Artist view of a young Solar System -- Credit: NASA/FUSE/Lynette Cook
Investigating the earliest and least known phases of the history of the Solar System, when the young Sun was still enveloped by the disk of gas and dust where its planets began to form, is probably one of the most complex challenges in modern planetary science. The celestial bodies formed at the time that survived intact to now are few and in the majority of cases their "memory" of the ancient processes that marked the birth of the Solar System has been canceled or otherwise altered by the environments to which they were exposed or by the later events that shaped their evolution.
For decades the asteroid Vesta has been one of our most reliable witnesses of this ancient past: in particular, the survival of its thin volcanic crust to impacts provided a powerful constraint to how violent the Solar System was in its youth. Recently, however, the data collected by NASA’s Dawn mission, which is now coming to its end after successfully exploring also asteroid Ceres, raised the possibility that Vesta’s memory may not be as good as we thought.
On one hand, the craters produced by impacts on its surface in the last 4 billion years seem to have erased the traces of the much older ones formed in the circumsolar disk. On the other hand, the possible greater thickness of its crust with respect to what was suggested by the HED meteorites (which the Dawn mission confirmed being Vesta’s crust fragments that landed on Earth) makes the information provided by the crust survival very vague. ...
The Late Accretion and Erosion of Vesta’s Crust Recorded by Eucrites and Diogenites as an
Astrochemical Window into the Formation of Jupiter and the Early Evolution of the Solar System ~ D. Turrini et al
Dwarf planet Ceres experienced an indirect polar reorientation of approximately 36 degrees, a new paper by Planetary Science Institute Senior Scientist Pasquale Tricarico says.
Using data from NASA’s Dawn mission, Tricarico determined the magnitude of the reorientation with three independent and corroborating lines of evidence. Global Gravity Inversion, from a paper Tricarico published in 2013, helped determine the density variations of Ceres, especially in the crust. This is what was used to find the equatorial density anomaly. Statistical analysis of topography was used for ridge analysis and the paleo-pole. And for matching the crustal fractures, a well-proven method by Matsuyama and Nimmo was used.
“The most surprising aspect of this paper is to me the observation that the pole of Ceres must have followed an indirect path to its current pole. A multi-step reorientation could mean that the equatorial density anomaly was still evolving during the reorientation, and this could be because the crust and mantle were weakly rotationally coupled, allowing the crust to start reorienting while the mantle would lag behind,” Tricarico said. “If crust and mantle are allowed to shift with respect to one another, that could point to a layer of reduced friction between crust and mantle, and one of the possible mechanisms to reduce friction could be an ancient water ocean beneath the crust.”
True Polar Wander of Ceres Due to Heterogeneous Crustal Density ~ P. Tricarico
Dawn Mission to Asteroid Belt Comes to End NASA | JPL-Caltech | Dawn | 2018 Nov 01
Click to play embedded YouTube video.
NASA's Dawn spacecraft has gone silent, ending a historic mission that studied time capsules from the solar system's earliest chapter.
Dawn missed scheduled communications sessions with NASA's Deep Space Network on Wednesday, Oct. 31, and Thursday, Nov. 1. After the flight team eliminated other possible causes for the missed communications, mission managers concluded that the spacecraft finally ran out of hydrazine, the fuel that enables the spacecraft to control its pointing. Dawn can no longer keep its antennae trained on Earth to communicate with mission control or turn its solar panels to the Sun to recharge. ...
Dawn launched in 2007 on a journey that put about 4.3 billion miles (6.9 billion kilometers) on its odometer. Propelled by ion engines, the spacecraft achieved many firsts along the way. In 2011, when Dawn arrived at Vesta, the second largest world in the main asteroid belt, the spacecraft became the first to orbit a body in the region between Mars and Jupiter. In 2015, when Dawn went into orbit around Ceres, a dwarf planet that is also the largest world in the asteroid belt, the mission became the first to visit a dwarf planet and go into orbit around two destinations beyond Earth. ...
A team led by Southwest Research Institute has concluded that the surface of dwarf planet Ceres is rich in organic matter. Data from NASA’s Dawn spacecraft indicate that Ceres’ surface may contain several times the concentration of carbon than is present in the most carbon-rich, primitive meteorites found on Earth.
“Ceres is like a chemical factory,” said SwRI’s Dr. Simone Marchi, a principal scientist who was the lead author of research published in Nature Astronomy today. “Among inner solar system bodies, Ceres has a unique mineralogy, which appears to contain up to 20 percent carbon by mass in its near surface. Our analysis shows that carbon-rich compounds are intimately mixed with products of rock-water interactions, such as clays.”
Ceres is believed to have originated about 4.6 billion years ago at the dawn of our solar system. Dawn data previously revealed the presence of water and other volatiles, such as ammonium derived from ammonia, and now a high concentration of carbon. This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter. An ensuing shakeup in the orbits of the large planets would have pushed Ceres to its current location in the main asteroid belt, between the orbits of Mars and Jupiter.
“With these findings, Ceres has gained a pivotal role in assessing the origin, evolution and distribution of organic species across the inner solar system,” Marchi said. “One has to wonder about how this world may have driven organic chemistry pathways, and how these processes may have affected the make-up of larger planets like the Earth.” ...
An Aqueously Altered Carbon-Rich Ceres ~ Simone Marchi et al