A DISTANT MIRROR: SOLAR OSCILLATIONS OBSERVED on NEPTUNE by the KEPLER K 2 MISSION

Starting in 2014 December, Kepler K2 observed Neptune continuously for 49 days at a 1 minute cadence. The goals consisted of studying its atmospheric dynamics, detecting its global acoustic oscillations, and those of the Sun, which we report on here. We present the first indirect detection of solar oscillations in intensity measurements. Beyond the remarkable technical performance, it indicates how Kepler would see a star like the Sun. The result from the global asteroseismic approach, which consists of measuring the oscillation frequency at maximum amplitude nu(max) and the mean frequency separation between mode overtones Delta nu, is surprising as the nu(max) measured from Neptune photometry is larger than the accepted value. Compared to the usual reference nu(max,circle dot) = 3100 mu Hz, the asteroseismic scaling relations therefore make the solar mass and radius appear larger by 13.8 +/- 5.8% and 4.3 +/- 1.9%, respectively. The higher nu(max) is caused by a combination of the value of nu(max,circle dot), being larger at the time of observations than the usual reference from SOHO/VIRGO/SPM data (3160 +/- 10 mu Hz), and the noise level of the K2 time series, being 10 times larger than VIRGO's. The peak-bagging method provides more consistent results: despite a low signal-to-noise ratio (S/N), we model 10 overtones for degrees l = 0, 1, 2. We compare the K2 data with simultaneous SOHO/VIRGO/SPM photometry and BiSON velocity measurements. The individual frequencies, widths, and amplitudes mostly match those from VIRGO and BiSON within 1 sigma, except for the few peaks with the lowest S/N.