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Comet 103P/Hartley 2 is at Opposition (2.500 AU) on the 17th March 2018.



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Comet 103P/Hartley 2 makes its closest approach to the Earth (2.438 AU) on the 25th February 2018.



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Title: Hyperactivity in 103P/Hartley 2: Chunks from the sub-surface in Type IIa jet regions
Author: Michael Belton

We analyse the observed radial distribution of column densities of water-ice particulates embedded in the primary jet region of 103Ps inner coma at altitudes between 439 and 1967 m (Protopapa et al, 2014) and determine the speed and acceleration of particles and their mass flow within the filaments of the jet. This is done by applying a CO2 driven type IIa jet model proposed by Belton (2010) The model utilizes water-ice particles dislodged in the source regions of the jet filaments and accelerated by CO2 to explain the radial distribution of water-ice particulates. We provide an explanation for the remarkably different radial distribution of refractory dust particles by hypothesizing that the majority of the dust originates directly from the nucleus surface in interfilament regions of the jet complex and is accelerated by H2O. Our model provides a mass-flow of water from the J1 jet complex that is 40 times greater than the constant speed sublimation model discussed by Protopapa et al. but is still too small to explain the hyperactivity of the comet. Speeds in the flow are increased by a factor up to 20 over those found by Protopapa et al. To account for the hyperactivity, most of the mass dislodged in the filament source regions must be in weakly accelerated large chunks that achieve only low speeds en route to the region of observation. These chunks soon leave the filamentary jet structure due to the rotation of the nucleus and do not contribute to the column densities observed at higher altitudes in the jet filaments.

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Comet 103P/Hartley 2 is at Opposition (4.163 AU) in the constellation Libra on the 22nd May 2015 

Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r    Elong.  Phase   Mag
2015 05 21    16 00 14.1 -14 20 44   4.1662  5.1733   173.7     1.2
2015 05 22    15 59 32.6 -14 17 45   4.1627  5.1702   173.9     1.2
2015 05 23    15 58 51.2 -14 14 48   4.1595  5.1671   173.8     1.2
2015 05 24    15 58 09.6 -14 11 51   4.1567  5.1641   173.5     1.3
2015 05 25    15 57 28.1 -14 08 56   4.1542  5.1610   173.1     1.4
2015 05 26    15 56 46.5 -14 06 01   4.1519  5.1579   172.5     1.5
2015 05 27    15 56 05.0 -14 03 07   4.1500  5.1548   171.8     1.6
2015 05 28    15 55 23.6 -14 00 15   4.1484  5.1517   171.0     1.8
2015 05 29    15 54 42.2 -13 57 24   4.1472  5.1486   170.2     1.9
2015 05 30    15 54 00.9 -13 54 34   4.1462  5.1455   169.3     2.1
2015 05 31    15 53 19.7 -13 51 46   4.1455  5.1424   168.3     2.3


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Title: Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2
Author: Silvia Protopapa, Jessica M. Sunshine, Lori M. Feaga, Michael S. P. Kelley, Michael F. A' Hearn, Tony L. Farnham, Olivier Groussin, Sebastien Besse, Frederic Merlin, Jian-Yang Li

On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05-4.83 micron wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ~10 kilometers of the coma collected 7 minutes and 23 minutes after closest approach. The extracted reflectance spectra include well-defined absorption bands near 1.5, 2.0, and 3.0 micron consistent in position, bandwidth, and shape with the presence of water ice grains. Using Hapke's radiative transfer model, we characterize the type of mixing (areal vs. intimate), relative abundance, grain size, and spatial distribution of water ice and refractories. Our modeling suggests that the dust, which dominates the innermost coma of Hartley 2 and is at a temperature of 300K, is thermally and physically decoupled from the fine-grained water ice particles, which are on the order of 1 micron in size. The strong correlation between the water ice, dust, and CO2 spatial distribution supports the concept that CO2 gas drags the water ice and dust grains from the nucleus. Once in the coma, the water ice begins subliming while the dust is in a constant outflow. The derived water ice scale-length is compatible with the lifetimes expected for 1-micron pure water ice grains at 1 AU, if velocities are near 0.5 m/s. Such velocities, about three order of magnitudes lower than the expansion velocities expected for isolated 1-micron water ice particles [Hanner, 1981; Whipple, 1951], suggest that the observed water ice grains are likely aggregates.

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Title: A Distribution of Large Particles in the Coma of Comet 103P/Hartley 2
Authors: Michael S. Kelley, Don J. Lindler, Dennis Bodewits, Michael F. A'Hearn, Carey M. Lisse, Ludmilla Kolokolova, Jochen Kissel, Brendan Hermalyn

The coma of comet 103P/Hartley 2 has a significant population of large particles observed as point sources in images taken by the Deep Impact spacecraft. We measure their spatial and flux distributions, and attempt to constrain their composition. The flux distribution of these particles implies a very steep size distribution with power-law slopes ranging from -6.6 to -4.7. The radii of the particles extend up to 20 cm, and perhaps up to 2 m, but their exact sizes depend on their unknown light scattering properties. We consider two cases: bright icy material, and dark dusty material. The icy case better describes the particles if water sublimation from the particles causes a significant rocket force, which we propose as the best method to account for the observed spatial distribution. Solar radiation is a plausible alternative, but only if the particles are very low density aggregates. If we treat the particles as mini-nuclei, we estimate they account for <16-80% of the comet's total water production rate (within 20.6 km). Dark dusty particles, however, are not favoured based on mass arguments. The water production rate from bright icy particles is constrained with an upper limit of 0.1 to 0.5% of the total water production rate of the comet. If indeed icy with a high albedo, these particles do not appear to account for the comet's large water production rate.

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The Deep Impact spacecraft, EPOXI, made a close approach (700 kilometres) of Comet 103P/Hartley 2 at 14:00 UTC on the 4th November, 2010.



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Title: Activity of comet 103P/Hartley 2 at the time of the EPOXI mission fly-by
Authors: Gian Paolo Tozzi, Elena Mazzotta Epifani, Olivier R. Hainaut, Patrizio Patriarchi, Luisa Lara, John Robert Brucato, Hermann Boehnhardt, Marco Del Bó, Javier Licandro, Karen Meech, Paolo Tanga

Comet 103P/Hartley~2 was observed on Nov. 1-6, 2010, coinciding with the fly-by of the space probe EPOXI. The goal was to connect the large scale phenomena observed from the ground, with those at small scale observed from the spacecraft. The comet showed strong activity correlated with the rotation of its nucleus, also observed by the spacecraft. We report here the characterisation of the solid component produced by this activity, via observations of the emission in two spectral regions where only grain scattering of the solar radiation is present. We show that the grains produced by this activity had a lifetime of the order of 5 hours, compatible with the spacecraft observations of the large icy chunks. Moreover, the grains produced by one of the active regions have a very red colour. This suggests an organic component mixed with the ice in the grains.

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Title: The Highly Unusual Outgassing of Comet 103P/Hartley 2 from Narrowband Photometry and Imaging of the Coma
Authors: Matthew M. Knight, David G. Schleicher

We report on photometry and imaging of Comet 103P/Hartley 2 obtained at Lowell Observatory from 1991 through 2011. We acquired photoelectric photometry on two nights in 1991, four nights in 1997/98, and 13 nights in 2010/11. We observed a strong secular decrease in water and all other observed species production in 2010/11 from the 1991 and 1997/98 levels. We see evidence for a strong asymmetry with respect to perihelion in the production rates of our usual bandpasses, with peak production occurring ~10 days post-perihelion and production rates considerably higher post-perihelion. The composition was "typical", in agreement with the findings of other investigators. We obtained imaging on 39 nights from 2010 July until 2011 January. We find that, after accounting for their varying parentage and lifetimes, the C2 and C3 coma morphology resemble the CN morphology we reported previously. These species exhibited an hourglass shape in October and November, and the morphology changed with rotation and evolved over time. The OH and NH coma morphology showed hints of an hourglass shape near the nucleus, but was also enhanced in the anti-sunward hemisphere. This tailward brightness enhancement did not vary significantly with rotation and evolved with the viewing geometry. We conclude that all five gas species likely originate from the same source regions on the nucleus, but that OH and NH were derived from small grains of water and ammonia ice that survived long enough to be affected by radiation pressure and driven in the anti-sunward direction. We detected the faint, sunward facing dust jet reported by other authors, and did not detect a corresponding gas feature. This jet varied little during a night but exhibited some variations from night to night, suggesting it is located near the total angular momentum vector.

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Comet's water 'like that of Earth's oceans'

Comet Hartley 2 contains water more like that found on Earth than prior comets seem to have, researchers say.
A study using the Herschel space telescope aimed to measure the quantity of deuterium, a rare type of hydrogen, present in the comet's water.
The comet had just half the amount of deuterium seen in comets.
The result, published in Nature, hints at the idea that much of the Earth's water could have initially came from cometary impacts.

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