Professor Sarah Seager pulled a small, petal-shaped object from her office and handed it over with a warning: the edges are sharp. It was a 1% scale model of Starshade, a specially shaped screen that may one day block out starlight from a distant sun so precisely that a space telescope could photograph the dim glow of an Earth-like planet orbiting beside it. The stakes behind that piece of hardware are about as large as stakes get. We have confirmed more than 6,000 planets beyond our solar system, and not one of them is a true Earth twin. Finding one, and then reading its atmosphere for signs of life, is the defining scientific chase of the era. Seager, who invented some of the key methods already used to detect and analyze exoplanet atmospheres, is at the center of that chase and pushing it forward on two fronts simultaneously.
How scientists went from a blank map to 6,000 planets
When Seager began her PhD, the exoplanet map was empty. The first confirmed exoplanet outside our solar system was discovered in 1995, and even that was contested. ‘It was incredibly controversial,’ Seager recalled. ‘There were many people who would say, well, you should talk to my adviser, he’ll tell you why it’s not a planet.’ She pressed on anyway, working on the transit method, where astronomers watch for the tiny dip in a star’s brightness as a planet crosses in front of it. The biggest such dip might be 1 or 2 percent. The smallest are spread across many decimal places. Alongside the transit method, the Doppler technique detects a star wobbling toward and away from Earth as a planet tugs on it, with precision down to tens of centimeters per second. Direct imaging captures reflected or re-emitted light from a planet itself, though stars outshine their planets by roughly 10 billion times in reflected light, which makes that separation extraordinarily hard. Two further methods fill in the map: astrometry, which tracks the looping path a star makes when a planet pulls it across the sky in three dimensions, and gravitational microlensing, where the gravity of an unseen star or planet bends and magnifies light from a more distant background star, acting as a natural lens.
The cone-shaped cluster visible in the full exoplanet map is not where planets prefer to form. It is simply the patch of sky where the Kepler Space Telescope stared for more than three years after its 2009 launch, recording transits across that fixed grid. Point a similar telescope in any other direction and a new cone would appear. The 6,000 confirmed planets are a tiny, directionally biased sample of what is everywhere.
The cinnamon problem, and the machine that could solve it
Finding that a planet exists is only the opening move. Reading its atmosphere is where the question of life begins. Seager developed the foundational framework for transit transmission spectroscopy, the technique of comparing a star’s light spectrum by itself against its spectrum while a planet is crossing in front, so that the difference reveals which gases in the planet’s thin atmosphere absorbed which wavelengths. She applied the method to the very first transiting exoplanet candidate available. ‘I was taken aside and told that they couldn’t include me on the team because I was too young,’ she said. The team proceeded, tried the method, and it worked.
For Earth twins orbiting sun-like stars, however, the atmosphere signal is far too faint to read through existing techniques. The planet is 10 billion times dimmer than its star in reflected light, and the two sources of light mix inside a telescope the moment they arrive together. Seager reached for a banana bread analogy to explain the problem: if there are 10 billion parts flour and one part cinnamon already baked together, no one is separating them after the fact. The solution is to keep them apart from the start, which is where Starshade comes in. The spacecraft would fly in precise formation with a space telescope far from Earth, blocking the target star entirely so that only the planet’s light enters the telescope’s optics. Its petal shape is not decorative. A circular or square screen would cause light to bend around its edges and create ripples brighter than any planet. The petal geometry, worked out by physicist Spitzer in the 1960s, causes the diffracted light to interfere with itself and cancel, leaving the surrounding darkness clean enough to detect a pale blue dot.
Starshade funding is currently on hold. NASA’s planned Habitable Worlds Observatory will use an internal coronagraph instead, though Seager noted that the coronagraph still has a significant way to go in laboratory demonstration, while Starshade has already been demonstrated to the contrast levels needed.
Five minutes in the clouds of Venus
While the exoplanet search looks outward across light-years, Seager is also running a parallel effort much closer to home. The Morning Star Missions are a privately funded series of small, focused probes aimed at the atmosphere of Venus, a planet roughly Earth’s size and mass that may once have had liquid water oceans before runaway greenhouse warming pushed surface temperatures past any threshold for life. About 50 kilometers above that surface, however, temperatures return to a range that could support biology, and the clouds there have been a subject of speculation since Carl Sagan first proposed the possibility.
The first mission in the series is a Rocket Lab probe that will have exactly five minutes in the Venusian clouds to collect data before drag carries it to the surface. A laser will fire through a window in the probe shell, strike cloud particles, and return information about what those clouds contain. Later missions aim to go further, using what Seager’s team calls a cloud catcher, a wire mesh structure that collects cloud droplets the way fog collects on a jacket, with the goal of eventually returning a liquid sample for analysis.
The complication is that the clouds are not water. They are concentrated sulfuric acid. Seager’s laboratory has been systematically placing organic molecules into concentrated sulfuric acid to find out what survives. Amino acids: stable. Nucleic acid bases: stable. Small peptides and lipids: stable. Most recently, the lab demonstrated that PNA, peptide nucleic acid, a molecule with the same base components as DNA but a different backbone, remains stable in pure concentrated sulfuric acid up to approximately 50 degrees Celsius. ‘This would tell me that in the clouds of Venus there could be life built using similar building blocks, but different things,’ Seager said, ‘not DNA, but other things.’
The smallest lights she held onto
Seager’s book, ‘The Smallest Lights in the Universe,’ carries a dual meaning she is careful to preserve. The small lights are the faint planetary signals, 10 billion times dimmer than their stars, that she has spent her career trying to detect. They are also the small sights of hope she held onto after her first husband, Mike, died while their children were still young. ‘When he died,’ she said, ‘life was meaningless all of a sudden.’ The work gave her a path. ‘It is my dream to find another Earth. And that is my purpose.’
For anyone who wants to engage with the search directly, Seager pointed to two things worth watching. The upcoming Nancy Grace Roman Space Telescope should help answer how common or rare a solar system arranged like ours actually is. And the full archives of TESS, Kepler, and the James Webb Space Telescope are public, including processed light curves that any careful reader can examine for unusual signals.
The 1% scale model still sitting on the desk
The Starshade model, its petal edges still sharp enough to warrant the warning Seager gave before handing it over, sat on the desk between two people talking about how to find signs of life 10 billion times fainter than the nearest star.
On a wall behind Seager, mounted as a single demonstration piece, was a full-size replica of one petal from the actual Starshade design.
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