The ESO 3,6-meter telescope on the Chilean mountain La Silla in this photo looks almost lonely. However, it is not alone: thousands of stars that are blurred by the long -term exposure of the camera to fine lines. And even inside the telescope, it is surprisingly sociable. Two spectrographs are looking for distant exoplanets together. The spectrographer Harps (High Accuracy Radial Velocity Planet Searcher) has been looking for a planetary search since 2003 – his partner nirps (Near Infrared Planet Searcher) has only been installed since 2022 and has now delivered initial results.
Both spectrographs use the so -called radial speed method to track down exoplanets. They take advantage of the fact that planets do not revolve around a standstill star, but that both move around a common focus. This movement easily lets the star “wobble”. If the star moves to the telescope, its light becomes blue – it moves away, the spectrum shifts into the red. Based on these periodic shifts, astronomers can indicate the presence and properties of a planet, even if they cannot see it themselves.
Unlike Harps, nirps works in the nearby infrared area. This is particularly suitable for this spectrographer to look for red dwarfs for planets. These stars are smaller and cooler than our sun and shine brighter in the nearby infrared area than in the visible light. About three quarters of all stars are red dwarfs.
If nirps and Harps work together, you can even examine the atmosphere of planets if they pass your star. For their first observations, astronomers with the two spectrographs analyzed the atmospheres of two well-known gas giant exoplanets: WASP-189 B and WASP-69 b. In the atmosphere of WASP-189 B, Harps demonstrated in the visible light, however, nirps not. “So there must be another chemical element that hides the iron signature in the nearby infrared, but not in the visible light area,” explains Valentina Vaulato from the University of Geneva. “The hydridanion – a hydrogen atom with two instead of an electron – is our main suspect.”
When observing the second exoplanet WASP-69 B, the researchers also found a long tail of helium gas using nirps, which escapes from the comet-like atmosphere of the planet. In the future, the cooperation between Harps and Nirps will enable many more exciting discoveries in distant worlds.
