For decades, astronomers have dreamed of directly photographing Earth-like planets orbiting other stars. The challenge is enormous: a planet similar to Earth can be billions of times fainter than the star it orbits. The overwhelming glare of the star can completely hide the tiny world.
Now, a NASA-led team is proposing an ambitious solution that could change how we search for potentially habitable planets. The concept, called the Hybrid Observatory for Earth-like Exoplanets (HOEE), would combine a giant space-based starshade with one of the world's most powerful ground-based telescopes.
If successful, the system could allow astronomers to directly image rocky exoplanets and potentially study their atmospheres for signs associated with life.
A Telescope That Works With a Giant Space Shadow
Instead of building an enormous space telescope, the HOEE concept takes a different approach. It would combine a space-based starshade, also known as an occulter, with a next-generation extremely large ground-based optical telescope.
The proposed starshade would operate roughly 175,000 kilometres (109,000 miles) away from Earth in a large elliptical orbit. One of its first potential partners could be the European Southern Observatory's Extremely Large Telescope (ELT), being constructed in northern Chile.
The ELT is designed to become one of the most powerful optical and infrared telescopes ever built. But even such a giant telescope faces a fundamental problem: the light from a nearby star can overwhelm the much weaker reflected light coming from an orbiting planet.
HOEE aims to solve that problem before the starlight even reaches Earth's atmosphere.
How Would the Starshade Work?
Imagine placing a giant screen directly between a powerful telescope and a distant star.
The screen would block the star's light while allowing the much fainter light reflected by planets around that star to reach the telescope.
That is essentially what the HOEE starshade would do.
The spacecraft would carefully position itself along the line of sight between the target star and the ground-based telescope. By creating an artificial eclipse, it would cast a highly controlled shadow over the telescope.
This would dramatically reduce the amount of unwanted starlight entering the telescope.
The result could be similar to switching off a bright lamp so that a much smaller, faint object beside it becomes visible.
The proposed starshade could have 48 large petals, with each petal measuring approximately 24.5 metres (80 feet) long. At its centre would be a disk about 50 metres (164 feet) across.
Such a structure would need extraordinary precision. The starshade would have to remain aligned with its target to within only a few metres. Microthrusters could be used for fine adjustments, while larger propulsion systems would help move the spacecraft between targets.
Why Not Just Use Space Telescopes?
Space telescopes such as NASA's James Webb Space Telescope have already transformed exoplanet science. They can study the atmospheres of some exoplanets and reveal valuable information about their temperatures and chemical compositions.
However, directly imaging a small, rocky planet similar to Earth is far more difficult.
The problem is not simply telescope size. The star itself is so much brighter than the planet that its glare can overwhelm the planet's signal.
NASA's planned Nancy Grace Roman Space Telescope will also carry a coronagraph designed to suppress starlight. But according to the HOEE researchers, directly observing Earth-like exoplanets in visible optical light remains extremely challenging with current space-based instruments.
HOEE takes advantage of something that already exists: the enormous light-collecting power of ground-based extremely large telescopes.
Instead of putting the entire observatory in space, the concept places only the star-blocking spacecraft in orbit.
A Shortcut to Earth-Like Exoplanets
The researchers believe this hybrid approach could offer a more practical path toward directly imaging nearby rocky worlds.
The initial targets would likely be planetary systems located within roughly 20 light-years of Earth.
At these relatively close distances, astronomers could potentially study individual planets rather than merely detecting their indirect effects on their host stars.
The extreme resolution of the combined system could also help astronomers distinguish different objects within an exoplanetary system.
In principle, HOEE could detect an Earth-like planet very quickly once the system is properly aligned. The researchers suggest that an exo-Earth could potentially be detected within the first minute of observation, although actual observing times would depend on the target and the planet's properties.
Searching for Signs of Life
Perhaps the most exciting part of the HOEE concept is not simply taking pictures of distant planets.
It is what those images could reveal.
Once astronomers can separate a rocky planet from its host star, they could potentially analyze the planet's light and search for spectral signatures associated with different chemicals in its atmosphere.
The team is particularly interested in young, active stars and rocky planets orbiting stars similar to our Sun.
Some of these stars can produce powerful flares. These stellar eruptions may interact with planetary atmospheres and create auroras.
Researchers could potentially look for characteristic colours and spectral lines produced by atmospheric gases.
For example, observations of red and green auroral emissions could provide clues about the presence and behaviour of gases such as nitrogen and oxygen.
That would not automatically prove that life exists. However, detecting atmospheric chemistry consistent with potentially habitable conditions could provide an important clue—and help scientists identify planets worthy of much deeper investigation.
A Giant Spacecraft With a Surprisingly Low Mass
Building a 50-metre-class structure for launch sounds extremely difficult. The researchers therefore envision a lightweight design that could potentially use an inflatable structure.
The goal would be to keep the total launch mass below approximately 1,500 kilograms.
The spacecraft would need to fold or collapse into a configuration compatible with a conventional launch vehicle. Once in space, it could deploy into its enormous operational shape.
The concept could cost around $1 billion, according to project estimates. That is a substantial investment, but it is far smaller than the cost of some massive space observatories.
The project has already been proposed for Phase B funding through NASA's Innovative Advanced Concepts (NIAC) program, with the team hoping to move toward further development in the coming years.
From Science Fiction to Engineering
Starshades have been discussed for many years. The basic idea is simple, but making such a spacecraft work in practice is extraordinarily complicated.
It must travel enormous distances from Earth, precisely align with a distant star and telescope, maintain that alignment, and repeatedly move between different targets.
The concept also requires sophisticated orbital mechanics and propulsion. The proposed orbit would need to work with Earth's rotation, while chemical propulsion could be used for station-keeping and solar-electric propulsion could help reposition the spacecraft.
These challenges are significant—but advances in lightweight structures, autonomous navigation and spacecraft propulsion are making concepts that once seemed impossible increasingly realistic.
If HOEE eventually becomes reality, astronomers could gain something that current observatories struggle to provide: direct optical images of rocky planets around nearby stars.
And those images could be far more than beautiful photographs.
They could become the first step toward answering one of humanity's oldest questions: Are we alone in the universe?
For decades, the starshade was viewed as an almost impossible idea. HOEE represents a new attempt to turn that idea into a practical astronomical observatory—by putting a giant artificial shadow in space and using it to reveal worlds that have been hidden in the glare of their stars.
Reference: Soliman, A., Mather, J., Shaklan, S. et al. The observation of Earth-like exoplanets with ground-based telescopes and a shared orbiting starshade. Nat Astron 10, 349–356 (2026). https://doi.org/10.1038/s41550-026-02787-9
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