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Carnival Musings on Planetary Find

The latest Carnival of Space is up at Out of the Cradle, where this week’s interstellar focus is delivered by Steinn Sigurdsson (Penn State), who takes a look at the new planet with the tongue-twisting name: MOA-2007-BLG-192Lb. We focused in on this one just a few days ago, intrigued by its small size (about three Earth masses) and its orbit around a low-mass star that is either a brown dwarf or a low mass M-dwarf.

But note the play in the numbers from this microlensing detection, which suggests the mass could actually be as low as 1.7 Earth masses or as high as 8.2. The discovery paper is stuffed with the relevant analysis of the statistics and how the team’s conclusions were arrived at. Let me quote Steinn on the possible significance of this find, which should have some resonance here:

It is very hard to draw a robust conclusion from a single data point, the formal uncertainties are infinite; but, this is a small corner of the observing parameters space, low mass stars have low cross-sections for microlensing, we only see them because there are so many of them.

That we already see evidence for a few Earth mass planet from microlensing observations, very strongly suggests that there are a lot of Earth mass planets out there, and that they are found all over the place.

It also tells us that the observational capability really is here. The microlensing groups, with enough stars to observe frequently enough, really can detect Earth mass planets around distant stars right now.

That last is significant, and you can see that we could be quite close to an Earth-mass planetary detection. The question is, by which method? For microlensing, transits and radial velocity methods are all in the hunt and becoming capable of such finds. In a comment below the post, Sigurdsson notes that the Las Cumbres Observatory Global Telescope Network, based on robotic, Internet-linked telescopes, could be a major player in such a detection depending on its choice of projects.

Note, too, the continuing interest in low-mass stars that this discovery will only accelerate. If we can expect Earth-mass planets around M-dwarfs and even brown dwarfs, the celestial inventory of such worlds is enormous, with conditions for life arising in settings far different than what we see around our own G-class star. MOA-2007-BLG-192Lb is probably not one of them — Sigurdsson considers it a planet with rocky core and substantial mantle of ice — but we can still wonder about worlds in more benign orbits, and consider that life around stars like our Sun may be heavily outnumbered by what is found around far dimmer stars.

Let me add that Bennett et al., “A Low-Mass Planet with a Possible Sub-Stellar-Mass Host in Microlensing Event MOA-2007-BLG-192” (accepted for publication in the Astrophysical Journal) is now available through the arXiv server.

Comments on this entry are closed.

  • James M. Essig June 8, 2008, 2:32

    Hi Folks;

    This is beautiful that we can apparently find Earth mass range planets around other stars, especially red dwarfs.

    The lifetime of a 0.1 solar mass M star is about 6 trillion years on the main sequence. Stars at the very lower mass limit of 0.086 solar mass for M type stars last even longer.

    If planets with viable ecosystems are found ubiquitously around such low mass range M stars, the possible evolution of life on these worlds to form ETI and the sub-sequent evolution of such ETI over periods of trillions of years on their home planets then becomes possible.

    Since according to quantum mechanics, as the general readership I am sure is aware, a particle, be it a fermion or boson, can be represented as a superposition of wave functions wherein the probability function, psi * psi, is normally localized for massive particles to an extent on the order of 1 Angstrom of less. The more massive the particle, the smaller its apparent cross-section.

    Now what if somehow, the mind, psyche, personality, consciousness, or whatever one chooses to call an ETI or human person can be imprinted on or embodied within the wave function of a single particle by some exotic future technology. Just imagine all of the ETI persons who could be created or “given birth to” that could inhabit such a planet!

    Now what if the individual trigonometric functions that go into the computed probability function psi * psi, whether or not we are considering a simplified case of a particle in a one dimensional well with sin and cosine functions, more complicated 2-D potential wells, or more complicated cases yet such as the spherical harmonic functions for the electrons in the electron clouds around atomic nuclei in atoms. What if somehow, a single simple trigonometric waveform component of the probability function of the particle could be used to embody the consciousness of an ETI or human being by some how using any process that would reify such basic trigonometric components of the psi * psi functions of individual particles. Imagine all of the persons that a 0.086 solar mass M star could support on any orbiting worlds.

    I will have further elaboration on this concept in the coming days.



  • Ronald June 9, 2008, 9:02

    @James Essig:
    “If planets with viable ecosystems are found ubiquitously around such low mass range M stars, the possible evolution of life on these worlds to form ETI and the sub-sequent evolution of such ETI over periods of trillions of years on their home planets then becomes possible”.

    As has been brought up before, I think the (or at least one) crucial question concerning the lifespan of such a living planet orbiting such a very long-lived red dwarf star, is: does the living ecosystem depend on the geological activity of the planet, in other words, will the living ecosystem end when geological activity ceases to recycle certain elements, or will stellar energy be enough to sustain live (beyond the simplest micriobiotic)? If geological activity is essential, giant terrestrials would be a better option for live near red dwarfs.

    The above makes all the difference for the potential lifespan of such planets. And hence for life in the universe in general, since metal-rich, extremely long-lived red dwarfs are the future of our universe.

  • Daniel June 9, 2008, 9:11

    that interest that microlensing its that only actual method that can detect a extragalactic planets (also transit method: http://arxiv.org/PS_cache/astro-ph/pdf/0604/0604242v2.pdf . however they go to need a large telescope like the extremely large telescope ELT of europeans and i think high precision radial velocity like astro comb but think that possible on near future ) and project like The Angstrom Project that is detect extragalactic microlesing on the real time on the galaxy of adromenda M31 for search gas giant planets http://arxiv.org/abs/astro-ph/0612704 and http://pos.sissa.it/archive/conferences/054/045/GMC8_045.pdf and OGLE search already research for microlensing on the Large and Small Magellanic Cloud (SMC and LMC) i think that we must pay more attention on extragalactic planets they maybe is already will discovery by the finish of this decade,for me its amazing that we already have such tecnology for detect planets outiside of our galaxy!

  • James M. Essig June 9, 2008, 10:48

    Hi Ronald;

    Thanks for the above response. The existence of massive terrestrial planets would indeed have eco systems that fare far better then Earth massed terrestrial planets, a idea that I seemed to have over looked or not contemplated in formulating my above thoughts.

    One possible mechanism for keeping an Earth massed terrestrial planet warm and geologically active over extended periods of time would be to instill radioactive isotopes into the core or mantel of the planet as its natural stocks of such isotopes were depleted by radioactive decay. One potential problem with this scenario is actually finding adequate reserves of naturally occurring radio-nucleids.

    Another option might be to encase the planet or portions of its surface with bubble like arrangements of transparent shielding or other materials to block dangerous high frequency radiation and dangerous stellar cosmic rays. One potential problem with such shielding is how to keep it from being damaged by meteors in a failsafe manner over trillions of years. Even a Tunguska sized event would cause a very bad day in the life of a civilization on a planet as such.


    Your Friend Jim

  • Ronald June 10, 2008, 15:22

    Hi James;

    If you mean ‘keeping an Earth massed terrestrial planet warm and geologically active’ by artificial means: I have no doubt that advanced civilizations would be able to keep a terrestrial planet near a red dwarf ‘alive’ for as long as the mother star would be active and stable.

    I was rather thinking of ‘the natural course of things’, i.e. the lifespan of the natural ecosystem of a planet near a red dwarf star: could it survive and adapt when geological activity ceases, any essential cycles purely based on stellar energy plus biological activity?
    If so, life on such a planet could indeed keep adapting and evolving for hundreds of billions, maybe even a trillion years.

    BTW: is the lifetime of a 0.1 solar mass M star indeed ‘about 6 trillion years on the main sequence’, as you state? I thought the lifespan of a 0.2 solar mass M star was about 100 gy, does halving the mass really increase lifespan so much, or am I mistaken about the lifespan of the 0.2 solar mass star as well?

  • Administrator June 10, 2008, 15:55

    Ronald, I don’t know about the six trillion year figure, but Jim is right that low mass red dwarfs can life to extreme old age, and I suspect six trillion might indeed be feasible. Here’s a useful article that discusses a 0.2 solar mass dwarf and its expected lifetime of 1 trillion years:


    along with a discussion of why these ages are possible.

  • Ronald June 10, 2008, 16:17

    Further to James’s and my previous post:

    If indeed a planet near a red dwarf star could sustain its living ecosystem for the entire lifespan of its star, this gave me the following idea:
    – a planet’s ecosystem can easily produce 1 biological species per year (e.g. assuming that the planet has only 1 million species at any given time, with an average species lifespan of 1 million years);
    – it follows that such a planet could produce some 100 billion species (for a typical red dwarf) during its lifespan;
    – the observable universe has an estimated minimum of 10^22 stars (probably a lot more), most of which are red dwarfs (if we exclude the brown dwarfs, not included in this estimate);
    – even if only 1 in ten thousand of these bring forth life (either naturally or induced by advanced intelligence), that would make 10^18, times the number of species mentioned above, times the number of generations of red dwarfs during the expected lifespan of the stelliferous universe (some 100 trillion years):
    the unimaginable number of biological species that our universe could produce during its life (this one is for you James, I know you like big numbers ;-) ).

  • James M. Essig June 10, 2008, 16:34

    Hi Ronald;

    The following sentence begins an abstract of a paper that can be found at the following URL.


    We present stellar evolution calculations for the lowest mass stars, i.e., those stars with masses in the range 0.08 M ≤ M* ≤ 0.25 M. Our particular emphasis is on the post-main-sequence evolution of these objects. We establish a hydrogen-burning timescale of τH 1.0 × 1013 years for the minimum-mass main-sequence star.

    The value of 10 EXP 13 years must correspond to a mass of 0.08 solar masses. I have seen other papers on the subject with fairly consistent figures for the life times of the smallest M stars.


    Your Friend Jim

  • James M. Essig June 10, 2008, 17:47

    Hi Ronald;

    Thanks for the above calculations.

    Your previous comment posted after I had shipped the above posting off to moderation.

    I can’t even imagine all of the great variety of genotypes, body types, levels of intellegence, personality types and traits, philosophical, religious, and faith based systems, cultural aspects, political organizations, economic systems, propulsion technologies, and the list goes on and on, that such a large number of ETI civilizations would entail. It simply boggles the mind.

    I am indeed fascinated with big numbers and also physical extremes. My thinking is that this interest may be a developmental artifact from growing up in a large family. I have 3 brothers and 2 sisters. We were all spaced about 1 to 2 years apart in birth order, and so during the formative years of my childhood, the family was already large.


    Your Friend Jim

  • Ronald June 11, 2008, 11:16

    Hi James,

    I developed a similar fascination for large numbers and scales, though I grew up in a tiny family ;-)

    My species calculations pertained to all biological species, not just intelligence, as you probably noticed. Intelligent life would be only a miniscule fraction of the total number (though possibly still significant on a cosmic scale).

    You were right about your lifespan estimates for red dwarfs, as I checked some literature: even a ‘typical’ 0.2 solar mass M dwarf can exist a trillion (main sequence) years!

    This positive aspect of an extremely long stable (i.e. main sequence, hydrogen fusing) lifespan is possibly countered by a few negatives: the already mentioned end to geological activity of a terrestrial planet, possibly also gradual atmospheric loss, and of course the very narrow habitable zone (for a 0.2 solar mass, 1% solar luminosity red dwarf about 8% of solar; for a 0.1 solar mass, 0.1% solar luminosity red dwarf only about 3% of solar) and tidal locking within that HZ.

    Maybe red dwarfs will appear to be poor places for naturally occurring living planets, but interesting subjects for terraforming by an advanced civilization.

  • ljk July 2, 2008, 12:23

    Transit Detection of Radial Velocity Planets

    Authors: Stephen R. Kane, Kaspar von Braun

    (Submitted on 30 Jun 2008)

    Abstract: The orbital parameters of extra-solar planets have a significant impact on the probability that the planet will transit the host star. This was recently demonstrated by the transit detection of HD 17156b whose favourable eccentricity and argument of periastron dramatically increased its transit likelihood.

    We present a study which provides a quantitative analysis of how these two orbital parameters effect the geometric transit probability as a function of period. Further, we apply these results to known radial velocity planets and show that there are unexpectedly high transit probabilities for planets at relatively long periods. For a photometric monitoring campaign which aims to determine if the planet indeed transits, we calculate the significance of a null result and the subsequent constraints that may be applied to orbital parameters.

    Comments: To appear in the Proceedings of the 253rd IAU Symposium: “Transiting Planets”, May 2008, Cambridge, MA. 4 pages, 4 figures

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0807.0006v1 [astro-ph]

    Submission history

    From: Stephen Kane [view email]

    [v1] Mon, 30 Jun 2008 20:10:01 GMT (35kb)


  • ljk July 2, 2008, 12:25

    Stellar proper motion and the timing of planetary transits

    Authors: Roman R. Rafikov (Princeton)

    (Submitted on 1 Jul 2008)

    Abstract: Duration and period of transits in extrasolar planetary systems can exhibit long-term variations for a variety of reasons. Here we investigate how systemic proper motion, which steadily re-orients planetary orbit with respect to our line of sight, affects the timing of transits.

    We find that in a typical system with a period of several days proper motion at the level of 100 mas/yr makes transit duration vary at a rate ~10-100 ms/yr. In some isolated systems this variation is at the measurable level (can be as high as 0.6 s/yr for GJ436) and may exceed all other transit timing contributions (due to the general relativity, stellar quadrupole, etc.). In addition, proper motion causes evolution of the observed orbital period via the Shklovskii effect at a rate $\gtrsim 10$ $\mu$s/yr for the nearby transiting systems (0.26 ms/yr in GJ436), which in some cases exceeds all other contributions to $\dot P$. Earth’s motion around the Sun gives rise to additional periodic timing signal (even for systems with zero intrinsic proper motion) allowing a full determination of the spatial orientation of the planetary orbit.

    Unlike most other timing effects the proper motion signatures persist even in systems with zero eccentricity and get stronger as the planetary period increases. They should be the dominant cause of transit timing variations in isolated wide separation (periods of months) systems that will be sought by Kepler.

    Comments: 7 pages, 2 tables, submitted to ApJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0807.0008v1 [astro-ph]

    Submission history

    From: Roman Rafikov [view email]

    [v1] Tue, 1 Jul 2008 17:39:45 GMT (25kb)


  • ljk July 2, 2008, 12:26

    Transiting Planets – Lightcurve Analysis for Eccentric Orbits

    Authors: David M. Kipping

    (Submitted on 1 Jul 2008)

    Abstract: Transiting planet lightcurves have historically been used predominantly for measuring the depth and hence ratio of the planet-star radii, p. Equations have been previously presented by Seager & Mallen-Ornelas (2003) for the analysis of the total and trough transit lightcurve times to derive the ratio of semi-major axis to stellar radius, a/R*, in the case of circular orbits.

    Here, a new analytic model is proposed which operates for the more general case of an eccentric orbit. We aim to investigate three major effects our model predicts: i) the degeneracy in transit lightcurve solutions for eccentricity, e>0 ii) the asymmetry of the lightcurve and the resulting shift in the mid-transit time, Tmid iii) the effect of eccentricity on the ingress and egress slopes. It is shown that a system with changing eccentricity and inclination may produce a long period transit time variation (LTTV).

    Furthermore, we use our model in a reanalysis of HD 209458 b archived data by Richardson et al. (2006), where we include the confirmed non-zero eccentricity and derive a 24 micron planetary radius of R_P = 1.275 +- 0.082 R_J (where R_J = 1 Jovian radius), which is 1% larger than is we assume a circular orbit.

    Comments: Accepted in MNRAS; 9 pages, 7 figures, 1 table

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0807.0096v1 [astro-ph]

    Submission history

    From: David Kipping Mr [view email]

    [v1] Tue, 1 Jul 2008 14:49:29 GMT (1366kb)


  • ljk July 31, 2008, 19:51

    TEST – The Tautenburg Exoplanet Search Telescope

    Authors: Philipp Eigmüller, Jochen Eislöffel

    (Submitted on 30 Jul 2008)

    Abstract: The Tautenburg Exoplanet Search Telescope (TEST) is a robotic telescope system. The telescope uses a folded Schmidt Camera with a 300mm main mirror. The focal length is 940mm and it gives a 2.2 square degree field of view. Dome, mount, and CCD cameras are controlled by a software bundle made by Software Bisque.

    The automation of the telescope includes selection of the night observing program from a given framework, taking darks and skyflats, field identification, guiding, data taking, and archiving. For the search for transiting exoplanets and variable stars an automated psf photometry based on IRAF and a lightcurve analysis based on ESO-Midas are conducted. The images and the results are managed using a PostgreSQL database.

    Comments: 4 pages, 2 figures, to appear in Proc. of’Transiting Planets’, IAU Symposium 253

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0807.4844v1 [astro-ph]

    Submission history

    From: Philipp Eigm\”uller [view email]

    [v1] Wed, 30 Jul 2008 13:09:50 GMT (169kb)