These products are often called precipitated silica or silica sols. A Martian year is approximately 668 sols, equivalent to approximately 687 Earth days. Jehannot de Bartillay 4,970 "livres" 12 sols for the delivery to Sr. Artificial sols may be prepared by dispersion or condensation. The Darian calendar is an arrangement of sols into a Martian year. Both rovers passed their original mission time of 90 sols many times over. Averaging over an entire orbital period gives a tropical year of 668.5921 sols. The stability of sols may be maintained by using dispersing agents. The lander was equipped with a non-rechargeable electric battery with enough power for four sols. On 19 May 2017, MOM reached 1,000 days (973 sols) in orbit around Mars. Pay was, at the beginning, 20 sols (1 livre) per day, double the agricultural wage. He and the crew are reunited after Mark's 560 sols alone on Mars. It was subdivided into 20 "sous" (also "sols"), each of 12 "deniers". It was subdivided into 20 "sols", each of 12 "deniers". However, smaller grained sols, such as those containing gold, could not be analyzed.