Life elsewhere

September 14, 2023   ·   0 Comments

By Gwynne Dyer                                                        

This week’s real news is the discovery of life on another planet. As Cambridge University’s Nikku Madhusudhan said in the first sentence of his report: “The search for habitable environments and biomarkers in exoplanetary atmospheres is the holy grail of exoplanet science.” And he has probably found the Holy Grail.

The planet orbits a star imaginatively named K2-18, about 120 light years from here. It is in the star’s ‘Goldilocks Zone’, where life could theoretically flourish because the temperature will allow water to remain liquid. (It will neither freeze nor boil off.)

Planet K2-18 b is far larger than Earth (8.6 times bigger) but it has an atmosphere containing carbon dioxide and methane, both commonly emitted by living things – and also dimethyl sulphide, a trace gas that is definitely a strong ‘biomarker’ for life. On Earth, it is  exclusively produced by life, mostly by plankton living in bodies of water.

K2-18 b belongs to a newly named ‘Hycean’ category of big ocean-covered planets with hydrogen-rich atmospheres that circle dim dwarf stars (so they are easier to see). It’s sort of like the drunk looking for the dropped car-keys under the street-light (“because the light’s better there”), but it’s letting astronomers spot lots of potential candidates for life.

Dr Madhusudhan is understandably excited (“It’s mind-boggling”), and at the same time professionally cautious. It will take more observations by the James Webb telescope to confirm the “tentative” finding of dimethyl sulphide, but he was feeling confident enough to say this:

“The atmospheric composition tells us that…there is an ocean underneath. It is very hard to get that composition otherwise. Planet-wide oceans and hydrogen atmosphere are just the right conditions to be able to host life similar to the conditions of what we see on Earth.”

It’s a triumph (‘We found life!’), and at the same time no surprise at all (‘What did you expect to find?’).

If only one in a million planets was a host to life, there would still be around half a million life-bearing planets in this galaxy alone. There are over thirty galaxies in our Local Group, and up to two trillion altogether.

Indeed, we have managed to see only 5,000 planets so far, and NASA says that 200 of them are potentially habitable. So there are probably lots of places with bacteria and maybe even algae and jellyfish. But what if only one in a million habitable planets has a civilisation on it at any given time?

That’s about the right ratio for Earth: our civilisation is around 4,500 years old; the planet is about 4.5 billion years old.

If civilisations are really that scarce, then we might be the only one in this galaxy at the moment, and there would be no more than two trillion civilizations in all of the universe right now. Makes you feel special, doesn’t it?

But let’s get back to the neighbourhood. Unless there is some way around the cosmic speed limit (the speed of light), human beings will never travel much farther than the very nearest stars, and even those are probably too far. However, there is a project under development to investigate the nearest star close up.

The star is a red dwarf called Proxima Centauri, it’s 4.2 light-years away, and one of its planets, Proxima b, is in the star’s habitable zone and about the same size as Earth. We don’t even know if it has an atmosphere, but it would be nice to know a bit more about it – and Breakthrough Starshot is working on sending a probe there.

Breakthrough Starshot is a privately funded proposal to send a thousand-strong fleet of tiny sensor ‘chips’ on a one-way trip to Proxima Centauri to get more information about that planet and its sun. (The high numbers are to allow for a good deal of attrition en route.)

The initial impulse would come from a gigawatt-range array of ground-based lasers pushing against the light-sails that carry the chips. That would get the chips up to 20% of light speed, and the rest of the trip would be on cruise.

Launch is projected “within the next generation”, and arrival for twenty years later (plus four more years to send the data back to Earth). And of course if you can do it for Proxima Centauri b, you can do it for any other celestial object of interest: no extra fuel is required.

The technology to do this does not now exist, but the next- or second-next generations of existing technologies would probably suffice. No conceptual leaps are required. Patience and persistence are essential – but if this bird doesn’t fly, another one will.

Nothing can stop the process now except nuclear war or climate collapse. So it’s a definite maybe.

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