Both planets would be destroyed, as the gravitational pull would rip off matter from both planets, and they would be ripped apart.
No. The moon formed after a planet-sized object collided with Earth.
The moon
It is small
No. Mars and Earth never collided. Around 4.6 billion years ago another planet is believed to have collided with Earth, resulting in the formation of the moon. This planet, known as Theia, was probably about the same size as Mars.
if a planet was close to earth it would cause earthquakes and more. if it collided if earth depending on the size if it is big it will collide with earth.
It is believed that Theia collided with Earth around 4.5 billion years ago, leading to the formation of the Moon. The debris ejected from this collision eventually coalesced to form the Moon, while some material merged with Earth. This event played a crucial role in shaping the early Earth and its satellite, the Moon.
Venus is often compared as Earth's "sister planet", being similar in size and internal composition.
Mars
Theia See related link for more information.
Scientist theorize that a planet-sized object collided with earth and the moon formed
We believe that the proto-Earth, very early in the formation of our solar system, probably collided with another planet, one that might have been as large as Mars. The collision probably entirely re-formed the resultant Earth, and that the heavy metallic cores of both planets merged. Debris blasted into space by the collision probably coalesced to form the Moon.
Before life existed on Earth a Mars like object collided with our planet. A big chunk of the Earth floated away from our planet due to the pressure of the collision. And that big chunk is now what we call, the Moon.