European
Southern
Observatory

Call for Letters of Intent
The aim of the Expanding Horizons process is for ESO to gather input from the community to decide on its next major programme, following the completion of ELT construction. ESO has now formally opened the call for Letters of Intent (LoI) for the Expanding Horizons process. The submission of a LoI is a requirement for submitting a proposal. Proposals will be accepted from the entire astronomical community as long as a leading role is played by the community of ESO Member States. This means that submissions led by a non-MS PI are allowed, as long as the strong interest of ESO Member States is demonstrated.
Key dates
  • Call opening: 15 July 2026
  • Submission deadline: 1 December 2026
Purpose of the Letters of Intent

The LoI will be used for two main purposes:

  • ESO will use the LoIs to plan internal resources for the evaluation of the proposals as well as assessing whether a change to the composition of the Senior Science Committee (SSC) is needed to fairly assess all proposals.
  • The list of LoI submitters will be used to define the content of a workshop in May 2027 where the LoI submitters will be invited to present their ideas and discuss them with the community and with ESO.

The Letter of Intent will not be used in the evaluation process but if a proposed concept is clearly inconsistent with the aims of the Expanding Horizons process, ESO will communicate this to the LoI submitters. The full proposals will be due by 1 December 2027. Here we do not provide details for the expected content for the proposal submission, this information will be provided at a later stage.

Content of the Letters of Intent

The LoI should briefly summarise the following points, if relevant, which will be expanded upon in the proposal:

  1. Scientific objectives;
  2. A description of the new concept;
    • Provide a high-level description of the facility with sufficient detail that ESO can assess what kind of engineering/operational expertise is needed for the assessment of the proposal.
  3. Synergies and complementarity (scientific, operational or other) with other ESO facilities;
  4. International context;
  5. Technical maturity, including any critical technologies that would need to be developed;
  6. An operations concept;
  7. Sustainability;
    • Comment which aspects are relevant for the reduction of the environmental, social and financial sustainability impact of the concept.
  8. Any potential partnerships, which ESO may select for the development of the new programme.

The total length should be no longer than five pages at 11 pt font size plus a cover page.

Submission form
  • Will become available soon.

To understand how your personal data are collected and processed by or on behalf of ESO, please read our Privacy Notice.

Publishing of Letters of Intent

In the interest of the openness of the process, the title, submitting team, science objectives and abstract for each concept as summarised in the LoI will be shared by ESO with the community through the http://next.eso.org web page. The other content of the LoI will be kept confidential but shared with the SSC, ESO management and with select ESO staff when needed for resource planning.

X

Our use of Cookies

We use cookies that are essential for accessing our websites and using our services. We also use cookies to analyse, measure and improve our websites’ performance, to enable content sharing via social media and to display media content hosted on third-party platforms.

You can manage your cookies preferences and find out more by visiting 'Cookie Settings and Policy'.

ESO Cookies Policy


The European Organisation for Astronomical Research in the Southern Hemisphere (ESO) is the pre-eminent intergovernmental science and technology organisation in astronomy. It carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities for astronomy.

This Cookies Policy is intended to provide clarity by outlining the cookies used on the ESO public websites, their functions, the options you have for controlling them, and the ways you can contact us for additional details.

What are cookies?

Cookies are small pieces of data stored on your device by websites you visit. They serve various purposes, such as remembering login credentials and preferences and enhance your browsing experience.

Categories of cookies we use

Essential cookies (always active): These cookies are strictly necessary for the proper functioning of our website. Without these cookies, the website cannot operate correctly, and certain services, such as logging in or accessing secure areas, may not be available; because they are essential for the website’s operation, they cannot be disabled.

Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
csrftoken
XSRF protection token. We use this cookie to protect against cross-site request forgery attacks.
1st party
Stored
1 year
user_privacy
Your privacy choices. We use this cookie to save your privacy preferences.
1st party
Stored
6 months
preferred_language
Language settings. We use this cookie to remember your preferred language settings.
1st party
Stored
1 year
_grecaptcha
We use reCAPTCHA to protect our forms against spam and abuse. reCAPTCHA sets a necessary cookie when executed for the purpose of providing its risk analysis. We use www.recaptcha.net instead of www.google.com in order to avoid unnecessary cookies from Google.
3rd party
Stored
6 months

Analytics cookies: These cookies collect information about how visitors interact with our website, such as which pages are visited most often and how users navigate the site. This data helps us improve website performance, optimize content, and enhance the user experience; these cookies are only placed if you provide your consent. We use the following analytics cookies.

Matomo Cookies:

This website uses Matomo (formerly Piwik), an open source software which enables the statistical analysis of website visits. Matomo uses cookies (text files) which are saved on your computer and which allow us to analyze how you use our website. The website user information generated by the cookies will only be saved on the servers of our IT Department. We use this information to analyze www.eso.org visits and to prepare reports on website activities. These data will not be disclosed to third parties.

On behalf of ESO, Matomo will use this information for the purpose of evaluating your use of the website, compiling reports on website activity and providing other services relating to website activity and internet usage.

ON | OFF

Matomo cookies settings:

Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
Settings
_pk_id
Stores a unique visitor ID.
1st party
Stored
13 months
_pk_ses
Session cookie temporarily stores data for the visit.
1st party
Stored
30 minutes
_pk_ref
Stores attribution information (the referrer that brought the visitor to the website).
1st party
Stored
6 months
_pk_testcookie
Temporary cookie to check if a visitor’s browser supports cookies (set in Internet Explorer only).
1st party
Stored
Temporary cookie that expires almost immediately after being set.

Additional Third-party cookies on ESO websites: some of our pages display content from external providers, e.g. YouTube.

Such third-party services are outside of ESO control and may, at any time, change their terms of service, use of cookies, etc.

YouTube: Some videos on the ESO website are embedded from ESO’s official YouTube channel. We have enabled YouTube’s privacy-enhanced mode, meaning that no cookies are set unless the user actively clicks on the video to play it. Additionally, in this mode, YouTube does not store any personally identifiable cookie data for embedded video playbacks. For more details, please refer to YouTube’s embedding videos information page.

Cookies can also be classified based on the following elements.

Regarding the domain, there are:

As for their duration, cookies can be:

How to manage cookies

Cookie settings: You can modify your cookie choices for the ESO webpages at any time by clicking on the link Cookie settings at the bottom of any page.

In your browser: If you wish to delete cookies or instruct your browser to delete or block cookies by default, please visit the help pages of your browser:

Please be aware that if you delete or decline cookies, certain functionalities of our website may be not be available and your browsing experience may be affected.

You can set most browsers to prevent any cookies being placed on your device, but you may then have to manually adjust some preferences every time you visit a site/page. And some services and functionalities may not work properly at all (e.g. profile logging-in, shop check out).

Updates to the ESO Cookies Policy

The ESO Cookies Policy may be subject to future updates, which will be made available on this page.

Additional information

For any queries related to cookies, please contact: pdprATesoDOTorg.

As ESO public webpages are managed by our Department of Communication, your questions will be dealt with the support of the said Department.