In this paper, Tonietti and colleagues proceed with a bibliometric analysis of astrobiology literature for the past 20 years and an investigation of keyword clusters, with a particular emphasis on biomining and bioleaching.

Tonietti et al. begin their analysis with a broad introduction to astrobiology and its increasing importance as space exploration progresses, which now includes biotechnological applications targeted at resource utilization. Examples of topics investigated by astrobiological research now include processes such as biomining and bioleaching, as well as space (micro)biology and astrobotany. Astrobiology is thus a multidisciplinary field of research, with contributions coming from physics, chemistry, biology, geology and varied planetary sciences such as geobiology, astrocheistry, exoplanet research and many others.

The authors then proceed with a brief historical overview: the first considerations that could be considered related to astrobiology came from Democritus, who laid the foundations of atomism theory, and Aristotle, considering that the Universe was an immutable and perfect celestial realm. Further work come from Ptolemy (geocentrism), Copernicus (heliocentrism), Bruno (the theory of infinite worlds), and Newton & Halley who first conceptualized a “Goldilocks Zone” that was described as the range of distance from a star where water could exist in its liquid phase. Many other scientists contributed to what would today become astrobiological research, such as Schiapparelli, Lowell, Darwin, Kelvin, Crick, Orgen, Oparin & Haldane, Urey & Miller, and Stuve.

That being said, they note that astrobiology’s main focus somewhat varies between biogeochemistry and astrochemistry, and seems to be moving towards a biologically-oriented view, with a particular emphasis on extremophiles. Moreover, with the recent success of space exploration missions, there is a pressing need to address practical limitations, such as the problem of resource utilization beyond Earth.

These new considerations have led to the development of novel techniques like biomining and bioleaching, that use microorganisms—such as microbes, archeobacteria and fungi—to extract metals of interest. The most valuable metals targeted with these new processes are copper, uranium, nickel, iron, PGEs (platinum group elements) and REEs (scandium, yttrium, etc.), with experiments being done on the International Space Station (ISS).

Tonietti and colleagues searched the Scopus database for articles containing either of the following two strings in their title, abstract or related keywords:

They then visualized network maps of the various keywords using VOSviewer, a software used for bibiometric analysis, with the position of elements showing the degree of relatedness and further grouping them into clusters. Keyword co-occurrence was assessed as well as time gradient maps. A summary of the methodology is given in Table 1.

The first string assessed, “astrobiology”, returned ~2500 documents, of which 2000 were downloaded because of the limits imposed by Scopus for exports. 8819 keywords were extracted, of which 200 are displayed below. The keywords were grouped into six clusters, which thereby represent “hot topics” in astrobiology and highlight multidisciplinary connections:

These clusters are shown on Figure 1 below.

Next, Tonietti and colleagues created a temporal perspective of those keywords, which hence represents the evolution of astrobiological research. This keyword network is shown on Figure 2.

A second search was performed, this time for “astrobiology” AND “biomining” OR “bioleaching”. 8 documents were returned and 224 keywords extracted, of which 30 are shown here. The keywords were grouped into four clusters:

Some observations from Tonietti and colleagues:

As with the previous search, the authors created a temporal visualization of these keywords, shown on Figure 4. We can see that there’s currently a focus in microbial research, particularly on extremophiles, on the ISS and on extreme environments on Earth.

Finally, here’s some conclusive remarks from the authors: