CHEOPS

Much of what makes science work is following up. After the discoveries are made, more research is needed to fill in the details. And the launch window for a spacecraft that’s all about the follow-up opens next week.
CHEOPS is a European mission that will study exoplanets — planets that orbit stars other than the Sun. It won’t hunt for new planets. Instead, it’ll make detailed observations of star systems with known planets.
CHEOPS will look for the planets to pass in front of their parent stars. Such a passage is called a transit. It causes a tiny “dip” in a star’s light. How much the star dims, and how long the transit lasts, reveals the size of the planet. Scientists especially want to study worlds that are between the size of Earth and the size of Neptune, the Sun’s fourth-largest planet.
The size will be combined with measurements of the planet’s mass made from the ground. The combination will tell astronomers how dense a planet is. And that will give them an idea of the planet’s c