@misc{indiciaeeec2e89e38c4,
  title = {Mercury's helium exosphere},
  author = {Hartle, R. E. and Curtis, S. A. and Thomas, G. E.},
  year = {1975},
  url = {https://ntrs.nasa.gov/citations/19750062209},
  note = {Source identifier: 19750062209}
}