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

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79 views

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.
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2answers
205 views

Interstellar bodies

As a solar system evolves the planets interact, and in trying to achieve a harmonious state some bodies are ejected. Space is big, but I have heard that some meteorites have been found with anomalous ...
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260 views

Solar System Capture of Orphan Planets

NASA recently announced (http://www.nasa.gov/topics/universe/features/planet20110518.html) that orphan planets, planets no longer orbiting a star, may be more numerous than the stars in our galaxy. ...
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2answers
69 views

Is it possible for a planet to be “axially locked”?

What I mean is, can a planet orbiting its sun have a fixed rotational axis relative to the sun ie in the case of earth the tilt is like this /........(sun)......./. as it goes around the sun. ...
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2answers
106 views

Stability of planet-enclosing shell supported by atmosphere

I understand that a hollow spherical shell of uniform density gives net zero gravitational attraction to objects inside it. So in vacuum, a ball at the centre of a spherical shell would not be stable ...
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1answer
184 views

Why is the Earth shaped like a sphere and not any other shape: cube, prism? [duplicate]

Why is the earth shaped like a sphere and not any other shape: cube, prism?
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1answer
88 views

What properties are used to quantify the odds of a star harboring earth-like life?

Say you start with a list of stars. What properties do we believe to be critical in the present existence or future formation of earth-like life in those star systems? How can one reasonably pare down ...
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2answers
1k views

Where do planets get energy to revolve around sun? [duplicate]

We know that every planet in our solar system revolve's around the sun in a particular orbit. But were to they get the energy to revolve around the sun. And why do they not drop into the sun there is ...
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1answer
141 views

Magnetic field line length

If I had a magnetic bar in space that was 2cm wide and 2cm high and was one Earth diameter long and had the same magnetic strength as the Earth, would the distribution of field lines be the same ...
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2answers
1k views

How does one measure Earth's speed of revolution around the sun?

I know that there are several formulae that one can plug numbers into to arrive an estimate of Earth's speed around the sun (Kepler's third law for instance), but I'm wondering how these things are ...
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1answer
3k 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 ...
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1answer
501 views

Metallic Hydrogen and Gaseous Planets

Jupiter has about twice the density of Saturn (1.33 versus 0.69 g/cm^3) because it apparently has a higher mass percentage of rocky core and of metallic hydrogen in its interior. Available density ...
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59 views

How strong can tidal forces get?

I am imagining a planet the size of Earth being in close proximity to something of high mass such as a gas giant or a star, but ultimately I'd be more interested in how to figure this out myself. So ...
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131 views

Only gravitation and Newton's $2^{\mathrm{nd}}$ law needed to derive Kepler's laws?

It is known that Kepler's laws of planetary motion can be derived from Newton's laws of motion and his law of universal gravitation. However, are all of Newton's laws of motion necessary? According ...
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49 views

What speed should have an alone planet to have a habitable zone due to relic radiation?

What speed should have an alone planet to have a habitable zone due to relic radiation, without any star involvement? How much time the planet will be able to remain in the habitable zone before the ...
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0answers
59 views

Stable planetary rotation states

In reading an article about theories as to how the slow retrograde rotation of Venus may have come into being, the article Why Venus Spins the Wrong Way (Franzen, 2001) stated that it is bound to ...
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0answers
413 views

For two planets in a 2:1 mean motion resonance , where will their periastron and apastron points be?

I want to animate the changing orbits of planets when they enter a mean motion resonance. Using a 2:1 resonance, I want to show a low-mass inner planet and a low-mass outer planet being tugged by a ...
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0answers
555 views

How do I find equations for the distance of the planets relative to one another?

I know I should be able to piece together some basic Newtonian equations for this, but I'm not sure where to start. I want to be able to choose one planet as the center and calculate its distance ...
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1answer
80 views

Single plane Ring system [duplicate]

Possible Duplicate: Why are our planets in the solar system all on the same disc/plane/layer? I've noticed this in many pictures, Planets are shown with a single ring around them (in some ...
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1answer
5k views

Why does the moon or the earth revolve anti-clockwise?

The question is very simple: Why does the moon or the earth or any another planet revolve anti-clockwise? And can any planet (or satellite) revolve clockwise? What is the physical law for this ...
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1answer
609 views

How easily can the Earth flip?

The recent media attention to sunspot activity (however warranted) reminds me of a question I had long ago. Given the angular momentum and the slight 'wobble' of the earth, and remembering the ...
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1answer
175 views

Is it possible for a solar system to have planets orbiting the star(s) in a spherical pattern?

By the question I mean that the planets spin in their ellipse but all ellipses describe the surface of a near-sphere shape around a star. Same question but for a solar system with 2 stars of ...
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2answers
270 views

What's the weight of the earth?

What's the weight of the earth? That is, what's the weight of the earth in the gravitational field of the sun? I imagine it's either $0$, because there's no net fall toward the sun, so the downward ...
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5answers
323 views

Age of universe estimates

I was recently involved in a discussion on a sister site regarding how tightly coupled Physics is with the age of the Universe (and Earth). I believe that the Earth and the Universe are both billions ...
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3answers
139 views

Is the Earth round?

Imagine you are a common man and want to prove that the Earth is Round, how would you prove it without any mathematical derivation or without the theory of the ships.
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2answers
98 views

If planet like Jupiter is massive enough to hold hydrogen with its gravity is it bound to become a star?

I have been reading about Jupiter as of late and reason I am asking is if Jupiter has strong enough gravity to pull hydrogen to itself then it should be only matter of time when it will acquire enough ...
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1answer
54 views

How have the duration of the martian day changed in the past?

There is a panspermia theory which claims that life might have begun on Mars and I currently read a post that the human circadian rhythm is closer to the martian day length (about 25h) than the day ...
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2answers
1k views

Will a spinning object come to rest?

Will a sphere spinning on its own axis come to rest given enough time, provided no other forces act upon it? I know that if you have two spinning spheres in the depths of space and orbiting each ...
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2answers
44 views

What conditions would allow planetary-sized objects to collide and remain intact?

I am modeling some off-the-wall scenarios to try out with a game engine. One idea is trying to make a planet where some weird catastrophic incident has creates a funny shaped planet. I'm hoping to ...
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1answer
1k views

Confusion over the gravitational potential energy inside a sphere

I'm confused over the concept of gravitational potential energy inside a sphere. I understand that the gravitational potential energy inside the sphere is supposed to be a constant $U = ...
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1answer
932 views

Atmospheric escape of gas molecules

Most of the objects in space are likely to have an atmosphere. Since space is void, the gases in atmosphere should have either dissolved or emptied into space. But, some of the objects still seem to ...
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2answers
56 views

Gravity underground on the moon?

They say that gravity Decreases as we dig into the earth. But I also read that gravity increases for the first approx. 2000km of distance underground. Using this rational, could we dig about 200 to ...
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1answer
129 views

Why are tidal forces pointing away from the Moon? [duplicate]

I am currently reading The Science of Insterstellar, which explains most things very well, but some things leave me confuzzled, which I hope to get answers to here. I am no physicist, but highly ...
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1answer
41 views

Helium confined to a gravity well

It's a well known problem that Earth is slowly losing its supply of helium due to helium's ability to "bubble off" the atmosphere. All the gas giants have significant percentages of helium in their ...
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1answer
100 views

Drift of Earth's orbit?

How much has Earth drifted (inwards or outwards) from its orbit about the sun? Or has Earth has not moved at all, compared to, say, 1000 years ago? 10,000 years ago?
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2answers
72 views

What should we do If we wanted to increase the angular velocity of a planet? [duplicate]

We could hit it with really fast objects, but could we manipulate the orbit of a large satellite to speed up its rotation? What would be the easiest way?
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1answer
64 views

How do you calculate density if you also account for gravity?

Consider this. I have an Earth-sized quantity of water that I throw into space. Naturally, it will assume the shape of a ball. Now hear me out. Density's definition generally assumes that it will ...
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1answer
183 views

Could this planetary superalignment happen?

Here's the 'superalignment' I'm referring to: We've all heard the stories about 'mystical planetary alignments' that will increase/decrease the effective surface gravity experienced on Earth (one ...
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1answer
50 views

If a planetoid was wet and you spun it would the water move to the equator?

If the moon was alone in space and covered in X feet of water and it began to rotate would it displace to a bias along the equator?
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1answer
674 views

Why do larger planets cool more slowly than smaller ones?

I learned it during my environment class. My professor introduced the concept--- ratio of surface area and volume. The numerator has connections with the radiative loss, while the denominator is ...
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2answers
253 views

Saturn ring stabilization

The rings of Saturn are the most extensive planetary ring system of any planet in the Solar System. I'm wondering, what power is primarily responsible for that stability? © Public Image by NASA ...
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1answer
310 views

What equations/constants were used to calculate the Kármán Line for Earth?

I am interested in how the original value of ~100 km was calculated for the Kármán line of earth. What equations and constants would need to be used to reproduce this value? Note: By constants, ...
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1answer
155 views

What's the amount of deviation of cellestial orbits from perfect ellipses

It's well known that the planets don't orbit the sun in perfect circles and the characteristics of the elliptical orbits which serve as better approximations to their motion have been calculated ...
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1answer
82 views

Planar motion in central forces

In a two body problem under central force, corresponding to a potential $V(r)$(assume one body is massive compared to the other so that its motion is negligible), conservation of angular momentum ...
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1answer
42 views

Spectroscopy and the current state of our ability to determine the composition of extra-solar planets

I was interested in learning more about the status of our scientific understanding and technological instruments regarding extra solar spectroscopy. I am motivated by this almost 3 year old ...
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1answer
41 views

Planetary Systems

How does one know the correct position of planets in relation to the sun when viewing the solar system from different angles makes the appearance of the planets different? I would think that it would ...
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1answer
289 views

Is there a simple formula for calculating semimajor axis bounds of “habitable zone”?

I understand that an accurate determination of the bounds of the "habitable zone" for a given stellar system depends on a large number of factors, including many beyond characteristics of the parent ...
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1answer
65 views

Function for heating of a planet by its star

I'm looking for an algorithmic model which will gives rough estimate of the average temperature of a planet's atmosphere (good enough to say whether there will be liquid water anywhere, or if metals ...
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1answer
3k 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 ...
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0answers
15 views

Calculating collapse factor in the crater equation [duplicate]

In the Crater Equation $$ D=0.07C_f\left(\frac{g_e}{g}\right)^{1/6}\left(E \frac{\rho_a}{\rho_t}\right)^{1/3.4} $$ where $\rho_a$ is the density of the impactor, $\rho_t$ that of the object, $g_e$ ...