Wayward Goldilocks Worlds

Habitable_Zone_01B_201406301654_600b

This is a new digital painting that I have completed, depicting a hypothetical planetary system at the fringes of a red dwarf star system. Here, an icy moon (foreground planetary body) orbits a tenuously ringed gas giant (the larger planet behind). Internal tidal flexing caused by an elliptical orbit around the gas giant has melted some of the moon’s ice to form an internal ocean. This subsurface water is under extremely high pressure beneath a thick ice crust, and when tidal flexing causes the crust to fracture intermittently near the southern pole, a geyser of liquid erupts hundreds of kilometers into the vacuum of space above the moon’s surface, becoming visible as the thin plume or jet near the lower edge of the moon. This is based on a very real phenomenon: in our own solar system, Saturn’s moon Enceladus exhibits just this sort of plume. Even more excitingly, direct sampling and chemical analysis of the plume by the Cassini orbiter as it passed through the plume yielded a suite of complex organic compounds as part of the plume composition (Combi et al. 2006).

So why am I posting a digital painting of space art instead of paleoart today? Well, four reasons, actually.

1. As a scientific illustrator, my work covers a broader scope than just paleoart — I know, shocking, isn’t it? In fact astronomical artwork is another one of my favourite subjects. I especially enjoy studying and depicting things that are difficult or impossible to image directly, either because they are too small (hence my research in microbiology), or too old (paleoart fits here) or too far away (hence space art).

2. I’m married to a planetary scientist, so there’s that bit of influence. My wife, Dr. Alexandra Lefort (yes, that would be the same Alexandra Lefort whose name appears at the bottom of this website’s pages, because she designed and built my website) studies the traces of ancient water that once flowed across the surface of Mars when it was warmer and wetter (Lefort et al., 2012), at a time over 3 billion years ago when there were at least two habitable planets in our solar system, and when an ocean hung more than 54 million km above Earth’s first life forms. This painting was a small anniversary project, as today is our anniversary.

3. Speaking of important dates, today, July 14, 2014, marks a year to the day until the next great interplanetary mission, the New Horizons spacecraft, reaches the Pluto system for a quick flyby of this perplexing little world that may have lost its planetary status but none of its mystique. Pluto may be distant, but its ruddy surface  shows patterns of irregular reflectance (Stern et al., 2012) that could indicate the presence of organic compounds. Therefore, a depiction of a planetary body with signs of habitability far from its parent star seemed appropriate today.

4. And speaking of habitability, I really wanted to underscore an important point about what is commonly known as “the Goldilocks zone”, in reference to “Goldilocks and the Three Bears”. This is that region of space in star systems that is not too far from the parent star (where it would be frigid) and not to near (where it would be too toasty), but in the middle where the temperature is just right for life to develop and persist on planets whose orbit resides in this habitable zone. This is where liquid water, critical to life as we know it, would be stable at the surface of an atmosphere-bearing planet, and not freeze solid or boil away. We normally think of the habitable zone as tracing out a fuzzy edged ring around the parent star, its diameter and thickness depending on factors such as the temperature of the star. However, it’s important to remember that the extent of the habitable zone is influenced by more than just the distance from the parent star. Moons such as Enceladus or Europa or Titan are far beyond the habitable zone for planets in our solar system. However, as the subsurface oceans of all of these moons demonstrate, factors such as tidal flexing caused by the peculiarities of their orbits around their parent planets can establish little habitable oases for life at distances from the parent star to which we would not normally expect the habitable zone to extend. This demonstrates that in our search for extrasolar habitable planets and ultimately life, we must be careful not to rule out environments before we can gain sufficient information about the fine structure of each planetary system.

References

Combi, M.R., Ip, W., Cravens, T.E., McNutt, R.L. Jr., Kasprzak, W., Yelle, R, Luhmann, J., Niemann, H., Gell, D., Magee, B., Fletcher, G., Lunine, J., Tseng, W. (2006) Cassini Ion and Neutral Mass Spectrometer: Enceladus plume composition and structure. Science. 311:1419-1422. DOI: 10.1126/science.1121290

Lefort, A., Burr, D.M., Beyer, R.A., Howard, A.D. (2012) Inverted fluvial features in the Aeolis-Zephyria Plana, western Medusae Fossae Formation, Mars: Evidence for post-formation modification. Journal of Geophysical Research: Planets. 117: E3. DOI: 10.1029/2011JE004008

Stern, S.A., Cunningham, N.J., Hain, M.J., Spencer, J.R., Shinn, A. (2012) First ultraviolet reflectance spectra of Pluto and Charon by the Hubble Space Telescope Cosmic Origins Spectrograph: Detection of absorption features and evidence for temporal change. The Astronomical Journal. 143(1):22. doi:10.1088/0004-6256/143/1/22