Planet Formation Research Articles

NIKA2 observations of starless cores in Taurus and Perseus

Dusty starless cores play an important role in regulating the initial phases of the formation of stars and planets. In their interiors, dust grains coagulate and ice mantles form, thereby changing the millimeter emissivities and hence the ability to cool. We mapped four regions with more than a dozen cores in the nearby Galactic filaments of Taurus and Perseus using the NIKA2 camera at the IRAM 30-meter telescope. Combining the 1mm to 2mm flux ratio maps with dust temperature maps from Herschel allowed to create maps of the dust emissivity index β1,2 at resolutions of 2430 and 5600 a.u. in Taurus and Perseus, respectively. Here, we study the variation with total column densities and environment. β1,2 values at the core centers (Av =12 – 19 mag) vary significantly between ~ 1.1 and 2.3. Several cores show a strong rise of β1,2 from the outskirts at ~ 4 mag to the peaks of optical extinctions, consistent with the predictions of grain models and the gradual build-up of ice mantles on coagulated grains in the dense interiors of starless cores.

Flux and fluence effects on the vacuum-UV photodesorption and photoprocessing of CO2 ices.

CO2 is a major component of the icy mantles surrounding dust grains in planet and star formation regions. Understanding its photodesorption is crucial for explaining gas phase abundances in the coldest environments of the interstellar medium irradiated by vacuum-UV (VUV) photons. Photodesorption yields determined experimentally from CO2 samples grown at low temperatures (T = 15 K) have been found to be very sensitive to experimental methods and conditions. Several mechanisms have been suggested for explaining the desorption of CO2, O2 and CO from CO2 ices. In the present study, the cross-sections characterizing the dynamics of photodesorption as a function of photon fluence (determined from released molecules in the gas phase) and of ice composition modification (determined in situ in the solid phase) are compared for the first time for different photon flux conditions (from 7.3 × 1012 photon per s cm-2 to 2.2× 1014 photon per s cm-2) using monochromatic synchrotron radiation in the VUV range (on the DESIRS beamline at SOLEIL). This approach reveals that CO and O2 desorptions are decorrelated from that of CO2. CO and O2 photodesorption yields depend on photon flux conditions and can be linked to surface chemistry. In contrast, the photodesorption yield of CO2 is independent of the photon flux conditions and can be linked to bulk ice chemical modification, consistently with indirect desorption induced by an electronic transition (DIET) process.

Protostellar Chimney Flues: Are Jets and Outflows Lifting Submillimeter Dust Grains from Disks into Envelopes?

Low dust opacity spectral indices (β < 1) measured in the inner envelopes of class 0/I young stellar objects (age ∼104–5 yr) have been interpreted as the presence of (sub-)millimeter dust grains in these environments. The density conditions and the lifetimes of collapsing envelopes have proven unfavorable for the growth of solids up to millimeter sizes. As an alternative, magnetohydrodynamical simulations suggest that protostellar jets and outflows might lift grains from circumstellar disks and diffuse them in the envelope. We reframe available data for the CALYPSO sample of Class 0/I sources and show tentative evidence for an anticorrelation between the value of β 1–3 mm measured in the inner envelope and the mass-loss rate of their jets and outflows, supporting a connection between the two. We discuss the implications that dust transport from the disk to the inner envelope might have for several aspects of planet formation. Finally, we urge for more accurate measurements of both correlated quantities and the extension of this work to larger samples, necessary to further test the transport scenario.

IRAS4A1: Multiwavelength continuum analysis of a very flared Class 0 disk

Context. Understanding the formation of substructures in protoplanetary disks is vital for gaining insights into dust growth and the process of planet formation. Studying these substructures in highly embedded Class 0 objects using the Atacama Large Millimeter-submillimeter Array (ALMA), however, poses significant challenges. Nonetheless, it is imperative to do so to unravel the mechanisms and timing behind the formation of these substructures. Aims. In this study, we present high-resolution ALMA data at Bands 6 and 4 of the NGC 1333 IRAS4A Class 0 protobinary system. This system consists of two components, A1 and A2, which are separated by 1.8″ and located in the Perseus molecular cloud at a distance of ~293 pc. Methods. To gain a comprehensive understanding of the dust properties and formation of substructures in the early stages, we conducted a multiwavelength analysis of IRAS4A1. Additionally, we sought to address whether the lack of observed substructures in very young disks could be attributed to factors such as high degrees of disk flaring and large scale heights. To explore this phenomenon, we employed radiative transfer models using RADMC-3D. We employed different approaches and compared the model outcomes with our observational data. This comparison allowed us to gain insights into the challenges in detecting substructures in nascent disks and shed light on the potential influence of the dust scale height on observations of protoplanetary disks. Results. The continuum data revealed the presence of two disks-envelopes around A1 and A2, along with structure connecting the two sources. Furthermore, spectral index measurements indicate lower optical depth within the A2 disk compared to the A1 disk. Our multiwavelength analysis of A1 discovered characteristics such as high dust surface density, substantial dust mass within the disk, and elevated dust temperatures. These findings suggest the presence of large dust grains compared to the ones in the interstellar medium (ISM), greater than 100 microns in size within the region. By employing RADMC-3D, we confirmed that increasing the scale height creates the appearance of an asymmetry in protoplanetary disks. Our findings indicate that a scale height of at least 0.3 (H/R) is necessary to produce this observed asymmetry. Furthermore, while there’s no direct detection of any substructure, our models indicate that some substructure, such as a small gap, must be present. However, reproducing the intensity profile along the major and minor axes necessitates considering other processes that may be occurring within the IRAS4A1 disk. Conclusions. The result implies that disk substructures may be masked or obscured by a large scale height in combination with a high degree of flaring in Class 0 disks.

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): HD 34700 A unveils an inner ring

Context. The study of protoplanetary disks is fundamental to understand their evolution and interaction with the surrounding environment, and to constrain planet formation mechanisms. Aims. We aim to characterise the young binary system HD 34700 A, which shows a wealth of structures. Methods. Taking advantage of the high-contrast imaging instruments SPHERE at the VLT, LMIRCam at the LBT, and of ALMA observations, we analyse this system at multiple wavelengths. We study the morphology of the rings and spiral arms and the scattering properties of the dust. We discuss the possible causes of all the observed features. Results. We detect for the first time, in the Hα band, a ring extending from ~65 au to ~120 au, inside the ring which is already known from recent studies. These two have different physical and geometrical properties. Based on the scattering properties, the outer ring may consist of grains with a typical size of aout ≥ 4 µm, while the inner ring has a smaller typical size of ain ≤ 0.4 µm. Two extended logarithmic spiral arms stem from opposite sides of the disk. The outer ring appears as a spiral arm itself, with a variable radial distance from the centre and extended substructures. ALMA data confirm the presence of a millimetric dust substructure centred just outside the outer ring, and detect misaligned gas rotation patterns for HD 34700 A and B. Conclusions. The complexity of HD 34700 A, revealed by the variety of observed features, suggests the existence of one or more disk-shaping physical mechanisms. Our findings are compatible with the presence inside the disk of an as of yet undetected planet of several Jupiter masses and the system interaction with the surroundings, by means of gas cloudlet capture or flybys. Further observations with JWST/MIRI or ALMA (gas kinematics) could shed more light on them.

Dusty Plasma: A Comprehensive Review

Dusty plasmas, characterized by the presence of micron or submicron-sized particles (dust) within a plasma of ions, electrons, and neutral species, represent a complex and intriguing state of matter. This review article provides a comprehensive overview of dusty plasmas, covering their formation mechanisms, fundamental properties, theoretical models, experimental techniques, and diverse applications. Dusty plasmas occur naturally in environments such as space, planetary atmospheres, and industrial processes, where they are formed through various mechanisms including micrometeorite impacts, volcanic eruptions, and cometary outgassing. In laboratory settings, they are generated in controlled discharge chambers using radio frequency or direct current sources, facilitating studies on their dynamic interactions and behavior. The physical characteristics and behavior of dusty plasmas are influenced by a range of forces including electrostatic, ion drag, gravitational, thermophoretic, and magnetic forces. These interactions give rise to collective phenomena such as dust acoustic waves, ion-dust interactions, and the formation of ordered structures like Coulomb crystals. Understanding these phenomena is essential for applications in astrophysics, materials science, semiconductor manufacturing, and environmental research. Theoretical approaches, including fluid dynamics, kinetic theories, and Particle-in-Cell (PIC) simulations, provide insights into the complex dynamics of dusty plasmas. Experimental methods such as Langmuir probes, laser scattering, and high-speed imaging are employed to characterize their properties and behaviors. Applications of dusty plasmas span diverse fields, from studying planetary formation processes to enhancing semiconductor device fabrication and environmental monitoring. Despite significant advancements, challenges remain in accurately modeling plasma dynamics and controlling dust particles in industrial applications. Future research directions include advancing diagnostic techniques, refining theoretical models, and exploring novel applications in materials science and technology. The interdisciplinary nature of dusty plasma research ensures continued exploration and innovation in understanding and utilizing this unique state of matter.

The Influence of Cold Jupiters in the Formation of Close-in Planets. I. Planetesimal Transport

The formation of a cold Jupiter (CJ) is expected to quench the influx of pebbles and the migration of cores interior to its orbit, thus limiting the efficiency of rocky planet formation either by pebble accretion and/or orbital migration. Observations, however, show that the presence of outer CJs (>1 au and ≳0.3M Jup) correlates with the presence of inner super-Earths (at <1 au). This observation may simply be a result of an enhanced initial reservoir of solids in the nebula required to form a CJ or a yet-to-be-determined mechanism assisted by the presence of the CJ. In this work, we focus on the latter alternative and study the orbital transport of planetesimals interior to a slightly eccentric (∼0.05) CJ subject to the gravity and drag from a viscously evolving gaseous disk. We find that a secular resonance sweeping inward through the disk gradually transports rings of planetesimals when their drag-assisted orbital decay is faster than the speed of the resonance scanning. This snowplow-like process leads to large concentration (boosted by a factor of ∼10–100) of size-segregated planetesimal rings with aligned apsidal lines, making their expected collisions less destructive, due to their reduced velocity dispersion. This process is efficient for a wide range of α-disk models (and thus disk lifetimes) and Jovian masses, peaking for values ∼1–5M Jup, which are typical of observed CJs in radial velocity surveys. Overall, our work highlights the major role that the disk's gravity may have on the orbital redistribution of planetesimals, depicting a novel avenue by which CJs may enhance the formation of inner planetary systems, including super-Earths and perhaps even warm and hot Jupiters.

Gas phase ions in protoplanetary discs from collisions of solids

ABSTRACT Ionization is important for magnetohydrodynamics and chemistry in protoplanetary discs but known ionization sources are often weak along the mid-plane. We present, for the first time, data from a laboratory experiment, where we measure ions from colliding mm-basalt grains emitted into the surrounding gas phase. This positive detection implies that very basic collisions in early phases of planet formation are sources of ionization. The mid-plane of protoplanetary discs might be ionized despite the lack of intense radiation sources.

Update on WASP-19

Tidal interaction between a star and a close-in massive exoplanet causes the planetary orbit to shrink and eventually leads to tidal disruption. Understanding orbital decay in exoplanetary systems is crucial for advancing our knowledge of planetary formation and evolution. Moreover, it sheds light on the broader question of the long-term stability of planetary orbits and the intricate interplay of gravitational forces within stellar systems. Analyzing Transiting Exoplanet Survey Satellite (TESS) data for the ultra-short period gas giant WASP-19, we aim to measure orbital period variations and constrain the stellar tidal quality parameter. For this, we fitted the TESS observations together with two WASP-19 transits observed using the Las Cumbres Observatory Global Telescope (LCOGT) and searched for orbital decay in combination with previously published transit times. As a result, we find a deviation from the constant orbital period at the 7σ level. The orbital period changes at a rate of P˙=−3.7±0.5msyear−1, which translates into a tidal quality factor of Q★′=(7±1)×105. We additionally modeled WASP-19 b’s phase curve using the new TESS photometry and obtained updated values for the planet’s eclipse depth, dayside temperature, and geometric albedo. We estimate an eclipse depth of 520±60 ppm, which is slightly higher than previous estimates and corresponds to a dayside brightness temperature of 2400±60 K and geometric albedo of 0.20±0.04.

Discovery of Two Different Full Disk Evolutionary Patterns of M-type T Tauri Stars with LAMOST DR8

The full disk, full of gas and dust, determines the upper limit of planet masses, and its lifetime is critical for planet formation, especially for giant planets. In this work, we studied the evolutionary timescales of the full disks of T Tauri stars (TTSs) and their relations to accretion. Combined with Gaia EDR3, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer data, 1077 disk-bearing TTS candidates were found in LAMOST DR8, and stellar parameters were obtained. Among them, 783 are newly classified by spectra as classical T Tauri stars (CTTSs; 169) or weak-lined T Tauri stars (WTTSs). Based on EW and FWHM of Hα, 157 TTSs in accretion were identified, with ∼82% also having full disks. For TTSs with M < 0.35M ☉, about 80% seem to already lose their full disks at ∼0.1 Myr, which may explain their lower mass, while the remaining 20% with full disks evolve at similar rates of non-full disks within 5 Myr, allowing enough time and material to form giant planets. The fraction of accreting TTSs to disk-bearing TTSs is stable at ∼10% and can last ∼5–10 Myr, suggesting that full disks and accretion evolve with similar rates as non-full disks. For TTSs with M > 0.35 M ☉, almost all full disks can survive more than 0.1 Myr, most for 1 Myr and some even for 20 Myr. For TTSs with M > 0.35 M ☉, almost all full disks can survive more than 0.1 Myr, most for 1 Myr, and some even for 20 Myr, which implies planets are more likely to be formed in their disks than those of M < 0.35 M ☉, and thus M dwarfs with M > 0.35 M ☉ can have more planets. The fraction of full-disk TTSs to disk-bearing TTSs decreases with age following the relation f ∝ t −0.35, and similar relations existed in the fraction of accreting TTSs and the fraction of full-disk CTTSs, suggesting faster full disks and accretion evolution than non-full disks. For full-disk stars, the ratio of accretion of lower-mass stars is systematically lower than that of higher-mass stars, confirming the dependence of accretion on stellar mass, which may be reflective of an observational bias in the detection of accretion levels, with the lower-mass stars crossing below the detection threshold earlier than higher-mass stars.

Particle Clustering in Turbulence: Prediction of Spatial and Statistical Properties with Deep Learning

We investigate the utility of deep learning for modeling the clustering of particles that are aerodynamically coupled to turbulent fluids. Using a Lagrangian particle module within the Athena++ hydrodynamics code, we simulate the dynamics of particles in the Epstein drag regime within a periodic domain of isotropic forced hydrodynamic turbulence. This setup is an idealized model relevant to the collisional growth of micron- to millimeter-sized dust particles in early-stage planet formation. The simulation data are used to train a U-Net deep-learning model to predict gridded three-dimensional representations of the particle density and velocity fields, given as input the corresponding fluid fields. The trained model qualitatively captures the filamentary structure of clustered particles in a highly nonlinear regime. We assess model fidelity by calculating metrics of the density field (the radial distribution function) and of the velocity field (the relative velocity and the relative radial velocity between particles). Although trained only on the spatial fields, the model predicts these statistical quantities with errors that are typically <10%. Our results suggest that, given appropriately expanded training data, deep learning could complement direct numerical simulations in predicting particle clustering within turbulent flows.

Insights into the first and second hydrostatic core stages from numerical simulations

The theory of how low mass stars form from the collapse of a dense molecular cloud core has been well-established for decades. Thanks to significant progress in computing and numerical modelling, more physical models have been developed and a wider parameter space explored to understand the early stages of star formation more fully. In this review, I describe the expected physical properties of the first and second core stages and how the inclusion of different physics affects those predicted characteristics. I provide an overview of chemical models and synthetic observations, looking towards the positive identification of the first core in nature, which remains elusive. However, there are a few likely candidate first cores, which are listed, and I briefly discuss the recent progress in characterising the youngest protostellar sources. Chemistry will be instrumental in the firm identification of the first core so we require robust theoretical predictions of the chemical evolution of protostellar cores, especially of the first and second core outflows. Looking ahead, simulations can shed light on how the protostellar collapse phase shapes the evolution of the protostellar disc. Simulations of dust evolution during protostellar core collapse show there is significant enhancement in grain size and abundance towards the centre of the core. Chemical models show that the warm, dense conditions of the first core drive chemical evolution. There is a wide scope for further study of the role that the first and second core stages play in determining the structure and composition of the protostellar disc and envelope and, of course, the eventual influence on the formation of planets.

Viscous heating as the dominant heat source inside the water snowline of V883 Ori

ABSTRACT FU Orionis-type objects (FUors) are embedded protostars that undergo episodes of high accretion, potentially indicating a widespread but poorly understood phase in the formation of low-mass stars. Gaining a better understanding of the influence exerted by these outbursts on the evolution of the surrounding protoplanetary disc may hold significant implications for the process of planet formation and the evolution of disc chemistry. The heating due to outbursts of high accretion in FUors pushes the snowlines of key volatiles farther out in the disc, so they become easier to observe and study. Among the known FUors, V883 Ori is of particular interest. V883 Ori was the first FUor to show indirect evidence of a resolvable snowline beyond 40 au. By introducing a radial-dependent model of this source including viscous heating, we show that active heating is needed to reproduce the steep thermal profile of dust in the inner disc of V883 Ori. Our disc modelling combines the effect of stellar irradiation and the influence on the disc shape caused by the outburst of accretion. The accuracy of our model is tested by comparing synthetic Atacama Larga Millimeter Array images with continuum observations of V883 Ori, showing that the model successfully reproduces the 1.3 mm emission of V883 Ori at high spatial resolution. Our final predictions underline the importance of viscous heating as a predominant heat source for this type of object, changing the physical conditions (shape and temperature) of the disc, and influencing its evolution.

Shaping the CO snowline in protoplanetary disks

Context. Characterizing the dust thermal structure in protoplanetary disks is a fundamental task because the dust surface temperature can affect both the planetary formation and the chemical evolution. Because the temperature depends on many parameters, including the grain size, it can be challenging to properly model the grain temperature structure. Many chemistry disk models usually employ a sophisticated single dust structure designed to reproduce the effect of a realistic population presumably composed of a large diversity of sizes. This generally represents a good approximation in most cases. Nonetheless, it dilutes the effects of the complex radiative interactions between the different grain populations on the resulting dust temperature, and thus, the chemistry. Aims. We seek to show that the radiative interactions between dust grains of different sizes can induce a nontrivial dust temperature structure that cannot be reproduced by a single dust population and that can significantly affect the chemical outcome. Methods. The disk thermal structures were computed using the Monte Carlo radiative transfer code RADMC-3D. The thermal structures were postprocessed using the gas-grain code NAUTILUS to calculate the evolution of the chemical abundance. Results. We find that simultaneously using at least two independent dust grain populations in disk models produces a complex temperature structure due to the starlight that is intercepted by the upper layers of the disk. In particular, we find that micron-sized dust grains are warmer than larger grains and can even show a radial temperature bump in some conditions. This dust temperature spread between the grain populations results in the segregation of the CO snowline and in an unexpected CO gas hole in the midplane. We compare the results with observed close to edge-on class I/II disks. Conclusions. Our study shows that the size dependence of the dust temperature significantly impacts the chemistry, and that two dust populations at least are required to account for this property of the thermal structure in protoplanetary disk models over a wide range of disk masses and dust properties.

A low-mass star with a large-mass planet.

A large planet orbiting a very low-mass star challenges theories of planet formation.

Water-rich Disks around Late M Stars Unveiled: Exploring the Remarkable Case of Sz 114

We present an analysis of the JDISCS JWST/MIRI-MRS spectrum of Sz 114, an accreting M5 star surrounded by a large dust disk with a shallow gap at ∼39 au. The spectrum is molecule-rich; we report the detection of water, CO, CO2, HCN, C2H2, and H2. The only identified atomic/ionic transition is from [Ne ii] at 12.81 μm. A distinct feature of this spectrum is the forest of water lines with the 17.22 μm emission surpassing that of most mid-to-late M star disks by an order of magnitude in flux and aligning instead with disks of earlier-type stars. Moreover, the flux ratios of C2H2/H2O and HCN/H2O in Sz 114 also resemble those of earlier-type disks, with a slightly elevated CO2/H2O ratio. While accretional heating can boost all infrared lines, the unusual properties of Sz 114 could be explained by the young age of the source, its formation under unusual initial conditions (a large massive disk), and the presence of dust substructures. The latter delays the inward drift of icy pebbles and helps preserve a lower C/O ratio over an extended period. In contrast, mid-to-late M-star disks—which are typically faint, small in size, and likely lack significant substructures—may have more quickly depleted the outer icy reservoir and already evolved out of a water-rich inner disk phase. Our findings underscore the unexpected diversity within mid-infrared spectra of mid-to-late M-star disks, highlighting the need to expand the observational sample for a comprehensive understanding of their variations and thoroughly test pebble drift and planet formation models.

Stability of coorbital planets around binaries

In previous hydrodynamical simulations, we found a mechanism for nearly circular binary stars, such as Kepler-413, to trap two planets in a stable 1:1 resonance. Therefore, the stability of coorbital configurations becomes a relevant question for planet formation around binary stars. For this work, we investigated the coorbital planet stability using a Kepler-413 analogue as an example and then expanded the parameters to study a general n-body stability of planet pairs in eccentric horseshoe orbits around binaries. The stability was tested by evolving the planet orbits for 105 binary periods with varying initial semi-major axes and planet eccentricities. The unstable region of a single circumbinary planet is used as a comparison to the investigated coorbital configurations in this work. We confirm previous findings on the stability of single planets and find a first order linear relation between the orbit eccentricity ep and pericentre to identify stable orbits for various binary configurations. Such a linear relation is also found for the stability of 1:1 resonant planets around binaries. Stable orbits for eccentric horseshoe configurations exist with a pericentre closer than seven binary separations and, in the case of Kepler-413, the pericentre of the first stable orbit can be approximated by rc,peri = (2.90 ep + 2.46) abin.

A Neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models.

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.

Planetary system architectures with low-mass inner planets

Context. The discovery of planets orbiting at less than 1 au from their host star and less massive than Saturn in various exoplanetary systems revolutionized our theories of planetary formation. The fundamental question is whether these close-in low-mass planets could have formed in the inner disk interior to 1 au, or whether they formed further out in the planet-forming disk and migrated inward. Exploring the role of additional giant planet(s) in these systems may help us to pinpoint their global formation and evolution. Aims. We searched for additional substellar companions by using direct imaging in systems known to host close-in small planets. The use of direct imaging complemented by radial velocity and astrometric detection limits enabled us to explore the giant planet and brown dwarf demographics around these hosts to investigate the potential connection between both populations. Methods. We carried out a direct imaging survey with SPHERE at VLT to look for outer giant planets and brown dwarf companions in 27 systems hosting close-in low-mass planets discovered by radial velocity. Our sample is composed of very nearby (&lt;20 pc) planetary systems, orbiting G-, K-, and M-type mature (0.5–10 Gyr) stellar hosts. We performed homogeneous direct imaging data reduction and analysis to search for and characterize point sources, and derived robust statistical detection limits. The final direct imaging detection performances were globally considered together with radial velocity and astrometric sensitivity. Results. Of 337 point-source detections, we do not find any new bound companions. We recovered the emblematic very cool T-type brown dwarf GJ 229 B. Our typical sensitivities in direct imaging range from 5 to 30 MJup beyond 2 au. The non-detection of massive companions is consistent with predictions based on models of planet formation by core accretion. Our pilot study opens the way to a multi-technique approach for the exploration of very nearby exoplanetary systems with future ground-based and space observatories.

Planetary companions orbiting the M dwarfs GJ 724 and GJ 3988

We report the discovery of two exoplanets around the M dwarfs GJ 724 and GJ 3988 using the radial velocity (RV) method. We obtained a total of 153 3.5 m Calar Alto/CARMENES spectra for both targets and measured their RVs and activity indicators. We also added archival ESO/HARPS data for GJ 724 and infrared RV measurements from Subaru/IRD for GJ 3988. We searched for periodic and stable signals to subsequently construct Keplerian models, considering different numbers of planets, and we selected the best models based on their Bayesian evidence. Gaussian process (GP) regression was included in some models to account for activity signals. For both systems, the best model corresponds to one single planet. The minimum masses are 10.75−0.87+0.96 and 3.69−0.41+0.42 Earth-masses for GJ 724 b and GJ 3988 b, respectively. Both planets have short periods (P &lt; 10 d) and, therefore, they orbit their star closely (a &lt; 0.05 au). GJ 724 b has an eccentric orbit (e = 0.577−0.052+0.055), whereas the orbit of GJ 3988 b is circular. The high eccentricity of GJ 724 b makes it the most eccentric single exoplanet (to this date) around an M dwarf. Thus, we suggest a further analysis to understand its configuration in the context of planetary formation and architecture. In contrast, GJ 3988 b is an example of a common type of planet around mid-M dwarfs.