Scientists predict that rocky planets formed from 'pebbles'

October 26, 2015, Southwest Research Institute
Southwest Research Institute scientists developed a new process in planetary formation modeling that explains the size and mass difference between the Earth and Mars. Mars is much smaller and has only 10 percent of the mass of the Earth. Conventional solar system formation models generate good analogs to Earth and Venus, but predict that Mars should be of similar-size, or even larger than Earth. Credit: NASA/JPL/MSSS

Using a new process in planetary formation modeling, where planets grow from tiny bodies called "pebbles," Southwest Research Institute scientists can explain why Mars is so much smaller than Earth. This same process also explains the rapid formation of the gas giants Jupiter and Saturn, as reported earlier this year.

"This numerical simulation actually reproduces the structure of the inner solar system, with Earth, Venus, and a smaller Mars," said Hal Levison, an Institute scientist at the SwRI Planetary Science Directorate. He is the first author of a new paper published in the Proceedings of the National Academy of Sciences of the United States (PNAS) Early Edition.

The fact that Mars has only 10 percent of the mass of the Earth has been a long-standing puzzle for solar system theorists. In the standard model of planet formation, similarly sized objects accumulate and assimilate through a process called accretion; rocks incorporated other rocks, creating mountains; then mountains merged to form city-size objects, and so on. While typical accretion models generate good analogs to Earth and Venus, they predict that Mars should be of similar-size, or even larger than Earth. Additionally, these models also overestimate the overall mass of the asteroid belt.

"Understanding why Mars is smaller than expected has been a major problem that has frustrated our modeling efforts for several decades," said Levison. "Here, we have a solution that arises directly from the planet formation process itself."

New calculations by Levison and co-authors Katherine Kretke, Kevin Walsh and Bill Bottke, all of SwRI's Planetary Science Directorate follow the growth and evolution of a system of planets. They demonstrate that the structure of the inner solar system is actually the natural outcome of a new mode of planetary growth known as Viscously Stirred Pebble Accretion (VSPA). With VSPA, dust readily grows to "pebbles"—objects a few inches in diameter—some of which gravitationally collapse to form asteroid-sized objects. Under the right conditions, these primordial asteroids can efficiently feed on the remaining pebbles, as aerodynamic drag pulls pebbles into orbit, where they spiral down and fuse with the growing planetary body. This allows certain asteroids to become planet-sized over relatively short time scales.

However, these new models find that not all of the primordial asteroids are equally well-positioned to accrete pebbles and grow. For example, an object the size of Ceres (about 600 miles across), which is the largest asteroid in the asteroid belt, would have grown very quickly near the current location of the Earth. But it would not have been able to grow effectively near the current location of Mars, or beyond, because aerodynamic drag is too weak for pebble capture to occur.

"This means that very few pebbles collide with objects near the current location of Mars. That provides a natural explanation for why it is so small," said Kretke. "Similarly, even fewer hit objects in the asteroid belt, keeping its net mass small as well. The only place that growth was efficient was near the current location of Earth and Venus."

"This model has huge implications for the history of the asteroid belt," said Bottke. Previous models have predicted that the belt originally contained a couple of Earth-masses' worth of material, meaning that planets began to grow there. The new model predicts that the asteroid belt never contained much mass in bodies like the currently observed asteroids.

"This presents the planetary science community with a testable prediction between this model and previous models that can be explored using data from meteorites, remote sensing, and spacecraft missions," said Bottke.

This work complements the recent study published in Nature by Levison, Kretke, and Martin Duncan (Queen's University), which demonstrated that pebbles can form the cores of the giant planets and explain the structure of the outer solar system. Combined, the two works present the means to produce the entire solar system from a single, unifying process.

"As far as I know, this is the first model to reproduce the structure of the solar system—Earth and Venus, a small Mars, a low-mass asteroid belt, two gas giants, two ice giants (Uranus and Neptune), and a pristine Kuiper Belt," said Levison. The article, "Growing the Terrestrial Planets from the Gradual Accumulation of Sub-meter Sized Objects," is published online by PNAS.

Explore further: Scientists think 'planetary pebbles' were the building blocks for the largest planets

More information: Growing the terrestrial planets from the gradual accumulation of submeter-sized objects, www.pnas.org/cgi/doi/10.1073/pnas.1513364112

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cantdrive85
2 / 5 (16) Oct 26, 2015
So, with this highly speculative VSPA model they are able to imagine dust "readily" grows into baseballs, which "gravitationally collapses" into "asteroid" sized objects. Then, due to "aerodynamics" of stuff- where there is no air- they grow larger still, then "fuse" together...

"We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture." Hannes Alfvén
kminotaur32
4.3 / 5 (17) Oct 26, 2015
cantdrive...Sounds like you prefer to cherry pick the data. This is a mathematical prediction. Unlike your religious cults, there are no absolutes in science. Science can say that "we just don't know", where as your religious cults claim to know it all, and without a shred of evidence.

Scientific theories like gravity, electricity, quantum mechanics, evolution, etc...Has given us cures for diseases, computers, cell phones, satellites, telescopes, cars, etc. What have your religious cults done for us lately?
Porgie
3.7 / 5 (3) Oct 26, 2015
Gee what a surprise.
24volts
1.9 / 5 (9) Oct 26, 2015
@kminotaur32 He does have a good point about the aerodynamic drag part of that explanation.... since space doesn't have air where is that drag going to come from?
Captain Stumpy
4.7 / 5 (12) Oct 26, 2015
He does have a good point about the aerodynamic drag part of that explanation
@24
not really. there is no indication that space is completely empty
...where is that drag going to come from?
how about we check the paper?
the PNAS link didn't work, but google scholar has it in arXiv
http://arxiv.org/...2095.pdf

Review of Pebble Accretion
After the formation of the protoplanetary disk, dust particles, which are suspended in the gas, slowly collide and grow because of electrostatic forces
I am assuming gas as in the protoplanetary disk, Hydrogen, Helium or even plasma

I also suggest reading the discussion and following, as well as the referenced material in the above quoted section

it includes studies on protoplanetary discs and more, and as a gas in space can be and has been been modeled...

Whydening Gyre
5 / 5 (12) Oct 27, 2015
So, with this highly speculative VSPA model they are able to imagine dust "readily" grows into baseballs, which "gravitationally collapses" into "asteroid" sized objects. Then, due to "aerodynamics" of stuff- where there is no air- they grow larger still, then "fuse" together...

Perhaps you would prefer the term - "hydro-dynamics"...
There is plenty of dust and potentially many gases that, combined can make up an "air"...
Whydening Gyre
5 / 5 (10) Oct 27, 2015
Scientific theories like gravity, electricity, quantum mechanics, evolution, etc...Has given us cures for diseases, computers, cell phones, satellites, telescopes, cars, etc. What have your religious cults done for us lately?

Dang, Kmin... Now I have THAT song stuck in my head.....
wduckss
1.4 / 5 (9) Oct 27, 2015
Nothing new. Bad plagiarism. Quote from: http://www.svemir...#1growth
Growth does not 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, the planets are created the same way. Then, when the planets grow to the 10% of the 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 records of objects' growth.
See also: http: //www.svemir-ipaksevrti.com/the-Universe-rotating.html#1b
my2cts
4.2 / 5 (10) Oct 27, 2015
So, with this highly speculative VSPA model they are able to imagine dust "readily" grows into baseballs, which "gravitationally collapses" into "asteroid" sized objects. Then, due to "aerodynamics" of stuff- where there is no air- they grow larger still, then "fuse" together...

"We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture." Hannes Alfvén

Have you read the paper? I thought so.
wduckss
1.5 / 5 (8) Oct 27, 2015
my2cts

Have you read the paper? I thought so.


"similarly sized objects accumulate and assimilate through a process called accretion; rocks incorporated other rocks, creating mountains, mountains then merged to form a city-size objects, and so on. ...

similarly sized objects accumulate and assimilate through a process called accretion; rocks incorporated other rocks, creating mountains; mountains then merged to form a city-size objects, and so on. "
Where do you see the difference of my work?
my2cts
3.3 / 5 (7) Oct 27, 2015
It is theorised that Jupiter has a rocky core 15 times the mass of Earth
The model appears to contradict the existence of such a core.
The paper does not mention this at all. That is not good science.

http://science.na...g_juno3/
someone11235813
3 / 5 (4) Oct 27, 2015
Surely there must be a great degree of chaos with regard to planets forming, otherwise the millions of stars that are virtually identical to the Sun, would all form a solar system like ours.
AGreatWhopper
1.4 / 5 (9) Oct 27, 2015
Hey, can't jive-I'm_not_alive, your religion makes me want to witness! Let's all sing along together now:

Jesus loves me this I know
For my butthole tells me so
His little dick is weak and limp
His mom's a whore and he's a pimp

Yes, Jesus fucks me
Yes, Jesus fucks me
Yes, Jesus fucks me
My asshole tells me so!
jljenkins
3.3 / 5 (7) Oct 27, 2015
mynoncts

5 / 5 (2) 2 hours ago
It is theorised that Jupiter has a rocky core 15 times the mass of Earth
The model appears to contradict the existence of such a core.
The paper does not mention this at all. That is not good science.


"Scientists predict that ROCKY planets formed from 'pebbles'"

No, that is not good reading comprehension.

bluehigh
2.6 / 5 (5) Oct 27, 2015
* not really. there is no indication that space is completely empty *

> Ok so let's be accurate when playing word games.

> Aerodynamic. Captain, you gonna argue there's Air in space?

> WG, Hydro-Dynanics doesn't work either. Water.

> Gas dynamics modelled? Based on what data? Do you have empirical evidence of the gas content of 'space' billions of years ago? PlayStation physics guys.

docile
Oct 27, 2015
This comment has been removed by a moderator.
Torbjorn_Larsson_OM
4.3 / 5 (6) Oct 27, 2015
I am viscously stirred by the predictive success of the mechanism. You could do a small Mars in earlier Nice models too, but this falls out naturally.

It also predicts the quick lull in the impact record that Bottke, Valley, Cavosier et cetera sees in asteroids, stable early oceans and our own unshocked early zircons. [ ihttps://astrobiol...ability/ ]

@my2cts: "The model appears to contradict the existence of such a core. The paper does not mention this at all."

No contradiction, no ovsersight: "This work complements the recent study published in Nature by Levison, Kretke, and Martin Duncan (Queen's University), which demonstrated that pebbles can form the cores of the giant planets".

@docile: "In dense aether model". There is no such model. That is why you don't give references or can make a quantitative prediction, only blather.
cantdrive85
2 / 5 (4) Oct 27, 2015
What exactly is "gravitational collapse"?

The "aerodynamics" they use are completely useless in describing the plasma, even the MHD models are highly misleading.

And what process causes matter to "fuse" to the surface of a gravitationally bound object? The boulders in my rock garden don't seem to magically fuse to the ground. These "scientists" like to invoke miracles and magic into their models, talk about religious!
docile
Oct 27, 2015
This comment has been removed by a moderator.
Captain Stumpy
4 / 5 (4) Oct 27, 2015
Aerodynamics... is a branch of Fluid dynamics
a very important part
Aerodynamics is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields. The term aerodynamics is often used synonymously with gas dynamics
thus, using the term aerodynamics is not uncommon when talking about the dynamics of an object moving through a medium like a gas, air etc... as it states in the Branches part
External aerodynamics is the study of flow around solid objects of various shapes
the rest of your post is really about semantics and comprehension. the above is a model of planetary building
a new model called Viscous Stirred Pebble Accretion (VSPA)
http://arxiv.org/...2095.pdf

in itself it may well be flawed (or too specific), but combined with other models it might hold a lot of promise

this is how science works: hypothesis, test/experiment, etc
docile
Oct 27, 2015
This comment has been removed by a moderator.
Captain Stumpy
3.4 / 5 (5) Oct 27, 2015
@blue (and likely bs) cont'd
Gas dynamics modelled? Based on what data?
based upon observations of other parts of space (which also answers your other question: gas content of space)

this is like forensics for planetary accretion or building from a protoplanetary disk. the study stated
the same models that produce reasonable Earth and Venus analogs tend to produce Mars analogs that are far too large
this is one means of explaining the Mars size and asteroid belt.

as noted above, this is how science works: ask questions (like: why?) and then build a hypothesis, test said hypothesis, etc
i will post this link again for people like bs
https://en.wikipe...c_method

as for space gas content in the past: this information is logical extrapolation of facts and data based upon known proven theory, like GR/SR, and working backwards

please also note this is a singular study
interesting in its own way and potentially powerful
docile
Oct 27, 2015
This comment has been removed by a moderator.
Captain Stumpy
3.4 / 5 (5) Oct 27, 2015
The "aerodynamics" they use are completely useless in describing the plasma, even the MHD models are highly misleading
@cdTROLLING
1- if you're not going to learn physics or actual plasma physics, you should shut up: you look stupid continuing to post the same lie over and over
http://ocw.mit.ed...ophysics

2- even the people at PPPL and plasma physics engineers working with fusion projects (that you linked, mind you) stated that MDH models include plasma physics and are functional and relevant, and work perfectly well for working with fusion, stars, and most plasma physics operations

do i really need to start re-linking all those arguments proving you stupid again?
And what process causes matter to
if you would open the link above, you would learn a lot more about reality than praying to your thunderbutts site

PS- it also includes gravitational discussion

Captain Stumpy
3.4 / 5 (5) Oct 27, 2015
This aspect of dense aether model also explains
absolutely nothing
daw/aw is falsified here: http://exphy.uni-...2009.pdf

the above is validated here: http://www.nature...174.html

repeating a lie doesn't make it more true: is this the best tactic pseudoscience and religion have?
simply repeat ad nauseum?

wishing something is true doesn't make it true any more than owning a house near a catholic nunnery makes you a Pope
Returners
1.8 / 5 (5) Oct 27, 2015
I have studied the spacial geometry of this concept before in the past, and found it to be somewhat viable, though it doesn't look like they necessarily modeled all interactions I would have liked to see.

The reason why planets stop growing is there are a couple geometrically inherent "negative feedbacks" which start to work against the largest objects, though they still maintain a net growth advantage.

as aerodynamic drag pulls pebbles into orbit, where they spiral down and fuse with the growing planetary body


This is actually one of the most important processes in colliding galaxies capturing one another too. The interaction of their ORDINARY matter haloes and internal distributed nebula exchange angular momenta, which causes the galaxies' relative motions to be slowed. Collisions of distributed nebula with one another is more common than actual stellar collisions.

Dark Matter, if it exists, is held together by ordinary matter, and NOT the other way around.
docile
Oct 27, 2015
This comment has been removed by a moderator.
Captain Stumpy
3.4 / 5 (5) Oct 27, 2015
Your remark doesn't belong here
trolls trolling a troll?
pot meet kettle

neither do your unsubstantiated conspiracist conjectures or constant repetitious aw.daw comments, which have been falsified (see links above in my last post)

repeating a lie doesn't make it more true: is this the best tactic pseudoscience and religion have?
simply repeat ad nauseum?

wishing something is true doesn't make it true any more than having a knife in your kitchen makes you Jack the Ripper
and if I consider the generally off-topic distracting character of your post, then the conclusion is, you're very dumb
but when someone actually applies the same logic to you.... when someone demonstrates using validated evidence that your religious beliefs are wrong, you call it pluralistic ignorance...

are you demonstrating pluralistic ignorance? bias? or simply being a dip sh*t? (being dumb)

valid question considering i'm using your very logic, as you spell it out, against you
my2cts
3.7 / 5 (3) Oct 27, 2015
mynoncts

5 / 5 (2) 2 hours ago
It is theorised that Jupiter has a rocky core 15 times the mass of Earth
The model appears to contradict the existence of such a core.
The paper does not mention this at all. That is not good science.


"Scientists predict that ROCKY planets formed from 'pebbles'"

No, that is not good reading comprehension.


Since you "comprehend", where does Jupiters rocky core com from
in the context of this model?
Comprehensive answer please.
my2cts
3 / 5 (2) Oct 27, 2015
I am viscously stirred by the predictive success of the mechanism. You could do a small Mars in earlier Nice models too, but this falls out naturally.

It also predicts the quick lull in the impact record that Bottke, Valley, Cavosier et cetera sees in asteroids, stable early oceans and our own unshocked early zircons. [ ihttps://astrobiol...ability/ ]

@my2cts: "The model appears to contradict the existence of such a core. The paper does not mention this at all."

No contradiction, no ovsersight: "This work complements the recent study published in Nature by Levison, Kretke, and Martin Duncan (Queen's University), which demonstrated that pebbles can form the cores of the giant planets".

That is quite casual . Th main point of the paper is that the model explains why Mars is so smal. Then why is the core of Jupiter so big ?
my2cts
4 / 5 (4) Oct 27, 2015
Lets see. ... I try to understand ... for a long time, but so far without success.

This stuff ain't in the Bible, so I advice a change of literature.
my2cts
3 / 5 (2) Oct 27, 2015

The "aerodynamics" they use are completely useless in describing the plasma,

No plasma involved. Is it true that you never heard about aerodynamics before?
my2cts
3 / 5 (2) Oct 27, 2015

@my2cts: "The model appears to contradict the existence of such a core. The paper does not mention this at all."

No contradiction, no ovsersight: "This work complements the recent study published in Nature by Levison, Kretke, and Martin Duncan (Queen's University), which demonstrated that pebbles can form the cores of the giant planets".

"it would not have been able to grow effectively near the current location of Mars, or beyond, because aerodynamic drag is too weak for pebble capture to occur."
I rest my case.
cantdrive85
2 / 5 (4) Oct 27, 2015

The "aerodynamics" they use are completely useless in describing the plasma,

No plasma involved. Is it true that you never heard about aerodynamics before?

Remarkable stupidity, remarkable. If you don't understand the medium in discussion is plasma, entirely plasma, you need go back downstairs into you mom's basement and do some more Googling. You should at least understand basic facts before announcing your stupidity to the world.

You're not alone in your ignorance, it would seem the "scientists" above are also in the dark regarding the proper physics which should be applied.
my2cts
4 / 5 (4) Oct 27, 2015
[
Remarkable stupidity, remarkable. ... you need go back downstairs into you mom's basement ... You should ... your stupidity .... your ignorance ... "scientists" ...

Mister "can't" can't control himself. Strong line of reasoning, "can't". Must read for anybody interested in borderline trolls.
reidhb
1.8 / 5 (5) Oct 28, 2015
Predict ? Like its a bet ? I'll bet they can't Effing PROVE it. How could they ? Point at the pebbles in outer space and say "SEE ??!!" ?
barakn
3.9 / 5 (7) Oct 28, 2015
Predict ? Like its a bet ? I'll bet they can't Effing PROVE it. How could they ? Point at the pebbles in outer space and say "SEE ??!!" ?

Most meteorites are composed of chondrules, round grains anywhere from a few microns to a few centimeters in diameter. These are the pebbles.
Captain Stumpy
4 / 5 (4) Oct 28, 2015
...logical extrapolation does not make evidence
@bs
really? since when? just because i don't believe your BS doesn't mean i dont think logically or that i don't accept logical extrapolations- especially with evidence
after all, what is forensic science?
GR/SR which have been shown to be completely incorrect
Really? when did that happen?
a claim like that would require links/sources, with validated studies, if you will, thanks
(mostly because it is pulled out of your *ss, extraordinary claims, etc...)
of space?
1. WTF?
2- ever hear of Spectroscopy? is has been effectively utilised not only in distant gases, stars, etc but also here on earth in the GC-MS which is a major workhorse of forensic analysis.

but i didn't think you would be familiar with it: perhaps you should go here? http://ocw.mit.ed...ophysics

maybe you could learn something?
(try it. join reality. we have cookies)
Captain Stumpy
5 / 5 (4) Oct 28, 2015
Is it true that you never heard about aerodynamics before?
@My2
well, for starters, a lot fo the above (bs, cd85, etc) are trolls looking for any justification to not believe in reality or mainstream science (note the heavy eu overtones in posters like cd85, etc or that bs routinely trolls any astrophysics thread with ad-hoc delusional rantings about astrophysics, mostly because she is not able to say "look at my published peer reviewed Journal publication that was validated" .. like zeph, but speaks better English)

secondly, i think they are getting hung up on the aero- part of the word, not realising that it has been repeatedly used in the past for the same basic idea, or (as noted above) the fact of the workings & the dynamics of an object moving through a medium like a gas, air etc...

see also my Oct 27th post above for more info on that, but i think you already are familiar with aerodynamics.

https://en.wikipe...dynamics
my2cts
4 / 5 (4) Oct 29, 2015

The "aerodynamics" they use are completely useless in describing the plasma,

No plasma involved. Is it true that you never heard about aerodynamics before?

Remarkable stupidity, remarkable. If you don't understand the medium in discussion is plasma, entirely plasma, you need go back downstairs into you mom's basement and do some more Googling. You should at least understand basic facts before announcing your stupidity to the world.

You're not alone in your ignorance, it would seem the "scientists" above are also in the dark regarding the proper physics which should be applied.

Let me teach you about plasma: it recombines. It takes a shitload of photons to keep it going. Those photons tend to take off to infinity at light speed. So in no time all plasma is gone. No planets formed.
cantdrive85
2 / 5 (4) Oct 31, 2015

The "aerodynamics" they use are completely useless in describing the plasma,

No plasma involved. Is it true that you never heard about aerodynamics before?

Remarkable stupidity, remarkable. If you don't understand the medium in discussion is plasma, entirely plasma, you need go back downstairs into you mom's basement and do some more Googling. You should at least understand basic facts before announcing your stupidity to the world.

Let me teach you about plasma: it recombines. It takes a shitload of photons to keep it going. Those photons tend to take off to infinity at light speed. So in no time all plasma is gone. No planets formed.

You display a gross dereliction of knowledge of real plasmas, anyone listening to your explanation is sure to learn complete ignorance. All of interplanetary/interstellar space is plasma you dolt, even the HI clouds.
viko_mx
1 / 5 (3) Oct 31, 2015
The big bang theoreticians claim that the universe is expanding and it expansion rate is accelerating with time -> dark energy hypothesis. And the most distant visible galaxies are moving away from us with the speeds closer to the speeds of light as they are obtained from the red shift . They also claim that not matter is moving with such a great speeds, but the space inself is expanding with this speads which idea is connected with the GR .
The question is how matter consolidate in cosmic structures like stars and galaxies, when the space which carry (dragging) it expand with the speed close to the speed of light. In their cosmic model expansion dominate gravity but if this is so from the begining, the matter will never have any chance to consolidate into cosmic structures.
viko_mx
1 / 5 (3) Oct 31, 2015
Also if space is expanding and matther is not moving with the speeds close to the spead of light, the red shift can not be the doppler effect, because this effect manifests itself only when the source of waves is moving in static space. We can not mesure the expansion of space in our visinity and to connect it with the doppler effect, because if such expansion exist , the solar system wil not have chance to emerge by consolidation of matter according to their models.

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