Abstract Recent discoveries of transiting giant exoplanets around M-dwarf stars (GEMS), aided by the all-sky coverage of TESS, are starting to stretch theories of planet formation through the ...core-accretion scenario. Recent upper limits on their occurrence suggest that they decrease with lower stellar masses, with fewer GEMS around lower-mass stars compared to solar-type. In this paper, we discuss existing GEMS both through confirmed planets, as well as protoplanetary disk observations, and a combination of tests to reconcile these with theoretical predictions. We then introduce the Searching for GEMS survey, where we utilize multidimensional nonparameteric statistics to simulate hypothetical survey scenarios to predict the required sample size of transiting GEMS with mass measurements to robustly compare their bulk-density with canonical hot Jupiters orbiting FGK stars. Our Monte Carlo simulations predict that a robust comparison requires about 40 transiting GEMS (compared to the existing sample of ∼15) with 5 σ mass measurements. Furthermore, we discuss the limitations of existing occurrence estimates for GEMS and provide a brief description of our planned systematic search to improve the occurrence rate estimates for GEMS.
Abstract We confirm TOI-4201 b as a transiting Jovian-mass planet orbiting an early M dwarf discovered by the Transiting Exoplanet Survey Satellite. Using ground-based photometry and precise radial ...velocities from NEID and the Planet Finder Spectrograph, we measure a planet mass of 2.59 − 0.06 + 0.07 M J , making this one of the most massive planets transiting an M dwarf. The planet is ∼0.4% of the mass of its 0.63 M ⊙ host and may have a heavy-element mass comparable to the total dust mass contained in a typical class II disk. TOI-4201 b stretches our understanding of core accretion during the protoplanetary phase and the disk mass budget, necessitating giant planet formation to take place either much earlier in the disk lifetime or perhaps through alternative mechanisms like gravitational instability.
Theories of planet formation predict that low-mass stars should rarely host exoplanets with masses exceeding that of Neptune. We used radial velocity observations to detect a Neptune-mass exoplanet ...orbiting LHS 3154, a star that is nine times less massive than the Sun. The exoplanet’s orbital period is 3.7 days, and its minimum mass is 13.2 Earth masses. We used simulations to show that the high planet-to-star mass ratio (>3.5 × 10
−4
) is not an expected outcome of either the core accretion or gravitational instability theories of planet formation. In the core-accretion simulations, we show that close-in Neptune-mass planets are only formed if the dust mass of the protoplanetary disk is an order of magnitude greater than typically observed around very low-mass stars.
Editor’s summary
Planets form in protoplanetary disks of gas and dust around young stars that are undergoing their own formation process. The amount of material in the disk determines how big the planets can grow. Stefánsson
et al
. observed a nearby low-mass star using near-infrared spectroscopy. They detected Doppler shifts due to an orbiting exoplanet of at least 13 Earth masses, which is almost the mass of Neptune. Theoretical models do not predict the formation of such a massive planet around a low-mass star (see the Perspective by Masset). The authors used simulations to show that its presence could be explained if the protoplanetary disk were 10 times more massive than expected for the host star. —Keith T. Smith
A low-mass star hosts a giant planet that is more massive than expected from theoretical models of planet formation
Recent discoveries of transiting giant exoplanets around M-dwarf stars (GEMS), aided by the all-sky coverage of TESS, are starting to stretch theories of planet formation through the core-accretion ...scenario. Recent upper limits on their occurrence suggest that they decrease with lower stellar masses, with fewer GEMS around lower-mass stars compared to solar-type. In this paper, we discuss existing GEMS both through confirmed planets, as well as protoplanetary disk observations, and a combination of tests to reconcile these with theoretical predictions. We then introduce the \textit{Searching for GEMS} survey, where we utilize multi-dimensional nonparameteric statistics to simulate hypothetical survey scenarios to predict the required sample size of transiting GEMS with mass measurements to robustly compare their bulk-density with canonical hot-Jupiters orbiting FGK stars. Our Monte-Carlo simulations predict that a robust comparison requires about 40 transiting GEMS (compared to the existing sample of \(\sim\) 15) with 5-\(\sigma\) mass measurements. Furthermore, we discuss the limitations of existing occurrence estimates for GEMS, and provide a brief description of our planned systematic search to improve the occurrence rate estimates for GEMS.
We characterize the LHS 1610 system, a nearby (\(d=9.7\) pc) M5 dwarf hosting a brown dwarf in a \(10.6\) day, eccentric (\(e \sim 0.37\)) orbit. A joint fit of the available Gaia two-body solution, ...discovery radial velocities (RVs) from TRES, and new RVs obtained with the Habitable-zone Planet Finder, yields an orbital inclination of \(117.2\pm0.9^\circ\) and a mass constraint of \(50.9\pm0.9\) M\(_J\). This gives LHS 1610 b the second most precise mass of brown dwarfs orbiting M stars within 25pc. We highlight a discrepancy between the Gaia two-body solution eccentricity (\(e=0.52 \pm 0.03\)) and that from the RVs (\(e=0.3702\pm0.0003\)), which requires the astrometric time-series release (Gaia DR4) for further diagnostics. With a flare rate of \(0.28\pm 0.07\) flares/day from TESS photometry, and a rotation period of \(84 \pm 8\) days, LHS 1610 joins other mid M stars -- including Proxima Centauri and YZ Ceti -- as nearby mid M dwarfs with flare rates on the higher end for their long rotation periods. These stars are promising candidates for searching for sub-Alfvénic star-companion interactions, raising the question whether LHS 1610 b could be driving the flares on its host star. However, the available TESS photometry is insufficient to confirm or rule out any orbital phase-dependence of the flares. We show that the LHS 1610 system, as a nearby mid M star with a large, short-period companion, is a promising target to look for evidence of star-companion interactions or aural emission from the brown dwarf at radio wavelengths.
We confirm TOI-4201 b as a transiting Jovian mass planet orbiting an early M dwarf discovered by the Transiting Exoplanet Survey Satellite. Using ground based photometry and precise radial velocities ...from NEID and the Planet Finder Spectrograph, we measure a planet mass of 2.59\(^{+0.07}_{-0.06}\) M\(_{J}\), making this one of the most massive planets transiting an M-dwarf. The planet is \(\sim\)0.4\% the mass of its 0.63 M\(_{\odot}\) host and may have a heavy element mass comparable to the total dust mass contained in a typical Class II disk. TOI-4201 b stretches our understanding of core-accretion during the protoplanetary phase, and the disk mass budget, necessitating giant planet formation to either take place much earlier in the disk lifetime, or perhaps through alternative mechanisms like gravitational instability.
In current theories of planet formation, close-orbiting planets as massive as Neptune are expected to be very rare around low-mass stars. We report the discovery of a Neptune-mass planet orbiting the ...`ultracool' star LHS 3154, which is nine times less massive than the Sun. The planet's orbital period is 3.7 days and its minimum mass is 13.2 Earth masses, giving it the largest known planet-to-star mass ratio among short-period planets (\(<\)\,100 days) orbiting ultracool stars. Both the core accretion and gravitational instability theories for planet formation struggle to account for this system. In the core-accretion scenario, in particular, the dust mass of the protoplanetary disk would need to be an order of magnitude higher than typically seen in protoplanetary disk observations of ultracool stars.
The Habitable Zone Planet Finder Over the past decade, our team designed and built a new instrument at Penn State capable of detecting the light from these dim, cool stars at wavelengths beyond the ...sensitivity of the human eye – in the near-infrared – where such cool stars emit most of their light. “Exoplanet” is a combination of the words extrasolar and planet, so the term applies to any planet-sized body in orbit around a star that isn’t Earth’s Sun. Astronomers know, from discoveries made with Habitable Zone Planet Finder and other instruments, that giant planets in close-in orbits around the most massive M stars are at least 10 times rarer than those around Sunlike stars.
