Mario H. Acuna, a senior astrophysicist at NASA Goddard Space Flight Center and Co-Investigator on the MESSENGER mission, died on March 5, 2009, after a long battle against multiple myeloma. During his four decades at NASA, he played a critical role in many NASA endeavors, serving as principal investigator or key developer of experiments flown on more than 30 missions to every planet in the solar system, as well as the Sun.

Acuna had been involved in the MESSENGER from its inception, 13 years ago. “He became an enthusiastic participant as soon as I mentioned MESSENGER to him, when it was just an idea without an acronym,” notes Stamatios M. Krimigis, chair of MESSENGER’s Atmosphere and Magnetosphere Group. “His deep technical knowledge and scientific insight, coupled with his absolute honesty and integrity made him an indispensable member of any technical review and a critical player when hard decisions had to be made.”

Acuna contributed to the development of the Magnetometer (MAG) and the analysis of MAG observations from MESSENGER’s first two flybys of Mercury. “He brought with him a wealth of experience that was truly irreplaceable,” says Brian Anderson, MESSENGER’s Deputy Project Scientist. “He was a fountain of knowledge about anything concerning magnetic fields and magnetometer instrumentation. His breadth of understanding was astonishing. From arcane properties of materials to the intricacies of the electronics design in his instruments, you could count on Mario to have gems of wisdom to offer. To work with Mario on any project was to learn from him. We did our best to be good students, but it will be difficult knowing that we can no longer pick up the phone when we feel the need of his advice.”

Born in Cordoba, Argentina, in 1940, Acuna also brought with him a certain “Argentinean spice,” Anderson says. “Whether it was a novel scientific interpretation that he was determined to get you to take seriously or an engineering detail for calibrating or operating the magnetometer, you always knew where Mario stood, and he was anything but bashful about making his point. Debate was something he loved – the hotter the better! But you could always catch a twinkle in his eye and knew that his heart was with you, and if he was passionate it was because he felt strongly about science and exploration.”

MESSENGER Project Scientist Ralph McNutt knew Acuna since the 1970s, having worked with him on the Voyager 1 mission. “Here you had this brilliant research scientist, but he never had ‘airs’ about him; no pretentions,” McNutt says.

Richard Starr, instrument scientist for the MESSENGER X-Ray Spectrometer, worked with Acuna on several projects, “but the one that stands out the most for me is our collaboration on the X-Ray Spectrometer for the Clark mission.”

Originally scheduled for launch in mid-1996, the Clark spacecraft was to scan Earth with a sophisticated high-resolution camera to provide environmental data. “The Clark mission never launched,” Starr says. “It was canceled by NASA due to cost overruns. But for me personally it was still a great success because of what I learned and accomplished working with Mario. We delivered our instrument on time and on budget.”

Starr also points out that Acuna bridged the gap between scientist and engineer. “For him there really was no difference; it was all part of the same job,” he said. “At Goddard we have the John C. Lindsay Memorial Award for Space Science and the Moe I. Schneebaum Memorial Award for Engineering. As far as I know, Mario is the only person to have won both.”

MESSENGER will enter Mercury’s orbit in less than two years, on March 18, 2011. “While the journey will continue, it won’t be nearly as enjoyable without Mario,” Anderson says. “Perhaps his memory is best served by recalling his devotion to inquiry and advancing human understanding and making sure that the science we do with the MESSENGER magnetometer is up to the Mario Acuna standard.”

For more details, including a blog posted by his family that chronicles the struggle with his illness, visit: http://supermarioAcuna.wordpress.com/.