Study identifies possible origins of “differentiated” celestial objects

An international group of researchers led by Brazil locates possible sources of asteroid fragments with basaltic crust.

By Elton Alisson

Agência FAPESP – In the Solar System’s main belt of asteroids, located between Mars and Jupiter, there is a small group of celestial objects known as V-type asteroids. These are, supposedly, fragments of the Vesta asteroid, the second largest object in the belt and one of the group of celestial bodies having a basaltic crust.

In recent years, an additional 127 V-type asteroid candidates have been identified. Although their origin is not very well understood, they are found in the central part of the main belt. Astronomers think it is very unlikely that they are all fragments of the Vesta asteroid because of the orbital position in which they are found.

A study conducted by researchers at the Universidade Estadual Paulista (Unesp) in Guaratinguetá, in collaboration with colleagues from the National Institute for Space Research (Inpe), the University of Namur in Belgium, the Paris Observatory, and the Pierre and Marie Curie University in France, has demonstrated that these new V-type asteroids in the main belt may be derived from other differentiated asteroids and not from the Vesta.

Differentiated celestial bodies are those that underwent processes by which they were structurally divided into layers that were geologically and chemically different from one another and have a basaltic crust, mantle, and nucleus.

The findings of the study, conducted under the scope of the project “Orbital mobility caused by close encounters with more than one massive asteroid”, funded by FAPESP, will be published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

“It’s very likely that there have been other differentiated objects that gave rise to these new V-type asteroids, but we don’t know how many,” Valério Carruba, Unesp professor and first author of the study, told Agência FAPESP.

“If we could determine the minimum number of differentiated objects that gave rise to these new asteroids, we would be able to better understand their origin and dynamic evolution,” he projected.

According to Carruba, the V-type asteroids are sparsely distributed throughout the main belt. The researchers have proposed the division of the central main belt into three regions where families of asteroids associated with the formation of V-type objects are situated, namely, Hansa, Eunomia, and Merxia and Agnia.

In making this division, the researchers determined that the V-type asteroids that originated from these families “respect the perimeter” in which they are situated.

“A V-type asteroid in the region of Hansa, for example, would hardly migrate to the Eunomia region,” Carruba explained. “It’s also highly unlikely that a V-type asteroid from the Eunomia region would migrate toward the regions of the Merxia and Agnia families.”

Sources of V-type asteroids

The researchers also demonstrated in the study that three different sources of asteroids – such as those of Eunomia, Merxia and Agnia, and Hansa – are enough to establish populations of V-type objects in the central main belt, where at least one more differentiated body, in addition to Vesta, is supposed to have existed.

The researchers hypothesize that the object that gave rise to the Eunomia family, for example, could have previously been a differentiated or partially differentiated body.

“The idea is that, in the past, the main body that gave rise to the family of Eunomia had a volcanic basaltic crust that was completely destroyed and scattered throughout the main belt,” said Carruba. “Other studies have also suggested that the Merxia and Agnia families could also have originated from differentiated bodies.”

The patterns of formation of these differentiated objects are based on parameters that are, as yet, not well understood, such as the minimum size for the differentiation, the shape of the region in which they were formed, and the efficiency with which they were scattered throughout the main belt.

According to these models, the number of differentiated objects that could have reached the main belt varies from two to a few hundred. “We still do not know how many differentiated objects were formed and when they reached the main belt,” said Carruba. He further stated that “establishing limits on these numbers can help us better understand the scenarios that led to the formation of the Solar System.”

The version of the article Dynamical evolution of V-type asteroids in the central main belt, by Valério Carruba and others, which will be published in the journal Monthly Notices of the Royal Astronomical Society, may be viewed at arxiv.org/abs/1401.6332.