Astronomy midterm question: habitability of Mars forming closer to the sun

Astronomy 210 Midterm 2, fall semester 2014
Cuesta College, San Luis Obispo, CA

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

Pd: If Mars had originally formed closer to the sun, would it be more habitable today?
qu: Mars closer to the sun would be warmer, but actually less habitable with less water and atmosphere.

Discuss how Mars forming closer to the sun would have less water and atmosphere today, and how you know this. Explain using the properties of planet mass, atmosphere, and geological activity.

[*] answers.yahoo.com/question/index?qid=20141101111207AAt4Wdm.

Solution and grading rubric:

• p:
  Correct. Discusses why both statements are correct about Mars located closer to the sun and being warmer would result in:
  1. less water, due to warmer temperatures evaporating all available water (or ultraviolet light breaking apart water molecules);
  2. less atmosphere, as warmer temperatures would allow atmosphere molecules to move faster and more easily escape from Mars' weak gravity.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of the two points (1)-(2) correct, other is problematic/incomplete.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Both points (1)-(2) problematic/incomplete, or one is correct while the other is garbled/missing.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between planet location and mass with atmosphere temperature and retention.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on relationships between planet location and mass with atmosphere temperature and retention.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02s0vA
p: 10 students
r: 4 students
t: 18 students
v: 10 students
x: 3 students
y: 0 students
z: 0 students

Section 70160
Exam code: midterm02n4Rs
p: 7 students
r: 6 students
t: 15 students
v: 2 students
x: 3 students
y: 0 students
z: 0 students

A sample "p" response (from student 1123):
A sample "x" response (from student):