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Emily LakdawallaMarch 18, 2008

Eurotas Chasmata, Janiculum Dorsa, and Evander Crater

Walk with me down one of the Padua Chasmata and we'll pass through the craters Amastryus, Pagasus, and Tereus along the way. The International Astronomical Union (IAU) has recently given its blessing to a host of new names for features on Saturn's moon Dione, a formal (and late-arriving) indication that Cassini has improved enough on Voyager's maps of the moon that new names are required to describe its features.

Here's a map of Dione, assembled from a variety of sources by Steve Albers, with the feature names mapped onto it by Jason Perry. The IAU decreed long ago that Dione's features shall be named for people and places from the Aeneid of Virgil. Sorry it's not too legible at this resolution -- you need to download the full 1.3 MB version to read well.

Feature names on Dione

NASA / JPL / SSI / mosaic by Steve Albers / map by Jason Perry

Feature names on Dione
On March 17, 2008, the International Astronomical Union approved a number of new names for features across Dione.
The craters are obvious, but what are all these other things -- chasmata, catena, fossae, and dorsa? Here are the definitions, which are available from the United States Geologic Survey's Gazetteer of Planetary Nomenclature, one of my favorite reference websites.Those are the features that can be found on Dione; the full list of planetary feature types is here. Clearly there is some level of subjectivity when it comes to deciding whether a feature has dramatic enough topography to be called a "chasma" or whether it's just a "fossa."

As of 1982, when the Voyager maps were drawn, only 25 craters and four chasmata had received names, and three bright streaks in Dione's leading hemisphere "wispy terrain" were tentatively lamed as "linea," a vague identifier meaning "a dark or bright elongate marking." Those three "linea" names have been dropped, now that better pictures are available to identify them for sure as chasma or fossae, two crater designations have shifted slightly, and 45 new feature names were approved. Here's the full list, with their origins.

Aufidus CatenaRiver in the Apulian territory of Diomedes, now called the Ofanto.
Pactolus CatenaA Lydian river said to carry gold dust after King Midas washed off his golden touch in its waters.
Pantagias CatenaeRiver of Sicily.
Larissa ChasmaA town in Thessaly, Achilles' native region.
Latium ChasmaThe Trojans' promised land in Italy.
Palatine ChasmataOne of the Seven Hills of Rome. Note: Descriptor term changed to plural (chasmata) and coordinates and size changed 3/17/2008.
Tibur ChasmataAncient town of Italy not far from Rome on the river Arno.
Aurunca ChasmataAn old town in Campania.
Drepanum ChasmaCoastal town of Sicily where Aeneas found a safe harbor during a raging storm, and where Anchises died.
Eurotas ChasmataThe river on which Sparta stood.
Padua ChasmataCity in northern Italy founded by Antenor. Note: Changed from Paudua Linea 3/17/2008.
Janiculum DorsaHill across the Tiber river from Rome.
Arpi FossaeTown in Apulia (now Puglia, southern Italy) founded after the Trojan war by Diomedes.
Clusium FossaeOne of the twelve chief cities of Etruria, situated on the river Clanis.
Fidena FossaeTown in Latium near Rome.
Petelia FossaeTown of Lucania in southern Italy, founded by Philoctetes.
Carthage FossaeA Punic (Phoenician) city in North Africa. Note: Name changed from Carthage Linea 3/17/2008.
AdrastusKing of Argos, one of the seven against Thebes, and the only one to return alive.
AeneasHero of the Aeneid. The son of Anchises and Venus and a member of the royal family of Troy.
AmataMother of Lavinia (wife of Aeneas). Note: Name moved 3/17/2008 to a smaller, well-defined crater.
AnchisesAeneas' father.
AntenorNephew of Priam. He escaped the fall of Troy and reached Italy before Aeneas, where he founded Padua.
ButesA famous boxer who had been defeated by Dares.
CaietaA nurse of Aeneas.
CassandraDaughter of Priam; she could fortell the future. Note: Name moved 3/17/2008 to a small, well-defined crater.
CatillusBrother of Tiburtus and twin brother of Coras.
CorasBrother of Tiburtus and twin brother of Catillus. He was founder of Tibur and an ally of Turnus against Aeneas.
CreusaDaughter of Priam; first wife of Aeneas.
DidoTyrian princess who founded Carthage.
HalysA Trojan defending Aeneas' camp against the Rutulian attack. He was killed by Turnus.
IliaAlso known as Rhea Silvia; Mother by Mars of Romulus and Remus, the founders of Rome.
ItalusAncient hero, eponymous ancestor of the Italians.
LatagusSoldier of Aeneas.
LaususSon of Mezentius, killed by Aeneas.
MagusA soldier of Turnus, killed by Aeneas.
MassicusAn Etruscan ally of Aeneas.
PalinurusPilot of Aeneas' fleet. Note: Defines 63 degrees longitude on Dione. This name was mistakenly applied to a larger crater (4.0S, 61.4W, 33 km), but was moved back to the longitude-defining crater (also a RAND control point crater) on Jan. 11, 2008.
RemusHe and his brother Romulus founded Rome.
RipheusA Trojan. He fought at the side of Aeneas during Troy's last night.
RomulusMythical founder of Rome in 754 or 753 B.C., son of Mars by Ilia (Rhea Silvia).
SabinusFabled ancestor of the Sabines.
TurnusRutililan king; Aeneas' rival for hand of Lavinia.
CamillaA warrior maiden; ally of Turnus.
AcestesKing of Sicily.
AllectoOne of the Furies.
AmastrusA Trojan, victim of Camilla.
AmycusA Trojan, comrade of Aeneas.
AnnaSister and confidante of Dido.
AscaniusSon of Aeneas by Creusa.
AulestesEtruscan chief, ally of Aeneas.
CretheusA Trojan warrior who took part in the defense of Aeneas' camp against the Rutulians.
DaucusA Rutulian, father of the twins Thymber and Larides.
DercennusAncient king of the Laurentians.
EntellusSicilian boxing champion.
ErulusSuperhuman son of the goddess Feronia.
EuryalusA Trojan companion of Aeneas, friend of Nisus.
EumelusA Trojan companion of Aeneas.
EvanderSon of Mercury by Carmentis, ally of Aeneas against the Latins, mythical king of Arcadia, founded and ruled Pallanteum, built on the future site of Rome.
HerbesusA Rutulian who besieged Aeneas' camp.
LagusA soldier of Turnus.
LaridesA Rutulian, member of Turnus' army, son of Daucus, twin brother of Thymber.
LatinusKing of Latium, husband of Amata.
LigerSoldier of Turnus, brother of Lucagus.
LucagusSoldier of Turnus, brother of Liger.
MetiscusA Rutulian, charioteer of Turnus.
MezentiusEtruscan king, ally of Turnus, father of Lausus.
MurranusA Rutulian.
NisusTrojan companion of Aeneas, friend of Euryalus.
PagasusAn Etruscan killed by Camilla.
PhalerisTrojan defending Aeneas' camp against Rutulian attack.
PrytanisTrojan defending Aeneas' camp against Rutulian attack.
SagarisServant of Aeneas.
SilviusSon of Aeneas and Lavinia.
TereusA Trojan, killed by Camilla.
ThymberA Rutulian, member of Turnus' army, son of Daucus, twin brother of Larides.
TiburtusBrother of the twins Catillus and Coras, founder of Tibur to which he gave his name.
TyrrhusKeeper of the herds for Latinus, father of Silvia.

hile researching this entry I made the happy discovery that the Gazetteer has a news page -- this must have existed for a long time, but I hadn't noticed it until now. In addition to this news about Dione, there's some other significant stuff in the Saturn system. They have decided that a spot in Dilmin, northwest of the Shangri-La region in which Huygens landed, can now be identified as a crater, "Selk." And they approved back in September a number of names for small lakes near Titan's north pole.
Map of names for lakes near Titan's north pole
Map of names for lakes near Titan's north pole
Click here to download the map in PDF format (1.6 MB). Credit: NASA / JPL / USGS
Prometheus, Saturn, and the rings
Prometheus, Saturn, and the rings
This photo (the blue image from a series taken for a red-green-blue composite) was taken by Cassini on April 13, 2007 and captures Prometheus in its orbit between the A ring on the left and the F ring on the right, a space now named the "Roche Division." All of the rings cross Saturn's disk, but because the F ring is mostly transparent, light from Saturn's disk shines through, making the F ring nearly impossible to see against it. To the left, the Encke Gap can be seen as a gap in the A ring through which light from Saturn's disk shines clearly. Credit: NASA / JPL / SSI
You might ask why they didn't give names to what are obviously much larger lakes on the same map. I don't know for sure, but I am guessing it is because it is not clear how many lakes those huge black spots represent. Depending on what lies in the still-unmapped area, we could be looking at two or three or five different lakes -- so naming them will have to wait for better maps.

Finally, they've officially renamed "Encke Division" to "Encke Gap" in order to make definitions more consistent (a usage I've been following for a while), and have named the division between the A and F rings (where Prometheus and Atlas orbit) the Roche Division. What's a division and what's a gap? According to this page, "Divisions are the separations between named rings, and gaps are the spaces within named rings. In general, divisions are large, gaps are small." And they've changed the spellings for a couple of the outer, irregular moons. Looks like I have a lot of editing to do on my Saturn pages!

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
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