Building a roadmap for detecting life on distant worlds

Astronomers have found more than 6,000 planets in the Milky Way and calculate that hundreds of billions of planets exist in our galaxy alone—which could be extrapolated to predict a mind-blowing number of planets throughout the cosmos.

Faced with this profusion of distant worlds, scientists are experiencing renewed vigor around one of humankind’s oldest questions: Are we alone in the universe? 

Picking a Target: 

“Sub-Neptunes are important for understanding habitability because they represent the transition between a rocky planet and a gas giant,” Shahar explains. 

Although these worlds, which are more massive than Earth but smaller than Neptune, dominate the known exoplanet population, there is no analog for them in our own Solar System. 

Adds Shahar: “We want to determine which rocky exoplanets which rocky exoplanets have the ingredients we think a planet needs to host and sustain life.” 

To answer this, Shahar and the nearly 40 members of the AEThER team set out to link observations of rocky planet atmospheres made by astronomers to an understanding of the solid planet below built through theoretical modeling and laboratory experimentation. 

“Our goals are ambitious because the challenge is multi-faceted,” Shahar says. “Habitability means more than just a planet’s distance from its star or the gases detected in its atmosphere.” 

In fact, habitability is the product of a planet’s entire life story—how it formed, what it’s made of, how its interior evolved, and how those characteristics shaped its atmosphere and surface over billions of years. 

In order to understand the nature of exoplanetary systems and select the most promising candidate worlds for habitability, it is critical to pursue an interdisciplinary approach that includes astronomy, astrophysics, cosmo- and planetary chemistry, planetary physics and dynamics, experimental and theoretical petrology, and mineral physics. 

This is why Shahar brought together a diverse team of scientists who are pursuing bold questions about the potential for life on other planets. 

How It Started:

The seed for AEThER was planted when Shahar and Earth and Planets Laboratory colleagues Peter Driscoll, Alycia Weinberger, and George Cody published a 2019 essay in Science urging the research community to recognize the vital importance of a planet’s interior dynamics in creating an environment that’s hospitable for life.

During a 2023 public program on the formative history of Earth’s core, Driscoll—an expert in geophysics and geodynamics—told the audience that our planet’s interior is central to maintaining its habitable surface over billions of years.

If we want to understand rocky planets, in general, and look for an Earth equivalent out there in the Milky Way, he explained, we need to consider how our home world cooled and differentiated into layers after its formation. Two key questions, according to Driscoll are: does mantle convection and melting reach the planet’s surface and can enough heat be transported out its core to drive a magnetic field?

“Earth has plate tectonics, it has liquid water on its surface, and it has had a magnetic field for as long as we can tell,” he said the following year in a Carnegie news video. “And it also has life, of course, and I don’t think these things are coincidences.”

It all starts with the formation process. Planets are born from the rotating ring of dust and gas that surrounds a young star. The elemental building blocks from which rocky planets form—silicon, magnesium, oxygen, carbon, iron, and hydrogen—are universal. 

But their abundances and the heating and cooling they experience in their youth will affect their interior chemistry and, in turn, things like ocean volume and atmospheric composition. A global magnetic field may also be needed to shield the atmosphere from the solar wind in order for a planet to retain water for billions of years.

“One of the big questions we need to ask is whether the geologic and dynamic features that make our home planet habitable can be produced on planets with different compositions,” Driscoll explained.

The AEThER project fully kicked into gear when Shahar was selected for an initial grant of $1.5 million from the Alfred P. Sloan Foundation, which was renewed for another $1.5 million in 2025. 

This funding enabled Shahar to assemble a team of experts from an array of international research institutions that currently includes Johns Hopkins University, University of Birmingham, MIT, University of Chicago, University of Groningen, UCLA, ETH Zurich, University of Rochester, University of Maryland, IPGP, and NASA Ames.

How It’s Going:

So far, they have published at least 60 papers in major research journals ranging from The Astrophysical Journal and Monthly Notices of the Royal Astronomical Society to Nature and the Journal of Geophysical Research. 

This breadth reflects the scope of the undertaking, although much of the early efforts were focused on modeling and several key laboratory experiments. 

Shahar and UCLA’s Edward Young, a member of the AEThER team, along with Hilke Schlichting showed that our planet’s water could have originated from interactions between the hydrogen-rich atmospheres and magma oceans of the planetary embryos that comprised Earth’s formative years. 

Then she and former Carnegie postdoc Francesca Miozzi, now at ETH Zurich, performed experimental tests of this theory, demonstrating that large quantities of water are created as a natural consequence of planet formation.

These results were compared with atmospheric signals seen of low-mass planets seen by JWST, with water being the most prevalent. 

Simultaneously, other experts were bringing together meteorite analysis, studies of planet-forming disks around distant stars, and simulations and experiments to understand how planets obtain other critical raw materials for life, including carbon and nitrogen. 

Together, this enables a three-pronged approach to understanding what makes a planet habitable: 

• Probing planetary interior dynamics and bulk composition in the lab and using models.
• Observing and characterizing of the diversity of exoplanet atmospheres using space- and ground-based telescopes
• And observational and analytical efforts to understand how planets acquire and retain so-called volatiles—planetary constituents that evaporate easily but are necessary for a planet to be considered capable of hosting life.

A Carnegie Story: 

The AEThER project is an ambitious extension of Carnegie’s long-standing excellence in studying every aspect of planets—from their interior dynamics to their atmospheres—in the lab, using sophisticated mathematical models, and at the telescope.

“Atmospheres carry the signals telescopes can measure, but those messages are shaped by deep, often hidden, planetary processes. By building a strategic and considered pathway for experts in complementary disciplines to act in concert, AEThER is creating a field map for distinguishing between atmospheric features of abiotic origin and genuine signs of life,” says Carnegie Science President John Mulchaey.

This work builds on Carnegie’s natural tendency to cross disciplinary boundaries as colleagues from different fields engage in the common areas of the Earth and Planets Laboratory campus in Washington, D.C.

Weinberger, an astronomer, said at a 2024 memorial symposium for legendary Carnegie Science President Maxine Singer that when she joined the institution in 2001, there were just a handful of scientific staff members who thought about exoplanets. But by 2024, that number had tripled to 15, Weinberger noted, in part due to hiring “young, broad-minded and curious scientists, as is the Carnegie way.” But also, because colleagues from other disciplines naturally started collaborating and contributing to exoplanet, planet-formation, and Solar System research. 

Now, this type of work touches nearly everyone at EPL and several at the Carnegie Science Observatories, too, she concluded.

Fundamentally, the story of AEThER is an only-at-Carnegie story.

“Carnegie’s commitment to empowering scientific researchers to follow their curiosity where it leads, traverse disciplinary boundaries, and pursue bold new research ideas enables us to establish new opportunities for leadership within the greater scientific enterprise,” Shahar concluded. “The best part? There’s still more great science on the way.”