By Alex Hill (UBC Okanagan) and the ACACS Committee
The SKA is under construction as the world’s largest telescope. It will consist of radio interferometers in Australia (a low-frequency, 50-350 MHz, array of dipoles, SKA-Low) and in South Africa (a mid-frequency, 350 MHz to 14 GHz, array of dishes, SKA-Mid). Canada is a treaty member of the SKA Observatory (SKAO). In this update, we report on SKA-related developments, especially in Canada, from the second half of 2025.
SKA construction is moving forward at both sites, as is the development of Canadian contributions to SKA. NRC has delivered the cryogenic low-noise amplifiers and the Mid Correlator/Beamformer to the SKA-Mid site in South Africa. Canada has begun the hiring of scientific and technical staff with SKA funds; the first two Canadian SKA Scientists , Dr Alice Curtin and Dr Adam Dong, have begun (or will shortly begin) their positions at McGill University and York University respectively. Canada has established an SKA Regional Centre (CanSRC) as an outgrowth of the Canadian Astronomy Data Centre (CADC). SRCs in member countries and regions will ultimately be responsible for serving and enabling analysis of SKA data; typically PIs will access and analyze their data remotely on SRCs rather than downloading the very large SKA data sets. CanSRC is one of 9 validated SRCNet “v0.1” nodes, and CADC products such as the Canadian Advanced Network for Astronomical Research (CANFAR) and Common Archive Observation Model (CAOM) are being incorporated as fundamental (and mandatory) parts of SRCNet going forward.
SKA-Low science commissioning proceeds apace, as described in the first SKAO science community webinar on November 18 (https://www.skao.int/en/science-users/670/skao-science-community-webinars). SKA-Low per-antenna sensitivity is as anticipated over the full frequency range, and interferometric fringes, continuum images, Faraday synthesis spectra, and pulsar timing results show that the end-to-end instrument is working as expected. Initial single-station polarization measurements also match expectations. SKA-Mid construction lags about two years behind SKA-Low, but construction is proceeding and first fringes are expected soon.
Funding is not yet fully secured for the baseline design, Array Assembly 4 (AA4). Therefore SKAO has implemented a staged delivery of SKA capabilities. An intermediate stage, AA*, is thus planned instead which will deliver all planned observing modes at reduced capacity while SKAO works to secure funding for AA4. SKA-Low at AA* was planned to consist of 307 Low stations (but see discussion of deferrals below) with a maximum baseline of 74 km; SKA-Mid at AA* will consist of 144 Mid dishes with a maximum baseline of 36 km (plus one dish at 108 km). AA4 is projected to have 512 Low stations (max baseline 74 km, as in AA*) and 197 Mid dishes (max baseline 197 km).
Fig 1. Timeline for key scientific milestones
There is increasing clarity on the timeline for key scientific milestones towards the delivery of the SKA’s capabilities, which is described in some detail on the SKAO web site and illustrated in Figure 1. The earliest Array Assembly that will be accessible to the international scientific community is AA2, from which the community will see the first science verification data from SKA-Low in 2027 and from SKA-Mid in 2029. It is expected that the international scientific community will have an opportunity to suggest science verification ideas to SKAO in the months leading towards AA2, i.e., in mid-2026 for SKA-Low. Both the visibilities and calibrated datasets will be made publicly available during science verification to allow the international community to test SKAO pipelines and assess the data quality directly. Observing modes and capabilities will be rolled out on the SKA starting with AA2, and will increase in complexity and variety as the system progresses through construction and early operations. Community members interested in the most recent updates regarding the path to science for the SKA can register their interest on the community webinars page as well as consulting documentation from past webinars. Future members who are interested in receiving updates or providing feedback about tools and capabilities can also register their interest. Community members may also join the science working groups.
In June, SKA announced a delay in timelines, primarily a two year delay in the delivery of SKA-Mid, as described in the June Cassiopeia update. In November, SKA Council approved the further deferral of some capabilities in AA* following a budget exercise which identified budgetary gaps. These deferrals were announced to the community in SKAO community webinars in November 2025, for which slides are available. SKAO’s stated intent is to restore these capabilities as soon as financially viable. 50 stations in the core of AA* Low will be deferred, reducing the number of stations from 307 to 257. The number of pulsar search beams will be reduced by ≈80%, to 50 for Low and 200 for Mid. For some science cases, this loss of sensitivity can be made up by integrating for longer. For other science cases, especially transients and pulsar search, the lost beams are a significant loss of capability. The reduced sensitivity due to the deferred capability would be particularly substantial for epoch of reionization HI science, depending on which stations are removed. The epoch of reionization SWG (co-chair: Dr Adrian Liu, McGill) is evaluating the impact.
Key Science Projects will not begin until Cycle 3, with the SKA instead operating as a PI-driven observatory in the initial cycles, including shared-risk time. SKA time allocation and data access policies are published. The ACURA-CASCA Advisory Committee on the SKA (ACACS; co-chairs Dr Alex Hill and Dr Greg Sivakoff) intends to consult the Canadian community to evaluate whether to advocate for changes such as considering both observing time and processing load, instead of only observing time as is currently planned for early observing cycles, when computing the resourcing cost of a program.
