  Solar extreme ultraviolet (EUV) waves are spectacular propagating
disturbances with EUV enhancements in annular shapes in the solar corona. These
EUV waves carry critical information about the coronal magnetised plasma that
can shed light on the elusive physical parameters (e.g. the magnetic field
strength) by global solar coronal magneto-seismology. EUV waves are closely
associated with a wide range of solar atmospheric eruptions, from violent
flares and coronal mass ejections (CMEs) to less energetic plasma jets or
mini-filament eruptions. However, the physical nature and driving mechanism of
EUV waves is still controversial. Here, we report the unique discovery of twin
EUV waves (TEWs) that were formed in a single eruption with observations from
two different perspectives. In all earlier studies, a single eruption was
associated at most with a single EUV wave. The newly found TEWs urge to
re-visit our theoretical understanding about the underlying formation
mechanism(s) of coronal EUV waves. Two distinct scenarios of TEWs were found.
In the first scenario, the two waves were separately associated with a filament
eruption and a precursor jet, while in another scenario the two waves were
successively associated with a filament eruption. Hence, we label these
distinguished scenarios as "fraternal TEWs" and "identical TEWs", respectively.
Further, we also suggest that impulsive lateral expansions of two distinct
groups of coronal loops are critical to the formation of TEWs in a single
eruption.
