Planetary Sciences as a field of modern science

The brief historiographical analysis made in previous posts The origins of Astronomy: of the
Sumerians to Copernicus and Astronomy as a Science: Galileo and the Telescope makes clear the dependence of Planetary Sciences on the quality of observational and measuring instruments available. Galileo’s discoveries, for example, were only possible thanks to the advent of the telescope, allowing the scientist to carry out observations that led to profound changes in the conceptions about several stars in the Solar System and, consequently, in the Universe. Even so, there were few later innovations, at least with regard to the characteristics of planetary bodies other than Earth; only at the end of the contemporary era there were considerable changes in the conceptions about the nature and characteristics of this
star class.

Source: Photo of the Orion Nebula (also known as Messier 42, or NGC 1976). Photo taken in Gaisberg, Salzburg (Austria). Rochus Hess, 2021.

In the centuries after Galileo’s discoveries, several improvements to telescopes were made, resulting in the creation of instruments with greater magnification capabilities and progressively better accuracy. However, until the mid-twentieth century, detailed observations of bodies farther away than Mars were not possible, mainly due to the instrumental barriers imposed by the equipment used. Images of the surface of Mars, for example, were limited to resolutions of 0.2 degree seconds, or approximately 60km, and heavily dependent on the star’s proximity (Kaula 1968). Such was the limitation that several of the planets in the Solar System, such as Neptune and Pluto, were no more than points luminous even on the best instruments, while several others, such as asteroids and some moons, had not been observed or were not even known (Wikipedia 2, 3, 7).

Source: Uranus/Neptune. Wikimedia Commons, 2021.

Changes in this landscape began in 1957, with the launch of the first space probes and the beginning of space exploration itself (Grayzeck 2012, 2016a). Early probes (e.g. Sputnik 1 and 2) did little in terms of data collection, focusing only on successful launch and operation once in orbit. It was only in 1959 that the Luna 3 mission, launched by the defunct Union of Soviet Socialist Republics (USSR), sent photos of the hidden side of the Moon, configuring the first data obtained by a space probe outside Earth (Grayzeck 2016b). Several missions followed, focusing on different planets or sets of planets, a process that continues today (see Recent Advances in Planetary Sciences).

Continuous technological advances, especially linked to computational technologies, allowed the construction of increasingly better probes, culminating in the progressive increase in the quality, quantity and variety of data obtained in these missions. Such changes have expanded the frontiers of planetary sciences in an unprecedented way, transforming technical barriers that existed until then into easily overcome obstacles (e.g. imaging of rocky outcrops on a centimetric scale on Mars).

Source: A composite Viking orbiter image of Olympus Mons on Mars, the tallest known volcano and mountain in the Solar System. Image by NASA, modifications by Seddon.

We currently live in a phase of constant discoveries, which is easily done verified by observing the number of publications related to Planetology in the main journals around the world (see Recent advances in Planetary Sciences). Some of these discoveries proved to be essential for the methodological advancement of this field of science, resulting in the establishment of base definitions that have long been neglected. The clearest example is the creation of a formal definition for the term ‘planet’, made only in 2006 by the International Astronomical Union (IAU). Until then, this and other terms, such as asteroid or dwarf planet, did not exist, making any classification arbitrary proposal, which highlights the great interdependence of Planetology in relation to several other areas of modern science.


Kaula, W. M. 1968. An Introduction to Planetary Physics – The Terrestrial Planets. editora John Wiley & Sons, Inc.

Grayzeck, E. 2012. Chronology of lunar and planetary exploration. Disponível em:

Grayzeck, E. 2016a. Chronology of lunar and planetary exploration – mission timeline. Disponível em:

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