Posted on 08/02/2011 3:01:36 AM PDT by SunkenCiv
Explanation: Why is the northern half of asteroid Vesta more heavily cratered than the south? No one is yet sure. This unexpected mystery has come to light only in the past few weeks since the robotic Dawn mission became the first spacecraft to orbit the second largest object in the asteroid belt between Mars and Jupiter. The northern half of Vesta, seen on the upper left of the above image, appears to show some of the densest cratering in the Solar System, while the southern half is unexpectedly smooth. Also unknown is the origin of grooves that circle the asteroid nears its equator, particularly visible on this Vesta rotation movie, and the nature of dark streaks that delineate some of Vesta's craters, for example the crater just above the the image center. As Dawn spirals in toward Vesta over the coming months, some answers may emerge, as well as higher resolution and color images. Studying 500-km diameter Vesta is yielding clues about its history and the early years of our Solar System.
(Excerpt) Read more at 129.164.179.22 ...
[Credit: NASA, JPL-Caltech, UCLA, MPS, DLR, IDA]
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WOW
the rotation video is awsome...more important to me than the pock marks are the GROOVES or rills or rifling or whatever you call it that is clearly visable around the middle while it rotates.... and you wonder if it once had a prolonged engagement with another large body kind of like 2 gears engaging each other...
The grooved surface must be fairly common. I know the martian moons have the same surface feature.
My theory is that they result from a small body impacting at a low angle and rolling along the surface in the low gravity.
Perhaps a prolonged heating-cooling cycle in the grip of a larger body? The pitting on the one face and the smoothness of the other are very interesting.
This fellow has had an interesting time...
It looks like conglomerate with striations produced by distinct layers as it gathered dust or formed in layers before it broke away form a larger object
Why is one side more cratered than the other?
It got hit more.
I took a second look at the larger photo and it is not conglomerate. What seemed to be contained rounded objects are impact marks and the striations are that, not layers
I took a second look at the larger photo and it is not conglomerate. What seemed to be contained rounded objects are impact marks and the striations are that, not layers
WTH is that thing in the center, a Vulcan mining base?
Or a photographic artifact-made by aliens!
The Dawn spacecraft uses ion propulsion. From the NASA website:
Ion Propulsion
The ion propulsion system will provide the Dawn spacecraft with the thrust that it will require to reach its target asteroids. The demanding mission profile would be impossible without the ion engines — even a mission only to asteroid Vesta (and not on to Ceres) would require a much larger spacecraft and a dramatically larger launch vehicle. Ion propulsion was proved on NASA’s Deep Space 1 mission, which tested it and 11 other technologies while journeying to an asteroid and a comet.
Each of Dawn’s three 30-centimeter-diameter (12-inch) ion thrust units is movable in two axes to allow for migration of the spacecraft’s center of mass during the mission. This also allows the attitude control system to use the ion thrusters to help control spacecraft attitude.
A total of three ion propulsion engines are required to provide enough thruster lifetime to complete the mission and still have adequate reserve. However, only one thruster will be operating at any given time. Dawn will use ion propulsion for years at a time, with interruptions of only a few hours each week to turn to point its antenna to Earth. Total thrust time through the mission will be about 2,100 days, considerably in excess of Deep Space 1’s 678 days of ion propulsion operation.
The thrusters work by using an electrical charge to accelerate ions from xenon fuel to a speed 10 times that of chemical engines. The electrical level and xenon fuel feed can be adjusted to throttle each engine up or down. The engines are thrifty with fuel, using only about 3.25 milligrams of xenon per second (about 10 ounces over 24 hours) at maximum thrust. The Dawn spacecraft carries 425 kilograms (937 pounds) of xenon propellant.
At maximum thrust, each engine produces a total of 91 millinewtons — about the amount of force involved in holding a single piece of notebook paper in your hand. You would not want to use ion propulsion to get on a freeway — at maximum throttle, it would take Dawn’s system four days to accelerate from 0 to 60 miles per hour.
As slight as that might seem, over the course of the mission the total change in velocity from ion propulsion will be comparable to the push provided by the Delta II rocket that carried it into space — all nine solid-fuel boosters, plus the Delta’s first, second and third stages. This is because the ion propulsion system will operate for thousands of days, instead of the minutes during which the Delta performs.
Groovy!
Wow! I had not seen that photo until now. I remember that this body had a goodly impact crater, but the striations were not apparent IIRC.
Although the striations in the case of Phobos could be attributed to the big impact, I don’t think so, as some of the apparent ejecta (or is it CO2 ice?) shades the elevations. This would indicate that the striations pre-date the impact.
We need to go and look.
“...Why is one side more cratered than the other?...”
It kept turning the other cheek.
It looks like a disguised alien spacecraft in the rotation movie.
Also, wasn’t there an old theory that the asteroid belt was once a planet that broke up? Maybe the grooves are strata. Maybe a lot of the moons in the solar system came from the asteroid belt that now comprises chunks of the former planet.
A planet’s breaking up must have been quite a spectacular disaster however-many millions of years ago.
The asteroids of the main belt, if all piled up together, wouldn’t be very large (a few percent of the mass of our Moon, not a euphemism), but that’s not to say that all the debris from such an exploded planet would wind up all nice and orderly in the main belt. Tom Van Flandern’s EPH (Exploded Planet Hypothesis) is a good place to see this discussed in detail, in fact exhaustively. The debris from the (unexplained) explosion would go every which way, and most of it would be absorbed by Jupiter, or ejected from the Solar System by Jupiter, or (some small percentage) strike other Solar System bodies. Jupiter would clean up most of it in about ten million years, sez the late TVF.
Okay, I just tracked down a PDF on the Web Archive that may have a different view about the combined mass...
It’s probably not a coinky-dinky that the lines appear to run off that large impact crater. Whatever struck was apparently shattered by the impact, and some of its larger fragments rolled and ripped the full length of Vesta.
Thanks kidd.
Related, like, totally:
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http://www.freerepublic.com/focus/news/653287/posts
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http://www.freerepublic.com/focus/chat/2343851/posts?page=5#5
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We’re going on a planet hunt
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http://www.freerepublic.com/focus/bloggers/1610016/posts?page=6#6
Astronomy Picture of the Day 8-27-02
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Posted on 08/26/2002 9:15:22 PM PDT by petuniasevan
http://www.freerepublic.com/focus/chat/739866/posts?page=3#3
And there’s really no excuse for this:
http://www.freerepublic.com/focus/chat/2185379/posts?page=32#32
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