An astro-comb is a type of frequency comb which increases the resolution of previous spectrographs by nearly a hundredfold, allowing it to be used as an observational tool in astronomy and detect redshift wobbles caused by smaller exoplanets than what was detectable with traditional calibrators. Existing frequency combs were too precise to be useful for astronomy, with "teeth" too close together. In other words, the repetition rate or the frequency spacing between the comb lines was much smaller (<1 gigahertz) than that required for astronomical applications (~tens of gigahertz or more). A "green astro-comb" was installed in January 2013 in the High Accuracy Radial velocity Planet Searcher in the Northern hemisphere (HARPS-N) spectrograph at the Telescopio Nazionale Galileo on the Canary Islands. The device was developed by a team led by Chih-Hao Li of Harvard University.
The astro-comb uses a pulsed laser to filter starlight before feeding the signal into a spectrograph. It has the potential to revolutionise astrophysical spectroscopy and discover other Earth-like planets outside our solar system. Currently, it is gathering data from Venus to demonstrate its ability to discover exoplanets.