* Astronomy

Title: Small crater populations on Vesta
Authors: S. Marchi (1-2), W.F. Bottke (1), D.P. O'Brien (3), P. Schenk (4), S. Mottola (5), M.C. De Sanctis (6), D.A. Kring (2), D.A. Williams (7), C.A. Raymond (8), C.T. Russell (9) ((1) NLSI-SwRI, Boulder, CO, (2) NLSI-LPI, Houston, TX, (3) PSI, Tucson, AZ, (4) LPI, Houston, TX, (5) DLR, Berlin, Germany, (6) INAF, Rome, Italy, (7) ASU, Tempe, AZ, (8) JPL, Pasadena, CA, (9) UCLA, CA)

The NASA Dawn mission has extensively examined the surface of asteroid Vesta, the second most massive body in the main belt. The high quality of the gathered data provides us with an unique opportunity to determine the surface and internal properties of one of the most important and intriguing main belt asteroids (MBAs). In this paper, we focus on the size frequency distributions (SFDs) of sub-kilometre impact craters observed at high spatial resolution on several selected young terrains on Vesta. These small crater populations offer an excellent opportunity to determine the nature of their asteroidal precursors (namely MBAs) at sizes that are not directly observable from ground-based telescopes (i.e., below ~100 m diameter). Moreover, unlike many other MBA surfaces observed by spacecraft thus far, the young terrains examined had crater spatial densities that were far from empirical saturation. Overall, we find that the cumulative power-law index (slope) of small crater SFDs on Vesta is fairly consistent with predictions derived from current collisional and dynamical models down to a projectile size of ~10 m diameter (Bottke et al., 2005a,b). The shape of the impactor SFD for small projectile sizes does not appear to have changed over the last several billions of years, and an argument can be made that the absolute number of small MBAs has remained roughly constant (within a factor of 2) over the same time period. The apparent steady state nature of the main belt population potentially provides us with a set of intriguing constraints that can be used to glean insights into the physical evolution of individual MBAs as well as the main belt as an ensemble.

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Vesta: Giant impacts delivered carbon

The protoplanet Vesta has been witness to an eventful past: images taken by the framing camera onboard NASAs space probe Dawn show two enormous craters in the southern hemisphere. The images were obtained during Dawns year-long visit to Vesta that ended in September 2012. These huge impacts not only altered Vestas shape, but also its surface composition. Scientists under the lead of the Max Planck Institute for Solar System Research (MPS) in Germany have shown that impacting small asteroids delivered dark, carbonaceous material to the protoplanet. In the early days of our solar system, similar events may have provided the inner planets such as Earth with carbon, an essential building block for organic molecules. These results were published in the November-December issue of the journal Icarus.
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What is Creating Gullies on Vesta?

In a preliminary analysis of images from NASA's Dawn mission, scientists have spotted intriguing gullies that sculpt the walls of geologically young craters on the giant asteroid Vesta. Led by Jennifer Scully, a Dawn team member at the University of California, Los Angeles, these scientists have found narrow channels of two types in images from Dawn's framing camera - some that look like straight chutes and others that carve more sinuous trails and end in lobe-shaped deposits. The mystery, however, is what is creating them?
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The International Astronomical Union (IAU) has approved new names for 15 features on Vesta.

Domna for a 13-km-wide crater located at -11°, 75.8°.
The feature was named in honour of Julia Domna, wife of Roman emperor Severus.

Eumachia for a 26.8-km-wide crater located at -0.1°, 167.1°.
The feature was named in honour of a Priestess and prominent citizen of Pompeii during the 1st century.

Albana for a 96-km-wide crater located at 74°, 56.3°.
The feature was named in honour of a Roman vestal virgin.

Eutropia for a 21-km-wide crater located at 22.4°, 105°.
The feature was named in honour of the wife of Maximian (c. 324).

Fonteia for a 20.8-km-wide crater located at -53.1°, 141.3°.
The feature was named in honour of a Roman vestal virgin (c. 69 B.C.).

Galeria for a 21-km-wide crater located at -29.9°, 228.4°.
The feature was named in honour of Galeria Fundana, wife of Emperor Vitellius, (c. 1st century).

Mamilia for a 35.6-km-wide crater located at 48.4°, 292.2°.
The feature was named in honour of a Roman vestal virgin (c. 240).

Myia for a 2.7-km-wide crater located at -50.5°, 106.2°.
The feature was named in honour of the daughter of Pythagoras and Theano, wife of Milon of Crotona.

Paulina for a 19-km-wide crater located at 11°, 343.1°.
The feature was named in honour of Aurelia Paulina, a priestess for Artemis Pergaia.

Pomponia for a 63-km-wide crater located at 70°, 114.2°.
The feature was named in honour of a Roman vestal virgin (c. 213).

Torquata for a 35-km-wide crater located at 46.4°, 354°.
The feature was named in honour of a Roman vestal virgin (c. 48).

Albalonga Catena for a 148-km-long Crater chain located at -7.68°, 284.78°.
The feature was named in honour of a Ancient city of Alba Longa founded by Ascanius.

Robigalia Catena for a 78-km-long Crater chain located at -14.1°, 230.1°.
The feature was named after the Roman festival where a dog was sacrificed to the god Robigus.

Lavinium Dorsum for a 92-km-long ridge located at -27.6°, 319.4°.
The feature was named in honour of the Roman city now known as Pratica de Mare.

Brumalia Tholus for a 47-km-wide domical mountain located at -6.3°, 274°.
The feature was named in honour of the Roman festival of Bacchus celebrated on winter solstice.