# Transit Detection of a "Starshade" at the Inner Lagrange Point of an Exoplanet

## TL;DR

This paper proposes that a large starshade placed at Earth's L1 point could be detected through its unique transit light-curve signature, offering a method to identify artificial geo-engineering structures around exoplanets.

## Contribution

It introduces the concept of detecting a starshade at L1 via transit photometry and analyzes the specific observational signatures that would distinguish it from natural phenomena.

## Key findings

- A starshade at 1.6 times Earth-L1 distance minimizes mass.
- Such a starshade would produce a characteristic maximum at mid-transit.
- Earth-sized planets around G dwarf stars are optimal targets for detection.

## Abstract

All water-covered rocky planets in the inner habitable zones of solar-type stars will inevitably experience a catastrophic runaway climate due to increasing stellar luminosity and limits to outgoing infrared radiation from wet greenhouse atmospheres. Reflectors or scatterers placed near Earth's inner Lagrange point (L1) have been proposed as a 'geo-engineering" solution to anthropogenic climate change and an advanced version of this could modulate incident irradiation over many Gyr or "rescue" a planet from the interior of the habitable zone. The distance of the starshade from the planet that minimizes its mass is 1.6 times the Earth-L1 distance. Such a starshade would have to be similar in size to the planet and the mutual occultations during planetary transits could produce a characteristic maximum at mid-transit in the light-curve. Because of a fortuitous ratio of densities, Earth-size planets around G dwarf stars present the best opportunity to detect such an artifact. The signal would be persistent and is potentially detectable by a future space photometry mission to characterize transiting planets. The signal could be distinguished from natural phenomenon, i.e. starspots or cometary dust clouds, by its shape, persistence, and transmission spectrum.