TUTCRIS

TY - JOUR

T1 - The violent collisional history of aqueously evolved (2) Pallas

AU - Marsset, Michaël

AU - Brož, Miroslav

AU - Vernazza, Pierre

AU - Drouard, Alexis

AU - Castillo-Rogez, Julie

AU - Hanuš, Josef

AU - Viikinkoski, Matti

AU - Rambaux, Nicolas

AU - Carry, Benoît

AU - Jorda, Laurent

AU - Ševeček, Pavel

AU - Birlan, Mirel

AU - Marchis, Franck

AU - Podlewska-Gaca, Edyta

AU - Asphaug, Erik

AU - Bartczak, Przemyslaw

AU - Berthier, Jérôme

AU - Cipriani, Fabrice

AU - Colas, François

AU - Dudziński, Grzegorz

AU - Dumas, Christophe

AU - Ďurech, Josef

AU - Ferrais, Marin

AU - Fétick, Romain

AU - Fusco, Thierry

AU - Jehin, Emmanuel

AU - Kaasalainen, Mikko

AU - Kryszczynska, Agnieszka

AU - Lamy, Philippe

AU - Le Coroller, Hervé

AU - Marciniak, Anna

AU - Michalowski, Tadeusz

AU - Michel, Patrick

AU - Richardson, Derek C.

AU - Santana-Ros, Toni

AU - Tanga, Paolo

AU - Vachier, Frédéric

AU - Vigan, Arthur

AU - Witasse, Olivier

AU - Yang, Bin

PY - 2020

Y1 - 2020

N2 - Asteroid (2) Pallas is the largest main-belt object not yet visited by a spacecraft, making its surface geology largely unknown and limiting our understanding of its origin and collisional evolution. Previous ground-based observational campaigns returned different estimates of its bulk density that are inconsistent with one another, one measurement1 being compatible within error bars with the icy Ceres (2.16 ± 0.01 g cm−3)2 and the other3 compatible within error bars with the rocky Vesta (3.46 ± 0.03 g cm−3)4. Here we report high-angular-resolution observations of Pallas performed with the extreme adaptive optics-fed SPHERE imager5 on the Very Large Telescope. Pallas records a violent collisional history, with numerous craters larger than 30 km in diameter populating its surface and two large impact basins that could be related to a family-forming impact. Monte Carlo simulations of the collisional evolution of the main belt correlate this cratering record to the high average impact velocity of ~11.5 km s−1 on Pallas—compared with an average of ~5.8 km s−1 for the asteroid belt—induced by Pallas’s high orbital inclination (i = 34.8°) and orbital eccentricity (e = 0.23). Compositionally, Pallas’s derived bulk density of 2.89 ± 0.08 g cm−3 (1σ uncertainty) is fully compatible with a CM chondrite-like body, as suggested by its spectral reflectance in the 3 μm wavelength region6. A bright spot observed on its surface may indicate an enrichment in salts during an early phase of aqueous alteration, compatible with Pallas’s relatively high albedo of 12–17% (refs. 7,8), although alternative origins are conceivable.

AB - Asteroid (2) Pallas is the largest main-belt object not yet visited by a spacecraft, making its surface geology largely unknown and limiting our understanding of its origin and collisional evolution. Previous ground-based observational campaigns returned different estimates of its bulk density that are inconsistent with one another, one measurement1 being compatible within error bars with the icy Ceres (2.16 ± 0.01 g cm−3)2 and the other3 compatible within error bars with the rocky Vesta (3.46 ± 0.03 g cm−3)4. Here we report high-angular-resolution observations of Pallas performed with the extreme adaptive optics-fed SPHERE imager5 on the Very Large Telescope. Pallas records a violent collisional history, with numerous craters larger than 30 km in diameter populating its surface and two large impact basins that could be related to a family-forming impact. Monte Carlo simulations of the collisional evolution of the main belt correlate this cratering record to the high average impact velocity of ~11.5 km s−1 on Pallas—compared with an average of ~5.8 km s−1 for the asteroid belt—induced by Pallas’s high orbital inclination (i = 34.8°) and orbital eccentricity (e = 0.23). Compositionally, Pallas’s derived bulk density of 2.89 ± 0.08 g cm−3 (1σ uncertainty) is fully compatible with a CM chondrite-like body, as suggested by its spectral reflectance in the 3 μm wavelength region6. A bright spot observed on its surface may indicate an enrichment in salts during an early phase of aqueous alteration, compatible with Pallas’s relatively high albedo of 12–17% (refs. 7,8), although alternative origins are conceivable.

U2 - 10.1038/s41550-019-1007-5

DO - 10.1038/s41550-019-1007-5

M3 - Letter

VL - 4

SP - 569

EP - 576

JO - Nature Astronomy

JF - Nature Astronomy

SN - 2397-3366

IS - 6

ER -