How the seeds of planets take shape

October 10, 2018 by Whitney Clavin

In theoretical research that could explain everything from planet formation to outflows from stars, to even the settling of volcanic ash, Caltech researchers have discovered a new mechanism to explain how the act of dust moving through gas leads to clumps of dust. While dust clumps were already known to play a role in seeding new planets and many other systems in space and on Earth, how the clumps formed was unknown until now.

Phil Hopkins, professor of theoretical astrophysics at Caltech, working with Jonathan (Jono) Squire, a former postdoctoral fellow at Caltech, began thinking about disturbances to moving through gas while studying how strong radiation from stars and galaxies drives dust-laden winds. Hopkins says that it was previously assumed that dust was stable in gas, meaning the would ride along with gas without much happening, or they would settle out of the gas if the particles were big enough, as is the case with soot from a fire.

"What Jono and I discovered is that dust and gas trying to move with one another is unstable and causes dust grains to come together," says Hopkins. "Soon we began to realize that these gas-dust instabilities are at play anywhere in the universe that a force pushes dust through gas, whether the forces are stellar winds, gravity, magnetism, or an electrical field." The team's simulations show material swirling together, with clumps of dust growing bigger and bigger.

"We actually started out studying dust-driven winds in space, but as we studied the problem, we noticed specific features of the instabilities that led us to think this was a more general phenomena," says Squire, who together with Hopkins has authored four articles on their new findings, one accepted for publication at The Astrophysical Journaland three at the Monthly Notices of the Royal Astronomical Society. "From here, it kind of snowballed, since we were able to study lots of different systems—galaxies, stars, , the gas close to supermassive black holes, supernovas, et cetera—and confirm our intuition. It wasn't a eureka moment but a series of eurekas that lasted about a week."

Perhaps the most notable implications for the newfound Hopkins-Squire instabilities are for the study of burgeoning planets. Planets take shape within dusty, rotating "protoplanetary" disks of gas and dust around young stars. In these disks, the dust coalesces to form bigger and bigger pebbles and boulders, then mountain-size chunks, and eventually full-grown .

At some point during this process, when the pieces of rock are big enough—about 1,000 kilometers in diameter—gravity takes over and smooshes the mountainous rocks into a round planet. The big mystery lies in what happens before gravity takes effect—that is, what is causing the dust particles, pebbles, and boulders to come together? Researchers once thought they might stick together in the same way dust bunnies accumulate under your bed, but there are problems with that theory.

"If you throw two pebbles together, they don't stick. They just bounce off each other," says Hopkins. "For sizes in between a millimeter and hundreds of kilometers, the grains don't stick. This is one of the biggest problems in modeling planet formation."

In the Hopkins-Squire instability model, which builds on previous models of dust-gas interactions, the formation of planetary dust clumps would begin with tiny dust grains moving through the gas orbiting in a protoplanetary disk. Gas would curl around a grain like river water around a boulder; the same thing would happen with another grain of dust nearby. These two gas flows might then interact. If there are many dust grains in relatively close proximity to one another, which is the case in planet formation, the net effect of the many resulting gas flows would be to channel the dust together into clumps.

"In our new theory, this sticking through clumping can occur for a much wider range of grain sizes than previously thought, allowing smaller to participate in the process and rapidly grow in size," says Squire.

"Understanding the origins of our solar system ranks among the most important problems in all of natural science, and the discovery of the Hopkins-Squire instability is a significant step toward attaining that understanding. This is an exciting development," says Caltech's Konstantin Batygin, assistant professor of planetary science and Van Nuys Page Scholar, who was not involved in the study.

The research team says these instabilities may also be important in completely different situations here on Earth. For instance, volcanic ash or raindrops interact with our atmosphere in exactly the same way that astrophysical dust interacts with its surrounding gas.

"It's very interesting to explore how these instabilities could operate in all these different scenarios," says Squire. "We're looking forward to understanding completely different instabilities in other areas of physics and applied mathematics—and, hopefully, to finding other entirely new and interesting systems where this occurs."

Explore further: Protoplanetary disk material found to be too sparse to form planet populations

More information: J. Squire et al. Resonant Drag Instability of Grains Streaming in Fluids, The Astrophysical Journal (2018). DOI: 10.3847/2041-8213/aab54d

Philip F Hopkins et al. The resonant drag instability (RDI): acoustic modes, Monthly Notices of the Royal Astronomical Society (2018). DOI: 10.1093/mnras/sty1982

Jonathan Squire et al. Resonant drag instabilities in protoplanetary discs: the streaming instability and new, faster growing instabilities, Monthly Notices of the Royal Astronomical Society (2018). DOI: 10.1093/mnras/sty854

Philip F Hopkins et al. Ubiquitous instabilities of dust moving in magnetized gas, Monthly Notices of the Royal Astronomical Society (2018). DOI: 10.1093/mnras/sty1604

Related Stories

Planetary influences on young stellar disks

December 14, 2015

A newborn star typically has a disk of gas and dust from which planets develop as the dust grains collide, stick together and grow. Stars older than about five million years lack evidence for these disks, however, suggesting ...

How do planets form?

September 9, 2014

We have a pretty good idea of how planets form around stars. We know that dust is formed from the remnants of supernovae, that protoplanetary disks of dust form around young stars, and that dust grains can clump together ...

Dusty protoplanetary disks

December 8, 2017

Planetary systems form out of disks of gas and dust around young stars. How the formation proceeds, however, is complex and poorly understood. Many physical processes are involved including accretion onto the star, photoevaporation ...

Rings and gaps in a developing planetary system

April 2, 2018

The discovery of an exoplanet has most often resulted from the monitoring of a star's flicker (the transiting method) or its wobble (the radial velocity method). Discovery by direct imaging is rare because it is so difficult ...

Recommended for you

Team finds evidence for carbon-rich surface on Ceres

December 10, 2018

A team led by Southwest Research Institute has concluded that the surface of dwarf planet Ceres is rich in organic matter. Data from NASA's Dawn spacecraft indicate that Ceres's surface may contain several times the concentration ...

InSight lander 'hears' Martian winds

December 7, 2018

NASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport InSight lander, which touched down on Mars just 10 days ago, has provided the first ever "sounds" of Martian winds on the Red Planet. A ...

7 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Steelwolf
2.2 / 5 (10) Oct 10, 2018
So, everything from dust to comets to planets, stars, globular clusters, galaxies, galactic clusters and even the filamentous structure of the Universe's matter seems to have been Directly affected by electrostatic attraction due to the dust movement through ionized gasses (plasma).

That this attraction is based on particles of all sized moving through an ionized field, leading to magnetically modified vorticity of particles within the moving plasma, which, by it's own motion creates a magnetic field, which the particles then align themselves along. Obviously gravity plays a part as well, but it does appear that below a certain size per scale that electromagnetism plays a larger part than previously considered.

This is what I have been trying to point out for decades. Now they not only show it to be a real effect, but are looking at how the effect scales up as they can see the evidence of it Being There, but now they want to know HOW and WHY it got that way.
barakn
3.8 / 5 (13) Oct 10, 2018
Steelwolf, do you have some sort of reading disability that inserts words beginning with 'electr' into whatever you're reading?
Steelwolf
2.8 / 5 (9) Oct 10, 2018
Anytime you have something magnetic that is moving, it WILL create an electrical flow of some sort, whether merely equalization with it's surroundings, or, if the plasma structure is correct, it can form tubes and filaments which travel an extremely long distance, and, it has been shown in recent papers published here, that the magnetic fields can carry energy much farther and faster than just the ionic flow that is present.

All I am doing is showing what they have proven is that electrostatic attraction, as well as particle entrainment, as shown in the vid, creates the conditions for gravity to take over just as they state.

It really is not hard to understand. It is the same thing as static cling from objects being moved through an ionic gas flow and exhibit mutual attraction, and a snapping, sometimes shocking charge results from pulling the two back apart.

The exact same mechanism is what they are explaining as for dust clumping, and showing that it scales up as well.

Surveillance_Egg_Unit
3 / 5 (2) Oct 10, 2018
Motion imparts Energy?
danR
3 / 5 (6) Oct 10, 2018
Steelwolf
I'm sure we've both had the eureka moment when brushing our teeth that the cleansing action has nothing to do with purported abrasive activity of toothpaste particles against plaque, but that the motion of the bristles over the teeth induce micro-cavitational triboluminiscent and electromagnetically excited and amplified plasmas of nanoscopic scale and actually detonate and blast bits of the offending biofilm from enamel and although I've explained all this on my Facebook page, and tried to lay it out visually to some of the profs at the local university but they started closing their doors as soon as they saw me coming but that doesn't matter because I really should be taking the matter to the research dentistry departments where the facts can be laid out for a more practical implementation of what my thoughts can accomplish in terms of dental care that is seriously needed in the third world and
wduckss
1.8 / 5 (5) Oct 11, 2018
"In our new theory" Ha, ha,.. Classic plagiarism.

Growth doesn't stop with atoms; on the contrary, joining goes on. Through joining, chemical reactions and combined, gas, dust, sand, the rocks named asteroids and comets, etc., are all created. Even further, planets are created the same way. Then, when planets grow to the 10% of Sun's mass, they become stars, which can be really gigantic (super-giants).
Millions of craters scattered around the objects of our Solar system are the evidence of objects' growth. Constant impacts of asteroids into our atmosphere and soil are the evidence of these processes being uninterrupted today, just the same as it used to be in any earlier period of the past. It is estimated that 4 000 – 100 000 tons of extraterrestrial material falls yearly to Earth. 2012/13 https://www.acade...rotation
dsylvan
3.7 / 5 (3) Oct 13, 2018
@wduckss


Growth doesn't stop with atoms; on the contrary, joining goes on. Through joining, chemical reactions and combined, gas, dust...

This is ground breaking research from Caltech. So many applications.

Dust moving through a gaseous environment might even explain how ideas take shape in your head!

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.