Astronomy current events question: Phobos composition

Astronomy 210L, Spring Semester 2010
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Astronomy.com editors, "Phobos Flyby Success," March 5, 2010
http://www.astronomy.com/asy/default.aspx?c=a&id=9644

What have European Space Agency researchers deduced about Mars' moon, Phobos, from the recent encounter by the Mars Express spacecraft?
(A) Not dense enough to be completely solid.
(B) An escaped moon from Jupiter.
(C) Primarily composed of dirty ices.
(D) Rich in highly radioactive elements.
(E) Interior still retains a significant amount of heat.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 44 students
(B) : 4 students
(C) : 1 student
(D) : 5 students
(E) : 4 students