Questions tagged [planets]

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

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55 votes
4 answers
136k views

How does gravity work underground?

Would the effect of gravity on me change if I were to dig a very deep hole and stand in it? If so, how would it change? Am I more likely to be pulled downwards, or pulled towards the edges of the hole?...
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39 votes
5 answers
33k views

Would you be weightless at the center of the Earth?

If you could travel to the center of the Earth (or any planet), would you be weightless there?
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18 votes
3 answers
4k views

If it was possible to dig a hole that went from one side of the Earth to the other...

...And you jumped in. What would happen when you got to the middle of the Earth? Would you gradually slow down, until you got to the middle and once you were in middle would every direction feel like ...
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11 votes
5 answers
8k views

How do the Planets and Sun get their initial spin?

How do the Planets and Sun get their initial rotation? Why do Venus and Mercury rotate so slowly compared to other planets? Why does Venus rotate in a different direction to Mercury, Earth and Mars?
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20 votes
5 answers
128k views

Why is Earth's gravity stronger at the poles?

Many sources state that the Earth's gravity is stronger at the poles than the equator for two reasons: The centrifugal "force" cancels out the gravitational force minimally, more so at the equator ...
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39 votes
6 answers
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Why don't planets have Circular orbits?

This might be a completely wrong question, but this is bothering me since many days ago. Given the mass (Sun) curves the space around it, gravitation is the result of such curved space (Correct me if ...
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6 votes
1 answer
2k views

Radial fall in a Newtonian gravitational field [duplicate]

Suppose an object of mass $m$ starts at rest at a radial distance $ r_0$ from a perfectly spherical mass $M$ (where $m << M$), $r_0 > R =$ radius of $M$. Can we analytically determine when ...
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15 votes
2 answers
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Is it possible to prove that planets should be approximately spherical using the calculus of variations?

Is it possible to use the Lagrangian formalism involving physical terms to answer the question of why all planets are approximately spherical? Let's assume that a planet is 'born' when lots of ...
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30 votes
3 answers
7k views

What nonlinear deformations will a fast rotating planet exhibit?

It is common knowledge among the educated that the Earth is not exactly spherical, and some of this comes from tidal forces and inhomogeneities but some of it comes from the rotation of the planet ...
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13 votes
4 answers
1k views

What is the general relativity explanation for why objects at the center of the Earth are weightless?

The idea that as you move through the earth you get a symmetric cancelling of gravitational acceleration which approaches zero acceleration due to gravity at the center of the earth makes a lot of ...
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32 votes
3 answers
9k views

Why does the Moon face Earth with the same side?

I know that the rotation period of the moon equals its revolution period. It's just so astonishing that these 2 values have such a small difference. I mean, what is the probability of these 2 values ...
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25 votes
9 answers
28k views

Why are orbits elliptical? [duplicate]

Almost all of the orbits of planets and other celestial bodies are elliptical, not circular. Is this due to gravitational pull by other nearby massive bodies? If this was the case a two body system ...
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10 votes
5 answers
31k views

Why does the Moon not revolve around the Sun directly?

The sun pulls on the moon with a force that is more than twice the magnitude of the force with which the earth attracts the moon. Why, then, doesn’t the sun take the moon away from the earth?
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2 votes
3 answers
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Two bodies of finite size treated as two point masses in Newtonian gravity

When discussing gravitation between two bodies of finite size, for instance Earth around the Sun, we suppose the mass of Earth and the Sun to be perfectly localized at the center of each body. Is this ...
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27 votes
1 answer
502 views

The transit of Venus and solar neutrino rates

The following question was posed at the end of Maury Goodman's June 2012 long-baseline neutrino newsletter. During the Venus transit of the sun, were more solar neutrinos absorbed in Venus, or ...
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3 votes
2 answers
1k views

Does the Earth emit gravitational waves?

We know about Bohr's model and his vague postulate challenging Rutherford regarding discrete orbits and not emitting electromagnetic waves during this. Extending this idea to our solar system, does ...
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4 votes
1 answer
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Proportionality constant in crater equations

I have searched for equations regarding craters and I came across two of them. The first one is from this NOAO website in the level two section. There, it says that, $$ D^3\propto E $$ where $E$ is ...
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9 votes
2 answers
2k views

Rotational oblateness

I am trying to compute the amount of oblateness that is caused by planetary rotation. I picture the force of gravity added to the centrifugal force caused by the rotation of the planet as follows: $\...
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11 votes
7 answers
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What's the biggest cube you could have before gravity rounded it?

I took this question from Quora because it seems interesting and this community would have some fun with it. I would assume that one would use the modulus formulas for force to counteract the gravity, ...
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9 votes
8 answers
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Why doesn't planet Earth expand if I accelerate upwards when standing on its surface?

According to General Relativity I am being accelerated upwards by planet earth while writing this question. But a curious person on the the other side of the planet relative to me would have the same ...
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19 votes
1 answer
1k views

Could there be a body of water the size of a planet?

My friend and I were reading the news of the discovery of a black hole spewing huge amounts of water vapor into space, and it got us thinking: could there be a blob of liquid water in space the size ...
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32 votes
1 answer
3k views

Using nuclear devices to terraform Mars: Elon Musk's nuclear proposal? [closed]

Elon Musk has recently suggested Using nuclear devices to terraform Mars. In the past, comet related ideas were mooted, but Musk seems, to me anyway, to be a man in a hurry and perhaps his idea has ...
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33 votes
2 answers
6k views

Why does the Earth even have a magnetic field? [closed]

From my knowledge of magnetism, if a magnet is heated to a certain temperature, it loses its ability to generate a magnetic field. If this is indeed the case, then why does the Earth's core, which is ...
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31 votes
3 answers
5k views

Why do the planets' orbital distances fall on an exponential curve?

Background: I was recently reading a book on the planets to my son and I noticed a pattern in the distributions of the planets. The planets' distances roughly follow an exponential distribution. ...
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35 votes
6 answers
13k views

Could there be a star orbiting around a planet?

I wonder if there ever could be a star (really small) which may orbit around a planet (really big)?
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25 votes
1 answer
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Causes of hexagonal shape of Saturn's jet stream

NASA has just shown a more detailed picture of the hexagonal vortex/storm on Saturn: http://www.ibtimes.com/nasa-releases-images-saturns-hexagon-mega-storm-may-have-been-swirling-centuries-1496218 ...
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1 vote
1 answer
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Crater equation

I found this crater equation $$ D=0.07 \cdot C_f \cdot (g_e/g)^{1/6} \cdot (W p_a/p_t)^{1/3.4} $$ on a website, where $$ \begin{align} D &= \text{Crater Diameter}\\ C_f &= \text{Crater ...
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15 votes
4 answers
3k views

Why is Uranus's axis of rotation tilted?

The poles of Uranus are 'in the wrong place', why is this? historically, do we have any evidence of its past? also, do we have an understanding of how its rotational axis might be evolving?
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3 votes
1 answer
998 views

Relativistic time dilation on Mars compared to Earth?

What is the time dilation in Mars, compared to earth? Can we accurately calculate it? What information is needed to do these calculations?
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1 vote
1 answer
9k views

What is the relationship between mass, speed and distance of a planet orbiting the sun?

After reading this fascinating story about a new exoplanet, I was wondering about how mass, speed and distance determine a circular orbit of a planet around a star. Given the mass of the sun and star,...
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10 votes
3 answers
4k views

What if the Moon was 100x more massive: Binary planets?

I was reading a couple of Earth-Moon related questions (Mars just collided with Earth! A question of eccentricity, Could the earth have another moon?) and they got me thinking about planet-moon ...
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31 votes
3 answers
5k views

When a planet is heated through gravitational pull, where is the energy taken from?

Jupiters moon Io is heated through the gravitational pull of Jupiter, but when Io is heated because of this, where does that energy come from? How does conservation of energy work for this effect, ...
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12 votes
3 answers
1k views

Planets and Pluto? Neptune?

If one of the rules to be a planet is that it needs to clear ALL objects from their orbit, does this also make Neptune a non-planet? Since it has thus far failed to clear Pluto from it's orbit. Or ...
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14 votes
2 answers
1k views

Do celestial objects experience drag from the near vacuum of space/does the near vacuum have a mean velocity?

For instance do the planets around the sun experience drag from the near vacuum of space? Or do the (hydrogen) atoms in interplanetary space have a mean velocity near orbital speeds, such that object ...
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7 votes
1 answer
334 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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14 votes
6 answers
10k views

Can low-gravity planets sustain a breathable atmosphere?

If astronauts could deliver a large quantity of breathable air to somewhere with lower gravity, such as Earth's moon, would the air form an atmosphere, or would it float away and disappear? Is there a ...
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24 votes
11 answers
11k views

Backyard experiments to falsify the Flat Earth theory [duplicate]

I recently became aware that the flat Earth theory still exists in the 21st century, and has colored the views of a friend of mine. Roughly speaking, the tenets are: The Earth is a flat disk, with ...
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6 votes
2 answers
8k views

How would gravity change on a planet rotating around itself very fast?

Let's take a planet identical to Earth, but with rotation speed multiplied by ten thousand. What would happen with the gravity if it was spinning madly around itself? Would the centrifugal force make ...
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27 votes
2 answers
10k views

How long until we fall into the Sun?

As a planet moves through the solar system, a bow shock is formed as the solar wind is decelerated by the magnetic field of the planet. Presumably the creation of this shock wave would cause drag on ...
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6 votes
6 answers
2k views

Why does the Earth rotate? [duplicate]

Possible Duplicate: Why does every thing spin? So why would the Earth, or any planet for that matter, rotate along an axis? I know of no force which could come into play here, so i assume it just ...
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5 votes
3 answers
892 views

Gravitational force of the Earth [duplicate]

Why does gravitational force of the Earth decrease as we move towards the centre of the Earth? Where as inverse square rule says that distance is less than gravitational force is more.
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2 votes
2 answers
9k views

Gravity beneath sea level [duplicate]

This is a very simple question, but I can't find an answer anywhere. Earth's gravity at sea level is 1 (approximately 9.8m/s^2) What happens being under sea level in a cavern/chasm/ravine, how much ...
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94 votes
4 answers
12k views

If Earth had rings?

If Earth had rings, would they center on the equator like Saturn's rings do on its equator?
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9 votes
3 answers
2k views

Binary Star system with one star stationary?

Can a Binary Star system be possible where in one star is stationary and the other star revolves around it? (Just like a planet revolving a star. i.e planets in the system and the star revolving ...
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15 votes
2 answers
3k views

What would be the rate of acceleration from gravity in a hollow sphere?

Lets say the Earth is hollow and you are in the center of it (Same mass except all of it is on the outside like a beach ball) If you move slightly to one side now your distance is closer to that side ...
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6 votes
1 answer
5k views

Why are the orbits of the planets in our solar system along the same basic plane? [duplicate]

Possible Duplicate: Why are our planets in the solar system all on the same disc/plane/layer? After watching this video I realized that the orbits of the planets in our solar system basically ...
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20 votes
2 answers
11k views

Why Aren't Saturn's Rings Clumping into Moons?

While reading with my son about how a Mars-like planet collided with the early Earth that resulted in our current moon, it said the initial debris also formed a ring, but that ring ended up getting ...
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  • 550
13 votes
4 answers
9k views

If there is friction and everything stops on earth why does earth not stop due to friction?

Why do planets revolve around the Sun if there is a force called frictional force? Why do planets not stop rotating while the objects in motion stop after a while? Why are they continuously moving? ...
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13 votes
2 answers
2k views

Falling into Saturn or Jupiter, would we pass through it until we hit the nucleus?

If we fall into Saturn or Jupiter, would we pass through it until we hit the nucleus? Or would we hit the surface and stop there?
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8 votes
6 answers
39k views

Lowest gravity on Earth's surface?

I am trying to determine which on Earth's surface has the lowest gravity. Googling is not finding anything concrete. My natural inclination would be to think of Mount Chimborazo in Ecuador, being on ...
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