Question: Which object in the solar system is named after a minor water deity in Greek mythology ?

text: List of Solar System objects by size
List of objects by radius -- From 100 to 199 km
This list contains a selection of objects estimated to be between 100 and 199 km in radius ( 200 and 399 km in diameter ) . The largest of these may lie above the boundary for hydrostatic equilibrium , but most are irregular . Most of the trans-Neptunian objects ( TNOs ) listed with a radius smaller than 200 km have `` assumed sizes based on a generic albedo of 0.09 '' since they are too far away to directly measure their sizes with existing instruments . Mass switches from 1021 kg to 1018 kg ( Zg ) . Main-belt asteroids have orbital elements constrained by ( 2.0 AU < a < 3.2 AU ; q > 1.666 AU ) according to JPL Solar System Dynamics ( JPLSSD ) . [ 86 ] Many TNOs are omitted from this list as their sizes are poorly known . [ 49 ]
This is a partial list of Solar System objects by size, arranged in descending order of mean volumetric radius, and divided into several size classes. These lists can also be sorted according to an object's mass and, for the largest objects, volume, density and surface gravity, insofar as these values are available. This list contains the Sun, the planets, dwarf planets, many of the larger small Solar System bodies (which includes the asteroids), all named natural satellites, and a number of smaller objects of historical or scientific interest, such as comets and near-Earth objects. Objects on this list are ordered by mean radius rather than mass; thus, objects on the lower portions of the table can be more massive than objects higher on the list if they have a higher density. Many trans-Neptunian objects (TNOs) have been discovered; in many cases their positions in this list are approximate, as there is frequently a large uncertainty in their estimated diameters. Solar System objects more massive than 1021 kilograms (one yottagram [Yg]) are known or expected to be approximately spherical. Astronomical bodies relax into rounded shapes (ellipsoids), achieving hydrostatic equilibrium, when their own gravity is sufficient to overcome the structural strength of their material. It was believed that the cutoff for round objects is somewhere between 100 km and 200 km in radius if they have a large amount of ice in their makeup; however, later studies revealed that icy satellites as large as Iapetus (1,470 kilometers in diameter) are not in hydrostatic equilibrium at this time, and a 2019 assessment suggests that many TNOs in the size range of 400-1000 kilometers may not even be fully solid bodies, much less gravitationally rounded. Objects that are ellipsoids due to their own gravity are here generally referred to as being round, whether or not they are actually in equilibrium today, while objects that are clearly not ellipsoidal are referred to as being irregular. Spheroidal bodies typically have some polar flattening due to the centrifugal force from their rotation, and can sometimes even have quite different equatorial diameters (scalene ellipsoids such as Haumea). Unlike bodies such as Haumea, the irregular bodies have a significantly non-ellipsoidal profile, often with sharp edges. There can be difficulty in determining the diameter (within a factor of about 2) for typical objects beyond Saturn.
Body Radius ( km ) Type Remarks - shape Refs r · M
2004 UX 10 144897 199 ± 19.5 plutino - ·
Mimas Saturn I 198.2 ± 0.4 moon of Saturn round ( smallest body currently known to have an ellipsoidal shape , but not in hydrostatic equilibrium ) ·
1998 SN 165 35671 196.5 ± 19.5 cubewano - · M
Ilmarë Varda I 180.5 +24 −19 moon of 174567 Varda - · M
Nereid Neptune II 178.5 ± 6.5 moon of Neptune probably irregular in shape · M
2001 UR 163 42301 ≈ 176 resonant KBO ( 4:9 ) - · M
1996 TL 66 15874 169.5 ± 10 SDO - · M
2004 XA 192 230965 169.5 +60 −47.5 SDO - · M
2002 WC 19 119979 ≈ 169 resonant KBO ( 1:2 ) ; binary - ·
Interamnia 704 166 ± 3 belt asteroid type F scalene ellipsoid ; likely in hydrostatic equilibrium ·
Hiʻiaka Haumea I ≈ 160 moon of Haumea probably irregular in shape ·
2010 TY 53 ≈ 158 extended centaur - · M
2010 TJ ≈ 158 SDO - · M
1999 CD 158 469306 ≈ 155 resonant KBO ( 4:7 ) - ·
Europa 52 152.0 ± 1.8 belt asteroid type C irregular shape ·
2004 EW 95 120216 145.5 plutino - · M
Davida 511 145.2 ± 1.1 belt asteroid type C irregular shape ·
2002 TX 300 55636 143 ± 5 cubewano ; Haumea family - · M
Sylvia 87 143 ± 5.5 outer belt asteroid type X ; trinary irregular shape ·
Actaea Salacia I 143 ± 12 moon of 120347 Salacia - · M