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An Infrared Hunt for Artificial Kuiper Belt Objects

If extraterrestrials were to set up a colony in our Solar System, where would they choose to settle? Gregory Matloff and Anthony R. Martin make the case for the Kuiper Belt in a recent paper for the Journal of the British Interplanetary Society. Kuiper Belt Objects (KBOs) are, after all, easy to exploit as a resource base without the burden of a planet’s gravity well. They are rich in volatile materials (more so than main belt asteroids), close enough to the Sun to harvest solar power, and far enough out that visits by those of us living in the inner Solar System would be few and far between.

Moreover, the orbits of KBOs are relatively unaffected by planetary perturbations. Matloff was intrigued enough by these factors to make a proposed infrared search of the Kuiper Belt the subject of a 2004 paper (“A Proposed Infrared Search for Artificial Kuiper Belt Objects,” JBIS 57, pp. 283-287). His new paper follows this up with an examination of the characteristics that artificial KBOs ought to display, comparing these to known objects.

How big would such an artificial habitat be? The earlier paper assumed a radius of five kilometers, on the same order of magnitude as some O’Neill designs that would house 10,000 people and more, but the authors of this new study factor in size variations up to 50 kilometers and weigh the effects of varying degrees of reflectivity. Certain assumptions are unavoidable: Matloff and Martin assume, for example, that the temperature of an artificial KBO is within the range 273-373 K, the temperature range of liquid water.

The authors find that the K-band astronomical photometric filter is sensitive to radiation temperature variations in their hypothetical artifical KBO (this is a significant result, for Earth’s atmosphere is relatively transparent in this spectral band). They also discuss visible bands of infrared in which artificial objects should be distinguishable from real KBOs. The authors then run their criteria against NASA’s Planetary Data System. A small number of real objects have characteristics similar to those predicted for artificial bodies.

This work thus results in an initial selection of targets for an advanced infrared search for artificial objects, using these criteria:

  • Low mass KBOs are favored, making plutinos primary targets (plutinos are small objects locked, as is Pluto, in an orbital resonance with Neptune).
  • Stable orbits are favored, making classical objects the next target (these are KBOs with circular orbits but often high inclinations (in excess of 30 degrees).
  • Highly eccentric orbits offer the least likely candidates.
  • The authors examine the facilities available for infrared observation, from large ground-based telescopes using adaptive optics (think ESO’s Very Large Telescope in Chile, or the twin Keck telescopes on Mauna Kea in Hawaii) to the Hubble Space Telescope, the Infrared Space Observatory and the Spitzer Space Telescope. “The intriguing situation exists that only a few real KBOs have photometric characteristics similar to those predicted for artificial bodies, but infrared observations of KBOs are limited,” Matloff and Martin write.

    Their paper concludes with a series of suggestions for improving such observational data, including studies in the K-band and coordinated use of Hubble and Spitzer to obtain full infrared data on the targeted KBOs. The paper is Gregory L. Matloff and Anthony R. Martin, “Suggested Targets for an Infrared Search for Artificial Kuiper Belt Objects,” JBIS 58 (January/February 2005), pp. 51-61.

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    • ljk February 21, 2007, 15:52

      Astrophysics, abstract
      astro-ph/0702538

      From: John Stansberry [view email]

      Date: Tue, 20 Feb 2007 18:49:52 GMT (396kb)

      Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope

      Authors: John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot

      Comments: 19 pages, 3 figures, 5 tables

      Detecting heat from minor planets in the outer solar system is challenging, yet it is the most efficient means for constraining the albedos and sizes of Kuiper Belt Objects (KBOs) and their progeny, the Centaur objects. These physical parameters are critical, e.g., for interpreting spectroscopic data, deriving densities from the masses of binary systems, and predicting occultation tracks. Here we summarize Spitzer Space Telescope observations of 47 KBOs and Centaurs at wavelengths near 24 and 70 microns. We interpret the measurements using a variation of the Standard Thermal Model (STM) to derive the physical properties (albedo and diameter) of the targets. We also summarize the results of other efforts to measure the albedos and sizes of KBOs and Centaurs. The three or four largest KBOs appear to constitute a distinct class in terms of their albedos. From our Spitzer results, we find that the geometric albedo of KBOs and Centaurs is correlated with perihelion distance (darker objects having smaller perihelia), and that the albedos of KBOs (but not Centaurs) are correlated with size (larger KBOs having higher albedos). We also find hints that albedo may be correlated with with visible color (for Centaurs). Interestingly, if the color correlation is real, redder Centaurs appear to have higher albedos. Finally, we briefly discuss the prospects for future thermal observations of these primitive outer solar system objects.

      http://arxiv.org/abs/astro-ph/0702538

    • ljk March 7, 2007, 23:06

      Astrophysics, abstract
      astro-ph/0703134

      From: Keith Noll [view email]

      Date: Wed, 7 Mar 2007 00:13:25 GMT (93kb)

      Binaries in the Kuiper Belt

      Authors: Keith S. Noll, William M. Grundy, Eugene I. Chiang, Jean-Luc Margot, Susan D. Kern

      Comments: Accepted for inclusion in “The Kuiper Belt”, University of Arizona Press, Space Science Series

      Binaries have played a crucial role many times in the history of modern astronomy and are doing so again in the rapidly evolving exploration of the Kuiper Belt. The large fraction of transneptunian objects that are binary or multiple, 48 such systems are now known, has been an unanticipated windfall. Separations and relative magnitudes measured in discovery images give important information on the statistical properties of the binary population that can be related to competing models of binary formation. Orbits, derived for 13 systems, provide a determination of the system mass. Masses can be used to derive densities and albedos when an independent size measurement is available. Angular momenta and relative sizes of the majority of binaries are consistent with formation by dynamical capture. The small satellites of the largest transneptunian objects, in contrast, are more likely formed from collisions. Correlations of the fraction of binaries with different dynamical populations or with other physical variables have the potential to constrain models of the origin and evolution of the transneptunian population as a whole. Other means of studying binaries have only begun to be exploited, including lightcurve, color, and spectral data. Because of the several channels for obtaining unique physical information, it is already clear that binaries will emerge as one of the most useful tools for unraveling the many complexities of transneptunian space.

      http://arxiv.org/abs/astro-ph/0703134