‘An exoplanet, or extrasolar planet, is a planet outside the Solar System’ – Wikipedia.
At least 175 multiple planetary systems have been found as of 25 November 2013. Stuart Graham investigates.
Exoplanets are a mixed bunch. Some are 10 times the size of Jupiter, others seem more like moons and may orbit their star in less than 2 days. Here we’ll look first at a small planetary body in the solar system, see how it relates to its neighbours, and then see what similarities and/or differences can be found in a few selected exoplanet systems. There may even be a few surprises.
Less well-known than Pluto is its supposed twin Orcus, or 90482 Orcus to give its full name. It’s a trans-Neptunian object or maybe a dwarf planet. As it even has its own moon Vanth, it has the reputation of being the ‘anti-Pluto’. Its orbit looks like a mirror image of Pluto’s orbit (red: Pluto, blue: Orcus, grey: Neptune).
— Symmetric orbits of Orcus and Pluto – image credit Wikipedia —
In fact it completes 99 orbits in about the same time as Pluto does 98, which in terms of a ‘simple ratio’ is 1:1. We’ll see various examples of near-perfect simple ratios like this as we go along. In fact the two biggest planets in the solar system – Jupiter and Saturn – show it with an orbit ratio of 149:60 (150:60 = 5:2). Orcus also does 41 orbits to Neptune’s 61 (40:60 = 2:3) and 49 to every 143 Uranus orbits (48:144 = 1:3). By comparison Pluto:Neptune is 165:248 (166:249 = 2:3) and Pluto:Uranus is 19:56 (19:57 = 1:3). Of course even the larger figures are themselves only very close approximations (mostly greater than 99.9%), not 100% matches.
Now let’s take a short tour of a few exoplanet systems.
Ratios note: list shows the number required to match the other planet.
Planet name note: letters b,c,d etc. are in order of discovery date (largest planet first) NOT orbit period (letter a belongs to the star).
Gliese 876 or GJ 876 : distance from Earth = 15.33 light years
Originally thought to be a two-planet system with a near 2:1 orbit ratio.
359:179 orbit ratio for the 2 planets 876b and 876c (360:180 = 2:1).
Then two other planets were found: 876d nearly 7 times bigger than Earth with an orbit period under 2 days, and 867e just over twice the orbit period of 876c.
876b : 876e orbit ratio = 61:30 (60:30 = 2:1)
876d : 876c = 31:2 approx. (1149:74)
Since 360:180 = 30:15 it can be seen that all four planets are closely linked to 30/31 and 60/61 one way or another, and that the ratio of c:b:e is close to 4:2:1.
Studies have shown other interesting properties, e.g. ‘the two planets [b and c] are locked in a secular resonance where they librate around apsidal alignment with an amplitude of 34◦, and their joint line of apsides precesses at a rate of 41◦ every year.’
Click to access 1202.5865v1.pdf
Also the semi major axis ratios include the following:
d:b 10:1
b:e 1.605:1 (close to phi)
c:b 1.6075:1 ( ” ” ” )
—–
Update 22/12/13 on Gliese 876:
SMA ratios:
c:b 2400:1493 — 2400:1500 = 8:5
b:e 337:210 — 336:210 = 8:5
c:e 129:50 — 130:50 = 13:5
Synodic periods:
c-b 58.95472 d
b-e 120.27145 d
Ratio of c-b:b-e = 102:50 or 51:25 — 52:26 = 2:1
—–
HR 8799 : distance from Earth = 128.5 light years
This has four giant planets, all 7-10 times the mass of Jupiter and much further away from their star than it. Let’s look at the simple ratios first.
Orbits – neighbours:
b:c = 2:1 (19995:10000)
c:d = 2:1 (20009:10000)
d:e = 9:4 approx.
Orbits – others:
b:d = 4:1 (9662:2415) — 9660:2415 = 4:1
b:e = 9:1 approx.(73:8 exactly*) — 72:8 = 9:1
c:e = 9:2 approx.(575:126) — 576:128 = 9:2
* e = exactly 18000 days, and 73 x e = 8 x b exactly (b = 164250 days)
b:c:d orbit ratio = 4:2:1 (99.98%) as a close fit but not exactly.
Semi-major axis ratios:
e:d 2:1 approx.(54:29) — 54:27 = 2:1
d:c 3:2 approx.(143:90) — 145:90 = 3:2
c:b 5:8 approx.(200:317) — 200:320 = 5:8
Mass (the stated figures compared to Jupiter are 10, 9 and 7):
b:c = 10:7
b:d = 10:7
b:e = 7:9
c:d = 1:1
c:e = 10:9
d:e = 10:9
Planets c and d have the same mass, are neighbours and have a very close 1:2 orbital relationship. They are the heart of the system.
Synodic conjunctions per 2.16 million years approx.:
c-b:d-c:e-d = 4800:9611:24608 (9611 is just over double 4800)
—-
Update 22/12/13 on HR 8799
Synodic periods:
e-d 87.759 y
d-c 224.6982 y
c-b 449.911 y
Synodic ratios:
e-d:c-b = 323:63 — 324:63 = 36:7 (35:7 = 5:1)
d-c:c-b = 2623:1310 — 2620:1310 = 2:1
e-d:d-c = 763:298 — 765:300 = 51:20 (50:20 = 5:2)
—-
Further reading:
‘Multiple mean motion resonances in the HR 8799 planetary system’
http://arxiv.org/abs/1308.6462
‘First Reconnaissance Of An Exoplanetary System’
http://blogs.scientificamerican.com/life-unbounded/2013/03/11/first-reconnaissance-of-an-exoplanetary-system/
Discussion of exoplanet resonances based on actual data:
http://iopscience.iop.org/0067-0049/197/1/8/article#apjs401183s5
HAT-P-17 : distance from Earth = 293.5 light years
In this two-planet system the nearest match to a whole number of orbits of the major planet with a whole number of the minor one seems to be:
HAT-P-17b = 10.338523 d x 2261 = 23375.4 days (64 years = 23376 d)
HAT-P-17c = 1798.0 d x 13 = 23374 days
2262 / 13 = 174
2262 / 6 = 377 (13 and 377 are Fibonacci numbers)
The ‘perfect ratio’ (2262:13) is avoided by 1 orbit of the minor planet (2261:13).
HD 82943 : distance from Earth = 89.56 light years
82943c and 82943b are a similar size and close to 2:1 orbit ratio. The third planet 82943d is much smaller and a lot further from the star. (Planets in order from star outwards: c, b, d)
c:b 2:1 approx. (466:231) — 462:231 = 2:1
b:d 2:5 approx. (158:385) — 156:390 = 2:5
c:d 1:5 approx. (12:59) — 12:60 = 1:5
—-
Update 22/12/13 on HD 82943
Synodic periods:
c-b 1.1906 y
b-d 1.52055 y
Synodic ratios:
c-b:b-d = 23:18 — 24:18 = 4:3
Semi-major axis data:
b:c = 331:528 — 330:528 = 5:8
d:b = 400:721 — 400:720 = 5:9
c:d = 23:8 — 24:8 = 3:1
—-
47 Uma : distance from Earth = 45.56 light years
Three-planet system, outermost completing 3 orbits every 115 years (115.00615y)
b:d 13:1 (1169:90) — 1170:90 = 13:1
d:c 1:6 approx. (7:41) — 7:42 = 1:6
b:c 4:9 approx. (500:1109) — 496:1116 = 4:9
—-
Update 22/12/13 on 47 Uma
Synodic periods:
b-c 5.37456 y
c-d 7.89423 y
b-d = 3.19758 y
Synodic ratios:
b-c:c-d = 47:32 — 48:32 = 3:1
b-d:c-d = 79:32 — 80:32 = 5:2
b-c:b-d = 47:79 — 48:80 = 3:5
Semi-major axis data:
b:c = 36:21 — 35:21 = 5:3
c:d = 29:9 — 30:10 = 3:1
—-
****
This is a very small selection from a very large database, so can only give a flavour of what’s happening outside the solar system. Selection basis was partly random, partly to highlight some of the (perhaps) more obvious planetary relationships e.g. 1:2 orbit ratios.
Nevertheless it’s enough to let us find evidence of some similarities in the behaviour of the exoplanets, especially the larger ones, with what is seen in our own solar system.
Data from: http://exoplanet.eu/catalog
Further comments on resonance:
http://en.wikipedia.org/wiki/Orbital_resonance#Mean-motion_resonances_among_extrasolar_planets
Paper on Titius-Bode law re. exoplanets: http://arxiv.org/pdf/1304.3341v4.pdf
Tallbloke's Talkshop 
It seems these ratios may be due to the interactions of gravity and the primordial dust clouds, which is obviously no great insight. It is fascinating that this seems to reitirate across a large number of start systems.
The note on Orcus is fascinating. I was unaware of Orcus and find the apparent symmetry to be amazing. It raises the question as to how many planetoids/small planets, comets, asteroids, etc. are in the solar community but so far away as to be effectively hidden.
@ hunter
Sedna also has a very elliptical orbit, even more so than Orcus, so can be a very long way from the Sun sometimes – upto 937 AU (Earth = 1 AU).
http://upload.wikimedia.org/wikipedia/commons/e/e3/Sedna_orbit.svg
These two exoplanet systems are also worth a mention:
http://www.caltech.edu/content/caltech-astronomer-finds-planets-unusually-intimate-dance-around-dying-star
In the case of HD200964 the periods of the two planets are 630 days and 830 days. That means an orbit ratio of 63:83 which is one away from 63:84 = 3:4. This kind of ‘almost simple’ relationship seems to be quite common, including in our solar system.
Update: exoplanets.eu gives the orbit periods as 613.8 and 825 days. The ratio then becomes 93:125 exactly, and 93:124 = 3:4.
@oldbrew: food for thought these relations, thank you.
You mention “is avoided by 1 orbit” and also “is one [orbit] away”, and I think by the well nown 1,2,many rule (aka intuitive reasoning) there can there be more systems of this one off kind? If so, we’d have to name them oldbrew systems 🙂
@ Chaeremon
Sounds good but to be fair ‘near-resonance’ is well-known, however I like to try and put exact figures on it wherever possible.
I believe the general rule is that the planet with the smaller orbit period usually ‘fails’ to reach the exact resonance number, e.g. the one in my last comment reaches 83 not 84. Sometimes they are both out by one (maybe more with big numbers), but less likely that the bigger orbit alone will be ‘one away’.
With Jupiter and Saturn, it’s Jupiter (smaller orbit) that is one off the exact match, so add 1 to its actual 149 and you get a notional 5:2 ratio with Saturn i.e. 150J : 60S.
More on that:
‘Prof. Schlichting described one explanation for these near resonances: while the planetary systems were still very young, interactions between the nascent planets and the protoplanetary gas disks from which the planets form gently tuned the gravitational interactions between the planets, keeping them slightly out of resonance.’
http://www.astrojack.com/?p=674
@oldbrew: wow, a possible general rule “smaller orbit period usually ‘fails’ to reach the exact resonance.” good think. I made a note under ‘prodigal’ / ‘thrifty’, will check again if and when rotation periods can/will be observed or approximated.
Hmm. I understand that Prof. Schlichting wants sensational happenings from alleged protoplanetary gas disks, but he has not shown us 1 (happening) of these. Mathematically these happenings take millions of years in mainstream “theory” to show a recognizable change. How old would Schlichting then be 😉
Belated congrats to Stuart ‘oldbrew’ Graham on his inaugural post as a talkshop editorial team member.
I noticed that ‘astrojack’ had looked at another of the systems we investigated, but didn’t write up here. The 4:3 resonance is unusual, and demonstrates that current planetary migration theory is incomplete. Plenty to go at in this field!
I’ve just re-submitted the second paper which looks at the solar system resonances and synchronies, Earth LOD variation, and solar differential rotation. Fingers crossed!
I’m hoping I’ll now have a bit more time to participate on the talkshop as well as posting new articles, before the politics silly season starts in earnest in the new year.
@ Chaeremon – ‘How old would Schlichting then be’
Judge for yourself 😉
http://web.mit.edu/hilke/www/Hilke/Welcome.html
@ TB – ‘The 4:3 resonance is unusual’
Yes, the only known solar system example involves the irregularly-shaped Jupiter moon Hyperion and its giant neighbour Titan. Their 4:3 ratio of orbits of Jupiter works out as:
16011 Titan = 12000 Hyperion in 3 x 233 years (233 = Fibonacci number)
Hyperion ‘has a pock-marked body and is the largest irregularly shaped satellite ever observed’
http://library.thinkquest.org/18188/english/planets/saturn/moons/hyperion.htm
@oldbrew: yes I know that Hilke falsifies planet formation hypotheses with hypothetical consequences of observations. But that does not make fact from the unfalsifiable remains (which was my thought).
Anyways, thanks again for including the exoplanets, new bits are always interesting.
This exoplanet is bigger than Earth and orbits its star in 8.5 HOURS. They were able to calculate its rotation too (a slow 12.5 days) meaning the ratio of orbit to rotation is 600:17.
http://phys.org/news/2013-10-kepler-78b-exoplanet-earth-like-mass.html
That the harmonic frequencies of the planets are just a smidgeon off, may be an intentional design feature. Harmonics in perfect frequency can be the ultimate weapon of destruction,if all the frequencies were perfect there would at some time be a harmonic alignment that caused destruction. Perhaps there is more to the slight off note than meets the eye.
@wayne of middle earth: good think.
‘Cases of extrasolar planets close to a 1:2 mean-motion resonance are fairly common.’
http://en.wikipedia.org/wiki/Orbital_resonance#Mean-motion_resonances_among_extrasolar_planets
‘It is much more common for pairs of planets to have orbital period ratios a few percent larger than a mean-motion resonance ratio than a few percent smaller (particularly in the case of first order resonances, in which the integers in the ratio differ by one). This was predicted to be true in cases where tidal interactions with the star are significant.’
Solar system example: 26 Neptune orbits = 51 Uranus (26:52 = 1:2)
Many folks here seem to have forgotten, or missed, that detecting an exoplanet is an ASTONISHINGLY low-probability event. We cannot actually SEE the planets; we have to detect them in other ways.
1. Perturbations; we can detect the “wiggle” caused by a planet (a truly MASSIVE planet!) orbiting the star, or…
2. Occultations; we detect that the planet sometimes blocks some minuscule fraction of the star’s light from reaching our detector.
THINK about that! How many other star systems might be able to detect the Earth? Answer: darned few! Only beings living on planets that are PRECISELY ON the ecliptic (the plane of the Earth’s orbit around the Sun) would ever see the Earth occult the Sun from their perspective. The Kepler Space Telescope was only in operation for four years; an exo-Kepler analog would, IF it were precisely on the ecliptic, had only four very short chances to detect the Earth.
So the fact that we detect any planets at all is a miracle; that we’ve detected a few hundred for sure, and a few thousand more that are awaiting the math processing time, means that there must be planets circling the majority of all stars, perhaps even the vast majority of all stars.
This also explains why the planets we’ve detected are either really large, or very close to the primary, or both. Just wait and see; when we develop better telescopes or go out there and actually look for ourselves, we’re going to discover that planets are as common as, well, “dirt”.
@ wayne of middle earth
The Kirkwood gaps provide clues about the reasons for near-resonances.
http://en.wikipedia.org/wiki/Kirkwood_gap
Watch how the GJ876 pair synchronise every second orbit of the inner planet at the same point, while the pair precess (click on the graphic). Below that, a similar thing for 3 of the 4 main Galilean moons.
‘Mean-Motion Resonances in the GJ 876 Extrasolar Planetary System and the Galilean Satellite System of Jupiter’
http://web.physics.ucsb.edu/~mhlee/resonances.html
Wow. Nice find.
How a recently discovered dust ring around Venus could help in exoplanet detection.
‘understanding resonance rings will help us to interpret future images of exoplanetary systems’
http://sen.com/news/circumsolar-dust-ring-confirmed-in-the-orbit-of-venus
Note: the dust ring has a diameter of 220 million kilometres.
TB said: ‘The 4:3 resonance is unusual, and demonstrates that current planetary migration theory is incomplete. ‘
Hanno Rein and co. investigate, but they’re still at the head-scratching stage.
‘Previous studies were successful in forming 2:1 and 3:2 resonances. This is generally believed to be evidence of planet migration. We highlight the main differences between those studies and our failure in forming a 4:3 resonance. ‘
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2012.21798.x/abstract
(abstract only)
And here’s a 2-planet system HD 82943 with exactly 1:2 orbit ratio, both planets nearly twice as big as Jupiter.
http://www.personal.psu.edu/jtw13/blogs/astrowright/2013/09/resonances-inclinations-and-true-masses-for-exoplanets.html
NASA’s beginner’s guide to exoplanet research methods – 3+ minutes video.
http://www.universetoday.com/106958/how-do-we-learn-about-an-alien-planets-size-and-atmosphere/
Plus a theory of why Mercury’s 3:2 spin-orbit ratio ‘should’ be found elsewhere in the universe.
http://www.universetoday.com/105345/mercurys-resonant-rotation-should-be-common-in-alien-planets/
An inconvenient ‘Planet that shouldn’t be there’ has been found to be there.
‘Weighing in at 11 times Jupiter’s mass and orbiting its star at 650 times the average Earth-Sun distance, planet HD 106906 b is unlike anything in our own Solar System and throws a wrench in planet formation theories.’
http://www.sciencedaily.com/releases/2013/12/131205141629.htm
Observation trumps theory again.
Update: ‘the solar system is an adopted family with a complex recent history.’
A 9 minute video about where gravity theory stands – or falls – as a result of the ‘impossible exoplanet’, and related matters.
http://www.thunderbolts.info/wp/2013/12/17/the-impossible-exoplanet-space-news/
@oldbrew: unbelievable [pun intended], this all follows from unobservables (fictitious parameters and unfalsifiable equations) of matheological physics who have already gambled away the infinitesimal remains of credibility by taking photos(hop) pictures from matheological black holes and also from the matheological edge of the universe.
Crazy, isn’t it 😉
Of course I cannot ask to just wait until 1 orbit was completed, like for the trans-Uranians.
Let’s take a look at a system that is definitely NOT ‘unlike anything in our own Solar System’ (see quote above). The data can then be compared to the solar system.
HD 40307 was reported about a year ago with the headline:
‘Habitable Planet: New Super-Earth in Six-Planet System May Be Just Right to Support Life’
http://www.sciencedaily.com/releases/2012/11/121108073927.htm
The planets are lettered from b to f. The orbit ratios of the neighbours are shown, followed by the accuracy (%) and a figure for what may be the ‘underlying’ ratio, with comments.
b:c 600:269 (99.999%) — 20:9 – see notes below
c:d 17:8 (99.965%) — 16:8 = 2:1
d:e 61:36 (99.997%) — 60:36 = 5:3
e:f 299:200 (99.994%) — 300:200 = 3:2
f:g 107:28 (99.998%) — 108:27 = 4:1
Clearly an adjustment of 1 to one or both of the figures mostly gives a simple ratio.
But in the case of b:c there is more than one interpretation, so we have to leave the possibilities open, e.g. is 20:9 more like 20:8 (5:2), 21:9 (7:3), 20:10 (2:1) or something else? With small orbit periods (4.3~ and 9.6~ days here) the patterns can be harder to read.
Note for the ‘neighbour + 1’ ratios:
b:d is 199:42 (99.999%) — 200:40 = 5:1
c:e is 5:18 (99.982%) — 6:18 = 1:3
d:f is 38:15 (99.998%) — 40:16 = 5:2
e:g is 7:40 (99.985%) — 8:40 = 1:5
The data can be found here:
http://exoplanet.eu/catalog/?f=%2740307%27+in+name
Now the solar system comparisons, using the same concept of adding/subtracting 1 from one or both of the ratio numbers to get a simple ratio. As usual, Mars is the awkward one.
Mercury:Venus 23:9 — 24:8 = 3:1
Venus:Earth 13:8 — as is
Earth:Mars 79:42 — doesn’t quite work, but 80:40 = 2:1
Mars:Jupiter 473:75 — 475:75 = 19:3
Jupiter:Saturn 149:60 — 150:60 = 5:2
Saturn:Uranus 77:27 — 78:26 = 3:1
Uranus:Neptune 51:26 — 52:26 = 2:1
The Mars situation is probably complicated by the asteroid belt between Jupiter and Mars, which some think could be the remains of a former planet.
Interestingly, the dwarf planet Ceres in the asteroid belt has a 232:90 orbit ratio (99.985%) with Jupiter, and 233:89 = phi²:1
(Mars:Ceres 22:9 approx.)
24 Sextantis is a popular exoplanet system for scientists to study. Its two planets are 0.86 and 1.99 times the mass of Jupiter.
Orbit ratio: 25:39 — 25:40 = 2:5
Semi-major axis ratio: 20:39 — 20:40 = 1:2
Another example that fits our concept of near-resonance very well.
A physics study of this system and HD 200964 says:
‘…we show that the planets are only feasible if they are currently trapped in mutual mean-motion resonance – the 2:1 resonance in the case of 24 Sex b and c, and the 4:3 resonance in the case of HD 200964 b and c. In both cases, the region of stability is strongest and most pronounced when the planetary orbits are mutually coplanar. As the inclination of planet c with respect to planet b is increased, the stability of both systems rapidly collapses.’
http://arxiv.org/abs/1211.1078
Along the same lines is another two-planet system, HD 108874.
Orbit ratio: 199:49 — 200:50 = 4:1
‘On the other hand, HD 108874 and HD 202206 suffer from large perturbations in their motion due to the closeness of the 4/1 and 5/1 resonances, respectively.’
http://www.aanda.org/articles/aa/abs/2007/02/aa5767-06/aa5767-06.html
The linked paper (below) says:
‘The multiple-planet systems discovered by the Kepler mission exhibit the following feature: planet pairs near first-order mean-motion resonances prefer orbits just outside the nominal resonance, while avoiding those just inside the resonance.’
http://arxiv.org/abs/1211.5603
Just in…
‘An international team of astronomers has discovered the first Earth-mass planet that transits, or crosses in front of, its host star. KOI-314c is the lightest planet to have both its mass and physical size measured. Surprisingly, although the planet weighs the same as Earth, it is 60 percent larger in diameter, meaning that it must have a very thick, gaseous atmosphere.’
http://phys.org/news/2014-01-newfound-planet-earth-mass-gassy.html
And to save us the bother they give the resonance info with its partner:
‘The second planet in the system, KOI-314b, is about the same size as KOI-314c but significantly denser, weighing about 4 times as much as Earth. It orbits the star every 13 days, meaning it is in a 5-to-3 resonance with the outer planet.’
There it is again! Good find.
It gets better – I think.
‘Transit Timing Variation of Near-Resonance Planetary Pairs. II. Confirmation of 30 planets in 15 Multiple Planet Systems’
http://arxiv.org/abs/1309.2329
‘All of these fifteen pairs are near first-order Mean Motion Resonances (MMR)’
Key word: near. Exactly what we would expect (see intro above). May I quote myself?
‘We’ll see various examples of near-perfect simple ratios like this as we go along.’
I think it’s caused by energy transfer pushing the orbits apart until the energy increase balances the tendency to fall into the resonsant ratio.
Kepler-88: ‘This system presents such strong interactions that it has earned the nickname of the “King of transit variations”.’
The orbit ratio of the two planets 88b and 88c is around 57:115, and 57:114 = 1:2.
http://www.iap.fr/actualites/avoir/2013/Decembre/ExoplaneteInvisible_en.html
The predicted planet was found using the TTV (‘Transit Timing Variations’) method, similar to how Neptune was found using the behaviour of Uranus as the clue.
‘The TTV technique is sensitive to planets in multiple systems down to the mass of the Earth, and can therefore be used to unveil the existence of non-transiting planets, that cause perturbations in the orbital motion of transiting planets.’
There’s an mp4 animation of the orbits of K-88b and K-88c at the bottom of the (above) linked web page.
The exoplanet group of KOI-730 even tops GJ 876 (featured above) for ‘near-perfect simple ratios’, in this case an 8:6:4:3 overall ratio of their orbit periods.
In order of orbit period length the planets are lettered: e, c, b and d – probably because there was some confusion about their orbit periods for a while. It was even reported that two of them shared an orbit period but this turned out to be a misreading of the data.
The orbit ratios of the planetary neighbours (accuracy in brackets) are:
e:c = 4:3 (99.941%)
c:b = 3:2 (99.896%)
b:d = 4:3 (99.994%)
For the non-neighbours:
e:b = 2:1 (99.837%)
c:d = 2:1 (99.890%)
e:d = 8:3 (99.831%)
The orbit periods are short, ranging from 7.38 to 19.72 days and the masses are not known.
For serious stats buffs, the semi-major axis ratios (all close to or exactly 100%) of the neighbours are:
e:c = 19:23
c:b = 23:30
b:d = 24:29
Data here: http://exoplanet.eu/catalog/?f=%27KOI-730%27+in+name
Recently discovered system KIC 11442793 seems to hold the record for transiting planets with seven.
Quote: ‘planets d, e and f are super-Earths close to a mean motion resonance chain (2:3:4), and planets b and c, with sizes below 2 Earth radii, are within 0.5% of the 4:5 mean motion resonance.’
‘…the requirement of the circularity of their orbits implies that, for the system to be stable, the mean motion resonance has to play a role to guarantee the survival of the system.’
http://arxiv.org/abs/1310.6248
Analysis – with a minimum accuracy of 99.96% the orbit ratios are:
h:g 47:74 — 48:72 = 2:3
g:f 51:86 — 51:85 = 3:5
f:e 39:53 — 39:52 = 2:3
e:d 13:20 — 14:21 = 2:3 (13:21 = Phi)
d:c 34:233 — Phi^4
c:b 86:107 — 88:110 = 4:5
Science News reports:
‘KIC 11442793’s clutch of planets consists of two that are roughly the size of Earth, three super-Earths and two much bigger bodies. Like our own solar system, the smaller planets orbit closer to the star, while the larger planets sit farther out, a rare observation the astronomers argue. Unlike our solar system, the outermost planet of KIC 11442793’s system orbits the star at roughly the distance at which Earth circles the sun, meaning that the seven-planet system is extremely compact.’
http://www.sciencenews.org/blog/science-ticker/solar-system-seven-planets-discovered
MEAN MOTION RESONANCES IN EXOPLANET SYSTEMS:
AN INVESTIGATION INTO NODDING BEHAVIOR
Click to access ms10612.pdf
Beware dodgy exoplanet ‘data’. Much-publicised Gliese 581d is probably just a sunspot.
‘First life-friendly exoplanet may not exist after all’
http://www.newscientist.com/article/dn25842-first-lifefriendly-exoplanet-may-not-exist-after-all.html
Yep, saw that last night.