This picture shows the spectrum of light. You may have seen similar images in the past, but this one is something special—because it’s made of star light.

In April 2015, two so-called laser frequency combs were installed at the High Accuracy Radial velocity Planet Searcher (HARPS) planet-finding instrument of the European Southern Observatory’s 3.6-metre telescope at the La Silla Observatory in Chile. ESO explains what these devices and the spectra they produce are good for:

A laser frequency comb can be used as a ruler with which spectra from astronomical objects can be measured with unprecedented precision. They will allow the tiny changes in stellar velocity induced by an Earth-like planet as it orbits a star to be detected. [...] The increase in accuracy made possible by this new installation should in future allow HARPS to be able to detect Earth-mass planets in Earth-like orbits around other stars for the first time.