Four families of extremely young asteroids have been identified

"We have identified the new families using digital simulation using the retrospective integration method (BIM), much more accurate than other methods of dating asteroid families." BIM only works for young people less than 20 million years ago Until recently, only eight families had been studied using this method.We now know 13, of which nearly one third have been identified by our group "Said Valerio Carruba, a professor in the department of mathematics at UNESP.

Carruba coordinated the research project on asteroid families conducted at the UNESP campus engineering school in Guaratinguetá. The four families in question, all of them less than 7 million years old, orbit between Mars and Jupiter as part of a grouping called the main asteroid belt.

The main dating parameters used were the longitudes of the pericenter and the ascending node. For a planet, comet or asteroid moving around the Sun in an elliptical orbit, the pericenter is the closest point to the Sun. The ascending node is the point where the orbit crosses the south side of a reference plane, usually the plane of the ecliptic, to the north side.

"When a family of asteroids is formed, all pericentres and ascending nodes of the asteroids are aligned, but as the family evolves, alignment is lost due to the gravitational disturbances produced by the massive planets and asteroids, "explained Carruba. "Based on the current data, BIM allows you to go back in time using digital simulation to reconstruct the setting in which the parameters have been aligned and thus date the asteroid family."

In addition to the four new families identified, the group studied 55 new families identified by other scientists. While dating the families, they drew up a diagram which, with considerable precision, distinguishes families formed by collision events and families formed by the fission of a precursor body.

When two asteroids collide, one or both can fragment, giving birth to a family with multiple objects. Fission, on the other hand, consists in ejecting matter by a precursor body, either because it has acquired a very rapid rotation on its own axis and has suffered a collision, or because it has recently expelled a secondary body which had broken.

"One of the four families we identified was formed by a collision event.The collision was most likely at the origin of another.The others were identified very recently and we we need more studies to formulate their hypothesis ". I said.

Motion resonance

The main belt is an extraordinary niche of asteroids, with more than 700 known objects. The number is increasing steadily thanks to improved detection methods and can be estimated at one million.

According to Carruba, asteroids in the main belt are far from being evenly distributed. Different regions formed in the belt because of the extremely complex gravitational interaction between many bodies and, above all, the powerful gravitational field of Jupiter.

An important factor in this structure is a phenomenon known as "mean motion resonance," which occurs when two bodies in orbit around the third have closely related orbital periods, reported as a ratio of two small integers.

Resonances create empty spaces in the radial distribution of asteroids. They are called Kirkwood Gaps, in the honor of the American astronomer Daniel Kirkwood (1814-1895), who identified and explained these asteroid-free areas in the main belt.

"Between 33% and 35% of asteroids in the main belt are family members," Carruba said. "There are more than 120 recognizable families and dozens of less statistically significant groups, large families with hundreds of members, while small families with ten or so members."

The age estimates of asteroid families in the belt range from a few million to hundreds of millions of years. The origin of the oldest family dates from 4 billion years ago. She participated in the first stage of the formation of the solar system.

Explore more:
Astronomers identify the oldest known family of asteroids

More information:
V Carruba et al, The search for young families of asteroids: new families, new results, Monthly Notices from the Royal Astronomical Society (2018). DOI: 10.1093 / mnras / sty1810