Jean-Baptiste Ruffio

Assistant Research Scientist, University of California, San Diego

Exploring exoplanets with direct imaging and novel high-resolution spectroscopy techniques.

As an astronomer interested in extra-solar planets, I strive to understand their diversity, evolution, and underlying formation mechanisms. I explore these new worlds through the largest direct imaging surveys and high-resolution spectroscopy. While the past decade was marked by the discovery of thousands of exoplanets, the next frontier will be population studies of their atmospheres for comparative exoplanetology. Moderate to high-resolution spectroscopy is a particularly promising and booming technique. It will for example unravel the mysteries of planet formation by measuring trends in atmospheric composition, expand the population of directly imaged exoplanets, and even allow the detection of exomoons.

Searching for exomoons

Io in front of Jupiter taken by the Cassini spacecraft.

Credit: NASA/JPL/University of Arizona

The development of novel instruments combining the power of high-resolution spectroscopy and high-contrast imaging is enabling the first direct radial velocity measurements of planets. This will allow us to detect wobble of these planets caused by orbiting satellites.

The figure below shows the future prospects for exomoon detections around the brown dwarf companion HR 7672 B. From ~1.5 nights of observations with the KPIC instrument, I have demonstrated a sensitivity to satellites with a mass ratio of 1-4% at separations similar to the Galilean moons (Dashed blue). The figure also includes simulated sensitivity for future instruments like Keck/KPIC II, Keck/HISPEC, and TMT/MODHIS (colored curves) assuming 6 nights of observations over a 25-day period.

The mass ratios of the Galilean satellites are shown as black dots for comparison. Their predicted scaled-up mass ratios, q, accounting for the larger mass, M, of the brown dwarf compared to Jupiter are shown as grey crosses. The Roche limit is computed for both a rigid and a fluid satellite shown as the inner and outer greyed region respectively. The black dashed lines represent the astrometric sensitivity of VLTI/Gravity and the vertical gray scale bars represent direct imaging of satellites.

Ruffio J.-B. et al. (submitted)

Measuring the composition of exoplanets

The formation of directly imaged planets, whether from accretion of planetesimals or from the collapse of the circumstellar disk, remains poorly understood. Different formation models predict different atmospheric compositions, so spectroscopic characterization of exoplanets might be used to inform their formation pathway.

Steps leading to the detection of water (H2O) and carbon monoxide (CO) in the atmospheres of the HR 8799 planets using the OSIRIS instrument at the Keck observatory and the new data reduction framework that I developed during my PhD. It allowed the study of planets that were so far inaccessible and enabled the measurements of the radial velocities of the planets themselves. I am developing a Python module for high-contrast imaging at high spectral resolution called BREADS (

(left) Using over a decade of Keck/OSIRIS observations, we have obtained the best moderate resolution spectra of the HR 8799 planets. (Right) While classical core accretion models predict super-stellar C/O, we showed that the four planets have similar C/O ratio and consistent with stellar.

High-resolution spectroscopy

A particularly exciting prospect for high-contrast imaging has been the recent development of dedicated high-resolution spectroscopic facilities. I have been working on the Keck planet imager and characterizer (KPIC; R=35000), which is the first instrument of its kind to come online. After two years on sky, our team has already opened new frontiers for exoplanet characterization. We have detected 20+ low-mass companions at high spectral resolution and measured the first spins of the HR 8799 planets. Exciting applications of high-resolution spectroscopy include the direct detection of new populations of planets, the characterization of their atmospheres, spin measurements and mapping their surface features with Doppler imaging, and even the search for exomoons from measurement of their radial velocities. It is a very active area of instrument development and innovative data analysis techniques.

Looking for new planets

During my PhD at Stanford University with Bruce Macintosh, I designed a statistically motivated planet detection algorithm for high-contrast imaging based on forward modeling and matched filtering. The open-source package is publicly available in python ( I analyzed the data for one of the largest and most sensitive searches for young gas giant planets around 524 nearby stars (Gemini Planet Imager Exoplanet Survey) enabling its derivation of planet occurrence rates. We showed that giant planets are more common around higher-mass stars and form a distinct population from brown-dwarf companions suggesting that they form differently.

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