Dawn soars over Vesta in 3D
Dawn soars over Vesta in 3D.
Dawn soars over Vesta in 3D.
Dawn soars over Vesta in 3D.
The Dawn scientists have released another spectacular image of the south polar mountain on Vesta whose relative size is three times that of Mount Everest. More information about the image can be found here. From the caption:
The peak of Vesta’s south pole mountain, seen in the center of the image, rises about 13 miles (22 kilometers) above the average height of the surrounding terrain. Another impressive structure is a large scarp, a cliff with a steep slope, on the right side of this image. The scarp bounds part of the south polar depression, and the Dawn team’s scientists believe features around its base are probably the result of landslides.
It appears the light gravity on Vesta allows for the formation of extreme topology.
Dawn begins close-up orbit observations of Vesta. More new results here.
In this orbit, the average distance from the spacecraft to the Vesta surface is 420 miles (680 kilometers), which is four times closer than the previous survey orbit.
NASA has released an update summarizing what scientists have found since Dawn went into orbit around Vesta in July. The video below, compiled from images Dawn has taken, gives a nice visual overview. The most interesting big feature, understated by the video, is the series of grooves that appear to encircle the asteroid’s equator. To my eye it almost looks like Vesta was once two asteroids that got merged into one, with these grooves indicating the weld point.
The direct link to the video can be found here.
Embedded video from
NASA Jet Propulsion Laboratory California Institute of Technology
On August 25 Cassini did a close fly-by of the small Saturn moon Hyperion, getting as close as 15,500 miles. The mission has just released images from that fly-by.
Looks like a sponge, doesn’t it? This moon is small, only 168 miles across, which makes it about half the size of the asteroid Vesta that Dawn is presently orbiting. Why it is so peppered with craters is of course the big science question. I would guess this has something to do with the environment around Saturn, with its rings and the innumerable particles that come from it. Yet, other moons of Saturn are not as crater-filled, so there is obviously more to this than meets the eye.
This fly-by was the second closest of Hyperion that Cassini has done, the first passing over the the moon’s surface by only 310 miles. Because the irregularly-shaped moon’s rotation is more like a chaotic tumble, scientists could not predict what part of the surface they would see. To their luck the new images captured new territory.
Another fly-by is scheduled in only three weeks, on September 16, 2011. This time, however, the spacecraft won’t get as close, passing at a distance of about 36,000 miles.
Below the fold are two images released today, one from Dawn at Vesta and the other from Messenger at Mercury. What makes them interesting to me is that, though the surfaces of both Vesta and Mercury are crater-packed, there are definitely distinct differences between them that one can spot if you look closely, all highlighting the fundamentally different environments of both worlds.
First, the Vesta photograph. The image looks out past the asteroid’s horizon, showing clearly that this dwarf planet is not spherical, with the south pole depression that puzzles scientists just on the planet’s limb. The parallel long deep grooves that are associated with this depression can be seen on the right. Notice also that the inside walls of all the craters slope downward in a very shallow manner. This gives the impression that the impacts that formed these craters smashed into an almost beachlike sandy surface. Note too the that the center of some craters have what appear to be flat small “ponds,” a phenomenon seen by the spacecraft NEAR when it orbited the asteroid Eros. These ponds are not liquid, but are actually made up of fine-grained particles that settle in the hollows of the asteroid.
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The images from Dawn keep rolling in. The picture on the right, released two days ago, shows the asteroid’s terminator. What makes it intriguing is the weird looking crater near the bottom of the image. It appears to have formed at impact on the wall of a cliff, something that at first glance seems impossible.
This is what I think happened: The impactor sliced down the wall of the cliff, but because of Vesta’s low gravitational field the impact scar never collapsed downward, filling in.
I once wrote an article about asteroids for Astronomy where I described these objects as having the consistency of mashed potatoes and ice cream sundaes. This image illustrates this nicely. The asteroid’s weak gravitational field limits the density of its material, so that puffy strange formations such as this crater can form.
The mystery of Vesta’s south pole depression.
The Dawn mission team released another image today of the giant asteroid Vesta, this time taken from about 2,300 miles away. At this distance the resolution is still somewhat coarse, with the smallest visible detail about 0.43 miles in size.
To the right is a cropped section of the full image, focusing in on what appears to be a very strange geological feature, indicated by the arrows. From what I can tell, the dark meandering streak looks like a rille or flow coming out of the mound or peak near the bottom of the image. Yet, this dark meander continues directly across a crater as if it were a wind-blown dust streak.
I really have no idea what geological process created this. I also suspect that the scientists don’t quite know yet either, though I am sure they have some good theories, mostly based on the very light gravity that should exist on a world only 330 miles in diameter. As I’ve already noted, however, it is going to take them a couple of months to digest the data they are getting and come up with some reasonable conclusions. It will be fun to finally find out what they have learned.
The Dawn science team today released what they are calling “the first full-frame image” of Vesta. The image is shown below the fold.
The picture was taken from 3,200 miles, and shows a pockmarked irregularly shaped world. While many features that resemble the Moon (the craters, the rays radiating out from those craters), that Vesta itself is not spherical makes it very much unlike the Moon. It is probably going to take scientists several months at least to decipher the data they are getting and come up with some concrete conclusions about this strange dwarf planet.
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A new image of Vesta from Dawn.
Some good news: Dawn has returned its first sharp close-up image of Vesta.
The image to below the fold is to me a relief, as it shows that the spacecraft’s camera is fine and that my engineering friends were correct in telling me so. Forgive me for being a skeptical and nervous reporter.
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Dawn enters orbit around Vesta.
A new analysis of the orbits of Ceres and Vesta says that in a surprisingly short time those orbits become chaotic and therefore unpredictable. More significantly, those orbits interact with the Earth’s and also make its long term orbit chaotic and unpredictable. From the abstract:
Although small, Ceres and Vesta gravitationally interact together and with the other planets of the Solar System. Because of these interactions, they are continuously pulled or pushed slightly out of their initial orbit. Calculations show that, after some time, these effects do not average out. Consequently, the bodies leave their initial orbits and, more importantly, their orbits are chaotic, meaning that we cannot predict their positions. The two bodies also have a significant probability of impacting each other, estimated at 0.2% per billion year. Last but not least, Ceres and Vesta gravitationally interact with the Earth, whose orbit also becomes unpredictable after only 60 million years. This means that the Earth’s eccentricity, which affects the large climatic variations on its surface, cannot be traced back more than 60 million years ago. This is indeed bad news for Paleoclimate studies. [emphasis mine]
The scientists found that it became impossible to calculate the orbits of the two largest asteroids after only several ten thousand years. They also found that “numerous asteroids in the main belt will behave in the same way with . . . much more chaotic behavior than previously thought.” Worse, the possibility of collisions was far higher than ever thought. Ceres and Vesta have a 1 in 500 chance of colliding with each other every billion years, while other asteroids have chances as low as 1 in 1000.
The importance of this discovery, which still needs to be confirmed by other researchers, cannot be understated.
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Another image of Vesta from Dawn has been released. This image was taken on July 9 from a distance of 26,000 miles away. It is definitely an improvement over the previous image, with more small details becoming visible. However, I once again wonder about the softness of the image. Look at the limb of the planet. It is soft against the black sky. This is not what one would expect from perfectly focused camera.
Dawn goes into orbit around Vesta next week. We sure learn then for sure if there is a problem with its camera, or whether I am merely being a bit too nervous.
I’ve posted earlier about Dawn’s approach to Vesta. However, in looking at the images from Dawn, it dawned on me recently that they seems more fuzzy for what you’d normally expect from a space probe. I am now wondering if there is something fundamentally wrong with Dawn’s camera, causing its images to be slightly out of focus.
Dawn continues to approach the large asteroid Vesta. Below is an image taken July 1st from about 62,000 miles. The image has a resolution of 5.8 miles per pixel.
Despite Vesta’s large size, 330 miles in diameter, it is nonspherical. This fact, combined with data that says it is differentiated with a core and mantle, suggests that it is the remains of a larger object that subsequently broke up.
Dawn’s approach to Vesta continues.
Starting at the beginning of the approach phase on May 3, Dawn interrupted thrusting once a week to photograph Vesta against the background stars. These images help navigators determine exactly where the probe is relative to its target. This technique does not replace other means of navigation but rather supplements them. One of the principal methods of establishing the spacecraft’s trajectory relies on accurately timing how long it takes radio signals, traveling, as all readers know, at the universal limit of the speed of light, to make the round trip between Earth and Dawn. Another uses the Doppler shift of the radio waves, or the slight change in pitch caused by the craft’s motion. These sensitive measurements remain essential to navigating the faraway ship as it sails the interplanetary seas.
Despite the very slow approach, the distance is small enough now that observing Vesta weekly is no longer sufficient. To achieve the navigational accuracy required to reach the intended orbit in early August, last week the frequency of imaging was increased to twice per week. In each session, half of the pictures are taken with long exposures to ensure many stars are detectable, thus overexposing the much brighter disc of the nearby Vesta. The other half use short exposures to ensure that the rocky world shows up correctly so its precise location can be measured. The visible and infrared mapping spectrometer has been commanded to observe Vesta during three of these sessions, each time providing valuable information that will help scientists select instrument settings for when Dawn is close enough to begin its detailed scientific measurements.
The asteroid Vesta is beginning to come into focus as the space probe Dawn approaches.
Dawn captures its first image of the asteroid Vesta as it closes in on a rendezvous set for July 16.
Dawn has begun its final if slow approach to the asteroid Vesta.
When is an asteroid not an asteroid?
The layered structure of Vesta (core, mantle and crust) is the key trait that makes Vesta more like planets such as Earth, Venus and Mars than the other asteroids, McCord said. Like the planets, Vesta had sufficient radioactive material inside when it coalesced, releasing heat that melted rock and enabled lighter layers to float to the outside. Scientists call this process differentiation.
This question immediately demonstrates once again the terrible mess the International Astronautical Union made when it decided several years ago to define what makes a planet, and came up with a definition that simply doesn’t work. For if Vesta should be considered a planet, why not Pluto?