210 captures

10 May 2003 - 10 Sep 2025

Sep	OCT	Jan
	22
2007	2008	2010

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About this capture

COLLECTED BY

Organization: Alexa Crawls

Starting in 1996, Alexa Internet has been donating their crawl data to the Internet Archive. Flowing in every day, these data are added to the Wayback Machine after an embargo period.

Collection: 51_crawl

this data is currently not publicly accessible.

TIMESTAMPS

The first trans-Neptunian object (TNO) was discovered in 1992. Given the remoteness of TNOs, it was years before sizes were first measured for a few TNOs. For a variety of reasons (direct and indirect), TNOs are believed related to comets which are generally quite dark. The conventional wisdom was an initial best estimate of 0.04 for the albedo of TNOs.

Accumulated measurements of size and albedo now suggest that, while some TNOs are indeed this dark, some are significantly brighter. Reported measurements are summarized below.

The above graph shows albedo vs. diameter for trans-Neptunian objects and centaurs for which diameters/albedos have been measured. Pluto and Charon are also included. Red points indicate TNOs and blue points indicate centaurs.

Most size determinations have been made by comparing thermal and visual observations. Some have been derived for binary TNOs by combining observed brightness, orbital dynamics, and reasonable assumed values of density. A few diameter measurements come from direct imaging or stellar occultations.

Approximate average albedos are as follows (with number of objects in parentheses):

• Centaurs, 0.075 (17);
• TNOs, all, 0.159 (38);
  • TNOs, over 1200 km in diameter, 0.601 (5)
  • TNOs, under 1200 km in diameter, 0.092 (33)
    • --better constrained only, 0.080 (23);
    • --lower limit on albedo only, 0.066 (4);
    • --dynamical measurement only, 0.154 (6).

The relevant diameter measurements are listed below. This includes 38 TNOs (of which 6 are binary) and 17 centaurs. The TNOs include the "dwarf" planets Pluto and Eris, and Pluto's satellite Charon is listed as well (for Pluto and Charon, representative measurements are given). All other diameter estimates on the pages Trans-Neptunian objects and List of known trans-Neptunian objects assume an albedo of 0.09. This is a revision in 2005 from a previous model (the old model assumed albedos of 0.09 for Centaurs, 0.04 for TNOs less than 660 km in diameter, and an increasing albedo for larger TNOs based on a best fit to observations through early 2004).

The number of listed objects on this page has increased about 50% over the 2006 version, due primarily to new results from the Spitzer Space Telescope. The average albedos for centaurs and smaller TNOs is relatively unchanged. Two noteworthy trends:

• The largest TNOs (over 1000 km in diameter) tend to have higher albedos, especially the largest objects. Modeling and spectroscopic observations suggests that this trend reflects condensation of frost from temporary atmospheres that only the largest object have enough gravity to retain.
• The average of dynamically-derived albedos for binary TNOs tends to be higher than the average for other TNOs. This mostly results from the high albedo of (58534) Logos. If lower densities are assumed for binary TNOs, the resulting albedos are lower as well.

Measured diameters:

Notes: For binary TNOs, diameter figures with * are for primary only; diameter figures with # are effective combined diameter for both components. Some reported albedos are for red (R), blue (B), or visible/yellow (V) filters; if unspecified, albedo is geometric visual albedo (or is unspecified by source). Some figures by Grundy, Noll, Stephens (2005) are reanalyses of previous results. Figures in brackets are my estimates based on tabulated data. For sources with *, data is from preliminary unpublished results and may have been superceded.

Methods include: eclipses (analysis of mutual eclipses and occultations of primary and secondary), imaging (direct imaging of disk), occultation (stellar occultation), thermal (thermal infrared or radiometric combined with visual photometry), photometric (derived from modeled spectral photometry), dynamical (fit based on observed brightness, dynamics of primary and secondary, and assumed density), and lightcurve/dynamical (fit based on observed lightcurve, derived rotational properties, and dynamics of primary and secondary).

For more information see: