One of the most exciting and ambitious goals of astronomy is finding planets like ours around other stars. These so-called Earth-like planets could be the best candidates for harboring life outside our solar system. But finding it is not easy.
They are small, dim, and often hidden by the glare of their host stars. To detect them, astronomers must use special techniques and instruments that can block out starlight and reveal the planet’s faint glow.
One of these techniques is called direct imaging, which means taking a photo of the planet directly, without relying on indirect methods such as measuring the wobble or dimming the star.
Direct imaging has many advantages, such as being able to measure the size, shape, color and even the atmospheric composition of the planet. But it also has many challenges, such as requiring very high contrast, resolution and stability.
To overcome these challenges, astronomers have have suggested an ambitious new technology that could revolutionize direct imaging: star shadows.
A starshade is a large, specially shaped screen that flies in formation with a space telescope and blocks the light from the star, creating a shadow through which the telescope can see the planet.
A starshadow could potentially achieve much higher contrast and resolution than any other existing or planned instrument, and allow direct imaging of Earth-like planets around nearby stars.
However, building and operating a star display is not an easy task. It requires precise engineering, coordination and control. The star shadow would have to be very large, about 30 meters in diameter, and fly at a distance of tens of thousands of kilometers from the telescope.
It should also be perfectly aligned with the star and the telescope, and maintain that alignment as they all orbit the sun. Any small error or disturbance can ruin the observation.
To test the feasibility and performance of a star display, NASA has funded several studies and experiments in recent years. One of these is called S5 (Starshade with a Small Space Telescope), which aims to demonstrate a scaled-down version of a starshade mission in low Earth orbit.
S5 would consist of a small telescope with a diameter of 0.5 meters and a starshade with a diameter of 3.5 meters, which would fly at a distance of about 25 kilometers. S5 would focus on bright stars with known planets and try to image them with the star shadow.
S5 is still in the early stages of development, but could pave the way for future star shadow missions that could image Earth-like planets around nearby stars.
Such missions could answer some of the most fundamental questions in astronomy and astrobiology: How common are Earth-like planets? What are their properties and diversity? Do they have signs of life? And are we ultimately alone in the universe?
