A new, robust catalog is out featuring 126 confirmed and candidate exoplanets discovered with the National Aeronautics and Space Administration (NASA) Transiting Exoplanet Survey Satellite (TESS) in collaboration with W. M. Keck Observatory on Maunakea, Hawaiʻi.
In this latest installment of the TESS-Keck Survey, the catalog consists of thousands of radial velocity (RV) observations that reveal a fascinating mix of planet types beyond our solar system, from rare worlds with extreme environments to ones that could possibly support life.
The study is published in today’s edition of The Astrophysical Journal Supplement.
“The results that have come from the TESS-Keck Survey represents the single largest contribution to understanding the physical nature and system architectures of new planets TESS has discovered,” says University of Kansas Physics and Astronomy graduate student Alex Polanski, the lead author of the paper. “Catalogs like this help astronomers place individual worlds in context with the rest of the exoplanet population.”
Polanski and a global team of astronomers from multiple institutions spent three years developing the catalog; they took TESS planetary data and analyzed 9,204 RV measurements, 4,943 of which were taken over the course of 301 observing nights using Keck Observatory’s planet-hunting instrument called the High-Resolution Echelle Spectrometer (HIRES).
“The TESS-Keck Survey results fundamentally depend on Doppler spectroscopy from Keck Observatory’s HIRES. The U.S. science community has relied on this workhorse instrument for exoplanet studies for nearly three decades,” says University of Kansas Associate Professor of Physics and Astronomy Ian Crossfield, a co-author of the paper.
The team also obtained an additional 4,261 RV with The University of California Observatories’ Automated Planet Finder at Lick Observatory in California. With the combined total of RV measurements, they were able to calculate the masses of 120 confirmed planets plus six candidate planets.
“RV measurements let astronomers detect, and learn the properties of, these exoplanetary systems. When we see a star wobbling regularly back and forth, we can infer the presence of an orbiting planet and measure the planet’s mass,” says Crossfield.
The wobble produces a regular change in wavelengths due to the Doppler effect, which is detected through the RV method — one of the techniques used to find exoplanets. The phenomenon refers to the gravitational effect an exoplanet has on its host star, where it tugs the star as the planet orbits around it. When the host star moves toward a telescope, its visible light turns slightly bluer; when it moves away from us, the light shifts slightly redder. This is much like how sound behaves; a fire truck’s siren gets higher-pitched as it travels closer to you, and sounds lower-pitched as it drives farther away.
Of the planets profiled in the TESS-Keck Survey, two planets — TOI-1824 b and TOI-1798 c — stand out as examples of worlds that have such peculiar characteristics they give new insight into exoplanet classification and serve as potential touchstones for deepening astronomers’ understanding of the diverse ways planets form and evolve.
TOI-1824 b: A Superdense Sub-Neptune
One of the densest sub-Neptunes in the TESS-Keck Survey catalog, and the subject of another TESS-Keck Survey paper by University of California (UC), Santa Cruz undergraduate Sarah Lange, TOI-1824 b is unusually dense for a planet its size.
“At nearly 19 times the mass of Earth, but only 2.6 times the size of our home planet, TOI-1824 b is an exoplanet oddity,” says co-author Joseph Murphy, a graduate student at the UC Santa Cruz. “Planets similar in size typically have a mass between roughly 6 and 12 times the mass of Earth.”
One explanation for why TOI-1824 b is so massive yet appears much smaller than usual is it could have an Earth-like core surrounded by an unusually thin, hydrogen-dominated atmosphere. Another possibility is the planet has a water-rich core beneath a steam atmosphere.
“This superdense sub-Neptune may be the massive cousin of water worlds, which are small planets with high H2O content purported to exist around red dwarf stars,” says Murphy.
Red dwarfs, or M dwarf stars, are the most common star type in the Milky Way galaxy. They make ideal targets in the search for habitable worlds because M dwarfs are cooler than the Sun; this allows for liquid water to exist on planets orbiting closer to them, therefore making these systems easier to study.
TOI-1798 c: A rare, extreme Super-Earth
TOI-1798 is an orange dwarf, or K-type star, with two planets: TOI-1798 b, a sub-Neptune that has an orbit of about eight days, and TOI-1798 c, a super-Earth that is so close to its host star, it completes one orbit in less than 12 hours. This rare planetary system is one of only a few star systems known to have an inner planet with an ultra-short period (USP) orbit.
“While the majority of planets we know about today orbit their star faster than Mercury orbits the Sun, USPs take this to the extreme. TOI-1798 c orbits its star so quickly that one year on this planet lasts less than half a day on Earth. Because of their proximity to their host star, USPs are also ultra hot — receiving more than 3,000 times the radiation that Earth receives from the Sun. Existing in this extreme environment means that this planet has likely lost any atmosphere that it initially formed,” says Polanski.
With the TESS-Keck Survey’s Mass Catalog, astronomers now have a new database to explore the latest research on worlds that TESS has detected; this paves the way for studying the variables and conditions of their environments in finer detail, particularly ones that could harbor life as we know it.
“There are still thousands of unconfirmed planets from the TESS mission alone, so large releases of new planets like this will become more common as astronomers work to get a handle on the diversity of worlds we see today,” says Crossfield.
COMPANION PAPERS
Subgiants Catalog: “The TESS-Keck Survey XXI: 13 New Planets and Homogeneous Properties for 21 Subgiant Systems” (Ashley Chontos et al.)
Individual Systems:
- TOI-1347: “The TESS-Keck Survey. XII. A Dense 1.8 R⊕ Ultra-Short-Period Planet Possibly Clinging to a High-Mean-Molecular-Weight Atmosphere After the First Gyr,” The Astronomical Journal, March 2024 (Ryan Rubenzahl et al.)
- TOI-1386: “The TESS-Keck Survey. XIX. A Warm Transiting Sub-Saturn Mass Planet and a non-Transiting Saturn Mass Planet Orbiting a Solar Analog,” The Astronomical Journal, March 2024 (Michelle Hill et al.)
- TOI-1437: “The TESS-Keck Survey XXII. A sub-Neptune Orbiting TOI-1437” (Daria Pidhorodetska et al.)
- TOI-1751: “The TESS-Keck Survey. XVIII. A sub-Neptune and spurious long-period signal in the TOI-1751 system,” The Astronomical Journal, April 2024 (Anmol Desai et al.)
- TOI-1824: “The TESS-Keck Survey. VII. A Superdense Sub-Neptune Orbiting TOI-1824” (Sarah Lange et al.)
TOP PHOTO: Artist’s rendition of the variety of exoplanets featured in the new NASA TESS-Keck Survey Mass Catalog, the largest homogenous analysis of TESS planets released by any survey thus far. Credit: W. M. Keck Observatory/Adam Makarenko
ABOUT HIRES
The High-Resolution Echelle Spectrometer (HIRES) produces spectra of single objects at very high spectral resolution, yet covering a wide wavelength range. It does this by separating the light into many “stripes” of spectra stacked across a mosaic of three large CCD detectors. HIRES is famous for finding exoplanets. Astronomers also use HIRES to study important astrophysical phenomena like distant galaxies and quasars, and find cosmological clues about the structure of the early universe, just after the Big Bang.
ABOUT W. M. KECK OBSERVATORY
The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, The University of California Observatories, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.