This pioneering strategy involves coupling massive terrestrial observatories—such as the Extremely Large Telescope (ELT), the Thirty Meter Telescope (TMT), and the Giant Magellan Telescope (GMT)—with a colossal starshade deployed in Earth’s orbit. Measuring approximately 99 meters in diameter, the starshade acts as a colossal cosmic shield, casting a deep and sharp shadow that effectively blocks out the overwhelming glare of a star. This shadow drastically reduces the starlight contaminating observations, allowing faint reflected light from orbiting exoplanets to emerge from obscurity.

Despite the transformative advantages of the starshade, Earth’s atmosphere remains a significant hurdle. Turbulence induced by atmospheric layers continuously blurs incoming light, disrupting the clarity needed for such delicate observations. To counter this, adaptive optics systems integrated within the ground-based telescopes dynamically adjust mirror shapes in real-time to compensate for atmospheric distortions. Notably, the ELT’s advanced adaptive optics machinery has been modeled to demonstrate its capability to restore image sharpness sufficiently to rival space-based observations, even through Earth’s turbulent sky.

The core of this new system’s potential lies in its ability to leverage the finest angular resolution achievable from Earth with the profound contrast enhancement uniquely provided by the orbiting starshade. By projecting a precise shadow well above the atmosphere’s disruptive layers, the starshade eliminates a substantial fraction of stellar light before it ever enters the telescope. This dual approach enables ground-based platforms to reach contrasts on the order of 10^−10, the threshold required for detecting reflected light signatures from terrestrial exoplanets analogous to Earth.

An intricate and realistic modeling of the entire system has been conducted, focusing particularly on the ELT’s performance under moderate weather conditions. The simulations encompass wavelengths spanning from the ultraviolet through the near-infrared (300 to 1,000 nanometers), where key biosignature molecules can be detected. Crucially, the adaptive optics’ Strehl ratio — a measure of image quality — was varied in the analysis to confirm that atmospheric turbulence corrections impose minimal penalties on sensitivity across this broad spectral range.

Beyond mere detection, the hybrid system advances exoplanet characterization by enabling spectral measurements. The reflected light spectra can reveal the presence of major molecular constituents such as oxygen and water vapor—substances intimately tied to the possibility of life. Identifying these markers from an Earth-analog exoplanet orbiting a Sun-like star represents a monumental leap toward answering whether our cosmic neighborhood harbors life.

The simulations further demonstrate promise by showcasing simulated images and spectra of a Solar System analogue, encompassing planetary bodies roughly akin to Venus, Earth, and Saturn. These synthetic observations affirm that with current technology complemented by the starshade, even relatively faint planetary signals can be teased out, heralding a new era for comparative planetology beyond our solar system.

Historically, direct imaging attempts suffered from the overwhelming brightness of host stars, forcing astronomers to depend heavily on indirect detection methods such as transit photometry or radial velocity measurements. Although powerful, these techniques provide limited insights, often failing to reveal atmospheric compositions or surface conditions. By contrast, the hybrid starshade-telescope concept enables direct reflected-light spectroscopy, paving the way for detailed studies of exoplanet atmospheres, climate, and potentially even seasonal changes.

Moreover, this hybrid configuration offers a cost-effective mitigation strategy by sharing the starshade among multiple giant telescopes, effectively distributing the high implementation expense of such a massive orbital structure. This democratizes deep-contrast imaging capabilities across the astronomical community and accelerates the availability of high-fidelity data.

Technological hurdles remain in deploying and maintaining precise starshade alignment from orbit, but ongoing advances in spacecraft navigation and formation flying instill optimism. The synergy highlighted in these studies underscores how ground-based adaptive optics and space-based starlight suppression can synergistically surmount challenges that neither could overcome alone.

Comparing this innovative hybrid method with upcoming space-only missions shows complementary strengths. While dedicated space telescopes boast stable, turbulence-free environments, they face limitations in aperture size and mission duration. Ground-based observatories harness the massive collecting areas needed for faint target spectroscopy, but have been hampered by atmospheric interference—now mitigated by the shared starshade.

Future work anticipates refining adaptive optics performance under variable atmospheric conditions and enhancing starshade positioning precision. Additionally, integrating high-contrast imaging coronagraphs within the telescopes’ optical trains can offer further improvements by removing residual scattered starlight, creating an even cleaner observational window.

The prospect of detecting biosignatures such as oxygen, ozone, and water vapor on exo-Earths, using a combination of Earth’s largest telescopes and a strategically deployed starshade, reshapes our roadmap for exoplanet science. This breakthrough would mark an epochal expansion of humanity’s reach into the cosmos, transforming speculative habitats into tangible worlds awaiting exploration.

In summary, the marriage of gigantic terrestrial optics with an orbital starshade represents a visionary yet technically achievable pathway toward realizing the long-sought goal of imaging and characterizing Earth analogs around Sun-like stars. By transcending the limitations imposed by our atmosphere and stellar glare, this hybrid framework unveils new territories for studying life beyond Earth through direct observational evidence.

As this concept advances from theoretical simulation toward experimental implementation, it holds the promise not only to revolutionize exoplanet discovery but also to deepen our understanding of planetary system architectures, atmospheric dynamics, and potentially, the universality of life itself across the galaxy.

Subject of Research: Observation and characterization of Earth-like exoplanets using hybrid space–ground telescope systems combined with an orbiting starshade.

Article Title: The observation of Earth-like exoplanets with ground-based telescopes and a shared orbiting starshade.

Article References:
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 (2026). https://doi.org/10.1038/s41550-026-02787-9

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41550-026-02787-9

At its core, PLACID utilizes the unique properties of liquid crystals to achieve high-contrast imaging of celestial bodies. Traditional coronagraphs, which are essential for blocking the intense light from host stars while allowing researchers to observe dim planets and other structures, typically rely on physical masks. However, the innovation behind PLACID lies in its use of a Spatial Light Modulator (SLM), which can adaptively create complex optical masks in real-time. This advanced technology not only enhances the instrument’s versatility but also allows for precision that was previously unattainable through conventional methods.

The importance of direct imaging in the study of exoplanets cannot be understated. While nearly 6,000 exoplanets have been discovered using indirect methods—such as variations in the brightness of their stars—direct imaging provides irreplaceable insights into the atmospheres, compositions, and formation processes of these distant worlds. PLACID’s ability to produce such images will be particularly beneficial in studying planets orbiting binary star systems, which account for roughly half of all stars in our galaxy. Until now, the direct imaging of exoplanets in these complex systems has posed a substantial challenge, but PLACID’s advanced mask capabilities will enable astronomers to adapt to the dynamic light sources of binary stars.

Professor Jonas Kühn, the lead investigator of the PLACID project, emphasizes the implications of this innovation for future exoplanet research. With PLACID, astronomers can look forward to a new wave of discoveries that will enhance our understanding of planetary formation and the potential for habitable worlds beyond our own. The potential to directly image exoplanets will unveil details about their atmospheres, chemical compositions, and possibly even signs of habitability, which may reshape our knowledge and perspectives on the cosmos.

Incorporating cutting-edge technology into astronomical research, PLACID’s design reflects a commitment to pushing the boundaries of what is possible within direct imaging techniques. The project has benefited from extensive support, including the National Center of Competence in Research and a grant from the European Research Council, ensuring that scholars have the necessary resources to validate their groundbreaking technology. This robust foundation has set the stage for PLACID to take its place among the elite observational instruments currently in operation.

As part of its ongoing development, PLACID will be paired with an Adaptive Optics (AO) system developed by Professor Laurent Jolissaint’s team at HEIG-VD. This will significantly mitigate the effects of atmospheric turbulence, which can distort the images captured during observations. Together, these instruments represent a monumental leap forward in the quest to capture the elusive images of exoplanets and their surrounding environments. The integration of both systems is expected to significantly enhance the fidelity of observations and provide unprecedented clarity in the images produced.

The assembly of the PLACID instrument has taken almost a decade of meticulous development. Once assembled in Switzerland, the instrument underwent rigorous laboratory testing to ensure its performance met expectations. Following this phase, it was transported to Turkey for installation at the DAG telescope, where it will become a pivotal part of the observatory’s arsenal. As the project progresses toward its initial observations, the anticipation surrounding PLACID is palpable within the astronomical community.

Ruben Tandon, a doctoral candidate and member of the PLACID team, elaborates on the group’s vision moving forward. Initially, they will target a select number of exoplanets that have previously been indirectly imaged, allowing researchers to gauge the instrument’s functionality and performance. Subsequently, the team hopes to break new ground by attempting to achieve direct images of exoplanets within binary star systems, a feat that has never been accomplished to date. The successful execution of these observations would mark a historic achievement in the field of astronomy.

As an unprecedented tool in the realm of space exploration, PLACID will contribute significantly to our understanding not just of exoplanets but also of the broader dynamics governing stellar systems. The knowledge gained from studying these distant worlds could inform future missions aimed at searching for life beyond Earth, fundamentally altering our perspective on life in the universe.

In conclusion, the advent of PLACID represents a transformative moment in the field of exoplanetary science. It showcases how groundbreaking research, enabled by innovative technologies, can open new pathways to understanding our universe. As preparations for its inaugural observations commence, the excitement surrounding this project reflects a shared enthusiasm for unveiling the mysteries that lie beyond our Solar System, potentially leading to discoveries that could alter humanity’s understanding of its place in the cosmos.

Subject of Research: Exoplanet Imaging
Article Title: Programmable Liquid-crystal Active Coronagraphic Imager (PLACID) Set to Revolutionize Exoplanet Detection
News Publication Date: October 2023
Web References:
References:
Image Credits: University of Bern/PLACID

Keywords

Exoplanets, PLACID, Coronagraph, Astronomical Imaging, Space Research, Liquid Crystals, Adaptive Optics, Binary Stars.

Background

Astronomical surveys have discovered nearly 6,000 exoplanets, including many habitable planets, which may harbor liquid water on their surfaces. The search for life on such planets is one of the most significant scientific endeavors of this century, with direct imaging observation projects currently under development.

On Earth-like planets, the characteristic reflectance spectrum of terrestrial vegetation, known as “vegetation red edge”, is considered as a key biosignature. However, ocean planets, with most of their surfaces covered by water, are unlikely to support terrestrial vegetation. To broaden the scope of life detection on ocean planets, this study examined the characteristics of reflectance spectra from floating plants and tested their detectability.

Results

The study investigated the reflectance spectra of floating plants across different scales, from individual leaves in laboratory settings to large-scale observation via satellite remote sensing of lake vegetation.

Although floating leaves exhibit considerable morphological variation among species, their general trend reveals a pronounced red edge, often comparable to or even exceeding that of terrestrial plants. This enhancement is attributed to air gaps in sponge tissue that provide buoyancy and specialized epidermal structures that offer water repellency. While floating leaves show slightly reduced reflectance when wet, they still display a more distinct red edge than submerged water plants (Figure 1).

However, on a larger scale, the red edge signature of floating vegetation weakens due to lower vegetation density and reduced leaf overlap on the water surface. Landscape-scale analyses using satellite remote sensing (Sentinel-2; ESA) with the Normalized Difference Vegetation Index (NDVI) flourishes in summer and disappears in winter, causing the NDVI to be relatively low when averaged over the year. Nevertheless, the fluctuation between minimum and maximum NDVI values is more pronounced for floating vegetation compared to forests. To further investigate this pattern, a large-scale survey of 148 lakes and marshes across Japan was conducted. The study revealed a characteristic seasonal NDVI variation, shifting from negative values in winter to positive values in summer (Figure 2). Importantly, while water suppresses the reflectance of floating vegetation, its own reflectance is even lower and remains stable. It enhances the detectability of seasonal NDVI fluctuations, which remain robust against atmospheric and cloud interference, suggesting that this method could be promising for detecting life on habitable exoplanets in the future.

Perspectives

If photosynthetic organisms, such as floating plants, exist universally on habitable exoplanets, then the scope of life exploration can be expanded to include ocean planets rather than being limited to Earth-like planets. It is important to understand the origin and evolutionary process of life as it coevolves with planetary environments to predict the morphology of organisms that may adapt to diverse planetary conditions. This study provides a foundation for future research on biosignatures, paving the way for the next generation of life-detection missions.

Journal

Astrobiology

Funder

Japan Society for the Promotion of Science

DOI

10.1089/ast.2024.0127