Space researchers often discuss the role of carbonates on Mars, meteors, dwarf planets, and in galaxies light years away. Astrobiology, a current buzzword in space research, is concerned with determining if life is possible elsewhere in the universe. What are carbonates and why are they of interest to astrobiologists?
Carbonates are negatively charged molecules, or anions, containing carbon and oxygen.
Many minerals result from the combination of carbonate anions with cations, positively charged compounds. The most prominent carbonate-containing minerals are calcite (CaCO3), aragonite (CaCO3), dolomite (CaMg(CO3)2), and natrite (Na2CO3).
On Earth, bicarbonate – the anionic component of baking soda – is produced when water reacts with carbon dioxide from the air. The product of this reaction is carbonic acid, which is also present in soda.
CO2 + H2O = HCO3– + H+
This species further dissociates from bicarbonate into carbonate, water, and carbon dioxide.*
HCO3– = H2O + CO2 + CO3–
Water is present in all the reactions listed above. As far as scientists currently understand, water is necessary to form carbonates.** Thus, any planet, meteor, moon, or rock in space that has carbonates on it strongly suggests that there was water on that surface at some point!
As I suspect you may know, water is
kind of super important for life (speaking of water- this is your friendly reminder to stay hydrated, you biological specimen, you!).
Thus, the discovery of carbonates on Mars nearly ten years ago was long anticipated by scientists hoping to discover water on Mars. Mars’ atmosphere is composed of 95% CO2. Thus, water on Mars would react with the CO2 in the atmosphere to form carbonate minerals.
This is also why researchers are studying Ceres, a dwarf planet in the asteroid belt. Data from a study published in 2016 indicated the presence of Na2CO3 on Ceres’ surface, suggesting a possible liquid water ocean under Ceres’ surface (similar to the proposed ocean on Europa). Coupled with the discovery of organic materials on its surface, Ceres also holds astrobiological potential.
Lastly, the header image shows carbonate globules present on a meteor that effectively launched the field of Astrobiology. ALH84001 is a Martian meteor that was found in Antarctica in 1982. Originally, scientists were excited to discover carbonate deposits (shown in the image) on the meteor. Scientists proposed that the meteor came from Mars carrying water and life – as a result, carbonate deposits were produced. Scientists today are still uncertain if this meteor actually did harbor life. Skeptics claim the meteor could have been contaminated by microbes already present here on earth. So, the debate continues, but research from Curiosity, Mars 2020, MRO, Pathfinder, and other current and future Mars missions can further elucidate whether these scientists’ original claims have merit.
So now, when you’re browsing through the AAAS magazine, Scientific American, or hear scientists discuss carbonates in long-winded science-jargon heavy talks about their research, hopefully you’ll have just a bit more background as to why their research is of importance and is so exciting! 🙂
* These chemical reactions are occurring in our oceans due to increased carbon dioxide concentrations in the atmosphere. I will be writing an article on ocean acidification in the future. For now, this is a good resource if you’d like to learn more.
** A 2002 study from Ciska Kemper in Nature reported the possible detection of carbonates in a solar system two light-years away. If the findings are accurate, they could indicate that water is not necessary to form carbonate species. However, this study was challenged by Anne Hofmeister, who claims the peaks in the spectra reported by Kemper could be attributed to other species. Thus, more research needs to be done to fully confirm or refute Kelger’s claim. Regardless, it is a known phenomenon that carbonates form readily in water. Whether or not water is always necessary is a question for further study. However, if carbonates are present on a body, it is very likely that water once resided on that planetary body.
Niles, Paul B. et al., 2012. Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments. Space Sci Rev. DOI 10.1007/s11214-012-9940-y.