Who Decides What a New Planet Looks Like? It’s an Artist, Not a Telescope

When I look at the night sky, I can point to the bright, steady lights and say, There’s a planet. I say this often to my toddler, though he still responds, pre-Galilean, “Yes, that a star.” I point to Venus, low in the sky after sunset, to Jupiter and Saturn, lately clinging to the sides of the moon. With a telescope, just like Galileo, I can even see Saturn’s rings. And the first time I did, on a college rooftop observatory, I felt that sudden shock: holy shit, that’s a planet. Something I’d always known, now known in an entirely new way.

Exoplanets, on the other hand, orbiting other stars, are so distant and so small and dim that they can almost never be directly photographed. Scientists aim their telescopes and then infer and deduce. I’ve heard it described as trying to photograph a gnat flying around a floodlight—and both the gnat and the floodlight are at the opposite end of a football field from you. Only rarely and with great effort have exoplanets been directly imaged, little dots on photographs we can point to and say Aha.

One way scientists find planets is by the tiny eclipses they make when they pass between us and their stars. The planets are too small, compared to their stars, to come close to fully blocking out their light, but they do slightly dim our view of the star when they pass in front of it. These dips in a star’s brightness, the line called its light curve, create a signature called a transit.

A transit is as close as we can come to seeing these planets, but the curve’s decisive shape is, if you know to understand it, as clear as a picture of the sky. Anthropologist Lisa Messeri embedded with teams of astronomers to write Placing Outer Space: An Earthly Ethnography of Other Worlds. Observing (and sometimes helping carry out) their research, she saw how as­tronomers learn to see a planet in a light curve, and learn to see a transit in far less decisive data. The interpretation—and imagination—in that work is formidable.

As Messeri sees it, astronomers make up for the lack of data-packed photographs of exoplanets by constructing a suite of “abstract representations,” light curves and data plots that, within the field of study, are how astronomers turn data into a planet and a planet into a place. She cites other scholars who describe the work as an aesthetic project—“an aesthetic not of beauty but of realism.” Worlds made real.

“Place,” Messeri writes, “suggests an intimacy that can scale down the cosmos to the level of human experience.” It is what distinguishes the study of exoplanets from that of other cosmic objects—galaxies and black holes and stars. The cosmos, for all its vastness, becomes speckled with islands of familiar scale, rest stops where we can catch our imaginative breath. And finding that familiarity out in space is a thrill. “Places are exciting,” Messeri writes, “because we know how to know them; we all have experience learning what it means to be somewhere.” And we know what sorts of questions to ask about them.

Artists are the ones who turn the place an astronomer can understand into one the public can imagine their way onto.

When I asked astronomer Jessie Christiansen, science lead at the NASA Exoplanet Archive, what’s happening inside her imagination when she’s thinking about an exoplanet, she told me she basically outsources that work to collaborators, artists who create the images that go along with press releases announcing the discovery of new exoplanets. Christiansen said, “I bring them the numbers—it’s this big, it weighs this much, and the star is this temperature. And then … they make something.” These artists are the ones who turn the place an astronomer can understand into one the public can imagine their way onto.

So I asked the artists how they do that.

Collaborators Tim Pyle and Robert Hurt came to the work from opposite poles. Hurt is an astronomer who had always dabbled in graphic design and art, and Pyle worked for years in visual effects in Hollywood and applied for his current job at Caltech with an animated short about bees taking over some NASA equipment and exploring space. Their work is far broader than creating art to accompany press releases—they craft visuals and videos and multimedia experiences, any way of “telling the science story”—but their illustrations of exoplanets are no small part of their project. These images, which often accompany news stories about the newly discovered exoplanets, have to draw readers in, to set up their framework for the story they’re about to read. Pyle says, “It has to be attractive on some level—in the sense of being eye-catching … It can be a very ugly planet that’s attractive,” a cosmic jolie laide. Hurt says, “We need to show them a picture that’s at least starting to be as cool as what you saw on the Guardians of the Galaxy trailer, if we want people to stop and linger and wonder what it was.”

Pyle and Hurt—and other artists like them—create vivid, evocative images with a very few pieces of data. As Christian­sen said, all that’s known is “it’s this big, it weighs this much, and the star is this temperature.” Pyle said that everything more than that is “educated likelihoods.” Hurt framed the artists’ decisions as part of the scientific process. “In the best case scenario, [it] should be viewed as a hypothesis,” he said, a foray or a positing, a few steps out on a limb. “We have to overcommit what we know.”

But fidelity is not the artists’ main goal. Instead, the artists and scientists have to overlay the decisive data with reflections of human ideas. For example, we have no way to definitively know if a planet in a certain range of sizes is a super-Earth, rocky and wet and big; or a mini-Neptune, with a thick, swirling atmosphere of hydrogen, helium, and methane gas enveloping a slushy mantle of frozen water and ammonia. That’s a particularly tricky kind of planet, at the transition between large rocky planets and small ice giants, but every example has its unknowns. To turn the data into an illustra­tion, an artist has to choose—not just what the data suggests but what sort of illustration serves the situation.

Artists and scientists have to overlay the decisive data with reflections of human ideas.

And, indeed, Pyle told me, “I know of at least one person who is actually of the mindset that because there could be these multiple routes you could go, we should not even be attempting to illustrate exoplanets,” because in doing so, the artists and scientists make choices based on factors other than data—on aesthetic preference or narrative power or some­thing even less tangible. “We know that whenever we do an artist’s concept, it will be wrong.”

One of Pyle’s illustrations is of a planet called Kepler-452b [the feature image at the top of this article]. At the time of its discovery in 2015, it was the smallest exoplanet that had been found in its star’s habitable zone, about sixty per­cent larger in diameter than Earth—and, warranting excitement and press releases, it was in its star’s habitable zone. Roughly.

Based on the planet’s size and location, it was possible that if this planet had an atmosphere, it could be like Venus, with a thick haze of clouds—scientifically meaningful, but rendering it in art would obscure the planet’s presumed rocky surface. But it was also possible this planet wasn’t a hothouse at all, just a slightly warmer, slightly bigger Earth. So Pyle split the difference, illustrating a planet with gray-brown continents and greenish-blue seas under hazy clouds. But the coastlines are shaded lighter, and riverbeds are crusted with salty white. There used to be more water here, the art suggests, but the planet is heating up, the rivers and oceans evaporating as the atmosphere fattens itself with water vapor, a thickening and thickening blanket.

I wouldn’t have noticed those salty shores, let alone thought through their implications, without Pyle’s guidance. I’d have seen a rocky planet with a little bit of water, less inviting than Earth. And Pyle’s version gives us a far less specific scene than one from the SETI Institute (below).

Image: Danielle Futselaar/SETI Institute

Their image, drawn not from the point of view of space but from right over the surface as if the viewer is in flight, is filled with golden fjords rising out of deep blue rivers, and volcanoes clouding the skies. In the foreground, thin fingers of rock jut out of the water. The caption here says, “This illustration imagines that a runaway greenhouse effect has begun to take hold on Kepler-452b, driving off much of the planet’s surface water.” The same story in a vastly different scene.

Excerpted from The Possibility of Life: Science, Imagination, and Our Quest for Kinship in the Cosmos by Jaime Green, Copyright © 2023 by Jaime Green. Published by Hanover Square Press.

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