30 January 2009

The MOC "Book": Introduction

Posted by Ryan Anderson

When the Mars Global Surveyor arrived at Mars in 1997, it brought with it the most powerful camera ever placed in orbit around another planet, the Mars Orbital Camera (MOC). In 2001, the principal investigators of MOC, Mike Malin and Ken Edgett, published a massive 134 page paper, summarizing the results of the mission and revolutionizing the world’s view of Mars.

Here in the MarsLab, the paper is fondly referred to as the “MOC Book” and “The Beast”. Recently, Briony, Melissa and I have decided that we are going to meet on a weekly basis and discuss bite-sized portions of this monstrous paper, and I thought our readers here might be interested in following along.

We skipped the first 24 pages devoted to the details of the camera and data processing and got straight down to business with the introduction to the science section. This section begins with one of the first pictures of Mars taken by MOC. It is a rather boring looking view of some craters, but the emphasis of the paper is that every single one of the tens of thousands of MOC images tells a story.

An eroded, dune filled crater hints at a period during which the while area may have been covered in dunes which have since blown away.

A: One of the first images of Mars taken by MOC; B: The same image, map-projected; C: A fresh-looking impact crater; D: An eroded, dune filled crater hints at a period during which the whole area may have been covered in dunes which have since blown away.

The authors point out that some craters cast shadows while others don’t. This indicates that the older craters are eroded so that their rims don’t stick up as much. They also point out that some craters are filled with dunes, while others of the same size are not. This means that after some of the craters formed on the pre-existing surface, there was a period of time when sand dunes were blown through the area. The sand has now been mostly blown away, except where it was trapped inside craters. Now, enough time has passed since the sand moved through that fresh craters have formed. All that from a boring looking photo of the surface! Just wait until we get to the “interesting” images!

The introduction to the paper also spells out some of the conventions, and summarizes the goals of the experiment. They emphasize here and throughout the paper the degree to which the feel “humbled” by the MOC images.

“Our sense of being humbled by what is visible in MOC images also comes from having seen, very early in the mission … that many of our Viking- and Mariner 9-based preconceptions of Mars were simply wrong or lacked important detail.”

Stay tuned for the next few weeks as we work our way through this classic paper and discover where the pre-MOC ideas were wrong, and how MOC changed the way people think about Mars.


M.C. Malin, K.S. Edgett (2001). Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission Journal of Geophysical Research – Planets, 106(E10), 23429-23570