Why celestial bodies come in different sizes

March 1, 2016

Our solar system contains one massive object—the sun—and many smaller planets and asteroids. Now researchers from Duke University in Durham, N.C. have proposed a new explanation for the size diversity, which is found throughout the universe and is called hierarchy. The researchers report their finding in the Journal of Applied Physics, from AIP Publishing.

"Since the 1700s scientists have known that gravity causes objects in the universe to get bigger, but the phenomenon of growth does not explain the hierarchy," said Adrian Bejan, a professor of mechanical engineering at Duke University. "To my huge surprise this question has been overlooked."

Bejan's specialty is in thermodynamics and he is the author of the Constructal Law, which states that natural systems evolve to facilitate flow. He had already applied the law of evolution to explain the shape of snowflakes, river basins, lungs and even airplanes, when a conversation with an undergraduate student prompted him to consider how the Constructal Law would manifest itself in the cosmos.

"This is my first trespass into planetary science," he said.

Bejan and his student, Russell Wagstaff, started by calculating the tension caused by gravitational attraction between bodies of the same size, uniformly distributed in space. They showed that if the bodies coalesce into some large bodies and some small bodies, the tension is reduced faster than if the bodies merged uniformly.

"The discovery is that hierarchy 'snaps' from the very beginning, spontaneously," Bejan said. The break-up of the uniform suspension of bodies into a few large and many small bodies occurs because it's the fastest way to ease the internal tension caused by gravity, he said.

The natural tendency of a system to evolve toward a state of reduced tension is a manifestation of the Constructal Law, Bejan said, and can be seen in other phenomena, such as soil cracking under a drying wind. "The working title for our paper was actually 'The Universe as Cracked Mud,'" he said.

Bejan said he hopes the application of the Constructal Law to the cosmological scale will inspire other researchers to consider how the could be applied in their own fields.

"I never thought I would have anything to say about celestial bodies in pure physics, but by chance I realized I have a key to open a new door," he said. "Everything has evolution and the Constructal Law can help predict it. The plan is to keep exploring."

Explore further: Unifying The Animate And The Inanimate Designs Of Nature

More information: A. Bejan and R.W. Wagstaff "The physics origin of the hierarchy of bodies in space," Journal of Applied Physics, March 1, 2016. DOI: 10.1063/1.4941986

Related Stories

Improving energy storage with a cue from nature

June 9, 2015

Materials melt faster when the lines of heat spread through the cold material like the branches of a tree—and the melting rate can be steadily increased by allowing the tree architecture to freely evolve over time, researchers ...

Rolling stones, turbulence connect evolution to physics

February 17, 2016

A law of physics explaining why larger animals live longer and travel further also extends to the simplest forms of mass migration on the planet—like rolling stones and turbulent eddies in water and air currents, according ...

Recommended for you

Color-changing water reflects a rainbow of colors and beyond

September 21, 2016

(Phys.org)—Scientists have created a water-based mixture that rapidly changes color when exposed to a variety of stimuli, such as a change in magnetic field, temperature, or pH. The scientists call the mixture "photonic ...

5 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

hemitite
5 / 5 (1) Mar 01, 2016
To see this paper: http://scitation.....4941986
bschott
1.8 / 5 (5) Mar 01, 2016
The natural tendency of a system to evolve toward a state of reduced tension is a manifestation of the Constructal Law, Bejan said, and can be seen in other phenomena, such as soil cracking under a drying wind.


LMAO!!! So, when it rains and the soil meshes into a uniform state, is that the destructal law at work?
What is the law that is applied which describes how and why there was increased tension in the first place?

Well, at least it makes more sense than the other theories applied to astrophysics. Perhaps some of the resident geniuses here can combine relativity and the constructal law to pinpoint the precise gravitational tension that leads to the formation of DM particles, DM soccerballs and DM chickenballs.

This stuff is priceless.

Nik_2213
not rated yet Mar 01, 2016
Uh, how does that go with Jupiter on the 'ice line' ??
ian_miller
not rated yet Mar 01, 2016
I am not convinced the issue has been overlooked. In my ebook on Planetary Formation, I propose the underlying mechanism is chemical, at least initially, and the sizes of bodies depend on simple rates, which depend largely on concentration of key species. Thus Neptune is bigger than Uranus and denser because the CO and N2 ices needed for Neptune ore in greater concentration than the methane/argon ices needed to get Uranus going. Once they get big enough, Uranus would grow faster by gravity because the total mass density is greater, but any Neptune equivalent will always be denser. The rocky planet sizes depend on silicate chemistry.
viko_mx
2 / 5 (4) Mar 02, 2016
"Since the 1700s scientists have known that gravity causes objects in the universe to get bigger, but the phenomenon of growth does not explain the hierarchy,"

How such a statement could be true since no one have observed closely how the cosmic objects become larger thanks to gravity. Must be a little more realistic to look like a bit of science.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.