These graphs compare data from identical instruments onboard NASA’s Voyager 1 and Voyager 2 spacecraft as they each exited the heliosphere. Voyager 1 exited in 2012, and Voyager 2 exited in 2018. The cosmic ray subsystem measures the rate of energetic particles hitting the radiation detector on the instrument. Credit: NASA/JPL-Caltech
Introduction to the Section on Signatures
Robert Duncan-Enzmann
This conference article is reprinted from the Annals of the New York Academy of Sciences, Vol. 140, Art. 1, pages 1-683, Planetology and Space Mission Planning, Consulting Editor, Robert D. Enzmann
N.Y, N.Y. Published by the Academy December 16th, 1966
The essence of the Signatures section of this volume is conveyed by such questions as: How can we look at things? For example: if magnetometers, cameras, seismographs, and Geiger counters are all means of looking at things, can generalizations be made concerning the use of one or several of these instruments? Can all such instruments and human sense organs be regarded as matched detectors? Is there a general approach to viewing the Earth from Space to viewing other planets, asteroids, comets, and the contents of their geospheres? Could a general approach like this be applied to all bodies of the Solar System; and also to the enormously extended, ghostly, and little understood structures of the Solar Corona, which seem to extend past Pluto and which we call the ‘environment of Interplanetary Space’?
These questions have practical answers – even as the questions asked of radar engineers over the past several decades concerning detection, discrimination, and un-ambiguous-identification have encouraged development of practical theories. The papers in the Signatures Session have been selected and arranged to indicate generalities concerning the portending shape of the new theories of planetary exploration.
For the reader who may not be fully oriented to the terminology, an explanation of the word “signature” as used here may be helpful. The word has not found its way generally into dictionaries. It was forced by necessity on radar analysts in the 1950s. Originally “signature” applied only to information gained from analysis of electromagnetic, radar-frequency echoes. In this monograph, the context is broadened to indicate information gained through sensing organs and instruments used singly or in combination. In brief, a signature may be defined as follows:
“A signature is a set of measurements sufficient to identify unambiguously an object or set of objects.”
To use a down-to-earth example, the footprint in the sand seen by Robinson Crusoe was an unambiguous identification of a human being but it was ambiguous as to sex and race. A set of fingerprints is almost without exception sufficient information to distinguish one human being from all others. Fingerprints are, therefore, signatures that identify one human being in a set of all human beings. Perhaps audio frequency spectrum analyses (voiceprints) of humans will also prove to be unambiguous signatures of individual humans in the set of all humanity.
We cannot explain here in a few sentences the complex methods employed to ensure the correct interpretation of signatures, but we should point out that only four modes of detecting entities are recognized, whether the observations are being made on earth, in alien geospheres, or in interplanetary space. The modes of detecting entities within terrestrial and alien geospheres are:
1) Fields
The object’s own field or an induced field.
2) Photons
Photons by any electromagnetic manifestation.
3) Wave energies
Wave-energy manifested by magnetohydrodynamic and related waves in plasmas, acoustic waves in gases, hydrodynamic waves associated with liquids, and seismic waves associated with solids.
4) Bulk-Messengers
These are such as cosmic rays, elements, and molecules.
The list below places the term signature in context with other expressions used to indicate the extent of observation.
Observables
These are actions by a single entity, or statistical collection of entities, upon an observer by field, photon, wave-energy, or bulk-messenger. An observable action is just sufficient to establish the presence, position, and/or movement of the observed entity relative to the observer.
Measurables
An entity with measurable quantities can be defined as acting upon an observer via field(s), photon(s), wave-energy(ies), or bulk-messenger(s) in such a manner that the observer can distinguish details of the observed. The details of the observed give it definition in geometric space and in time.
Signature
A signature defines the basic entities (such as nuclear fragments), sets, and sub-sets that can be composed thereof (such as the hierarchy of organizations including atoms, molecules, colloids, fine grains, boulders, etc.). The signature defines the entity, set, or sub-sets through measurements numerous enough and accurate enough to describe them unambiguously.
Target Language
Target language pertains to an entity under observation. It will include sets of signatures sufficiently inclusive to indicate the history of the set, sub-set, or object. At best, target language indicates the ‘history’ of the observed from genesis through to death and dissipation. If the observed has a brief duration as compared with the observer, the measurements may be statistical. If events associated with the evolution of the observed are of long duration, as say the evolution of a mountain range, the object may be mapped as a moment in time.
It is worthwhile to briefly define observed entities and observing entities. First of all, for an observation to take place, an observed entity must act upon the observer. This action can take place only through the medium of: fields, photons, wave-energy, or bulk messengers.
Secondly, mindless action of an inorganic entity upon other non-guided entities, such as the pounding of waves upon a seashore, is not observation. The sand does not observe the waves; the waves to not observe the sand. For an observation to take place, the observer must be able to abstract energy of substance from the action of field, photon, wave-energy, or bulk messenger upon its (the observer’s) sensor.
Furthermore, the observer must be physiologically or mechanically able to reduce this action to ‘bits.’ For example, a photographic film contains dark and light grains. Observation becomes possible only with the ‘setting of bits’, i.e., during the process of exposing and developing the film, bits are set. Setting patterns of erasable bits in the mind is a mode by which observers gain information while at the same time protecting themselves from painful and physically damaging effects upon their bodies. This implies that observing entities must be relatively highly organized structures of organic, mechanical, electromechanical, or other nature. On Earth, observing entities are all of organic nature, or ultimately definable as structures constructed by self-organizing organisms, which are almost without exception human.
