Access Planetary | Information on planets and the universe

Isn’t the planets‘ day and night determined by the speed of rotation. If so, then why would a planet have a shorter day and longer night sometimes?

If the planet’s axis of rotation is tilted, then the nights will be longer in areas that are tilted away from the Sun. As the planet orbits the Sun, which hemisphere is tilted away from the Sun will change. This is why we have seasons here on Earth.

Recently I read that Mercury, Venus, Earth and mars are the rocky planets in our solar system. Should have been opposite as they are closer to the heat source.

This is explained by the Lewis Model. In the early Solar System, which was a cloud of gasses, the inner parts were warmer than the outer parts. In the inner region, only things like metal or rock could condense, so the inner planets (Mercury, Venus, Earth, and Mars) are composed chiefly of metal and rock. As you move out to the cooler outer regions, it gets cool enough for things like water ice, and then ammonia and methane ice to condense.

The reason why the outer layers of the gas giants (Jupiter, Saturn, Uranus, and Neptune) are composed of lighter elements is that these planets grew larger than the Earth, quickly. There are two reasons why. One is that, in the outer regions, it was cool enough for a larger range of materials to condense — not only rock and metal, but also things that condense at cooler temperatures such as water ice and ammonia ice, so there was more "raw materials" for the planets to be made of. The other reason is that ice sticks together better than rocks and metals, so when the ice that had condensed in small pieces ran into other pieces of ice, it tended to make bigger pieces, rather than bounce off or fragment as pieces of rock do. The outer planets originated as big planets made of ice and rock. They were massive enough that their gravity allowed them to accumulate hydrogen and helium, which the inner planets did not have enough mass to hold on to, and grow to their current titanic proportions.

Besides Earth, what is the greenhouse effect doing to other planets, like Venus?

Well, the martians think its simply pathetic what we are doing to our planet!