Rosetta data sheds light on planet formation process

Study confirms dust pebbles combine to form larger bodies, such as comets and planets.
By Laurel Kornfeld | Nov 03, 2017
A study that analyzed data returned by the European Space Agency's (ESA) Rosetta mission to Comet 67P/Churyumov-Gerasimenko has provided scientists with a missing link in their understanding of the planet formation process.

The Rosetta spacecraft orbited Comet 67P for nearly two years. Its Philae lander successfully touched down on the comet but lost battery power after two days because it landed in a shaded area that did not receive sufficient sunlight.

Rosetta's primary goal was providing scientists with data that would help them better understand the evolution of the solar system and the formation of its planets.

At approximately four-and-a-half billion years old, Comet 67P dates back to the solar system's earliest days.

Led by Jurgen Blum of Technische Universitat in Braunschweig, Germany, a research team analyzed Rosetta data and in the process realized that just one of several models accurately explains the formation of large solar system objects.

Rosetta revealed the comet to be porous, composed of numerous millimeter- and centimeter-sized dust pebbles. While the outer layers, which are exposed to sunlight, do not contain ice, the pebbles inside the comet are made up of a mixture of ice and dust.

"Our results show that only a single model for the formation of larger solid bodies in the young solar system may be considered for Chury (a nickname given to Comet 67P). According to this formation model, 'dust pebbles' are concentrated so strongly by an instability in the solar nebula that their joint gravitational force ultimately leads to a collapse," Blum explained.

The solar nebula is the cloud of gas and dust from which the Sun, planets, and other solar system objects formed.

Scientists have long been aware of the process in which dust pebbles, which act as the building blocks of planets, accrete, or stick together through collisions with one another and with ice particles.

They have also understood the way small objects known as planetesimals gravitationally accrete into planets.

Data captured by Rosetta's science instruments on Comet 67P provides scientists with a missing link between these two processes.

"Although it sounds very dramatic, it's actually a gentle process in which the dust agglomerates are not destroyed, but are combined into a larger body with an even greater gravitational attraction--the accumulation of the dust agglomerates into a coherent body is virtually the birth of the comet," Blum emphasized.

This model accurately explains various properties of Comet 67P, including its porous nature and the amount of gas escaping from within it, he added.

Findings of the study have been published in a recent edition of the Monthly Notices of the Royal Astronomical Society.


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