 About 20 large ( 40 – 150 m across ) ejecta blocks have been identified , embedded in Ida 's regolith . Ejecta blocks constitute the largest pieces of the regolith . Because ejecta blocks are expected to break down quickly by impact events , those present on the surface must have been either formed recently or uncovered by an impact event . Most of them are located within the craters Lascaux and Mammoth , but they may not have been produced there . This area attracts debris due to Ida 's irregular gravitational field . Some blocks may have been ejected from the young crater Azzurra on the opposite side of the asteroid . 
