FAQ

These targets are not lost because of the CfP update. They are being strictly flagged now according to the duplication policy described in Section 4.8.1 of the Policies & Procedures document, available and applicable since the opening of the AO-1 Call. Without this CfP update, there was a risk that proposers would have missed these instructions and assumed these targets are allowed, but they would have been filtered out after the deadline during technical review. This, in turn, would have risked an incomplete proposal reaching the TAC.

Proposers still have time to reassess these flagged targets, confirm that they are technically viable in terms of brightness and separation, and, where appropriate, request upgraded observing modes. Importantly, such upgrades remain possible in many cases, as stated in Section 4.8.1 of the Policies & Procedures document. This ultimately strengthens the technical and scientific quality of the proposal, and ensures the TAC receives a complete package.

No. The policy remains unchanged. The applicable rules are defined in Section 4.8.1 of the Policies & Procedures document, as discussed and agreed by the PLATO Science Working Team.

The previous CfP version was not designed to serve as a “filter” for the Policies & Procedures, and thus only included the duplication rules to prevent targets being selected within 120 arcsec of Prime Sample targets. This singular check was clearly stated in its User Manual. All other checks were to be done by the proposers. The new CfP version implements however a more extensive set of these Policies & Procedures rules. In that respect, it captures significantly more of the intended policy logic already at the proposal stage.

The Policies & Procedures document remains the definitive reference for what is allowed in terms of duplication checks. As a result of the CfP version update, it now automatically highlights more of these rules directly to the user, including:

1. Proposing observations (within 120 arcsec) of Prime sample targets do not pass the CfP checks in any configuration.
2. Proposing observations (within 108 arcsec) of the P1 sample may pass the CfP checks if requesting F-CAMs. However, any such requests continue to also be flagged to the SOC. This will allow the associated science case to be checked by the SOC and, if necessary, by the TAC.
3. Proposing observations (within 108 arcsec) of the P4/P5 sample may pass the CfP checks if requesting N-CAMs imagettes or F-CAMs. However, any such requests continue to also be flagged to the SOC. This will allow the associated science case to be checked by the SOC and, if necessary, by the TAC.
4. Proposing observations (within 108 arcsec) of the fgPIC sample (excluding scvPIC targets) may pass the CfP checks if requesting N-CAMs imagettes or light curves. However, any such requests continue to also be flagged to the SOC to check for compliance with the duplication policy.
5. Proposing observations (within 108 arcsec) of the scvPIC sample is allowed if the user requests N-CAMs imagettes or F-CAMs. However, any such requests continue to also be flagged to the SOC to check for compliance with the duplication policy.

In practice, it became clear that the rules outlined in the Policies & Procedures document since the AO-1 Call opening were not being interpreted as intended by the wider community. Many proposers erroneously assumed that either the CfP readily enforced all rules, or that certain cases may fall into a grey zone even if they were not allowed. The update effectively introduces an extra safety net for users, ensuring that proposals are better aligned with the policy before submission, rather than being automatically rejected later in the technical review.

The statements referring to violations being "flagged to the SOC" in the Policies & Procedures document for targets remain valid in that the new CfP not only informs the user if a constraint has been broken, but also flags to SOC once the proposal is submitted which targets have been set to a higher observing mode than what is currently in the PIC.

The separation requirements of 108 or 120 arcsec serve several important purposes, including but not limited to:

1. Prevent the observation of Prime Sample targets as required by the Science Management Plan.
2. Avoid duplication with other PIC observations readily providing public data.
3. Serve as general instruction to prevent blending with PIC targets in most cases, which would compromise on-board light curve extraction and scientific value. This general instruction is necessary as it is not operationally feasible for the SOC to evaluate blended targets one-by-one at the level of detail of arcsecs vs. magnitudes for all proposals received.
4. Ensure operational efficiency through a set of clear, consistently applicable rules.

As time passed since the AO-1 Call opened, we found that there was not significant attention being placed by the proposals on the constraints described within the Policies & Procedures document. The fact that duplications are found when you run your target list against the new CfP version unfortunately demonstrates this to be case. Our goal here is to avoid significant disappointment after the AO-1 Call closes, where targets would have to be removed and the prepared science case could be impacted. We wish to relay your proposal to the TAC in its most complete form with consistent targets mapping with your science case.

The TAC evaluates proposals primarily on scientific merit, taking into account all applicable constraints, including the justification for PLATO and the efficient use of telescope resources. Reviewers may therefore consider technical details such as target-level observing modes and cumulative telemetry requirements. Individual reviewers assign grades and comments, which are then discussed during panel meetings where assessments are consolidated. After these meetings, renormalisations per panel are considered, and a single ranked list of proposals is generated. The TAC Chair and Panel Chairs jointly review this list, considering reviewer comments, cumulative telemetry needs, and the overall balance across science categories. Adjustments may be made to ensure appropriate representation.

There are no fixed numerical rules, meaning the TAC is not bound to prioritise proposals based on category or telemetry quotas. This flexibility is intentional for the inaugural AO Call, allowing recognition of high-impact proposals even if they require larger telemetry resources or fall within less‑subscribed categories. Both large and focused programmes may be equally compelling. Final decisions are based on informed scientific discussion rather than preset criteria.

The TAC may recommend partial acceptance of a proposal. For instance, if the science case is strong but does not depend on the full target sample, the TAC may recommend allocating time to only a subset of the proposed targets.

Proposers are responsible for ensuring their original submission contains a single, complete, well‑justified target list that is integral to their project. Proposals are not expected to highlight pre‑prioritised subsets to the TAC, as this would imply that the proposal considers only part of the sample to be essential. However, proposers may order their target lists according to their priorities (see below).

If only part of the requested telemetry can be granted, the SOC will use this sequence as a first‑order guide when selecting targets, while optimising within available telemetry. This optimisation may require skipping certain targets (e.g., high‑telemetry or time‑critical ones) in favour of more feasible options. Due to resource constraints and the complexity of science operations, iterative exchanges between the TAC, SOC, and proposers are generally not feasible. Therefore, the initial submission must be sufficiently complete to allow SOC to perform any required optimisation.

Team expertise is visible only to ESA and is reviewed solely to confirm that the proposing team has the resources necessary to make effective use of the observations. The TAC evaluates proposals purely on scientific merit and does not receive any non‑anonymous information. In cases where the TAC needs verification of specific claims in the science case (e.g., access to proprietary observing time), ESA may anonymously confirm these claims without revealing team identities. This process supports fair evaluation while enabling necessary factual checks.

Proposers and reviewers remain fully anonymous throughout the evaluation process. Limited personal information is disclosed only after the Director of Science issues the final awards. At that point, the principal investigators’ surnames, affiliations, and countries of affiliation for successful proposals are published on the PLATO website. Reviewers who later choose to conclude their service may list their TAC role in their CVs or professional profiles.

In some cases, the TAC may recommend awarding observing time to multiple proposals with overlapping target lists. When this occurs, the TAC may provide specific guidance. Typically, teams are put in contact to decide whether to collaborate, coordinate, or continue independently. In all cases, each team retains the standard proprietary period for their data. In exceptional circumstances (for example, if a team voluntarily waives its proprietary rights), the TAC may recommend awarding time under explicit conditions.

Targets that are in the contaminant table (e.g., identified by the CfP tool as “isPICContaminantFlag = 1”) are allowed provided they follow all other duplication rules in respect to Prime Sample and other PIC targets as defined in Section 4.8.1. of the Policies & Procedures document.

The key requirement is that all information remains clear, legible, and easy for reviewers to follow. Any standard journal-style reference format (e.g., Nature, Science, A&A, MNRAS, ApJ) is acceptable. References may be presented in various styles (e.g., bullet points, continuous text, dual column). Stylistic variations (e.g., font family, italics) are also acceptable. Proposals must follow the Policies & Procedures formatting guidelines for the main text, and are generally encouraged to do so for the full document. However, in line with common practice in other observing or funding proposal calls, minor deviations in references, captions, and footnotes may be tolerated, provided they remain reasonable (e.g., definitely not smaller than 10 pt font and single line spacing).

PLATO has different configuration modes for N‑CAMs and F‑CAMs, and targets are configured for each independently. Due to these constraints, a target may be observed by F‑CAMs but not by N‑CAMs, or vice versa. This can occur even in the centre of the field of view where 26 cameras overlap. However, once a target is configured for N‑CAM observations, it will be observed with all N‑CAMs in which it is visible. This is verified using full‑frame images taken in flight to ensure the target lies on functioning pixels.

No. Due to the technical constraints described above, it is not possible to restrict N‑CAM usage to save telemetry.

No. Proposers may only request existing operating modes. New observing modes cannot be implemented.

During nominal science operations, PLATO will acquire full‑frame images for all cameras at the beginning and end of each quarter as part of calibration. These calibration data may be released together with the L0 and L1 data, although the exact schedule is not yet finalised. Calibration data are generally released after validation, whose timing depends on in‑orbit performance and available resources. Validation is expected to take longer early in the mission and may become faster as operations stabilise.

Targets of Opportunity (ToOs) are accommodated on a best‑effort basis, as they introduce significant technical and scheduling constraints into observation planning. Because of these complexities, it is not possible to define in advance which ToOs can be scheduled or which existing targets may need to be displaced. Only strongly justified ToOs that receive high rankings from the TAC will be considered and, if approved, integrated on a case‑by‑case basis.

Please carefully follow the instructions on the registration website.

You most likely have logged in with a valid ESA Cosmos ID but haven't yet completed your registration as a PLATO user. Please carefully follow the instructions on the registration website.

The PLATO Mission Handbook serves as the detailed reference for the different observing mode, while the CHS & CfP User Manual offers additional information in relation to the proposal software's input and output files. In short and for added clarity, proposals have the following options to define their desired processing type:

The observation lengths for proposal targets have to be given in days. One quarter is described to be 3 months long. In practice, the first quarter may be shorter depending on the exact launch window, and there will be observing gaps between quarters when the satellite is rotated. As such, a reasonable rule-of-thumb for proposals is:

• 1 quarter = 3 months = 90 days
• 3 quarters = 9 months = 270 days
• 2 years = 8 quarters = 24 months = 720 days

If your target is fainter than Pmag=17, we have a brief explanation on our AO-1 Call recipes webpage, stating "It is not generally recommended to propose for observations of targets with Pmag ≳ 17 because this is close to PLATO's ultimate detection limit. The corresponding predictions of the system behaviour become significantly less accurate due to the impact of photon noise from the background and smearing, readout noise, digitalisation noise, and later in operations, charge transfer inefficiency. Proposers wishing to observe targets with Pmag ≳ 17 should foresee a clear feasibility study to convince the TAC that their scientific question(s) can be answered from PLATO observations, even if using it beyond its foreseen capacity." To add more nuances: it is not straightforward to state a single, sharp faint magnitude limit for PLATO, as in-orbit performance has to still be determined during commissioning and further depends on several case-dependent factors (e.g. contaminants, spectral type, observing mode, cadence, and required signal to noise ratio). As a general guideline, the signal to noise ratio becomes low for sources fainter than about Pmag ≈ 16 mag, but scientifically useful observations may still be possible down to Pmag ≈ 17, and in some cases slightly fainter. For such faint targets, users have to use an SNR calculator (e.g. PLATOSim) to assess whether the required precision for their science case can be achieved.

Recent work by the mission team (e.g. Cabrera et al., 2026) notes that model uncertainties increase significantly beyond Pmag ≳ 17. Simulations presented in Jannsen et al. (in preparation; see our "recipes" webpage) explore targets as faint as Pmag ≈ 19, but the noise predictions at these levels are highly uncertain. That study suggests that Pmag ≈ 18–19 may represent PLATO’s ultimate detection limit, though all results at this faint end should be treated with caution.

In summary, while detections of a full loss-of-light or a drastic brightness increase due to a long superflare may be possible down to Pmag ≈ 18–19 in idealised cases (and likely requiring imagette stacking), robust science is more realistically expected for targets brighter than Pmag ≈ 17, depending on the observing strategy and science requirements. Observations of faint sources will also likely require using imagettes, where temporal stacking can be applied if high time or spatial resolution is not required. In some cases, such an approach may make it possible to push to Pmag ≈ 18 mag or even fainter. By contrast, on board photometry is less well suited for very faint sources. It relies on pixel summation over a mask, basic on board processing, and time averaging over 50 s or 600 s, with additional outlier rejection. If a faint source intermittently disappears, this may trigger outlier rejection, making on board photometry unreliable for such targets.

On another note: if your target is brighter than Pmag=17, and the light disappears during the transit leaving only mainly instrumental noise, there may be a problem when subtracting the background by resulting in, for example, fluxes with negative values. These errors in the background correction will be flagged in the light curve. Therefore, it is also recommended here to use imagettes to ensure a proper light curve derivation.