Jupiter had growth disorders
by Staff Writers
Zurich, Switzerland (SPX) Aug 29, 2018
With an equator diameter of around 143,000 kilometers, Jupiter is the largest planet in the solar system and has 300 times the mass of the Earth. The formation mechanism of giant planets like Jupiter has been a hotly debated topic for several decades. Now, astrophysicists of the Swiss National Centre of Competence in Research (NCCR) PlanetS of the Universities of Bern and Zurich and ETH Zurich have joined forces to explain previous puzzles about how Jupiter was formed and new measurements. The research results were published in the magazine Nature Astronomy.
"We could show that Jupiter grew in different, distinct phases," explains Julia Venturini, postdoc at the University of Zurich. "Especially interesting is that it is not the same kind of bodies that bring mass and energy," adds Yann Alibert, Science Officer of PlanetS and first author of the paper.
First, the planetary embryo rapidly accreted small, centimeter-sized pebbles and quickly built a core during the initial one million years. The following two million years were dominated by slower accretion of larger, kilometer-sized rocks called planetesimals.
They hit the growing planet with great energy, releasing heat. "During the first stage the pebbles brought the mass," Yann Alibert explains: "In the second phase, the planetesimals also added a bit of mass, but what is more important, they brought energy." After three million years, Jupiter had grown to a body of 50 Earth masses. Then, the third formation phase started dominated by gas runaway accretion leading to today's gas giant with more than 300 Earth masses.
Solar system divided into two parts
It could therefore be concluded that Jupiter acted as a kind of a barrier when it grew from 20 to 50 Earth masses. During this period, the forming planet must have perturbed the dust disk, creating an over-density that trapped the pebbles outside of its orbit. Therefore, material from outward regions could not mix with material of the inner ones until the planet reached enough mass to perturb and scatter rocks inwards.
"How could it have taken two million years for Jupiter to grow from 20 to 50 Earth masses?" asked Julia Venturini.
"That seemed much too long," she explains: "That was the triggering question that motivated our study."
A discussion by email started among NCCR PlanetS researchers of the Universities of Bern and Zurich and ETH Zurich and the following week the experts in the fields of astrophysics, cosmochemistry and hydrodynamics arranged a meeting in Bern. "In a couple of hours we knew what we had to calculate for our study," says Yann Alibert: "This was only possible within the framework of the NCCR, which links scientists from various fields."
Explanation for delayed growth
"Pebbles are important in the first stages to build a core quickly, but the heat provided by planetesimals is crucial to delay gas accretion so that it matches the timescale given by the meteorite data," the astrophysicists summarize. They are convinced that their results provide as well key elements for solving long-standing problems of the formation of Uranus and Neptune and exoplanets in this mass regime.
Study helps solve mystery under Jupiter's coloured bands
Canberra, Australia (SPX) Aug 10, 2018
Scientists from Australia and the United States have helped to solve the mystery underlying Jupiter's coloured bands in a new study on the interaction between atmospheres and magnetic fields. Jupiter is the largest planet in our solar system. Unlike Earth, Jupiter has no solid surface - it is a gaseous planet, consisting mostly of hydrogen and helium. Several strong jet streams flow west to east in Jupiter's atmosphere that are, in a way, similar to Earth's jet streams. Clouds of ammonia a ... read more
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