Which statement about extrasolar planets found to date is true?

a)All are terrestrials, comparable in size to Earth.


b)All lie more than 2 A.U. from their star.


c)Most have orbital periods of more than a year.


d)Some are so close to their stars that their periods are just a few days.


e)Few are found by Doppler shifts of their stars, due to their gravity.





Please answer and explain! Thank you very much!|||The correct answer:


d)Some are so close to their stars that their periods are just a few days.











Why the others are incorrect:


A: No...our survey of exoplanets is highly biased to discovering more massive planets. Most known to date are Jupiter-like or perhaps Neptune-like. Very few are terrestrial-class...in fact, even the majority of them are "super-Earths" of mass greater than Earth, and we don't exactly know what the mass basis boundary between a Uranus-like gas giant and a terrestrial class planet is.





B: No...not true at all. In fact, our surveying does much better discovering them closer than 1 AU to their parent star.





C: No...humans are impatient. We want to discover those we can discover quickly, and we do so observing data that shows conclusive evidence rather quickly, meaning it needs to have a quick orbital period if we are to conclude its existence quickly.





Only those who are patient discover slow planets far from the parent star...and don't get me wrong...we know we need to be patient and we have discovered many that have slow orbital periods. I wouldn't go so far as to say most though.








E: no...in fact, this is just about the easiest method to discover them|||Only D is true. A is completely wrong, as nearly all are Jovians or even larger.


B is false, most lie within less than 0.5 AU of their stars.


C is false as most have periods of only a matter of days.


And E is also false, as most afre found by doppler shifts. A few by transits.|||I guess reading about exoplanets would be too hard.





Here, try it:


http://planetquest.jpl.nasa.gov/


http://en.wikipedia.org/wiki/Exoplanets





Its amazing what you can learn by reading about things.|||C.|||d) is the only one that could be true. If you want to do some research see attached link.





http://exoplanet.eu/