Brazilian Study Evaluates the Impact of Asteroid Encounters

Hello reader!

It follows one article published day (11/21) in the english website of the Agência FAPESP highlighting that a Brazilian Study evaluates the impact of Asteroid Encounters.

Duda Falcão

Study Evaluates the Impact

of Asteroid Encounters

By Elton Alisson

November 21, 2012

Extremely rare encounters

between large and small

asteroids provoke changes in

their orbits, says a study carried

out by Brazilian researchers

presented in Italy at the

Accademia dei Lincei

Agência FAPESP – Among the more than 500,000 asteroids already catalogued inside our Solar System, there is a select group—comprising approximately 20 bodies—of so-called massive asteroids, whose mass (size) is much greater than that of other asteroids.

In the rare event that a massive asteroid comes near a smaller asteroid, the orbit of the second body is disturbed, causing “orbital diffusion”. This provokes a change in the smaller asteroid’s orbital elements, such as its semi-major axis, eccentricity and inclination.

A study carried out by researchers from the Mathematics Department of the Universidade Estadual Paulista (UNESP) School of Engineering in Guaratinguetá, from the National Institute for Space Research (INPE) and from the National Observatory in Rio de Janeiro evaluated the orbital diffusion caused by close encounters with 2 Pallas, 10 Hygiea and 31 Euphrosyne, the third, fourth and 22nd largest asteroids, respectively.

The results of the study, part of a FAPESP-funded project, were presented in September at an international conference on exploration of the Solar System.

The event was held in Rome, Italy, at the Accademia dei Lincei—one of the world’s oldest scientific institutions and where Galileo Galilei (1564-1642) was a  member. The study is also expected to be published in the journal Astronomy & Astrophysics.

According to the numerical simulations performed, the disturbance caused by the asteroid 2 Pallas—which has a high orbital inclination angle and whose encounters with smaller asteroids in its orbital region occur at a relatively high velocity and distance—is quite limited.

31 Euphrosyne also has a high inclination angle but is from a much larger family than that of Pallas. Because of its great size, 31 Euphrosyne was used as a model by researchers to verify whether massive asteroids with high inclinations are effective at causing mobility changes in the orbital elements of small asteroids.

However, the diffusion of the semi-major axis of a small asteroid provoked by an encounter with the asteroid 10 Hygiea was nearly equal to that caused by 1 Ceres—the largest known asteroid, which was classified as a dwarf planet in 2006.

“The diffusion levels of the semi-major axis of a small asteroid caused by an encounter with 10 Hygiea are nearly the same as those caused by Ceres, which we weren’t really expecting,” Valério Carruba, professor at UNESP and one of the study’s authors, told Agência FAPESP.

According to Carruba, some studies had already been conducted on close encounters with two of the largest massive asteroids: 1 Ceres and 4 Vesta. The latter is the second-largest asteroid in the Solar System and was promoted to the “protoplanet” category in May.

In 2011, another study published in Astronomy & Astrophysics by scientists from the Paris Observatory in France showed that when the five largest asteroids were included in simulations with all the other planets, not only did the orbits of the massive asteroids become more chaotic, but even the precision of Earth’s orbital elements was limited to 50 million years (Myr).

The effects on asteroid mobility caused by close encounters in the regions of 2 Pallas, 10 Hygiea and 31 Euphrosyne, which were the objects of the study by the Brazilian scientists, had not previously been detailed.

“We know that the effects of chaotic diffusion caused by encounters with massive asteroids only count for asteroids whose orbits cross paths with larger asteroids,” explained Carruba.

“These effects can be especially significant for objects that are members of the massive asteroid family, such as 10 Hygiea and 31 Euphrosyne, which we intend to study now,” he said.

Rare Encounters

In a study performed in collaboration with other researchers published in the July edition of Astronomy & Astrophysics, Carruba showed that changes to the semi-major axis, eccentricity and inclination caused by the long-term effects of close encounters of the Vesta asteroid with other smaller bodies could have contributed to the diffusion of some members of its family to a region outside its orbit.

Aside from this, the current orbit of some of these asteroids could not be easily justified by the migration of orbital elements by other mechanisms such as the Yarkovsky effect (a small “push” that an asteroid undergoes when it absorbs solar light and emits heat) or orbital resonance.

“Because of close encounters with massive asteroids, there is an energy change in the orbit of small asteroids reflected in an alteration of the semi-major axis, the eccentricity and the inclination of its orbit,” explained Carruba.

According to the researcher, the mechanism of the encounters with massive asteroids is similar to that used to send probes to study planets like Jupiter and Saturn and their respective moons.

When NASA began sending the Voyager probes into space, first to Jupiter and Saturn and then Neptune—they had a close encounter with Jupiter that changed their relative orbits. “They gained energy and can now explore the outer Solar System,” said Carruba.

“It’s clear that massive asteroids are small in comparison to planets. But as hundreds of thousands of years pass, the chaotic diffusion effects caused by close encounters with them are not negligible,” he affirmed. He said, however, that encounters with massive asteroids are rare.

Of the approximately 3,000 objects they studied in the 10 Hygiea region, the Brazilian researchers identified some 4,000 close encounters over a 30-Myr period.

“Close encounters with massive asteroids depend a lot on how the orbits are oriented. When they intersect, we can verify the occurrence of close encounters and calculate the variation of the semi-major axis of the smaller asteroids,” said Carruba.

The article “Chaotic diffusion caused by close encounters with several massive asteroids The (4) Vesta case” (doi: 10.1051/0004-6361/201218908) can be read by Astronomy & Astrophysics subscribers at: www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361/201218908&Itemid=129.

Source: English WebSite of the Agência FAPESP