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To date, infrared interferometry at best achieved contrast ratios of a fewtimes $10^{-4}$ on bright targets. GRAVITY, with its dual-field mode, is nowcapable of high contrast observations, enabling the direct observation ofexoplanets. We demonstrate the technique on HR8799, a young planetary systemcomposed of four known giant exoplanets. We used the GRAVITY fringe tracker tolock the fringes on the central star, and integrated off-axis on the HR8799eplanet situated at 390 mas from the star. Data reduction includedpost-processing to remove the flux leaking from the central star and to extractthe coherent flux of the planet. The inferred K band spectrum of the planet hasa spectral resolution of 500. We also derive the astrometric position of theplanet relative to the star with a precision on the order of 100$\,\mu$as. TheGRAVITY astrometric measurement disfavors perfectly coplanar stable orbitalsolutions. A small adjustment of a few degrees to the orbital inclination of HR8799 e can resolve the tension, implying that the orbits are close to, but notstrictly coplanar. The spectrum, with a signal-to-noise ratio of $\approx 5$per spectral channel, is compatible with a late-type L brown dwarf. UsingExo-REM synthetic spectra, we derive a temperature of $1150\pm50$\,K and asurface gravity of $10^{4.3\pm0.3}\,$cm/s$^{2}$. This corresponds to a radiusof $1.17^{+0.13}_{-0.11}\,R_{\rm Jup}$ and a mass of $10^{+7}_{-4}\,M_{\rmJup}$, which is an independent confirmation of mass estimates from evolutionarymodels. Our results demonstrate the power of interferometry for the directdetection and spectroscopic study of exoplanets at close angular separationsfrom their stars.

First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e