The nature of the far side of the Moon has always been a mystery.
Throughout the ages of human history, the far side of the Moon has been
so near, its presence so obvious, and yet so hidden. It was only in the
decade of the 1960’s that we have been able to observe it, as
opposed to inferring its existence. I have been fortunate to live
during the period when the far side became visible and has been
extensively examined by means that were not even known fifty years ago.
During this time, we have learned much but of course we have asked new
questions about secrets still hidden on the Moon. Some of these secrets
will be revealed in the course of future exploration and robotic
This book is about what we now know of the far side of the Moon, about
what the current questions are, and about some possible answers.
It is a companion book to “The Lunar Orbiter Photographic
of the Near Side of the Moon,” my first book, also published
Springer in 2005. Together, these books cover the entire Moon in
photographs taken by the robotic spacecraft that have done their work
behind the Moon, out of communication with Earth for half of their
The photographs of the near side book were taken by a single mission of
the Lunar Orbiter project, Lunar Orbiter 4 that was flown in 1967. This
book is primarily composed of photographs from each of the Lunar
Orbiter missions of the National Aerospace and Space Agency (NASA) and
from the Clementine mission of the Naval Research Laboratory (NRL). In
addition, it contains images from the Russian Luna 3 and Zond 3,
NASA’s Apollo 16, and Japan’s Nozomi.
The Clementine mission provided a comprehensive survey of altitude,
albedo (intrinsic brightness) and multispectral data in 1994. Lunar
Prospector provided gamma ray spectroscopy in 1998. The data from these
spacecraft has added insight into the mineral composition of the lunar
surface (supported by ground truth from analysis of lunar rocks and
soil returned by Apollo and Luna missions).
Clementine imagery is used extensively in this book where it is
superior in topographic resolution or uniformity of coverage.
The reason for using photos from so many missions is that there has not
been a single mission to systematically take pictures to show the
topography of the far side of the Moon. Yet it has been possible to
provide complete coverage of the far side by assembling photos from
Many years ago, I had the pleasure of working on the Lunar Orbiter
project, representing the Apollo program in its search for safe and
interesting landing sites. I worked for Bellcomm, a contractor to NASA
headquarters. The Lunar Orbiter project was amazingly successful for
the time, providing extensive new images in five out of five missions.
This performance is a credit to Boeing, the prime contractor and
manufacturer of the spacecraft, to Eastman Kodak, who made the camera
system, and to the project management team at NASA’s Langley
Research Center, directed by Lee Scherer of NASA headquarters. The
Langley team, who included Cliff Nelson, Israel Taback, and Norm
Craybill, later managed the Viking project, which sent the first lander
The limited scanning technology of the time resulted in artifacts in
the images that distract a viewer. There are bright lines running
across the mosaics between framelets and brightness variations from the
spacecraft’s scanner that appear as streaks within the
Lunar scientists have become used to these artifacts, but they detract
from the value to students and casual observers.
Since the first photos were received, I have wanted to clean up the
scanning artifacts. Advances in the art of computation and the capacity
of modern computers has enabled processing of the photos to remove
nearly all of the scanning artifacts, resulting in clear images that
are much easier to view.
Drawing on an understanding of the nature of the artifacts, I have
written a software program that measures and compensates for the
systematic artifacts and designed a filter that further reduces them,
with minimal impact on the images of the Moon. This process is
described in Appendix A.
It was with great satisfaction that, with the publication of this book,
I have completed the publication of a comprehensive set of
cleaned photographs from the Lunar Orbiter project. The photos are
those that were selected by D. E. Bowker and J. K. Hughes for their
book “Lunar Orbiter Photographic Atlas of the
Moon.” All of
the far side photographs of Lunar Orbiter and the other photographs in
the book are on the enclosed Compact Disk. A CD with the near side
photographs was provided with my near side book.
While preparing these two books, I attended a series of yearly meetings
of the Lunar and Planetary Science Conference (LPSC), sponsored by the
Lunar Planetary Institute, a NASA contractor. In the course of these
meetings, where lunar and planetary scientists report on their current
work, I became interested in the differences between the near and far
sides of the Moon, and the attempts to explain that
Consequently, while preparing for this book on the far side, I took
some time off to see if I could contribute to this question.
turned out that my background in communication research, specifically
the art of finding signals in noise, led to a new hypothesis, with
supporting quantitative evidence. I took the approach that a giant
basin on the near side would be a signal, a pattern of elevation data,
and the subsequent history of bombardment of the Moon would be noise,
random perturbations of the signal. Just as noise adds to a signal in
communications, the principle of superposition establishes that the
characteristic form of an impact adds to the form of an earlier basin,
especially on of a much larger scale.
Accordingly, I modeled the elevation signal that would be produced by a
giant basin, and varied the characteristics of such a basin, much like
tuning a radio, until the maximum signal-to-noise ratio was found. Then
the Near Side Megabasin revealed itself. This resulted in the
parameters of the Near Side Megabasin that I reported to LPSC 2006. The
method of this analysis is described in Chapter 13.
It remained to explain the crustal thickness data, which was
qualitatively in agreement with the Near Side Megabasin, but in
quantitative disagreement with the parameters I had first
estimated (Byrne, 2006) by nearly an order of magnitude. Fortunately, I
was able to contact H. Hikida and M. A. Wieczorek, who are actively
studying the crustal thickness problem (Hikida, 2007), and they
generously shared their new data. This reinforced the qualitative
agreement with the ejecta that would be generated by the Near Side
Megabasin, but also reiterated the quantitative disagreement.
The point that I had missed in 2006 was that the Moon was soft and
easily deformed in the early times when the megabasins were formed.
This has long been known (Lemoine, 1997) but not by me. The great
weight of the ejecta on the far side would have caused it to sink,
retaining its shape, but not its scale. This phenomenon is known as
isostatic compensation. Given the accepted densities of the mantle and
crust, isostatic compensation would cause the ejecta of the Near Side
Megabasin to sink into the mantle, leaving only one-sixth of the
initial depth of the deposit, accounting for the quantitative
discrepancy. The great weight of the ejecta on the far side could have
subsided, retaining its shape, but not its scale.
The implication of the crustal thickness data is that both the cavity
of the Near Side Megabasin and its ejecta would have been 6 times
deeper at the time of its formation, before isostatic compensation,
than the current topography would require.
This new modification to the Near Side Megabasin hypothesis is in
quantitative agreement with all the relevant data that I have been able
to review, and it answers many questions about the topography, and
crustal thickness of the Moon. I hope that it will be a lasting
contribution to the understanding of the Moon, and that it will
stimulate further questions and topics of research.
Several sources contributed to the digital imagery in this book. Lunar
Orbiter photography has been archived as hard copy photographs, each
about 60 cm (about 2 feet) wide, at each NASA Regional Planetary Image
Facility, including one at the Lunar and Planetary Institute (LPI) in
Houston, Texas. LPI has digitized this important archival source and
published the images in the Digital Lunar Orbiter Photographic Atlas of
the Moon on the LPI web site (www.lpi.usra.edu). Further, the LPI staff
has added annotations to the photos, outlining nearly all of the named
A team led by Jeff Gillis carried out this important work; Jeff was
supported by Washington University at St. Louis and is currently with
the University of Hawaii. LPI technical and Administrative support was
provided by Michael S. O'Dell, Debra Rueb, Mary Ann Hager, James A.
Cowan with assistance from Sandra Cherry, Mary Cloud, Renee Dotson, Kin
Leung, Jackie Lyon, Mary Noel, Barbara Parnell, and Heather Scott. The
selection of photos that were made available on the LPI Digital Archive
is that selected for “Lunar Orbiter Photographic Atlas of the
Moon” by Bowker and Hughes.
NASA, the Navy Research Laboratory (NRL), the Russian space agency and
the Japan Aerospace Exploration Agency (JAXA) have made public the base
data for the photos in this book. Processed images were downloaded from
USGS, NRL, and JPL web sites. Ricardo Nunes and Phil Stookes have
Photos with annotated overlays identify the major features within each
of the photos. These overlays were extracted digitally from those
published by LPI, but I made additions, especially for the Clementine
images, in the style established by LPI.
The names of features, both by LPI and myself, are aligned with the
list approved by the International Astronomical Union (IAU), as
maintained by Jennifer Blue of the United States Geological Survey
(USGS) Astrogeology Branch. Notes with each photo point out salient
aspects of the feature. These notes, as well as those for my near side
book, have been reviewed by Don Wilhelms, USGS retired, the author of
my primary reference, who has taught me a great deal about lunar
geology. The assignments of geological age to many far side features
are derived from his book with John McClauley and Newell Trask.
(Wilhelms 1987). A reference that I used heavily in the preparation of
this book is “The Clementine Atlas of the Moon” by
Bussey and Paul Spudis. The dimensions of features (except for basins)
are taken from this book, which is in turn based on the IAU catalog at
USGS. Of course, I am personally responsible for any errors in this
The combination of cleaned photos, labeled features and notes are
intended to serve as powerful aids to learning the geography of the
Moon as well as valuable reference material.
My love and gratitude go to my wife Mary, who read and re-read the
early drafts of this book and made many helpful comments.
Throughout the project of cleaning the photos and writing this book
helpful suggestions and comments were made by Tammy Becker, Jeff
Gillis, Mary Ann Hager, Ray Hawke, Paul Spudis, Ian Garrick-Bethell,
Mark Robinson, Peter Schultz, Ewen Whitaker, and Don Wilhelms.
Charles J. Byrne
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