|Operator||Under evaluation by NASA|
|Mission duration||7.3 years (proposed)|
|Start of mission|
|Launch date||Cancelled; 2016 (was proposed)|
|Comet Wirtanen lander|
|Landing date||Cancelled; 2022 (was proposed)|
Comet Hopper (CHopper) was a proposed lander to NASA's Discovery Program that, had it been selected, would have orbited and landed multiple times on Comet Wirtanen as it approached the Sun. The proposed mission was led by Jessica Sunshine of the UMD, working with Lockheed Martin to build the spacecraft and the NASA Goddard Spaceflight Center to manage the mission.
The CHopper mission had three primary science goals for the 7.3 years of its lifetime. At roughly 4.5 AU the spacecraft would have rendezvoused with Comet Wirtanen to map the spatial heterogeneity of surface solids as well as gas and dust emissions from the coma - the nebulous envelope around the nucleus of a comet. The remote mapping would also allow for any nucleus structure, geologic processes, and coma mechanisms to be determined. After arriving at Comet Wirtanen, the spacecraft would have approached and landed, then subsequently hopped to other locations on the comet. As the comet approached the sun, the spacecraft would land and hop multiple times to record surface changes as the comet became more active. The final landing would occur at 1.5 AU.