P/2005 U1
Comet 238P/Read by the James Webb Space Telescope on September 8, 2022
Discovered byMichael T. Read
Discovery date24 October 2005
Main-belt comet[1][2]
Encke-type comet[3]
Orbital characteristics[3]
Epoch 7 January 2006
Uncertainty parameter 1
Aphelion3.9645 AU (Q)
Perihelion2.3647 AU (q)
3.1646 AU (a)
5.63 yr
28.566° (M)
2022-Jun-05 (previous)[5]
Physical characteristics
Mean diameter
0.6 km (approx.)[6]
Mean density
1.0 g/cm3 (assumed)[6]
Albedo0.04 (assumed)[6]
Surface temp. min mean max
Kelvin[6] 142 K 159 K 184 K
19.62 to 23.41

238P/Read (P/2005 U1) is a main-belt comet[1][2] discovered on 24 October 2005 by astronomer Michael T. Read using the Spacewatch 36-inch telescope on Kitt Peak National Observatory. It has an orbit within the asteroid belt and has displayed the coma of a traditional comet. It fits the definition of an Encke-type comet with (TJupiter > 3; a < aJupiter).[3]


Before it was discovered 238P came to perihelion on 2005 July 27.[3] When it was discovered on 2005 October 24, it showed vigorous cometary activity until 2005 December 27.[6] Outgassing likely began at least 2 months before discovery.[6] The activity of 238P is much stronger than 133P/Elst-Pizarro and 176P/LINEAR.[6] This may indicate that the impact assumed to have triggered 238P's activity occurred very recently.[6]

Observations of 238P when it was inactive in 2007 suggests that it has a small nucleus only about 0.6 km in diameter.[6]

It came to perihelion on 2011 March 10,[6] 2016 October 22.[7][5] and 2022 June 5.[5] It will next come to perihelion on 2028 January 24.[4]

238P/Read was the target of a mission proposal in NASA's Discovery Program in the 2010s called Proteus, however it was not selected for further development.[8] Discovery program's founding mission was to an asteroid, but it went to a Near-Earth asteroid.[9] A mission to a main-belt asteroid was proposed in the 1990s (also see Deep Impact (spacecraft)).[10]

The comet was observed by James Webb Space Telescope during the 2022 perihelion and it was found spectrographicaly that its coma was composed by water vapor, due to water sublimation, and lacked significant CO2 coma.[11]

See also


  1. ^ a b Henry H. Hsieh (May 2010). "Main Belt Comets". Hawaii. Archived from the original on 2011-08-06. Retrieved 2010-12-15. (older 2010 site) Archived August 10, 2009, at the Wayback Machine
  2. ^ a b David Jewitt. "Main Belt Comets". UCLA, Department of Earth and Space Sciences. Retrieved 2010-12-15.
  3. ^ a b c d "JPL Small-Body Database Browser: 238P/Read (2005 U1)" (last observation: 2011-09-14). Archived from the original on 2020-07-26. Retrieved 2012-08-08.
  4. ^ a b "Horizons Batch for 238P/Read on 2028-Jan-24" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 2023-04-30. (JPL#37/Soln.date: 2023-Jan-03)
  5. ^ a b c "238P/Read Orbit". Minor Planet Center. Retrieved 2014-06-20.
  6. ^ a b c d e f g h i j k Hsieh, Henry H.; Jewitt; David C.; Ishiguro, Masateru (2009). "Physical Properties of Main-Belt Comet P/2005 U1 (Read)". The Astronomical Journal. 137 (1): 157–168. arXiv:0810.1351. Bibcode:2009AJ....137..157H. doi:10.1088/0004-6256/137/1/157.
  7. ^ Syuichi Nakano (2010-08-20). "P/Read (2005 U1 = 2010 N2)". OAA Computing and Minor Planet Sections. Retrieved 2011-07-25.
  8. ^ "PROTEUS – A MISSION TO INVESTIGATE THE ORIGIN OF EARTH'S WATER: CREATING HABITABLE WORLDS" (PDF). Astrobiology Science Conference 2015. Retrieved January 11, 2016.
  9. ^ "Technical Digest" (PDF). Archived from the original (PDF) on 2018-02-26. Retrieved 2017-01-05.
  11. ^ Kelley, Michael S. P.; Hsieh, Henry H.; Bodewits, Dennis; Saki, Mohammad; Villanueva, Geronimo L.; Milam, Stefanie N.; Hammel, Heidi B. (15 May 2023). "Spectroscopic identification of water emission from a main-belt comet". Nature: 1–2. doi:10.1038/s41586-023-06152-y. PMC 10371862.

Numbered comets Previous237P/LINEAR 238P/Read Next239P/LINEAR