Free Astronomy Magazine July-August 2020

JULY-AUGUST 2020 ASTROBIOLOGY other technological species out there, why haven’t they come into contact with us yet? Maybe they don’t exist, maybe they don’t want to contact us, maybe they don’t know we exist, or maybe we are the most advanced at the moment. The worst alternative is the last one, because the Milky Way is more than double the age of the Earth. Even if the metallicity has grown over time (thanks to the death of countless stars), it is difficult to imagine that life never appeared and evolved to the point of reaching an aware- ness of itself and the cosmos during our galaxy’s first five or six billion years. According to Whitmire, if our species were to become extinct within a much shorter formation of the former in planetary sys- tems. Various studies indicate that gaseous planets generally formed beyond the water condensation radius (4-6 AU for solar-type stars) and subsequently migrated into the interior of their planetary system. If the mi- gration is relatively slow, the gaseous plan- ets push the planetesimals of the less massive planets that are still forming in the warmer regions towards the star, preventing the birth of future potentially habitable planets. In short, living in a spiral galaxy is arguably the more typical scenario for a tech- nological species, while the existence of technological species within elliptical gal- axies should be considered more of a violation of the principle of mediocrity. Even so, our supposed “typ- ical-ness” may not be good news. In fact, since we have only been technological for a century or so, if we are not among the very first in the Milky Way to reach this level, it means that those who preceded us did not last long. Paraphrasing the Fermi Paradox, if there are O n the left, the spiral galaxy NGC 772 in the constella- tion Aries. It is twice the size of our own and has an asymmetric shape caused by gravitational in- teractions with its numerous satellite galaxies. [Cima Rest Astro- nomical Observa- tory, Magasa, Valvestino, Italy] Below, a part of the Virgo Cluster, dominated by the two large el- lipticals M86 (near the center) and M84. [Greg Morgan (Sierra Remote Observa- tories)]