The origin of the differing tilts in the orbits of the planets in our solar system may have been revealed through the discovery of subtle warps spotted in many planet-forming disks around young stars.
A major observing program with ALMA (Atacama Large Millimeter/submillimeter Array), called exoALMA, has surveyed 15 planet-forming, or protoplanetary, disks in detail. In particular, astronomers led by Andrew Winter of Queen Mary University of London measured the Doppler shift of carbon monoxide gas in each of the disks. The Doppler shift can tell us a gas' velocity and direction of travel, while carbon monoxide is an excellent proxy for other contents of the disks because it has a strong signal at the submillimeter radio wavelengths that ALMA observes at.
