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New Exomoon Project Will Use Kepler Data

Exomoons are drawing more interest all the time. It may seem fantastic that we should be able to find moons around planets circling other stars, but the methods are under active investigation and may well yield results soon. Now David Kipping (Harvard-Smithsonian Center for Astrophysics) and colleagues have formed a new project called HEK — the Hunt for Exomoons with Kepler. We thus move into fertile hunting ground, for there has never been a systematic search for exomoons despite the work of ground-breaking researchers like Kipping, Gaspar Bakos (Princeton) and Jean Schneider (Paris Observatory). It’s definitely time for HEK as Kepler’s exoplanet candidate list grows.

Kepler, of course, works with transit methods, noting the dip in starlight as an exoplanet passes in front of the star under observation. HEK will use Kepler photometry to look for perturbations in the motion of the host planet that could flag the presence of a moon. Variations in transit timing (TTV) and duration (TDV) should be the most observable effects, the former being variations in the time it takes the planet to transit its star, while transit duration variation is caused by velocity changes induced by the fact that the planet and moon orbit a common center of mass.

The team will also look for eclipse features, where the moon might occult the planet during a planet-star eclipse. Back in 2009, Kipping and team ran a feasibility study on Kepler’s ability to find the moon of a gas giant in the habitable zone of a star (see Habitable Moons and Kepler). Assuming moons on circular, coplanar orbits around the host planet, the results showed that Kepler could detect exomoons down to 0.2 Earth masses. This is a large moon indeed, for as Kipping’s new paper on this work points out, the most massive moon in our Solar System, Ganymede, is 0.025 Earth masses (our own Moon is 0.0123 Earth masses). No question, then, that HEK will be looking for large moons, moons bigger than any we see in our own system.

Image: The view from a large exomoon would be like nothing we’ve seen in our own system, especially if that world proved suitable for life. Credit: Dan Durda.

Of course, binary planets also fall within the scope of this study — Kipping draws the line between a binary planet and a true planet-moon pair at the point where the center of mass of the two bodies is outside the radius of both bodies, but HEK can work comfortably with both scenarios. The paper runs through the likelihood that such large objects might exist, forming either around the host planet as it undergoes planetary growth, or (more likely) being captured by the host — here we think of moons like Triton in our own system, or of impact scenarios between planetesimals or young planets like that thought to have produced our own Moon.

Other scenarios are also possible, as the paper announcing HEK notes:

For planets which do not migrate through a proto-Kuiper belt or under the assumption that such objects will never reach sufficient mass to qualify as large moons, an alternative source of terrestrial mass objects is required. This object could be an inner terrestrial planet encountered during the gas giant’s inward migration or even a large, unstable Trojan which librates too close to the planet. Indeed, Eberle et al. (2010) have shown that a gas giant planet (in their case HD 23079b) can capture an Earth-mass Trojan into a stable satellite orbit, occurring in 1 out of the 37 simulations they ran.

How long would such a system be stable? The capture process would produce what the paper describes as ‘very loosely-bound initial orbits,’ but there has been work showing that captured moons have relatively high survival rates, as high as 50 percent in various configurations. Producing binary planets through the same methods is plausible, and the paper notes that a Jupiter orbited by an Earth-class planet could be considered an example of an extreme binary.

Examining these origin scenarios as well as the evolution of large moons in detail, the paper goes on to note the project’s objectives:

1. The primary objective of HEK is to search for signatures of extrasolar moons in transiting systems.

2. The secondary objective of HEK will be to derive posterior distributions, marginalised over the entire prior volume, for a putative exomoon’s mass and radius, which may be used to place upper limits on such terms (where conditions permit such a deduction).

3. The tertiary objective of HEK is to determine… the frequency of large moons bound to the Kepler planetary candidates which could feasibly host such an object (in an analogous manner to η⊕ – the frequency of Earth-like planets).

We know that in our own system, Europa, Titan and even tiny Enceladus are possible candidates for life. The Hunt for Exomoons with Kepler project won’t be able to tell us anything about astrobiology on an exoplanet’s moon, but if we begin to find Earth-sized objects orbiting gas giants in the habitable zone, we’ll have taken a first step toward learning whether exomoons could be just as viable a place for life as a planetary surface. The HEK home page goes so far as to speculate that planet-based life could actually be outnumbered by life on habitable moons. Step one, of course, is to find out if such moons actually exist, using Kepler’s crucial data.

The paper is Kipping et al., “The Hunt for Exomoons with Kepler (HEK): I. Description of a New Observational Project,” submitted to the Astrophysical Journal (preprint). The 2009 study is Kipping et al., “On the detectability of habitable exomoons with Kepler-class photometry,” Monthly Notices of the Royal Astronomical Society, published online 24 September, 2009 (abstract).


Comments on this entry are closed.

  • andy January 13, 2012, 14:33

    Talking of Trojan planets, I wonder if there are any out there. The system KOI-730 that was announced as containing co-orbital planets turns out not to be in such a configuration.

  • djlactin January 14, 2012, 7:34

    I’m stunned that within a fraction of my lifetime, ‘we’ have progressed from wondering whether we can detect exoplanets to whether we can detect moons around them. Next (I predict), ‘we’ will be imaging exoplanets to determine whether their atmospheres show evidence of thermodynamic disequilibrium (= ‘life’).

  • Tom Mazanec January 14, 2012, 9:04

    What will we name the exomoons? Something like the asteroid moon nomenclature…S/2012 (Keplar 17b) 1 for example?

  • A. A. Jackson January 14, 2012, 10:00

    I returned Thursday from the:
    8-12 JANUARY 2012

    Here is a list of the sessions on extra solar solar planets (exoplanet is used, but the AAS formal name is the latter). I am not going to list the poster presentations there were just too many. I know I saw three presentations and posters about exomoons. A lot of interest in Habitability Zones. Planetary System formation is in a huge state of flux now, have to include binaries and maybe multiple star systems.
    As a part of astronomy this is a huge new area of research.
    There were sessions and poster presentations from Monday to Thursday.

    Monday Sessions and Events
    110 Extrasolar Planets: Habitable Zones
    Monday, 10:00am-11:30am, Ballroom F
    110.00C Chair
    Lisa Kaltenegger1 1Harvard University, CfA.
    110.01 Eta-Sub-Earth Projection from Kepler Data
    Wesley A. Traub1 1Jet Propulsion Laboratory.
    110.02D Characterization of Exoplanet Atmospheres and Kepler Planet Candidates with Multi-Color Photometry from the Gran Telescopio Canarias
    Knicole Colon1, E. B. Ford1 1University of Florida.
    110.03 On The Existence Of Earth-like Planets In The Circumbinary System Kepler-16
    Billy L. Quarles1, Z. E. Musielak1, M. Cuntz1 1UTA.
    110.04 Constraining the Mass, Age, and Orbital Architecture of HR 8799 Planetary System
    Nader Haghighipour1, J. Sudol2 1Univ. of Hawaii, 2West Chester University.
    110.05 The GJ 876 System: Fundamental Stellar Parameters and Planets in the Habitable Zone
    Kaspar von Braun1, T. S. Boyajian2, J. Jones2, S. R. Kane1, S. N. Raymond3,G. T. van Belle4, D. R. Ciardi1, M. Lopez-Morales5, T. A. ten Brummelaar6,H. A. McAlister2, G. Schaefer6, S. R. Ridgway7, J. Sturmann6, L. Sturmann6, N. H. Turner6, C. Farrington6, P. J. Goldfinger6 1Caltech, 2Georgia State University, 3Bordeaux, France, 4Lowell, 5CSIC-IEEC, Spain, 6CHARA Array, 7NOAO.
    110.06 55 Cancri: A Coplanar Planetary System that is Likely Misaligned with its Star
    Nathan A. Kaib1, S. N. Raymond2, M. J. Duncan1 1Queen’s University, Canada, 2Universite de Bordeaux, France.
    110.07 Orbital Motion Of HR 8799 b, c, d Using Hubble Space Telescope Data From 1998: Constraints On Inclination, Eccentricity And Stability
    Remi Soummer1, J. B. Hagan1, L. Pueyo1, A. Thormann2, A. Rajan1, C. Marois3 1Space Telescope Science Institute, 2Johns Hopkins University, 3NRC Herzberg Institute of Astrophysics, Canada.
    110.08 Studying Photometric Orbital Modulations Of Kepler Objects Of Interest
    Avi Shporer1, B. J. Fulton2, Kepler team 1University of California, Santa Barbara, 2Las Cumbres Observatory Global Telescope

    155 Exoplanet Mission Technologies
    Monday, 9:00am-6:30pm, Exhibit Hall
    This poster session features papers which highlight technology progress and plans toward space missions which will detect and characterize low-mass extrasolar planets around nearby stars. The main focus is on techniques for starlight suppression, allowing the direct detection of light from an exoplanet and enabling studies based on photometry and spectroscopy of the planet’s light. Progress has been made on several distinct techniques for achieving the needed starlight rejection. The session will also include technology developments toward other kinds of exoplanet measurements, such as microlensing, precision astrometry, and transit spectroscopy.

    228 Extrasolar Planets and Brown Dwarfs: Formation, Evolution
    Tuesday, 2:00pm-3:30pm, Ballroom F
    228.00C Chair
    Gerard van Belle1 1Lowell Observatory.
    228.01D Heterogeneous Giant Planet Thermal Evolution with MESA
    Neil Miller1, J. Fortney1 1UC Santa Cruz.
    228.02 Candidates for Solar Siblings
    Mauri J. Valtonen1, A. Myllari2, A. Bajkova3, V. Bobylev3 1Univ. of Turku, Finland, 2Abo Akademi University, Finland, 3Pulkovo Astronomical Observatory, Russian Federation.
    228.03 A Young Exoplanet Caught at Formation
    Adam L. Kraus1, M. J. Ireland2 1Univ. of Hawaii-IfA, 2Macquarie University, Australia.
    228.04D Giant Planet Companions to T Tauri Stars
    Christopher Crockett1, N. Mahmud2, L. Prato3, C. Johns-Krull2, D. T. Jaffe4, P. Hartigan2, C. A. Beichman5 1USNO, 2Rice University, 3Lowell Observatory, 4U.T. Austin, 5NExSci.
    228.05 Discovery of Massive Brown Dwarf Companions to BAF stars in Upper Scorpius
    Sasha Hinkley1, M. J. Ireland2, A. L. Kraus3, J. M. Carpenter1, P. Tuthill4 1California Institute of Technology, 2MacQuarie University, Australia, 3Institute for Astronomy, Univ. of Hawaii, 4University of Sydney, Australia.
    Tuesday Sessions and Events
    228.06 WITHDRAWN: The Origin of Retrograde Hot Jupiters
    Smadar Naoz1, W. Farr2, Y. Lithwick2, F. Rasio2, J. Teyssandier2 1Harvard-Smithsonian Center for Astrophysics ITC, 2Northwestern Univ
    228.07 The TERMS Project: More Than Just Transit Exclusion
    Stephen R. Kane1, Transit Ephemeris Refinement and Monitoring Survey(TERMS) 1NASA Exoplanet Science Institute, Caltech.
    245 Extrasolar Planets: Detection
    Tuesday, 9:00am-6:30pm, Exhibit Hall
    301 The Solar System & Extrasolar Habitable Zones
    Wednesday, 10:00am-11:30am, Room 12A
    301.00C Chair
    Lee Anne M. Willson1 1Iowa State Univ
    301.01 Chemistry of the Moon-Forming Impact
    Bruce Fegley1, L. Schaefer2, K. Lodders1 1Washington Univ., 2Harvard University.
    301.02D Observations and Models of Iapetus’s Microwave Emissivity
    Paul Ries1 1University of Virginia.
    301.03 Searching the Southern Skies with the La Silla-QUEST KBO Survey: Probing the Inventory of Large and High Inclination Kuiper belt
    Megan E. Schwamb1, D. L. Rabinowitz1, S. Tourtellotte1, R. Brasser2 1Yale University, 2Academia Sinica Institute of Astronomy and Astrophysics, Taiwan.
    301.04 The Habitable Zone Gallery
    Dawn M. Gelino1, S. R. Kane1 1NASA Exoplanet Science Institute, Caltech.
    301.05 Super-earths – Atmospheres And Conditions For Life
    Lisa Kaltenegger1 1MPIA/CfA, Germany.

    326 Extrasolar Planets I
    Wednesday, 2:00pm-3:30pm, Ballroom F
    326.00C Chair
    Peter R. Lawson1 1JPL.
    326.01 Ground-based Infrared Spectroscopy of the Extremely Hot Jupiter WASP-12b
    Ian J. M. Crossfield1, B. Hansen1, T. Barman2 1UC Los Angeles, 2Lowell Observatory.
    326.02 Near-infrared Thermal Emission of hot Jupiters
    Bryce Croll1 1M.I.T
    326.03 Planet-Disk Interactions on a Moving Mesh
    Diego Munoz1 1Harvard University.
    Wednesday Sessions and Events
    326.04 Planet Distribution Evolution Towards Destruction By Roche Lobe Overflow
    Stuart F. Taylor1 1National Tsing Hua University, Taiwan.
    326.05D Hot Jupiter Upper Atmospheres: Model Transit Signals in Lyman-alpha for HD 209458b
    George B. Trammell1, P. Arras1, Z. Li1 1University of Virginia.
    326.06 Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating
    Rory Barnes1, K. Mullins1, C. Goldblatt2, V. S. Meadows1, J. F. Kasting3 1University of Washington, 2University of Victoria, Canada, 3Pennsylvania State University.
    326.07 Uniform Modeling of the Kepler Objects of Interest Catalog
    Jason Rowe1, E. V. Quintana1, T. S. Barclay2, S. T. Bryson3, J. L. Christiansen1,F. R. Mullally1, S. E. Thompson1, Kepler Team 1NASAames/SETI Institute, 2NASAames, 3NASAames Research Center.
    326.08 Direct Detection of Exoplanets with Polarimetry
    Sloane Wiktorowicz1, G. Laughlin1 1University of California, Santa Cruz.

    339 Extrasolar Planetary Systems
    Wednesday, 9:00am-6:30pm, Exhibit Hall

    405 Extrasolar Planets II
    Thursday, 10:00am-11:30am, Ballroom F
    405.00C Chair
    Nader Haghighipour1 1Univ. of Hawaii.
    405.01 The California-Kepler Survey: Precise Planet Radii and Metallicities
    Andrew Howard1, G. W. Marcy1, J. A. Johnson2, T. D. Morton2, H. Isaacson1 1UC Berkeley, 2Caltech.
    405.02D Retrieval of Atmosphere Structure and Composition of Exoplanets from Transit Spectroscopy
    Jae-Min Lee1, L. N. Fletcher1, P. G. J. Irwin1 1Atmospheric, Oceanic and Planetary Physics, University of Oxford, United Kingdom.
    405.03D The Hypatia Catalog: Chemical Abundances in the Habitable Solar Neighborhood
    Natalie R. Hinkel1 1Arizona State University.
    405.04 C/O Ratios In Exoplanetary Atmospheres – New Results And Major Implications
    Nikku Madhusudhan1 1Princeton University.
    405.05 Infrared Spectroscopy of the Transiting Exoplanets HD189733b and XO-1 Using Hubble WFC3 in Spatial Scan Mode
    Drake Deming1, A. Wilkins1, P. McCullough2, N. Madhusudhan3, E. Agol4, A. Burrows3, D. Charbonneau5, M. Clampin6, J. Desert5, R. Gilliland2, H. Knutson7, A. Mandell6, S. Ranjan5, S. Seager8, A. Showman9 1Univ. of Maryland, 2STScI, 3Princeton Univ., 4Univ. of Washington, 5CfA, 6GSFC, 7Caltech, 8MIT, 9Univ. Arizona.
    Thursday Sessions and Events
    405.06 New Imaging of the beta Pictoris Planet and Debris Disk
    Thayne M. Currie1, C. Thalmann2, S. Matsumura3, N. Madhusudhan4, A. Burrows4, M. Kuchner1 1NASA-Goddard Space Flight Center, 2University ofamsterdam, Netherlands, 3University of Maryland, 4Princeton University.
    405.07 First: Florida Ir Silicon Immersion Grating Spectrometer
    Jian Ge1, B. Zhao1, J. Wang1, X. Wan1, S. Powell1 1Univ. of Florida.
    432 The Sun, The Solar System and Extrasolar Planets

  • FrankH January 15, 2012, 21:56

    Is a Trojan planet going to be stable over billions of years? A factional Earth mass at 5.5 AU (Jupiter’s Trojan asteroids) is probably not going to be the same as a Trojan Earth and Jupiter at 1AU.

  • A. A. Jackson January 16, 2012, 11:56

    The ‘stable’ Lagrange points are only strictly stable in the idealized three body problem , and even then it’s a bit complex.
    When one introduces a perturbing body, the Sun for the Earth Moon Lagrange points stability is only valid over a finite time.
    There probably does not exist in any planetary system anywhere where the idealized three body problem , especially the restricted three body problem, is realized.