Ralf Gellert


  • The APXS on board the Mars Rover Curiosity
  • Terrestrial APXS calibration chamber 
  • Various x-ray detector setups

Education and Employment Background

Dr. Ralf Gellert received his MSc in 1994 and PhD in 1999 from Darmstadt University of Technology, Germany, working in the field of Conversion Electron Moessbauer Spectroscopy. He then worked as a research scientist at the University of Mainz and the Max-Planck Institute for Chemistry, Germany, where he was part of the team that developed the miniaturized Moessbauer spectrometer that flew on the NASA Mars Exploration Rover mission (MER) and the ESA Beagle mission. From 2001 on, his research focus was on the development and building of the Alpha-Particle X-ray Spectrometer (APXS) for the same NASA MER rovers and the ESA Rosetta comet mission. Gellert joined the department of Physics at the University of Guelph in 2005 after an improved version of the APXS was selected for the follow-up NASA Mars Science Laboratory (MSL) rover Curiosity, which is supported by the Canadian Space Agency.

Research Themes

Gellert’s research is focused on designing and applying nuclear spectroscopy methods for planetary exploration. This includes developing hardware for future missions and the related analysis software. His laboratory examines radiation sources, X-ray detector technology, their readout electronics and supporting digital electronics under the rigid mechanical, radiation and temperature conditions in outer space. 

Main themes of research are:

  1. Mars Exploration Rover. The twin rovers Spirit and Opportunity landed in 2004 and lasted till 2010 and 2018, respectively. The APXS was one of the in-situ instruments on board that worked until the end. Gellert led and supported the daily operation of the APXS since 2005. This included data analysis, long term calibration checks and interpretation of the results in concert with the other science instrument. Even after the rover ceased, the in-detail APXS data analysis continues, since the data from this instrument allows to combine geologic interpretation from four landing sites on Mars.
  2. Mars Science Laboratory. After coming to Guelph, Gellert and his team set up a lab for the development and calibration of the improved APXS instrument on MSL, which was built by MDA in Brampton and supported by the CSA. Since landing in 2012, the team at Guelph and other Canadian and U.S. institutions operates the APXS, does the in-detail data analysis and interpretation of the continuously returned data. 
  3. Future missions or instruments. Gellert and his team work together with other Universities and partners to improve the APXS or other instruments, e.g. X-ray diffraction, for future planetary missions. His group investigates X-ray Spectroscopy theory to fully understand the method and investigate possible improvements in instrument setup and the analysis approach.  
  4. X-ray Spectroscopy data analysis. Gellert works on various ways to further improve the quality of the APXS analysis results from Mars by combining the APXS chemical data with various other results, like mineralogy or fine-scale chemistry. 


  • Several NASA MER and MSL Group Achievement Awards
  • NASA Outstanding Public Leadership Medal 2013
  • CSA Commendation for the successful landing of the MSL APXS, 2011-12
  • Breakthrough of the Year, The Journal Science and its publisher, AAAS, 2003-04
  • ESA Award for the development of the APXS on Rosetta, 2002-03

Media Coverage

Alpha particle X-ray spectrometer

Geology of Mars

Mars Rover


Name Role
Nick Boyd Research Associate
Michael McCraig Postdoctoral Fellow
Raphael Caruso MSc Student
Adam Desousa MSc Student
Salvador Fernandez MSc Student


Post Docs

  • Scott Annett 2022
  • Scott VanBommel 2017-18
  • Jeff Berger 2016 - 19
  • Elstan Desouza 2014-17
  • Irina Pradler , 2012-15

PhD Students

  • Scott VanBommel, PhD, 2018

MSc Students

  • Victoria Flood, MSc, 2020
  • Jordan Hanania, MSc, 2020
  • Brent Wilhelm, MSc, 2020
  • Dustin, Tesslaar, MSc, 2016
  • Shawn Stargardter, MSc, 2014
  • Scott VanBommel, MSc, 2013
  • Nick Boyd, MASc 2012 (Co-supervised with Stefano Gregory)
  • May Lee, MSc, 2010