Chuck Bednar for redOrbit.com – @BednarChuck
Scientists have long been puzzled how Jupiter and other gas giants survived their formation period, but new research published Wednesday in the journal Nature has revealed that heat produced by in-falling material could keep them from falling into their stars.
In the study, Pablo Benitez-Llambay of the National University of Cordoba in Argentina and his colleagues explain that the heat given off by that material generates a force that is strong enough to push the forming planet away from the sun it orbits, keeping it from an untimely demise.
The effect of “heating torque” on evolving gas giants
The increasing temperature combined with the accreting in-falling material combine to produce a phenomenon that the authors refer to as “heating torque,” which basically counters the inward migration of the forming planet. In addition to solving the three-decade-old mystery of gas giant formation, it also explains the heavy-element abundance of their host stars, they said.
“Our calculations show that embryo planets can either migrate outward as they form or stay near the orbit where they are forming, instead of migrating inward and ending on an orbit very close to the star,” co-author Gloria Koenigsberger of the Institute of Physical Sciences in Mexico told Space.com. “This tells us the conditions under which a planetary system can form.”
Koenigsberger, Benitez-Llambay and their fellow investigators simulated how the force impacts developing gas giants, both in our solar system and elsewhere. Their research could help solve a long-recognized issue over the so-called “death spiral” that should affect gas giants.
So what causes this “death spiral” to happen, anyway?
As Space.com explains, the primary model of gas-giant formation involves the formation of a solid core from a disk of dust and gas surrounding a new star. This core constantly adds material from the disk, and if the core grows quickly enough, it can become so massive that it accretes gas and becomes a gas-giant before said gas dissipates over the next 10 million years.
However, there’s a problem with this model. As the core grows, it creates ripples in the disk that should cause it to spiral inwards faster than it can grow. Those cores either reach a stable orbit as a “super-Earth” planet or spiral into the star. Adding heating torque to the equation helps address the issue by pushing the embryonic planet outwards away from the sun, the authors report.
The new theory that keeps gas giants from self-destructing
When the falling material strikes the core’s surface, the impact produces heat, radiating energy away from the planet and causing the gas surrounding it to become hotter. As it rotates and the gas in the disk orbiting the star flows, pieces of heated material form in front of and behind the young core, eventually causing both lobes to expand and become less dense.
The degree to which the growing planet is pushed outward varies based on the amount of solid material that the disk itself contains, which is dependent upon the abundance of elements heavier than helium.
“Planetary systems such as ours can form only from disks in which there is sufficient solid material that, when being accreted by the protoplanet, can lead to a sufficiently large heating torque – one that can keep rocky planets from plunging towards the host star and can help embryos migrate outward beyond the snow line, where they can later accrete large quantities of gas and become gas giants,” Koenigsberger told Space.com.
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