5th Announcement of Opportunity (AO-5)

for participation in the CHEOPS Guest Observers (GO) Programme


This 5th Announcement of Opportunity (AO-5) marks the second year of opportunities in CHEOPS' first extended mission. AO-5 opens on 12 March 2024 and will close on 25 April 2024, soliciting proposals for observations to be carried out as part of the CHEOPS Guest Observers (GO) Programme, with the observation window spanning from 1 October 2024 to 30 September 2025 (inclusive). CHEOPS offers the GO observers space-based ultra-high precision photometry for the observation of exoplanet transits, eclipses, occultations, phase-curves, and more. Science cases may range to exomoons, ring structures, stellar activity, trans-Neptunian objects, and beyond. The timely overlap of several space- and ground-based missions can provide opportunities for synergies with NASA/ESA/CSA JWST, NASA/ESA HST, NASA TESS, ESO ground-based facilities, and more.



The CHEOPS AO-5 Call provides several modernised tools to further enhance the community access and GO experience:

  • Brand-new Visibility Checker available via Python scripts and Jupyter notebooks for Phase 1
  • Now optional Scheduling Feasibility Checker (SFC) for Phase 1 (now also more lightweight & faster, and only needed for Phase 2)
  • Streamlined Proposal Submission and a new Proposal Handling Tool for Phase 1 (PHT-1)

Itl also repeats the successful novelties introduced with the first extended mission:

  • More targets: only 50 GTO reserved targets, with all the rest generally being open to the entire Community
  • More time: up to 30% science observing time dedicated to the GO Programme
  • Modern approach: double-anonymous peer-review of proposals



Opening of AO-5 Call for Phase 1 observing proposals  12 March 2024 at 12:00 (noon) CET
Deadline for submission of Phase 1 observing proposals 25 April 2024 at 12:00 (noon) CEST
Meeting of the CHEOPS Time Allocation Committee 5 - 7 June 2024
Announcement of award of observing time on CHEOPS (foreseen by) 28 June 2024
Start of preparation of Phase 2 inputs (if awarded observing time) 5 July 2024
Start of observations of AO-5 Programmes (if awarded observing time) 1 October 2024


Important Notes

Prospective observers must take note of the following points:

  • Read the Policies and Procedures document carefully before starting any proposal preparation, as it is the definitive document for this opportunity. It highlights details of CHEOPS' science programme, available time for the community, observing strategy and constraints, and required contents of observing proposals. It also lists the tools and documents available to support observers in their proposal preparation and submission. Remember that all proposal material and file names must be fully anonymous, and that failure to comply will result in rejection on formal grounds. Also thoroughly consult the Observers Manual and all relevant documentation on this website.
  • Follow 7 easy steps
    1. Registration: Register immediately if you do not already have a user account. Waiting with this step until the deadline might cause you to miss the opportunity.
    2. Coordinates: Familiarise yourself with the correct coordinate system to use. Use the Target Checker, Simbad, or MAST. Do not copy & paste from ExoFOP, as it uses a different format.
    3. Visibility Checks: Get familiar with the visibility maps to see which targets might be in reach. Then verify if and when your targets are observable with the brand-new Visbility Tool or (optionally) the Scheduling Feasibility Checker.
    4. Target Status Checks: Make sure your target is eligible by checking the publicly available list of all of CHEOPS' targets (reserved and unreserved ones) and the GTO programme information. Ensure that your observations will contribute something new by checking the CHEOPS Mission Archive to see what data CHEOPS has already gathered.
    5. Exposure Time Calculation: Make sure you can achieve the desired signal-to-noise by using the exposure time calculator.
    6. Proposal Templates: Download, fill in, and you are all set up.
    7. Submission: Phase 1: Submit your proposal via the Proposal Handling Tool for Phase 1 (PHT1).

Please also note that:

  • Updates related to this AO Call and its material will be published at the bottom of this webpage.
  • Note the special case of Alpha Cen (including Alpha Cen A and Alpha Cen B): The system is currently on the Reserved Target List (RTL) but due to its high proper motion and orbital motion, the Target Checker will not resolve its RTL coordinates if querying by name. Alpha Cen’s RTL coordinates are given in the RTL csv file, please use these for any Target Checker queries for this system.
  • We list detailed examples helping you with making your proposals dual-anonymous on the FAQ pages. Please read these carefully and do not hesitate to contact us with any questions.
  • The CHEOPS team will do everything we can to observe and complete awarded programmes if possible. However, it is important to appreciate that an award of observing time does not guarantee that the observations can be conducted, even if a programme is considered to be high priority science. Due to the nature of the science that CHEOPS addresses, time pressure can be high, unforeseen events can occur, and some observations might not be feasible to schedule.
  • CHEOPS is a small mission, with a correspondingly small team to support the GO Programme. Never leave proposal preparation to the very last moment, as it may take a couple of days to answer your questions.


Key Documentation



No updates yet. Happy proposing!


Are You Ready?

Have you read all the above information and key documents carefully and are ready to start the submission process? Then go to the Proposal Submission webpage or click the button below to follow the step-by-step guide.



Questions about CHEOPS or the GO Programme? Please email cheops-support at cosmos.esa.int and we will be happy to help!
This website was last updated on 2 July 2024.