The surprising transit revealed exciting details about a rare planet “with no known equivalent”.
The CHEOPS space telescope accidentally discovered a unique long-period transiting exoplanet – Nu2 Lupi d, which takes 107 days to loop once around its star. At the same time, the telescope helped scientists determine the approximate structure of all three exoplanets in the system.
The goal of the CHaracterising ExOPlanet Satellite (CHEOPS) space observatory, unlike the similar telescopes CoRoT, Kepler, and TESS, is to study already known exoplanets around bright stars, rather than looking for new ones. CHEOPS was launched into space in December 2019 and began a science program in April 2020.
It is equipped with a telescope with an effective aperture of 30 centimeters and is capable of high-precision photometric observations of stars, registering the periodic passage of planets along their disk, which makes it possible to refine their properties, such as mass, radius, temperature, and properties of the atmosphere.
A unique exoplanet “photobombed” the study of a star system
A group of astronomers led by Laetitia Delrez from the University of Liège has published the results of CHEOPS observations of a system of a bright sun-like star Nu 2 Lupi, located 47.5 light-years from the Sun.
Earlier observations of the star helped detect three exoplanets with masses in the range between Earth and Neptune and orbital periods of 11.6, 27.6, and 107.6 Earth days using the method of radial velocities. Two of these exoplanets were subsequently observed by the TESS telescope, which saw them transiting across the star’s disk.
Scientists noticed that during the observations, the telescope accidentally saw the passage of the farthest planet in the system, Nu2 Lupi d, across the disk of a star, which marked it as a unique long-period transiting exoplanet. In addition, the researchers were able to determine the approximate structure of all three exoplanets.
The radius ν 2 Lupi b was estimated at 1.664 of the Earth’s radius, and the bulk density turned out to be similar to that of the Earth. The radii Nu2 Lupi c and Nu2 Lupi d were estimated at 2.916 and 2.562 of the Earth’s radius, and the bulk densities – 0.453 and 0.522 of the Earth’s bulk density, respectively.
It is assumed that the exoplanet closest to the star is rocky, contains little water (12.6 percent of the total mass of the planet) and gas, and could have been actively losing its atmosphere in the past. Nu2 Lupi c and Nu2 Lupi d (the unique transiting exoplanet) contain much more water (25-27 percent of the total mass of the planet) and a small shell of gas, which most likely consists of hydrogen and helium.
These two exoplanets are massive enough and far from the parent star for significant atmospheric loss. Scientists believe that further observations of this system are necessary, as it appears to be an excellent natural laboratory for testing models of the formation and evolution of low-mass planets.
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• Delrez, L. (2021, June 28). Transit detection of the long-period volatile-rich super-Earth ν2 Lupi d with CHEOPS. Nature News.
• ESA. (n.d.). Unique exoplanet photobombs Cheops study of nearby star system.
• EurekAlert. (n.d.). CHEOPS unexpectedly detects a unique exoplanet.
• ScienceDaily. (2021, June 28). Unique exoplanet photobombs CHEOPS study of nearby star system.