magazine Nature publishes this week the discovery of six exoplanets This orbits a nearby sun-like star HD110067. It is located in the constellation Coma Berenices, about 100 light-years away, and is visible from Earth’s northern hemisphere.
The study led by an astrophysicist Rafael Luque from the University of Chicago (USA) was possible thanks to observations from NASA’s Transiting Exoplanet Survey Satellite (TESS) and ESA’s Characterizing ExOPlanets Satellite (CHEOPS).
Brightness changes in HD 110067 and other signals detected by these and other instruments allowed us to confirm the existence of the six planets that passed in front of their star Resonance pathwaysa kind of synchronized “waltz”.
Although multiplanetary systems are common in our galaxy, those in a tight gravitational formation are known as known resonance (orbits synchronized in a certain way) are observed much less frequently.
In this case, the planet closest to the star makes three orbits for every two orbits of the next planet called Resonance 3/2a pattern that repeats itself on the four nearest planets.
For the other, more distant planets, there are four orbits for every three of the nearest planets, one Resonance 4/3.
Such resonant orbital systems are extremely important because they inform astronomers about the formation and subsequent evolution of the planetary system.
A fossil planetary system
These systems tend to form in resonance but can be easily disrupted. For example, a very massive planet in the system, a close encounter with a passing star, or any type of merger or collision can upset the delicate balance. Therefore, the search for a resonance system is like observing a fossil planetary system.
HD 110067 invites Keep studying itas it shows us the unchanged configuration of a planetary system that has maintained its resonance since its formation: it is likely that the planets have practiced the same gravitational dance since the system’s formation more than a billion years ago.
In addition, it is the brightest known system with four or more planets. Because all of these planets are smaller than Neptune and likely have extensive atmospheres, they are ideal candidates for studying the composition of their atmospheres with the James Webb Space Telescope from NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
Various Spanish research centers took part in this study: the Institute of Space Sciences (ICE CSIC), the Institut d’Estudis Espacials de Catalunya (IEEC), the Institute of Astrophysics of Andalusia (IAA CSIC), the Astrobiology Center (TAXIINTA-CSIC) and the Institute of Astrophysics of the Canary Islands (IAC).
Juan Carlos Morales, Guillem Anglada-Escudé And Ignasi Ribasfrom ICE-CSIC and the IEEC, contributed observations made with CARMENES, the exoplanet search instrument co-developed by the IAA at the Calar Alto Observatory (Almería).
They also collaborated by programming the observations using this instrument’s scheduler, based on the Stars software, a solution from artificial intelligence for the planning of space missions and astronomical instruments developed by ICE-CSIC, the IEEC and the Institute of Cosmos Sciences of the University of Barcelona (ICCUB).
“The high-resolution spectroscopic observations from CARMENES over a year, together with those from the HARPS-N spectrograph (at the Roque de los Muchachos Observatory, Canary Islands), were used to determine the mass of three planets in the system,” and set strict standards boundaries for the others, which shows that they are what we call sub-Neptune class planets,” explains Morales.
This Sub-NeptunesPlanets with radii between Earth’s and Neptune’s are found in close orbits in more than half of Sun-like stars, but the details of their composition, formation and evolution are not precisely known.
The MuSCAT2 instrument installed on the Carlos Sánchez telescope at the Teide Observatory (Canary Islands) was also used to detect transits.
The detective story of discovery
The discovery of these planets is reminiscent of a detective story. The first clues came from TESS satellite from NASA, whose goal is to study the entire sky piece by piece to find short period (short years) exoplanets. In 2020, it detected a decrease in the brightness of the star HD 110067, indicating the passage of planets in front of its surface. These small eclipses are called transits by astronomers.
Two years later, TESS observed the same star again. By adding both series of measurements, the scientists were able to examine a number of transits. However, it was difficult to distinguish how many planets they represented or to determine their orbits. The two series of observations did not seem to agree with each other.
“That’s when we decided to use it CHEOPS“Luque remembers. This exoplanet characterization satellite is the first ESA mission dedicated to studying bright, nearby stars already known to host exoplanets, involving ICE-CSIC and the IEEC.
“We looked for signals between all possible periods that these planets could have,” explains the first author.
Finally, astronomers identified the two innermost planets with orbital periods of 9 days for the closest and 14 days for the next. A third planet with a year of about 20.5 days was identified using data also from the European satellite.
The CHEOPS mission was key to exploring the strange system of six exoplanets. / THE
Then scientists made the extraordinary observation: the orbits of the three planets corresponded to those that would be expected if they were fixed on a Resonance 3/2. They had found the key to unlock the entire system.
The researchers reviewed a known list of resonances that could occur in this type of system and attempted to match them with the rest of the transits detected by TESS. They were able to predict that the three outer planets have orbital periods of 31, 41 and 55 days.
“CHEOPS gave us this resonance configuration that allowed us to predict all other periods. Without this detection it would have been impossible,” admits Luque.
However, TESS observations that had a chance of confirming the predicted orbits of the two outermost planets were left out of processing because they had too much scattered light.
A new analysis of the data to correct for this excess of light revealed two hidden transits, one for each planet, at exactly the times expected in the predictions. Finally, all puzzle pieces fit together.
“Among the more than 5,000 exoplanets discovered orbiting stars other than our Sun, resonances are not rare, nor are systems with multiple planets,” says the co-author. Enric Palle of the IAC: “What is it?” very rare“But the point is to find systems in which the resonances extend over such a long chain of six planets, showing that this system has not undergone any major changes since its formation more than a billion years ago.”
“The universe shows us that our solar system does not appear to be the norm when it comes to planet formation, and once again provides us with an example of the great diversity of planetary systems that exist. This is in addition to his interest in “If we understand how they form and evolve, we may be able to gain additional information about why our planetary system is the way it is,” concludes another author. Pedro J. AmadoIAA researchers.
Orbital movement of the six planets relative to a single planet Year c. For every 360 degree rotation around HD110067 from this planet, Planet B moves 540 degrees, Planet D moves 240 degrees, Planet E moves 160 degrees, Planet F moves 120 degrees, and Planet G moves 90 degrees. / Dr. Hugh Osborn (University of Bern)
Rafael Luque et al. “A resonant sub-Neptune sextuplet transiting the bright star HD 110067.” Nature2023