'Unique' Meteorite Likely Came From Long-Dead Asteroid
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.
A well-known meteorite that was the first to be tracked by ground-based cameras as it blasted through the Earths atmosphere and quickly recovered at its Australian fall site has been identified as a geological oddity.
The Bunburra Rockhole meteorite was recovered from the Nullarbor Plain in Western Australia in 2007 and, after recent isotopic tests, its basaltic composition started a cosmic forensics investigation that has led researchers to believe it originated from an asteroid that no longer exists.
“This (meteorite) has a particular composition — which makes us think that it comes from a different body that has not been sampled before,” said geochronologist and geochemist Fred Jourdan, associate professor at Curtin University, Perth. Jourdan and his team’s work has been accepted for publication in the journal Geochimica et Cosmochimica Acta.
Most basaltic meteorites are thought to originate from the massive 500-kilometer wide asteroid (or protoplanet) Vesta that occupies the solar system’s Main Asteroid Belt. Basaltic rock forms from volcanic activity and it is believed that early in Vesta’s formation 4.5 billion years ago, vulcanism extinguished the majority of Vesta’s heat. Therefore, any basaltic meteorites originating from Vesta can be dated to 4.5 billion years old.
But through isotopic analysis of the Bunburra Rockhole specimen, the basaltic rock’s dateline was reset around 3.6 billion years ago.
“There’s no way, with our knowledge of the current laws of physics, that we would have vulcanism at this time because all the heat is long gone from the asteroids,” said Jourdan.
This can mean only one thing. As volcanic activity in large asteroids would have long been extinguished, the Bunburra Rockhole meteorite must have originated from an energetic asteroid collision, an event that would have been common around this time.
“It (the unknown asteroid) was born 4.5–6 billion years ago and then it probably got shattered 3.6 billion years ago.”
As there are no other known meteorites with this specific chemistry, Jourdan pointed out that meteorites like Bunburra Rockhole must be very rare and its parent asteroid was likely completely destroyed by that single collision event.
As director of Curtin University’s Argon Laboratory, Jourdan vaporized a small sample of the meteorite and analyzed the argon gas released in a spectrometer. By looking at the ratio of Argon 39 and Argon 40 (two Argon isotopes that contain different numbers of neutrons in their nuclei), a timeline can be revealed, allowing Jourdan to see when the asteroid was destroyed and the Argon dateline was ‘reset’ by this catastrophic collision.
Until now the only basaltic meteorites known came from asteroid Vesta. Through this valuable isotopic analysis, we now know that there were more basaltic asteroids out there. And one of them was probably completely destroyed 3.6 billion years ago, providing a unique insight to our solar system’s ancient and violent past.