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Quadruple System Planets?

Artist's conception of HD98800

HD 98800 is an unusual system indeed. About 150 light years away in the constellation TW Hydrae, the four stars that make it up consist of two binary pairs that circle each other. The distance between the two pairs is about 50 AU, which is roughly the average distance between Pluto and the Sun. Imagine having, instead of icy Kuiper Belt objects, a binary star system at the edge of our Solar System. Note: The reference above should probably be to the TW Hydrae association, not ‘constellation,’ as noted in the comments below.

Image: This artist concept depicts the quadruple-star system HD 98800. The system is approximately 10 million years old, and is located 150 light-years away in the constellation TW Hydrae. HD 98800 contains four stars, which are paired off into doublets, or binaries. The stars in the binary pairs orbit around each other, and the two pairs also circle each other like choreographed ballerinas. Credit: NASA/JPL-Caltech/T. Pyle (SSC-Caltech).

The idea of planet formation here may not be completely far fetched, because HD 98800B, one of the binary pairs, has a dusty disk around it. The evidence coming in from the Spitzer Space Telescope shows that the disk is actually made up of two belts, one at about the distance from the Sun to Jupiter, the other at around 1.5 to 2 AU (think of Mars and the asteroid belt in our own system). If planets did form here, we could certainly wind up talking about some interesting orbital mechanics. But the evidence is hardly complete. Says Elise Furlan UC-Los Angeles):

“Typically, when astronomers see gaps like this in a debris disk, they suspect that a planet has cleared the path. However, given the presence of the diskless pair of stars sitting 50 AU away, the inward-migrating dust particles are likely subject to complex, time-varying forces, so at this point the existence of a planet is just speculation.”

Speculation indeed. The paper on this work zeroes in on the factors involved, noting that the object under study appears to be a debris disk rather than a protoplanetary disk in the process of formation. As to the gravitational perturbations of the second binary pair:

This type of perturbation can pump up eccentricities and inclinations of particles, and cause particles to be trapped in mean motion resonances, as was likely the case for Kuiper Belt objects under the influence of the giant planets and possibly a close encounter by a passing, nearby star. Periodic stirring of planetesimals in the outer disk around HD 98800 B by the A pair could be responsible for generating copious amounts of dust. HD 98800 B is thus a unique type of debris disk, whose infrared excess is elevated to levels comparable to that of protoplanetary disks due to the particular configuration of the four components in this system, resulting in gravitational perturbations that prevent the dust from settling into a flat disk.

So that second binary pair 50 AU away complicates the picture considerably. Dust particles migrating to the inner disk following outer system collisions between rocky objects should produce a relatively continuous disk unless perturbed. We’re either seeing the beginnings of a planetary system, with the new planets clearing out debris in their orbital path, or we’re finding gaps created by the complex gravitational pull of the four stars in this curious system. Or perhaps both? Spitzer’s infrared spectrometer can give us that much, but to this point not much more.

As we find more binary and multiple systems with planets, we’re learning how complicated the process of disk formation in these environments can be. The paper is Furlan et al., “HD 98800: A 10-Myr-Old Transition Disk,” accepted by the Astrophysical Journal and available online.

Comments on this entry are closed.

  • Darnell Clayton July 25, 2007, 14:02

    This sure is interesting! Does anyone know what type of stars these are?

    As in red dwarf, yellow sun like or burning hot blue? I’d go by the image, although that may just be an artists interpretation.

  • andy July 25, 2007, 14:18

    According to SIMBAD, they’re K dwarfs. Interesting that the observed dust disc is around the B pair, which has the higher eccentricity.

  • John Sheff July 25, 2007, 21:44

    Huh? “… in the constellation TW Hydrae”? There is no such constellation. They probably mean the constellation Hydra, the (female)Water Snake (incidentally, not to be confused with the constellation Hydrus, the (male) Water Snake.

  • Adam July 26, 2007, 3:09

    Hi All

    They’re currently a bit young to have terrestrial planets in an advanced state of assembly, but it’s an interesting finding. There’s a lot of wide double binaries which are practically separate star-systems, and thus should have no problems at all making separate batches of planets. If all the stars have planets then such a system would be a prime target for colonisation. Once we have experience – as a species – terraforming the small bodies of our system we’ll be ready to use such systems to our best advantage.

  • djlactin July 26, 2007, 6:54


    zeta reticuli?

  • andy July 26, 2007, 7:37

    I guess what is meant is the TW Hydrae association, not constellation.

  • Administrator July 26, 2007, 8:50

    I think Andy’s right, and have inserted a correction into the original text. Thanks for catching this, guys.

  • Adam July 26, 2007, 18:19

    Hi djlactin

    Zeta Reticuli A & B are a particularly wide binary system and not a double binary. They stand out because they’re relatively close and relatively bright, but plenty of other wide binaries exist out there too.

  • djlactin July 26, 2007, 19:56

    adam: yeah, you’re correct. i checked out the info after i posted. my error. my (flawed) recollection was that it’s a double binary. should aim before i shoot.

  • Adam July 27, 2007, 17:54

    Hi djlactin

    It’s ok. I’ve always had a soft spot for Zeta Reticuli – the location of ‘Alien’ and ‘Aliens’, of Betty & Barney Hill’s interrogators, and of Greg Benford’s “In Alien Flesh”. There’s more than a few wide M-dwarf binaries yet to be deciphered out there because they’re far apart and dim.

  • ljk November 16, 2007, 19:56

    Planetary Science Goals for the Spitzer Warm Era

    Authors: Carey Lisse, Mark Sykes, David Trilling, Josh Emery, Yanga Fernandez, Heidi Hammel, Bidushi Bhattacharya, Erin Ryan, John Stansberry

    (Submitted on 15 Nov 2007)

    Abstract: The overarching goal of planetary astronomy is to deduce how the present collection of objects found in our Solar System were formed from the original material present in the proto-solar nebula. As over two hundred exo-planetary systems are now known, and multitudes more are expected, the Solar System represents the closest and best system which we can study, and the only one in which we can clearly resolve individual bodies other than planets.

    In this White Paper we demonstrate how to use Spitzer Space Telescope InfraRed Array Camera Channels 1 and 2 (3.6 and 4.5 um) imaging photometry with large dedicated surveys to advance our knowledge of Solar System formation and evolution. There are a number of vital, key projects to be pursued using dedicated large programs that have not been pursued during the five years of Spitzer cold operations. We present a number of the largest and most important projects here; more will certainly be proposed once the warm era has begun, including important observations of newly discovered objects.

    Comments: 29 pages, 17 figures, to appear in “Science Opportunities for the Warm Spitzer Mission”

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0711.2352v1 [astro-ph]

    Submission history

    From: Carey Lisse [view email]

    [v1] Thu, 15 Nov 2007 07:28:16 GMT (1993kb)


  • ljk January 11, 2008, 11:08

    Four Stars Found in Amazingly Tight Bunch

    By Jeanna Bryner

    Staff Writer

    posted: 10 January 2008 11:30 a.m. ET

    AUSTIN, Texas — A quartet of stars has been discovered
    in an intimate cosmic dance, swirling around each other
    within a region about the same as Jupiter’s orbit around
    the sun.

    Astronomers say a gaseous disk might have once
    engulfed and pushed the stars into their tight orbits.

    Though bright, the stellar system was thought to be
    a single star dubbed BD -22°5866. Now, research
    presented here today at a meeting of the American
    Astronomical Society reveals the pinpoint of light is a
    rare system of four closely orbiting stars. The group
    is located about 166 light-years from the sun. In our
    sky, they are just south of the constellation Aquarius.

    Each of the stars is about half as massive as the sun
    and older than 500 million years. The sun, by
    comparison, is 4.6 billion years old.

    Since most stars form as part of a multiple-star system,
    the new findings could have implications for understanding
    the evolution of stars.

    Full article here:


  • ljk June 24, 2008, 11:21

    Comparative statistics and origin of triple and quadruple stars

    Authors: A. Tokovinin

    (Submitted on 19 Jun 2008)

    Abstract: The statistics of catalogued quadruple stars consisting of two binaries (hierarchy 2+2) is studied in comparison with triple stars, with respective sample sizes of 81 and 724. Seven representative quadruple systems are discussed in greater detail. The properties of multiple stars do not correspond to the products of dynamical decay of small clusters, hence the N-body dynamics is not the dominant process of their formation. On the other hand, rotationally-driven (cascade) fragmentation possibly followed by migration of inner and/or outer orbits to shorter periods is a promising scenario to explain the origin of triple and quadruple stars.

    Our main results are: (i) Quadruple systems of Epsilon Lyr type with similar masses and inner periods are common. (ii) The distributions of the inner periods in triple and quadruple stars are similar and bimodal. The inner mass ratios do not correlate with the inner periods. (iii) The statistics of outer periods and mass ratios in triples and quadruples are different. The median outer mass ratio in triples is 0.39 independently of the outer period, which has a smooth distribution. In contrast, the outer periods of 25% quadruples concentrate in the narrow range from 10yr to 100yr, the outer mass ratios of these tight quadruples are above 0.6 and their two inner periods are similar to each other. (iv) The outer and inner mass ratios in triple and quadruple stars are not mutually correlated. (v) The inner and outer orbital angular momenta and periods in triple and quadruple systems with inner periods above 30d show some correlation, the ratio of outer-to-inner periods is mostly comprised between 5 and 10^4. In the systems with small period ratios the directions of the orbital spins are correlated, while in the systems with large ratios they are not.

    Comments: Accepted by MNRAS, 14 pages, 12 figures. Two electronic tables at this http URL

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.3263v1 [astro-ph]

    Submission history

    From: Tokovinin Andrei [view email]

    [v1] Thu, 19 Jun 2008 19:21:29 GMT (152kb)


  • ljk July 1, 2008, 13:29

    What to Expect from Transiting Multiplanet Systems

    Authors: Daniel C. Fabrycky

    (Submitted on 26 Jun 2008)

    Abstract: So far radial velocity (RV) measurements have discovered ~25 stars to host multiple planets. The statistics imply that many of the known hosts of transiting planets should have additional planets, yet none have been solidly detected. They will be soon, via complementary search methods of RV, transit-time variations (TTV) of the known planet, and transits of the additional planet.

    When they are found, what can transit measurements add to studies of multiplanet dynamical evolution? First, mutual inclinations become measurable, for comparison to the solar system’s disk-like configuration. Such measurements will give important constraints to planet-planet scattering models, just as the RV measurements of eccentricity have done. Second, the Rossiter-McLaughlin effect measures stellar obliquity, which can be modified by two-planet dynamics with a tidally evolving inner planet. Third, TTV is exquisitely sensitive to planets in mean motion resonance.

    Two planets differentially migrating in the disk can establish such resonances, and tidal evolution of the planets can break them, so the configuration and frequency of these resonances as a function of planetary parameters will constrain these processes.

    Comments: To appear in the Proceedings of the 253rd IAU Symposium: “Transiting Planets”, May 2008, Cambridge, MA. 7 pages, 3 figures

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.4314v1 [astro-ph]

    Submission history

    From: Daniel Fabrycky [view email]

    [v1] Thu, 26 Jun 2008 19:35:53 GMT (341kb)


  • ljk December 30, 2008, 13:39

    High Inclination Planets in Multistellar Systems

    Authors: P.E. Verrier (Cambridge), N.W. Evans (Cambridge)

    (Submitted on 24 Dec 2008)

    Abstract: The Kozai mechanism often destabilises high inclination orbits. It couples changes in the eccentricity and inclination, and drives high inclination, circular orbits to low inclination, eccentric orbits.

    In a recent study of the dynamics of planetesimals in the quadruple star system HD98800 (Verrier & Evans 2008), there were significant numbers of stable particles in circumbinary polar orbits about the inner binary pair which are apparently able to evade the Kozai instability.

    Here, we isolate this feature and investigate the dynamics through numerical and analytical models. The results show that the Kozai mechanism of the outer star is disrupted by a nodal libration induced by the inner binary pair on a shorter timescale. By empirically modelling the period of the libration, a criteria for determining the high inclination stability limits in general triple systems is derived.

    The nodal libration feature is interesting and, although effecting inclination and node only, shows many parallels to the Kozai mechanism. This raises the possibility that high inclination planets and asteroids may be able to survive in multistellar systems.

    Comments: MNRAS, submitted

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0812.4528v1 [astro-ph]

    Submission history

    From: N. W. Evans [view email]

    [v1] Wed, 24 Dec 2008 12:31:05 GMT (359kb)