Tag: Ceres

Third reaction wheel on Dawn fails

7:33 pm

The third of four reaction wheels on Dawn failed on April 23, forcing the spacecraft to use its conventional thrusters to orient itself.

The team discovered the situation during a scheduled communications session on April 24, diagnosed the problem, and returned the spacecraft to its standard flight configuration, still with hydrazine control, on April 25. The failure occurred after Dawn completed its five-hour segment of ion thrusting on April 22 to adjust its orbit, but before the shorter maneuver scheduled for April 23-24. The orbit will still allow Dawn to perform its opposition measurements. The reaction wheel’s malfunctioning will not significantly impact the rest of the extended mission at Ceres.

This might shorten Dawn’s remaining mission, but since it is in its final days anyway, the loss will not be severe.

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Landslides on Ceres reveal presence of ice

4:37 pm

An analysis of data from Dawn has shown that Ceres’s landslides are distributed in greater numbers towards the poles, which suggests the presence of water ice just below the surface.

Georgia Tech Assistant Professor and Dawn Science Team Associate Britney Schmidt led the study. She believes it provides more proof that the asteroid’s shallow subsurface is a mixture of rock and ice. “Landslides cover more area in the poles than at the equator, but most surface processes generally don’t care about latitude,” said Schmidt, a faculty member in the School of Earth and Atmospheric Sciences. “That’s one reason why we think it’s ice affecting the flow processes. There’s no other good way to explain why the poles have huge, thick landslides; mid-latitudes have a mixture of sheeted and thick landslides; and low latitudes have just a few.”

The data also showed that Ceres has far more landslides than expected, which also supports the idea that the shallow subsurface has a lot of water ice in it, as much as 10% to 50% by volume.

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Scientists estimate age of bright spots in Occator Crater on Ceres

8:22 am

Using crater counts and a careful analysis of features in Occator Crater on Ceres, scientists have estimated that the last major eruption occurred about 4 million years ago.

Nathues and his team interpret the central pit with its rocky, jagged ridge as a remnant of a former central mountain. It formed as a result of the impact that created Occator Crater some 34 million years ago and collapsed later. The dome of bright material is much younger: only approximately four million years. The key to determining these ages was the accurate counting and measuring of smaller craters torn by later impacts. This method’s basic assumption is that surfaces showing many craters are older than those that are less strongly “perforated”. Since even very small craters are visible in highly resolved images, the new study contains the most accurate dating so far.

“The age and appearance of the material surrounding the bright dome indicate that Cerealia Facula was formed by a recurring, eruptive process, which also hurled material into more outward regions of the central pit”, says Nathues. “A single eruptive event is rather unlikely,” he adds. A look into the Jupiter system supports this theory. The moons Callisto and Ganymede show similar domes. Researchers interpret them as volcanic deposits and thus as signs of cryovolcanism.

The volcano itself has slumped away, leaving behind the bright depression. Whether any cryovolcanism is still occurring underground remains unknown.

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Dawn finds organics on Ceres

9:34 pm

The spacecraft Dawn has detected evidence of organic molecules in Ceres’ northern hemisphere.

The organic materials on Ceres are mainly located in an area covering approximately 400 square miles (about 1,000 square kilometers). The signature of organics is very clear on the floor of Ernutet Crater, on its southern rim and in an area just outside the crater to the southwest. Another large area with well-defined signatures is found across the northwest part of the crater rim and ejecta. There are other smaller organic-rich areas several miles (kilometers) west and east of the crater. Organics also were found in a very small area in Inamahari Crater, about 250 miles (400 kilometers) away from Ernutet.

This detection does not mean that Dawn has found life on Ceres. It means that the spacecraft has detected molecules that contain carbon, which is the chemical definition of organics. Nor is it unusual for asteroids to have carbon molecules. In fact, there is an entire asteroid class dubbed carbonaceous chondrites that are rich in carbon. In addition, the press release overplays this narrative by making it seem as if the discovery of organics in the solar system is rare and unusual. It is not. Molecules containing carbon have been found in many places, on Mars, on Venus, in asteroids, and elsewhere. All that is happened here is that the scientists have gained more information about the make-up Ceres itself. This is good, but it isn’t what is being sold by the press release.

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The vanishing volcanoes of Ceres

10:02 am

New research based on Dawn data suggests that volcanoes on Ceres flatten and disappear over time.

NASA’s Dawn spacecraft discovered Ceres’s 4-kilometer (2.5-mile) tall Ahuna Mons cryovolcano in 2015. Other icy worlds in our solar system, like Pluto, Europa, Triton, Charon and Titan, may also have cryovolcanoes, but Ahuna Mons is conspicuously alone on Ceres. The dwarf planet, with an orbit between Mars and Jupiter, also lies far closer to the sun than other planetary bodies where cryovolcanoes have been found.

Now, scientists show there may have been cryovolcanoes other than Ahuna Mons on Ceres millions or billions of years ago, but these cryovolcanoes may have flattened out over time and become indistinguishable from the planet’s surface. They report their findings in a new paper accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. “We think we have a very good case that there have been lots of cryovolcanoes on Ceres but they have deformed,” said Michael Sori of the Lunar and Planetary Laboratory at the University of Arizona in Tucson, and lead author of the new paper.

The cause of the flattening?

Viscous relaxation is the idea that just about any solid will flow, given enough time. For example, a cold block of honey appears to be solid. But if given enough time, the block will flatten out until there is no sign left of the original block structure. On Earth, viscous relaxation is what makes glaciers flow, Sori explained. The process doesn’t affect volcanoes on Earth because they are made of rock, but Ceres’s volcanoes contain ice – making viscous relaxation possible.

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Flying over Occator Crater on Ceres

12:23 am

Cool movie time! Using data from Dawn the German Aerospace Center (DLR) has produced a short animation that gives a 3D flyover of Occator Crater on Ceres.

The animated flyover includes topographic and enhanced-color views of the crater, highlighting the central dome feature. The central area has been named Cerealia Facula. Occator’s secondary group of bright spots is called Vinalia Faculae.

The movie is definitely worth watching, especially the sections that show in close-up the bright areas near the crater’s center.

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Lots of ice on Ceres

12:34 pm

New data from Dawn now suggests that Ceres contains a large amount of ice on or near its surface.

“On Ceres, ice is not just localized to a few craters. It’s everywhere, and nearer to the surface with higher latitudes,” said Thomas Prettyman, principal investigator of Dawn’s gamma ray and neutron detector (GRaND), based at the Planetary Science Institute, Tucson, Arizona. Researchers used the GRaND instrument to determine the concentrations of hydrogen, iron and potassium in the uppermost yard (or meter) of Ceres. GRaND measures the number and energy of gamma rays and neutrons coming from Ceres. Neutrons are produced as galactic cosmic rays interact with Ceres’ surface. Some neutrons get absorbed into the surface, while others escape. Since hydrogen slows down neutrons, it is associated with a fewer neutrons escaping. On Ceres, hydrogen is likely to be in the form of frozen water (which is made of two hydrogen atoms and one oxygen atom).

Rather than a solid ice layer, there is likely to be a porous mixture of rocky materials in which ice fills the pores, researchers found. The GRaND data show that the mixture is about 10 percent ice by weight.

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Ceres’ cratered surface

10:27 am

Ceres' crated surface

Cool image time! The picture on the right, reduced to show here, was taken on October 17 and was the tenth image taken by Dawn in its new extended mission in orbit around Ceres.

This image of the limb of dwarf planet Ceres shows a section of the northern hemisphere. A shadowy portion of Occator Crater can be seen at the lower right — its bright “spot” areas are outside of the frame of view. Part of Kaikara Crater (45 miles, 72 kilometers in diameter) is visible at top left.

The image was taken from 920 miles away and has a resolution of about 460 feet per pixel.

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Oxo Crater on Ceres

10:13 am

Oxo Crater on Ceres

Cool image time! The Dawn image at the right, cropped to show here, was taken on April 19, 2016. It shows the crater Oxo on Ceres and is especially intriguing because it not provides high resolution imagery of the crater’s bright rim, the second brightest feature on Ceres, it also shows how the southeastern part of the crater’s rim has literally slide down into the crater, leaving behind a gaping rombus-shaped pit.

The slumping, combined with the bright material on the rim, is more evidence that at some point in the past Ceres was geologically active.

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The surface of Ceres lacks water

9:40 am

The uncertainty of science: Despite significant evidence that water ice has helped form specific features on Ceres, other data collected by Dawn suggest that there is not much ice on the surface.

Angular polygonal craters on the surface suggest that Ceres’ crust is fractured, furthering the conclusion that the near-surface crust “must be both brittle enough to fracture and strong enough to retain fractures for long periods of time.”

“Based on our analysis, the crust of Ceres is too strong to be dominated by ice,” said Debra Buczkowski of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, the study’s lead author. “While surface features such as the lobate flows show that water ice is present in the dwarf planet’s upper crust and on the surface in some locations, it appears not to be a major factor in creating surface features.”

In addition to studying the surface, researchers drew conclusions about the dwarf planet’s interior makeup. Beneath a strong crust composed of rock, ice and salt hydrates lays a water-rich mantle and a silicate core. 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.

Note that in just two days, Dawn researchers released two press releases, the first noting that water ice played a significant role in molding major features on Ceres, and the second noting that the surface doesn’t have much water ice. How’s that for a nice demonstration of the uncertainty of science?

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Ahuna Mons, Ceres’s biggest mountain, is an ice volcano

11:39 am

Ahuna Mons

Using data from Dawn scientists have concluded that Ceres’s biggest mountain, Ahuna Mons (shown on the right), was created by water volcanism.

“Ahuna is the one true ‘mountain’ on Ceres,” said David A. Williams, associate research professor in Arizona State University’s School of Earth and Space Exploration. “After studying it closely, we interpret it as a dome raised by cryovolcanism.” This is a form of low-temperature volcanic activity, where molten ice — water, usually mixed with salts or ammonia — replaces the molten silicate rock erupted by terrestrial volcanoes. Giant mountain Ahuna is a volcanic dome built from repeated eruptions of freezing salty water.

The implications of this fact are important, as it suggests that Ceres’s interior was warm enough for long periods, enough to melt ice. Where that heat came from however is a mystery, considering the dwarf planet’s small size.

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Dawn moves to higher orbit around Ceres

9:41 am

In order to save fuel as well as obtain a different view of Ceres, engineers are moving Dawn to a higher orbit.

On Sept. 2, Dawn will begin spiraling upward to about 910 miles (1,460 kilometers) from Ceres. The altitude will be close to where Dawn was a year ago, but the orientation of the spacecraft’s orbit — specifically, the angle between the orbit plane and the sun — will be different this time, so the spacecraft will have a different view of the surface.

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Craters on Ceres

4:10 pm

craters on Ceres
Cool image time! The image above, cropped and reduced in resolution to show here, was taken on May 30, 2016 by Dawn from 240 miles away. It looks northward at the dwarf planet’s horizon, and has a resolution of about 120 feet per pixel.

My only comment is to note how soft the terrain looks. I realize this is not really an accurate description, but data has shown that Ceres has a somewhat low density and is somewhat malleable. It sure looks that way here.

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The interior of Ceres

11:06 am

Using data from Dawn, scientists have created their first rough map of the internal structure of Ceres.

The data indicate that Ceres is “differentiated,” which means that it has compositionally distinct layers at different depths, with the densest layer at the core. Scientists also have found that, as they suspected, Ceres is much less dense than Earth, the moon, giant asteroid Vesta (Dawn’s previous target) and other rocky bodies in our solar system. Additionally, Ceres has long been suspected to contain low-density materials such as water ice, which the study shows separated from the rocky material and rose to the outer layer along with other light materials. “We have found that the divisions between different layers are less pronounced inside Ceres than the moon and other planets in our solar system,” Park said. “Earth, with its metallic crust, semi-fluid mantle and outer crust, has a more clearly defined structure than Ceres,” Park said.

Scientists also found that high-elevation areas on Ceres displace mass in the interior. This is analogous to how a boat floats on water: the amount of displaced water depends on the mass of the boat. Similarly, scientists conclude that Ceres’ weak mantle can be pushed aside by the mass of mountains and other high topography in the outermost layer as though the high-elevation areas “float” on the material below. This phenomenon has been observed on other planets, including Earth, but this study is the first to confirm it at Ceres.

In other words, Ceres behaves more like a semi-hardened blob of jello than a rock.

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Ceres lacks large craters

10:59 am

The uncertainty of science: Using data from Dawn, scientists have found that the solar system’s largest asteroid, Ceres (also called a dwarf planet by confused scientists), has a mysterious lack of large craters.

Marchi and colleagues modeled collisions of other bodies with Ceres since the dwarf planet formed, and predicted the number of large craters that should have been present on its surface. These models predicted Ceres should have up to 10 to 15 craters larger than 250 miles (400 kilometers) in diameter, and at least 40 craters larger than 60 miles (100 kilometers) wide. However, Dawn has shown that Ceres has only 16 craters larger than 60 miles, and none larger than 175 miles (280 kilometers) across.

They postulate two theories to explain the lack. First, Ceres might have formed far out beyond Neptune, though this theory is not favored because some models still say that even here Ceres should have large craters. Second,

One reason for the lack of large craters could be related the interior structure of Ceres. There is evidence from Dawn that the upper layers of Ceres contain ice. Because ice is less dense than rock, the topography could “relax,” or smooth out, more quickly if ice or another lower-density material, such as salt, dominates the subsurface composition. Recent analysis of the center of Ceres’ Occator Crater suggests that the salts found there could be remnants of a frozen ocean under the surface, and that liquid water could have been present in Ceres’ interior.

Past hydrothermal activity, which may have influenced the salts rising to the surface at Occator, could also have something to do with the erasure of craters. If Ceres had widespread cryovolcanic activity in the past — the eruption of volatiles such as water — these cryogenic materials also could have flowed across the surface, possibly burying pre-existing large craters. Smaller impacts would have then created new craters on the resurfaced area.

This theory doesn’t really work that well either, because it fails to explain why only the big craters got erased.

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More bright spots on Ceres

10:17 am

More bright spots on Ceres

Cool image time! The most recently released Dawn image of Ceres, cropped on the right, included these bright streaks running down the side of an unnamed crater. They are especially intriguing because they so much resemble the seepage lines scientists have found on slopes on Mars. On Mars the lines appear to come and go on a seasonal basis, while on Ceres they appear to have been caused by a one-time event, after which not much has changed. In both cases, however, they appear to be caused by some liquid seepage that came from below the surface.

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Permanently shadowed regions on Ceres

9:53 am

Using data from Dawn scientists have calculated that Ceres could have significant regions on the floors of crater, which are permanently shadowed and which could accumulate water ice.

In this study, Schorghofer and colleagues studied Ceres’ northern hemisphere, which was better illuminated than the south. Images from Dawn’s cameras were combined to yield the dwarf planet’s shape, showing craters, plains and other features in three dimensions. Using this input, a sophisticated computer model developed at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, was used to determine which areas receive direct sunlight, how much solar radiation reaches the surface, and how the conditions change over the course of a year on Ceres.

The researchers found dozens of sizeable permanently shadowed regions across the northern hemisphere. The largest one is inside a 10-mile-wide (16-kilometer) crater located less than 40 miles (65 kilometers) from the north pole. Taken together, Ceres’ permanently shadowed regions occupy about 695 square miles (1,800 square kilometers). This is a small fraction of the landscape — much less than 1 percent of the surface area of the northern hemisphere.

Because Ceres is much farther than the Sun that the Moon or Mercury, the scientists believe it very likely that water ice could have accumulated in these cold traps.

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Dawn data suggests recent hydrothermal activity on Ceres

11:38 am

New data from Dawn now suggests that the bright spot in Occator Crater on Ceres contains the highest concentration of carbonate materials found so far outside of Earth, and was caused by recent hydrothermal activity.

De Sanctis’ study finds that the dominant mineral of this bright area is sodium carbonate, a kind of salt found on Earth in hydrothermal environments. This material appears to have come from inside Ceres, because an impacting asteroid could not have delivered it. The upwelling of this material suggests that temperatures inside Ceres are warmer than previously believed. Impact of an asteroid on Ceres may have helped bring this material up from below, but researchers think an internal process played a role as well.

More intriguingly, the results suggest that liquid water may have existed beneath the surface of Ceres in recent geological time. The salts could be remnants of an ocean, or localized bodies of water, that reached the surface and then froze millions of years ago.

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Ceres’s brightest spot

2:30 pm

Brightest Spot in Occator Crater on Ceres

Cool image time: While I was in Washington the Dawn science team released a very nice close-up image of the bright spots inside Occator Crater on Ceres. On the right is a cropped version which focuses solely on the central brightest spot. The spot appears to overlie a central dome with a depression in the middle. Other data says the spot is the low area in the crater, and the linear cracks that radiate away as well as in concentric rings around the spot suggest that this central area has subsided, causing those cracks.

Make sure you look at the full image, as it includes the other smaller spots that are also inside Occator.

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An extended Dawn mission might go to another asteroid

10:05 am

The Dawn science team is proposing that NASA extend the mission by allowing them to use the remaining fuel on the spacecraft to send it away from Ceres and towards another asteroid.

Originally mission managers had planned to park it in a stable orbit around Ceres later this summer, creating a permanent artificial satellite. They could not crash the spacecraft into Ceres, as is customary with many similar missions, because Dawn has not been sterilized in accord with planetary protection procedures. But the extra xenon has created an additional opportunity.

Scientists involved with the spacecraft say they could visit a third object in the asteroid belt. “Instead, we want to go the other way, away from Ceres, to visit yet another target,” principal investigator Chris Russell told New Scientist. Russell would not name the destination without approval of the plan from NASA, but we should learn about it in a few months.

Up until now they had said that they didn’t have enough remaining fuel to do much more than remain in orbit at Ceres. It appears now that they have saved enough fuel to give them more options.

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Evidence of water on Ceres?

9:21 am

water on Ceres?

New data from Dawn suggests that there is significant water locked in surface of Ceres’s north polar regions.

These data reflect the concentration of hydrogen in the upper yard (or meter) of regolith, the loose surface material on Ceres. The color information is based on the number of neutrons detected per second by GRaND. Counts decrease with increasing hydrogen concentration. The color scale of the map is from blue (lowest neutron count) to red (highest neutron count). Lower neutron counts near the pole suggest the presence of water ice within about a yard (meter) of the surface at high latitudes.

Note that the data has not detected water. The blue areas on the image to the right suggest an increased amount of hydrogen, which could only be held to the surface if it was locked in some molecule, with water being the most likely candidate. Like the Moon, until we actual capture some samples, it will be difficult to confirm with certainty the presence of water.

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Update on Dawn at Ceres

10:07 am

Link here. Though the story initially focuses on the possibility that the mission might be extended a few extra months until the spacecraft’s fuel runs out, it also gives a good summary of what has been learned so far about the dwarf planet, including the theory that Ceres was once an “ocean world.”

[Carol Raymond, Dawn’s deputy principal investigator,] said Ceres appears to be a former ocean world and could have once been similar to Europa or Enceladus, the icy moons of Jupiter and Saturn. “One of the things that we anticipated about Ceres before getting there is that it’s a former ocean world,” Raymond said. “We’re so interested in going to Europa and Enceladus, and these other interesting objects in the outer solar system because we think they harbor subsurface oceans at present, and possible habitable environments, and possibly even locations where there’s extant life.

“Ceres appears to have been one of those objects in the past, when it was younger and hotter,” Raymond said. “What we’re looking at now is, we believe, the remnant of a frozen ocean. The salt is left over from the brines that were concentrated as the ocean froze out, so it’s all a fairly consistent story that Ceres is a former ocean (world) where the ocean froze, and now we’re interrogating the chemistry, essentially, of that ocean-rock interface through the subsurface layers that we’re detecting on Ceres.”

The data has found the high latitudes to have lots of hydrogen, suggesting water-ice on or near the surface. The bright salt patches also suggest frozen water below the surface that left behind the salt when it reached the surface and evaporated away.

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New close-up of Occator Crater’s spots

1:57 pm

Occator Crater central spot

The Dawn science team have released new images taken from the spacecraft’s low orbit observations, including a close-up of the central white spot at Occator Crater, the brightest spot on Ceres.

The image on the right is a cropped though full resolution version of the full image. I have reduced it only slightly. As they note,

Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, contains the brightest area on Ceres, the dwarf planet that Dawn has explored since early 2015. The latest images, taken from 240 miles (385 kilometers) above the surface of Ceres, reveal a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome. Prominent fractures also surround the dome and run through smaller, bright regions found within the crater.

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Changes in Ceres’s white spots

3:56 pm

The uncertainty of science: Ground-based observations of Ceres now suggest that the white spots imaged by Dawn undergo subtle unexpected variations

As Ceres rotates every 9 hours, HARPS is so sensitive that it can detect the very slight Doppler shift in spectrum frequency as the bright spots rotate toward and away Earth, but during observations for 2 nights in July and August 2015, more changes not related to Ceres’ spin were detected. “The result was a surprise,” said co-author Antonino Lanza, also from the INAF–Catania Astrophysical Observatory. “We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night.”

And it appears that these changes are consistent with some kind of volatile (ice) being exposed to sunlight and venting vapor into space, causing an increase in reflectivity. It seems that when Occator experiences solar heating, plumes are produced and then evaporate, creating a complex spectroscopic signal that evolves during that hemisphere’s daytime. This finding appears to be consistent with earlier observations made by Dawn showing a mysterious haze over Occator.

The problem with this theory is that it assumes the white spots are comprised of water ice. However, data from Dawn has instead suggested that the white spots are not water but salt deposits.

It could be that the white spots are salt left behind when water vented from inside Ceres evaporates away, but so far the data from Dawn has not found any evidence of water at the spots. If it was venting there, Dawn should have seen it.

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Ceres’s big mountain

10:26 pm

Ahuna Mons on Ceres

The Dawn science team has released an oblique angle image of Ceres’s big mountain, Ahuna Mons. I have cropped and reduced it above to show it here.

Despite looking almost toylike in this image, the mountain is quite monstrous, especially considering Ceres’s relatively small size.

This mountain is about 3 miles (5 kilometers) high on its steepest side. Its average overall height is 2.5 miles (4 kilometers). These figures are slightly lower than what scientists estimated from Dawn’s higher orbits because researchers now have a better sense of Ceres’ topography.

Consider: Mount Everest is not quite six miles high, on a planet with a diameter about 7926 miles across. Ceres however is only about 600 miles across at its widest, which means a 3 mile high mountain is 0.5% of Ceres’s entire width! Such a thing could only occur on such a small body, whose gravity is not quite great enough to force things into a completely spherical shape. It is for this reason it could be argued that Ceres doesn’t qualify as a dwarf planet, but would be better labeled a giant asteroid.

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Dawn’s chief engineer reviews the mission

8:45 am

In a long and very detailed post, the chief engineer and mission director of Dawn gives us a very detailed update on the successful state of the spacecraft’s mission.

Not only does he describe what has been gathered at Ceres since the spacecraft arrived a year ago, he gives us this crucial information about the state of this paradigm-shattering ion engine spacecraft, the first to travel to two different objects in the solar system:

Dawn has faced many challenges in its unique voyage in the forbidding depths of space, but it has surmounted all of them. It has even overcome the dire threat posed by the loss of two reaction wheels (the second failure occurring in orbit around Vesta 3.5 years and 1.3 billion miles, or 2.0 billion kilometers, ago). With only two operable reaction wheels (and those no longer trustworthy), the ship’s remaining lifetime is very limited.

A year ago, the team couldn’t count on Dawn even having enough hydrazine to last beyond next month. But the creative methods of conserving that precious resource have proved to be quite efficacious, and the reliable explorer still has enough hydrazine to continue to return bonus data for a while longer. Now it seems highly likely that the spacecraft will keep functioning through the scheduled end of its primary mission on June 30, 2016.

NASA may choose to continue the mission even after that. Such decisions are difficult, as there is literally an entire universe full of interesting subjects to study, but resources are more limited. In any case, even if NASA extended the mission, and even if the two wheels operated without faltering, and even if the intensive campaign of investigating Ceres executed flawlessly, losing not an ounce (or even a gram) of hydrazine to the kinds of glitches that can occur in such a complex undertaking, the hydrazine would be exhausted early in 2017. Clearly an earlier termination remains quite possible.

Dawn has proven the value of ion engines. I would expect to see them used many more times in the future, especially missions heading to low gravity environments.

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The cratered surface of Ceres

5:23 pm

Craters on Ceres

Cool image time! As Dawn continues its survey of Ceres the science team is beginning to release images looking sideways at the planet, rather than straight down, in order to get a better understanding of the topography. The image to the right is an example. It shows the area around 37-mile-wide Fluusa Crater. I have cropped it to emphasize the most rugged areas, especially the jagged cliff meandering away towards the horizon.

This image provides a hint at the differences between Ceres and the Moon. Up until now Dawn images have given the impression that Ceres is very much like the heavily cratered lunar surface. The terrain in this image however suggests to me that Ceres’ surface crust is much less dense because of the low gravity, and thus has a light puffy feel to it. The Moon’s surface is rarely this uneven, as its higher gravity has pounded things down, smoothing them out somewhat.

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Flying over Ceres

8:43 am

The Dawn science team has released a new animation using the images taken by the spacecraft. The colors have been enhanced to emphasize the geological differences on the surface. I have embedded it below the fold.

The movie was produced by members of Dawn’s framing camera team at the German Aerospace Center, DLR, using images from Dawn’s high-altitude mapping orbit. During that phase of the mission, which lasted from August to October 2015, the spacecraft circled Ceres at an altitude of about 900 miles (1,450 kilometers).

» Read more

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Dantu Crater on Ceres

11:30 am

bright areas on crater wall on Ceres

Cool image time! As Dawn continues its close survey of Ceres, the science team has released this image of Dantu Crater, showing the bright spots on its rim as well as fractures on the crater floor. The picture was taken in December and has a resolution of about 120 feet per pixel.

Though scientists now favor salt deposits of some kind as the cause of the bright areas on Ceres, they also recognize that this theory is not yet proven. Moreover, the theory suggests that the salt was deposited as part of a water brine. When the water in the brine evaporated away, it left the salt behind. The problem, however, is that we do not yet have direct evidence that there is any water on Ceres at all, either on the surface or in the interior, which makes this theory exceedingly uncertain.

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