Astronomy

What's the composition of Ceres?

What's the composition of Ceres?


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Strangely, there isn't a lot of information on Ceres on the internet. I want to know the specific percentages of its composition.

Thanks in advance!


The details are not known for certain, however it is generally thought to have a rocky core, formed of silicates (aluminium and magnesium silicate for example) and a large mantle of water ice, perhaps 50% by volume, 25% by mass. The surface crust is formed of various carbonaceous and iron minerals: siderite, dolomite, cronstedtite. There may be a small iron core.


What's the composition of Ceres? - Astronomy

Asteroid 1 Ceres is the largest main-belt asteroid. Ceres has been the subject of increased attention of late, with our knowledge of this body increasing rapidly since its identification as a target of NASA's Dawn spacecraft mission. Despite much work, consensus as to the surface composition of Ceres has remained elusive. Its spectrum in the visible and near-IR (0.4-2.5 μm) is typical of C-class and related asteroids, and consistent with carbonaceous chondrites, though not diagnostic of them. An absorption at 3 μm indicative of hydrated (water- or OH-bearing) minerals has been seen on Ceres for nearly 30 years (Lebofsky 1978), though identification of a sub-band at 3.05 μm has been controversial: Lebofsky et al. (1981) proposed water ice frost, and King et al. (1992) later proposed ammoniated clays. Neither of these identifications are cut-and-dried, however: water ice frost is only stable near Ceres’ poles (and only marginally there), while ammoniated clays have never been seen in meteorites.

In order to address this issue, we observed Ceres in the 2-4 μm region over two nights in May 2005 using the IRTF. After thermal correction, Hapke mixture modeling of full-night averages of Ceres’ spectrum indicates that an iron-rich clay, such as those discussed in Calvin and King (1997) and found in carbonaceous chondrites, could be responsible for the 3.05 μm band. A spectrum of Ceres from the KAO strengthens the interpretation of iron-rich clays rather than the competing hypotheses. In addition, the Ceres data show evidence of carbonate minerals near 3.8-3.9 μm with a contribution of 4-6%, similar to what is seen in CI meteorites. We will discuss the observations and modeling and the implications thereof.

We acknowledge NASA Planetary Astronomy Grant NNG05GR60G and the people of Hawai'i for allowing telescopes on their sacred mountain.


Ceres is an ocean world!

Ceres should definitely be on the short list for a lander and rover.

#4 Tony Flanders

It's amazing -- one after another, whenever we get a close-up look at any object, it proves to be far more interesting than we ever imagined it would be. Just look at the New Horizons mission! Even Alan Stern himself never imagined that Pluto would turn out to be a diverse and complex as it really is.

Add Ceres to the long list of solar system objects known to be geologically active.

And just think: every other object the same size as Ceres or bigger -- and we now know many of them -- is probably at least as different from Ceres and each one of its similar-sized brethren as Earth is from Mars or Venus.

#5 Keith Rivich

I'm curious why the ocean would be salty. On earth the oceans are salty from the interplay of rain, carbon dioxide and rock weathering. The slightly acidic rain dissolves the rock releasing the salts to dissolve into the water.

I wonder what other process could create the salt content?

#6 BillP

It's amazing -- one after another, whenever we get a close-up look at any object, it proves to be far more interesting than we ever imagined it would be. Just look at the New Horizons mission! Even Alan Stern himself never imagined that Pluto would turn out to be a diverse and complex as it really is.

Add Ceres to the long list of solar system objects known to be geologically active.

And just think: every other object the same size as Ceres or bigger -- and we now know many of them -- is probably at least as different from Ceres and each one of its similar-sized brethren as Earth is from Mars or Venus.

So very true! Wouldn't it be funny if the asteroid belt, the last place anyone really thinks of, turns out to be the place that we can gain the most knowledge from it we only explore it thoroughly!


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In: Icarus , Vol. 204, No. 1, 11.2009, p. 183-193.

Research output : Contribution to journal › Article › peer-review

T1 - On the composition and differentiation of Ceres

N1 - Funding Information: The paper is benefited from review comments and conversations with William McKinnon. The work is supported by Grants from NASA Cosmochemistry Program (NNX07AJ73G) and NASA Astrobiology Institute (NNA09DA79A).


Ceres: The Wet Look

By: J. Kelly Beatty November 28, 2006 0

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Ceres' shape is almost round like Earth's, suggesting that the asteroid may have a "differentiated interior," with a rocky inner core, a thick water-ice mantle, and a thin, dusty outer crust.

NASA, ESA, and A. Feild (STScI)

The surface of Ceres, as revealed by the Hubble Space Telescope's Advanced Camera for Surveys, includes several brighter and darker regions that could be caused by impacts. Ceres itself is slightly wider at its equator than at its poles.

NASA, ESA, J. Parker (Southwest Research Institute), and others

Dawn, a NASA spacecraft that narrowly avoided outright cancellation earlier this year. Now scheduled for launch next summer, Dawn will spend time orbiting both Ceres and Vesta, an equally intriguing asteroid.


Dwarf planet Ceres has reservoirs of salty water

The dwarf planet Ceres, about 940 kilometers (585 miles) in diameter, is the largest body in the main asteroid belt. NASA’s Dawn spacecraft mapped the planet and found evidence — a low-density region of the crust (blue) — of an underground brine reservoir. A crater named Occator is to the left of the blue area This composite image shows gravity anomalies (red is high, blue is low) on the right side and Ceres’ real colors on the left. The bright spots are near the center of Occator. (Image courtesy of Anton Ermakov, UC Berkeley, NASA/JPL)

The dwarf planet Ceres, the largest object in our Solar System’s main asteroid belt, once harbored a global subsurface ocean that likely froze solid long ago. Today, if any liquid water — a key requisite for habitability — still exists on Ceres, a good place to look for it is beneath the youngest of its large impact craters.

An analysis of low-altitude data from flyovers of Ceres’ 92-kilometer (57-mile) Occator crater by NASA’s Dawn spacecraft in 2018 has allowed researchers to characterize the underground structure near the crater and conclude from gravity data that there is a low density region beneath Occator consistent with a briny slush reservoir of water and various salts.

The data suggest that the impact that created the Occator crater 20 million years ago likely fractured Ceres’ crust, and those fractures today tap into deeper brine reservoirs. This hypothesis explains the formation of bright regions, or faculae, on the crater floor: brine erupted through these fractures, and a highly reflective salt crust was left behind as the water evaporated.

These bright regions were previously found to consist of sodium carbonates. The regions in Occator came into focus when Dawn first reached Ceres in 2015, and were photographed in sharp detail during the final extended mission. These deposits appear to have erupted within the last 2 million years, far too recent to have come from the melt generated by the initial impact.

The brines may still be percolating up to the surface today.

This false-color mosaic image highlights the recently exposed brine, or salty liquids (red), that were pushed up from a deep reservoir under Ceres’ crust. (Image courtesy of NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

“In order for the bright deposits to form later, relative to the impact event, you need to be able to transport the briny material to the surface somehow over an extended period of time,” said geophysicist Anton Ermakov, a University of California, Berkeley, postdoctoral fellow who works with the Dawn team. “The potential mechanism would be that the impact-induced fracturing provided the connection between the surface and deeper brine reservoirs.”

The analysis, conducted by a team of scientists led by Carol Raymond of the Jet Propulsion Laboratory (JPL) at the California Institute of Technology in Pasadena, indicates that Ceres could have liquid water in its interior at present. While ice on the icy moons in the outer Solar System — Saturn’s Enceladus and Jupiter’s Europa, for example — is warmed and melted by gravitational tidal interactions with the planets, it now seems likely that dwarf planets and asteroids may also preserve reservoirs of liquid water, despite the fact that they do not benefit from the same tidal heating.

And as NASA often states, to find life on other planets, follow the water.

The findings are presented in a special collection of papers published today (Aug. 10) in the journals Nature Astronomy, Nature Geoscience and Nature Communications.

Probing cerean subsurface with gravity

Ceres was the first object discovered in the main asteroid belt, a vast region containing planet building blocks encircling the Sun — leftovers from the formation of the Solar System — between the orbits of Mars and Jupiter. Now referred to as a dwarf planet, like Pluto, Ceres is named after the Roman goddess of agriculture.

This mosaic of Ceres’ Occator Crater is composed of images NASA’s Dawn spacecraft captured on its second extended mission, in 2018. Bright pits and mounds (foreground) were formed by salty liquid released as Occator’s water-rich floor froze after the crater-forming impact about 20 million years ago. (Image courtesy of NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/USRA/LPI)

NASA launched the Dawn mission of the asteroid belt in 2007 to study Vesta, the second most massive object in the belt, and Ceres. After a successful survey of both objects, the spacecraft used up all its fuel in October 2018. It remains parked in a long-term orbit around Ceres.

Dawn’s final task in 2017 and 2018 was to get as close to Ceres as possible — about 35 kilometers, or 22 miles, above the surface at the closest approach. There, it could capture high-resolution pictures of the surface and map the gravity field, which tells scientists about the density variations of the subsurface layers of the planet.

One major question the team hoped to solve was the nature and origin of the bright regions, which had been noticed, long before Dawn arrived at Ceres, by scientists peering through telescopes. During 106 close approaches, Dawn captured images of two distinct, highly reflective areas within Occator that were officially named Cerealia Facula and the Vinalia Faculae.

The spacecraft also measured the gravity close to the surface, data that Ermakov and the Dawn team analyzed. They discovered a low-gravity region just outside Occator that indicated an underground blob of low-density material about 40 kilometers, or 25 miles, below the surface and hundreds of kilometers in extent. However, since the gravity data could not tell researchers what the actual composition of the underground anomalous blob was, they had to cross-analyze the gravity data against other available observations, such as local geology and composition inferred from spectroscopy. Such combined analysis led to the most likely scenario that the low-density region could be a reservoir of briny water.

The team proposed that initially, the impact melted ice underground in a small reservoir that mostly froze again within a few million years. However, the scientists recognized that the impact could have fractured rock deep enough to reach the reservoir inferred from the observed low gravity. Such fractures today would be conduits for brines moving upward and erupting on the surface.

“For the large deposit at Cerealia Facula, the bulk of the salts were supplied from a slushy area just beneath the surface that was melted by the heat of the impact that formed the crater about 20 million years ago,” said Raymond, principal investigator for the Dawn mission. “The impact heat subsided after a few million years. However, the impact also created large fractures that could reach the deep, long-lived reservoir, allowing brine to continue percolating to the surface.”

Ermakov emphasized that this interpretation is consistent with the gravity survey data and other measurements of the surface, but the data are insufficient to determine what that deep reservoir looks like or exactly how big it really is. However, it is possible to characterize the total mass deficiency created by the low-density reservoir.

“This paper provides the first coherent story for the connection between the surface evaporates and the deep brine for the region of Occator and leaves the question about whether the brine layer is global open to future investigation,” he said.

Ceres still geologically active

The research not only confirmed that the bright regions are young — some less than 2 million years old — but also found that the geologic activity driving these deposits could be ongoing. This conclusion depended on scientists making a key discovery: salt compounds — sodium chloride chemically bound with water and ammonium chloride — concentrated in Cerealia Facula.

On Ceres’ surface, salts bearing water quickly dehydrate. But Dawn’s measurements show they still have water, so the fluids must have reached the surface very recently. This is evidence both for the presence of liquid below the region of Occator and for the ongoing transfer of material from the deep interior to the surface.

Some of the evidence for recent liquids in Occator comes from the bright deposits, but other clues come from an assortment of unusual conical hills. These features are reminiscent of Earth’s pingos, small ice mountains in polar regions formed by frozen pressurized groundwater. Such features have been spotted on Mars, but the discovery of them on Ceres marks the first time they’ve ever been observed on a dwarf planet.

On a larger scale, Ermakov and his colleagues were able to map the density of Ceres’ crustal structure as a function of depth, a first for an ice-rich planetary body. Using the gravity measurements, they found Ceres has a complex crust that becomes denser as it gets deeper.

Researchers inferred that at the same time Ceres’ brine reservoir is freezing, salt and mud are incorporating in the lower part of the crust.

“Dawn accomplished far more than we hoped when it embarked on its extraordinary extraterrestrial expedition,” said Dawn mission director Marc Rayman of JPL. “These exciting new discoveries from the end of its long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.”


What's the composition of Ceres? - Astronomy

Ceres, the largest object between Mars and Jupiter, is not easily classified. Its low density suggests a significant ice fraction, like the icy satellites. It is too warm for ice to remain stable over much of its surface, but may maintain ice at a depth of a few meters [1,2]. It is large enough to be in hydrostatic equilibrium, but is probably differentiated rock from ice rather than the metal-rock separation seen in the planets [3,4]. It is considered a "dwarf planet" in the current IAU scheme, the only one interior to Neptune. What we know about Ceres has to this point been determined via remote sensing. The first observations of Ceres were made in the visible-near IR (0.4-2.5 μm) spectral region, and established an overall similarity to carbonaceous chondrites based on a low albedo and relatively flat spectrum. Its visible specrtum places it within the C class, which dominates the middle of the asteroid belt [5,6]. Positive identifications of absorptions have been rare in this spectral region, beyond a decrease in reflectance shortward of 0.4 μm due to oxidized iron. A broad band centered near 1.1 μm is consistent with magnetite, which is also found in some carbonaceous chondrites [7]. Longer wavelengths have provided more quantitative identifications. A series of absorptions in the 3-4 μm region have been interpreted most recently as due to brucite and carbonates [8-11]. Mid-IR (8-13 μm) observations have inconsistently found evidence for carbonates, but on the whole are consistent with the 3-4 μm observations [12,13]. A list of identified and yet-unidentified [14,15] absorptions in Ceres' spectrum is presented in Table 1. In addition to these identified species, the possibility of near-surface ice on Ceres combined with a low obliquity and resultant low temperatures at high latitudes leads to the prospect of polar caps, undetected in our low spatial resolution data but observable from orbit. The possibility of solar wind-created OH and impactor contamination on Ceres' surface, as has been suggested for the Moon and Vesta [16,17], also needs to be considered when considering in detail what Dawn may find. Over the last 35 years, astronomers and geologists have pieced together our ideas of Ceres' surface composition, which along with modeling and laboratory efforts leads to our overall interpretation of this body. We will present our current synthesis of Ceres research as it stands in the pre-Dawn era. References: [1] Fanale and Salvail (1989) Icarus, 82, [ [2] Schorghofer (2008) ApJ, 682. [3] McCord and Sotin (2005) JGR, 110. [4] Thomas et al. (2005) Nature, 437. [5] Bus and Binzel (2002), Icarus, 158. [6] Johnson and Fanale (1973), JGR, 35. [7] Larson et al. (1979) Icarus, 39. [8] Lebofsky et al. (1981) Icarus, 48. [9] King et al. (1992) Science, 255. [10] Rivkin et al. (2006) Icarus, 185. [11] Milliken and Rivkin (2009) Nature Geo., 2. [12] Cohen et al. (1998), AJ, 115. [13] Lim et al. (2005) Icarus, 173. [14] Parker et al. (2002) AJ, 123. [15] Li et al. (2006) Icarus, 182. [16] Clark/Sunshine et al./Pieters et al. (2009) Science 326.[17] McCord et al. (2012) LPSC 43.Identified spectral features on Ceres


New SOFIA Observations Show Ceres’ True Composition

The column of material at and just below the surface of dwarf planet Ceres (box) – the top layer contains anhydrous (dry) pyroxene dust accumulated from space mixed in with native hydrous (wet) dust, carbonates, and water ice. (Bottom) Cross section of Ceres showing the surface layers that are the subject of this study plus a watery mantle and a rocky-metallic core.

New SOFIA observations show the true composition of Ceres, revealing that it does not appear to have the carbon-rich surface composition that telescopes previously indicated.

Using data primarily from NASA’s Stratospheric Observatory for Infrared Astronomy, SOFIA, a team of astronomers has detected the presence of substantial amounts of material on the surface of Ceres that appear to be fragments of other asteroids containing mostly rocky silicates. These observations are contrary to the currently accepted surface composition classification of Ceres as a carbon-rich body, suggesting that it is cloaked by material that partially disguises its real makeup.

“This study resolves a long-time question about whether asteroid surface material accurately reflects the intrinsic composition of the asteroid,” said Pierre Vernazza, research scientist in the Laboratoire d’Astrophysique de Marseille (LAM–CNRS/AMU). Our results show that by extending observations to the mid-infrared, the asteroid’s underlying composition remains identifiable despite contamination by as much as 20 percent of material from elsewhere,” said Vernazza.

Astronomers have classified the Ceres asteroid, as well as 75 percent of all asteroids, in composition class “C” based on their similar colors. The mid-infrared spectra from SOFIA show that Ceres differs substantially from neighboring C-type asteroids, challenging the conventional understanding of the relationship between Ceres and smaller asteroids.

“SOFIA, with its airborne location and sensitive FORCAST instrument, is the only observatory, currently operating or planned, that can make these kind of observations,” said Franck Marchis, planetary astronomer at the SETI Institute and one of Vernazza’s co-authors. “These and future mid-infrared observations are key to understanding the true nature and history of the asteroids.”

Ceres and asteroids are not the only context where material transported from elsewhere has affected the surfaces of solar system bodies. Dramatic examples include Saturn’s two-faced moon Iapetus and the red material seen by New Horizons on Pluto’s moon Charon. Planetary scientists also hypothesize that material from comets and asteroids provided a final veneer to the then-forming Earth that included substantial amounts of water plus the organic substances of the biosphere.

“Models of Ceres based on data collected by NASA’s Dawn spacecraft plus ground-based telescopes indicated substantial amounts of water- and carbon-bearing minerals such as clays and carbonates,” explains Vernazza. “Only the mid-infrared observations made using SOFIA were able to show that both silicate and carbonate materials are present on the surface of Ceres.”

To identify where the pyroxene on the surface of Ceres came from, Vernazza and his collaborators, including researchers from the SETI Institute in Mountain View, and NASA’s Jet Propulsion Laboratory, both in California, turned to interplanetary dust particles (IDPs) that form meteors when they are seen streaking through Earth’s atmosphere. The research team had previously shown that IDPs blasted into space by asteroid collisions are an important source of material accumulated on the surfaces of other asteroids. The implication is that a coating of IDPs has caused Ceres to take on the coloration of some of its dry and rocky neighbors.

NASA is exploring the solar system and beyond to better understand the universe and our place in it. We explore asteroids and comets, which may hold clues about the history of our solar system and how life arose on Earth.

Publication: P. Vernazza, et al., “DIFFERENT ORIGINS OR DIFFERENT EVOLUTIONS? DECODING THE SPECTRAL DIVERSITY AMONG C-TYPE ASTEROIDS,” Astronomical Journal, 2017 doi:10.3847/1538-3881/153/2/72


Types of Asteroids

Asteroids can be categorized in various ways, e.g. according to their size, color, and composition. But according to their composition, there are 3 main types of asteroids which are carbon, metallic, and stony asteroids.

  • Carbon Asteroids – These asteroids are black in color due to the high percentage of elemental carbon they contain around 75% carbon.
  • Metallic Asteroids – Most parts of these asteroids are metallic along with some rocky surfaces. There are various metals from which they are formed, but most common are iron and nickel.
  • Stony Asteroids – The major constituent of these asteroids is silica, also called silicon dioxide. It is the same silica that makes sand on the Earth on which you step-on.

Is There Life on Ceres?

Ceres is, by most astronomers’ accounts, both a dwarf planet and an asteroid. It’s neither fish nor fowl, in other words, but—depending on whether the structure of an average solar system includes more planets than asteroids, or vice versa—it may actually be more representative of cosmic habitats than Earth is. We just don’t know yet.

What we do know is that there is considerable evidence that Ceres has an underground ocean, which exobiologists have historically taken to be a good indicator that a planet or moon may contain life. Our reasoning behind investigating Enceladus, Ganymede, and Europa is certainly predicated on the idea that where there is water, life may follow.

The likely structure of Ceres. Image: NASA.

But we’re still not entirely sure we’re dealing with a liquid ocean here. That all boils down to two questions: (1) What is the chemical composition of the ocean, and (2) What is its temperature? We can’t answer either question yet (that blurry image in the header above is our best photograph yet of Ceres, taken by the Hubble Space Telescope, and tells us little about its surface features). We know enough to know that the surface temperature of Ceres is well below freezing, but if Ceres is geologically active (it probably isn’t, but it could be), it could easily be much warmer—hospitably warmer, even—underground.

We’ll get a better look at Ceres in February 2015 when the DAWN Mission arrives at Ceres, give us a better idea of the dwarf planet’s composition and features. Unless DAWN finds that Ceres is surprisingly bland, it will remain on the short, but growing, list of celestial objects in our solar system that host underground water in some form and could therefore also host some form of life.