The CHaracterising ExOPlanet Satellite (CHEOPS) is a partnership between the European Space Agency and Switzerland with important contributions by 10 additional ESA member States. It is the first ...S-class mission in the ESA Science Programme. CHEOPS has been flying on a Sun-synchronous low Earth orbit since December 2019, collecting millions of short-exposure images in the visible domain to study exoplanet properties.
A small yet increasing fraction of CHEOPS images show linear trails caused by resident space objects crossing the instrument field of view. CHEOPS’ orbit is indeed particularly favourable to serendipitously detect objects in its vicinity as the spacecraft rarely enters the Earth's shadow, sits at an altitude of 700 km, and observes with moderate phase angles relative to the Sun. This observing configuration is quite powerful, and it is complementary to optical observations from the ground.
To characterize the population of satellites and orbital debris observed by CHEOPS, all and every science images acquired over the past 3 years have been scanned with a Hough transform algorithm to identify the characteristic linear features that these objects cause on the images. Thousands of trails have been detected. This statistically significant sample shows interesting trends and features such as an increased occurrence rate over the past years as well as the fingerprint of the Starlink constellation. The cross-matching of individual trails with catalogued objects is underway as we aim to measure their distance at the time of observation and deduce the apparent magnitude of the detected objects.
As space agencies and private companies are developing new space-based surveillance and tracking activities to catalogue and characterize the distribution of small debris, the CHEOPS experience is timely and relevant. With the first CHEOPS mission extension currently running until the end of 2026, and a possible second extension until the end of 2029, the longer time coverage will make our dataset even more valuable to the community, especially for characterizing objects with recurrent crossings.
We report the discovery of the 1.008-day, ultra-short period (USP) super-Earth HD 213885b (TOI-141b) orbiting the bright (\(V=7.9\)) star HD 213885 (TOI-141, TIC 403224672), detected using photometry ...from the recently launched TESS mission. Using FEROS, HARPS and CORALIE radial-velocities, we measure a precise mass of \(8.8\pm0.6\) \(M_\oplus\) for this \(1.74 \pm 0.05\) \(R_\oplus\) exoplanet, which provides enough information to constrain its bulk composition, which is similar to Earth's but enriched in iron. The radius, mass and stellar irradiation of HD 213885b are, given our data, very similar to 55 Cancri e, making this exoplanet a good target to perform comparative exoplanetology of short period, highly irradiated super-Earths. Our precise radial-velocities reveal an additional \(4.78\)-day signal which we interpret as arising from a second, non-transiting planet in the system, HD 213885c (TOI-141c), whose minimum mass of \(19.95\pm 1.4\) \(M_\oplus\) makes it consistent with being a Neptune-mass exoplanet. The HD 213885 system is very interesting from the perspective of future atmospheric characterization, being the second brightest star to host an ultra-short period transiting super-Earth (with the brightest star being, in fact, 55 Cancri). Prospects for characterization with present and future observatories are discussed.
To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision is essential. In this paper, we report the ...discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15 %. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31^{+0.04}_{-0.03} MJ, 1.13^{+0.03}_{-0.03} RJ, 0.22^{-0.03}_{-0.02} rhoJ and 1, 290^{+20}_{-10} K, and 0.39^{+0.02}_{-0.02} MJ, 1.55^{+0.10}_{-0.08} RJ, 0.11^{+0.02}_{-0.02} rhoJ and 1, 700^{+40}_{-40} K, respectively. Their host stars are early G type stars (with magV ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a Super-Neptune orbiting a K type star (magV = 11.6) . It has a mass of 0.128^{+0.010}_{-0.009} MJ, a radius of 0.51^{+0.02}_{-0.02} RJ, a density of 1.0^{+0.1}_{-0.1} rhoJ, an equilibrium temperature of 970^{+30}_{-20} K and an orbital period of 3.83 days. WASP-151b is slightly inflated, while WASP-153b presents a significant radius anomaly. WASP-156b, being one of the few well characterised Super-Neptunes, will help to constrain the formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms the tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behaviour for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.
Nature Astronomy, Volume 5, Pages 775-787, June 2021 Exoplanets transiting bright nearby stars are key objects for advancing our
knowledge of planetary formation and evolution. The wealth of photons ...from the
host star gives detailed access to the atmospheric, interior, and orbital
properties of the planetary companions. $\nu^2$ Lupi (HD 136352) is a naked-eye
($V = 5.78$) Sun-like star that was discovered to host three low-mass planets
with orbital periods of 11.6, 27.6, and 107.6 days via radial velocity
monitoring (Udry et al. 2019). The two inner planets (b and c) were recently
found to transit (Kane et al. 2020), prompting a photometric follow-up by the
brand-new $CHaracterising\:ExOPlanets\:Satellite\:(CHEOPS)$. Here, we report
that the outer planet d is also transiting, and measure its radius and mass to
be $2.56\pm0.09$ $R_{\oplus}$ and $8.82\pm0.94$ $M_{\oplus}$, respectively.
With its bright Sun-like star, long period, and mild irradiation ($\sim$5.7
times the irradiation of Earth), $\nu^2$ Lupi d unlocks a completely new region
in the parameter space of exoplanets amenable to detailed characterization. We
refine the properties of all three planets: planet b likely has a rocky mostly
dry composition, while planets c and d seem to have retained small
hydrogen-helium envelopes and a possibly large water fraction. This diversity
of planetary compositions makes the $\nu^2$ Lupi system an excellent laboratory
for testing formation and evolution models of low-mass planets.
We present the discovery of TOI-2136b, a sub-Neptune planet transiting every
7.85 days a nearby M4.5V-type star, identified through photometric measurements
from the TESS mission. The host star is ...located $33$ pc away with a radius of
$R_{\ast} = 0.34\pm0.02\ R_{\odot}$, a mass of $0.34\pm0.02\ M_{\odot}$ and an
effective temperature of $\rm 3342\pm100\ K$. We estimate its stellar rotation
period to be $75\pm5$ days based on archival long-term photometry. We confirm
and characterize the planet based on a series of ground-based multi-wavelength
photometry, high-angular-resolution imaging observations, and precise radial
velocities from CFHT/SPIRou. Our joint analysis reveals that the planet has a
radius of $2.19\pm0.17\ R_{\oplus}$, and a mass measurement of $6.4\pm2.4\
M_{\oplus}$. The mass and radius of TOI2136b is consistent with a broad range
of compositions, from water-ice to gas-dominated worlds. TOI-2136b falls close
to the radius valley for low-mass stars predicted by the thermally driven
atmospheric mass loss models, making it an interesting target for future
studies of its interior structure and atmospheric properties.
We report the discovery and characterization of a small planet, TOI-1408 c, on a 2.2-day orbit located interior to a previously known hot Jupiter, TOI-1408 b (\(P=4.42\) d, ...\(M=1.86\pm0.02\,M_\mathrm{Jup}\), \(R=2.4\pm0.5\,R_\mathrm{Jup}\)) that exhibits grazing transits. The two planets are near 2:1 period commensurability, resulting in significant transit timing variations (TTVs) for both planets and transit duration variations (TDVs) for the inner planet. The TTV amplitude for TOI-1408 c is 15% of the planet's orbital period, marking the largest TTV amplitude relative to the orbital period measured to date. Photodynamical modeling of ground-based radial velocity (RV) observations and transit light curves obtained with the Transiting Exoplanet Survey Satellite (TESS) and ground-based facilities leads to an inner planet radius of \(2.22\pm0.06\,R_\oplus\) and mass of \(7.6\pm0.2\,M_\oplus\) that locates the planet into the Sub-Neptune regime. The proximity to the 2:1 period commensurability leads to the libration of the resonant argument of the inner planet. The RV measurements support the existence of a third body with an orbital period of several thousand days. This discovery places the system among the rare systems featuring a hot Jupiter accompanied by an inner low-mass planet.
Large-scale exoplanet surveys like the TESS mission are powerful tools for discovering large numbers of exoplanet candidates. Single-transit events are commonplace within the resulting candidate list ...due to the unavoidable limitation of observing baseline. These single-transit planets often remain unverified due to their unknown orbital period and consequent difficulty in scheduling follow up observations. In some cases, radial velocity (RV) follow up can constrain the period enough to enable a future targeted transit detection. We present the confirmation of one such planet: TOI-2010 b. Nearly three years of RV coverage determined the period to a level where a broad window search could be undertaken with the Near-Earth Object Surveillance Satellite (NEOSSat), detecting an additional transit. An additional detection in a much later TESS sector solidified our final parameter estimation. We find TOI-2010 b to be a Jovian planet (\(M_P = 1.29 \ M_{\rm Jup}\), \(R_P = 1.05 \ R_{\rm Jup}\)) on a mildly eccentric orbit (\(e = 0.21\)) with a period of \(P = 141.83403\) days. Assuming a simple model with no albedo and perfect heat redistribution, the equilibrium temperature ranges from about 360 K to 450 K from apoastron to periastron. Its wide orbit and bright host star (\(V=9.85\)) make TOI-2010 b a valuable test-bed for future low-insolation atmospheric analysis.
We present the discovery of a highly irradiated and moderately inflated ultra-hot Jupiter, TOI-1431b/MASCARA-5b (HD 201033b), first detected by NASA's Transiting Exoplanet Survey Satellite mission ...(TESS) and the Multi-site All-Sky CAmeRA (MASCARA). The signal was established to be of planetary origin through radial velocity measurements obtained using SONG, SOPHIE, FIES, NRES, and EXPRES, which show a reflex motion of \(K=294.1\pm1.1\) m s\(^{-1}\). A joint analysis of the TESS and ground-based photometry and radial velocity measurements reveals that TOI-1431b has a mass of \(M_{p}=3.12\pm0.18\) \(\rm{M_J}\) (\(990\pm60\) M\(_{\oplus}\)), an inflated radius of \(R_{p}=1.49\pm0.05\) \(\rm{R_J}\) (\(16.7\pm0.6\) R\(_{\oplus}\)), and an orbital period of \(P=2.650237\pm0.000003\) d. Analysis of the spectral energy distribution of the host star reveals that the planet orbits a bright (\(\mathrm{V}=8.049\) mag) and young (\(0.29^{+0.32}_{-0.19}\) Gyr) Am type star with \(T_{\rm eff}=7690^{+400}_{-250}\) \(\rm{K}\), resulting in a highly irradiated planet with an incident flux of \(\langle F \rangle=7.24^{+0.68}_{-0.64}\times\)10\(^9\) erg s\(^{-1}\) cm\(^{-2}\) (\(5300^{+500}_{-470}\mathrm{S_{\oplus}}\)) and an equilibrium temperature of \(T_{eq}=2370\pm70\) K. TESS photometry also reveals a secondary eclipse with a depth of \(127^{+4}_{-5}\)ppm as well as the full phase curve of the planet's thermal emission in the red-optical. This has allowed us to measure the dayside and nightside temperature of its atmosphere as \(T_\mathrm{day}=3004\pm64\) K and \(T_\mathrm{night}=2583\pm63\) K, the second hottest measured nightside temperature. The planet's low day/night temperature contrast (\(\sim\)420 K) suggests very efficient heat transport between the dayside and nightside hemispheres.
