AO-4: Approved Programmes

Announced on 14 July 2023

The 4th Announcement of Opportunity (AO-4) for the CHEOPS Guest Observers (GO) Programme opened on 4 April 2023 and closed on 26 May 2023. The opportunity marks the start of the first extended mission and covers observing time in the period from 25 September 2023 until 30 September 2024. Notably, the available GO share of the science observing time was recently increased from 20% (in the Nominal Mission) to 30% (in the first Extended Mission).

A total of 29 proposals were received in reply to AO-4, requesting 1811.1 orbits (with each orbit circa 99 minutes in duration). The requests represented 120% of the available science observing time foreseen in the AO-4 observing cycle (circa 1505.5 orbits).

The CHEOPS Time Allocation Committee (TAC) met on 19 - 20 June 2023. Based on the TAC's recommendations, the Director of Science has awarded CHEOPS observing time to the proposals listed in the table below. In the end, 24 proposals were awarded observing time totaling 1472.1 orbits. Of these, 19 proposals were on exoplanet science, 3 on stellar science, and 2 on other science/goals. The TAC-recommended allocation of observing time represents up to 98% of the available GO science observing time foreseen in the AO-4 observing cycle (circa 1505.5 orbits). Of these, 3 pairs of programmes have duplicate targets, for which the TAC recommends sharing observing time. We will be in contact with the teams and liaise the next steps.

Succesful proposals will be implemented as GO programmes. Targets that are part of these GO programmes can generally not be included in other observing programmes unless in specific cases. All programmes have been assigned a priority from 1 (high) to 3 (low), in some cases at the level of individual targets. This priority is taken into account by the automated planning tool used in the weekly/biweekly planning, and is a strong indicator of the likelihood that observations will be scheduled. Observers are reminded that the award of observing time provides no guarantee that the observations can be executed, and that generally more observing timeis awarded than can be physically scheduled to minimise idle time.

Principal Investigators (PIs) of proposals that have been awarded time will be contacted by email, and are required to complete and submit observation requests at their earliest convenience. Guidelines on how to prepare observation requests will be posted on this webpage shortly. The TAC feedback will be provided to all PIs of proposals.

A fraction of up to 25% of the GO Programme time will remain available to the community to apply for time via the Discretionary Programme (DP), which is foreseen to continue running throughout the mission lifetime. This is in line with a possible over-allocation of up to 133% to facilitate the efficient scheduling of time critical observations. 

*, ** and *** mark three pairs of programmes with duplicate targets, for which the TAC recommends sharing observing time. We will be in contact with the teams and liaise the next steps.

Abstracts

ID0001 — Inspiration through space science – a CHEOPS-based education activity for high-school students (PI: Kate Isaak)
The topic of exoplanets speaks directly to the very simple and profound question of whether we are alone in the Universe and is easy to relate to. As such, it provides an excellent means through which to engage young people in some of the thrills of science and, critically, a vehicle with which to teach analytical skills. We propose to use CHEOPS data as the basis for a schools activity to run in 2023/2024. For this, we request a total of 24 orbits to observe transits of the ultra-short period, hot super-Earth K2-141b. 14-19 year olds will be invited to analyse the data and to work through a series of challenges based on the exoplanet light curve, using supporting resources designed specifically for the students and teachers (available in 21 different European languages). Student teams will use the knowledge they gain to address an open-ended question on exoplanets, with the opportunity to showcase their work at a European online event at the end of the school year.

ID0002 — CHEOPS transits of two 48-Myr mini-Neptunes in the Taurus-Orion II moving group (PI: Sydney Vach)
Within the first 100 Myr, planets undergo critical evolutionary events. Observing young planetary systems allow us to gain insights into the physical processes that shape the mature planetary population. TIC 434398831 is a pre-main-seqeunce, Sun-like star (G7V, G = 11.7893) hosting two transiting mini-Neptunes. Gaia kinematics place TIC 434398831 in the 48-Myr Taurus-Orion II moving group. We identified two planetary candidates, TIC 434398831.01 (Rp = 3.65 Rearth, P = 3.61 days) and TIC 434398831.02 (Rp = 5.41 Rearth, P = 6.12 days), through an independent search for young planets located in known moving groups from the TESS's Full Frame Images (FFIs) light curves. We propose to use 4 visits of CHEOPS to observe two transits of both TIC 434398831.01 and TIC 434398831.02, which is necessary for the confirmation of this exemplar system, as high-precision, space-based photometry is needed to overcome the photometric modulations of the young star. Our CHEOPS observations will have the capability to anchor the optical transit depths of the two young planets, which will enable us to distinguish between different cloud and haze scenarios in future atmospheric observations.

ID0003 — Investigating Sub-Saturns through CHEOPS Observations: Envelope-Rich K2-19b and Envelope-Poor K2-19c (PI: Ing-Guey Jiang)
With more than 5000 discovered exoplanets, the field of exoplanet research has entered it is a completely new era in which exotic planets – whose properties may be rare but which reveal important astrophysical processes – could be studied in detail through the combination of long-term observations by ground-based and space telescopes. The sub-Saturn planets K2-19b and K2-19c are exemplary cases for detailed study by CHEOPS in that they pose a challenge to the standard planet formation model of core-nucleated accretion. Here we propose to use CHEOPS to observe transits of K2-19b and K2-19c to use the TTV technique to further improve the mass measurements of these interesting planets with the goals on (1) studying the envelope fraction of K2-19b, K2-19c, and (2) studying the resonant relation between K2-19b and K2-19c.

ID0004 — HIP 67522 b – a Hot Jupiter that triggers flares on its host (PI: Ekaterina Ilin)
The habitability of exoplanets depends crucially on the space weather they experience. A planet orbiting _inwards_ of the habitable zone is a natural probe of the magnetized winds and energetic radiation traveling towards a potentially habitable planet. When a planet orbits close enough to its host, it can perturb the star’s magnetic field, setting off energetic flares in the stellar corona. In the optical, these flares appear as recurrent brightenings in phase with the orbit. If we measure such flares, we immediately know that the planet moves inside the closed-field corona, critical information for space weather modelers. To measure this planet-induced flaring, we have to find flares occurring in excess of intrinsic stellar flaring. This is done by testing for deviations from a random distribution of flares with the orbital phase of the planet. HIP 67522, a 17 Myr Sun with a Hot Jupiter in a 7-day orbit, detected in 2020, has the ideal properties to exhibit such excess flares. But there is more: In recent TESS data, HIP 67522 flared a total of four times. Each time, the flare took place within 10h after transit, the same 4% of the planet’s orbit. This is very unlikely to happen if these flares occurred randomly. We propose to observe HIP 67522 using CHEOPS' high sensitivity for flares for 16 visits for 8 orbits each during the critical 4% of HIP 67522 b's orbit to measure, for the first time, planet induced flares at high significance.

ID0005 — Escape from the “V1298 Tau e labyrinth”: following the CHEOPS’ thread to confirm the orbital period and large TTVs/TDVs of an infant planet (PI: Mario Damasso)
The object of the proposal is the star V1298 Tau, which hosts a system of four transiting planets. The focus of the science case is the confirmation of the orbital period of planet V1298 Tau e, and the determination of its transit timing variations (TTVs) and transit duration variations (TDVs) also using archival photometric data collected by Kepler/K2 in 2015, and by TESS in 2021. Previous observations with CHEOPS allowed to identify P=45.00 days as the actual orbital period of planet e (private communication). This results must be necessarily confirmed with further follow-up, aimed at detecting additional transits. The same CHEOPS observations revealed a significant TTV and TDV. Observing new transits with CHEOPS is the only way to measure the average orbital period and the TTVs/TDVs, and to inform dynamical simulations in order to characterise the evolution of the planets’ orbits over very short timescale (of the order of a few years). The outstanding results expected from the follow-up with CHEOPS will be of great benefit for a proper modelling of hundreds of radial velocities of V1298 Tau collected so far, whose analysis has proved very challenging so far.

ID0007 — CHEOPS can confirm an Earth-sized planet in the habitable zone of a metal-poor M-dwarf neighbour (PI: Larissa Palethorpe)
The number of confirmed exoplanets has grown exponentially since the field was first established almost 30 years ago. However, our understanding of how these planets form and evolve has been severely impacted by our ability to precisely characterise certain types of exoplanets. The characterisation of Earth-analogues in particular, which are vital in gaining an understanding of our own planet’s history, remains a very small pool. One such candidate first discovered by TESS is TOI-6251 b, a nearby temperate, Earth-sized planet orbiting a metal-poor M-dwarf. However, multiples transits could have fallen in TESS’s data gaps – meaning that we are unable to conclusively state the period of the planet as either 12.7 or 25.5 days. Without this parameter the radius of the planet is unable to be precisely constrained, meaning that even with our secured time to obtain high-precision RV observations, from which the planets mass can be determined, we would be unable to model the composition and interior structure. CHEOPS can confirm this habitable zone M dwarf planet, however, enabling us to further our knowledge on theories of how stellar compositional environment affects planetary internal structure, as well as how planet formation and evolution has led to the observed density and radius valleys. With CHEOPS observations we can precisely pinpoint the orbital period and radius of TOI-6251 b – a planet of which the characterisation could unlock ground-breaking studies.

ID0008 — Confirming the Transit Timing Variations of a Neptune-Sized Inner Companion to a Hot Jupiter (PI: Emma Nabbie)
The presence of inner companions to Hot Jupiters reveals a rarely-treaded path of Hot Jupiter formation, one lacking its customary violence. Though intrinsically rare, such systems provide valuable opportunities to directly constrain migrational pathways and understand the multi-faceted origins of Hot Jupiters. TOI-5143 presents one such opportunity, hosting a confirmed Hot Jupiter TOI-5143.01 and a statistically-validated inner Neptune TOI-5143.02. TOI-5143.01 is one of the shortest-period Hot Jupiters to host an interior companion, second only to WASP-47. Preliminary ground-based photometric observations suggest that TOI-5143.02 exhibits tentative transit timing variations (TTVs). This program will use CHEOPS to confirm the TTV signals of TOI-5143.02. The TTV observations will be used with existing radial velocity data of the system to precisely constrain the mass and dynamical history of the system.

ID0009 — Refining parameters of grazing transiting exoplanets with CHEOPS and TESS (PI: Zoltan Garai)
Grazing transiting exoplanets still constitute only a tiny fraction of the known exoplanet population. However, confirming/investigating grazing transiting exoplanets is also important. In a grazing transit, the second and third contact points are missing, the transit profile is V-shaped, similar to that of an eclipsing binary. Consequently, the light-curve solution is degenerate. Fortunately, there is a solution: we need very high-quality multicolour photometric observations. Following this possibility, we propose to utilise the colour difference between TESS and CHEOPS in order to refine the parameters and to confirm the grazing nature of selected transiting exoplanets, namely TOI-3540 b and TOI-2193 b.

ID0010 — Hidden Gems - Giant Exoplanets around Main-Sequence Stars (PI: Lauren Doyle)
We have conducted an extensive search for non-transiting exoplanets in the TESS data via subtle photometric effects – primarily in the form of atmospheric modulation due to the orbiting exoplanet. We searched the 140,000 highest precision TESS light curves in the southern ecliptic hemisphere. We find 27 new short-period, giant exoplanet candidates, which are currently being monitored for radial velocity variations with HARPS. Of these two are ideal candidates to be followed up with CHEOPS, which will provide a high precision phase curve at a wavelength bluer than TESS to disentangle reflection and thermal emission. The candidates have extremely short periods of 0.88 and 0.74 days. The host stars are bright (g=11.2 and 11.5), and well-isolated from other bright sources. If successful, these would be the FIRST non-transiting exoplanets discovered by phase curves from the TESS/CHEOPS missions.

ID0011 — Treating exoplanets as planets: a deep dive into the reflective properties of an ultra-hot Jupiter (PI: Matthew Hooton)
Designing observations to bridge the gap between our wealth of knowledge about solar system bodies with our relative dearth of knowledge about the composition of exoplanets is one of the biggest challenges of our age. Most studies of the reflected properties of transiting exoplanets have been limited to measurements of geometric albedo, an important but incomplete part of the global picture. We propose to supplement previous TESS and Spitzer full-phase curves of MASCARA-1b by acquiring two CHEOPS full-phase curves. Ultra-hot Jupiters like MASCARA-1b are expected to radiate like blackbodies, simplifying the separation of thermal and reflected signals in the phase curve. This will allow us to measure the phase integral, geometric albedo, spherical albedo and Bond albedo separately for three bandpasses across the optical and infrared. As knowledge of these parameters can be used to discriminate between the dominant scattering mechanism during the orbit, this will constitute one of the most in-depth studies of the reflective properties of a transiting exoplanet to date. Additionally, the transit will be used to search for evidence of nodal precession in the orbit of MASCARA-1b, which if detected will yield information about tidal interactions between the planet and star.

ID0012 — Characterising the nearest known temperate Earth-sized exoplanet with CHEOPS (PI: Alexander Venner)
In the study of exoplanets, special interest is often given to those most similar to Earth. Recent observations of a bright and nearby (12 pc) M-dwarf by TESS have revealed the presence of an Earth-sized exoplanet with a relatively low incident flux (no more than twice Earth's insolation). However, the unfortunate coincidence of the planetary orbital period with gaps in the TESS photometry means that there is a factor-of-two uncertainty in the orbital period. We propose CHEOPS observations to resolve this period ambiguity, and to more precisely characterise the physical parameters of the planet. Transit observations from CHEOPS will contribute significantly to our understanding of this system, and will form a key basis for current and future characterisation efforts of this remarkable planet.

ID0013 — Determining the architecture of the K2-19 system (PI: José Manuel Almenara Villa)
The K2-19 system consists of three known transiting planets, with two of them (planets b and c) close to 3:2 Mean Motion Resonance (MMR) and exhibiting large Transit Timing Variations (TTVs). Recent characterisation of the system revealed moderate eccentricities for these planets. However, convergent migration whitin a protoplanetary disk does not favour significant orbital eccentricity excitation. An additional fourth planet has been proposed to reduce the eccentricities of planets b and c. To distinguish between the proposed scenarios, additional transit observations are necessary. We aim to improve our understanding of the system’s architecture, particularly its planetary eccentricities, by observing three transits of K2-19c using CHEOPS to refine the TTV model.

ID0014 — Stellar Occultation by Minor Bodies in our Solar System with CHEOPS (PI: Altair Ramos Gomes Junior)
Stellar Occultation is one of the leading techniques in accessing important physical characteristics of solar system bodies. With it, it was possible to discover rings around the Centaur Chariklo and the TNOs Haumea and Quaoar, detect sub-km TNOs, and variations of Pluto's atmospheric pressure. The knowledge of such characteristics has been important in understanding the origin and evolution of the solar system. Since the technique translates photometric resolution into astrometric resolution, a better photometric condition will provide improved constraints in the determination of the body’s physical characteristics. As a natural step forward, observing stellar occultation by spacecraft will provide better photometric circumstances avoiding the noise caused by atmospheric fluctuations. With CHEOPS, fourteen interesting stellar occultations have considerable chances of being observed, involving the dwarf planet Pluto and other TNOs larger than 500 km in diameter, including Quaoar, which has a known ring system. We can further study the atmosphere of Pluto, the rings of Quaoar, and improve our knowledge about the presence of rings or materials around these distant bodies.

ID0015 — Hunting a second transit of the long-period Neptune exoplanet HIP41378 e in the gaps of TESS (PI: Salome Grouffal)
Among more than 800 planetary systems discovered up to now, the system HIP 41378 offers wide opportunities for future atmospheric characterization of exoplanets. Observed for the first time in 2015 by the mission K2, this system is rich of at least five transiting planets around a bright late F-type star. Among them, the planet f is an interesting target for studying its atmosphere. This planet has a low density (< 0.2 g/cm3) for a planet in the habitable zone, which is not yet understood. The comparison with its twin planet, HIP41378 e (Teq ~ 400 K), offers an opportunity to understand the unique properties of the puffy planet f. However, with just one transit detected in 2015, the precise period of planet e is unknown. With this CHEOPS proposal, we aim at hunting for a second transit of planet e. No transit of this planet has been detected in the TESS data at the expected period, albeit with large gaps. We require CHEOPS observations to search for the missing transit of planet e in these gaps. The detection of a second transit of planet e will secure its orbital period and allows us to schedule follow-up observations with, e.g., HST and/ or JWST for comparative studies. It will also help to understand the architecture of this fascinating planetary system.

ID0016 — Probing the M-dwarf Radius and Temperature Discrepancies with the 72-day G-M EB TOI-2065 (PI: Daniel Stevens)
At fixed mass, measured M-dwarf radii are inflated, and effective temperatures cooled, by ~5% relative to those from stellar evolutionary models. Most M-dwarfs with directly measured masses, radii, and temperatures are those in double-lined eclipsing binaries (EBs) -- and, however, in mostly short-period EBs, in which strong binary-star interactions can deform and heat the stellar surfaces. To date, only a handful of M-dwarfs with sufficiently precise (couple-percent) mass, radius, and temperature measurements are in long-period EBs, in which the component behave like essentially single star. We request 30 CHEOPS orbits in a single visit to measure the day-long primary eclipse of the 72-day single-lined EB TOI-2065 (TIC 356710041), which consists of a G-type subgiant and an M-dwarf. With a CHEOPS primary eclipse plus the in-hand TESS secondary eclipse, archival broad-band and Gaia spectro-photometry, and Gaia radial velocity orbit, we will measure the M-dwarf's fundamental properties to 2% precision or better. TOI-2065 B will be the longest-period M-dwarf with a precisely and directly determined mass, radius, and temperature, making it a crucial laboratory for studying the M-dwarf "radius inflation" phenomenon.

ID0017 — Accurate and precise characterisation of the HIP 67522 system in the presence of significant stellar variability (PI: Hritam Chakraborty)
Young planets are excellent laboratories to test planet formation and evolution pathways. However, the accurate characterisation of parameters like the radius of the planet is limited by the enhanced activity of the host star. The impact of features like unocculted and occulted active regions is a growing challenge in the era of high-precision photometry and transmission spectroscopy, and better characterisation of these features is now more vital than ever for the correct interpretation of atmospheres on exoplanets. Here we propose to precisely characterise the HIP 67522 system, a 17 Myr Solar-like star exhibiting significant stellar activity and one of the youngest planet-hosting stars discovered to date. The HIP 67522 system consists of one confirmed transiting hot Jupiter (planet b) and an unconfirmed outer planet candidate (planet c). To characterise this key young system we aim to: i) obtain an accurate and precise radius measurement for the known transiting planet (planet b) by quantifying the effect of stellar activity on its transit depth, and ii) confirm the candidate exoplanet (planet c) by following up the most likely period aliases of its two known transits. While accurately measuring the radius of planet b is vital for testing different planet formation and evolution models for hot Jupiters, confirming planet c will make this the youngest multi-planet transiting system ever discovered, making this a very compelling system to be observed by CHEOPS.

ID0018 — Confirming the orbital parameters of a super-puff-host system to prepare for future atmospheric studies (PI: Belinda Nicholson)
The proposal request time to observe one transit each of HD152843 b and c, an intriguing planet system hosting a super-puff sub-Saturn planet (planet c) alongside a Neptune-size planet of equal mass (planet b). These transit observations are crucial for precisely determining the orbits of these planets for future atmospheric characterisation. The improved radii and orbital parameters of the CHEOPS will in turn allow of better mass determination from an extensive RV campaign, improving the bulk density and interior structure models, and thus helping test the super-puff nature of planet c, and improve the atmospheric characterisation from future atmospheric observations.

ID0019 — Understanding stellar activity patterns by coupling absolute photometry and intense RV monitoring (PI: Manu Stalport)
Nowadays, stellar activity constitutes the main obstacle to the detection of planets with sub-meter per second radial velocity (RV) amplitudes. In the near future, the PLATO mission will survey with high precision the photometric variations of bright stars in specific areas of the sky. The combination of those observations with the most precise spectrographs will certainly be of upmost interest to alleviate stellar activity effects, and provide mass measurements below the meter per second level needed to reach PLATO’s science goals. CHEOPS represents a unique opportunity to take a step ahead in prevision of PLATO, and valuably support extensive RV surveys. The goal of this program is to combine parallel RV and CHEOPS photometric monitorings on a moderately active star, to unveil the nature of the activity patterns in both datasets.

ID0022 — Constraining the Prevalence of Metallic Clouds within the Neptune Desert (PI: James Jenkins)
With the recent stunning discovery of a very high albedo for the extreme Neptune Desert planet LTT9779b, a result that is likely due to the presence of high-altitude metallic clouds in the atmosphere scattering the incoming starlight, we are finally beginning to understand the chemical structure and evolution of these desert worlds. However, given their rarity, one may wonder whether such cloud structures are normal for these types of planets, and if so, what are the physical processes driving this. In order to respond to this question, we request observations using CHEOPS to observe two other planets that have recently been confirmed to reside in the Neptune Desert, and who orbit stars bright enough to significantly detect their secondary eclipses in the optical. We shall measure the eclipses of the planets TOI-1997b and TOI-2352b, allowing us to place strong constraints on their albedos, and therefore model their atmospheric structures. This work will provide evidence for or against the presence of highly reflective silicate and titanium clouds in these planets, and allow us to begin to build a global picture of the atmospheric constituents of some of the most extreme Neptune planets currently known.

ID0023 — 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 was confirmed with a transit detection in previous CHEOPS observations (priv. comm.). This object is a terrestrial-size exoplanet with three transits, each separated by 718 days (two in TESS, one in CHEOPS). This even separation and minimal phase coverage means that the period still needs to be determined. 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 an alias of that spacing, in the 34-60 day range. This planet is therefore a likely-terrestrial planet candidate in its star’s optimistic habitable zone (OHZ). It has potential for future mass measurement and even transmission spectroscopy thanks to its bright (for an M star) host. In fact, no other OHZ terrestrial has a host star as bright as TOI4353.01. Because of the 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.

ID0024 — Confirmation of the first planet to be associated with the Pleiades cluster (PI: Sydney Vach)
The processes that drive planet formation and evolution within the first billion years are key in sculpting the planet population we observe today. Observing young planetary systems is the only opportunity to characterize these processes as they happen in real time. The Pleiades open cluster is one of the most well aged stellar groups, at 120 Myr making it the ideal parent population to anchor planet evolution models. We propose to use CHEOPS to observe two transits of the first planetary candidate, TOI-5358.01, kinematically affiliated with the Pleiades group. TOI-5358.01 is a mini-Neptune (P = 2.66 d, Rp = 2.754 Rearth), orbiting the young K4V star TOI-5358, originally discovered by TESS. CHEOPS observations are critical in the confirmation and characterization of the system, and will enable us to distinguish between different atmospheric characteristics, such as clouds and haze, in future transmission spectroscopy observations.

ID0025 — Constraining the orbital period of HD 114082 b, the most massive among the youngest exoplanets (PI: Carlos del Burgo Díaz)
HD 114082 is a bright, relatively nearby, very young F-type star in the Scorpius-Centaurus (Sco-Cen) OB Association. It bears a nearly edge-on debris disk (Wahhaj et al. 2016) and HD 114082 b, a massive planet that defies current theoretical planet formation models (Zakhozhay et al. 2022, Engler et al. 2023). The planet produced a single-transit event during the TESS observations and its orbital period was later determined using radial velocities. A second transit event detected in March by the NGTS survey provided a set of three plausible orbital periods, one of them similar but still different from that derived from the radial velocity curve. The other two are quite unlike. This is not entirely surprising, as constraining the orbital period of young planets solely from radial velocity measurements is very challenging and prone to underestimate uncertainties due to limitations in the stellar activity modelling. The most reliable way of confirming the orbital elements is detecting and analysing new transit events, preferably from space. We propose to use 86.1 CHEOPS orbits to observe HD 114082 during three candidate transit events, in accordance with the estimated orbital periods, to confirm and refine the planet ephemeris and improve its characterisation.

ID0026 — Period Confirmation for The Sub-Neptune Exoplanet with The Longest Period (PI: Amanda Mohr)
In support of the study of long period planets, we analyzed TESS data, and found 5527. TOI5527.01 was identified as a potential, long period planet by the Transiting Exoplanet Survey Satellite, or TESS. In-depth analysis of TOI5527.01 paints the planet as an exciting low-temperature sub-Neptune planet, with the ability for future follow up. This candidate is one of the longest-period planets discovered by TESS around a bright host star. Simulations of the TESS data performed before the mission suggested that the upper 95th percentile orbital period of discovered candidates is 35 days (e.g. Barclay et al., 2018). This implies that it is improbable for TESS to find many other planets with a period as long as TOI5527.01, making it an exciting and unique target. We request observation time for the two most probably periods, 86.5 days and 69.2 days.

ID0028 — Detection of the third transit of a sub-Neptune with the longest orbital period ever discovered (PI: Neda Heidari)
Transiting planets with orbital periods longer than 40 d are rare over the 5000+ discovered planets, accounting for only 1% of them. This lack is even more extreme when it comes to smaller planets (< 4 RE), with only 4 well-characterized long-period planets detected to date. We study the HD88986 system, consisting of a transiting sub-Neptune with the longest known orbital period (146.05 +/- 0.49 d) and its massive companion, both of which orbit one of the closest and brightest stars (Gmag=6.30). To validate this discovery, we used extensive SOPHIE observations with 377 data points and a single transit event in the TESS sector 21. HD88986 b, thanks to its long period, was not subjected to strong XUV radiation, preserving its primordial composition and offering a unique opportunity to probe formation conditions. Follow-up Rossiter-McLaughlin studies on HD88986 b and its massive companion, whose configuration has some similarities with that of our solar system, will have an impact on our knowledge of planet-planet interaction, and migration. HD88986's temperate nature (Teff=476 K) will open up exciting prospects for atmospheric cold planet chemistry studies. However, without an exact period, performing follow-up studies on this unique system is impossible. Therefore, we propose a CHEOPS observation to constrain HD88986 b's period and improve precision on its radius by 50 %, which is essential for internal structure and atmospheric modeling.

This page was last updated on 14 July 2023.