quarta-feira, 19 de agosto de 2015

Study Explains Origin and Evolution of Smallest Asteroid Group

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It follows an article published on day (08/19) in the english website of the Agência FAPESP noting that Study explains origin and evolution of Smallest Asteroid Group.

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Study Explains Origin and Evolution
of Smallest Asteroid Group

By Elton Alisson
August 19, 2015

(Image: NASA/JHUAPL)
Asteroid Eros in an image captured in 2000 by NASA's Near
Earth Asteroid Rendezvous (NEAR) mission.

Agência FAPESP – At the edge of the main asteroid belt, between the orbits of Mars and Jupiter, lies a class of astronomical objects called Cybele.

The Cybele asteroid region intrigues astronomers because the number of objects it contains is small, despite its location in a relatively stable part of the Solar System where no major disturbances are known to have occurred since planetary migration.

An international group of researchers led by Valerio Carruba, a professor at the Guaratingetá campus of São Paulo State University (UNESP) in Brazil, may have found an explanation for this mystery.

Developed as part of the project “Secular families”, supported by FAPESP, the researchers’ hypothesis about how the dynamic evolution of the Cybele asteroids occurred was recently outlined in an article published in Monthly Notices of the Royal Astronomical Society (MNRAS).

The research findings will be presented at the next general assembly of the International Astronomical Union (IAU), scheduled for early August in Hawaii (USA). “We showed by means of numerical simulations that asteroids like the Cybele cluster can’t be primordial but must have reached the region they now occupy after the end of the last stages of planetary migration, during the late lunar bombardment approximately 4 billion years ago [when Earth and other objects from the Solar System were hit by countless asteroids],” Carruba told Agência FAPESP.

“This might explain why only 1,500 Cybele objects are known, compared with more than half a million objects in the main asteroid belt.”

The researchers based their numerical simulations of the dynamic evolution of the Cybele asteroids on planetary migration scenarios such as the “jumping Jupiter model.”

Proposed by David Nesvorny, a researcher in the Department of Space Studies at the Southwest Research Institute in Boulder, Colorado (USA), and one of the authors of the article published in MNRAS, the jumping Jupiter scenario hypothesizes that the planet Jupiter collided with a fifth gas giant between 3.8 billion and 4.2 billion years ago.

The clash ejected this fifth gas giant from the Solar System and caused Jupiter’s orbit to jump to its current location, the scenario claims.

As a result of this planetary migration, the entire region containing the Cybele asteroids was affected by a series of mean-motion resonances between celestial bodies that destabilized it and left few objects there. Orbital resonance occurs when two orbiting bodies exert a gravitational influence on each other. In mean-motion orbital resonance, the bodies’ periods of revolution are a simple integer ratio of each other.

“The objects that once inhabited the region in which the Cybele asteroids are located today couldn’t have survived that phase of planetary migration,” Carruba said. “This reinforces our hypothesis that the objects now found in the Cybele region arrived long after that phase of planetary migration. Hence their relatively small number compared with the number of objects in the main asteroid belt.”

Dynamic maps of the Cybele region, located between the 2J:-1A and 5J:-3A mean-motion resonances with Jupiter, show that it became dynamically stable once the planets were in position following planetary migration.

This finding refutes the hypothesis that there are relatively few asteroids in the Cybele region compared with other parts of the main asteroid belt because objects have been lost from the region over the last few million years, according to Carruba.

“The region in which the Cybele-class asteroids are located could contain many more objects,” he said.

Outer Boundary Extended

Carruba said that most Cybele-class objects are dark asteroids of low density and are associated with primitive taxonomic groups. Many are C-type objects, the most common type of asteroid, with little capacity to reflect light and a low density, as are typically found in the outer regions of the Solar System.

“C-type objects are less evolved from the standpoint of chemistry and composition,” he said. “They originated from less differentiated bodies during their evolution.”

He added that several binary and triple asteroids have also been identified in the Cybele region. Binary asteroids are two asteroids of similar size that revolve around each other at close range. Triple asteroids consist of two small asteroids orbiting a larger one.

The latter include 87 Sylvia, a triple asteroid associated with the region’s most dynamic asteroid family, according to Carruba.

“When we reidentified the asteroid families in the Cybele region, we found, although with some doubt, that a new asteroid family called Helga that was proposed by a Russian research group in 2014 is the furthest from Cybele and may be the outermost family in the main asteroid belt,” he said.

“This would extend the outer boundary of the Cybele region well beyond the distance estimated to date.”

Another conclusion drawn from the simulations performed by the researchers is that none of the asteroid families observed in the Cybele region can be older than 3 billion years.

The article “Dynamical evolution of the Cybele asteroids” (doi: 10.1093/mnras/stv997) by Carruba et al. can be read by subscribers to Monthly Notices of the Royal Astronomical Society at mnras.oxfordjournals.org/content/451/1/244.abstract.


Source: English WebSite of the Agência FAPESP

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