Exomoon Archives

Schematic loosely sketching the parameter space accessible using the astrometric technique as compared to the transit methods of exomoon detection in the context of the moon survival rate as a function of planetary orbital period. Additionally, the expected peak of the gas giant occurrence around the water ice line as well as the predicted ELT planet detection range are indicated. -- astro-ph.IM

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Hunting Exomoons With A Kilometric Baseline Interferometer

by Keith CowingDecember 25, 2025December 25, 2025

Despite numerous search campaigns based on a diverse set of observational techniques, exomoons – prospective satellites of extrasolar planets – remain an elusive and hard-to-pin-down class of objects.

Final semi-major axes of satellites versus their initial orbital distance (in Hill radii) for TRAPPIST-1 e. -- astro-ph.EP

Exoplanets, -moons, -comets, Status Report, TRAPPIST-1

Orbital Stability Of Moons Around The TRAPPIST-1 Planets

by Keith CowingDecember 23, 2025December 23, 2025

We investigate the dynamical stability of potential satellites orbiting the seven planets of the TRAPPIST-1 system using a suite of N-body simulations.

Upper mass limits for a potential lunar companion to β Pic b as a function of orbital period. The color is proportional to the density of MCMC posterior samples, and the solid curves indicate the 68%, 95%, and 99.7% confidence intervals. The upper panel covers longer orbital periods (≲ 1450 days, within the dynamical stability limit), where companions more massive than ∼ 0.5 MJup (∼ 60 M⊕) are excluded. The dashed line marks the Earth–Moon mass ratio scaled to β Pic b, and the solid green curve shows the moon/binary planet boundary from Stern & Levison (2002), which marks the theoretical separation between large moons and binary planetary systems based on mass ratios and orbital stability criteria. The lower panel zooms in on short orbital periods (≲ 50 days), where the constraints are weaker. The dashed line indicates the Pluto–Charon mass ratio, while the solid green curve again shows the Stern & Levison (2002) moon/binary planet boundary. -- astro-ph.EP

Astronomy & Telescopes, Beta Pictoris, Exoplanets, -moons, -comets, Status Report, Stellar Cartography

First Astrometric Limits On Binary Planets And Exomoons Orbiting β Pictoris b

by Keith CowingDecember 11, 2025December 10, 2025

The search for exomoons, or moons in other star systems, has attracted significant interest in recent years, driven both by advancements in detection sensitivity and by the expanding population of […]

Analytical predictions for the astrometric effect of a moon with varying mass and distance to HD 206893 B. GRAVITY could in principle detect moons lower than a Neptune mass at larger periods. The fit of the GRAVITY data is shown as a green point assuming the mass and period as upper limits in our tentative detection. The orange area shows the plausible parameter space where a moon could be located, and still be potentially detectable with GRAVITY assuming an astrometric accuracy of 10 µas (see section 3.3). -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Exomoon Search With VLTI/GRAVITY Around The Substellar Companion HD 206893 B

by Keith CowingNovember 26, 2025June 10, 2026

Direct astrometric detection of exomoons remains unexplored. This study presents the first application of high-precision astrometry to search for exomoons around substellar companions.

Astronomy & Telescopes, Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Imaging & Spectroscopy, Status Report

A JWST Transit Of A Jupiter Analog: II. A Search For Exomoons

by Keith CowingNovember 22, 2025June 10, 2026

We present a search for exomoons around the Jupiter-like exoplanet Kepler-167e using a NIRSpec JWST transit.

Self-consistent obliquity and spin rate evolution for several realizations of exoplanet Kepler-79 d. Trajectories go from right to left. The planet is initalized with a spin rate of 7.5 hours (i.e. ω/np ≈ 170) and different obliquities equispaced in cos θ. A moon with mass mm/mp = 10−6 is initialized at a distance am = 4 Rp. Integrations are stopped when the moon’s pericenter goes below the Roche limit. The three largest resonances reacheable by Kepler-79 d appear in red, blue, and green. The hatched blue zone is the E1 region. For definitiveness, the resonances and E1 region in the background are drawn assuming that the moon is on a circular orbit at am = 4 Rp; for moons that do not cross the E1 region, this remains approximatively true during the whole simulation. -- astro-ph.EP

Astrogeology, Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Status Report, Stellar Cartography

The Coupled Tidal Evolution of the Moons and Spins of Warm Exoplanets

by Keith CowingNovember 10, 2025

Context: The Solar System giant planets harbour a wide variety of moons. Moons around exoplanets are plausibly similarly abundant, even though most of them are likely too small to be […]

The time-series spectra with the full wavelength range (in microns) of the observations shown on the x-axis, observation time (in hours) on the y-axis, and a color bar representing the amplitude variability for any given flux value as a percent deviation from the mean. The 2 wavelength regions used to construct the light curves are shown where each has a distinct variability pattern. Region 1: negative, positive, negative positive amplitude; Region 2: negative, positive amplitude. The picket fence pattern (narrow striping) visible in region 2 is due to CO absorption. -- astro-ph.SR

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

A Deep Search For Exomoons Around WISE 0855 With JWST

by Keith CowingNovember 7, 2025November 7, 2025

JWST is collecting time-series observations of many free-floating planets (FFPs) to study their weather, but these light curves are the ideal datasets to search for exomoons that transit the FFP […]

An artistic rendering of a dust and gas disk encircling the young exoplanet, CT Cha b, 625 light-years from Earth. Spectroscopic data from NASA’s James Webb Space Telescope suggests the disk contains the raw materials for moon formation: diacetylene, hydrogen cyanide, propyne, acetylene, ethane, carbon dioxide, and benzene. The planet appears at lower right, while its host star and surrounding circumstellar disk are visible in the background. Illustration: NASA, ESA, CSA, STScI, Gabriele Cugno (University of Zürich, NCCR PlanetS), Sierra Grant (Carnegie Institution for Science), Joseph Olmsted (STScI), Leah Hustak (STScI)

Astrochemistry, Astrogeology, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Callisto, Exoplanets, -moons, -comets, Ganymede, Icy Worlds, Imaging & Spectroscopy, Press Release

Webb Studies A Carbon-rich Moon-Forming Disk Around A Massive Planet

by Keith CowingSeptember 30, 2025September 30, 2025

NASA’s James Webb Space Telescope has provided the first direct measurements of the chemical and physical properties of a potential moon-forming disk encircling a large exoplanet. The carbon-rich disk surrounding […]

Signal amplitudes in the vicinity of the putative exomoon around β Pic b suggested by Poon et al. (2024) as a function of moon mass and semi-major axis for RV studies on the left and astrometric searches on the right. The grey shaded region is the parameter space where a P24- moon is likely to reside if it is indeed real. The dashed lines indicate contours delineating the provided signal strengths. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Habitable Zones, Status Report

Astrometric Exomoon Detection By Means Of Optical Interferometry

by Keith CowingSeptember 27, 2025September 27, 2025

Context: With no conclusive detection to date, the search for exomoons, satellites of planets orbiting other stars, remains a formidable challenge. Detecting these objects, compiling a population-level sample and constraining […]

Physical parameters of the simulated events with and without detected moons. In each panel, the grey points show the events our simulation where a moon was not detected, i.e., these are the distributions of the physical parameters of the planets and moons we simulated. The stars show events where the moon was detected. The blue markers indicate the locations of the light curves shown in Figure 6 in these parameter spaces. Each panel shows (a) the planet/star mass ratio versus planet projected separation in units of the Einstein ring radius of the system. The lines indicate the boundaries of the resonant caustic region that we exclude from our sample; (b) the planet mass versus the planet semimajor axis; (c) moon/planet mass ratio versus the moon-planet separation in units of the Einstein ring radius of the planet; (d) moon mass versus semimajor axis of the moon in units of the Hill radius. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Gas Giants, Imaging & Spectroscopy, Status Report

Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. III. Detectability of Giant Exomoons of Wide Separation Giant Planets

by Keith CowingSeptember 7, 2025September 7, 2025

Roman should be sensitive to lenses with mass down to ~ 0.02 M⊕, or roughly the mass of Ganymede. Thus the detection of moons with masses similar to the giant […]