Astronomy current events question: variations in Mercury's rotational speed

Astronomy 210L, fall semester 2015
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!)

Leigh Cooper, "Mercury’s Movements Give Scientists Peek inside the Planet" (September 9, 2015)
blogs.agu.org/geospace/2015/09/09/mercurys-movements-give-scientists-peek-inside-the-planet/

Mercury's core composition and gravitational interactions with the outer planets can be analyzed from __________ data measured by NASA's Messenger spacecraft.
(A) seismic.
(B) rotation rate.
(C) temperature.
(D) polar ice.
(E) magnetic field.

Correct answer: (B)

Student responses
Sections 70178, 70186
(A) : 1 student
(B) : 20 students
(C) : 3 students
(D) : 1 student
(E) : 5 students