Exoplanet exploration has taken off in recent years, with over 5500 being discovered so far. Some have even been in the habitable zones of their stars. Imaging one such potentially habitable exoplanet is the dream of many exoplanet hunters, however, technology has limited their ability to do that. In particular, one specific piece of technology needs to be improved before we can directly image an exoplanet in the habitable zone of another star – a starshade. Christine Gregg, a researcher at NASA Ames Research Center, hopes to contribute to the effort of developing one and has received a NASA Institute for Advanced Concepts (NIAC) grant as part of the 2025 cohort to work on a star shade that is based on a special type of metamaterial.

The Functionality of Starshades

To understand the goal of Dr. Gregg and her team, it’s best first to understand what starshades do and what’s holding them back from being deployed. A starshade is designed to float in tandem with a space telescope and block out the light from a specific star, allowing the telescope to capture light directly from the much-less bright planet that is orbiting the star. That light can contain information about its size, orbital period, and even its atmospheric composition that would otherwise be lost in the overwhelming brightness of the planet’s star.

The shape of a starshade, which traditionally looks like a flower petal, might seem counterintuitive at first – if you’re trying to block a star’s light, why not just make the shape circular? But starlight coming from far away can diffract around a simple circular structure. The petals are explicitly designed to stop that from happening and completely block out even diffracted light around the shape’s edges.

The Challenges of Deployment

However, it’s not the shape that makes it hard to deploy—it’s its size. Starshades are typically designed to be hundreds of meters across. Therefore, they are impossible to fit inside a traditional rocket fairing fully assembled. What’s more, they have to move along with the telescope—if the telescope the starshade is meant to accompany is pointed at another star and redirected, the starshade has to move with it.

The wrinkle is that the starshade is likely tens of thousands of kilometers from the telescope it is designed to assist. So, a slight change of a few degrees of inclination for the telescope would mean hundreds of thousands of kilometers of travel for its associated starshade. That kind of movement requires a lot of fuel, which is also costly due to the weight requirements of launching these objects so far away.

No wonder a starshade has yet to be successfully deployed in space. Combining gigantic sizes that don’t fit inside rocket fairings and massive amounts of fuel to relocate every time the telescope needs to look at a different star are significant strikes against the concept. However, if humanity wants to directly image an exoplanet in the habitable zone of another star, there is still no better way to do so.

The Proposal by Dr. Gregg

Enter Dr. Gregg’s idea—she proposes using metamaterials for her starshade, which is robotically constructed in orbit. Metamaterials have several advantages over existing proposed starshades (one of which, by Nobel Prize winner John Mather, is another NIAC recipient this year).

Advantage	Description
Lighter Material	Metamaterials are generally lighter, reducing launch costs.
Durability	Metamaterials can be designed for greater durability, reducing the likelihood of failure.
Vibration Dampening	Specific metamaterials suppress vibrations better than traditional materials.

Material Properties

The metamaterial Dr. Gregg and her colleagues have proposed uses a type of material that both holds its structure well but also suppresses vibration by a unique use of a material called a phononic crystal. These were initially engineered to dissipate sound waves. This means that when used as a material in a starshade, it could dampen any feedback on the structure from things like micrometeoroid impacts, solar radiation, or even the process of deployment and assembly.

Robotic Deployment Strategies

Using robots to deploy the starshade is another focal point of Dr. Gregg’s work, as she discusses with Fraser. Still, for this Phase I NIAC project, she is focusing on developing the model for the starshade itself and selecting the appropriate material. As with all NIAC projects, she can apply for more funding in a Phase II round upon completion of her Phase I. If she receives it, humanity will be one step closer to seeing a giant floating petal in space – but one with very particular mechanical and structural properties.

Conclusion

In conclusion, Dr. Gregg’s work on the starshade represents a significant step toward overcoming existing limitations in exoplanet imaging technology. By leveraging the properties of metamaterials and exploring innovative deployment strategies, this research could pave the way for groundbreaking discoveries in the field of astronomy.