High up in the Chilean Atacama Desert the hillsides are dotted with clusters of telescopes. The absence of clouds and lack of light pollution make it an ideal spot to inspect the night sky. Beginning with his PhD research, Peter Pedersen has been using one of these telescopes to search for signs of habitable planets in our galaxy.

Peter came to Corpus as a student in the Centre for Doctoral Training Sensor Technologies for a Healthy and Sustainable Future, a four-year interdisciplinary and research-focused training programme structured as a one year Master of Research (MRes) course followed by a three-year PhD research project. It was his interest in sensor technology that led him to his PhD subject, working on instrumentation for astronomy under Professor Didier Queloz, a pioneer in the discovery of exoplanets for which he was awarded a Nobel Prize in 2019.

Peter’s research is part of a mission called SPECULOOS
(The Search for habitable Planets EClipsing ULtra-cOOl Stars), which looks for potentially habitable exoplanets orbiting nearby stars. Promising target planets identified by the mission can then be examined in more detail by giant observatories such as the newly launched James Webb Space Telescope. Ultimately, the goal is to find rocky worlds similar to Earth, with the possibility of finding signs of biological activity.

SPECULOOS operates a network of robotic telescopes which include four located at the European Southern Observatory (SSO) of Paranal in Chile. Named Io, Europa, Ganymede, and Callisto, each telescope has a primary mirror one metre in diameter and is equipped with a highly sensitive astronomical camera.

The telescopes can be operated remotely to focus on stars looking for ‘transits’, dips of light that indicate a planet
passing across the disc of a star. The project follows on from
a previous transit study known as TRAPPIST, which discovered a promising planetary system orbiting a cool star, TRAPPIST-1. SSO is looking at stars similar to and cooler than TRAPPIST-1:
ultra-cool dwarfs (UCDs). As a star’s temperature decreases, its peak light emission shifts towards longer wavelengths than those of visible light, into the infrared. So UCDs must be imaged using cameras that capture infrared light. The data from the images can then be plotted to produce a light curve, a graph that shows the varying brightness of the starlight reaching the telescope.

Peering through the mist

Even using infrared light to observe UCDs presents challenges, mainly because the varying precipitable water vapour in the earth’s atmosphere causes the measured brightness of a star to change with time. When Peter joined SPECULOOS, the telescopes were observing light at near-infrared wavelengths, but the resulting data were sometimes contaminated by noise induced by this atmospheric variability. "With our telescopes, it’s sometimes like trying to look outsidethrough a moving, dirty window. I wanted to find a way to see more clearly through that window."

Furthermore, instruments who traditionally use infrared cameras are not only extremely expensive, but they require high-maintenance cryogenic cooling systems, something that wasn’t possible for SPECULOOS’ unmanned robotic telescopes. Peter looked for a new type of camera that could capture the specific short-wave-infrared wavelengths to improve the signal-to-noise ratio of the resulting light curves as well as try and find a way to overcome the effects of atmospheric variability.

My job was to first figure out if it was possible to find this type of instrument and also whether it was financially viable. There are not many of these infrared cameras. They are usually employed for military applications so getting hold of a good one is quite hard. After contacting various manufacturers, Peter was able to identify a short-wave-infrared camera with an indium gallium arsenide-based sensor that he believed could be installed on one of the telescopes.

The camera had to be ordered from the United States and it was delayed by two years due to the COVID pandemic. When it finally arrived, Peter set to work, developing a correction method and filter bandpass to mitigate the effects of water vapour in the atmosphere and writing software to enable the camera to work with the robotic telescope and to transmit
its data to an archive. He also had to engineer a liquid cooling system to maintain the camera at a steady temperature on
a moving telescope.

At the end of 2021, Peter shipped the camera off to Chile (placing an electronic tracker in the box so he could follow its journey over the busy Christmas period). He and the camera were united in Chile and he set off for the observatory for the first of two missions to affix the camera to the telescope Callisto.

“The first mission was about just testing the camera and making sure that we actually saw an image that made sense because I hadn’t actually attached a telescope to this camera before. And then the second mission was ironing out any of the software bugs or hardware issues that we were having so that we could start to do some science.”

Once Peter and the other astronomers were confident that the final images were of the data quality that they had hoped for, they permanently connected the camera to the telescope. We look extensively at a target star every night for a few weeks. This allows us to get phase coverage which include enough periods of time that if a planet did exist, we would see a dip in the starlight. We’re getting about 1,000 images a night, sometimes even more than that. Early results have revealed features that would not have been visible before SPIRIT, and Peter feels that the camera is already making an impact. “I think it offers a new opportunity with small- and medium-size telescopes. Infrared has been out of the reach of many astronomers because of the complications and the expense.
But this technology presents an interesting avenue for the future of exoplanet exploration.”

During his PhD, Peter was also part of a team recognised for their contributions to education by the University of Cambridge’s Centre for Teaching & Learning. Peter and colleagues from the open-seneca initiative were highly commended in the Access & Outreach category in the Centre’s Outstanding Student Contribution to Education Awards.