Based on studies of planetary systems around other stars, which of the following statements are currently believed to be true about how common or rare it is for stars to have planets in orbit around them? A) Planets in general are believed to exist around less than half of all stars. B) Giant planets like Jupiter are extremely common, but terrestrial ("Earthlike") planets are extremely rare. C) Planets are believed to exist around most, if not all stars, and terrestrial ("Earthlike") planets are not especially rare. D) Planets around other stars are too hard to detect with current technology, and so we are very uncertain how common or rare it is for stars to have planets in orbit around them.

Answer: D) Planets around other stars are too hard to detect with current technology, and so we are very uncertain how common or rare it is for stars to have planets in orbit around them.

Explanation:

The current methods involved in ascertaining if planets are orbiting a star are wobbles and shadows.

With Wobbles, planets are found by how much gravitational pull they exert on the star.

With Shadows, the telescopes look for a reduction in the light of a star based on if a planet passed. The logic is that the bigger the planet, the bigger the reduction. There are two main problems with this though,

1. Some planets take years to go around their sun so the telescope will have to observe for quite a period of time and,

2. Some stars like our sun are so bright that a reduction caused by a planet going passed it is too miniscule sometimes to be detected.

The general consensus therefore is that we don't know if Earths or other planets orbiting suns like ours are rare or if the technology we have currently just isn't advanced enough to see them.