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Register a new userDiscovery of a hot, transiting, Earth-sized planet and a second temperate, non-transiting planet around the M4 dwarf GJ 3473 (TOI-488)
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We present the confirmation and characterisation of GJ 3473 b (G 50--16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal ($P=1.1980035pm0.0000018mathrm{,d}$) was first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass, $M_b = 1.86pm0.30,mathrm{M_oplus},$ and radius, $R_b = {1.264pm0.050},mathrm{R_oplus}$. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass, $M_c sin{i} = {7.41pm0.91},mathrm{M_oplus,}$ and orbital period, $P_c={15.509pm0.033},mathrm{d}$. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy.
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We report the discovery of a transiting, temperate, Neptune-sized exoplanet orbiting the nearby ($d$ = 27.5 pc), M3V star TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program. Combining the photometric data sets, we find that the newly discovered planet has a radius of 3.65$^{+0.16}_{-0.15}$ R$_{oplus}$, and an orbital period of 24.246 days. Radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5$pm$3.3 M$_{oplus}$. With an equilibrium temperature of just 330K TOI-1231 b is one of the coolest small planets accessible for atmospheric studies thus far, and its host stars bright NIR brightness (J=8.88, K$_{s}$=8.07) make it an exciting target for HST and JWST. Future atmospheric observations would enable the first comparative planetology efforts in the 250-350 K temperature regime via comparisons with K2-18 b. Furthermore, TOI-1231s high systemic radial velocity (70.5 kms) may allow for the detection of low-velocity hydrogen atoms escaping the planet by Doppler shifting the H I Ly-alpha stellar emission away from the geocoronal and ISM absorption features.
We report the detection of a transiting Earth-size planet around GJ 357, a nearby M2.5V star, using data from the Transiting Exoplanet Survey Satellite (TESS). GJ 357 b (TOI-562.01) is a transiting, hot, Earth-sized planet (Teq=525+-11 K) with a radius of Rb=1.217+-0.084 Re and an orbital period of Pb=3.93 d. Precise stellar radial velocities from CARMENES and PFS, as well as archival data from HIRES, UVES, and HARPS also display a 3.93-day periodicity, confirming the planetary nature and leading to a planetary mass of Mb=1.84+-0.31 Me. In addition to the radial velocity signal for GJ 357 b, more periodicities are present in the data indicating the presence of two further planets in the system: GJ 357 c, with a minimum mass of Mc=3.40+-0.46 Me in a 9.12 d orbit, and GJ 357 d, with a minimum mass of Md=6.1+-1.0 Me in a 55.7 d orbit inside the habitable zone. The host is relatively inactive and exhibits a photometric rotation period of Prot=78+-2 d. GJ 357 b is to date the second closest transiting planet to the Sun, making it a prime target for further investigations such as transmission spectroscopy. Therefore, GJ 357 b represents one of the best terrestrial planets suitable for atmospheric characterization with the upcoming JWST and ground-based ELTs.
Kepler-730 is a planetary system hosting a statistically validated hot Jupiter in a 6.49-day orbit and an additional transiting candidate in a 2.85-day orbit. We use spectroscopic radial velocities from the APOGEE-2N instrument, Robo-AO contrast curves, and Gaia distance estimates to statistically validate the planetary nature of the additional Earth-sized candidate. We perform astrophysical false positive probability calculations for the candidate using the available Kepler data and bolster the statistical validation by using radial velocity data to exclude a family of possible binary star solutions. Using a radius estimate for the primary star derived from stellar models, we compute radii of $1.100^{+0.047}_{-0.050} R_{Jup}$ and $0.140pm0.012 R_{Jup}$ ($1.57pm0.13 R_{oplus}$) for Kepler-730b and Kepler-730c, respectively. Kepler-730 is only the second compact system hosting a hot Jupiter with an inner, transiting planet.
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We report the confirmation of a transiting planet around the bright, inactive M0.5 V star TOI-1235 (TYC 4384-1735-1, V = 11.5 mag), whose transit signal was detected in the photometric time series of Sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise radial velocity measurements with CARMENES and HARPS-N spectrographs. A comparison of the properties derived for TOI-1235 bs with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than Earths. In particular, we measure a mass of M_p = 5.9+/-0.6 M_Earth and a radius of R_p = 1.69+/-0.08 R_Earth, which together result in a density of rho_p = 6.7+1.3-1.1 g/cm3. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass puts our discovery in the radius gap, a transition region between rocky planets and planets with significant atmospheric envelopes, with few known members. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 R_Earth or larger at the insolation levels received by TOI-1235 b (~60 S_Earth), which makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.
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