Asteroids Scarred by Solar System's Violent Youth
David A. Aguilar (CfA)
Artist's impression of Jupiter's migration through the solar system, sweeping asteroids out of stable orbits, sending them careening into one another. As the gas giant planets migrated, they stirred the contents of the solar system.
NASA's Dawn spacecraft orbited the massive asteroid Vesta in 2011 and 2012, giving us an unprecedented look at the protoplanet's landscape, craters and mineral composition. The probe, which is now on its way to dwarf planet Ceres, not only revealed the evolution of Vesta, it also provided vital clues as to the evolution of our solar system. Now,in new images published by NASA
, an unusually colorful Vesta landscape is on display. Using data from the mission, scientists at Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany have produced a rather psychedelic view of this otherwise bland landscape. Dawn's camera system is equipped with seven filters, each filter sensitive to a specific wavelength of light. Normally, Vesta would look gray to the naked eye, but when analyzing the ratios of light through Vesta's filters, the landscape pops with color. Shown here, the flow of material inside and outside a crater called Aelia is demonstrated. As different minerals reflect and absorb different wavelengths of light, this composite image is alive with color, each shade representing different kinds of minerals littering Vesta's landscape.
This is Antonia, a crater located inside the huge Rheasilvia basin in the southern hemisphere of Vesta. From this image, planetary scientists have been ableto deduce that
"the light blue material is fine-grain material excavated from the lower crust. The southern edge of the crater was buried by coarser material shortly after the crater formed. The dark blue of the southern crater rim is due to shadowing of the blocky material."
The impact crater Sextilia can be seen in the lower right of this image. The mottled dark patches are likely impact ejecta from a massive impact and the redish regions are thought to be rock that melted during the impact. The diversity of the mineralogy is obvious here. "No artist could paint something like that. Only nature can do this," said Martin Hoffman, a member of the framing camera team at Max Planck Institute.
Earlier images of Vesta have shown an unusual "pitted terrain" on the floors of the craters named Marcia (left) and Cornelia (right). Once again, the varied colors demonstrate the different minerals and processes that cover Vesta's surface.
of Vesta shows the abundance of hydrogen on Vesta's surface. Note that the hydrogen signal is enhanced near the asteroid's equator. The hydrogen is likely from hydroxyl or water bound to minerals in Vesta's surface.
Another, earlier view of Antonia crater, demonstrating the mineral diversity of the region.
Telltale evidence of the solar system’s traumatic childhood can be found in the main asteroid belt, which contains a far more integrated assortment of bodies than previously believed, a new study shows.
Previous observations of the 2,000 or so biggest asteroids in the belt -- those with diameters of roughly 100 kilometers (62 miles) or larger -- showed a neat structure, with asteroids closer to the sun having surface temperatures warmer than those located farther away.
The observations neatly match theories about the formation of the solar system, which posits that bodies formed in warm environments would be found closer to the sun and those formed in cold environments are farther away.
"We said, 'Oh look, this has been preserving the conditions from the original formation. Case closed. It all makes sense,'" astronomer Francesca DeMeo, with the Harvard-Smithsonian Center for Astrophysics, told Discovery News.
But a new analysis, this time based on 100,000 asteroids of varying sizes, tells a far different story.
"Everything is mixed. Pieces are everywhere, like they’ve been just kind of thrown all over the asteroid belt," said DeMeo, lead author of a study that appears in this week’s journal Nature.
"It’s certainly overturned a lot of traditional thinking," added University of Arizona planetary scientist Dante Lauretta, lead researcher for an upcoming NASA asteroid sample return mission.
"There is still an underlying structure and composition, but there is evidence of mixing and that just makes so much sense to me," he said.
Scientists don’t yet know why smaller asteroids buck the trend of their larger siblings, but that it is related to the gravitational elbowing by jostling planets early in the solar system’s history.
"What we’re leaning toward now is that asteroids, rather than forming in the asteroid belt, formed throughout the entire solar system ... as close (to the sun) as Mercury and as far away as Neptune, and then, through the planetary migration, you scatter them all over the place. What’s left is what you see in the asteroid belt today," DeMeo said.
A more detailed understanding of what happened to the asteroids is one of the primary goals of NASA’s OSIRIS-REx sample return mission, which is slated for launch in September 2016. Samples from a cold asteroid named Bennu are due back on Earth in 2023.
Already in hand are samples from a warm asteroid collected by Japan’s Hayabusa spacecraft in 2005 and returned in 2010.
Together, the analyses will help scientists match information about asteroids collected by telescopes to the actual chemical and physical processes that shaped them.
"Asteroids’ compositions tell us about where they formed. Where they are today tells us the whole evolution of where they’ve gone since," DeMeo said.