ASU astronomers lead 2 Gemini programs shaping future exoplanet science

Arizona State University astronomers now lead two of the largest high-resolution exoplanet spectroscopy programs at the international Gemini Observatory.

One program focuses on the infrared and the other on the optical, both using instruments that are direct predecessors of those planned for the Giant Magellan Telescope. Together, these programs are developing the methods, datasets and trained scientists who will shape GMT exoplanet research when the telescope begins operating in the 2030s.

The new program, Roasting S’more Marshmallows: Revealing Exoplanet Composition, Chemistry, and Climate with IGRINS-2, is led by ASU Associate Professor Michael Line. The Gemini Observatory's Large and Long Programs time allocation committee selected it for 150 hours over six semesters, starting in August 2026. The name connects it to Line's earlier Gemini program, Roasting Marshmallows, which studied hot Jupiter atmospheres with the IGRINS spectrograph at Gemini South from 2021 to 2024. That program has already produced five peer-reviewed publications, with more expected.

"Every result from Marshmallows told us what to do next," Line said. "S’mores is the natural follow-up — a bigger sample, more extensive observational coverage of any given planet, and a new instrument that takes us one step closer to what the Giant Magellan Telescope will ultimately deliver."

Using IGRINS-2 on Gemini North in Hawai'i, S’mores will study about 10 hot and ultra-hot Jupiter atmospheres in both transmission and emission. By observing each planet from two perspectives, the team can build a three-dimensional view of its composition and climate. This amount of detail has not been possible before on such a large scale.

"S'mores will enable exciting new discoveries about exoplanet atmospheres and offer a glimpse of the scientific potential of the even more powerful instruments being developed for the Giant Magellan Telescope," said Daniel Jaffe, president of the Giant Magellan Telescope, leader of the team that developed the original IGRINS spectrograph on which IGRINS-2 is based, and a member of the S'mores team.

This program joins an ongoing Gemini survey led by Adam Langeveld, a postdoctoral researcher at Johns Hopkins University who will become an Exploration Fellow at ASU's School of Earth and Space Exploration in July. Langeveld's program, SPECTRE-GHOST (Spectroscopically Probing Extremely hot Climates of TRansiting Exoplanets with GHOST), was chosen in 2024 for 220 hours on the GHOST spectrograph at Gemini South and is now in its second year of observations. While S’mores studies infrared volatile species, SPECTRE-GHOST looks for optical atomic and ionic features in the same types of planets.

"Combining GHOST's hundreds of optical atomic features with IGRINS-2's infrared molecular lines gives us a uniquely complete picture of what these worlds are actually like," Langeveld said.

IGRINS and IGRINS-2 are the direct technological predecessors to GMTNIRS, the planned high-resolution infrared spectrograph for GMT. GHOST is the direct counterpart to G-CLEF, GMT's main high-resolution optical spectrograph. The methods, pipelines and expertise developed in these surveys will form the foundation for future GMT exoplanet research.

The results so far show this potential. In 2021, Line's team published the first precise measurements of carbon and oxygen in a transiting exoplanet's atmosphere in Nature, before JWST. Earlier this year, ASU doctoral student Jorge Antonio Sanchez led a study in Nature Communications that reported the first direct measurement of magnesium and silicon in an exoplanet's atmosphere, confirming that planets inherit their rocky makeup from their host stars. Both findings came from earlier ASU-led IGRINS programs using the same techniques that S’mores will now expand.

The momentum extends well beyond these two flagship surveys. In the same Gemini review cycle, ASU-led teams won three additional programs on Gemini North: Langeveld secured time to map the day- and nightside hemispheres of the hottest known exoplanet; Luis Welbanks will push high-resolution methods to their limits on a rocky, terrestrial-sized planet; and a third led by recent PhD student Peter Smith will fully map the orbit of another extreme, highly irradiated world. Taken together with S'mores, ASU researchers will lead roughly 75 hours of Gemini North observing time — about 10 full nights — this cycle alone, a concentration of telescope time that reflects the depth of exoplanet expertise the university has assembled.

These programs have also helped train the next generation of exoplanet scientists. Three ASU doctoral students (Peter Smith, Krishna Kanumalla and Jorge Sanchez) have based their thesis work directly on Gemini data. Two well-known Pegasi 51b Postdoctoral Fellows — Welbanks and Megan Weiner Mansfield — did research at ASU using these datasets. In December 2025, Line organized Hi-Res in the Desert, a weeklong NSF-funded workshop at ASU that brought together 50 researchers from around the world to learn the high-resolution exoplanet spectroscopy methods that GMT will need.

ASU has partnered with GMT since 2017. With Marshmallows, S’mores and SPECTRE-GHOST as leading Gemini programs, ASU's exoplanet group stands out. They are already doing the kind of science GMT was designed to advance, using similar instruments and preparing the researchers who will continue this work in the future.

"The exoplanet characterization foundation we're building at Gemini is the foundation the Giant Magellan Telescope will stand on," Line said. "Every result, every student, every pipeline makes ASU more ready to lead exoplanet science in the Giant Magellan Telescope era."