Astronomy final exam question: massive main sequence stars and the extraterrestrial hypothesis

Astronomy 10 Final Exam, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal F.1

[3.0 points.] Which one of the following choices best explains why planets that orbit O- and B-type main sequence stars are not thought to be good candidates to search for the presence of advanced extraterrestrial civilizations?
(A) These planets would be geologically dead.
(B) These planets would be tidally locked, where the same side would always face inwards.
(C) These planets would be too large.
(D) O- and B-type main sequence stars are very luminous.
(E) O- and B-type main sequence stars have short lifetimes.

Correct answer: (E)

Massive O- and B-type stars would have extremely short main sequence lifetimes on order of millions of years, which is probably much too short for an advanced technological civilization to arise, much less for any form of life to evolve (which may take on order of billions of years).

Students are probably confusing response (B) with planets that orbit in the habitable zones around low mass red dwarf stars. These orbits would be so close in that that the planets would be tidally locked, making it unlikely (but not completely impossible) for life and for an advanced technological civilization to arise.

Student responses
Section 5166
(A) : 4 students
(B) : 15 students
(C) : 1 student
(D) : 4 students
(E) : 16 students

Section 4160
(A) : 0 students
(B) : 16 students
(C) : 1 student
(D) : 3 students
(E) : 15 students