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Synestia, A New Planetary Object, Resembles a Donut

A new planetary body existing in the heavens has been proposed. It goes by the name of synestia. The findings are published in the Journal of Geophysical Research: Planets.

A rocky planet, a molten disk structure, and a synestia. The image is to the scale, and all three have the same mass. Photo credits: Simon Lock, Harvard University.

We have something new to contemplate in the skies: a planetary body called synestia, says planetary scientists. The latter describe it as an enormous, rotating, donut-shaped vaporised rock that is the result of planets colliding into each other. Another interesting hypothesis is that our very own planet Earth was once a synestia.

The existence of the synestia has been proposed by Simon Lock from Harvard University, and Sarah Stewart from the University of California, Davis. The pair of researchers came to these findings upon studying planet formation from massive impacts. The world of science believes that rocky planets (like, Earth, Mars, and Venus) came to be when smaller bodies smashed into one another, impacts that would be so powerful that the bodies would initially be melting, and partly vaporised, but would ultimately cool down, and solidify into spherical planets. The new study focuses on a specific type of collision: that occurring between rotating objects.

Spinning bodies have angular momentum—the quantity of their rotation—which is a constant. When two rotating objects collide into each other, their individual angular momentum combine, and this total also remains the same. Lock and Stewart devised a model to describe two Earth-sized, rotating, rocky planets hitting into other big objects at high energy, and high angular momentum. Their results show that giant impacts of this nature would create a completely new, larger structure, as explained by Stewart. This resulting mass would be vaporised rock, in the form of an indented disk (much like a donut or a red blood cell) without a solid or liquid surface. This is synestia for you.

Were our Earth to collide with an object, forming a synestia, the latter would not last very long (only a hundred years, maybe), and it would eventually condense into a solid. However, synestias forming from larger and hotter objects might last much longer.

If synestias do exist, the new research could be broadening our horizons when it comes to other heavenly events. Stewart says that lunar formation might be explained in new ways. Our moon bears close resemblance to our own planet in terms of composition, and scientists normally interpret this as implying that the moon formed when material was snatched from Earth following a collision, and then falling into orbit, becoming our satellite. Now, the new study provides an alternative narrative: maybe, a giant impact led to the formation of a synestia which then condensed into the Earth and its moon.


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