Planetary systems get swallowed by their stars, and it’s thought that this will happen to Earth 5 billion years from now when the Sun swells to its red giant phase. For the first time, evidence for a moment when such an engulfment actually happened has been found, by a team of 26 astronomers led by Kishalay De of MIT (the Massachusetts Institute of Technology). ZTF SLRN-2020, a Sun-like star 12,000 light-years away, underwent an outburst very like those that happen when binary stars merge, but with much lower energy; what was engulfed must have been less than 10 Jupiters in size, a planet.
Perhaps the most interesting aspect of this is the evidence they think they can extract for chemical remains of planets inside stars. This could in turn be evidence for the likely number of stars with planetary systems. And this is one of the factors in the Drake equation for the likelihood of extraterrestrial life with which we could communicate.
I thought I had already blogged about the Drake equation, but I see that I mentioned it only in connection with climate-crisis deniers such as Donald Trump. There will be an entry on it in the new edition of Albedo to Zodiac that I’m gradually preparing.
Frank Drake, who died in 2022, was a radio astronomer who pioneered the search for extra-terrestrial intelligence. In 1961 he convened a meeting of ten scientists and other thinkers, the “Order of the Dolphin,” at Green Bank radio observatory in West Virginia to discuss SETI, and in preparation for it he devised his equation. It suggests that the number of presently existing civilizations in the Milky Way galaxy able and willing to communicate with ours is the product of seven terms:
N = R * fp * ne * fl * fi * fc * L
Properly it’s written in mathematical notation with subscript second letters, but I’m writing it in a simpler way that will be easier for you to refer to.
It means that N, the number of such civilizations, is found by multiplying:
R: the yearly rate at which stars are born in the galaxy. (The guess by Drake and the Order of the Dolphin: 1.)
fp: the fraction of stars that have planets. (0.2 to 0.5.)
ne: the average number of planets in a planetary system that have life-possible conditions. (1 to 5.)
fl: the fraction of those on which life does develop. (1.)
fi: the fraction of those where the life evolves intelligence. (1.)
fc: the fraction of those where life reaches a technological level at which it can send and receive signals across interstellar space. (0.1 to 0.2.)
L: the average lifetime in years of such civilizations. (1,000 to 100,000,000.)
These guesses would give answers ranging from 20 to 50,000,000!
The first four terms are becoming closer to being known. The recent discovery could lead toward a firmer estimate for fp, the fraction of stars that have planets.
The overall uncertainty is obviously still enormous.
And there are some who suggest that N may be zero – we are alone – because fl may be close to zero: several freakishly unlikely coincidences allowed life to arise and survive on Earth. Or that the operative factor is L: advanced civilizations may tend to destroy themselves through nuclear war or failure to deal with pandemics or environmental collapse; or, oppositely, may learn to become indestructible.
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One argument AGAINST the existence of extra terrestrial life is that If ET’s were out there they would have eaten us by now.
An argument FOR extra terrestrial life was presented by Fred Hoyle (an atheist), who thought that life arose on another planet and was transported here. He said that the chances of random events creating the order of life are about as great as a tornado blowing through a junkyard and constructing a Boeing 747.
I’ve become almost convinced that once a civilization reaches a certain point of technological prowess, its individual members cocoon themselves increasingly in their own little self-directed “environments”, first the rich or ruling classes and then as the technology becomes cheaper that spreads to the middle and lower classes until everyone is in their own bubble and at that point creativity, innovation, scientific advancement and curiosity comes to an end and that civilization then eventually sapped of its original vigor becomes extinct. This would provide one answer to Enrico Fermi’s question. I hope this actually isn’t true—but I see signs of it already in our civilization.