how the planets get in spherical shape if the they are formed by a big explosion ?
Spheres of matter are the most stable shapes when pitted against the relentless force of gravity.
and they werent formed by a big explosion :)
google accretion disk and solar system formation
Planets get a spherical shape from gravity. Once a protoplanet (Baby Planet) reaches a certain radius, gravity crushes it into a spherical shape.
The key concept you're looking for is hydrostatic equilibrium. If a celestial body is massive enough, its gravity will cause it to assume the optimal shape which balances gravity and pressure. This is a spheroid.
What explosion? Most current theories have planets condensing out of stellar nebulas.
If I remember correctly, there was an experiment with particles in the space station (wasn't it salt?) and the particles formed together in a spheroid shape.
It is natural.
I thought that planets needed an explosion (shockwave) to be formed out of nebulae... for example an explosion would allow a condensate (not like the boson ones) to be formed -as an origin of initial gravitational attraction- and thus the whole gas around would start "falling" into that and form the planet.
Due to the geometry of a sphere, it's the most favorable (energetically) shape to be formed... of course it's not a perfect sphere (for example the spin makes it more like an oval).
Separate names with a comma.