These newly discovered worlds are hot, gassy, and unlikely to be pleasant places to visit. Their cozy orbits around their parent star put them well within what astronomers consider the “habitable zone” of a planetary system. The hunt for Earth 2.0 continues.
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But these planets are unusual in that, in addition to their large numbers, they resonate with each other as they orbit the star. For example, one planet makes exactly three orbits, while a nearby planet makes two.
“These resonance chains are very rare in nature,” lead author Raphael Luke of the University of Chicago said in a webinar with reporters on Tuesday.
This remarkable reminder that mathematics governs the universe comes with another implication, namely that these six planets have been in a stable, predictable, two-by-three orbital pattern since their formation at least 4 billion years ago. Most planetary systems, including our own, are not like that.
The planets’ vibrational orbits are consistent with the idea that the system has been free of any major disturbance—say, a cataclysmic impact or a close pass by another star—for billions of years. In this scenario, planets formed from a cloud of gas and dust along with their parent star and found their resonant orbits relatively quickly. And then nothing amazing happened to change that.
This unusual orbital structure is central to the new paper’s graphic title: “A Vibrant Sextuplet of Sub-Neptunes Passing a Bright Star HD 110067.”
“Once in a while, nature reveals an absolute gem,” Sarah Seeger, a professor of planetary science at the Massachusetts Institute of Technology and co-author of the new paper, said in an email. “HD 110067 is an immediate astronomical Rosetta stone – providing a key system that could help unlock some of the mysteries of planet formation and evolution.”
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A new paper written by more than 150 scientists from 12 countries describes the planetary system. HD 110067 is a star in our galaxy. It is located in the constellation Coma Berenices Cannot be seen by the naked eye.
Still, it’s 100 light-years away, meaning it’s in our neighborhood, on the outskirts of the Milky Way galaxy. Its proximity to Earth makes it brighter compared to many stars previously known to have planetary systems. It is 10,000 times brighter than, for example, the red dwarf star Trappist1, and contains an intriguing cluster of rocky planets.
Starlight is a valuable currency for astronomers, who can study the star’s glare for clues to the presence of unseen planets. When a planet passes the face of a star as seen through a telescope — an event called a transit — the star’s light dims, depending on the planet’s size.
Astronomers can use a second technique to see periodic wobbles in starlight as an orbiting planet and star interact gravitationally. By combining these methods, astronomers can get an estimate of a planet’s size and density. Further investigation may reveal the molecular composition of the atmosphere, if any.
Astronomers discovered the first pair of planets orbiting HD 110067 in 2020 using NASA’s Transiting Exoplanet Survey Satellite (TESS), which scans the entire sky looking for subtle signals from the planets. The list of planets will be filled out in 2022 during another observation by TESS and the European Space Agency’s CHEOPS (“Classification of Exoplanets Satellite”) satellite, which has more targeted tracking capabilities.
The new planets are called “sub-Neptunes” because they are larger than the closest, rocky worlds in our solar system, such as Earth and Venus, but not as large as the ice giants Neptune and Uranus. They are two to three times the diameter of the Earth. The innermost planet orbits the star in just 9 days, while the outer one completes the journey in 54. Other planets may not be detected in this system.
For some reason, the universe is ugly with sub-Neptune planets, which is one reason the new system is so exciting for astronomers.
“With six major planets, its architecture is intriguing,” Nicole Colon, NASA’s astrophysicist and exoplanet expert, said in an email. “These planets aren’t going to support life because they’re all too hot and too big. But still the whole sub-Neptune angle is the intriguing part, [because] We still don’t know why our solar system doesn’t have one.
It is an open question whether the Universe simply supports planets of this size or whether our detection methods are biasing the results. It is difficult to find small, rocky worlds like ours orbiting at a comfortable distance from an old, quiescent star like our Sun. They are less likely to cross the star’s face when viewed from Earth, and have minimal gravitational effects on the star’s motion.
The discoverers of the new planets claimed evidence of having atmospheres based on their density. But, Luke noted, “we don’t know much about them. We don’t know what they are made of.
We’ll know more soon. This new planetary system will get a closer look from NASA’s James Webb Space Telescope, which orbits the Sun about a million miles from Earth and is designed to gather information about the atmospheres of the outer planets.