This answer to First satellite of an asteroid (or double asteroid) ever imaged by delay-Doppler radar? mentions that Wikipedia's 1866 Sisyphus; Binary system says:

In 1985, this object was detected with radar from the Arecibo Observatory at a distance of 0.25 AU. The measured radar cross-section was 8 square kilometers.[6][a] During the radar observations, a small minor-planet moon was detected around Sisyphus, although its existence was not reported until December 2007. Robert Stephens confirmed that it is a suspected binary,[7] and Brian Warner added additional weight to this conclusion, giving 27.16±0.05 hours as the satellite's orbital period, longer than the 25 hours previously reported by Stephens.[8]

6Ostro, S. J.; Campbell, D. B.; Chandler, J. F.; Shapiro, I. I.; Hine, A. A.; Velez, R.; et al. (October 1991). "Asteroid radar astrometry". Astronomical Journal. 102: 1490–1502. doi:10.1086/115975.

aBenner (1985), gives a diameter of 8 kilometer. Summary figures listed at LCDB

7Stephens, Robert D.; French, Linda, M.; Warner, Brian D.; Wasserman, Lawrence H. (October 2011). "The Curse of Sisyphus". The Minor Planet Bulletin. 38 (4): 212–213. Retrieved 12 December 2016.

8Warner, Brian D. (October 2016). "Near-Earth Asteroid Lightcurve Analysis at CS3-Palmer Divide Station: 2016 April-July". The Minor Planet Bulletin. 43 (4): 311–319.

Reference 7, "The Curse of Sisyphus" is the only reference I am currently unable to read. Unfortunately Bulletin of the Minor Planets Section of the Association of Lunar and Planetary Observers, Vol. 38, No. 4, p. 212-213 (2011) doesn't seem to be available online when I click "pdf".

With a title like that I wonder if it might contain some information on how the the small minor moon was "detected" in 1985 but, apparently, not reported.

Question: What exactly was "The curse of Sisyphus" and why did it take so long to find out about the radar detection of its companion?

note: I'm not asking about Greek mythology. I'm hoping the choice of the title for the Minor Planet bulletin describes more recent events.

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    $\begingroup$ There are no notes on ssd.jpl.nasa.gov/sb/sats.html But the Horizons record for 1866 Sisyphus has just been updated: Soln.date: 2024-Apr-13_06:20:31 ssd.jpl.nasa.gov/api/… $\endgroup$
    – PM 2Ring
    Commented Apr 13 at 14:52
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    $\begingroup$ found it on researchgate researchgate.net/publication/252604347_The_Curse_of_Sisyphus $\endgroup$
    – James K
    Commented Apr 14 at 13:20
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    $\begingroup$ Here are notes on the CW radar measurements in 1985 updated in 2013. echo.jpl.nasa.gov/asteroids/Sisyphus/sisyphus.html $\endgroup$
    – eshaya
    Commented Apr 15 at 13:38
  • $\begingroup$ @eshaya Wow, thanks! that definitely rises to the level of another answer post. It's the actual observed data from 1985 that we're talking about, plus (near the bottom) a nicely quotable explanation of it's re-interpretation. Also, posting it as an answer will allow me to ask the next question about the structure of the spectrum and it's interpretation. $\endgroup$
    – uhoh
    Commented Apr 15 at 22:00

2 Answers 2


The article is humourously named, but there doesn't seem to any particular curse mentioned.

The authors describe a process of getting a accurate light curve, establishing that there is a 2.4 hour periodicity (showing the rotation of the asteroid). And, when this 2.4 hour signal is subtracted, they detect a weak secondary signal of 25.25h, which they interpret as being the result of a moon.


The lack of mutual events (occultations and/or eclipses due to a satellite), leaves the issue of binarity still unresolved.

Although this secondary period is within the realm of orbital periods seen for satellites of other binary systems, due to the noisiness of the data, we cannot consider it to be definitive. It would be appropriate to have future studies of this suspected binary system. It is time for others to take up the task of pushing this boulder up the mountain.

So the only "curse" is that they don't get definitive results, and moreover, they don't plan to follow-up this research. It's just a bit of "cute" and doesn't explain the gap between the radar observations and the "discovery" of a satellite.

The short paper is available online https://www.researchgate.net/publication/252604347_The_Curse_of_Sisyphus

  • $\begingroup$ I think that the paragraph starting with "Since a longer period seemed to be present, we inquired about previous radar data." does kind-of explain the gap. My take is that it was only after "Lance Benner took another look at (the previous radar data)" with a better understanding of how to read Doppler-only data that the binary nature of the data was recognized. Since the data was inconclusive, it's probably not a case of a precovery (pre-discovery recovery). $\endgroup$
    – uhoh
    Commented Apr 14 at 15:01

Here are notes on the CW radar measurements in 1985 updated in 2013. echo.jpl.nasa.gov/asteroids/Sisyphus/sisyphus.html

They could not detect it with the ranging technique, using a single wavelength and timing, but the continuous wave showed a spike off center that changed in relative velocity. After 2000, there were several binary asteroids detected in CW radar by noting that the velocity period of the secondary was different from the rotation period of the primary. They then understood that 1866 Sisyphus was a binary.


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