Image 1 |
Image 2 |
"The large impact basins on the moon are all quite old," said David O'Brien, a Dawn participating scientist from the Planetary Science Institute in Tucson, Ariz. "The fact that the largest impact on Vesta is so young was surprising."
Scientists now see Vesta as a layered, planetary building block with an iron core – the only one known to survive the earliest days of the solar system. The asteroid's geologic complexity can be attributed to a process that separated the asteroid into a crust, mantle and iron core with a radius of approximately 68 miles (110 kilometers) about 4.56 billion years ago. The terrestrial planets and Earth's moon formed in a similar way.
Dawn observed a pattern of minerals exposed by deep gashes created by space rock impacts, which may support the idea the asteroid once had a subsurface magma ocean. A magma ocean occurs when a body undergoes almost complete melting, leading to layered building blocks that can form planets. Other bodies with magma oceans ended up becoming parts of Earth and other planets.
Data also confirm a distinct group of meteorites found on Earth did, as theorized, originate from Vesta. The signatures of pyroxene, an iron- and magnesium-rich mineral, in those meteorites match those of rocks on Vesta's surface. These objects account for about 6 percent of all meteorites seen falling on Earth.
Scientists now know Vesta's topography is quite steep and varied. Some craters on Vesta formed on very steep slopes and have nearly vertical sides, with landslides occurring more frequently than expected.
Another unexpected finding was that the asteroid's central peak in the Rheasilvia basin in the southern hemisphere is much higher and wider, relative to its crater size, than the central peaks of craters on bodies like our moon. Vesta also bears similarities to other low-gravity worlds like Saturn's small icy moons, and its surface has light and dark markings that don't match the predictable patterns on Earth's moon.
"We know a lot about the moon and we're only coming up to speed now on Vesta," said Vishnu Reddy, a framing camera team member at the Max Planck Institute for Solar System Research in Germany and the University of North Dakota in Grand Forks. "Comparing the two gives us two storylines for how these fraternal twins evolved in the early solar system."
Caption of Image 1
"This image, made from data obtained by NASA's Dawn spacecraft, shows the mineral distribution in the southern hemisphere of the giant asteroid Vesta. The mineral data came from Dawn's visible and infrared mapping spectrometer, which captures different wavelengths of reflected and emitted radiation. The areas in purple have a higher proportion of diogenite minerals, and yellow areas have a higher proportion of eucrite minerals. Diogenites are silicate rocks with more magnesium than the eucrites, which are richer in iron. The mineral data lies on a mosaic obtained by Dawn's framing camera.
The small-scale variation and the fact that mixtures of diogenite and eucrite appear all over Vesta suggest a complex crust dominated by eucrite with intrusions of diogenitic materials. However, since diogenites appear in greater proportion at depth, the patterns suggest Vesta likely melted all the way through early in its evolution."
"This image shows three slices of a class of meteorites that fell to Earth that NASA’s Dawn mission has confirmed as originating from the giant asteroid Vesta. The meteorites, known as howardite, eucrite and diogenite meteorites, were viewed through a polarizing microscope, where different minerals appear in different colors. The texture of the rocks reveals that they crystallized at different rates. The image on the left comes from a meteorite named QUE 97053 (Antarctica), which is basaltic eucrite. The image in the middle comes from the Moore County (North Carolina) cumulate eucrite. The image on the right comes from a diogenite meteorite named GRA 98108 (Antarctica)."
This story has edited by author of threelas
Source: NASA
Post a Comment