stability of the Solar System

{{main|n-body problem}}

The orbits of the planets are open to long-term variations. Modeling the Solar System is a case of the n-body problem of physics, which is generally unsolvable except by numerical simulation. Because of the chaotic behavior embedded in the mathematics, long-term predictions can only be statistical, rather than certain.

File:Semimajorhistogramofkbos.svgs for a given distance (in AU; i.e., the distance from the Sun to Earth) from the Sun]]

An orbital resonance happens when the periods of any two objects have a simple numerical ratio. The most fundamental period for an object in the Solar System is its orbital period, and orbital resonances pervade the Solar System. In 1867, the American astronomer Daniel Kirkwood noticed that asteroids in the main belt are not randomly distributed.

{{cite book

|last=Hall |first=Nina

|date=September 1994

|title=Exploring Chaos

|publisher=W.W. Norton & Company

|isbn=9780393312263

|page=110

|url=https://books.google.com/books?id=xhm3m-ka0XUC&q=C.+J.+Cohen+astronomer

|via=Google books

}}

There were distinct gaps in the belt at locations that corresponded to resonances with Jupiter. For example, there were no asteroids at the 3:1 resonance — a distance of {{convert|2.5|AU|e6km e6mi|abbr=unit}} — or at the 2:1 resonance, at {{convert|3.3|AU|e6km e6mi|abbr=unit}}. These are now known as the Kirkwood gaps. Some asteroids were later discovered to orbit in these gaps, but when closely analyzed their orbits were determined to be unstable and they will eventually break out of the resonance due to close encounters with a major planet.{{cn|date=January 2024}}

Another common form of resonance in the Solar System is spin–orbit resonance, where the rotation period (the time it takes the planet or moon to rotate once about its axis) has a simple numerical relationship with its orbital period. An example is the Moon, which is in a 1:1 spin–orbit resonance that keeps its far side away from Earth. (This feature is also known as tidal locking.) Another example is Mercury, which is in a 3:2 spin–orbit resonance with the Sun.

The planets' orbits are chaotic over longer time scales, in such a way that the whole Solar System possesses a Lyapunov time in the range of 2~230 million years.

{{cite journal

| first=Wayne B. |last=Hayes

| year=2007

| title=Is the outer Solar system chaotic?

| journal=Nature Physics

| volume=3 | issue=10 | pages=689–691

| doi=10.1038/nphys728 | s2cid=18705038

| bibcode=2007NatPh...3..689H

| arxiv = astro-ph/0702179

}}

In all cases, this means that the positions of individual planets along their orbits ultimately become impossible to predict with any certainty. In some cases, the orbits themselves may change dramatically. Such chaos manifests most strongly as changes in eccentricity, with some planets' orbits becoming significantly more – or less – elliptical.

{{cite book

|first=Ian |last=Stewart

|year=1997

|title=Does God Play Dice? |edition=2nd

|publisher=Penguin Books

|pages=246–249

|isbn=978-0-14-025602-4

}}

{{efn|

The effect of orbital eccentricity oscillation on the shape of the orbit is analogous to the shape change of the rim of a ringing bell, neglecting the side-to-side displacement of the orbit's geometric center. The analogy fails to represent the entire orbital change, because while the gravitational center of the orbit remains nearly fixed on the Sun, its geometric center swings from side to side at the same rate as the eccentricity oscillation; a ringing bell's geometric center remains fixed, or can only swing several orders of magnitude more slowly than its edge vibrates.

}}

In calculation, the unknowns include asteroids, the solar quadrupole moment, mass loss from the Sun through radiation and the solar wind, drag of the solar wind on planetary magnetospheres, galactic tidal forces, and effects from passing stars.

{{cite AV media

|last=Shina

|date=17 September 2012

|title=The stability of the Solar system

|medium=slides & captions

|website=SlideServe |lang=en

|url=http://www.slideserve.com/shina/the-stability-of-the-solar-system

|access-date=2017-10-26

}} — Includes source citations.

The Neptune–Pluto system lies in a 3:2 orbital resonance. C.J. Cohen and E.C. Hubbard at the Naval Surface Warfare Center Dahlgren Division discovered this in 1965. Although the resonance itself will remain stable in the short term, it becomes impossible to predict the position of Pluto with any degree of accuracy, as the uncertainty in the position grows by a factor {{mvar|e}} with each Lyapunov time, which for Pluto is 10–20 million years.

{{cite journal

| last1 = Sussman | first1 = Gerald Jay

| last2 = Wisdom | first2 = Jack |author2-link = Jack Wisdom

| year = 1988

| title = Numerical evidence that the motion of Pluto is chaotic

| journal = Science

| volume = 241 | issue = 4864 | pages = 433–437

| bibcode = 1988Sci...241..433S

| doi = 10.1126/science.241.4864.433

| pmid = 17792606 | s2cid = 1398095

| hdl = 1721.1/6038 | hdl-access = free

| url = http://groups.csail.mit.edu/mac/users/wisdom/pluto-chaos.pdf

| via = groups.csail.mit.edu

}}

Thus, on a time scale of hundreds of millions of years Pluto's orbital phase becomes impossible to determine, even if Pluto's orbit appears to be perfectly stable on 10 myr time scales.{{cite journal|last1=Ito|first1=Takashi|last2=Tanikawa|first2=Kiyotaka|date=October 2002|title=Long-term integrations and stability of planetary orbits in our Solar system|journal=Monthly Notices of the Royal Astronomical Society|volume=336|issue=2|pages=483–500|doi=10.1046/j.1365-8711.2002.05765.x|url=https://academic.oup.com/mnras/article/336/2/483/1158666|url-access=subscription}}

The planet Mercury is especially susceptible to Jupiter's influence because of a small celestial coincidence: Mercury's perihelion, the point where it gets closest to the Sun, precesses at a rate of about 1.5 degrees every 1,000 years, and Jupiter's perihelion precesses only a little slower. At one point, the two may fall into sync, at which time Jupiter's constant gravitational tugs could accumulate and pull Mercury off course, with 1–2% probability, 3–4 billion years into the future. This could eject it from the Solar System altogether or send it on a collision course with Venus, the Sun, or Earth.

{{cite news

| first = David | last = Shiga

| date = 23 April 2008

| title = The Solar system could go haywire before the Sun dies

| department = News service

| magazine = New Scientist

| url = https://www.newscientist.com/article/dn13757-solar-system-could-go-haywire-before-the-sun-dies.html

| access-date=2015-03-31 | url-status=live

| archive-url=https://web.archive.org/web/20141231165529/http://www.newscientist.com/article/dn13757-solar-system-could-go-haywire-before-the-sun-dies.html

| archive-date=2014-12-31

}}

Mercury's perihelion-precession rate is dominated by planet–planet interactions, but about 7.5% of Mercury's perihelion precession rate comes from the effects described by general relativity.

{{cite journal

|last1=Park |first1=Ryan S. |last2=Folkner |first2=William M.

|last3=Konopliv |first3=Alexander S. |last4=Williams |first4=James G.

|last5=Smith |first5=David E. |last6=Zuber |first6=Maria T.

|date=2017-02-22

|title=Precession of Mercury's perihelion from ranging to the Messenger spacecraft

|journal=The Astronomical Journal

|volume=153 |issue=3 |pages=121

|s2cid=125439949 |issn=1538-3881

|bibcode=2017AJ....153..121P

|doi=10.3847/1538-3881/aa5be2 |doi-access=free

|hdl=1721.1/109312 |hdl-access=free

}}

The work by Laskar and Gastineau (described below) showed the importance of general relativity (G.R.) in long-term Solar System stability. Specifically, without G.R. the instability rate of Mercury would be 60 times higher than with G.R. By modelling the instability time of Mercury as a one-dimensional Fokker–Planck diffusion process, the relationship between the instability time of Mercury and the Mercury–Jupiter 1:1 perihelion-precession resonance can be investigated statistically.

{{cite journal

|last1=Mogavero |first1=Federico

|last2=Laskar |first2=Jacques |author2-link=Jacques Laskar

|date=2021

|title=Long-term dynamics of the inner planets in the Solar system

|journal=Astronomy & Astrophysics

|volume=655 |page=A1

|doi=10.1051/0004-6361/202141007 |s2cid=239651491

|arxiv=2105.14976 |bibcode=2021A&A...655A...1M

}}

This diffusion model shows that G.R. not only distances Mercury and Jupiter from falling into a 1:1 resonance, but also decreases the rate at which Mercury diffuses through phase space.

{{cite journal

|last1=Brown |first1=Garett

|last2=Rein |first2=Hanno

|date=2023-03-10

|title=General relativistic precession and the long-term stability of the solar system

|journal=Monthly Notices of the Royal Astronomical Society

|volume=521 |issue=3 |pages=4349–4355

|doi=10.1093/mnras/stad719 |doi-access=free

|issn=0035-8711

|arxiv=2303.05567 |lang=en

}}

Thus, not only does G.R. decrease the likelihood of Mercury's instability, but also extends the time at which it is likely to occur.

Jupiter's Galilean moons experience strong tidal dissipation and mutual interactions due to their size and proximity to Jupiter. Currently, Io, Europa, and Ganymede are in a 4:2:1 Laplace resonance with each other, with each inner moon completing two orbits for every orbit of the next moon out. In around 1.5 billion years, outward migration of these moons will trap the fourth and outermost moon, Callisto, into another 2:1 resonance with Ganymede. This 8:4:2:1 resonance will cause Callisto to migrate outward, and it may remain stable with approximately 56% probability, or become disrupted with Io usually exiting the chain.

{{cite journal

|first1=Giacomo |last1=Lari

|first2=Melaine |last2=Saillenfest

|first3=Marco |last3=Fenucci

|date=July 2020

|title=Long-term evolution of the Galilean satellites: The capture of Callisto into resonance

|journal=Astronomy & Astrophysics

|volume=639 |pages=A40

|doi=10.1051/0004-6361/202037445 |arxiv=2001.01106

|bibcode=2020A&A...639A..40L |s2cid=209862163

}}

Another example is Earth's axial tilt, which, due to friction raised within Earth's mantle by tidal interactions with the Moon, will be rendered chaotic between 1.5 and 4.5 billion years from now.

{{cite journal

|last1=de Surgy |first1=O. Neron

|last2=Laskar |first2=J. |author2-link=Jacques Laskar

|date=February 1997

|title=On the long term evolution of the spin of the Earth

|journal=Astronomy and Astrophysics

|volume=318 |pages=975–989

|bibcode=1997A&A...318..975N

}}

{{efn|name=old_Sun_note}}

{{see also|cataclysmic pole shift hypothesis}}

Objects coming from outside the Solar System can also affect it. Though they are not technically part of the Solar System for the purposes of studying the system's intrinsic stability, they nevertheless can change it. Unfortunately, predicting the potential influences of these extrasolar objects is even more difficult than predicting the influences of objects within the system simply because of the sheer distances involved. Among the known objects with a potential to significantly affect the Solar System is the star Gliese 710, which is expected to pass near the system in approximately 1.281 million years.

Though the star is not expected to substantially affect the orbits of the major planets, it could substantially disrupt the Oort cloud, potentially causing major comet activity throughout the Solar System. There are at least a dozen other stars that have a potential to make a close approach in the next few million years.

{{cite magazine

| last=Dodgson | first=Lindsay

| date=8 January 2017

| title=A star is hurtling towards our Solar system and could knock millions of comets straight towards Earth

| magazine=Business Insider

| url=http://www.businessinsider.com/star-hurting-towards-solar-system-2016-12

}}

In 2022, Garett Brown and Hanno Rein of the University of Toronto published a study exploring the long-term stability of the Solar System in the presence of weak perturbations from stellar flybys. They determined that if a passing star altered the semi-major axis of Neptune by at least 0.03 astronomical unit (4.49 million km; 2.79 million miles) it would increase the chance of instability by 10 times over the subsequent 5 billion years.{{efn|name=old_Sun_note}} They also estimated that a flyby of this magnitude is not likely to occur for 100 billion years.

{{cite journal

|last1=Brown |first1=Garett

|last2=Rein |first2=Hanno

|date=30 June 2022

|title=On the long-term stability of the Solar system in the presence of weak perturbations from stellar flybys

|journal=Monthly Notices of the Royal Astronomical Society

|volume=515 |issue=4 |pages=5942–5950

|arxiv=2206.14240 |doi=10.1093/mnras/stac1763

|doi-access=free

}}

Project LonGStOP (LOng-term Gravitational Study of the Outer Planets) was a 1982 international consortium of Solar System dynamicists led by A.E. Roy. It involved creation of a model on a supercomputer, integrating the orbits of (only) the outer planets. Its results revealed several curious exchanges of energy between the outer planets, but no signs of gross instability.

{{cite journal

|last1=Roy, A.E. |last2=Walker, I.W. |last3=Macdonald, A.J.

|last4=Williams, I.P. |last5=Fox, K. |last6=Murray, C.D.

|last7=Milani, A. |last8=Nobili, A.M. |last9=Message, P.J.

|last10=Sinclair, A.T. |last11=Carpino, M. |display-authors=6

|year=1988

|title=Project LonGStOP

|journal=Vistas in Astronomy

|volume=32 |issue=2 |pages=95–116

|doi=10.1016/0083-6656(88)90399-6

|bibcode=1988VA.....32...95R

}}

Another project involved constructing the Digital Orrery by G. Sussman and his MIT group in 1988. The group used a special-purpose computer whose multiprocessor architecture was optimized for integrating the orbits of the outer planets. It was used to integrate out to 845 million years – some 20% of the age of the Solar System. In 1988, Sussman and Wisdom found data using the Orrery that revealed that Pluto's orbit shows signs of chaos, due in part to its peculiar resonance with Neptune.

If Pluto's orbit is chaotic, then technically the whole Solar System is chaotic. This might be more than a technicality, since even a Solar System body as small as Pluto might affect the others to a perceptible extent through cumulative gravitational perturbations.

{{cite web

|title=Is the Solar system stable?

|website=fortunecity.com

|url=http://www.fortunecity.com/emachines/e11/86/solarsys.html

|archive-url=https://web.archive.org/web/20080625235601/http://www.fortunecity.com/emachines/e11/86/solarsys.html

|archive-date=2008-06-25

}}

In 1989, Jacques Laskar of the Bureau des Longitudes in Paris published the results of his numerical integration of the Solar System over 200 million years. These were not the full equations of motion, but rather averaged equations along the lines of those used by Laplace. Laskar's work showed that the Earth's orbit is chaotic (as are the orbits of all the inner planets) and that an error as small as 15 metres in measuring the position of the Earth today would make it impossible to predict where the Earth would be in its orbit in just over 100 million years' time.

Jacques Laskar and his colleague Mickaël Gastineau in 2008 took a more thorough approach by directly simulating 2,501 possible futures. Each of the 2,501 cases has slightly different initial conditions: Mercury's position varies by about {{convert|1|m|ft|lk=on|abbr=off}} between one simulation and the next.

{{cite magazine

|first=Stephen |last=Battersby

|date=10 June 2009

|title=Solar system's planets could spin out of control

|magazine=New Scientist

|url=https://www.newscientist.com/article/mg20227125.000-solar-systems-planets-could-spin-out-of-control.html

|access-date=2009-06-11

}}

In 20 cases, Mercury goes into a dangerous orbit and often ends up colliding with Venus or plunging into the Sun. Moving in such a warped orbit, Mercury's gravity is more likely to shake other planets out of their settled paths: In one simulated case, Mercury's perturbations sent Mars heading toward Earth.

{{cite journal

|first1=J. |last1=Laskar

|first2=M. |last2=Gastineau

|year=2009

|title=Existence of collisional trajectories of Mercury, Mars, and Venus with the Earth

|journal=Nature

|volume=459 |issue=7248 |pages=817–819

|doi=10.1038/nature08096 |bibcode=2009Natur.459..817L |pmid=19516336

|s2cid=4416436

}}

Independently of Laskar and Gastineau, Batygin and Laughlin were also directly simulating the Solar System 20 billion years into the future.{{efn|name=old_Sun_note}} Their results reached the same basic conclusions as did Laskar and Gastineau, while additionally providing a lower bound of a billion years on the dynamical lifespan of the Solar System.

{{cite journal

|last=Batygin |first=Konstantin |author-link=Konstantin Batygin

|date=2008

|title=On the dynamical stability of the Solar system

|journal=The Astrophysical Journal

|volume=683 |issue=2 |pages=1207–1216

|doi=10.1086/589232 |arxiv=0804.1946

|bibcode=2008ApJ...683.1207B |s2cid=5999697

}}

In 2020, Garett Brown and Hanno Rein of the University of Toronto published the results of their numerical integration of the Solar System over 5 billion years.{{efn|name=old_Sun_note}} Their work showed that Mercury's orbit is highly chaotic and that an error as small as {{convert|0.38|mm|in|lk=on|sp=us|abbr=off}} in measuring the position of Mercury today would make it impossible to predict the eccentricity of its orbit in just over 200 million years' time.

{{cite journal

|last1=Brown |first1=Garett

|last2=Rein |first2=Hanno

|year=2020

|title=A repository of vanilla long-term integrations of the Solar system

|journal=Research Notes of the American Astronomical Society

|volume=4 |issue=12 |page=221

|doi=10.3847/2515-5172/abd103 |doi-access=free

|bibcode=2020RNAAS...4..221B |arxiv=2012.05177

|s2cid=228063964

}}

{{notelist|notes=

{{efn|name=old_Sun_note|

The dynamical modelling of the Solar System beyond approximately 4 billion years into the future is greatly complicated by the transition of the Sun into its old-age giant phase: The Sun will lose mass at an uncertain rate, heat up, and greatly expand, all of which will change the dynamics of planetary orbits.

:

Solar mass-loss will slow all planetary orbits, uniformly slowing the time scale of change in the Solar System. The mass-loss will also reduce Solar perturbations on planets and in relative terms increase perturbations by planets on the Sun and on each other. The gas ejected by the aged Sun may slightly perturb planetary orbits, either by drag (unlikely) or adding to planetary masses (only slightly more likely).{{cn|date=January 2024}}

:

Heating up and expansion of the Sun will severely affect some of the inner planets: It will at least ablate their atmospheres and possibly some of their surfaces (reducing their mass and hence diminishing their perturbations on other planets and the Sun). The only planet certain to be drastically affected is Mercury, which will be enclosed inside the Sun, and presumably slowly dissolved (hence smearing out and removing its perturbations entirely), if it has not previously been ejected from its close Solar orbit.{{cn|date=January 2024}}

}}

}}

• Clearing the neighbourhood
• Future of Earth
• Global catastrophic risk
• Resonant trans-Neptunian object

{{reflist|25em|refs=

{{cite journal

|last1=Bailer-Jones |first1=C.A.L.

|last2=Rybizki |first2=J

|last3=Andrae |first3=R.

|last4=Fouesnea |first4=M.

|date=2018

|title=New stellar encounters discovered in the second Gaia data release

|journal=Astronomy & Astrophysics

|volume=616 |page=A37

|arxiv=1805.07581 |bibcode=2018A&A...616A..37B

|doi=10.1051/0004-6361/201833456

|s2cid=56269929

}}

}}

• {{cite journal

|first=Jacques |last=Laskar |author-link=Jacques Laskar

|date=2024

|title=Stability of the Solar System

|journal=Scholarpedia

|volume=19 |issue=4 |page=5216 |doi=10.4249/scholarpedia.5216 |doi-access=free |bibcode=2024SchpJ..19.5216L }}

• {{cite web

|title=Long shot: Planet could hit Earth in distant future

|website=Space.com

|date=10 June 2009

|url=http://www.space.com/scienceastronomy/090610-planets-colllide.html

}}

• {{cite journal

|title=Project LonGStOP - long-term gravitational study of the outer planets

|bibcode=1988VA.....32...95R

|type=article abstract

|url=http://adsabs.harvard.edu/abs/1988VA.....32...95R

|via=adsabs.harvard.edu

|last1=Roy

|first1=A. E.

|last2=Walker

|first2=I. W.

|last3=MacDonald

|first3=A. J.

|last4=Williams

|first4=I. P.

|last5=Fox

|first5=K.

|last6=Murray

|first6=C. D.

|last7=Milani

|first7=A.

|last8=Nobili

|first8=A. M.

|last9=Message

|first9=P. J.

|last10=Sinclair

|first10=A. T.

|last11=Carpino

|first11=M.

|journal=Vistas in Astronomy

|date=1988

|volume=32

|issue=2

|page=95

|doi=10.1016/0083-6656(88)90399-6

}}

{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}

Category:Chaos theory

Category:Dynamics of the Solar System

Category:Orbital perturbations