Blog: High contrast imaging and the search for habitable worlds

UK ATC project scientist Dan Dicken on the UK’s ambition to join NASA’s mission to find Earth-like planets around distant stars.

High Contrast Imaging (HCI) is, at the most basic level, imaging things that are very faint, next to very bright things. It sounds simple, but in practice it’s incredibly complex. The challenge is to null the light from the bright object – such as a star – so that you can see a faint object next to it – in this case a planet.

The key difficulty is scale. The light from an Earth-like planet can be 10 billion times fainter than its host star, so you have to cancel out that starlight by the same factor. That’s why HCI sits at the heart of NASA’s next major space astronomy mission, the Habitable Worlds Observatory (HWO). If you can’t directly image these planets, you can’t meet the mission’s core objective.

Until now, most exoplanets have been found using transit methods, where a planet passes in front of a star and dims its light. But that only works when systems are aligned just right, and most aren’t. So if we want to find and study Earth-like planets, we have to move toward direct imaging, and that means mastering HCI.

This was really the focus of our recent meeting at UK ATC in Edinburgh. How we actually deliver HCI for HWO. How to bring the community together to build a near-infrared coronagraph as an international contribution to this next generation space telescope. NASA has made it clear they will develop part of the system, but they’re looking for partners – particularly for the near-infrared channel – and that’s where Europe comes in.

The big outcome from the meeting was that, collectively, the community decided to move forward and create a consortium. With colleagues from across Europe, along with contributions from Canada and the US, and NASA in the room, there was agreement to organise as a community and respond to ESA’s [the European Space Agency] upcoming call for instrument proposals for HWO. That’s a major step forward, because it turns what could have been a loose collaboration into something structured and purposeful.

For me, the collaboration model is a no-brainer. It’s very similar to how the MIRI instrument on the James Webb Space Telescope was delivered, which was half US, half European, and hugely successful. We’re trying to follow that same approach, with contributions across Europe supported by NASA and ESA. The UK in particular has a strong role to play, building on its experience in spectrographs and pushing ahead with new detector technology.

That detector work is especially exciting. We’re talking about avalanche photodiode technology that can count single photons, essential when dealing with such faint signals. It’s an area where the UK can lead, and it could become a defining contribution to the instrument.

More broadly, the atmosphere at the meeting was extremely positive. HCI is already a well-established field on ground-based telescopes, but this feels like a new adventure in space. There’s a shared sense that the goal is challenging, but also that everyone is pulling in the same direction. Support from NASA, ESA and national space agencies is strong, and there’s a real willingness across the community to collaborate.

The science case also helps. Searching for habitable worlds is something people immediately understand. But it’s not just about Earth-like planets – there are many other possibilities, from ice-encrusted snowball Earths to super-Mars analogues, which widen the scope and make the science even more interesting.

Ultimately, the key takeaway is that the community is ready to move forward. The decision to form a consortium, the alignment with ESA’s upcoming call, and strong international partnerships all point in the same direction. The next challenge is funding, but the foundations are there. And if we get this right, HCI will sit right at the centre of HWO and the search for life on other planets.