Thomas E. Cravens

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Thomas E. Cravens
NationalityAmerican
Alma mater Harvard University (Ph.D.)
State University of New York at Stony Brook (B.A.)
Known forCometary X-ray emission model
Solar wind interactions with planets and comets
AwardsFellow of the AAAS (2018) [1]
Higuchi Award (2005) [2]
Fellow of AGU (2001) [3]
AGU Editors' Citation for Excellence in Refereeing (2003) [4]
Scientific career
Fields Space physics, Planetary science
Institutions University of Kansas
University of Michigan [5]
Doctoral advisor Alex Dalgarno [6]

Thomas E. Cravens is an American space physicist and Professor Emeritus [7] in the Department of Physics and Astronomy at the University of Kansas. [8] He is known for developing the widely accepted model explaining the emission of X-rays from comets, a phenomenon discovered unexpectedly in 1996. [9] [10] [11]

Contents

Early life and education

Cravens received his B.A. in physics from State University of New York at Stony Brook in 1970. [8] He then pursued graduate studies at Harvard University, where he earned his Ph.D. in astronomy in 1975 under the supervision of Alex Dalgarno. [8] [6] His doctoral dissertation was titled "Astrophysical Applications of Electron Energy Deposition in Molecular Hydrogen.". [6]

Career

After receiving his Ph.D., Cravens worked at the Space Physics Research Laboratory at the University of Michigan. [5] He later joined the faculty of the University of Kansas Department of Physics and Astronomy, where he is currently a Professor Emeritus. [8] [7]

His research spans a range of topics in space plasma physics, focusing on the interactions of the solar wind with planets (including Earth, Mars, Venus, and the outer planets) and comets. [8] He also investigates the physics of planetary ionospheres and magnetospheres, and the interstellar medium. [8]

Cometary X-ray emission

A significant contribution by Cravens is his model explaining the emission of X-rays from comets. [9] [12] [11] Prior to the observation of X-rays from Comet Hyakutake in 1996 by the ROSAT satellite, cold bodies like comets were not generally expected to be significant X-ray sources. [10]

Cravens proposed that the primary mechanism is charge exchange (also known as charge transfer) between highly charged heavy ions in the solar wind and neutral atoms and molecules in the cometary coma. [9] The solar wind contains ions such as O6+, O7+, C5+, and C6+. When these ions encounter the neutral gas sublimating from the comet's nucleus (the coma), they can capture electrons from the neutral species (e.g., H2O, CO2, CO). [9] [11]

The process can be represented as:

Xq+ + M → X(q-1)+\* + M+

where Xq+ is a highly charged solar wind ion, M is a neutral cometary molecule, X(q-1)+\* is the resulting ion in an excited state after capturing an electron, and M+ is the newly ionized cometary molecule.

The excited ion (X(q-1)+\*) rapidly relaxes to a lower energy state by emitting a photon, typically in the X-ray or extreme ultraviolet (EUV) part of the spectrum. The photon's energy reflects the large energy difference between the ion's states. [9] [11]

Cravens' model successfully explained the observed spectral characteristics and spatial distribution of cometary X-rays. [9] [11] This discovery provided a new tool for studying both cometary atmospheres and the composition (particularly the heavy ion component) of the solar wind. [11] The charge exchange mechanism identified by Cravens is now recognized as an important X-ray emission process in various astrophysical environments, such as planetary atmospheres and the heliosphere. [12]

Other research

Cravens has contributed significantly to other areas of space physics, including: [8]

Awards and recognition

Selected publications

Cravens has authored or co-authored numerous publications in space physics and planetary science, including:

A more extensive list of publications is available through databases such as NASA Astrophysics Data System. [17] and Google Scholar. [18]

References

  1. 1 2 "AAAS Honors Accomplished Scientists as 2018 Elected Fellows". American Association for the Advancement of Science. Retrieved 2025-04-10.
  2. 1 2 "Higuchi-KU Endowment Research Achievement Awards". University of Kansas Office of Research. Retrieved 2025-04-10. 2005... Thomas E. Cravens, Physics and Astronomy
  3. 1 2 "AGU Fellows". American Geophysical Union. Retrieved 2025-04-10. 2001... Thomas E Cravens
  4. 1 2 "2003 Editors' Citations for Excellence in Refereeing" . Eos, Transactions American Geophysical Union. 84 (34). American Geophysical Union: 331. 26 August 2003. doi:10.1029/2003EO340006 . Retrieved 2025-04-10. Journal of Geophysical Research–Space Physics... Thomas E. Cravens
  5. 1 2 "Thomas E. Cravens - Space Physics Research Laboratory". University of Michigan College of Engineering. Retrieved 2025-04-10.
  6. 1 2 3 Cravens, Thomas E. (1975). "Astrophysical Applications of Electron Energy Deposition in Molecular Hydrogen". Ph.D. Thesis. Harvard University. Bibcode:1975PhDT.........1C . Retrieved 2025-04-10– via NASA/ADS. Advisor: Alexander Dalgarno
  7. 1 2 "Emeritus Faculty". University of Kansas, Department of Physics and Astronomy. Retrieved 2025-04-10. Thomas Cravens, Professor Emeritus
  8. 1 2 3 4 5 6 7 8 9 "Thomas Cravens". University of Kansas, Department of Physics and Astronomy. Retrieved 2025-04-10.
  9. 1 2 3 4 5 6 Cravens, T. E. (1997). "Comet Hyakutake x-ray source: Charge transfer of solar wind heavy ions". Geophysical Research Letters. 24 (1): 105–108. Bibcode:1997GeoRL..24..105C. doi:10.1029/96GL03780.
  10. 1 2 "X-Rays From Comet Hyakutake Discovered by ROSAT". NASA HEASARC. May 7, 1996. Retrieved 2025-04-10.
  11. 1 2 3 4 5 6 Dennerl, K. (2010). "X-rays from comets". Space Science Reviews. 157 (1–4): 57–91. Bibcode:2010SSRv..157...57D. doi: 10.1007/s11214-010-9720-5 . The most likely process responsible for cometary X-ray emission is charge exchange (CX) between highly charged heavy ions of the solar wind and cometary neutrals (Cravens 1997).
  12. 1 2 3 Bhardwaj, A.; Elsner, R. F.; Gladstone, G. R.; Cravens, T. E.; Lisse, C. M.; Waite Jr, J. H. (2007). "X-rays from solar system objects". Planetary and Space Science. 55 (9): 1135–1189. arXiv: 1012.1088 . Bibcode:2007P&SS...55.1135B. doi:10.1016/j.pss.2006.11.011.
  13. ↑ "KU professor plays vital role in MAVEN mission to Mars". KU News. August 5, 2013. Retrieved 2025-04-10.
  14. ↑ "MAVEN Team Directory". NASA. 4 December 2017. Retrieved 2025-04-10.
  15. ↑ "Cassini: The Team". NASA. 2024-11-03. Retrieved 2025-04-27.
  16. ↑ Waite, J. H.; Perryman, R. S.; Perry, M. E.; Miller, K. E.; Bell, J.; Cravens, T. E.; Glein, C. R.; Grimes, J.; Hedman, M.; Cuzzi, J.; Brockwell, T.; Teolis, B.; Moore, L.; Mitchell, D. G.; Persoon, A.; Kurth, W. S.; Wahlund, J.-E.; Morooka, M.; Hadid, L. Z.; Chocron, S.; Walker, J.; Nagy, A.; Yelle, R.; Ledvina, S.; Johnson, R.; Tseng, W.; Tucker, O. J.; Ip, W.-H. (5 October 2018). "Chemical interactions between Saturn's atmosphere and its rings". Science. 362 (6410): eaat2382. Bibcode:2018Sci...362.2382W. doi: 10.1126/science.aat2382 . hdl: 2027.42/149200 . PMID   30287634.
  17. ↑ "ADS Search Results for author:"Cravens, T."". NASA/ADS. Retrieved 2025-04-10.
  18. ↑ "Thomas E. Cravens". Google Scholar. Retrieved 2025-04-10.
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