Introduction to Planetary Habitability

Lessons Learned from Terrestrial Analogues.

Analogue sites are places with assumed, past or present, geological, environmental, or biological conditions of a celestial body. Studying terrestrial (Earth) analogues supports space exploration and accessing habitability of other worlds vastly. When it comes to Astro-Biological studies on habitability of different environmental parameter sets and the biological mechanisms for survival in extreme environmental conditions, terrestrial analogues provide a critical ground truth. For example, we are currently defining principal habitability criteria as extended regions of liquid water, conditions favorable for the assembly of complex organic molecules and arguably most important, energy sources to sustain metabolism. It is inarguable that this criterion has been reached mostly with the study of terrestrial analogues. (Preston and Dartnell, 2014)

Impact of Stellar Super flares

Super flares are large explosive events on stellar surfaces one to six orders-of-magnitude larger than the largest flares observed on the Sun throughout the space age (Karoff, et al., 2016). The high energy radiation events triggered by these flares can play a crucial role in destroying or promoting habitability of celestial bodies. Simulations have shown that these flares even affect in ionizing in certain elements and affecting directly to planetary compositions. Expected radiation doses at ground level can fairly determine the effects of these events as shown in research. (Yamashiki et al., 2019)

SEPHI - Statistical-likelihood Exo-Planetary Habitability Index

Searching for life outside of our Solar system involves achieving several goals. One of these goals is to discover as many potentially habitable exo-Earths as possible. That is, planets having the same necessary physical conditions for life as Earth has. This catalogue of potentially habitable exoplanets will be the steppingstone for the next stages in the search for life.

SEPHI is an index which is used to estimate the habitability potential of a planet. It is defined as the geometric mean of four sub-indexes related to four comparison criteria: Is the planet telluric? Does it have an atmosphere dense enough and a gravity compatible with life? Does it have liquid water on its surface? Does it have a magnetic field shielding its surface from harmful radiation and stellar winds? SEPHI can be estimated with only seven physical characteristics: planetary mass, planetary radius, planetary orbital period, stellar mass, stellar radius, stellar effective temperature, and planetary system age.(Rodríguez-Mozos and Moya, 2017)

References

Preston, L. J. and Dartnell, L. R. (2014) ‘Planetary habitability: Lessons learned from terrestrial analogues’, International Journal of Astrobiology, 13(1). doi: 10.1017/S1473550413000396.

Rodríguez-Mozos, J. M. and Moya, A. (2017) ‘Statistical-likelihood Exo-Planetary Habitability Index (SEPHI)’, Monthly Notices of the Royal Astronomical Society, 471(4). doi: 10.1093/MNRAS/STX1910.

Yamashiki, Y. A. et al. (2019) ‘Impact of stellar superflares on planetary habitability’, arXiv. arXiv. doi: 10.3847/1538-4357/ab2a71.

Karoff, C. et al., 2016. Observational evidence for enhanced magnetic activity of superflare stars.. Nature Communications, , 7(1), pp. 11058-11058.