Questions tagged [planetary-formation]

Questions about the processes, theories and evidence for the formation of planetary bodies.

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Why do most dwarf planets have mass comparable to moon?

It was quite interesting to spot that most dwarf planets have masses close to that of our moon (if we let an error to fluctuate within two orders of magnitude). Why it is so? Is there any common ...
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3 votes
0 answers
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Extract surface density profile from a temperature profile?

I have a protoplanetary disk model which outputs a temperature vs. radius profile, based on radiative transfer. Looks something like this... One of the inputs to the model is the surface density ...
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Can a destroyed earth reform into another habitable planet?

Let's say a planet-sized object collide with earth, disintegrate it, then reform at the same orbit as earth. Will it eventually formed into a habitable, life-supporting planet with living organism?
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18 votes
3 answers
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How is asteroidal rock formed?

So when planets form, dust from the protoplanetary nebula gets collected by gravity and then heated and reformed under pressure until it forms dense masses of stuff which we call rock. However, ...
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1 vote
1 answer
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What is a Keplerian shear

I was reading an article on Gas Giants and how some form close to their host star. One line in the article says: A region of the proto-planetary disk will be susceptible to gravitational instability ...
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2 answers
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Is the gas in a planet forming disk around a star comparable in density to an atmosphere?

If you were standing on a planetesimal in the planet forming disk of a new solar system (or our own, billions of years ago), would you be able to feel "interplanetary wind"? Would it be ...
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Could or has a Ninth planet ever be "formed" in our solar system?

As I get along with the answers in my previous question, that planet formation depends on accumulation of planetesimals. So is there any chance that a planet nine would form or any of the Trans-...
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3 votes
1 answer
93 views

The reason for an exoplanet density increase of planets closer to a star

From the NASA exoplanet archive system it can be seen that in the range of $0.02-0.06~\text{AU}$ distance an exoplanet is to its star, as distance drops down, the planet density increases linearly: A ...
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9 votes
3 answers
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Why is the composition of the sun so distinct from that of earth?

Given that the sun is – in astronomical distances – quite close to the earth, why are the two composed of such distinctly different substances? Sun Composition Hydrogen 74.9% Helium 23.8% Oxygen ~1% ...
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1 vote
1 answer
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Envelope Enrichment?

While I was researching about planet formation, I repeatedly came across the term envelope enrichment. What does this mean? I searched it up and looked at many websites, but no helpful definitions ...
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Farthest observed protoplanetary disk observed at radio frequencies? Catalog

This could be a naive question or maybe too easy to solve (I do not really know!). Brief context: I'm interested in a certain planetary system at $d \sim 300 \, \mathrm{pc}$. It would be really nice ...
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12 votes
1 answer
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How do rocky objects between 1cm and 1m accrete to form planetesimals?

I am having a hard time gaining an intuitive understanding of some of the middle stages of planetary formation from a protoplanetary accretion disk. I understand that microscopic dust particles may ...
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9 votes
1 answer
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What's the expected distribution of planet masses in a given system?

Given that the mass of a planet at a given orbital distance r is dependent on the protoplanetary material in the neighborhood of r at the time of formation (assuming no planetary migration), what ...
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5 votes
2 answers
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How do scientists know that Earth used to spin much more rapidly?

News has just been released all over my news feeds about how paleontologists now believe that early photosynthetic organisms became much more efficient at producing oxygen after the Earth started to ...
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Where will the frost line be when the Sun becomes a red giant and what effect will it have on the solar system?

I understand the frost line is currently about 5.2 AU and earlier in the solar systems formation was 2.7 AU. But when the Sun becomes a red giant the frost line should move outward. I understand the ...
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23 votes
2 answers
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Intuitive explanation of the source of energy that cause Jupiter and Saturn to migrate outward in the Grand Tack Hypothesis?

The Grand Tack Hypothesis states that Jupiter first migrate inward, but it was caught up by the faster inward migration of Saturn, and when the two planets reached 3:2 mean-motion resonance they ...
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Can the pebbles growth model be applied to the rotations of planetary systems? [duplicate]

I've just read the University of Amsterdam 2019 News item Pebbles determine the direction in which planets rotate (which links to R.G.Visser et al (2020) Spinning up planetary bodies by pebble ...
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3 votes
2 answers
114 views

Spin-down of gas-giants during formation

In the paper https://arxiv.org/abs/1712.00457 about rotation rates of gas giants it says: "owing to accumulation of angular momentum stored in the source material, a planetary mass object should ...
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What does it mean for a planet to have an "icy" core?

My understanding of the physics of planets leans heavily on my understanding of the physics of stars - of course there are important differences. One important difference that I've found is the nature ...
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1 vote
1 answer
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What is the meaning of grain opacity and why does it affect the formation time of gas giants?

While doing research for my presentation on the formation of gas giants, more specifically the "core-accretion model", I have been stumbling across the term "grain opacity" and don'...
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2 votes
1 answer
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Are accretion disks the only way stellar planetary systems form?

The accepted theory for the formation of our Solar System is from an accretion disk. A molecular cloud is thought to have collapsed under its own gravity and formed a disk. Most of the matter in the ...
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Assuming a hypothetical system without gas but only solid rocks, how big of a planet can form through the coalescing of these rocks?

I have heard that gas giants are primarily huge solid bodies like regular rocky planets that exponentially gained more and more gas in their atmosphere through their increase in mass which they use ...
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River-like artifact in perseverance rover's photo of Mars

Good to know that perseverance rover has touched the surface of Mars finally. We will have nice new opportunity window for exploring our closest "friendly" planet of solar system. Here's one ...
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6 votes
1 answer
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Why is Mercury's Density So Low?

I know the title sounds odd. You might be thinking "Doesn't Mercury have the highest uncompressed density of any terrestrial planet? Much higher than a planet its size normally should have?&...
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Can we see traces of exo-moon formation?

Our Moon was likely formed by the collision of a Mars-size object with the Earth soon after the planets first formed. Would traces of such an event be detectable by observing the protoplanetary disc ...
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After a supernova, why don't new stars coalesce with higher heavier element content?

May be a beginner's question but I couldn't find the answer anywhere. Given a supernova event and the cloud left by it, why does a new star coalesce with a disproportionally higher hydrogen(and helium)...
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8 votes
1 answer
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Feasibility of Grand Tack Hypothesis

Something I've been wondering lately is how much the grand tack hypothesis stands up to present scrutiny. While the grand tack proposes that Jupiter and Saturn were caught in a 3:2 mean-motion ...
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Why do the solar system planets go rock-gas-ice instead of rock-ice-gas when moving away from the sun?

The sun and the solar wind seem to do a good job of fractionating lighter materials to the outer solar system and leaving heavier materials in the inner solar system. So we end up with rocky/metallic ...
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Why are most discovered exoplanets heavier than Earth?

Looking at all discovered exoplanets (4393 exoplanets), I found than only 17 of them (less than one percent!) have masses less or equal to Earth's mass. Why so? Is it because it is very difficult to ...
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3 votes
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What is the YORP effect exactly? Is it just the non-central component of the Yarkovsky effect?

This answer to Where have all the Vulcanoids gone? links to the aptly-titled The YORP Effect Can Efficiently Destroy 100 Kilometer Planetesimals At The Inner Edge Of The Solar System which says in ...
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Where have all the Vulcanoids gone?

This answer to Does anything orbit the Sun faster than Mercury? explains that while Vulcanoid asteroids may have been plentiful in the past, large ones have currently been ruled out though smaller ...
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4 votes
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Why isn't the moon's surface made of mini craters?

I thought that the millions of mini rocks that hit the moon would cause it to be entirely cratered and not flat. Why is the moon not like this: why aren't craters visible in the footprint photo?
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1 vote
1 answer
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Life cycle of a gas planet?

I am interested in learning more about the (simplified) life cycle of gas planets which are not brown dwarfs (meaning less than 13 Jupiter masses). It obviously starts off with their creation within a ...
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1 vote
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Can we make reliable models to estimate what the angular momentum was in preplanetary stellar disks?

I have recently become aware of how important the angular momentum of a preplanetary disc may have been in determining what type of a planetary system a star may have. We are able to measure the spin ...
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0 votes
1 answer
416 views

Did Mercury clear its neighborhood?

For a body to qualify as a planet according to the IAU definition it must have "cleared its neighborhood". What evidence is there Mercury indeed cleared its neighborhood? Perhaps it migrated ...
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8 votes
2 answers
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How likely are planets to form after neutron star collisions?

It is well known that planetary collisions can create moons orbiting the result of the merger if they happen in the correct way, and this is how the Earth's moon is believed to have been formed. See ...
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1 answer
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Could rocks from Earth have reached the Kuiper belt, or Neptune at least? If so, how?

This answer (currently edit 3) to How certain are we that we have not sent life to other planets/moons? begins: First of all, rocks from Earth are probably just about everywhere in the Solar System. ...
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5 votes
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Can the order of planets change in a young planetary system?

The Nice model and the Grand Tack model both show that the distance between a planet and its host star can change greatly over time. Is it possible in either of these models for the order of planets ...
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3 votes
1 answer
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Are all the planets differentiated?

The Earth is differentiated, as it has a distinguishable core, mantle and crust with different compositions and densities. Are all the other planets differentiated as well?
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6 votes
1 answer
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What's the critical mass of a rocky planet before its gravity traps enough gas in its atmosphere to start becoming a gassy planet

Looking at the latest theories, I've noticed that most rocky planets are below a certain mass range. I speculate that maybe the way gas giants and gas dwarfs form is a rocky planet during the ...
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1 vote
1 answer
179 views

What's the exact story of jupiter and our earth, not becoming a super-earth?

I've been watching the Cosmos documentaries by Neil DeGrass Tyson and the ones from Brian Cox, and in one episode (I don't remember from which series) there's something about the creation of the rocky ...
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Why is there so little nitrogen in the Martian and Venusian atmospheres?

Why don't our neighbors have much nitrogen? You would think that, without 'nitrogen-fixing' organisms and such, there might be more.....
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5 votes
1 answer
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Are there other planetary systems where gas giants are on the inside to rocky planet orbits?

I understand that formation theories for gas giants suggest they should be born further away where there is more gas for them to monopolize vs the sun, and then to form Hot Jupiters they need to ...
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Was the solar system flat before the planets formed? Or does the Kozai-Lidov mechanism flatten orbits after the gas giants form?

An astronomer living on Jupiter measures the orbits of the inner planets against Jupiter's ecliptic. Their inclinations are; Mercury 5.7 deg. Venus 2.1 deg. Earth 1.3 deg. Mars 0.6 deg. It looks ...
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4 votes
1 answer
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Composition of ice giants

After reading the paper "The Measured Compositions of Uranus and Neptune from their Formation on the CO Ice Line", I was left with doubts which I would like to clarify. Firstly, the paper proposes ...
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3 votes
1 answer
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Is there any thing special with an axial tilt of roughly 25°?

Half of the planets in the solar system have an axial tilt of $25.5\pm 3^\circ$: earth (23.5°), mars (25.3°), saturn (26.7°) and neptune (28.3°). If random collisions in the early solar system caused ...
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1 vote
0 answers
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Binary stars and gas giant formation

Say there's a young s-type binary star system with 2 Sun-like stars. From what I understand for a stable orbit to be possible, a planet's farthest orbital point from its host star has to be around 1/5 ...
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3 votes
2 answers
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Is this a potential planetary setup for the Alpha Centauri System?

I originally posted this on the World Building SE, but I was suggested to post it here for a better answer. I am attempting to create a [semi]plausible star system in Alpha Centauri for a series. The ...
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1 vote
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Why does half of a planet's radius end up being the radius of the core?

This answer makes the assumption that the ratio between the radius of a planet and the radius of its core is roughly constant shortly after planetary formation. Why should this be the case? Do we know ...
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15 votes
1 answer
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The compatibility of the Grand Tack hypothesis with the "core-warping impact" theory of Jupiter's diffuse core

In recent years, the Juno mission revealed that Jupiter's core was much more diffuse than astronomers had expected. One theory is that "within a few million years" of its formation, Jupiter ...
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