Discretionary Programme (DP): Approved Proposals

Up to 5% of the observing time on CHEOPS may be taken up by the Discretionary Programme (DP). Proposals can be submitted at any time. All details and criteria can be found at this link.

Abstracts

ID001 — Constraining the scattering properties of condensates in the ultrahot Neptune, LTT 9779b (PI: James Jenkins)
By studying the thermal emission and reflected light from transiting exoplanets when they pass behind their host stars, we can study in detail their atmospheric properties. The emission in the infrared allows us to determine the radiant heat from the planet, providing a dayside temperature for example, whereas in the optical the detected energy generally comes from the host star’s scattered light, allowing a calculation of the planet’s albedo. The recent discovery of the first Ultrahot Neptune, LTT 9779b, provides a benchmark planet to study Neptune-like atmospheres in extreme environments. We already have Spitzer infrared secondary eclipses from the planet, providing a dayside temperature of 2100 K, and a likely detection of CO. The TESS lightcurve that originally detected the primary transits, also allowed a marginal detection of the optical secondary eclipse. The measured value of 60 ppm, is more than two times higher than the maximum planetary emission at these wavelengths, suggesting strong scattering is at play due to high altitude aerosols. We therefore aim to detect the optical secondary eclipse using CHEOPS, with a precision of ~20 ppm, confirming the tentative results from TESS. The bluer CHEOPS passband will anchor our global circulation models, allowing us to constrain the reflected light component and characterize the layer of absorbers in the atmosphere. This work will be a first for such a world, representing a genuine landmark in the field.

ID005 — Solving the orbital ambiguity of a new transiting circumbinary planet TIC 172900988b (PI: Veselin Kostov)
One of the most exciting breakthroughs in the field of exoplanets was the discovery of circumbinary planets (CBPs). Only about a dozen were found, however, leaving a vast gap in our understanding of these fascinating worlds - similar to the state of the field 20 years ago when only a handful of hot Jupiters were known. Using a new detection technique we have developed - the occurrence of multiple transits during one conjunction - and data from TESS, we can detect an order of magnitude more CBPs. In addition to enchanting individual-case discoveries and their intriguing dynamics, this will enable deeper understanding of the formation and evolution of CBPs, and of their binary hosts. Here we propose to observe a new transiting CBP we recently detected in TESS data and break the degeneracy between four photodynamical solutions for the system. CHEOPS is uniquely-suited for the task due to the combination of precision photometry, instrument stability and duty cycle it offers.

ID007 — Observing the second HD88986b transit event: a temperate sub-Neptune characterised by TESS and SOPHIE (PI: Neda Heidari)
Here, we confirm the planetary nature of one of the TESS single transit events with 189± 11 ppm depth and duration of 14.5_{0.9}^{0.8} h, using 365 SOPHIE radial velocity measurements. We show that the planet is a sub-Neptune orbiting every 146.31^{+0.31}_{-0.31} d around one of the nearest and brightest star HD88986 (G2v type, G_{mag}=6.30, T_{eff}=5960_{180}^{280} K). The planet mass and radius are 19.4_{2.7}^{2.6} M_{E} and 2.36 ± 0.1 R_{E} which translate to the high density of 8.1^{+1.7}_{-1.5} g cm^{-3}. HD88986 b has the longest periods among the accurately characterized transiting sub-Neptune, hence it is a temperate (T_{eff}= 476^{+13}_{-10.}) sub-Neptune, which make it an interesting target for the study of the internal structure. we propose to use CHEOPS's unique photometric capability to have \sim 40 \% better estimation on the planet radius uncertainty, which highlights the importance of the high-precision CHEOPS photometry to achieve the better precision on the bulk density needed for internal structure modeling.

ID008 — Catching the Transit of a Long Period Planet to Support Future Atmospheric Characterisation (PI: Billy Edwards)
Across the population of 5000 currently-known exoplanets, only a handful are transiting long-period worlds. Understanding the nature of these far-out planets is of the utmost importance, but their rareness, coupled with the scarcity of observational opportunities, creates challenges for detailed characterisation. Here we seek to utilise the excellent precision of CHEOPS to obtain crucial data of CoRoT-9 b, one of the best large, cool planets for atmospheric characterisation with JWST. We will capture only the sixth transit light curve of this planet to have ever been obtained. It is vital that the ephemerides of this planet are updated and, due to its long period (95 days) and transit time (8 hours), a space-based facility is required. Therefore, CHEOPS offers an exclusive opportunity to study this world and lay the foundations for future atmospheric characterisation. Only one transit of CoRoT-9 b is observable in 2022 with CHEOPS and, as it happens before the expected scheduling window of AO-3, the discretionary programme offers the sole chance for it to be observed.

ID010 — Resolving the dynamical history of the hot Jupiter WASP-132b and its inner mini-Neptune companion (PI: Tunde Akinsanmi)
With the exception of a few cases, stars with Hot Jupiters (HJs) rarely possess other close-in planets in the system. TESS has revealed another exceptional case of a mini-Neptune interior to the orbit of the known Hot Jupiter (HJ), WASP-132b. The existence of this mini-Neptune provides valuable insight into the formation mechanism and dynamical history of the HJ. We aim to understand the migration history and orbital architecture of the WASP-132 system using Rossiter-McLaughlin observations with our obtained time on ESPRESSO. By measuring the planets' spin-orbit angles, we will assess the coplanarity of their orbits and that of their star to understand their dynamical history. This science case requires timing precisions of around 2 mins, which in turn implies the acquisition of new precise photometric transit observation close to the ESPRESSO observations. CHEOPS observations of the transit of the mini-Neptune will enable refining its ephemeris and transit parameters, a goal that cannot be achieved by ground-based observations given the small transit depth and faint star. The improved radius precision obtained from CHEOPS in addition to our RV follow-up of the target will also allow constraining the internal structure of the planet.

ID014 — Period measurement of the brightest-host transiting habitable zone terrestrial exoplanet (PI: Nicholas Scarsdale)
We propose to use CHEOPS photometry to measure the period of the Transiting Exoplanet Survey Satellite (TESS) planet candidate TOI4353.01 (TIC176797879), initially a duo-transit object that we confirmed with a transit detection in our AO3 program (ID 24). This object is a terrestrial-size exoplanet with two transits separated by 718 days in the TESS photometry, and a third detected in AO3 at the same separation. Based on the transit duration and a priori likelihood of transit, the true period is very unlikely to be 718 days, and instead is more likely to be one of the fractions in the range 25-60 days. This planet is therefore a likely-terrestrial planet candidate with a strong probability of being in the optimistic habitable zone (OHZ) and potential for future mass measurement and even transmission spectroscopy thanks to its bright (for an M star) host. Because of the great rarity of terrestrial OHZ exoplanets and the difficulty of discovering more with TESS due to its short sectors, followup of candidates like this one is of critical importance, and this followup must begin with a period measurement, as we propose to do here.

ID015 — The coolest small planet: Catching the transit of a small planet orbiting an M dwarf with P>100d and a precise mass from HARPS-N (PI: Annelies Mortier)
For smaller planets, precise bulk densities are crucial to understand their interior composition and to distinguish between a super-Earth or a sub-Neptune. This is essential input for understanding planet formation and evolution. With this proposal, we are asking for DDT CHEOPS time to detect and confirm the transit of only the second small planet with a precisely known mass orbiting its star with a period above 100 days. It would furthermore be the coldest (212) small planet around a bright star (G<13) ever. The host is an M2 dwarf with a well-characterised ultra-short period small planet. We found a dip in flux at the start of one of our CHEOPS GO data following up on this planet. By co-analysing the CHEOPS, TESS, and radial velocity data, we could rule out systematics and found the dip is consistent with a new small planet candidate orbiting the M dwarf beyond its habitable zone (P=101d). The only other known star with a well-characterised small planet at such orbits is nu2 Lupi (also done by CHEOPS). Confirming the transiting nature of our new planetary candidate would thus double the known small planets with precise densities on orbits beyond 100 days and be of great scientific interest.

ID018 — Confirmation of four planet candidates around an extremely young star (PI: Anne Dattilo)
We request 64 orbits of CHEOPS observations to confirm and characterize the planetary system orbiting the star TOI-6109, a young, approximately 80Myr-old Sun-like star in the Alpha Persei cluster. It hosts at least 4 transiting planet candidates, all about the size of Neptune orbiting within 16 day orbital periods. The planets orbit near mean motion resonances, so transit timing variations should reveal their masses. The system's youth and near-resonant configuration present a unique opportunity to test theoretical models of atmospheric mass loss.

ID019 — Period Confirmation for The Sub-Neptune Exoplanet with The Longest Period (PI: Amanda Mohr)
TOI-5527.01 was identified as a potential cool sub-Neptune (2.5 ± 0.8 Rearth) exoplanet with transits in TESS sectors 32, 43, and 44. This candidate is likely one of the longest-period planets discovered by TESS around a bright host star. Assuming one of the high-probability period aliases is confirmed, the candidate will be the TESS discovered transiting sub-Neptune exoplanet with one of the longest orbital periods (between 70 to 364 days), making it an extremely attractive candidate for future followup. The most likely transit is already being observed as part of CHEOPS AO4: PR240026 (priv. comm.). Therefore, we request 10 orbits to check the second most likely period alias of this planet candidate while it is visible to CHEOPS.

ID020 — An Optical Lever-arm for JWST Spectra of K2-22b (PI: Nicholas Tusay)
The disintegrating ultra-short period exoplanet K2-22b offers the opportunity to probe the interior composition of a specific rocky exoplanet for the first time, via the transmission spectrum and phase curve of the dust evaporating from K2-22b obtained with MIRI LRS slitless spectroscopy on JWST, and simultaneous with CHEOPS optical observations. JWST GO program 3315 will observe two transits, as well as a complete phase curve of the orbit from one transit to another, for a total of four transit observations of K2-22b. By comparing the transit transmission spectra to detailed extinction and scattering models, the program aims to determine the mineralogical make-up of the dust outflowing from K2-22b, and therefore the composition of the planet's interior. The phase curve data will enable measurement of the temperature and spatial extent of the dust, which will further constrain its morphological properties, as well as the dynamics of the dust-outflow around the planet itself. The relative mineralogical abundances in the dust will provide insight into whether it is crustal, mantle or core material that is evaporating. To complement the JWST observations, we propose to use CHEOPS to get as much simultaneous optical coverage during these observations as the orbital phases will allow. Adding optical data to a MIR detection will enable the breaking of degeneracies in the mineralogical models.

ID022 — The First Neptune Desert Progenitor System (PI: Shreyas Vissapragada)
The origin of the high-density planets residing within the Neptune desert (a region of the planetary mass-period plane otherwise devoid of planets) is a major new mystery of the TESS era. In this programme, we propose to confirm an object that provides a direct origin story for the formation of objects within the desert. TOI-XXXX.01 is a high-mass Neptune and the most eccentric short-period planet candidate ever identified, which will migrate deep into the Neptune desert on a relatively short (less than 1 Gyr) timescale. It also has a stellar companion capable of driving past dynamical migration, and it resides exactly at the tidal disruption boundary for a Jupiter-sized object, suggesting that this planet is indeed the exposed interior of a would-be hot Jupiter. With 30 CHEOPS orbits, we can definitively confirm this system, precisely measure its density (placing it into context with other super-Neptunes in the desert), and independently validate its remarkably high eccentricity.

ID023 — Characterisation of TESS Multi-planet Circumbinary System (PI: Matthew Standing)
Circumbinary planets orbit around both stars of a tight binary and offer unique insights into planetary formation and migration. Ascertaining the correct orbital parameters of these planets is crucial to correctly characterise them. The HD29037 eclipsing binary system has recently been preliminarily identified as the third ever multiplanetary circumbinary system with TESS. Four planetary transits have been identified so far, candidate planet b has shown 3 TESS transits with an orbital period of around 64 days, while candidate c has transited once. From this we have calculated three possible families of solutions for the system with periods for the outer planet c at either 150, 225, or 449 days. With CHEOPS observations we will be able to observe two secondary eclipses and one primary transit of the binary, two additional transits of planet b, and one possible transit of planet c. These observations will allow us to ascertain the true orbital parameters of the system, and aid in characterisation in collaboration with ground based radial velocity observations. Exact timing of the transits are key to measuring planet masses and for accurate dynamical solutions, this is essential before ARIEL and JWST observations. Precise timings will also be key to finding any additional planets in the system.

ID024 — Confirming a transiting super-Earth in the optimistic habitable zone with CHEOPS (PI: Jose Manuel Almenara Villa)
The proposed CHEOPS observations aim to confirm and characterize a transiting super-Earth in the optimistic habitable zone around an M dwarf. TESS discovered a transiting sub-Neptune (TOI-3494 b) with a period of 7.75 days and a radius of 2.3 Earth radii. Follow-up observations revealed transit-timing variations (TTVs), suggesting the presence of a super-Earth (TOI-3494 c) in a 2:1 mean motion resonance, placing it in the optimistic habitable zone. Candidate transits for TOI-3494 c have been identified, but re-observation is required due to low signal-to-noise ratio. If confirmed, TOI-3494 c will have a period of 15.4 days, a radius of 1.34 Earth radii, and an equilibrium temperature of 294 K. The mass of TOI-3494 c can be precisely measured using a combination of TTVs and radial velocities, allowing for detailed compositional characterization. The proposed observations will provide critical data to confirm the existence of TOI-3494 c and enhance our understanding of planetary systems in resonance.

ID025 — Neptune Stellar Occultation: Measure Neptune’s Stratosphere and Determine the Feasibility of Space-Based Stellar Occultation Observations with CHEOPS (PI: William Saunders)
We propose to use CHEOPS to observe a Neptune stellar occultation on 07 October 2025. CHEOPS has observed stellar occultations before, most notably an occultation by (50000) Quaoar in 2020 (Morgado et al. 2022), but it has never observed a stellar occultation by a giant planet to study that planet’s atmosphere. We intend to use this occultation to measure the temperature of Neptune’s stratosphere and determine the feasibility of space and/or airborne observations of stellar occultations. The temperature of Neptune’s stratosphere has not been studied in detail in decades, and discrepancies exist between the Voyager 2 data from 1989 and several ground-based stellar occultation observations made around that time and since. Recent observations from JWST indicate that Neptune’s thermosphere has cooled significantly since the Voyager 2 flyby, but it is not known whether the stratosphere has cooled or remains around the same temperature. An observation of the October occultation may enable a measurement of Neptune’s stratospheric temperature today, which will allow us to determine how it has changed in the past few decades. We will follow the observing and reduction procedure of Morgado et al. (2022) and then use standard stellar occultation analysis for giant planet atmospheres to extract the temperature measurement. We will also this observation as a test of the feasibility and benefit of space-based observations of future occultations.

ID026 — DS Tuc A b (PI: Amy Louca)
We request CHEOPS observations of DS Tuc A b, a 45 ± 4 Myr warm Neptune (5.6 R⊕, <14.4 M⊕) orbiting a bright G6V star (J = 7.1). Simultaneous HST/WFC3 and JWST/NIRSpec observations will probe the atmosphere from 1.1–5.3 µm. Visible-light photometry from CHEOPS is crucial for breaking degeneracies between atmospheric metallicity and cloud pressure, providing key constraints on atmospheric composition. Since DS Tuc A b is too young for significant atmospheric escape, detecting a metal-enriched atmosphere would support enrichment during formation. At the same time, a non-detection would favor enrichment through long-term evolution. CHEOPS will also enhance the removal of stellar variability and help diagnose the transit light source effect, both of which affect accurate transmission spectra. Additionally, CHEOPS will bridge spectral coverage between Swift UV and HST/JWST IR, enabling rare UV–visible–IR flare characterisation if stellar activity occurs. We request a single 9-orbit CHEOPS visit, overlapping with scheduled HST and JWST observations to enable robust, simultaneous, multi-wavelength analysis.

ID027 — Measuring the Orbital Tilt and Composition of the Disintegrating Planet BD+05 4868 Ab with Simultaneous High-Resolution Spectroscopy and CHEOPS Photometry (PI: Steven Giacalone)
We propose to use CHEOPS to observe six transits of the disintegrating planet BD+05 4868 Ab simultaneously with upcoming ground-based spectroscopic observations. Recently discovered in TESS data, BD+05 4868 Ab orbits a bright star (V = 10.16) and induces deep (0.8-2.0%) transits, making it a significantly more favorable target for follow-up observations than previously discovered disintegrating planets around relatively faint stars. When analyzed together, the CHEOPS and ground-based observations will enable both the precise measurement of the sky-projected orbital tilt of the planet (i.e., the stellar obliquity) via the Rossiter-McLaughlin effect and the determination of the elemental composition of the outflowing planetary interior. In doing so, we will obtain first-of-its-kind insight into the natures of low-mass, rocky exoplanets on close-in orbits and the origins of disintegrating planets. In the absence of simultaneous photometry, our spectroscopic observations would be challenging to interpret due to degeneracies between intrinsic system properties and transit depth. CHEOPS will play the critical role of breaking these degeneracies by revealing the instantaneous depth of each transit during our ground-based observations.

ID028 — Pinning down the period of a TESS planetary candidate (PI: Jose Manuel Almenara Villa)
We propose CHEOPS observations to determine the orbital period of TIC 118798035 d, a Jupiter-sized exoplanet in a uniquely compact system containing three transiting giant planets. While the two inner planets have orbital periods near a 2:1 resonance, the third planet's period remains uncertain due to sparse transit detections in the TESS data. Resolving this alias degeneracy is critical to knowing the true system’s architecture. Some of the aliases are compatible with the system forming a rare mean-motion resonant chain. Observations from CHEOPS are essential, as we cannot assure observations of the proposed aliases of TIC 118798035 d from the ground.

ID029 — Lost and Found: Constraining the radius and mass of a progenitor of sub-Neptunes (PI: Pietro Leonardi)
V1298 Tau is a young (20 ± 10 Myr), pre-main-sequence K-type star (mV = 10.12) hosting at least four transiting planets, making it one of the most promising systems for studying the early evolution of planetary architectures. We propose a CHEOPS-led photometric campaign to monitor V1298 Tau e, the outermost known transiting planet in the system. Our goals are twofold: (1) to refine the planet’s radius through high-precision transit photometry, and (2) to map its TTV signal, which, through dynamical modeling, can be used to constrain the masses and orbital parameters of multiple planets in the system.

ID030 — Investigating the giant TTVs around a Solar-type star (PI: Luca Naponiello)
TOI-1422 is a bright (V=10.6 mag) metal-poor G-dwarf star hosting a known low-density Neptune-sized planet (P=13d) ideal for atmospheric follow-up (TSM=100), and a newly revealed transiting sub-Neptune farther away (P=35d; private comm.). Recently, TESS has observed this system again, revealing very large transit-time-variations (TTVs), with amplitudes up to 320 minutes, among the 7 observed transits of TOI-1422b. Our simulations suggest that such TTV amplitudes cannot be attributed to the presence of TOI-1422c, but rather they hint at the existence of a third body in the system, possibly in a 3:2 resonance with TOI-1422b, though this object has not been revealed neither by TESS nor by HARPS-N radial velocity (RV) follow-up. Since TOI-1422 won’t be observed again by TESS, we propose dedicated observations of TOI-1422b transits with CHEOPS, the only facility that could shed light on this system. With additional transits of the Neptune-sized planet, we plan to model the TTVs along with an expanded RV dataset using TRADES, in order to reveal the hidden perturbing body. Furthermore, this analysis will provide updated ephemerides for TOI-1422b, making it possible to try and probe its atmospheric content with transmission spectroscopy.

ID031 — Probing the Youngest Transiting Exoplanet's Atmosphere: Investigation TOI-6963 b by combining spectroscopy and photometry (PI: Pietro Leonardi)
Characterizing young exoplanets is key to unveiling the early processes of planetary formation, migration, and atmospheric evolution. TOI-6963 b, with an estimated age of only 3 Myr, currently stands as the youngest transiting exoplanet known. It orbits a K-type star in the Taurus star-forming region with a period of 8.83 days, a radius of 10.7 R⊕, and a 95% confidence upper mass limit of 90 M⊕. Its inflated size and low density suggest it may represent an early-stage sub-Saturn or sub-Neptune. Owing to its large radius and likely extended atmosphere, TOI-6963 b is a prime target for atmospheric studies. Its location near the upper edge of the Neptunian “savanna” in the radius–period diagram, shaped by atmospheric escape, further highlights its importance. This proposal seeks to observe four transits of TOI-6963 b simultaneously with awarded high-resolution ground-based spectroscopy observations. The spectroscopic component will target the He I triplet as a diagnostic of atmospheric escape and will probe molecular species such as CO, H₂O, and CH₄. Simultaneously, CHEOPS will deliver uninterrupted, high-precision light curves to refine the transit geometry and provide the temporal baseline needed to interpret the spectroscopic signals, as well as to detect possible contamination from stellar heterogeneities.

ID036 — Constraining the Orbit of a Temperate Long-Period Sub-Neptune around a Young K-Dwarf (PI: Alton Spencer)
Young transiting exoplanet systems offer critical insights into the evolutionary history and properties of small planets within their first 1 GYR. The 330 MYR K-dwarf TOI-6710 hosts 3 small transiting planets, including TOI-6710 d, a rare young temperate Sub-Neptune suitable for JWST follow-up. However, limited coverage from TESS and inconclusive results from ground-based transit observations have prevented any of its orbital period aliases from being confirmed or rejected, leaving the planet’s ephemeris unconstrained. We aim to observe one transit window of the highest probability alias (P=86.78d) with CHEOPS, which will either confirm this as the true orbital period, or place improved constraints in the event of non-detection.

ID037 — Precise Mass Determination of Kepler-1647AB b Through Eclipse Timing Variations (PI: Jenni French)
Circumbinary planets provide direct tests of planet formation and migration models since they must have formed further out and disc-migrated to occupy the short orbits they are detected in. To investigate these models through the lens of circumbinary planets, precise mass measurements are required. However, of the 17 confirmed circumbinary planets orbiting main sequence binaries, only 6 of these have masses measured at a precision > 3σ. Due to dynamical interactions with the planet, binary systems with a circumbinary planet do not have static Keplerian orbits. Instead, the binary experiences apsidal precession which is observable through eclipse timing variations. Measuring precise timings of binary eclipses over a long baseline thus allows the mass of the planet to be well constrained. We propose to observe Kepler-1647, a 1.22 M⊙ F8 + 0.97 M⊙ G2 eclipsing binary with a high-mass, long-period circumbinary planet. Kepler-1647 is the only Kepler circumbinary system whose planet is far from the instability region. With CHEOPS we will observe 3 primary eclipses and 3 secondary eclipses with a total request of 66 orbits. Utilising the 12 year baseline since Kepler we will precisely determine the apsidal precession rate, and thus the mass of the circumbinary planet, from the precise eclipse timings CHEOPS can obtain. These observations will improve the mass precision by at least a factor of 3, a crucial part of understanding the formation and evolution of circumbinary planets.

ID041 — CHEOPS confirmation and characterisation of a resonant maturing multi-planet system (PI: Cynthia Ho)
Processes driving the diversity in planet compositions and system architectures are poorly understood, because the vast majority of confirmed planets reside in mature systems (t > 1 Gyr). Young and maturing planets are required to reveal planetary evolution mechanisms, such as disc migration, yet they are challenging to detect because their transits are often obscured by the much stronger photometric variability of their host stars. Using our refined algorithm, we detected a second transit signal in the TESS light curve of TOI-1775 with P = 20.4697 d, which we designate as TOI-1775 c. This system is near a 2:1 mean-motion resonance (MMR) with the inner TOI-1775 b. Notably, the inner planet is larger than the outer planet, hence setting it apart from most other young and maturing planetary systems in MMR. Probing this system would allow us to investigate the mechanisms that cause this oddity in the planetary architecture. This maturing system also provides a valuable window into the important evolutionary stage between the young population, where resonant chains are most common, and the mature population in which resonances are scarce. We therefore request to observe, using CHEOPS, one transit of TOI-1775 c, to (i) confirm the shallow transit in TESS with the more sensitive CHEOPS, (ii) significantly improve the planet radius precision, and (iii) refine the precision of the orbital period and transit ephermeris to confirm the 2:1 MMR and investigate the possibility of TTVs.

ID043 — Eclipse Timing Variations of HD 177329 to Constrain a Putative Massive Outer Companion (PI: Babatunde Akinsanmi)
We propose CHEOPS observations of HD 177329, a bright eclipsing binary that shows evidence for a massive outer companion consistent with a quiescent black hole (BH). Existing TESS photometry and radial velocities reveal a hierarchical triple system, but the limited timing baseline leaves a degeneracy between solutions hosting either a ∼12–15 M☉ BH on a ~925–955 day orbit or a shorter-orbit low-mass stellar companion. These BH scenarios predict eclipse timing differences of >5 minutes within the coming months, allowing CHEOPS to decisively break the degeneracy through high-precision eclipse timing. The light-travel-time (Rømer) delay of the inner binary encodes the mass of the outer companion, while secular variations in eclipse depth and duration trace the 3D orbital architecture. CHEOPS’s continuous, high-precision photometry of long (∼12 hr) eclipses (unachievable from the ground) will extend the timing baseline, refine orbital parameters, and enable a photodynamical solution combining timing and radial velocity constraints. If the companion mass exceeds ∼3 M☉, this would be the first eclipsing binary with a confirmed quiescent BH outer companion and a unique laboratory for probing black hole formation. The measured outer eccentricity and mutual inclination will constrain the natal kick and mass loss at birth, testing whether the BH formed via direct collapse or a low-kick core-collapse channel. At only 460 pc, it would be the closest BH to the Earth.

ID045 — Constraining planetary masses in a new TESS system exhibiting TTVs (PI: Jose Manuel Almenara Villa)
Recent TESS data have unequivocally determined the orbital periods of the two planets in the TOI-XXXX system. These planets exhibit TTVs that can be used to estimate their masses. However, current mass determinations have large uncertainties. As no additional TESS observations are planned, we propose to observe one transit of each planet with CHEOPS in order to significantly improve the mass determinations, enabling a more robust discussion in the discovery paper (in prep.). Since both planets are prime targets for atmospheric characterisation via transit spectroscopy with JWST (TSM > 100), this system is one of the few allowing for comparative planetology.

ID047 — A new TESS-enhanced attempt to detect the transit of KOBE-1c with CHEOPS (PI: Jose Ignacio)
The main goal of this proposal is the confirmation of the transiting nature of the radial-velocity detected planet KOBE-1c, the outer component of the two planetary signals detected around the K7-M0 dwarf HIP 5957. The updated TESS ephemeris, based on sectors #17 and #84, now provides a more precise transit window, and the proposed CHEOPS observations aim to verify the transit and measure the planetary radius. The planet has an expected radius of about 1.8 Earth radii, placing it close to the radius valley. Confirming whether KOBE-1c transits would provide the planetary radius and, together with the existing radial-velocity mass, enable a bulk-density determination. The proposed observations would also improve the ephemeris, which is important for future follow-up observations. Two CHEOPS visits are requested, each covering the transit together with baseline before ingress and after egress, for a total allocation of 13 CHEOPS orbits.

This page was last updated on 10 July 2026.