Year: 2025
Type: article
Abstract: The Deep Impact eXtended Mission flyby of comet 103P/Hartley 2 offered a rare opportunity to study a hyperactive comet with high-cadence and high-resolution observations from a fixed vantage point. Using the high signal-to-noise data from the HRI-IR instrument, the H2O and CO2 distributions in the comet’s coma are mapped and quantified over one complete rotation period, revealing two major sources of water: direct sublimation from the nucleus, and sublimation of icy grains in the coma in the antisunward direction. These icy grains contributed 25%–40% of the total water production during the 2010 perihelion passage, quantifying the source of Hartley 2’s hyperactivity. In addition, sublimation from slower-moving icy grains redeposited at the comet’s gravitational low is detectable within 5.2 km of the nucleus, accounting for a few percent of the water production. CO2 production distinctly tracks with the nucleus’s small lobe, which is seen to be active throughout Hartley 2’s rotation even when not illuminated and thus is less dependent on instantaneous solar illumination than water. Differences in CO2 and H2O sources lead to spatially resolved CO2/H2O ratios ranging from 5% to 21% sampled at various times and locations in the coma throughout a single rotation, while the global abundance ratio varies by a factor of ∼2 throughout a single rotation (6%–12%). These observations highlight the complex interaction between solar insolation, comet rotation, and volatile outgassing and suggest that the lobes of Hartley 2 may have different formational or evolutionary origins, implying large-scale mixing in the protoplanetary disk.
Source: The Planetary Science Journal
DOI: 10.3847/psj/adc094
Authors: L. M. Feaga, J. M. Sunshine
Institution: University of Maryland, College Park
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,800
Awards: THE ROSETTA MISSION ACCOMPLISHED AN UNPRECEDENTED AND SUCCESSFUL 2-YEAR STUDY OF COMET 67P/CHURYUMOV-GERASIMENKO AS IT ORBITED THE SUN BEGINNING AT ~3.8 AU BEFORE PERIHELION FOLLOWING IT THROUGH ITS ACTIVE PERIOD AROUND PERIHELION AT 1.24 AU AND THEN OUT AGAIN AFTER PERIHELION AT ~3.8 AU. WHILE MANY THINGS HAVE BEEN LEARNED BY THE FIRST ROUND OF ANALYSES OF THE MEASUREMENTS OBTAINED MUCH IS LEFT TO BE INVESTIGATED IN THE VAST WEALTH OF DATA OBTAINED AND ARCHIVED. WE DEVELOPED A SPHERICAL HARMONICS INVERSION METHOD THAT WAS ORIGINALLY APPLIED TO ROSINA DFMS MASS SPECTROMETER MEASUREMENTS TO OBTAIN POTENTIAL SURFACE ACTIVITY MAPS OF H2O CO2 CO AND O2 ON THE NUCLEUS OF COMET 67P (FOUGERE ET AL. 2016A&B) AVERAGED OVER LARGE TIME SLICES OF THE MISSION. WE DEMONSTRATED SOME SUCCESS IN SYNTHESIZING VIRTIS-M SPECTRAL IMAGES AND VIRTIS-H SPECTRA OF H2O AND CO2 DENSITIES USING THE SURFACE POTENTIAL DISTRIBUTION DERIVED FROM IN SITU MASS SPECTROMETER MEASUREMENTS ALONG WITH OUR FULLY-KINETIC ADAPTIVE MESH PARTICLE SIMULATOR (AMPS) MODEL FOR THE COMA THAT USES THE TECHNIQUE CALLED DIRECT SIMULATION MONTE CARLO. WE HAVE SINCE ADAPTED THE INVERSION METHOD TO INGEST COLUMN DENSITY MAPS AND VALUES FROM IMAGING DATA RATHER THAN IN SITU DENSITY MEASUREMENTS AND ARE ABLE TO DERIVE POTENTIAL SURFACE ACTIVITY MAPS. HERE WE PROPOSE TO ANALYZE A SIGNIFICANT FRACTION OF H2O AND CO2 DISTRIBUTIONS DERIVED FROM VIRTISM SPECTRAL IMAGES AND VIRTIS-H SPECTRA USING SPHERICAL HARMONICS INVERSION SCHEME. THE ONE ADVANTAGE OF VIRTIS REMOTE SENSING MAPS OVER DFMS DENSITIES IS THAT REMOTE SENSING MEASURES THE DISTRIBUTION OF GAS IN COMA VERY CLOSE TO THE NUCLEUS AT KILOMETER AND SUB-KILOMETER SCALES WHEREAS THE MASS SPECTROMETER MEASURES THE DISTRIBUTION OF GAS FAR FROM THE NUCLEUS (10-400 KM) WHERE DETAILED INFORMATION OF THE DISTRIBUTION OF THE SOURCE REGION AT THE NUCLEUS HAS BEEN SMEARED OUT. OUR MAJOR SCIENTIFIC GOALS ARE (1) TO DETERMINE THE POTENTIAL SURFACE ACTIVITY DISTRIBUTIONS OF H2O AND CO2 FROM THE NUCLEUS AT MUCH HIGHER SPATIAL RESOLUTION THAN POSSIBLE FROM MASS SPECTROMETER MEASUREMENTS (2) TO DETERMINE THE CHANGE IN SURFACE ACTIVITY DISTRIBUTION OF H2O AND CO2 AS A FUNCTION OF TIME OVER THE MISSION (3) TO INVESTIGATE THE APPARENT INCONSISTENCY OF WATER ABUNDANCES DURING THE FEW MONTHS AROUND PERIHELION IN MID-2015 BETWEEN MASS SPECTROMETER AND REMOTE SENSING INSTRUMENTS AS CONTRASTED WITH THE CONSISTENCY DURING THE FIRST ONE-THIRD OF THE MISSION FROM RENDEZVOUS THROUGH THE FIRST EQUINOX (4) TO CORRELATE THE DISTRIBUTIONS OF THESE MAJOR VOLATILE COMPONENTS WITH THE MORE STRUCTURED DISTRIBUTIONS OF DUST PRODUCTION AS SEEN IN OSIRIS IMAGES. ALL OF THE DATA FROM VIRTIS AND OSIRIS REQUIRED FOR THIS INVESTIGATION IS ALREADY ARCHIVED IN THE SMALL BODIES NODE OF THE PLANETARY DATA SYSTEM THUS MAKING THIS STUDY APPROPRIATE FOR THE ROSETTA DATA ANALYSIS PROGRAM. THE TEAM INCLUDES INVESTIGATORS AND COLLABORATORS WITH ALL OF THE NECESSARY EXPERTISE INCLUDING ANALYSIS ANALYSIS TOOLS FOR THE DATA IN QUESTION CALIBRATION OF THE DATA AND AN INTIMATE KNOWLEDGE OF ALL THE NECESSARY DETAILS. ANALYSIS TOOLS INCLUDE THE SPHERICAL HARMONICS INVERSION METHOD AND THE AMPS COMET COMA MODEL. TEAM MEMBERS ARE THE EXPERTS IN THE DETAILS OF BOTH THE VIRTIS-M AND VIRTIS-H CHANNELS. WE HAVE EXPERIENCE IN RETRIEVING AND USING OSIRIS IMAGES FROM THE PDS., G5071886669, 103P/HARTLEY 2 WAS STUDIED EXTENSIVELY IN 2010 BY THE EPOXI DISCOVERY MISSION (A'HEARN ET AL. 2011) AND ITS ASSOCIATED GROUND-BASED CAMPAIGN (MEECH ET AL. 2011). THE FLYBY REVEALED ONE OF THE MOST DETAILED VIEWS OF VOLATILE OUTGASSING EVER OBSERVED IN A COMET. EPOXI FOUND ABUNDANT MICRON-SIZED ICY GRAINS AS WELL AS LARGER CHUNKS RELEASED FROM A SMALL BILOBATE NUCLEUS. ALL PREVIOUS IN DEPTH ANALYSES OF EPOXI DATA HAVE FOCUSED ON THE MAJOR VOLATILES: H2O RELEASED IN THE GAS-PHASE FROM THE NUCLEUS AND THE ICY GRAINS IN THE COMA AND CO2 A PLAUSIBLE DRIVER OF THE PRIMARY NUCLEUS ACTIVITY. THIS PROJECT FILLS TWO MAJOR GAPS IN COMPREHENDING THE EPOXI DATA. WE PROPOSE THE FIRST IN DEPTH STUDY OF INTEGRATED INTENSITY AND SPECTRAL CONTENT OF THE ORGANIC EMISSION FEATURE PROMINENT IN EPOXI HRI-IR SPECTROSCOPIC DATA BETWEEN ~3-4 MICRONS. WE ALSO PROPOSE FULL EXAMINATION OF SPATIAL AND TEMPORAL RELATIONSHIPS BETWEEN VOLATILES IN THE COMA OF THIS HYPERACTIVE COMET IN PARTICULAR CO2 AND ORGANIC GASES. ORGANICS WERE NOT ADDRESSED IN PREVIOUS STUDIES AND UNDERSTANDING THEIR COMPOSITION VARIABILITY AND RELATION TO OTHER VOLATILES IS VITAL IN DETERMINING HOW VOLATILES ARE ASSOCIATED IN THE NUCLEUS. OUR GOALS CAN ONLY BE REALIZED UTILIZING COMPLEMENTARY (AND CONTEMPORANEOUS) EPOXI AND HIGH SPECTRAL RESOLUTION GROUND-BASED INFRARED (IR) SPECTRA. THIS PROJECT ADDRESSES VOLATILE ABUNDANCES AND SPATIAL RELATIONSHIPS IN THE COMA OF 103P/HARTLEY 2 IN A SYSTEMATIC INTEGRATED STUDY AT BOTH LOCAL AND GLOBAL SPATIAL SCALES. - A WEALTH OF IR SPECTRAL DATA ACQUIRED CONTEMPORANEOUSLY BY THE EPOXI HRI-IR AND KECK II NIRSPEC INSTRUMENTS ARE PUBLICLY AVAILABLE FOR DIRECT COMPARISON AND SYNERGY. - HIGH SPATIAL RESOLUTION NEAR-NUCLEUS EPOXI DATA CAPTURING ACTIVITY AND VOLATILE RELEASE FROM THE NUCLEUS WILL BE USED TO INVESTIGATE THE DISTRIBUTION OF VOLATILE ORGANICS IN THE INNERMOST COMA THE TEMPORAL VARIABILITY OF THE ORGANIC FEATURE SOURCES OF ORGANIC VOLATILE RELEASE AND THEIR CORRELATION (OR LACK THEREOF) WITH H2O AND CO2. - PREVIOUSLY ANALYZED AND WELL-UNDERSTOOD HIGH SPECTRAL RESOLUTION GROUND-BASED DATA FROM KECK ARE NEEDED TO (1) VALIDATE AND EXTEND FLUORESCENCE MODELS IN ORDER TO ESTABLISH LIMITATIONS IN INTERPRETING LOWER SPECTRAL RESOLUTION EPOXI DATA WITHIN THE INNER COMA AND (2) DETERMINE SPATIAL DISTRIBUTIONS OF GAS ROTATIONAL TEMPERATURE AND COLUMN ABUNDANCE OF VOLATILES IN THE GLOBAL COMA OF HARTLEY 2. THIS PROJECT WILL EXTEND THE SCIENTIFIC RETURN OF AND BROADEN PARTICIPATION IN THE EPOXI MISSION AND PLACE HARTLEY 2 EPOXI RESULTS INTO THE CONTEXT OF THE CONTEMPORANEOUS LARGER FIELD OF VIEW AND MUCH HIGHER SPECTRAL RESOLUTION DATA OBTAINED FROM EARTH UTILIZING THE TWO DATA SETS AS ORIGINALLY DESIGNED. OUR UNIQUELY QUALIFIED TEAM LEVERAGES EXTENSIVE EXPERTISE FROM COMET MISSIONS THE EPOXI HRI-IR ANALYSES OF H2O AND CO2 AND STATE-OF-THE-ART GROUND-BASED SPECTROSCOPY AND MODELING OF COMETS (FEAGA ET AL. 2012 2017; FOUGERE ET AL. 2013; DELLO RUSSO ET AL. 2011; BONEV ET AL. 2013; AND REFERENCES THEREIN).
OpenAlex ID: W4409550684