New breakthrough in the exploration of extraterrestrial life, the "Drake Equation" may help solve it!

Drake equation crucial to calculating the amount of extraterrestrial life

Figure 1 This is the spiral galaxy M74 captured by NASA's James Webb Space Telescope.

This article originally appeared on The Conversation.

How many intelligent civilizations are there in our galaxy? In 1961, astrophysicist Frank Drake proposed an equation for estimating the number of intelligent civilizations in the Milky Way. He died on September 2, 2022 at the age of 92. The equation he proposed when he was young has become famous and is named after him. Drake himself later commented that he was "too young and too imprecise" at the time.

Since then, the Drake equation has often been associated with equations named after famous physicists such as James Clerk Maxwell and Irving Schrodinger. However, the Drake equation does not contain laws of nature. Instead, it combines unknown probabilities into an estimate.

No matter what reasonable values ​​you put into Drake's equation, we will conclude that we are not the only life in the universe. Drake persisted in the search for extraterrestrial life throughout his life, but does his equation really give us some clues?

Figure 2 Drake equation expansion.

The Drake equation may look complicated, but its principle is actually quite simple: It states that in a galaxy that has existed for a similar amount of time as ours, the number of intelligent civilizations capable of radio communication with us must be equal to their rate of development multiplied by their average lifetime.

Focusing the calculation on the rate at which civilization was growing might have seemed speculative, but Drake realized that the calculation could be broken down into more manageable pieces.

He showed that the total rate is equal to the rate of star formation in the Milky Way, times the fraction of those stars that have planets, and then times the average number of planets suitable for life per star system that has planets, times the fraction of those planets that actually support life, times the fraction of those planets that give rise to intelligent life, and times the fraction of those planets that have civilizations capable of radio communications.

Tricky value

Frank Drake

After Drake first proposed his formula, he obtained a result that he could not doubt - the rate of star formation was about 30 stars per year.

In the 1960s, we had no evidence to prove that other stars had planets orbiting them, and even the guess that "one out of ten stars could have such a star" seemed overly optimistic. Since the 1990s, we have conducted long-term observations of exoplanets, and until this century, we have made a major discovery that most stars have planets orbiting them.

Common sense suggests that in most multi-planet systems, planets at the right distance from their stars are likely to harbor life. Earth is the planet in our solar system that harbors life. Moreover, Mars is likely to have had life in the past—and could have even continued to have life today.

Today we also realize that a planet's surface temperature need not be right for water to exist in liquid form in order to sustain life. Life can exist in the interior oceans of planets covered in ice, relying on heat generated by radioactivity or tides rather than sunlight.

For example, there are several moons between Jupiter and Saturn that would qualify, and when we assume that moons have the potential to harbor life, the average number of habitable bodies per planetary system is more than one.

However, the right-hand side of the Drake equation remains open-ended, and some argue that if the timescale is calculated over millions of years, life will emerge in any suitable environment.

This means that the probability of life actually existing and continuing is almost equal to 1. Some people also believe that we have no evidence to prove the existence of life other than Earth, and the origin of life may actually be an extremely rare event.

Will all life eventually evolve intelligence? This process may first require it to transcend the microbial stage and become multicellular organisms.

There is evidence that multicellularity evolved on Earth more than once, so becoming multicellular may not be a barrier to evolution. However, some have suggested that multicellular life that continued to evolve into a "proper intelligent species" only occurred once on Earth, and may be rare on a galactic scale.

Intelligence is a competitive advantage over other species, and species with intelligence are more likely to evolve, but we are not sure about this speculation yet.

Could intelligent life develop technology to the point of radio communication and (accidentally or deliberately) spread it to the universe? Maybe for surface dwellers like us, but the probability is low for inhabitants of the interior oceans of icy worlds without atmospheres.

The Fermi Paradox asks: "Where are all the aliens?"

How long can civilization last?

What is the average existence time of a detectable civilization? Our TV station has been exploring the Earth since the 1950s, and the conclusion is that the average existence time of a detectable civilization is at least 70 years.

But overall, the average lifetime of a detectable civilization might be constrained by its own demise (what are the odds that ours will last another 100 years?), by its own disuse of radio broadcasts due to the development of the Internet, or by its own deliberate silence from broadcasting for fear of hostile galactic life.

It's especially fun when you crunch the numbers yourself! If a civilization lasts longer than 1,000 years, then the number of detectable civilizations is likely to be greater than 100. In an interview recorded in 2010, Drake said his best guess for the number of detectable civilizations is around 10,000.

We are learning more about exoplanets every year, and we are entering an era where it is becoming increasingly feasible to measure the composition of their atmospheres to reveal evidence of life.

In the next decade or two, we hope to have more reliable estimates of the fraction of Earth-like planets where life originated.

We may not discover life in the interior oceans, but we can hope to gain insights from explorations of moons like Jupiter, Saturn, and Uranus, or even detect actual signals from extraterrestrial intelligence.

Regardless, Frank Drake's equation has inspired many fields of research, and it will continue to provide us with a thought-provoking perspective. For this we should be grateful.

BY:David Rothery

FY: Bringing back the moon

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