September 10, 2016 | David F. Coppedge

Dawn of a Young Ceres

The largest asteroid has a problem: she’s too young to get a date.

New scientific papers are out on the Dawn mission to asteroid Ceres, named for the goddess of grain (cereal, get it?). We left off July 6 with five puzzles the planetary science team were dealing with. Now, more detail is available in a special section in Science Magazine, Sept 2. Here’s what you need to know. First, from the popular media: watch for the “surprise” factor —

New studies provide unexpected insights into dwarf planet Ceres (PhysOrg): “Given the conditions on Ceres, water ice should be removed from the surface within tens of years; consequently, only a relatively recent exposure or formation of water would explain Dawn’s findings.

Ice Volcanoes and More: Dwarf Planet Ceres Continues to Surprise (Space.com): “Ahuna Mons appears to be quite young, the researchers said. Analyses of crater counts suggest that the mountain formed in the last 200 million years or so” (which would be about 1/22 the assumed age of 4.56 billion years).

Ceres’ geological activity, ice revealed in new research (Science Daily): “Dawn has revealed that Ceres is a diverse world that clearly had geological activity in its recent past,” the principal investigator says.

Ceres: The tiny world where volcanoes erupt ice (PhysOrg): “Ahuna is truly unique, being the only mountain of its kind on Ceres,” says David Williams of Arizona State. “It shows nothing to indicate a tectonic formation, so that led us to consider cryovolcanism as a method for its origin.

Ceres’ Geological Activity, Ice Revealed in New Research (Astrobiology Magazine): Ahura Mons “is the only known example of a cryovolcano that potentially formed from a salty mud mix, and that formed in the geologically recent past,” said Ottaviano Ruesch of Goddard Space Flight Center.

Ice not a major factor of dwarf planet Ceres’ surface features (PhysOrg): “Evidence of cryomagmatism is found in the floor-fractured craters, while Ahuna Mons and other domical features have been shown to be cryovolcanic in nature. These surface features suggest that Ceres has been geologically active at some point in its past, perhaps even its recent past.”

Ceres asteroid may have an ‘ice volcano’ and other signs of water, NASA mission reveals  (Monica Grady on The Conversation):

The data provides a global geological map of the asteroid showing that its entire surface appears to be covered in phyllosilicates, an important group of clay minerals. Two specific clays are identified: one that is magnesium-rich, the second an ammonium-rich species. There seems to be little or no pattern to the distribution of the two minerals – they are both almost everywhere.

This ubiquity is what is important. The minerals could not have been formed in a local event, such as an impact into an ice-filled crater. They must have been produced by planet-wide alteration, presumably implying there must have been volumes of water. It is clear that enormous quantities of liquid water are not present on Ceres now. But the signal of water-ice has been detected in at least one crater.

Cryovolcanism is the currently preferred model for this surface alteration, she says, so it’s not just at Ahura Mons. Grady also points out an uneven distribution of craters, recently exposed water ice, and evidence of three types of mineral flows. These are all indicative of recent events.

Here’s a quick rundown on the papers in Science Magazine’s Sept 2 cover story on the Dawn mission.

Dawn arrives at Ceres: Exploration of a small, volatile-rich world (Russell et al): “Exposed ice on Ceres at such mid-latitudes should become undetectable within hundreds of years, implying that Oxo has an active or recently exposed surface.

Detection of local H2O exposed at the surface of Ceres (Combe et al): “Oxo crater appears to be geologically very young (~1 million to 10 million years); it has sharp rims and its floor is almost devoid of impacts, suggesting a recent exposure of surface H2O…. Other high-albedo units and young craters observed across Ceres may be preferential locations for searching for H2O-rich materials.”

Cryovolcanism on Ceres (Ruesch et al): “Both ages indicate that Ahuna Mons formed in the geologically recent past. Downslope lineations occur on young steep slopes of bodies where the regolith is immature. On asteroid Vesta, where the regolith develops at a lower rate than on Ceres, downslope lineations are erased on surfaces older than 200 to 400 million years. Thus, these features on the flanks of Ahuna Mons are consistent with the young age inferred from crater size-frequency distributions.

Distribution of phyllosilicates on the surface of Ceres (Ammannito et al): “The widespread presence of these two types of minerals is a strong indication of a global and extensive aqueous alteration—i.e., the presence of water at some point in Ceres’ geological history.”

The geomorphology of Ceres (Buczkowski et al): “Before Dawn’s arrival, it was expected that most craters on Ceres would be relaxed, but instead there is a large inventory of craters with sharp walls and deep floors.”

Cratering on Ceres: Implications for its crust and evolution (Hiesinger et al): “Craters are heterogeneously distributed across the surface, indicating crustal heterogeneities and a complex geologic evolution of Ceres’ crust and upper mantle, an interpretation supported by FC and VIR color data. Dating the smooth deposits around Kerwan, one of the largest and most relaxed craters on Ceres, revealed young retention ages of 550 and 720 My, indicating that at least some geologic activity took place in the recent history of Ceres.

We congratulate the excellent engineering that has brought these superb images and data to Earth. But once again, a solar system body has surprised scientists with its youth. In almost every case of first visits to a new planet, moon, asteroid or comet, observations did not match predictions. The assumption of billions of years clashes with reality of young features and unexpected youth. Even when they derive ages of tens or hundreds of millions of years, we must remember that those are but tiny fractions of the assumed age (e.g., 100 million years is 1/45th the assumed age). Ponder that; what was going on for the previous 44/45ths of the time, only to change so recently? It doesn’t make sense. When you continue to see surprised looks on the faces of secular scientists, you should ask whether their assumptions are misleading them.

Congratulations also to NASA/JPL for the successful launch Sept. 8 of OSIRIS-REx, a mission to bring samples from an asteroid named Bennu back to Earth in 2023 (see Space.com). That will be a long wait because of the looping trajectory around the sun, but a historic first if all goes well. Best of luck.

 

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