Exoplanet photobombs observations of its star system

As the star is visible to the naked eye and the system is close to Earth, the planet will be an invaluable target for future studies

Researchers involved in the European Space Agency’s exoplanet-hunting Cheops mission spotted a surprise transit in front of a nearby star. While exploring two exoplanets of the system, the satellite has spotted a new planet, the system’s third one known until date, crossing the face of the star. 

This is the first time an exoplanet with a period of over 100 days has been found transiting a star that is bright enough to be visible to the naked eye. As long-period exoplanets orbit so far from their stars, the chances of seeing one during a transit are incredibly low, making this finding, one of the firsts from ESA’s Cheops (CHaracterising ExOPlanet Satellite), a real surprise.

Named Nu2 Lupi, this bright, Sun-like star is located just under 50 light-years away from Earth in the constellation of Lupus (the Wolf). The system hosts three known exoplanets and the two innermost planets (designated planet b and planet c) had been previously observed transiting the star. As such, the star was one of only three naked-eye stars known to host multiple transiting planets.

Image: Infographic of the Nu2 Lupi planetary system
Caption: This infographic reveals the details of the Nu2 Lupi planetary system, which was recently explored by ESA’s exoplanet watcher Cheops (CHaracterising ExOPlanet Satellite). 
Credits: ESA

“Transiting systems such as Nu2 Lupi are of paramount importance in our understanding of how planets form and evolve, as we can compare several planets around the same bright star in detail,” says Dr. Laetitia Delrez, researcher at the University of Liège (Belgium), and lead author of the new finding. “We set out to build on previous studies of Nu2 Lupi and observe planets b and c crossing the face of the star with Cheops, but during a transit of planet c we spotted something amazing: an unexpected transit by planet d, which lies further out in the system.”

Planetary transits create a valuable opportunity to study a planet’s atmosphere, orbit, size and interior. A transiting planet blocks a tiny but detectable proportion of its star’s light as it crosses in front of it – and it was this drop in light that led Dr. Delrez and colleagues to their discovery. 

Using the high-precision capabilities of Cheops, planet d was found to be about 2.5 times the radius of Earth, confirmed to take just over 107 days to loop once around its star and, using archival observations from ground-based telescopes, found to have a mass 8.8 times that of Earth. 

Most long-period transiting exoplanets discovered to date have been found around stars that are too faint to allow detailed follow-up observations, meaning that little is known about their planets’ properties. Nu2 Lupi, however, is bright enough to be an attractive target for other powerful telescopes based in space — such as the NASA/ESA Hubble Space Telescope or the forthcoming NASA/ESA/CSA James Webb Space Telescope  — or large observatories on the ground. 

Cheops, the ESA mission in which IEEC participates as part of the Science Team and the Mission Board, is designed to collect ultra-high precision data of individual stars known to host planets, rather than sweeping more generally for possible exoplanets around many stars – and this focus and precision are proving exceptionally useful in understanding the star systems around us. 

“While still at the beginning of its mission of measuring exoplanets and identifying interesting targets for further studies, Cheops already lives up to the expectations and is delivering impressive results”, said Prof. Ignasi Ribas, member of the Cheops mission team, researcher at the Institute of Space Sciences (ICE, CSIC) and director of IEEC. 

Observatories and Instruments

Cheops is an ESA mission developed in partnership with Switzerland, with a dedicated consortium led by the University of Bern, and with important contributions from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden and the UK. ESA is the Cheops mission architect, responsible for procurement and testing of the satellite, the launch and early operations phase, and in-orbit commissioning, as well as the Guest Observers’ Programme through which scientists world-wide can apply to observe with Cheops. The consortium of 11 ESA Member States led by Switzerland provided essential elements of the mission. The prime contractor for the design and construction of the spacecraft is Airbus Defence and Space in Madrid, Spain.

The Cheops mission consortium runs the Mission Operations Centre located at the Instituto Nacional de Técnica Aeroespacial (INTA), in Torrejón de Ardoz (Madrid, Spain), and the Science Operations Centre, located at the University of Geneva (Switzerland).

Links

– IEEC
– Cheops ESA

More information

This research is presented in the paper “Transit detection of the long-period volatile-rich super-Earth Nu2 Lupi d with CHEOPS” by Delrez, L. et al. (2021), published in Nature Astronomy.

The Institute of Space Studies of Catalonia (IEEC  — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centers, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.  

IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the University of Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Autonomous University of Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Polytechnic University of Catalonia (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. IEEC is a CERCA (Centres de Recerca de Catalunya) center.

Main Image

Image: Artist’s impression of the Nu2 Lupi planetary system
Caption: This artist’s impression shows the Nu2 Lupi planetary system, which was recently explored by ESA’s exoplanet watcher Cheops (CHaracterising ExOPlanet Satellite). 
Credits: ESA

Contacts

IEEC Communication Office
Barcelona, Spain
Ana Montaner 
E-mail: comunicacio@ieec.cat 

HE Space Operations for European Space Agency’s Communication Office
European Space Research and Technology Centre (ESTEC)
Noordwijk, The Netherlands
Iris Nijman
E-mail: Iris.Nijman@esa.int

Contact Researcher
Barcelona, Spain
Ignasi Ribas
Institute of Space Studies of Catalonia (IEEC) and Institute of Space Sciences (ICE, CSIC)
E-mail: iribas@ice.cat