Axel, a research prototype rover for exploring the Moon, Mars and other planets, is remotely driven over rocks as engineers from Jet Propulsion (JPL) and grad students from Caltech (California Institute of Technology) demonstrate its mobile over the steep and rocky grounds of the JPL Mars Yard on January 14, 2009 in Pasadena, California. The rover is capable of descending cliffs or into craters and returning by a cable tethered to its starting point. Development of the Axel rover is a point effort funded by NASA Exploration Systems Mission Directorate (ESMD) and lead by Principal Investigator Issa Newnas and Co-Investigator and Caltech professor of mechanical engineering bio engineering Joel Burdick. (Photo by David McNew/Getty Images)

India: A sweeper cleans the side of a road near a replica of the Eiffel Tower amid heavy fog in the early morning in the northern Indian city of Chandigarh January 18, 2010. (Photo by Ajay Verma/Reuters)

A schoolgirl collects rubbish from Karachi's Clifton beach early morning April 22, 2013, during a cleaning campaign as part of the commemoration of Earth Day. (Photo by Akhtar Soomro/Reuters)

Brush your teeth and get cleaned up for the week ahead! These animals answered the call of good dental hygiene. Here: Hamster holds toothbrush. (Photo by Neo Vision/Getty Images/Amana Images RM)

A woman villager cleans garbage in front of her house as flood hits Tanjungsari village in Tasikmalaya, Indonesia, February 23, 2018. (Photo by Adeng Bustomi/Reuters/Antara Foto)

A worker cleans a statue of the founder of the Soviet Union Vladimir Lenin at Moscow Square in front of the House of Soviets in Saint-Petersburg on April 21, 2022. (Photo by Olga Maltseva/AFP Photo)

A truck driver cleans the mirror of his decorated truck in Charsadda outside Peshawar, Pakistan October 18, 2016. (Photo by Fayaz Aziz/Reuters)

Workers clean empty cooking oil containers at a roadside recycling workshop in Kolkata, India, July 13, 2016. (Photo by Rupak De Chowdhuri/Reuters)