Exoplanet-Hunting Satellite CHEOPS Unexpectedly Detects a Strange Planet “Without a Known Equivalent”

By Crystal Jones on August 25, 2021

This artist’s impression shows the Nu2 Lupi planetary system, which was recently explored by ESA’s exoplanet observer CHEOPS. Credit: © ESA

The exoplanetAn exoplanet (or extrasolar planet) is a planet that is outside the Solar System, orbiting around a star other than the Sun. The first suspected scientific detection of an exoplanet occurred in 1988, with the first confirmation of detection coming in 1992.”>exoplanet satellite hunter CHEOPS of the European Space Agency (ESA), in which the Instituto de Astrofísica de Canarias (IAC) is participating along with other European institutions, has unexpectedly detected a third planet passing in front of its star while it was exploring two previously known planets around the same star. This transit, according to researchers, will reveal exciting details about a strange planet “without a known equivalent.”

The discovery is one of the first results of CHEOPS (CHaracterising ExOPlanet Satellite) and the first time that an exoplanet has been seen with a period longer than 100 days transiting a star that is sufficiently bright to be seen with the naked eye. The discovery was published in the journal Nature Astronomy.

This bright star similar to the sun, called Nu2 Lupi, is a little more than 50 light-years from Earth, in the constellation of Lupus. In 2019, HARPSThe High Accuracy Radial velocity Planet Searcher (HARPS) is one of the most successful planet hunters in the history of astronomy. Housed at ESO’s La Silla Observatory and attached to the 3.6-meter telescope, the HARPS spectrograph searches for exoplanets by detecting minute wobbles in a star’s motion.”>HARPS (High Accuracy Radial velocity Planet Searcher) of the European Southern Observatory (ESOCreated in 1962, the European Southern Observatory (ESO), is a 16-nation intergovernmental research organization for ground-based astronomy. Its formal name is the European Organisation for Astronomical Research in the Southern Hemisphere.”>ESO) in Chile discovered three exoplanets in this system (called b, c, and d) with masses between those of the Earth and NeptuneNeptune is the farthest planet from the sun. In our solar system, it is the fourth-largest planet by size, and third densest. It is named after the Roman god of the sea.”>Neptune, and with orbital periods of 11.6, 27.6 and 107.6 days respectively. Afterward, NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. It’s vision is “To discover and expand knowledge for the benefit of humanity.””>NASA’s TESSLaunched on April 18, 2018, aboard a SpaceX Falcon 9 rocket, NASA’s Transiting Exoplanet Survey Satellite (TESS) is a mission to search nearby stars for undiscovered worlds with a gold of discovering thousands of exoplanets around nearby bright stars.”>TESS satellite, designed to detect transiting planets, found that the two interior planets, b and c, transit Nu2 Lupi, making it one of the only three naked-eye stars which have more than one transiting planet.

This infographic reveals the details of the Nu2 Lupi planetary system, which was recently explored by ESA’s exoplanet watcher Cheops (CHaracterising ExOPlanet Satellite). Credit: ESA, Data: L. Delrez et al (2021)

“Transiting systems such as Nu2 Lupi are of great importance in our understanding of how planets form and evolve, because we can compare several planets around the same bright star in detail,” explains Laetitia Delrez, a researcher at the University of Liege (Belgium) and first author of the article.

“Our idea was to follow up previous studies of Nu2 Lupi and to observe planets b and c passing in front of Nu2 Lupi with CHEOPS, but during a transit of planet c we were amazed to see an unexpected transit of planet d, which is further out within the system,” she adds.

Transits of planets give a valuable opportunity to study their atmospheres, their orbits, their sizes, and their compositions. A transiting planet block out a tiny but detectable proportion of the light of its star when it passes in front of it, and it was this tiny drop in the light that led the researchers to their discovery. Because exoplanets with long periods orbit far away from their stars, the possibility of detecting a planet during transit is very small indeed, which makes the finding with CHEOPS a real surprise.

Using the high precision techniques of CHEOPS planet d was found to have some 2.5 times the radius of the Earth, and its orbital period around its star of a little over 107 days, was confirmed. In addition, using archive observations from terrestrial telescopes its mass could be estimated at 8.8 times that of the Earth.

“The amount of radiation from the star which falls onto planet d is quite small compared to many other known exoplanets. If it were in our own solar system Nu2 Lupi d would orbit between Mercury and VenusVenus, the second planet from the sun, is named after the Roman goddess of love and beauty. After the moon, it is the second-brightest natural object in the night sky. Its rotation (243 Earth days) takes longer than its orbit of the Sun (224.7 Earth days). It is sometimes called Earth’s “sister planet” because of their similar composition, size, mass, and proximity to the Sun. It has no natural satellites.”>Venus,” says Mahmoudreza Oshagh, a senior postdoctoral researcher at the IAC, and a co-author of the paper. “Combined with its bright parent star, its long orbital period and its ideal situation for follow-up, this means that planet d is very exciting: it is an exceptional object, with no known equivalent, and it will certainly be a fundamental object for future studies.”

The majority of long period transiting exoplanets discovered until now are orbiting stars that are too faint to allow detailed follow-up observations, which means that we know little about their properties. Nu2 Lupi is, however, sufficiently bright to be an attractive object for other powerful space telescopes such as the NASA/ESA Hubble Space TelescopeThe Hubble Space Telescope (often referred to as Hubble or HST) is one of NASA’s Great Observatories and was launched into low Earth orbit in 1990. It is one of the largest and most versatile space telescopes in use and features a 2.4-meter mirror and four main instruments that observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. It was named after astronomer Edwin Hubble.”>Hubble Space Telescope, the future James Webb Space TelescopeThe James Webb Space Telescope (JWST or Webb) is an orbiting infrared observatory that will complement and extend the discoveries of the Hubble Space Telescope. It covers longer wavelengths of light, with greatly improved sensitivity, allowing it to see inside dust clouds where stars and planetary systems are forming today as well as looking further back in time to observe the first galaxies that formed in the early universe.”>James Webb Space Telescope, as well as major observatories on the ground. “Given its general properties and its orbit, planet d will be an exceptionally favourable objective to study an exoplanet with a moderate atmospheric temperature around a star similar to the Sun,” adds Laetitia Delrez.

Combining the new data from CHEOPS with archive data from other observatories, the researchers found that planet b is mainly rocky, while planets c and d appear to have large quantities of water surrounded by hydrogen and helium gas. In fact, planets c and d contain much more water than the Earth, a quarter of the mass of each of them is water, in comparison with less than 0.1% on Earth. But this water is not liquid, it is high-pressure ice, or high-temperature water vapor.

“Although none of these planets would be habitable, their diversity makes the system very exciting and a great future perspective to show how these bodies formed and how they have changed with time,” explains Enric Pallé, an IAC researcher and a co-author of the article. “We can also look for rings or moons within the Nu2 Lupi system, because the extreme accuracyHow close the measured value conforms to the correct value.”>accuracy and stability of CHEOPS could allow us to detect bodies close to the size of MarsMars is the second smallest planet in our solar system and the fourth planet from the sun. Iron oxide is prevalent in Mars’ surface resulting in its reddish color and its nickname “The Red Planet.” Mars’ name comes from the Roman god of war.”>Mars.”

CHEOPS is designed to gather high-precision data of individual stars known to harbor planets, rather than to make a more general survey of possible exoplanets around many stars. This approach and accuracy are proving exceptionally useful to understand the planetary systems around the stars around us.

“These exciting results show, yet again, the major potential of this satellite,” says Enric Pallé. CHEOPS will not only give us a better understanding of known exoplanets, but as shown by this result and others in the initial phase of the mission, it will enable us to discover new ones, and to reveal their secrets.”

Exoplanet-Hunting Satellite CHEOPS Unexpectedly Detects a Strange Planet “Without a Known Equivalent”

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