Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1900 exoplanets have now been discovered and confirmed, 1 none are still in the process of formation. Transition discs, protoplanetary disks with inner clearings 2-4 best explained by the influence of accreting planets 5 , are natural laboratories for the study of planet formation. Some transition discs show evidence for the presence of young planets in the form of disc asymmetries 6, 7 or infrared sources detected within their clearings, as in the case of LkCa 15. 8,9 Attempts to observe directly sig-Author Contributions: This work merged two independently acquired and analysed data sets. S.S. led preparation of the manuscript, the orbital fits, and the acquisition and analysis of the LBT data while K.B.F. led the acquisition and analysis of the MagAO data, development of the MagAO SDI pipeline, and drafted MagAO manuscript sections.

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10(-6) and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.

The Gemini Planet Imager is a dedicated facility for directly imaging and spectroscopically characterizing extrasolar planets. It combines a very high-order adaptive optics system, a diffractionsuppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution. Every aspect of the Gemini Planet Imager has been tuned for maximum sensitivity to faint planets near bright stars. During first-light observations, we achieved an estimated H band Strehl ratio of 0.89 and a 5-σ contrast of 10 6 at 0.75 arcseconds and 10 5 at 0.35 arcseconds. Observations of Beta Pictoris clearly detect the planet, Beta Pictoris b, in a single 60-s exposure with minimal postprocessing. Beta Pictoris b is observed at a separation of 434 ± 6 milliarcseconds (mas) and position angle 211.8 ± 0.5°. Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of 3 improvement in most parameters over previous solutions. The planet orbits at a semimajor axis of 9:0 +0:8 −0:4 AU near the 3:2 resonance with the previously known 6-AU asteroidal belt and is aligned with the inner warped disk. The observations give a 4% probability of a transit of the planet in late 2017.high-contrast imaging | extreme adaptive optics | debris disks D irect imaging is a powerful complement to indirect exoplanet detection techniques. In direct imaging, the planet is spatially resolved from its star, allowing it to be independently studied. This capability opens up new regions of parameter space, including sensitivity to planets at >5 AU. It also allows spectroscopic analysis of the light emitted or reflected by the planet to determine its composition (1, 2) and astrometry to determine the full Keplerian orbital elements (3, 4).Imaging planets is extremely challenging-Jupiter is 10 9 times fainter than our sun in reflected visible light. Younger extrasolar planets are more favorable targets. During their formation, planets are heated by the release of gravitational potential energy. Depending on the exact formation process and initial conditions, a 4-Jupiter mass ðM J Þ planet at an age of 10 million years could have a luminosity between 10 −6 and 2 × 10 −5 L ⊙ (5), but this is still a formidable contrast ratio. To overcome this, astronomers combined large telescopes (to reduce the impact of diffraction), adaptive optics (to correct for phase errors induced by atmospheric turbulence), and sophisticated image processing (6, 7). This recipe in various combinations had achieved several notable successes (8-12). However, the rate of these discoveries remains low (13-15) in part because the number of suitable young stars in the solar neighborhood is low, and for all but the closest stars, such detection is limited to >20 AU, where planets may be relatively rare. To move beyond this limited sample, dedicated instruments are needed that are designed specifically for high-contrast imaging. One such instrument is the Gemini Planet Imager (GPI). GPI is a fully optimized high-con...

Gas-giant planets emit a large fraction of their light in the mid-infrared ( 3 μm), where photometry and spectroscopy are critical to our understanding of the bulk properties of extrasolar planets. Of particular importance are the L-and M-band atmospheric windows (3-5 μm), which are the longest wavelengths currently accessible to ground-based, high-contrast imagers. We present binocular LBT adaptive optics (AO) images of the HR 8799 planetary system in six narrow-band filters from 3 to 4 μm, and a Magellan AO image of the 2M1207 planetary system in a broader 3.3 μm band. These systems encompass the five known exoplanets with luminosities consistent with L → T transition brown dwarfs. Our results show that the exoplanets are brighter and have shallower spectral slopes than equivalent temperature brown dwarfs in a wavelength range that contains the methane fundamental absorption feature (spanned by the narrow-band filters and encompassed by the broader 3.3 μm filter). For 2M1207 b, we find that thick clouds and non-equilibrium chemistry caused by vertical mixing can explain the object's appearance. For the HR 8799 planets, we present new models that suggest the atmospheres must have patchy clouds, along with non-equilibrium chemistry. Together, the presence of a heterogeneous surface and vertical mixing presents a picture of dynamic planetary atmospheres in which both horizontal and vertical motions influence the chemical and condensate profiles.

We utilized the new high-order 585 actuator Magellan Adaptive Optics system (MagAO) to obtain very high-resolution visible light images of HD142527 with MagAO's VisAO science camera. In the median seeing conditions of the 6.5m Magellan telescope (0.5 − 0.7′′), we find MagAO delivers 24-19% Strehl at Hα (0.656 µm). We detect a faint companion (HD142527B) embedded in this young transitional disk system at just 86.3±1.9 mas (~12 AU) from the star. The companion is detected in both Hα and a continuum filter (∆mag=6.33±0.20 mag at Hα and 7.50±0.25 mag in the continuum filter). This provides confirmation of the tentative companion discovered by Biller and co-workers with sparse aperture masking at the 8m VLT. The Hα emission from the ~0.25 solar mass companion (EW=180 Angstroms) implies a mass accretion rate of ~5.9x10 -10 M sun /yr, and a total accretion luminosity of 1.2% L sun . Assuming a similar accretion rate, we estimate that a 1 Jupiter mass gas giant could have considerably better (50-1000x) planet/star contrasts at Hα than at H band (COND models) for a range of optical extinctions (3.4-0 mag). We suggest that ~0.5-5 M jup extrasolar planets in their gas accretion phase could be much more luminous at Hα than in the NIR. This is the motivation for our new MagAO GAPplanetS survey for extrasolar planets.