# Specific impulse of cometary outgassing?

Note: This question is related to Average DeltaV applied to a comet during outgassing?

Rocket engines have a parameter called "specific impulse," which is the measurement (in seconds) of how efficient the propellant consumption is. As comets propel themselves via geysers near perihelion, I am wondering how efficient this process is in terms of specific impulse. Has this been directly measured?

• What do you mean by "how efficient" it is, or by "comets propel themselves"? Neither of these is clear. Comets outgas. It causes velocity changes. But efficiency - how would you define it? Nov 12 '21 at 17:24
• @RoryAlsop See en.wikipedia.org/wiki/Specific_impulse, how much mass is ejected per unit velocity change. Nov 12 '21 at 17:44
• I don't have any misunderstanding as to what specific impulse is. But what does your question mean? What are you trying to ask? Nov 12 '21 at 18:28
• Since $v_e = g_0 I_{sp}$ this is equivalent to asking what the effective velocity of cometary outgassing is and avoid the confusion with rockets. You could just as for typical or average velocity.
– uhoh
Nov 14 '21 at 10:50
• It's been modeled link.springer.com/content/pdf/10.1007/s10569-020-09973-5.pdf not sure if it's ever been measured. Nov 14 '21 at 13:17