Where Is Everybody? This is the question Enrico Fermi asked in the 1950s, referring to the little green men who were supposed to inhabit the galaxy. This question is still with us. Efforts have been made to search for extraterrestrial life. Science Fiction books are full of worlds peopled by clever creatures.
It would be reassuring to know that the galaxy is full of clever creatures. After all, if we, human beings disappeared, well, we were just not good enough, no big deal: those out there, better than us, would pursue the mission we are named after, wisdom (sapiens in Latin).
Yet I see plenty of reasons why Earth’s advanced biosphere is unique. I go even further. In my opinion, the fact Earth has a radioactive, high density metallic core is crucial. I will reinforce this argument today (in light of just published research).
Fermi, Nobel for discovering the neutrino (“little neutron” in Italian), discovered the Fermi principle and statistics (which posits that matter does not collapse because Fermions refuse to be in the same “state” in the same place at the same time). Fermi, who had fled from fascist Italy, was also the scientific head of the Manhattan project.
Fermi was both a theoretician and an experimentalist. Thus immensely clever, but yet down to earth. He obviously found that the obvious absence of civilization out there in space was a striking fact. And it is.
The idea that the stars had little Earths orbiting them, graced with little green men, with their own little green Christs, came all the way back to another Italian, Giordano Bruno. Bruno had lectured in universities around Europe, and was a friar. However, to suggest the world was not exactly as Christianism described it, was a capital crime in places ruled by Christianism.
To punish Bruno’s mental exuberance, the Vatican imprisoned and tortured him for seven years. Then the Vatican and its horrid Fundamentalist Jihadists stripped Bruno naked, pierced his palate with iron (so that he could not address the public), and burned him alive after he refused to submit to infamy. I am still waiting for the excuses from the institution at fault, the world’s oldest, the Catholic Church.
Yet, although he was a genius, Bruno was probably wrong about the little green men. Why? Where is everybody? Indeed. I argued that the nuclear reactor at Earth’s core has been crucial for plate tectonics, and preserving Earth from the runaway greenhouse which destroyed venus as a potential biosphere. I even argued that said nuclear reactor may have generated the Moon, by far the largest satellite in the Solar System relatively to the size of the planet it orbits around. (The Moon is larger than Jupiter’s third largest satellite, Europa.)
To generate a large radioactive core to a planet, one needs, first of all, metals. Actually metals enable to make very complicated molecules central to the wealth of biology. Hemoglobin carries iron which is used to transport oxygen.
Where do metals come from? Supernovae.
(Submitted on 8 Sep 2015)
“We used a sample of super-Earth-like planets detected by the Doppler spectroscopy and transit techniques to explore the dependence of orbital parameters of the planets on the metallicity of their host stars. We confirm the previous results that super-Earths orbiting around metal-rich stars are not observed to be as distant from their host stars as we observe their metal-poor counterparts to be. The orbits of these super-Earths with metal-rich hosts usually do not reach into the Habitable Zone (HZ), keeping them very hot and inhabitable. We found that most of the known planets in the HZ are orbiting their GK-type hosts which are metal-poor. The metal-poor nature of planets in the HZ suggests a high Mg abundance relative to Si and high Si abundance relative to Fe. These results lead us to speculate that HZ planets might be more frequent in the ancient Galaxy and had compositions different from that of our Earth.”
So the (empirical) argument is that, if a planet has metal content similar to Earth, it orbits so close to its parent star that it will be too hot for life. Reciprocally, planets which orbit in the Habitable Zone are found to be metal poor.
Planets are built from the same elements as their stars. Most of the properties of planets of different types strongly depend on their host stars’ chemistry, and chemistry varies. It seems Habitable Zone planets were formed long ago. After supernovae formed and exploded, spewing heavy metals such as Iron and Uranium, second generation stars such as the Sun formed, and were metal rich. However, the observations on hundreds of planets tend to show that metal-rich stars like our sun have large rocky planets wrapped in huge gaseous envelopes (caveat: it may still be a bit of a statistical fluke, at this point!).
If not a fluke (and that’s a big if), it gives a new reason to doubt that Earth-like planets are frequent in the galaxy: I argued that not just metal, but the very heaviest metals, the ones which have such large nuclei that they fission, are indispensable for life. Now it turns out that Earth orbits a metal rich star, but at a respectable distance.
So it may well be that Earth is a very special case. Maybe some day the Galactic Human Empire will be able to colonize habitable planets in various Habitable Zones, because thanks to human technology, humans, or, rather, transhumans, will capable of synthesizing metals, as needed (one could do this, if one had a mastery of accelerator technology to fine-tuned nuclear fusion as needed).
Philosophically, this rarity of Earth’s circumstances tells us, once again, that life is more precious that we ever imagined. It’s not just our unborn great grandchildren who will suffer from the holocaust of the biosphere we are engaged in. It’s the universe itself, because we may well be that unique.