The first week of my stressful (but fun!) two-internship summer is over, and I couldn't be happier with how well it went! I love the different projects I'm doing and the students and scientists I get to do them with. But I also love weekends! And this weekend is especially lovable because I'm spending it in New York with my roommate and her family as they celebrate my roommate's brother's graduation. So I had a 5-hour long train ride, terrible wifi, and a list of scientific articles that I had downloaded before I left. Can you guess what I spent my time doing?
You got it (I'm assuming; I can't really read your mind)! I spent those 5 hours reading about science. I read about the Meter Size Barrier, the the Meszaros Effect, and the death of galaxies. All of those were interesting, but none were quite as applicable to my senior thesis (more on that in a bit) as an article sent to me by Dr. Sarah Rugheimer--who just graduated from Harvard University this year!--about plant colors on extrasolar planets, and I'll tell you why here.
You may have heard the joke (perhaps on 30 Rock, as I did just this morning) that at Harvard, we don't have majors. We have concentrations. And if that weren't pretentious enough, we don't even have double concentrations, we have joint concentrations, which require students to write a joint thesis that combines their two fields. You may have figured out by reading some of the posts on this blog that I'm kind of, sort of, a little bit interested in astronomy. Yeah, I love astronomy enough that I'm planning on devoting the next 6 to 8 years of my life learning it, and the rest of my adulthood after that putting what I learned to use. But I don't love it enough to give up my other passion: folklore. I am what we Harvardians call a joint concentrator in Astrophysics and Folklore & Mythology. I'm the first one, so the two departments don't really know exactly how to deal with it or me, but I've always been a fan of trailblazing.
People always ask me how astrophysics and folklore go together, and I love it when they do because there are SO MANY WAYS. There are connections as basic as the stories that accompany each constellation and ones as complex as identifying which ancient cultures may have been more knowledgeable about astronomy than we thought based on their creation myths. I'm doing neither of those, and I'm not really doing anything in between them. Instead (and, yes, I do get an insanely excited smile on my face every time I get to tell someone this), I'm going to write a science fiction novel based on the exoplanet research I do this summer. And I want that novel to be as scientifically accurate as possible, all the way down to the color of the plants.
I know it's common for kids to ask why the sky is blue, but have you ever wondered why plants are green? I mean, beyond the fact that they have chlorophyll, because they haven't always. Why have plants evolved to have chlorophyll? That's what I spent part of my train ride learning.
Our sun emits most of its energy in the range of wavelengths we call "visible." In fact, we call it visible light because our eyes evolved to see wavelengths at the peak of our sun's spectrum. So it makes sense that plants would evolve in a similar way, but it's more complex than that.
If you paid attention in high school science class (or if you didn't, but you did your own reading on the subject), you probably know that plants look green to us because they absorb all the other colors and reflect green. What's wrong with green? Does it not taste as good as all the other colors or something? The answer, as in most physics/astronomy questions, has to do with photons.
By the time sunlight makes it through Earth's upper atmosphere, most of the photons traveling around are red, and the numbers decrease as you move down the spectrum to blue. But blue photons don't have it all bad! They're more energetic than their longer-wavelength counterparts. And green is somewhere in the middle--it doesn't have super impressive quantity or quality. Plants "know this" and have optimized to get photons high in energy and in numbers, so they just don't need the green photons to make their fuel.
But in extrasolar systems, the star might be totally different from ours! In the system I'm studying this summer, for example, the star is smaller and dimmer than out own sun. This means that the plants on a planet in the habitable zone won't get as much light, and will need to absorb all the light they can get, so they'll look black! Isn't that cool?? It gets even cooler when you think about the ways this seemingly insignificant detail could affect the culture on that planet.
In America, we associate the color green with freshness, rebirth, and nature (the good, clean kind of nature). We have those associations because plants are green! On a planet where plants are black, color symbolism could be totally shifted from our own. Black = birth. Maybe green = death. Red = peace. Wouldn't that be so weird and trippy and awesome? It will be for me, and I hope it will be for anyone who ends up reading my thesis.
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