On July 16, 2011, NASA’s Dawn mission entered orbit around the asteroid Vesta, a first in the history of solar system exploration. “It was a magical moment, with a very strong emotion”, remembers Maria Cristina De Sanctis of INAF, scientific director of the Italian Vir spectrometer on board the probe
Ten years ago, a probe he wrote a remarkable page of history of space exploration, entering for the first time in orbit around a body in the main belt of asteroids between the orbits of Mars and Jupiter. The probe, which had left Earth nearly four years earlier (and had twice risked not leaving at all), is called Dawn , ‘dawn’ in English. His goal: to study the dawn of the solar system.
It was July 16, 2011 and Dawn, a NASA mission that boasts a strong Italian contribution with the Italian Space Agency (ASI) and the National Institute of Astrophysics (Inaf), reached its first destination : the asteroid Vesta , a body of the diameter of about 500 meters, the second largest in the main belt. It will remain in orbit there for 14 months, until 5 September 2012, before heading to Ceres , the most massive object in the main asteroid belt, elevated in 2006 to the rank of dwarf planet . Upon arrival, in 2015, Dawn will become the first probe to orbit two distinct celestial bodies in deep space, continuing to study Ceres from orbit until the mission ends., in November 2018.
Among the four experiments on board the probe is the visible and infrared spectrometer Vir (Visible and Infrared Mapping Spectrometer) under Italian responsibility, funded and coordinated by ASI under the scientific guidance of INAF, built by the Leonardo company. This instrument sent over 11 million images and 90 GB of data to Earth, making a decisive contribution to the characterization of both Vesta and Ceres and to the study of their origin and evolution.
«The arrival of Dawn in Vesta was for me a truly unique moment that I had been waiting for over ten years», Maria Cristina De Sanctis , Inaf researcher and scientific director of Vir , tells Media Inaf . “Seeing that everything was working perfectly, that the data was of extremely high quality and that we were seeing an ‘alien’ world for the first time was a magical moment with a very strong emotion. I wish all scientists to feel emotions like the one I felt in setting eyes on Dawn’s first data in Vesta ».
The observations collected by Dawn in the fourteen months in orbit around Vesta have shown that this celestial body can be counted among the protoplanets, with characteristics that make it more similar to the Moon than to other asteroids. More generally, the mission data allowed scientists to compare two planet-like worlds that evolved very differently from each other, demonstrating the importance of the relative positions of different bodies within the early Solar System for their training and evolution.
To celebrate the 10th anniversary of Dawn’s arrival in Vesta, NASA has created a poster with a mosaic of images of the asteroid obtained from the camera on board the spacecraft. The central mosaic in black and white, made from many smaller images, shows a region near the equator of Vesta, where a vast system of depressions, called Divalia Fossae , is visible , which exceeds the dimensions of the Grand Canyon and covers the surface of the asteroid for 465 km in length and 22 km in width. The image also shows the irregular, non-spherical shape of Vesta. At the origin of this there would be two major impacts, the largest of which would have produced the Rheasilva crater, visible in the color image at the bottom right, and would also be at the origin of the system of ridges and depressions at the equator, formed over a billion years ago.
Dawn has also shown that Vesta, due to the violent collisions suffered, is the progenitor of a family of smaller asteroids, the so-called vestoids , as well as a particular class of meteorites known as Hed meteorites., where Hed stands for howardites-eucrites-diogenites. A name that is all a program and that describes the origin of these meteorites respectively from the crust (howardites), from the shallow magma chambers (eucrites) or from the lower crust or upper mantle (diogenites) of the asteroid. In the color image at the bottom left, the material around the three impact craters is seen in purple whose shape vaguely resembles that of a snowman, rich in minerals found in eucrites, according to the analysis of data from Vir and of the Gamma Ray and Neutron Detector. The regions in yellow and green in the lower right image, on the other hand, at the base of the Rheasilvia crater, are rich in minerals found in the diogenites, excavated from the upper mantle of Vesta.
It was precisely the mineralogical similarities between these meteorites, studied in the laboratory, and Vesta, observed with telescopes from Earth, that in the second half of the last century renewed the scientific interest in this asteroid discovered in 1807, leading to the definition of one of the objectives of the Dawn mission.
Featured image: The Dawn probe and the asteroid Vesta. Credits: Nasa / Jpl-Caltech
Provided by INAF