1. OH Observations of Comets Ellen Howell (Arecibo Observatory) and Amy Lovell (Agnes Scott College)

2. Hyakutake

3. Comets: where do they come from? Icy bodies ejected during giant planet formation Remnants of early solar system

4. Why Study Comets? Solar System Origin: Remnants of Giant Planet formation Kuiper Belt and Oort cloud are sources of comets -“New” comets were preserved -”Old” comets processed by solar heating - Source of water on Earth? Maybe. Coma gases released from nuclear ices -composition of the solar nebula -physical conditions present at formation

5. Anatomy of a comet Nucleus is 1-30 km solid body of ice/rock Coma - can extend few 10 5 km around nucleus –Gas mostly water, ammonia, methane, HCN, other trace gases –Dust – silicates and organic solids Tail – can extend for degrees (few AU) –Ion tail is anti-sunward at solar wind velocity (400 km/s) –Neutral gas and dust outflow at 0.5-2 km/s

6. Blueshift to sun Redshift to sun Extent depends on lifetime, outflow Dense inner coma (thermal/collisional) maser quenched

7. OH Radio Bands OH 18cm  -doublet 1667, 1665 MHz primary 1612, 1720 weaker Pumped by solar UV amplifies or absorbs background Despois et al. (A&A, 1981); Schleicher & A'Hearn (ApJ, 1988)

8. Emission lines Absorption lines

9. Mapping Layout ON OFF

10. Arecibo Spatial resolution 4' Green Bank Telescope (100m GBT) Spatial resolution 7.4'

11. Observational Goals Radio spectra (and maps) can assess: –Gas production rates –Gas outflow velocities –Day/Night Asymmetries –Coma density Support optical/IR observations

13. Monte Carlo coma simulation Free parameters: outflow v, quenching r Q Day/Night independent Random production/destruction time/angle Distribution binned to spectrum  2 minimized for BEST FIT water/OH lifetimes 8.2 x 10 4 s (~1 day) 1.5 x 10 5 s (1.7 days) OH photodissociation “kick” 1.05 km/s

14. Mapping Arecibor H = 2 AU 4’205,000 km

17. Outflow Velocity & Gas Production Production rate Q –# molecules/second to produce observed column density Velocities (widths) 0.5–2.5 km/s Low velocity for low-Q or distant Q 1.0 km s -1 Large variations near sun, large Q

18. 300 kg/s, would fill swimming pool in 4 minutes

19. Outflow Velocity

20. OH Collisional Quenching At high density, OH is thermalized -no pumping sustained -”ons” suppressed -”offs” enhanced -Production rates under-estimated

21. Quenching

22. Summary Observed “average” comets for “big picture” Exploiting unique capabilities of radio astronomy: Gas production monitoring Outflow velocities vary widely Mapping observations are essential

23. Rosetta spacecraft views nucleus of Comet 67P/Churyumov-Gerasimenko

24. Surface terrain

25. Landing Site

26. If you don’t have $1 billion… Groundbased radar images can show surface features – like a fly- by mission:

27. Comet 209P/LINEAR 27 May 2014 First comet nucleus closer than 0.06 AU since 1983 Resolution of 15-m Rotation rate 11-hrs, Movie is in two parts with pause between, analysis ongoing