At least ________ of stars host at least one planet. A) 70 B) ...

[CQXA]

At least ________  of stars host at least one planet.
 
  A) 70 B) 1 C) 10 D) 30

Question 2

Explain what synchronous rotation is. What is it caused by? Give an example.
 
  What will be an ideal response?

[s.meritte]

Answer to Question 1

A

Answer to Question 2

Synchronous rotation is when the rotational period of an object is the same as its orbital period around another object. As an object orbits another, it is stretched by the varying force of gravity across it. The resulting tidal bulges lag behind the rotation of the object slightly and cause it to rotate slower. This continues over time until the rotational period becomes the same as the orbital period, at which point there is no longer any tidal friction and the rotational and orbital periods are synchronized. An example is the Moon always presenting the same face to Earth through its orbit. A variation on this is Mercury which rotates 3 times for every 2 orbits around the Sun.