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More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses -- companion-disk interaction and gravitational instability (GI) -- predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ${sim}5$ yr using the SPHERE instrument on the Very Large Telescope (VLT), we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint missing planet driving the disk arms. The average spiral pattern speed is $0.!^circ22pm0.!^circ03$ yr$^{-1}$, pointing to a driver at $172_{-14}^{+18}$ au around a $1.9$ $M_odot$ central star if it is on a circular orbit. In addition, we witness time varying shadowing effects on a global scale that are likely originated from an inner disk.
The formation of planetesimals requires that primordial dust grains grow from micron- to km-sized bodies. Dust traps caused by gas pressure maxima have been proposed as regions where grains can concentrate and grow fast enough to form planetesimals,
Spiral arms in protoplanetary discs are thought to be linked to the presence of companions. We test the hypothesis that the double spiral arm morphology observed in the transition disc MWC 758 can be generated by an $approx 10$ M$_{rm Jup}$ companion
Asymmetrical features in disks provide indirect evidences of embedded objects, such as planets. Observed with the Atacama Large Millimeter/submillimeter Array (ALMA), the circumstellar disk in MWC 758 traced with thermal dust continuum emission at wa
Spiral arms have been observed in more than a dozen protoplanetary disks, yet the origin of nearly all systems is under debate. Multi-epoch monitoring of spiral arm morphology offers a dynamical way in distinguishing two leading arm formation mechani
Transition disks offer the extraordinary opportunity to look for newly born planets and investigate the early stages of planet formation. In this context we observed the Herbig A5 star MWC 758 with the L band vector vortex coronagraph installed in th