NASA has approved a second extension of the Dawn mission at Ceres, the largest object in the asteroid belt between Mars and Jupiter.During this extension, the spacecraft will descend to lower altitudes than ever before at the dwarf planet, which it has been orbiting since March 2015, the US space agency said on Thursday.The spacecraft, which has already completed 10 years of spaceflight, will continue at Ceres for the remainder of its science investigation and will remain in a stable orbit indefinitely after its fuel runs out.Dawn completed its prime mission in June 2016, and its first extension was also approved that year. The Dawn flight team is studying ways to manoeuvre Dawn into a new elliptical orbit, which may take the spacecraft to less than 200 kilometres from the surface of Ceres at closest approach. Previously, Dawn's lowest altitude was 385 kilometers.A priority of the second Ceres mission extension is collecting data with Dawn's gamma ray and neutron spectrometer, which measures the number and energy of gamma rays and neutrons, NASA said.
This information is important for understanding the composition of Ceres' uppermost layer and how much ice it contains.The spacecraft also will take visible-light images of Ceres' surface geology with its camera, as well as measurements of Ceres' mineralogy with its visible and infrared mapping spectrometer.The extended mission at Ceres additionally allows Dawn to be in orbit while the dwarf planet goes through perihelion, its closest approach to the Sun, which will occur in April 2018. Because of its commitment to protect Ceres from Earthly contamination, Dawn will not land or crash into Ceres. Instead, it will carry out as much science as it can in its final planned orbit, where it will stay even after it can no longer communicate with Earth.Mission planners estimate the spacecraft can continue operating until the second half of 2018.Dawn is the only mission ever to orbit two extraterrestrial targets. It orbited giant asteroid Vesta for 14 months from 2011 to 2012, then continued on to Ceres, where it has been in orbit since March 2015.