Exoplanet team in Antarctica celebrate their darkest night

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“The summer solstice might mark the longest day of the year in the northern Hemisphere but in Antarctica, today marks the darkest night of year.”

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The summer solstice might mark the longest day of the year in the northern Hemisphere but in Antarctica, today marks the darkest night of year. The 2021 overwintering staff manning research stations throughout the frozen continent are celebrating tonight, including Concordia base, where the University of Birmingham conducts an active and productive campaign of astronomical observations to detect exoplanets - planets that orbit other stars than the Sun. This special day of the Antarctic year is a good time to reminisce on the past year, one of the most extraordinary to date.

Because of its extreme location, staff at the permanently-occupied Franco-Italian base of Concordia are only able to travel to and from the site in a small two-month window between December and January. The base is known as one of the world’s most remote, more so than the International Space Station, and staff there can only rely on themselves to solve any issue for 10 months out of every year. This means that back in January 2020 Concordia closed its doors, and staff entered their usual Austral winter lockdown. At the time, little did they know that soon afterwards the world would be gripped by the most severe pandemic in a century. Protected by hundreds of kilometres of surrounding ice, they operated the station and its telescope throughout the winter when most other astronomical facilities closed as countries fought to protect their population. The data collected during the Austral winter campaign of 2020 is being progressively analysed and shared with the scientific community.

Researchers at the University of Birmingham collaborate with the ASTEP (Antarctic Search for Transiting ExoPlanets) telescope, built next to Concordia base, and located at Dome C – one of several ice plateaus on the Antarctic continent – at 3,200 m in altitude. The temperatures regularly reach down to -80ºC. The cold strips the atmosphere of all moisture and reduces the ambient pressure, making Concordia 10 times drier than the driest desert, the Atacama Desert in Chile, and its atmospheric pressure is equivalent to being at altitudes above 4,000 m. This makes Dome C one of the most interesting sites in the world to conduct astronomical observations. 

The University of Birmingham is the only university in the UK with access to an optical telescope in Antarctica. ASTEP’s main research activity is to detect and study exoplanets through the transit method. A transit is when a planet passes between us and its host star, hiding it in the process, a light signal is created that appears as a slight but periodic reduction in the brightness of the host star. ASTEP’s unique location allows us to observe more easily planetary transits and systems that are otherwise very difficult to collect data on. 

The long Austral winter night, and the total absence of any light pollution also make Concordia particularly attractive for astronomers. Between mid-May and mid-July, observations can happen near continuously. This allows the ASTEP team to collect rare planetary transit signals; those that are hard to observe from elsewhere on Earth, for instance, because the signal would last longer than a typical night at other observatories. In more ways than one, ASTEP is akin to observing from space, but from the ground.

Because of the unique environmental conditions at Concordia, a rich and unique seam of data has been collected. Much of this is still being analysed, but some of the data have already led to several important detections. These include the detection of a planet orbiting a young star, which allows researchers to better understand the process behind planet formation [put a link to the paper]. Observations were also used to precisely measure the time between successive transits of a pair of gas-giants orbiting the TOI-216 system, where both planets are so close to one another that gravity makes their path around the star oscillate ever so slightly, a property that allows us to measure their masses very precisely. Finally, the telescope also participated in the discovery of a rare temperate Neptune-like planet, orbiting a nearby star, and soon the object of detailed atmospheric investigations.

After the 2020 campaign finished, come December, the overwintering staff returned to Europe, and a new contingent took the relay at Concordia. Just like last year, they have been collecting very valuable astronomical observation since late March, including several exciting results that researchers at the University of Birmingham will be publishing in the coming months. For the moment, the Concordia staff are celebrating the darkest night, and the progressive return of daylight. We wish them a Happy Midwinter Day, and thank them infinitely for their dedication and work.

ASTEP, the Antarctic Search for Transiting ExoPlanets is a project led by the Observatoire de la Cote d’Azur of the University of Nice (France), in collaboration with the University of Birmingham, the European Space Agency, and the Institut Paul-Emile Victor, the French polar institute. Research related to ASTEP at Birmingham is funded by the European Union’s Horizon 2020 programme (BEBOP project), and by the Science Technology Facilities Council, part of UK Research and Innovation.

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