Astronomy midterm question: Mars and Mercury both low in the west at sunrise?

Astronomy 210 Midterm 1, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board was asked and answered[*]:

Pdg: Can be Mars and Mercury be both low in the west at sunrise?
CON: No. Mars can be low in the west at sunrise, but Mercury cannot.

Discuss how this answer is correct, and how you know this. Support your answer using a diagram showing the positions of the sun, Mars, Mercury, Earth, and an observer on Earth.

[*] answers.yahoo.com/question/index?qid=20170106000722AAkerYG.

Solution and grading rubric:

• p:
  Complete diagram and reasoning includes the following explanations for an observer on Earth at sunrise (6 AM):
  1. Mars can be placed in an orbit around the sun outside of Earth's orbit such that it is visible low over the observer's west horizon; and
  2. Mercury can be placed in an orbit around the sun inside of Earth's orbit but will never be visible low over the observer's west horizon.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Problems with either diagram or discussion. May have:
  1. Mars in an inner orbit and/or Mercury in an outer orbit; or
  2. observer not placed at sunset and/or east/west horizons switched.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram and discussion problematic.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30674
Exam code: midterm01nghT
p: 14 students
r: 0 students
t: 6 students
v: 0 student
x: 2 students
y: 0 students
z: 1 student

A sample "p" response (from student 9433):