- 4348
- ORBITAL RESONANCE
- Orbital resonance is the
striking gravitational dance done by planets with aligning orbits. Planets can gravitationally affect each other
when their orbits line up.
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------------------------- 4348 -
ORBITAL RESONANCE?
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- 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.
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- But sometimes, their orbits display
striking patterns. 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.
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- This type of gravitational alignment is
called “orbital resonance”. Astronomers
have discovered over 5,600 exoplanets in the past 30 years,(as of 2023) and
their extraordinary diversity continues to surprise astronomers.
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- Greek mathematician Pythagoras discovered
the principles of musical harmony 2,500 years ago by analyzing the sounds of
blacksmiths' hammers and plucked strings.
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- 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 eye
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- Orbital resonance, as seen with Jupiter’s
moons, happens when planetary bodies’ orbits line up, for example, Io orbits
Jupiter four times in the time it takes Europa to orbit twice and Ganymede to
orbit once.
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- 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.
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- He called the book he wrote on these
mathematical relationships "The Harmony of the World." 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.
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- 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.
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- In our 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.
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- 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.
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- 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.
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- 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.
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- Orbital resonance can cause planets or
asteroids to speed up or start to wobble.
The star “Gliese 876” has three planets with orbit period ratios of
4:2:1, just like Jupiter's three moons. “Kepler 223” has four planets with
ratios of 8:6:4:3.
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- The red dwarf “Kepler 80” has five planets
with ratios of 9:6:4:3:2, and “TOI 178”
has six planets, of which five are in a resonant chain with ratios of
18:9:6:4:3.
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- “TRAPPIST-1” is the record holder. It has
seven Earth-like planets, two of which might be habitable, with orbit ratios of
24:15:9:6:4:3:2.
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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.
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- 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.
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- 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.
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- A similar musical translation has been done
for the TRAPPIST-1 system, with the orbital frequencies scaled up by a factor
of 212 million to bring them into audible range.
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- 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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- Scientists have discovered a rare sight in a
nearby star system: Six planets orbiting their central star in a rhythmic beat.
The planets move in an orbital waltz that repeats itself so precisely that it
can be readily set to music.
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- This discovery is going to become a
benchmark system to study how sub-Neptunes, the most common type of planets
outside of the solar system, form, evolve, what are they made of, and if they
possess the right conditions to support the existence of liquid water in their
surfaces.
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- The six planets orbit a star known as
“HD110067” lies around 100 light-years away in the northern constellation of
Coma Berenices. In 2020, NASA's
“Transiting Exoplanet Survey Satellite” (TESS) detected dips in the star's
brightness that indicated planets were passing in front of the star's surface.
Combining data from both TESS and the European Space Agency's “CHaracterizing
ExOPlanet Satellite” (Cheops), a team of researchers analyzed the data and
discovered a first-of-its-kind configuration.
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- While multi-planet systems are common in our
galaxy, those in a tight gravitational formation known as "resonance"
are observed by astronomers far less often.
In this case, the planet closest to the star makes three orbits for
every two of the next planet out, a 3/2 resonance, a pattern that is repeated
among the four closest planets. Among the outermost planets, a pattern of four
orbits for every three of the next planet out (a 4/3 resonance) is repeated
twice.
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- Orbitally resonant systems are extremely
important to find because they tell astronomers about the formation and
subsequent evolution of the planetary system. Planets around stars tend to form
in resonance but can be easily perturbed. For example, a very massive planet, a
close encounter with a passing star, or a giant impact event can all disrupt
the careful balance.
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- As a result, many of the multi-planet
systems known to astronomers are not in resonance but look close enough that
they could have been resonant once. However, multi-planet systems preserving
their resonance are rare.
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- Only about one percent of all systems stay
in resonance, and even fewer show a chain of planets in such configuration.
That why HD110067 is special and invites further study, It shows us the pristine configuration of a
planetary system that has survived untouched.
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February 8, 2023 ORBITAL
RESONANCE
4348
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--------------------- --- Friday, February 9,
2024
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