained. The chondrules stayed as effectively closed systems throughout the heating and melting."

The researchers determined that in order for the molten droplets that formed the chondrules to remain as closed systems and retain constant levels of sodium, the initial dust cloud must have been far denser than previously supposed.

"If the droplets were crowded close enough together, then the sodium vapor in the spaces in between would reach a saturation point," says Alexander, "and that would prevent further evaporation."

To achieve this condition, the density of dust in the chondrule-forming regions of the early solar system must have been at least about 10 grams per cubic meter, and possibly much more.

This is at least 100 times the densities considered by previous models of chondrule formation, which had assumed at most densities of only about 0.1 grams per cubic meter, and normally considerably less.

At densities of 10 grams per cubic meter or more, regions only a few thousand kilometers across, small by astronomical standards, could collapse under their own gravity to make objects that would be 10s of kilometers across.

"What's notable about this result is that it raises the possibility that the formation of chondrules in these high-density regions was linked to the formation of kilometer-sized objects called planetesimals, which were the first stage in building Earth-like planets," says Alexander.

"It will also help narrow down the possibilities for the cause of the heating that produced the chondrules, as well as the sizes of the regions where they formed.

"Heating chondrules to their peak temperatures and then quickly cooling them down when they are present at such high densities is a significant challenge for any mechanism proposed to explain chondrule origin. These tiny objects still have a lot to tell us about how our solar system took shape."

This research was supported by the Carnegie Institution, the NASA Origins of Solar Systems Program, and the NASA Cosmochemistry Program.

.


Related Links
Carnegie Institution
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
Astronomers discover clutch of 'super-Earths'
Nantes, France (AFP) June 16, 2008
European scientists on Monday said they had located five 'super-Earths', each of them four-to-30 times bigger than our planet, in a trio of distant solar systems. The discovery suggests that at least one third of stars similar to our own Sun host these difficult-to-detect celestial bodies, multiplying previous estimates by five. It also brings astronomers closer to finding planets ... read more


EXO WORLDS
One Million Names To The Moon And Counting

Solstice Moon Illusion

NASA Tests Lunar Robots And Spacesuits On Earthly Moonscape

NASA Awards Contract For Lunar Constellation Spacesuit

EXO WORLDS
Frozen Water Confirmed On Mars

Mars Science Is A Sublime Affair For Phoenix Lander

Computer Glitch Delays Mars Phoenix Lander Work

Mars Science Is A Sublime Affair For Phoenix Lander

EXO WORLDS
Mikulski Announces Nearly 18 Billion Dollars For NASA, Vows To Get More

Smithsonian's Folklife Festival Celebrates NASA's 50 Years

Harris Selected For Potential New NASA Space Suit Communications System

NASA Selects Explorer Mission Of Opportunity Investigations

EXO WORLDS
Gallup Poll Shows Americans Unconcerned About China Space Program

Chinese company develops 'UFO': report

China manned space flight set for October: state media

Two Suits For Shenzhou

EXO WORLDS
Discovery undocks from ISS

Shuttle astronauts bid farewell to space station crew

Shuttle Astronauts Bid Farewell To Space Station Crew

Astronauts test Japanese robotic arm

EXO WORLDS
Pratt And Whitney Rocketdyne Engine Launches New Ocean-Mapping Satellite Into Orbit

Russia Launches Six Birds For Orbcomm

Russia Set To Launch Batch Of Orbcomm Birds Today

ProtoStar One Is Fueled For Its Launch From Kourou

EXO WORLDS
Chemical Clues Point To Dusty Origin For Earth-Like Planets

Astronomers discover clutch of 'super-Earths'

Vanderbilt Astronomers Getting Into Planet-Finding Game

NASA Selects MIT-Led Team To Develop Planet-Searching Satellite

EXO WORLDS
BAE Computers To Manage Data Processing For Satellite Missions

Space Radar To Improve Mining Safety

'Spore' computer game aliens coming to virtual life

Integral Systems Integrated Solution To Support JCSAT-12




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