H/WTSOSS

The Hubble Wide Field Camera 3 Test of Surfaces of the Outer Solar System

Here you can find information about H/WTSOSS (pronounced Hot Sauce) Fraser and Brown, 2012.

Other papers that use the H/WTSOSS data or are related to the H/WTSOSS project are:

  • Fraser, Brown, and Glass 2015
  • Brown, Schaller, and Fraser 2011
  • ...and more to follow...
  • About the Survey


    The survey was designed to utilize the amazing IR+Optical imaging, and fast filter switching capabilities introduced with the Wide Field Camera 3 on the Hubble Space Telescope to acquire precision photometry of approximately 100 Kuiper belt objects. The sample of KBOs were selected as those too faint (approximately) to be observed spectroscopically from the ground in the J,H,K passbands. Each target was observed exactly the same way, with 2 images at each of 0.6, 0.8, 1.3, and 1.5 microns with exposure times chosen to achieve roughly the same signal-to-noise at each wavelength. The result was SNR~20 or more in each filter.

    Compositional Classes of Small Kuiper belt Objects


    The main result of this survey was the identification of two compositional classes of small Kuiper belt object. Each class can be identified by the class's correlated optical and infrared colours. This is well presented in the following figure, were we present the three colours of all the low perihelion H/WTSOSS targets (Figure 6 of the paper).

    Figure 6

    Solar colours are shown by the black star. The blue and red boxes show the approximate visual extent of the two classes of object.

    The colours of each class are well described by two separate branches of a two component mixing model. Each mixing model shares the same neutral component (approximately Solar coloured) but with two separate red components.

    This result has solved a long standing issue with KBO colours. Specifically, the centaurs exhibit bifurcated optical colours, falling into either a "blue" or red group, much like that shown above, while the more distant objects did not show this same bifurcation. These more distant objects are the precursor bodies of the centaurs, and continually replenish the centaur zone when they are dynamically scattered inwards. Thus, the discrepancy in colours between the centaurs and more distant things was really confusing.

    It turns out, size matters. Our observations have revealed that only the small objects appear to exhibit the bifurcation into two classes. The large objects, or those with an absolute magnitude brighter than H~5.6 do not exhibit this bifurcation. But as all known centaurs are smaller than this threshold, this fact wasn't realized previously.

    The Data


    The H/WTSOSS photometry and all additional object parameters presented in the paper (Table 1) can be downloaded as a text file here.