Planets orbit their parent stars while separated by enormous distances – in our solar system, planets are like grains of sand in a region the size of a football field. The time that planets take to orbit their suns have no specific relationship to each other.
But sometimes, their orbits display striking patterns. For example, astronomers studying six planets orbiting a star 100 light years away have just found that they orbit their star with an almost rhythmic beat, in perfect synchrony. Each pair of planets completes their orbits in times that are the ratios of whole numbers, allowing the planets to align and exert a gravitational push and pull on the other during their orbit.
This type of gravitational alignment is called orbital resonance, and it’s like a harmony between distant planets.
Harmony of the spheres
Greek mathematician Pythagoras discovered the principles of musical harmony 2,500 years ago by analyzing the sounds of blacksmiths’ hammers and plucked strings.
He believed mathematics was at the heart of the natural world and proposed that the Sun, Moon and planets each emit unique hums based on their orbital properties. He thought this “music of the spheres” would be imperceptible to the human ear.
Four hundred years ago, Johannes Kepler picked up this idea. He proposed that musical intervals and harmonies described the motions of the six known planets at the time.
To Kepler, the solar system had two basses, Jupiter and Saturn; a tenor, Mars; two altos, Venus and Earth; and a soprano, Mercury. These roles reflected how long it took each planet to orbit the Sun, lower speeds for the outer planets and higher speeds for the inner planets.
He called the book he wrote on these mathematical relationships “The Harmony of the World.” While these ideas have some similarities to the concept of orbital resonance, planets don’t actually make sounds, since sound can’t travel through the vacuum of space.
Resonance happens when planets or moons have orbital periods that are ratios of whole numbers. The orbital period is the time taken for a planet to make one complete circuit of the star. So, for example, two planets orbiting a star would be in a 2:1 resonance when one planet takes twice as long as the other to orbit the star. Resonance is seen in only 5% of planetary systems.
In the solar system, Neptune and Pluto are in a 3:2 resonance. There’s also a triple resonance, 4:2:1, among Jupiter’s three moons: Ganymede, Europa and Io. In the time it takes Ganymede to orbit Jupiter, Europa orbits twice and Io orbits four times. Resonances occur naturally, when planets happen to have orbital periods that are the ratio of whole numbers.
Musical intervals describe the relationship between two musical notes. In the musical analogy, important musical intervals based on ratios of frequencies are the fourth, 4:3, the fifth, 3:2, and the octave, 2:1. Anyone who plays the guitar or the piano might recognize these intervals.
Orbital resonances can change how gravity influences two bodies, causing them to speed up, slow down, stabilize on their orbital path and sometimes have their orbits disrupted.
Think of pushing a child on a swing. A planet and a swing both have a natural frequency. Give the child a push that matches the swing motion and they’ll get a boost. They’ll also get a boost if you push them every other time they’re in that position, or every third time. But push them at random times, sometimes with the motion of the swing and sometimes against, and they get no boost.
For planets, the boost can keep them continuing on their orbital paths, but it’s much more likely to disrupt their orbits.
Exoplanets, or planets outside the solar system, show striking examples of resonance, not just between two objects but also between resonant “chains” involving three or more objects.
The newest example of a resonant chain is the HD 110067 system. It’s about 100 light years away and has six sub-Neptune planets, a common type of exoplanet, with orbit ratios of 54:36:24:16:12:9. The discovery is interesting because most resonance chains are unstable and disappear over time.
Despite these examples, resonant chains are rare, and only 1% of all planetary systems display them. Astronomers think that planets form in resonance, but small gravitational nudges from passing stars and wandering planets erase the resonance over time. With HD 110067, the resonant chain has survived for billions of years, offering a rare and pristine view of the system as it was when it formed.
Astronomers use a technique called sonification to translate complex visual data into sound. It gives people a different way to appreciate the beautiful images from the Hubble Space Telescope, and it has been applied to X-ray data and gravitational waves.
With exoplanets, sonification can convey the mathematical relationships of their orbits. Astronomers at the European Southern Observatory created what they call “music of the spheres” for the TOI 178 system by associating a sound on a pentatonic scale to each of the five planets.
Astronomers have also created a sonification for the HD 110067 system. People may not agree on whether these renditions sound like actual music, but it’s inspiring to see Pythagoras’ ideas realized after 2,500 years.
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"The newest example of a resonant chain is the HD 110067 system. It’s about 100 light years away and has six sub-Neptune planets, a common type of exoplanet, with orbit ratios of 54:36:24:16:12:9. The discovery is interesting because most resonance chains are unstable and disappear over time. Despite these examples, resonant chains are rare, and only 1% of all planetary systems display them. Astronomers think that planets form in resonance, but small gravitational nudges from passing stars and wandering planets erase the resonance over time. With HD 110067, the resonant chain has survived for billions of years, offering a rare and pristine view of the system as it was when it formed."Reply
This is intriguing. HD 110067 properties can be seen at this site, https://exoplanet.eu/home/
All six orbit well inside where we see Mercury in our solar system with masses ranging 3.9 earth to 8.52 earths. The host star is listed as 8.1 Gyr. Somehow these super earths formed very close to the host star, maintained their orbits and resonance, perhaps over some 8.1 billion years or more. The timescale for the age of the system could also be wrong, not nearly so old.
That's not what I see. It appears to me that each orbit is independent and UN-affected by the other orbits. I didn't see any change in their speed or direction when they grouped up. Or spread apart.Reply
I think we could put a duplicate earth in earth's orbit without any effects at all. And even slowly nudge it to earth and even dock with it, if it didn't spin. Just like satellites.
I even think one could pluck or more planets out and the ones left would continue.
I think a planet orbit is in resonance with itself. One small stretched out spin formed into a another rotation. I think a planet orbit is a one turn closed helix. 1 to 1 ratio.
It has always seemed a little odd to me that the swinging analogy is used to support unchanging (ie stable) orbits. The point in pushing at the right time on the swing is to cause the person to go higher and higher and higher....Reply
I think in most cases, resonance is destabilizing. This, apparently, is very true for small bodies orbiting a large one, like ring particles around Saturn. The gaps found in the asteroid belt are other examples.
But when it's more massive objects, the resonance serves to hold them from wandering. Funny how the same forces of nature can, in certain cases, produce opposite results.
The animation is of too small a scale to show the perturbations that keep them in their stable orbits. Note the fixed rendezvous points. If a planet is slightly early, the other won't be in place yet, the two will be farther away than usual, the early arriver will receive a slight pull to slow it down. When a late arriver gets into position, the other planet will be ahead in its orbit, pulling the laggard ahead.Reply
My (new) way of conceptualizing gravity is with space as the orthogonal foundation and gravity describes the eccentric distribution of time-speed across it.Reply
Time runs slower proximate to matter, which would be the definition of mass.
Inertia favors slowed time because conceptually either a moving object (matter) 'speeds up' or space 'shrinks' in the vicinity of slowed time.
Planets in resonance are temporally slipstreaming.
Aligning in a temporal trough not a spatial one.
Depending on the distance between planets, planet sizes and the distance to their star they might be in a constant eclipse state except for the innermost planet. Constantly in the shade of another planet(s).
Also people/beings on middle planets quite possibly can see only the two planets they are between because any planet further from them in the sequence are in constant occultation.
Hard to imagine this wouldn't be a problem keeping an orbiting moon in orbit unless it was perfectly perpendicular to planet chain axis.
Otherwise it would constantly be hitting temporal 'speed bumps'.
There are 894 solar systems documented now at this site, https://exoplanet.eu/catalog/, and 947 documented here, https://exoplanetarchive.ipac.caltech.edu/index.htmlReply
None of these solar systems look like ours here. HD 11067 system is also found in my queries, TRAPPIST-1 too, and others like KOI-351 with 8 planets., also Kepler-90. Others have 2 or more exoplanets confirmed now. I would think astrobiology needs to show some of these extra-solar systems, indeed have an earthlike exoplanet with life on it, whether microorganisms or planets and trees. K2-18 system shows up and there are a number of reports attempting to show life on this possible hycean world. Others keep popping up indicating a magma world is likely here and not phytoplankton swimming around in a habitable ocean world.
JWST data suggest exoplanet K2-18b may have molten surface rather than a watery ocean, https://phys.org/news/2024-02-jwst-exoplanet-k2-18b-molten.html
Ref - Distinguishing Oceans of Water from Magma on Mini-Neptune K2-18b, https://iopscience.iop.org/article/10.3847/2041-8213/ad206e, 02-Feb-2024. "Abstract Mildly irradiated mini-Neptunes have densities potentially consistent with them hosting substantial liquid-water oceans ("Hycean" planets). The presence of CO2 and simultaneous absence of ammonia (NH3) in their atmospheres has been proposed as a fingerprint of such worlds. JWST observations of K2-18b, the archetypal Hycean, have found the presence of CO2 and the depletion of NH3 to <100 ppm; hence, it has been inferred that this planet may host liquid-water oceans. In contrast, climate modeling suggests that many of these mini-Neptunes, including K2-18b, may likely be too hot to host liquid water. We propose a solution to this discrepancy between observation and climate modeling by investigating the effect of a magma ocean on the atmospheric chemistry of mini-Neptunes. We demonstrate that atmospheric NH3 depletion is a natural consequence of the high solubility of nitrogen species in magma at reducing conditions; precisely the conditions prevailing where a thick hydrogen envelope is in communication with a molten planetary surface. The magma ocean model reproduces the present JWST spectrum of K2-18b to ≲3σ, suggesting this is as credible an explanation for current observations as the planet hosting a liquid-water ocean."
Still looking for ET phoning home :)