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How the Moon Formed: Violent Cosmic Crash Theory Gets Double Boost

This image depicts the catastrophic collision of two planetary bodies similar in composition that led to the formation of the Earth and its moon 4.5 billion years ago.
This image depicts the catastrophic collision of two planetary bodies similar in composition that led to the formation of the Earth and its moon 4.5 billion years ago.
Credit: Hagai Perets

The formation of the moon has long remained a mystery, but new studies support the theory that the moon was formed from debris left from a collision between the newborn Earth and a Mars-size rock, with a veneer of meteorites coating both afterward.
Earth was born about 4.5 billion years ago, and scientists think the moon arose a short time later. The leading explanation for the moon's origin, known as the Giant Impact Hypothesis, was first proposed in the 1970s. It suggests the moon resulted from the collision of two protoplanets, or embryonic worlds. One of those was the just-forming Earth, and the other was a Mars-size object called Theia. The moon then coalesced from the debris.
The long-standing challenges this scenario faces are rooted in the chemistry of the moon. Most of the models of the giant-impact theory often say that more than 60 percent of the moon should be made of material from Theia. The problem is that most bodies in the solar system have unique chemical makeups, and Earth, Theia and therefore the moon should as well. However, rock samples from the moon reveal that it is puzzlingly more similar to Earth than such models would predict when it comes to versions of elements called isotopes. (Each isotope of an element has different numbers of neutrons.) [Evolution of the Moon: A Visual Timeline (Gallery)]


"In terms of composition, the Earth and moon are almost twins, their compositions differing by at most few parts in a million," study lead author Alessandra Mastrobuono-Battisti, an astrophysicist at the Israel Institute of Technology in Haifa, told Space.com. "This contradiction has cast a long shadow on the giant-impact model."

The moon's violent birth

To shed light on this mystery, Mastrobuono-Battisti and her colleagues simulated collisions in the early solar system of between 85 to 90 protoplanets — each of which had up to 10 percent of Earth's mass, — and 1,000 to 2,000 smaller bodies, called planetesimals. Each of the latter had masses that were about 0.25 percent of Earth's. [How the Moon Was Made (Infographic)]
The researchers simulated the collisions taking place in a disk pattern that extended from half an astronomical unit (AU) to 4.5 AU from the sun. (An astronomical unit is the average distance between the sun and Earth, which is about 93 million miles, or 150 million kilometers.)
The scientists found that within 100 million to 200 million years after the models began, each simulation typically produced three to four rocky planets, with the largest comparable to Earth's mass. These worlds often were composed of material that was distinct from one another. However, they also found that 20 to 40 percent of the time, the composition of one planet was very similar to the makeup of the last protoplanet that had collided with it. This likelihood is about 10 times higher than previous estimates.
"The most exciting and surprising thing was to find out that we can shed new light on a 30-year-old mystery," study co-author Hagai Perets, an astrophysicist at the Israel Institute of Technology in Haifa, told Space.com. "Compositionally similar planet-impactor pairs are not rare at all."



The reason for this similarity in composition has to do with the orbits occupied by these colliding bodies. The composition of these objects varied with the amount of heat they received — for instance, the farther away a protoplanet was from the sun, the colder it was, and therefore the more likely it was to retain a relatively heavy isotope of oxygen. The scientists found that as each planet assembled, the last protoplanet to collide with it probably shared a similar orbit. Thus, protoplanets that share similar birthplaces can also share a similar composition.
This finding suggests that the similar compositions of the Earth and moon could be a natural consequence of a giant impact. This theory also explains why their compositions differ from that of other bodies in the solar system, the researchers say. Mastrobuono-Battisti, Perets and their colleague Sean Raymond, of the University of Bordeaux in France, detailed their findings in the April 9 issue of the journal Nature.
This NASA image depicts the moon as it coalesced from debris created when a Mars-size object slammed into the early Earth.
This NASA image depicts the moon as it coalesced from debris created when a Mars-size object slammed into the early Earth.
Credit: NASA/Goddard Space Flight Center

A moon made of Earth

Another challenge to understanding how the moon and Earth were formed has to do with tungsten. This metal has highly siderophile characteristics, meaning it binds tightly with iron, and it would have a strong tendency to move into Earth's iron-rich core. However, Earth's crust and mantle have an excess of siderophile elements such as tungsten.
Prior research suggests that the iron-loving elements now seen on Earth come mainly from a "late veneer" of material from space that accumulated both after the giant, moon-forming impact and after Earth's core formed. If this theory is true, then Earth's tungsten isotope levels should be different from those found on the moon. 




Now another two independent studies reveal there is indeed this predicted difference between the amount of tungsten isotopes on Earth and on the moon.
Scientists analyzing lunar rocks discovered an excess in the abundance of the isotope tungsten-182 on the moon compared with the present-day Earth's mantle. "It is the first time that we can resolve such a small difference," cosmochemist Thomas Kruijer at the University of Münster in Germany, lead author of one of the two studies, told Space.com. "Defining this value precisely is a very important step forward."
This difference is best explained by the theory that differing proportions of tungsten-182 each accumulated after the giant moon-forming impact, the researchers say. "Our results provide independent evidence for the late-veneer hypothesis," Kruijer said. The research in these two studies was also detailed in the April 9 issue of the journal Nature.

Up to 6,000 Europeans joined ISIS in Syria – EU


(Reuters/Social media via Reuters TV)

Between 5,000 and 6,000 Europeans have traveled to Syria to join the Islamic State, the EU Commissioner for Justice says stressing that 1,450 of them are French citizens.
The EU officials believe that “the figures are strongly under-estimated,” as foreign fighters are hard to keep track of, French newspaper Le Figaro reported citing Vera Jourova, the EU justice commissioner.
"At the European level, we estimate that 5,000 to 6,000 individuals have left for Syria," she told the paper in an interview.
Jourova added that the majority of them – 1,450 people – are French nationals.
The Commissioner added that they are eyeing more measures to avoid the suspected jihadists leaving the EU countries, considering “prevention [measures] rather than suppression” of the flow.
“We’ve allotted a budget of €2.5 million to provide training of prison and probation staff, as well as that of European prosecutors,” Jourova said.


The EU nationals traveling to Syria cause authorities’ concern, as the European governments fear they may return and carry out attacks on home soil.
At least one European, Mehdi Nemmouche, participated in such an attack, and suspected of killing four people in Jewish Museum in Brussels last year.
"At the time of the attacks in Paris and Copenhagen, we decided not to allow ourselves to be guided by fear," Jourova said, speaking of January’s deadly assaults in the French capital, and the fatal shootings in Denmark a month later.

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The reasons behind the Europeans leaving are “a desire for adventure, boredom, dissatisfaction with their situation in life or a lack of prospects,” a UK research conducted to look into the matter has found, according to the Commissioner.
She added that the EU is accelerating the sharing between police forces and court systems of different states, plus there is an increase in intelligence exchange.
"We want the exchange of information to intensify between Europol and Eurojust [judicial cooperation unit of the EU]," and this exchange should become “systematic and automatic,” Jourova said.
For that, "joint investigation teams are created so that prosecutors and police officers from several EU countries can work together."
Islamic State (also known as ISIS, or ISIL) currently has control over a significant amount of territory in Syria and Iraq, and has attracted thousands of foreigners to fight in their ranks.

23 dead, more than 900 injured in Siberian grassland fire

The massive fires that swept through nearly 60 villages and towns in the Siberian republic of Khakassia have left 23 people dead, and more than 900 injured, according to an official committee investigating the tragedy.

“Currently the
committee can confirm 23 deaths,”
head of the investigative
committee Vladimir Markin was quoted as saying by TASS.


More than 1,400 homes were destroyed in the fire, leaving some
6,000 people homeless, according to regional governor Viktor
Zimin.

Russian President Vladimir Putin had personally coordinated
emergency services operations in Khakassia, according to his
spokesperson.

Some 5,000 firefighters as well as thousands of volunteers worked
to contain the blazes through the night, extinguishing the fires
by Monday morning. Temporary camps have been set up in the Beisky
and Shirinksy districts nearby for those displaced by the fire.



Local residents observe the fire on the outskirts of Abakan.(RIA Novosti / Denis Mukimov)
Local residents observe the fire on the outskirts of Abakan.(RIA Novosti / Denis Mukimov)

Local residents observe the fire on the outskirts of Abakan.(RIA Novosti / Denis Mukimov)

The fires started after mass grass burning by residents in the
region. Grass burning is a springtime tradition among farmers in
some parts of Russia, meant to clear the fields of dry grass and
prepare them for planting.

Officials blamed the extreme severity of this year’s fire on
“uncontrolled burning, dry weather and uncharacteristically
strong and rough winds.”

“As soon as snow melts, while rivers are still covered by
ice, dry grass burns like gunpowder,”
said emergency
Situations Minister Vladimir Puchkov, “People begin to burn
grass on their plots and fire spreads to agricultural land and
pastures are burnt.”

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