I bet u cant answer this....?

Question

recently i read that as earth has escape velocity of 11.2 km/sec, hence,as theair molecules do not have that much velocity,they do not escape,...and thats why there is atmosphere on earth.....but wat about in asteroids???they have more escape velocity...smthng like 238kms/sec ....why is there no atmosphere there???..and so is it for many planets

Answer 1

I'm just sorry to say that your concept of 'escape velocity is wrong.

In physics, for a given gravitational field and a given position, the escape velocity is the minimum speed an object without propulsion, at that position, needs to have to move away indefinitely from the source of the field, as opposed to falling back or staying in an orbit within a bounded distance from the source. The object is assumed to be influenced by no forces except the gravitational field; in particular there is no propulsion, as by a rocket, there is no friction, as between the object and the Earth's atmosphere (these conditions correspond to freefall) and there is no gravitational radiation.

It means, if you throw a ball from earths surface at 11.8km/s speed, it will never come back.

How is it calculated
In the simple case of the escape velocity from a single body, it can be calculated by setting the kinetic energy equal to minus the gravitational potential energy. This is because the positive kinetic energy is needed to increase the negative gravitational potential energy to zero, which applies when the object is at an infinite distance.

.5mv^2 = GMm/r or, v = sqrt(2GM/r)

[sqrt means square root]

For a body with a spherically-symmetric distribution of mass, the escape velocity ve from the surface (in m/s) is approximately 2.364×10−5 m1.5kg−0.5s−1 times the radius r (in metres) times the square root of the average density ρ (in kg/m3), or:

v = 2.364*10^5 r sqrt(density)

Escape velocity is directly proportional to the radius of a spherical object with constant density.
if an asteroid has equal density of earth, and has a radius of 1km,
what will be it's escape velocity? (Earths radius is 6400 km)

its escape velocity, v= 11200/6400 m/s = 1.75 m/s
which is quite small

I think you meant the asteroids drifting velocity to be 238kms/sec.


This is a quote from my wikipedia "All of the planets have atmospheres as their large masses mean gravity is strong enough to keep gaseous particles close to the surface. " Even some of the satellites of Jupiter and Neptune have atmospheres

Answer 2

The main reason in easy terms is that the asteroids are soo small that they cannot be able to sustain its own atmosphere and together adding with the movement of the asteroid well you figure that out.
Now to planets:
plannets have atmospheres infact the only plannets that doesnt have any atmosphere are the planets that are quite small in volume and mass. actually gravity is sirectly related to size & mass of the planet.. or body. And as you can notice the escape velocity is greatley affected on the commets direction

Answer 3

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Answer 4

Asteroids have much lower escape velocity because they are small. There's not much mass to create gravity.

Answer 5

You win there are lots of asteroid like things on our solar system particularly HYPERION and its a surprise not to see it have an atmosphere.

Answer 6

They have no magnetic field to prevent the solar wind from blowing any kind of atmosphere away. Even if they did have a magnetic field, because of their low mass, any atmosphere would be extremely thin.

Answer 7

because there wasn't any to begin with.