Astronomers Uncover a Harmonious Ensemble of Six Exoplanets

Subscribe to CNN's Wonder Theory science newsletter to delve into the latest news on intriguing discoveries, scientific breakthroughs, and more. Join us as astronomers utilize two distinct exoplanet-detecting satellites to unravel a cosmic enigma, unveiling a unique cluster of six planets situated roughly 100 light-years away from our planet. This groundbreaking discovery has the potential to provide valuable insights into the process of planet formation.

Six exoplanets are in orbit around a star called HD110067, which is similar to the sun in brightness. The star is located in the Coma Berenices constellation in the northern sky. The planets are larger than Earth but smaller than Neptune, belonging to a class known as sub-Neptunes that are commonly found orbiting sunlike stars in the Milky Way. These planets, known as b through g, perform a celestial dance called orbital resonance as they revolve around the star.

A recent study published in the journal Nature has identified discernible patterns as the planets complete their orbits and exert gravitational forces on one another. It was found that for every six orbits completed by the closest planet to the star, planet b, the outermost planet g completes one orbit.

Planet c completes three orbits around the star, while planet d completes two orbits. As planet e finishes four orbits, planet f completes three. This harmonious rhythm results in a resonant chain, with all six planets aligning every few orbits.

has been uncovered in this planetary family, as it has remained virtually unchanged since its formation over 1 billion years ago. This discovery has the potential to provide insights into the development of planets and the origins of sub-Neptunes that are common in our galaxy.

The star system first caught the attention of researchers in 2020 when NASA's TESS detected changes in the brightness of HD110067. Changes in starlight can indicate the presence of a planet passing between its host star and an observing satellite as it moves along its orbital path. This method, known as the transit method, is a key strategy used by scientists to identify exoplanets using telescopes on the ground and in space.

Based on the 2020 data, astronomers were able to determine the orbital periods of two planets orbiting the star. Two years later, TESS observed the star again, and the data indicated different orbital periods for the planets.

When the data sets didn't align, astronomer and lead study author Rafael Luque and some of his colleagues opted to reexamine the star using a different satellite—the European Space Agency's CHaracterising ExOPlanet Satellite, or Cheops. While TESS is utilized to observe portions of the night sky for brief observations, Cheops focuses on one star at a time.

This artist's illustration shows Cheops in orbit around Earth as it searches for exoplanets.

ESA/ATG medialab

Luque, a postdoctoral scholar in the University of Chicago's department of astronomy and astrophysics, explained that they searched for signals among the potential periods of the planets. The data collected by Cheops aided the team in solving the "detective story" initiated by TESS. Cheops identified a third planet in the system, which was essential in confirming the orbital periods of the other two planets and their rhythmic resonance.

The team matched the remaining unexplained TESS data with the Cheops observations and found three more planets orbiting the star. Follow-up observations with ground-based telescopes confirmed the discovery of the planets. Cheops' dedicated observation time helped astronomers clarify the mixed signals from the TESS data and determine the number of planets crossing in front of the star and the resonance of their orbits.

The nearest planet completes an orbit around the star in just over nine Earth days, while the farthest takes about 55 days. In comparison, all planets have faster revolutions around their star than Mercury, which takes 88 days to complete a full orbit around the sun.

The proximity of the planets to HD110067 suggests they have extreme average temperatures, like those of Mercury and Venus, ranging from 167°C to 527°C.

The process of planetary system formation, such as our own solar system, can be tumultuous. Although astronomers theorize that planets typically begin by forming in harmony around stars, this balance can be disrupted by the gravitational pull of large planets, a close encounter with another star, or a collision with another celestial object.

It is rare for planetary systems to remain in harmony, and those with multiple planets that maintain their initial orbits are uncommon. Therefore, astronomers are eager to study HD110067 and its planets as a unique and valuable "fossil" in order to gain a more detailed understanding, according to Luque.

This artist's concept shows what the exoplanet WASP-17 b could look like.

WASP-17 b, also known as Ditsö, orbits its star extremely close at only 0.051 AU, completing a full orbit in just 3.7 Earth-days. The system is located in the Milky Way, about 1,300 light-years away in the constellation Scorpius. This hot gas giant has a volume over seven times that of Jupiter and less than half its mass, making it exceptionally large and fluffy. Its unique characteristics, including its short orbital period and thick atmosphere, make it optimal for observation using transmission spectroscopy to study the effects of its atmosphere on the starlight passing through it.

The atmosphere of WASP-17 b consists mainly of hydrogen and helium, with traces of water vapor, carbon dioxide, and other molecules. Observations of infrared light from Webb's MIRI reveal the presence of clouds containing quartz nanocrystals in the atmosphere of WASP-17 b. The planet is tidally locked with a retrograde orbit, and its temperature varies from around 1,000 kelvins on the cooler nightside to almost 2,000 kelvins on the side in constant daylight.

The star, known as WASP-17 or Diwö, is an F-type star, which is slightly larger, more massive, hotter, and whiter than the Sun. This artist's concept is based on new data collected by MIRI and previous observations from other telescopes, including NASA's Hubble and retired Spitzer space telescopes. Webb has not yet captured any images of the planet.

NASA, ESA, CSA, Ralf Crawford (STScI)

Quartz crystals detected swirling in an exoplanets atmosphere

This is the second time that Cheops has assisted in uncovering a planetary system with orbital resonance. The first one, called TOI-178, was announced in 2021.

is the Cheops, which has made remarkable discoveries seem commonplace. Cheops has already identified a total of two six-planet resonant systems, out of the mere three that are known to exist, all within just three years of conducting operations," stated Maximilian Günther, the project scientist for ESA Cheops.

The researchers noted that the system can also be utilized for the study of the formation of sub-Neptunes. These planets are prevalent in the Milky Way galaxy, but are not present in our own solar system. With a lack of consensus among astronomers about their formation and composition, the abundance of sub-Neptunes in the system could provide valuable insights into their origin, according to Luque.

Numerous exoplanets have been discovered orbiting dwarf stars that are significantly cooler and smaller than our own sun, as seen in the well-known TRAPPIST-1 system and its seven planets, which was announced in 2017. The faintness of the host star in the TRAPPIST-1 system presents challenges for observations, despite its resonant chain.

exoplanet K2-18 b illustration

NASA/ESA/CSA/Joseph Olmsted (STScI)

Webb data reveals that planets in the habitable zone could potentially have rare oceans, indicating a possible sign of life. The star HD110067, with 80% the mass of our sun, is the brightest known star with over four planets in orbit, making it much easier to observe the system.

Initial planet mass detections indicate that some planets have hydrogen-rich atmospheres, making them ideal for study by the James Webb Space Telescope. By using Webb to analyze the composition of these atmospheres as starlight passes through, we can gain insight into the nature of each world.

Study coauthor Jo Ann Egger, a doctoral student in astrophysics at the University of Bern in Switzerland, stated that the low masses of the sub-Neptune planets in the HD110067 system suggest they may be rich in gas or water. She noted that future observations, such as those with the James Webb Space Telescope, could help determine whether the planets have rocky or water-rich interiors.