How Artists Illustrate Exoplanets With Just A Few Data Points

The following is an excerpt from The Possibility of Life: Science, Imagination, and Our Quest for Kinship in the Cosmos by Jaime Green.

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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.

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. 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. 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.