Electronic Telegram No. 5593
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


S/2025 U 1
     M. El Moutamid, Southwest Research Institute; M. Hedman, University of
Idaho; M. Showalter and M. Tiscareno, SETI Institute; I. de Pater, University
of California, Berkeley; J. Lissauer, Ames Research Center, NASA; and D.
Souami, Laboratoire d'Instrumentation et de Recherche en Astrophysique, CNRS,
Paris Observatory, report the discovery of a previously unknown regular
satellite of Uranus.  This object was detected in a series of images obtained
by the Near-Infrared Camera (NIRCam) onboard the James Webb Space Telescope
on 2025 Feb. 2 (as part of Guest Observer Program 6379).  This observation
included ten 2137-s exposures in which the object could be detected.
Sub-exposures within each of these images were co-added in a way that
accounted for the predictable pixel shifts associated with the expected
motion of bodies on circular, equatorial orbits around Uranus.  Observation
times and measured offsets from Uranus are as follows:

2025 Date UT           Offset (arcsec)
                        R.A.    Decl.
Feb. 2.05788            2.70    -2.74
Feb. 2.08461            3.55    -1.34
Feb. 2.11132            3.79     0.31
Feb. 2.13816            3.30     1.87
Feb. 2.16488            2.33     3.18
Feb. 2.19296            0.82     3.89
Feb. 2.21980           -0.77     3.87
Feb. 2.24653           -2.21     3.20
Feb. 2.27324           -3.27     1.96
Feb. 2.30021           -3.77     0.39

The object is located at a projected radial distance of 56250 +/- 250 km from
Uranus' center in the planet's equatorial plane, between the orbits of Uranus
VII (Ophelia) and Uranus VIII (Bianca).  Initial astrometry is consistent with
the moon orbiting on a nearly circular orbit with a mean motion of 896 +/- 1
degrees/day (orbital period 0.402 days).  The observed flux from this object
at wavelengths around 1.5 microns is 70 +/- 10 nJy, which corresponds to an H
magnitude of 25.5 +/- 0.2.  Assuming it has a reflectance comparable to other
nearby satellites (between 0.05 and 0.1), this object has a radius of 4-5 km,
placing it well below the detection threshold of earlier images from Voyager
and the Hubble Space Telescope.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2025 CBAT
2025 August 19                   (CBET 5593)              Daniel W. E. Green