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

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Saturn's polar versus equatorial gravity

Wikipedia's reference for Saturn's gravity gives $10.44 m/s^2$ at the equator, but this conflicts with Britannica, which gives $8.96 m/s^2$ at the equator and $12.14 m/s^2$ at the poles. All values ...
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160 views

What is the maximum mass of planet HD 40307 g

Recently discovered planet HD 40307g around HD40307 Star system is claiming that its inside a habitual zone of a solar system. Besides It has water where life could be evolved. I tried to calculate ...
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2k views

How gravitation affects tides

I know that tide is caused by the gravitational pull of moon but what I don't know is how it affects water. I have actually these doubts. Why does gravity of the moon creates tides only in water? ...
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80 views

Physics of tidal locking: can the process be underdamped?

Is it possible for a satellite undergoing the process to overshoot the required rotation rate for tidal locking? For example, if its rotation rate is being slowed, can it become slower than it needs ...
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1answer
68 views

How to find the force of the compression at the core of a planet?

For example the core of the planet Jupiter, how to find out the magnitude of the force that compresses its core? and can that be thought of as the total force that holds the planet together?
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Is nuclear fusion possible on planets in our Solar system?

Apart from thermo-nuclear reactions in the Sun, (and in hydrogen bombs and other methods developed by scientists) does nuclear fusion occur naturally in the planets? If not, why? Also, do the Sun ...
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187 views

Could a planet sized bubble of breatheable atmostphere exist?

I'm reading a book (Sun of Suns by Karl Schroeder) that the main location is a planet called Virga, which contains air, water, and floating chunks of rock, and has no or a very small amount of ...
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267 views

Does the Earth have a semi-solid body at its core because of lower pressure at the center of the Earth?

I have read that the Earth has a semi-solid iron body at its core, even though that object is surrounded by liquid magma.... I'm wondering if this is because of a pressure (and resulting temperature) ...
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1k views

Where to find the current positions and velocities of the planets?

I've written a program which simulates the motions of planets and other bodies. I'd like to run it on our own solar system, but to do so I need to know the current positions (preferably in ...
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1answer
174 views

Keeping air in a well

Let's say I've got an Earth-like planet with no atmosphere: it's just a barren ball of rock. I want to live there, but I don't like domes, so instead I'm just going to dig a big hole and let gravity ...
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1answer
822 views

Altering Venus rotational speed to match Earth's via weather manipulation

Venus rotates approximately 6.5 km an hour Earth rotates approximately 1650 km/h how fast could we speed up Venus's rotation via only weather manipulation ( maybe a giant fractal lens between Venus ...
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1answer
40 views

Protoplanet formation & Kessler Syndrome

In the early stages of the solarsystem rocks clumped together randomly until their gravity drew in more material which led to protoplanet formation. But how does the dust and do the rocks form bigger ...
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140 views

Is there a connection between the core of the earth and heaviest element produced by stars?

I was unable to answer this question from my daughter. Is it just a coincidence or is there a connection between the following two observations: (1) the core of the earth is made of an iron (-nickel ...
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1answer
158 views

Has martian sunset same spectra than this earthly bluish-violet sunset?

Has martian sunset same spectra than this earthly bluish-violet sunset? What about sunset on Mercury?
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1answer
302 views

What is the critical mass of a planet to have an atmosphere like Earth's? [closed]

Small planets/orbits like Moon cannot have atmosphere because of their masses. They don't have enough gravity to hold an atmosphere. Then what is the critical mass that makes enough gravity to keep an ...
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1answer
98 views

Cassini: What information could be gained from the 2017 impact with Saturn?

First of all: Will Cassini be operational in 2017 (pending no unforeseen equipment failures)? Power Communications ... What information could we gain? Properties of Saturn How to build more ...
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1answer
165 views

Mars Circular Intercept Orbit

I've been trying to simulate a spacecraft entering a circular capture orbit about Mars using Mathematica, but am having a little trouble. The simulation starts when the spacecraft enters Mars' sphere ...
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68 views

Would a rocky planet orbiting so close to a very hot star eventually vaporize?

I was thinking about the physics behind a hypothetical scenario where a planet the size and the mass of the Earth is orbiting so close to a very hot star and what the long-term fate of such a planet ...
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52 views

Could there be a dark matter planet? [duplicate]

Since dark matter is gravitationally "charged", by which I mean it has mass and attracts things, could it bunch together to form a planet?
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84 views

Protoplanetary disks, angular momentum and prograde orbits

So you've got a protoplanetary disk and you're going to gravitate yourself some planets together. The disk is made up of the usual planetary system stuff, dust and gas and whatnot, orbiting a common ...
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31 views

The collision of Phobos [duplicate]

Possible Duplicate: the collision of Phobos Mars has two moons: Phobos and Deimos. Both are irregular and are believed to have been captured from the nearby asteroid belt. Phobos always ...
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0answers
17 views

How did the radiative flux of each gas giant planet change with respect to time (since their formation)?

We know that each gas giant planet was warmest when it was young. This warmth came from internal heating from both radioactive decay and from gravitational potential energy. This warmth, in turn, ...
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2answers
165 views

How does gravity behave outside the geoid?

I was watching a program about the geoid recently and the relative "height" of the Himalayan plateau gave me an idea. It makes sense for the geoid to be "highest" (is that the correct term?) there as ...
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2answers
377 views

Why do we orbit around the sun instead of one the other stars?

I am still very new to many physics theories, however while sat in class today, a thought came to mind that I have not been able to answer from simple googling. What is so specific about our sun ...
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2answers
299 views

Infinity problem: Why is gravity $g=0$ zero at the center of Earth if according to Newton gravity formula $g=GM/R^2$? [duplicate]

It is said that value of $g=0$ at the centre of the Earth. $g$ is calculated using the formula $$ g=G*M/R^2.$$ When $R = 0$, $g$ approaches infinity. I have two ...
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1answer
365 views

Presence of planets in Milky Way and other galaxies

Are there only planets in the Milky Way galaxy, or are there other planets in other galaxies? If planets are only in the Milky Way, why aren't there planets in others?
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Does anybody actually do astrometry in the 21st century?

I mean the nitty-gritty measurements of positions of stars and planets using transit circles. The transit instruments I've seen are mostly in national observatories and are essentially museum pieces: ...
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3answers
549 views

The theory of moon creation when a Mars size planet hit Earth

As we know the predominant theory where does the moon come from is that a Mars size planet hit the earth and took a chunk out of it which eventually materialized into moon. My question is that if a ...
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2answers
873 views

How can I visualize a gas giant?

From wikipedia Gas giants are commonly said to lack solid surfaces, but it is closer to the truth to say that they lack surfaces altogether since the gases that make them up simply become ...
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2answers
58 views

Do the outer gas planets radiate their mass?

We know that the sun experiences angular momentum loss, and radiates a portion of it's mass (though helicity is conserved). Can we say the same about massive Jupiter, or even Saturn, Uranus or ...
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185 views

Does gravity affect radiation incident on the planet?

Just curious ... Known facts: When outside the atmosphere levels of radiation are higher Typically such radiation is CBR, Solar Radiation Question: If the matter of the atmosphere and ...
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2answers
215 views

The size of the planets

What calculations were done to discover the size of all the planets?
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270 views

Calculate Initial Velocity For Orbital (Gravity) Slingshot

I am trying to find the initial velocity to slingshot a planet around the sun and through a gap. The green ball is the planet, and the yellow ball is the sun. In this trial I need to get the ...
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154 views

Would a magnetic rod through Mars shield it from solar wind?

Would a magnetic rod going all the way through Mars shield it from solar wind?
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159 views

Does Planet revolution time is always greater the more it's getting away from the center?

The entire question is in the title . It's the case for the solar system but is it always the case ? Can a planet do a revolution faster than another that is closer to the center ? As far as I ...
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1answer
147 views

How should I be thinking about tides?

I am working on a project for physics that involves tides. This is my current mind set when thinking about tides: The earth applies a gravitational force on some mass ...
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1answer
105 views

Does spacetime have symmetric curvature around an object? If yes, then why do planets revolve around the Sun in elliptical orbits?

Does spacetime have symmetric curvature around an object? If yes, then why do planets revolve around the Sun in elliptical (as opposed to circular) orbits?
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3answers
301 views

Could the sky on a planet theoretically be any color?

The sky on the Earth is blue. Could the color of the sky on a planet with an atmosphere be of any color theoretically? Which colors are the most likely? I think it would be really awesome to have ...
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1answer
115 views

Tidal locking of a planet to a satellite

As in the case of Pluto and its moon Charon, both the bodies are tidally locked to each other, will the Earth ever be tidally locked to the Moon? Is there any effect on the rotation of the Earth ...
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3answers
2k views

Moment of inertia of a planet

Is there a good way to directly measure a moment of inertia of the Earth, or say, other planet?
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1answer
252 views

Motion of mercury [duplicate]

I studied that mercury motion around the sun slightly displace by a certain value in each year. But, this is not predicted by kepler until general theory of relativity. What does general theory does ...
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2answers
3k views

Artificial planetary magnetic field

I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need? The question is inspired by thinking about possible colonization of ...
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3answers
922 views

Would a Helium powered balloon vehicle work on Mars?

Would a Helium powered balloon vehicle work on Mars? Things that might need to be answered: How much liquidHelium would you need to pack in order to fill a balloon with enough helium gas to travel ...
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1answer
133 views

Are the inner planets on planar orbits because there was more dust in the inner solar system (early on in planetary accretion)?

Question inspired by a question thread here. So when there's lots of dust in a galaxy, the galaxy tends to collapse into a spiral galaxy (to maintain angular momentum and to minimize gravitational ...
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1answer
850 views

What causes the collapse of a Magnetic Field?

It's theorized that Mars once had a magnetic field which collapsed at some point. There's also lots of speculation that a similar process will eventually happen to Earth. More recently has been the ...
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1answer
104 views

Synchronising the Earth's rotation via mass redistribution

How much material would have to be moved per year from mountain-tops to valleys in order to keep the Earth's rotation synchronised with UTC, thus removing the need for leap seconds to be periodically ...
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1answer
56 views

Why do Uranus and Venus rotate from East to west?

Why do only Uranus and Venus rotate from East to west, while others rotate in opposite direction? Is it because of the angle of their tiltness? Or due to the process of their formation?
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1answer
44 views

Calculating the size of exoplanets with moons

When astronomers detect an exoplanet using its transit and calculate its size to be, say twice the earths size, do they have any way of knowing that its actually not a slightly smaller planet with a ...
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1answer
80 views

Help understanding centre of mass

So basically the question I posed myself a few days ago was for a torus shaped planet, what would the gravitational field be like inside the torus? After viewing some answers on the internet, (Gravity ...
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2answers
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What is the value of $g$ at centre? [duplicate]

What is the value of $g$ at the centre of the Earth? Is it zero or infinity? My attempt: I know it's zero but applying law made me on fused.