"Secular Light Curve of Comet 103P/Hartley 2, Target of the EPOXI Mission"

TL;DR

This study compiles a detailed secular light curve of comet 103P/Hartley 2, revealing its activity patterns, physical properties, and potential lifespan, providing insights into its composition and evolution relevant to the EPOXI mission.

Contribution

It presents the first comprehensive secular light curve of 103P/Hartley 2 with new photometric parameters, and analyzes its activity, composition, and physical characteristics in detail.

Findings

Comet's activity begins at -4.2 AU from the Sun.

The comet's diameter is approximately 1.14 km.

It may disappear in about 17 revolutions at current activity levels.

Abstract

In support of the EPOXI mission, we have compiled the secular light curve (SLC) of comet 103P/Hartley 2, the next target of EPOXI. a) Of the order of 30 photometric parameters are measured, over 20 of them new. The turn on point of activity is -4.2 +/- 0.1 AU from the Sun, which corresponds to -400 +/- 40 d before perihelion. The total active time is TACTIVE= 1484 +/- 43 d. b) 103P is a young dwarf comet, young because it has a photometric age P-AGE(1,1) = 15 +/- 2 cy (comet years), and dwarf because its diameter is DEFFE = 1.14 +/- 0.16 km. c) The nucleus is very active, and the amplitude of the SLC is ASEC= 10.8 +/- 0.1 mag in 1997. This comet is as active as 1P/Halley, but much smaller. d) After remaining active up to aphelion, the comet spills-over its activity into the next orbit. e) Two linear laws change slope at a break point located at RBP = -1.20 +/- 0.1 AU before perihelion, and magnitude mBP = 9.4 +/- 0.1. Sublimation is not controlled by water ice. The controlling substance may be CO or CO2 ice. CO2 has been detected spectroscopically. f) The water budget of this comet is calculated. The comet expends 1.88 10^10 kg of water per apparition. A new water-budget age is defined and it is found that WB-AGE = 19 cy vs WB-AGE = 0.65 cy for 1P/Halley and 28 cy for 9P. g) The values of Af{\rho} are calculated on two dates and we find dust production rates of 106 and 37 kg/s. h) The thickness of the layer lost per apparition is calculated, and we find {\Delta}r = 39 m where r is the radius. Since the radius of this comet is r = 570 m, it is found that at the present rate the comet may disappear in only 17 revolutions (~109 y). i) All comets visited by spacecraft are young objects. 103P follows the same trend. It is expected that the surface morphology that will be found in future EPOXI images should be very similar to that of previous comets.