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The consistently low activity level of the old solar analog 51 Peg not onlyfacilitated the discovery of the first hot Jupiter, but also led to thesuggestion that the star could be experiencing a magnetic grand minimum.However, the 50 year time series showing minimal chromospheric variabilitycould also be associated with the onset of weakened magnetic braking (WMB),where sufficiently slow rotation disrupts cycling activity and the productionof large-scale magnetic fields by the stellar dynamo, thereby shrinking theAlfven radius and inhibiting the efficient loss of angular momentum tomagnetized stellar winds. In this Letter, we evaluate the magnetic evolutionarystate of 51 Peg by estimating its wind braking torque. We use newspectropolarimetric measurements from the Large Binocular Telescope toreconstruct the large-scale magnetic morphology, we reanalyze archival X-raymeasurements to estimate the mass-loss rate, and we detect solar-likeoscillations in photometry from the Transiting Exoplanet Survey Satellite,yielding precise stellar properties from asteroseismology. Our estimate of thewind braking torque for 51 Peg clearly places it in the WMB regime, driven bychanges in the mass-loss rate and the magnetic field strength and morphologythat substantially exceed theoretical expectations. Although our revisedstellar properties have minimal consequences for the characterization of theexoplanet, they have interesting implications for the current space weatherenvironment of the system.

Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg