1. THE 2002/2003 APPARITION OF 67P/CHURYUMOV- GERASIMENKO Mark R. Kidger Instituto de Astrofísica de Canarias

2. Introduction 67P/Churyumov-Gerasimenko is the probable new target of the ROSETTA mission after the failure of ROSETTA to meet the strict launch window for an Ariane-boosted encounter with 46P/Wirtanen. 67P is a comparatively recent visitor to the inner solar system having had q=4.0AU prior to 1840 and q>2.75AU until a Jupiter encounter in 1959. Its high level of activity is a potential risk for ROSETTA which must survive in the cometary environment for  2 years.

3. Introduction The recent large downward jumps in perihelion distance are the drivers of 67P/Churyumov- Gerasimenko's high level of activity. –The jump in “q” leads to increased pressure from sublimation of volatiles that “blows off” the insulating layer of surface dust that suffocates activity in evolved comets and causes thermal inertia. The light curve, photometric evolution and morphology of the comet during the 2002/2003 apparition are studied through the observations of the international Spanish language "Observadores_cometas" group.

4. 46P/Wirtanen v 67P/Churyumov- Gerasimenko 46P/Wirtanen –Discovery, 1947 Dec. 02 –10 apparitions, 9 observed (1980 missed) –Period 5.44 years, q=1.06AU 67P/Churyumov-Gerasimenko –Discovery, 1969 Sep. 11 (initially mistaken for 32P Comas-Solá) –6 apparitions –Period 6.57 years, q=1.29AU 67P is a much larger object. Tancredi et al. (2000, A&AS, 146, 73) estimate radii of: –46P, 0.7km, H 0 =18.4 –67P, 2.5km, H 0 =15.6 –Both are high-quality Q=1, multi-return estimates –Both are high-quality Q=1, multi-return estimates.

5. The light curves 67P has shown outbursts at perihelion –1996, at T-5d., amplitude 1.5 mags. –2002, at T-1(?)d, amplitude 1.5 mags. –Seiichi Yoshida finds post-perihelion fits of 1996: m 1 = 9.3 + 5 log  + 11.5 log r 2002: m 1 = 9.3 + 5 log  + 15.0 log r but not supported by Spanish/Italian CCD data46P may have shown a 3 magnitude outburst in late September 2002 (but not supported by Spanish/Italian CCD data) –Seiichi Yoshida finds post-perihelion fits of 1996: m 1 = 8.5 + 5 log  + 27.0 log r 2002: m 1 = 8.4 + 5 log  + 25.0 log r

6. Both comets have rather consistent light curves between the last two returns. –Their activity for the ROSETTA encounter in 2014 should be predictable. exciting science!! –We should expect a new outburst of 67P at perihelion in early 2009  prediction for an outburst during the encounter (exciting science!!). 46P/Wirtanen shows a much larger decrement with “r”  it is a much more evolved object with a thicker surface mantle and thus high thermal inertia.

7. Know 67P! There is an international campaign to observe and characterise 67P in preparation for ROSETTA. The “Observadores-Cometas” group has targeted 67P in a effort to provide valuable data. see Saturday’s talk –Observers in 6 countries who observe with standard methods (see Saturday’s talk).

8. 67P: Morphology 67P shows a faint tail even at perihelion. It gets brighter with time, but note that the November image has 3 times as much exposure!

9. December 28th 2002: Ramón Naves & Montse Campàs The gas tail seems offset, but this is due to an extension of the comaa to the south-west. Note how the coma becomes more difuse as “r” increases.

10. The Ligustri image (left) has the same exposure time as the previous image. The gas tail is clearly brighter. Teide Observatory images show the tail was at least 7 minutes long at this time. By early March the tail has started to fade rapidly. By April it had almost disappeared.

11. Spanish CCD lightcurve: 2002/2003 Maximum brightness is after perihelion. Small outburst at the end of December 2002?

12. Spanish CCD lightcurve: 2002/2003 Outburst at or a few days after perihelion. Sharp change of slope in mid-December 2002 (T+120d).

13. Spanish CCD lightcurve: 2002/2003 Initial rapid fade with “r” in 10” aperture: n=15.5. Slope change at r=1.85AU  n=6.7 (10”  d=11500km). Large change in 10” aperture at 1.85AU  important change in gas emission from nucleus, but it is increasingly less defined with increasing aperture. For 30-60”, n  7 ( 1.85AU).

14. The coma profile The coma profile shows a steeper brightness index with radius further from perihelion.

15. The coma profile (II) The coma radial brightness index decreases from  1.5 at perihelion to  3.3 at T+240 days.

16. The coma profile (III) The amount of light in the centre of the coma decreases considerably with time  much less “dust” close to the nucleus.

17. Conclusions The light curve of 67P seems to be rather constant between returns. Exciting science for ROSETTAThe last two returns have shown a 1.5 mag outburst at T  5 days  Exciting science for ROSETTA. The activity of the nucleus shows a major breakpoint at r  1.8AU within radius=5700km. The degree of condensation of the nucleus declines rapidly after perihelion.