# Questions tagged [planets]

Celestial body that orbits following an elliptical path around a star or stellar remnant.

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### A simple proof that under Newtonian gravity rotating massive bodies are ellipsoids?

Here is my attempt at deriving the shape of an idealized rotating massive body under Newtonian gravity, assuming that the gravity force points towards the center of mass and shape of the body is ...
1 vote
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### A problem Understanding how a two-body system of planets starts rotating around barycentre

Consider,We are Creating a Two-body system in free space,Where no other mass exists,Let's Take First Mass M1 and hold it,Now bring Second Mass M2,hold it up,Now we are giving a suddenly impulse To M1 ...
1 vote
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### Does the Lagrange Point $L_3$ exist in practice in the multi-body solar system?

Lagrange Points ($L_1$ through $L_5$) in a restricted 3-body system are well documented. Traditionally body 1 (M1) is the central object with a mass much greater than the other two objects. M2 is ...
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### Earth colliding into planet-sized object faster than speed of light [duplicate]

Imagine the following scenario: Earth is travelling in one direction at just over half the speed of light Another planet-sized object is traveling in the opposite direction towards Earth, also at ...
1 vote
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### Would a gyroscope have solved the longitude problem?

So I was thinking about the longitude problem, which was the problem of determining the longitude at sea. It caused great problems in sea navigation. See: https://en.wikipedia.org/wiki/Longitude#...
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### What would happen if the Earth rotated at the rate required to achieve orbit at its radius? I.e ~7k m/s instead of ~460 m/s

To achieve a circular orbit, you need to have a velocity of $$v = \sqrt{Gm/r}$$ which is about 7 km/s at the Earth’s radius, but the Earth’s rotational speed is only about 460 m/s (by taking the ...
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### Would it be possible to ride a bicycle on the surface of Mars?

Could you ride a standard bicycle on the surface of mars? Assumptions: You are wearing a suit to provide life-support You are riding on a prepared smooth flat martian 'road' If you were to ride ...
1 vote
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### Quantifying how much would Jupiter heat up if you accelerate Jupiter out of orbit around the sun using fusion candles? [closed]

So, I responded to a post of someone saying that you could turn Jupiter into a spaceship using fusion candles. I mentioned that doing so would dramatically heat up the planet, especially if you were ...
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### Why is the shape of the orbit of the Earth as it is?

My View: I think that if the sun were only force acting on earth (as a centripetal force), the earth would have a circular orbit. Since other planets also exist , there also exists gravitational force ...
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### Why do moons not get pulled into the planet while they clear their neighborhood? [duplicate]

Today, my 6 year old and I were discussing dwarf planets and their characteristics. We were talking about how, to be a considered a planet, the planet needs to clear it's neighborhood (as explained in ...
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### Gravitational potential when $n \geq 2$ [closed]

The standard gravitational potential given by Newton is $V(r) = \frac{k}{r}$. What happens when $V(r) = \frac{k}{r^2}$ and when $V(r) = \frac{k}{r^n}$ with $n \geq 2$? Does it matters if $n$ is odd or ...
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### What's responsible for the earth to rotate and for the objects on it to rotate with it? [duplicate]

Three questions arose to me: The first is what is responsible for the earth spinning? Is this just newton's first law in action - having been formed out of the material in the cluster of clouds after ...
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### Why exactly do higher frequency (>240 Hz) sounds on Mars travel ~4% faster than lower frequencies? What's the physics and are there optical analogies?

SciTech Daily's April 1, 2022 Variable Speed of Sound on Mars: What Sounds Captured by NASA’s Perseverance Rover Reveal About the Red Planet says The result of the recordings: a new understanding of ...
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### Could a moon keep orbiting a planet forever?

Our Moon orbits the Earth further away each year due to the tidal forces but could there be a moon orbiting a planet where somehow keeps going further away by the tidal forces but its attracted again ...
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### The work done by an external agent and gravitational force of a planet on an object of much smaller mass

The work done on an object by an external agent in bringing it closer to a planet is given by mΔV. So, when the object is brought closer to a planet, the work done by the external agent is negative. ...
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### Necessary mass and speed of asteroid required to make Venus spin

Suppose we are going to push a large asteroid (or two) from the belt and use them to make Venus rotate at approximately the same rotational speed as earth. Here are some questions regarding that: If ...
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### Distance between two points on Earth (arc length) doesn't increase with altitude (radius) according to GPS

Consider the following example: Point A has coordinates 45 lat, 0 long. Point B has coordinates 45 lat, 2 long. Both points are 5000 ft above sea level. The distance between them is X. Point C has ...
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### On a Torus World and the force upon inhabitants

I am looking into torus worlds for fiction, and I know how to calculate the necessary speed to rotate, and necessary radius, for such a world to get a specific force of gravity. But what I am ...
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### Can a planet's rotational axis be determined with a Cavendish torsion beam?

Assuming an arbitrary planet with rotation was explored but for whatever reason (perhaps cloud cover?) the axis of rotation was unknown. Or they needed confirmation... the situation honestly does not ...
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### Newtonian contribution to perihelion precession of Mercury

We have seen that the orbits of the planets around the sun can be found, to a good approximation, by only considering a two-body system (a planet and the sun) interacting through a central force. ...
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1 vote
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### How do we find the centripetal forces of 3 planets revolving around a point given that they have the same mass?

Let's say we have three planets revolving around a point. We know that the force of gravity acting on all of these planets can be taken from $g = G{m_1m_2 \over r^2}$. We can derive the velocity of ...
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### How to make the Moon spiral into Earth?

I recently watched a video of what would happen if the Moon spiraled into Earth. But the video is pretty sketchy on the physics of just what would have to happen for that to occur. At first I thought ...
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### Body falling through Earth

Imagine a body with mass $m$ moves through a pipe through the centre of earth. The gravitational force is given by $\vec{F}=-C \vec{r}$ where $C$ is constant. I want to determine the 1D equation of ...
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### How close can Jupiter be to Earth without making Earth unhabitable? [closed]

How close can Jupiter be to Earth without making Earth unhabitable? What's the closest distance possible? Can Jupiter be twice or three or four times as close to Earth as Mars without having any ...
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### Does gravity slow down sound (does sound travel faster downwards than upwards)?

I have read this question: So assuming the heavier planet has the same atmosphere as Earth, and that we can treat the atmosphere as an ideal gas, the speed of sound on the heavier planet would be the ...
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### Difference between the Sphere of Influence and Hill Sphere

I am looking through astronomy topics, and I found two ideas which sound very similar, but have very different formulae which come to different results. That is the Sphere of Influence, and Hill ...
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### Help finding the eccentricity of an orbit

I am trying to find the eccentricity of a planet in order to be able to calculate perihelion and aphelion distances. I can get a lot of the equation, but am having issues with the angular momentum, ...
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### Are there planets orbiting something else than a star?

Exoplanet is a planet that orbits a star different from our Sun. Are there any planets (that we know of) which orbit something else? (Like different giant planet or black hole or maybe neutron star.)
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### In which direction do the perihelions of the planets show? Is this somehow correlated with the solar apex?

I just found a Wikipedia page that showed that almost all perihelion where at the same position (except for Mars) and I was wondering, if someone has more information /data/pictures. Thank you!
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### How to represent orbital velocity of a planet on an elliptical path in terms of time?

Before reading this long message, please know that this is question is posted to know whether there is a method to find the relation between between the orbital velocity of a planet on an elliptical ...
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### Is it possible to pin superconductors inside the gas giants/ice giants?

So I had read an interesting question about pinning superconductors to earth's magnetic field but this was deemed impractical (even if we had high temperature superconductors) because the field is so ...
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### Does the formula $v = \sqrt{GM/r}$ work for elliptical planetary orbits?

Suppose we have a central mass $M$ and a smaller mass $m$ orbiting around the central mass in an ellipse: The other point is the other focus. We know that elliptical orbits have the central mass in ...
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### Simulating solar system with Newton's law

I made a simulation in C++ with Newtons law and test it comparing the planets positions with the position from Solar system Calculator Don Cross (which I converted from JavaScript to C++) http://...
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### How close could a 1 solar mass star get to our solar system without disrupting the planets' orbits

Is there an easy way to calculate how close a star of given mass could get to our solar system without disrupting the orbits of the planets? Just looking for a rough estimate, nothing too involved
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### Inner and outer orbital limit of planets in single-star systems

I am trying to find a rough cut-off of the inner and outer orbits of native planets around a single star. I know about the Roche limit and Hill Sphere, but these are not the limits I am looking for. I ...
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### Calculating the offset for a Fly-by past Mars. Hohmann/Patched Conic Approx. Transfer from Earth to Mars [duplicate]

Would anyone know where to look or know how to calculate the offset distance at which fly-by on Mars may be performed. It’s the variable ‘x’ in the formula 8.3-20. (Bate Mueller Astrodynamics ...
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### Mathematical Derivation of Expression for the Total Power Received By Earth from Sun, via Integration [closed]

I recently tried to derive an expression for the total power received by the earth from the sun, using integration. However, I am stuck at an integration step. Would appreciate if anyone could help ...
1 vote
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### How would water pool on a disc-shaped planet of Earth mass?

All this flat-earthism stuff is best ignored (although that is sometimes difficult) but it did get me wondering about the physics behind the pooling of water on a disc-shaped planet. Not for the sake ...
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### Basic question about orbital speed

I was reading a Sci-Fi book recently and had a weird thought: I know that objects closer to a gravitational well need to move faster to stay in orbit and objects further away move slower. But if you ...
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### How to derive Kepler's third law of planetary motion using angular momentum of Earth around the Sun?

While I was trying to derive Kepler's third law of planetary motion, I tried the gravitational force for the Earth method which goes something like this: $$\frac{mv^2}{r}=\frac{GMm}{r^2}$$ \...
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### How does general relativity explain tides?

How general relativity explains tides using spacetime curvature? and if the full moon can affect water, inside the international space station did the ever observe small things like water droplets ...
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### What is the precise internal structure of Jupiter?

I've been trying to find out exactly where the layers of molecular hydrogen, and metallic hydrogen are precisely, inside Jupiter, in kilometres from the centre. Ideally with an error margin of 1-10kms....
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### How does formula for universal gravitation between mass $M$ and mass $m$ collapse to $mg$ on Earth? [duplicate]

Can anyone give a mathematical demonstration of this? I assume it has to do with the fact that Earth’s mass is much bigger than the mass of any object on Earth, but I think it would be interesting to ...
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### I am a bit stuck with the patched conic approximation for interplanetary travel between the Earth and Mars

I am writing an internal assessment for first year university on patched conic approximation. I am having some trouble calculating the departure angle from earth. This is because I have to calculate ...
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### How much differs the Mercury speed at perihel from its theoretical speed with no frame dragging involved?

How much differs the Mercury speed at perihel from its theoretical speed with no frame dragging involved? Can a formula of frame dragging velocity be calculated regarding the distance of a point of ...
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### What's the formula for the Critical impact parameter?

What is the formula for the critical impact parameter for an asteroid with excess velocity $v_∞$, approaching a planet of radius $r$ and escape velocity $v_e$. Here I'm defing the Critical impact ...
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I'm trying to solve the following problem but do not quite understand it. Assume that a planet with mass $m_{1}$ is orbiting the sun with radius $r_{1}$ (that is $a=r_{1}$ in Keplers 3. law) in a ...