A major limitation to the discovery rate of extrasolar planets is the hardware available with which to detect them. Instruments like HST, Spitzer and Keck have revolutionized astronomy, and have provided a major source of extrasolar planet science — both in atmospheric characterisation and planet detection. These instruments are not dedicated to extrasolar planets, though, and time on the instruments must be shared with astronomers investigating cosmology, interstellar dust, galactic structure, and dark matter, to name a few. There is considerable interest in dedicated exoplanet science instruments – instruments that were designed to do extrasolar planet science, as opposed to instruments and spacecraft designed years ago that we have been fortunate enough to be able to torture exoplanet data out of.
One such dedicated observatory is the Automated Planet Finder, a robotic 2.4 metre telescope whose task is to search for extrasolar planets around nearby stars with a Doppler precision of ~1 m s-1. It observes ten starts a night, and will observe about a thousand stars in the solar neighbourhood. By now, the APF has been in service for a few months, but its data has already been crucial in confirming a new four-planet system of gas giants at HD 141399, and a Neptune-mass planet at GJ 687 (.pdf link) which is only 4.5 pc away.
The age of the dominance of Doppler spectroscopy in the discovery of new planets is clearly over. Doppler spectroscopy has fallen to second place behind transit detection, largely as a result of Kepler‘s superb performance and its discovery of over 3,000 planet candidates, as well as a change in strategy by ground-based Doppler surveys. The discovery of planets are no longer interesting for the most part, so important assets are being targeted away from large surveys of bright, metal-rich stars in the hopes of detecting intermediate- to long-period Jovian planets, and toward focoused observations of nearby stars in the hopes of detecting low-mass planets that more closely resemble our solar system. The interest now is in attaining higher precision spectrometers to observe nearby stars to try to detect very low mass planets. This takes a lot of time, and explains both why the nature of discoveries from Doppler spectroscopy has changed in recent years, as well as why the discovery cadence has trailed off. As we move away slightly from discovery for the sake of understanding the underlying planet population distribution, and toward looking for nearby targets for future follow-up, the motto is quality over quantity.
However, the outer regions of planetary systems have been largely unprobed, as Doppler surveys and transit surveys are both biased toward short-period planets. Microlensing results have shed some light on the planet population distribution at higher separation, comparable to the outer Solar System, and it seems that the abundance of gas giant planets picks up quite a bit, but this will need to be confirmed. Fortunately, new instruments are coming online that will help address these issues.
The Gemini Planet Imager on the Gemini Observatory is another new toy that has come to light. It will be used to conduct a 890 hour survey of ~600 stars from 2014 to 2016, and this January they posted first-light images, including one of β Pictoris b.
Another imaging instrument that is about to contribute to extrasolar planet science is SPHERE for ESO’s Very Large Telescope, capable of detecting giant planets with orbital radii >5 AU. It will observe nearby young star associations with ages of 10 – 100 Myr within 30 – 100 parsecs, as the planets of these stars will be both bright in infrared due to their age, and well separated from their star due to their proximity. All stars within 20 parsecs will also be observed, as well as stars with known long-period planets. First light is expected to be soon in 2014, perhaps as early as within the month.
A more long-term instrument of interest is ESO’s ESPRESSO spectrograph, also on the VLT. ESPRESSO will surpass the highly successful HARPS spectrograph. With a required accuracy of 10 cm s-1 (and a goal of a few cm s-1), It is expected to be sensitive to terrestrial and Earth-like planets around sun-like stars as faint as V ~ 9. First light is expected to occur in 2016.
With new planet transit search missions such as TESS and PLATO to identify transiting planets around bright stars, and improved spectrographs for mass and density determination of those planets, in addition to new direct imaging instruments and astrometry with the GAIA mission to probe the population statistics of the middle to outer regions of planetary systems, the post-Kepler era is promising to be quite an exciting, with a diverse array of complementary instruments working together to further illuminate the nature of planetary systems in the Galaxy.