Revising Drake

Most of you probably know about the Drake Equation, a way to estimate the number of intelligent civilizations in the universe.  The Equation is one of those curiosities that is looked upon as valid science by some and as pointless speculation by others.  Here's what it looks like:

Math-phobes, fear not; it's not as hard as it looks.  The idea, which was dreamed up by cosmologist Frank Drake back in 1961, is that you can estimate the number of civilizations in the universe with whom communication might be possible (Nb) by multiplying the probabilities of seven other independent variables, to wit:

R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the fraction of those stars with planets whose planets are in the habitable zone
fl = the fraction of planets in the habitable zone that develop life
fi = the fraction of those planets which eventually develop intelligent life
fc = the fraction of those planets with intelligent life whose inhabitants develop the capability of communicating over interstellar distances
L = the average lifetime of those civilizations

Some of those (such as R*) are considered to be understood well enough that we can make a fairly sure estimate of their magnitudes.  Others -- such as fp and ne -- were complete guesses in Drake's time.  How many stars have planets?  Seemed like it could have been nearly all of them, or it perhaps the Solar System was some incredibly fortunate fluke, and we're one of the only planetary systems in existence.

The encouraging thing, at least for people like me who would love nothing better than to find we lived in a Star Trek universe where there's intelligent life wherever you look, just about all of these parameters have been revised upward since Drake first put his equation together.  Exoplanets, including ones in the so-called "Goldilocks zone," have turned out to be pretty much everywhere; not having planets turns out to be a much rarer situation.  There are over a hundred billion stars in the Milky Way alone; the number of planets in our galaxy is almost certainly in the trillions.  

As far as developing life... well, that one is still open to question, given that thus far we have a sample size of one to draw inferences from.  But that parameter -- fl -- just got a significant boost from a study done collaboratively by Hokkaido University and NASA of samples brought back from the asteroid Bennu by NASA's OSIRIS-REx mission, which found significant traces of all five nitrogenous bases that make up the genetic material in every living thing known (adenine, cytosine, guanine, thymine, and uracil).

Not only that, but they found the organic compounds xanthine and hypoxanthine (precursors of many bioactive compounds, including caffeine and theobromine), and nicotinic acid (vitamin B3).

This is an absolutely astonishing result.

"In previous research, uracil and nicotinic acid were detected in the samples from asteroid Ryugu, but the other four nucleobases were absent," said Toshiki Koga, who co-authored the paper, which appeared last week in Nature Astronomy.  "The difference in abundance and complexity of N-heterocycles between Bennu and Ryugu could reflect the differences in the environment to which these asteroids have been exposed in space."

What it brings to mind for me, though, is that if these five critical compounds can form on an airless, icy rubble pile (which is what Bennu honestly is), they've got to be pretty much everywhere in the universe that isn't so hot they fall apart.  And in case I haven't made the case strenuously enough, they are the basis of the genetic information shared by all life on Earth.

I think N -- the all-important Drake Equation estimate of the number of technological civilizations in the universe -- just got revised upward again.

Of course, even with my excited leaping about, I have to admit there's still a great deal we don't know, especially about the parameters that are lower on the list.  How many planets that do develop life end up with intelligent, technological life?  A while back I did a post about the rather terrifying idea of the Great Filter, which looks at the roadblocks that might prevent technological civilizations from forming or persisting.  Because the fact remains that when we look out there, we don't see signals from other civilizations -- something called the "Fermi Paradox" after the great physicist Enrico Fermi, who after listening to all the arguments for extraterrestrial life, famously quipped, "Then where is everybody?"

And we still have no idea about the scary parameter L -- how long, on average, technological civilizations last.  Given recent horrific developments in U.S. politics, I rather think I'm revising my own estimate of this one in the downward direction.  Maybe a benevolent alien will come and fix the mess we're in.  I know who I'm hoping for:

But even so, the Bennu study is exciting, and gives me hope that we might still one day find extraterrestrial life.  Perhaps even from the recently-launched Europa Clipper mission, which in April 2030 will do flybys of Jupiter's moon Europa -- widely considered to be our best shot of a place hosting extraterrestrial life in our own Solar System -- in the hopes of picking up biosignatures.

So we continue to wait, and wonder, and learn.  And -- as astronomer Neil deGrasse Tyson always says, at the end of his talks -- "Keep looking up!"

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The astronomical pogo stick

It's all too easy lately to find reasons to criticize humans.  I'm guilty of contributing to it myself, by my focus on pseudoscientific nonsense; you can jump from "some humans do stupid stuff" to the cynical "all humans are irreparably stupid" without even realizing it.

It's worthwhile focusing instead on our accomplishments, some of which are downright amazing.  This year, I think we all need something to cheer us up and make us feel a little more optimistic about our potential as a species.  So today we're going to look at: the mind-blowing reconnaissance mission NASA has undertaken to collect, and bring back to Earth, material from the asteroid Bennu.

Bennu is interesting from a number of standpoints.  It's a carbonaceous asteroid, meaning it is high in the carbon-containing compounds that were probably abundant in the early Earth's atmosphere -- carbon dioxide and monoxide, methane, and hydrogen cyanide.  Because these were the raw materials from which the first biochemicals were synthesized, it's of serious interest to people like me who are obsessed with the possibilities of extraterrestrial life.  Astronomers tend to be more curious about Bennu because its composition is thought to be very similar to the material from which the Solar System originally coalesced, so learning about it might give us a lens into our region of the galaxy's very distant past.

And if you needed another reason, Bennu is one of the asteroids which periodically crosses the Earth's orbit, making it high on the list of eventual Earth strikes.  (Not to worry: it's not going to hit the Earth, or anything else, for at least another two hundred years, and the current surmise is that it's much more likely to hit Jupiter than it is to hit Earth.)

So in 2016, NASA launched the OSIRIS-REx mission, which first did a near pass and mapped out its surface to look for good spots for rock collecting, and then on the second encounter -- which happened three days ago -- dropped onto the asteroid with a maneuver that looked like someone bouncing on a pogo stick.  The six-second contact stirred up material from the surface, which was sucked into a collector.  OSIRIS-REx then zoomed back off into space for its return voyage to Earth, carrying what scientists hope is a sixty-gram sample of the surface of the asteroid.

Okay, that's already impressive, right?  If you want your mind boggled further, consider this:

OSIRIS-REx's trip (one way) from Earth to Bennu covered about 820 million kilometers.  The asteroid's diameter is about 530 meters; the spacecraft's is a little under seven meters.  I did a bit of back-of-the-envelope calculation, and discovered that our ability to hit Bennu from this distance is equivalent to hitting a target the size of a bacterium with a bullet the size of a virus -- from a kilometer away.

Oh, and it's hardly standing still.  Bennu is a fast-moving target, zooming along at 28 kilometers per second.

If that doesn't impress you, I can't imagine what would.

OSIRIS-REx's sampling arm, seconds before impact on asteroid Bennu on October 20, 2020 [Image is in the Public Domain courtesy of NASA/JPL]

"The spacecraft did everything it was supposed to do," said mission principal investigator Dante Lauretta of the University of Arizona.  "I can’t believe we actually pulled this off."

His elation and incredulity are understandable considering all of the things that could have gone wrong, and how slight the error would have to be to result in the spacecraft either plunging into a destructive crash or else missing the asteroid entirely.  And at that point, OSIRIS-REx had to function perfectly on its own -- at that distance, radio signals traveling at the speed of light take over eighteen minutes to reach Earth, and (even assuming an instantaneous response by NASA scientists) another eighteen to send back a command like "NO NO NO DON'T DO THAT!"

By that time, the spacecraft would either be rubble or else zooming away into space, and away from the target.

So the mission went off without a hitch.  Well, the first half of it -- they still have to get OSIRIS-REx back to Earth safely.  But I'd say given how flawless the first bit was, there's a good chance they'll accomplish the whole shebang, and we'll have some really interesting stuff to study.

When you consider things like this, it's reassuring -- the capacity for human accomplishment is limitless.  Yes, I know there's still idiotic stuff going on down here.  But I'm not ready to give up on humanity yet.  I find the OSIRIS-REx mission incredibly inspirational.

Gives me hope that there may be a bright future for our species yet.

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