When I was in college, long before most readers of this blog were born, I was a double major in physics and mathematics. There was a fairly predictable path of eight physics courses over four years for the physics major, and a fairly predictable path of eight math courses over four years for the math major. Not much room for other things. In my case I came within a couple of credits of also earning a triple major in philosophy. But I did not quite get there.
Conspicuously absent from my four-year course of study was geology. At the college that I attended there was a geology course that was part of the physics department. There was never room in my packed course schedule for that geology course. That course had a counterpart at many colleges and universities, I later learned, and at many schools it was somewhat condescendingly nicknamed “rocks for jocks”, the course that a student might sign up for as a way of satisfying a requirement for getting a certain minimum number of science credits if the student otherwise was not going to find it very easy to satisfy that requirement.
Decades have passed and over and over again I have been reminded how much I missed by never having taken that geology course, or any other geology course. Pretty much all I knew was that there are three kinds of rocks: sedimentary, metamorphic, and igneous. That was it. Which brings me around to the word “regolith”. What does “regolith” mean?
A chief reason why I think about words like this is that I keep hoping that life will eventually return to normal and there will be things like cocktail parties and salon dinners where people can talk about stuff and learn new things from each other. Yes by now I have despaired that this return to normalcy would happen in 2020, but maybe in 2021? 2022? Anyway, what does “regolith” mean?
As it turns out, “regolith” is a really important word. I never knew that word, part of the explanation for my never having learned that word being that I had not ever taken a geology course. But anyway, regolith is an important word.
In recent years I keep running into this word “regolith”, and finally I decided I needed to try to get a clue about it. I kept running into it because there would be news article after news article about, for example, exploration of Mars, and exploration of asteroids and, the big topic, exoplanets. You know, those planets that are orbiting around stars that are tens or hundreds of light-years away, and the only reason that we know the planets exist is that, and I am not making this up, some telescope will have been focused on some star that is very far away and the telescope does not blink for months or even years on end, and the telescope somehow notices that the light from that incredibly far-away star would get dimmer for a couple of days out of every couple of years, in a very repeatable pattern, but dimmer by how much? Oh, maybe instead of 100% brightness the star would drop to a mere 99.999% brightness because … yeah … we think a planet must have orbited into place between that star and our telescope for a couple of days. Yeah the brightness drops by a zillionth of a percent and the telescope has sensors that are apparently so precise as to pick this out from the noise, and then somebody keeps track of this for years on end and the pattern is so consistent that the conclusion is yes that must be a planet orbiting around that star.
And then these astronomers study their data sets even more closely to look at just exactly how fast or how slow did the brightness drop from 100% to a mere 99.999%? If it happened fast, then the occluding body probably had a sharp edge. Meaning no atmosphere. If it took a second or two to drop from 100% to 99.999%, well, then, it must be that the occluding body had an atmosphere.
And then those astronomers study their data sets even more closely, carrying out spectroscopic analysis on the colors of the photons that came through or got blocked, a differential analysis based on colors and stuff. And they work out that this planet, yes we have decided it must be a planet, not only had an atmosphere but the atmosphere has methane in it or carbon dioxide or nitrogen or some such.
Not to mention those astronomers study their data sets even more closely and they work out that for the occlusions to happen every two years instead of every one year or every three years, given the size of that particular star, the orbit must be this big instead of being bigger than that or smaller than that. And so the planet is probably this warm instead of being colder or warmer. And then we get this Goldilocks thing where we somehow work out that the particular exoplanet is not too cold and not too warm but just right. Yeah, Goldilocks. Yeah, you know where this is going, everybody gets wound up and says it might be a planet could support life. Maybe not our kind of life with sophisticated things like the National Enquirer newspaper, but at least fungi or algae or lichens or something. But … there is always this one last question. Before we can say that this particular exoplanet might possibly support life, we are going to need to know … you know where this is going … does this particular exoplanet have a regolith?
And there you are. This word that you can save up because someday, I promise, once again there will be cocktail parties and salon dinners and somebody will mention that yet another exoplanet has been identified, and somebody else will ask “oh yes but we don’t really know, do we, whether that particular exoplanet has a regolith?” And you can nod knowingly.
So what is a “regolith”?
As it always is in 2020, the answers to such questions come from Wikipedia (article about regolith). Regolith means:
a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock.
Wikipedia goes on to explain that although the term, coined in 1897, originally only referred to something on our planet Earth, by now
… it includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons.
Yeah. There are those nasty planets that are “gas giants” like Jupiter and Saturn, places where you can’t actually stand anywhere because it is all gas or liquid or mush or something, and poisonous besides, and probably super hot or super cold or something. But any planet that is going to be at least a candidate for supporting Life As We Know It, like fungi or algae or lichens or maybe more advanced life that develops things like the National Enquirer newspaper, is going to have to be a place where you can stand on something. And when you walk around, there are crunchy sounds on the gravel. Only a planet with crunchy sounds when you walk, it turns out, is even remotely a candidate for Life As We Know It.
And the geek term for this is, you now know where this was going, the geek term is that only a planet with a regolith is a candidate for Life As We Know It. Yes it has to be Goldilocks temperature, not too cold, not too warm. Yes it has to have water. But finally, it has to have a regolith. It has to have something like solid ground, and if you were to walk around on it, you would encounter soil or gravel or lots of dust or something.
Which then brings us to the various Mars explorer robots. Yet another one just got launched, this one from the United Arab Emirates from a launch pad in Japan. And the US has another one that will launch Real Soon Now. And the whole point of all of these various Mars explorer robots is … yes you know where this is going … to explore the regolith on Mars.
There are other explorers that got launched over the past few years to try to explore the regolith of some asteroids.
So anyway yes you can save this one up, and I promise you some day life will be normal again, and you will be at some cocktail party or salon dinner and you can make use of it. I promise.