The current advances in our exploration of Mars have made us think of the human species as a multiplanetary species. However, we have certain challenges before we can truly consider ourselves such a species, especially moral ones. Therefore, astrobioethics would be the right one to examine what it takes to consider ourselves a multiplanetary species. The purpose of this paper is to analyse the meaning and significance of being an inter- and multiplanetary species. To achieve this, a philosophical and critical analysis will be made, using as input aspects of biology, ethics and moral community. We conclude that to be a truly multiplanetary species, more than the technological aspects that allow us to reach other planets, a change at different levels will be needed.

The appellation ‘habitable zone’ in astrobiology in sooth evinces an overlooked and winding history that can be traced back to the 19th century. This paper sketches how this term from geography was generalized to encompass planetary habitability. The people involved in this narrative are numerous, but the bulk of their musings were rather nebulous. Yet, during this period appear the first true insights, although sadly this saga is not altogether sans blights.

There are different criteria that are usually analysed independently before identifying a new trace fossil, such as morphological regularity, completeness, dispersion, recurrence and complexity, surface morphology, and context. The synthesis of these criteria, as utilized in paleosol ichnology, composes a protocol that is presented herein for the first time and can be used for testing the ichnogenicity of trace-like structures in any paleoenvironment of Earth or Mars. As a study case, the Martian ‘stick-like structures’ do not fulfil any of the requirements posed by this protocol to be postulated as trace fossils. The ichnogenicity test, focussed exclusively on morphology and context, is simpler but equally useful as the biogenicity ones. It may be applied in the future with other potential cases before carrying on more complex analyses or to evaluate the astrobiological interest of trace-like structures.

Mars is a primary target of astrobiological interest: its past environmental conditions may have been favourable to the emergence of a prebiotic chemistry and, potentially, biological activity. In situ exploration is currently underway at the Mars surface, and the subsurface (2 m depth) will be explored in the future ESA ExoMars mission. In this context, BIOlogy and Mars EXperiment was performed to evaluate the stability and detectability of organic biomarkers under space and Mars-like conditions. Our data suggested that some target molecules, namely melanin, azelaic acid and nucleic acids, can be detected even after 16 months exposure to Low Earth Orbit conditions by multidisciplinary approaches. We used the same techniques as onboard the ExoMars rover, as Raman and infrared spectroscopies and gas chromatograph-mass spectrometer, and polymerase chain reaction even if this is not planned for the imminent mission to Mars. These results should be taken into account for future Mars exploration.

Interstellar travel in the Milky Way is commonly thought to be a long and dangerous enterprise, but are all galaxies so hazardous? I introduce the concept of galactic traversability to address this question. Stellar populations are one factor in traversability, with higher stellar densities and velocity dispersions aiding rapid spread across a galaxy. The interstellar medium (ISM) is another factor, as gas, dust grains and cosmic rays all pose hazards to starfarers. I review the current understanding of these components in different types of galaxies, and conclude that red quiescent galaxies without star formation have favourable traversability. Compact elliptical galaxies and globular clusters could be ‘super-traversable’, because stars are packed tightly together and there are minimal ISM hazards. Overall, if the ISM is the major hindrance to interstellar travel, galactic traversability increases with cosmic time as gas fractions and star formation decline. Traversability is a consideration in extragalactic surveys for the Search for Extraterrestrial Intelligence (SETI).