146 research outputs found
The Evolving Activity of the Dynamically Young Comet C/2009 P1 (Garradd)
We used the UltraViolet-Optical Telescope on board Swift to observe the
dynamically young comet C/2009 P1 (Garradd) from a heliocentric distance of 3.5
AU pre-perihelion until 4.0 AU outbound. At 3.5 AU pre-perihelion, comet
Garradd had one of the highest dust-to-gas ratios ever observed, matched only
by comet Hale-Bopp. The evolving morphology of the dust in its coma suggests an
outburst that ended around 2.2 AU pre-perihelion. Comparing slit-based
measurements and observations acquired with larger fields of view indicated
that between 3 AU and 2 AU pre-perihelion a significant extended source started
producing water in the coma. We demonstrate that this source, which could be
due to icy grains, disappeared quickly around perihelion. Water production by
the nucleus may be attributed to a constantly active source of at least 75
km, estimated to be more than 20 percent of the surface. Based on our
measurements, the comet lost kg of ice and dust during this
apparition, corresponding to at most a few meters of its surface.Even though
this was likely not Garradd's first passage through the inner solar system, the
activity of the comet was complex and changed significantly during the time it
was observed
Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2
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.Comment: 51 pages, 12 figures, accepted for publication in Icaru
Uncorrelated Volatile Behavior during the 2011 Apparition of Comet C/2009 P1 Garradd
The High Resolution Instrument Infrared Spectrometer (HRI-IR) on board the Deep Impact Flyby spacecraft detected H2O, CO2, and CO in the coma of the dynamically young Oort Cloud comet C/2009 P1 (Garradd) post-perihelion at a heliocentric distance of 2 AU. Production rates were derived for the parent volatiles, Q_(H2O) = 4.6 ± 0.8 × 10^(28), Q_(CO2) = 3.9 ± 0.7 × 10^(27), and Q_(CO) = 2.9 ± 0.8 × 10^(28) molecules s^(–1), and are consistent with the trends seen by other observers and within the error bars of measurements acquired during a similar time period. When compiled with other observations of Garradd's dominant volatiles, unexpected behavior was seen in the release of CO. Garradd's H_2O outgassing, increasing and peaking pre-perihelion and then steadily decreasing, is more typical than that of CO, which monotonically increased throughout the entire apparition. Due to the temporal asymmetry in volatile release, Garradd exhibited the highest CO to H_2O abundance ratio ever observed for any comet inside the water snow line at ~60% during the HRI-IR observations. Also, the HRI-IR made the only direct measurement of CO_2, giving a typical cometary abundance ratio of CO_2 to H_2O of 8% but, with only one measurement, no sense of how it varied with orbital position
First detection of CO emission in a Centaur: JWST NIRSpec observations of 39P/Oterma
Centaurs are minor solar system bodies with orbits transitioning between
those of Trans-Neptunian Scattered Disk objects and Jupiter Family comets.
39P/Oterma is a frequently active Centaur that has recently held both Centaur
and JFC classifications and was observed with the JWST NIRSpec instrument on
2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO
gas emission was detected in a Centaur, with a production rate of Q =
(5.96 0.80) 10 molecules s. This is the lowest
detection of CO of any Centaur or comet. CO and HO were not detected
down to constraining upper limits. Derived mixing ratios of Q/Q
2.03 and Q/Q 0.60 are consistent with CO
and/or CO outgassing playing large roles in driving the activity, but not
water, and show a significant difference between the coma abundances of
29P/Schwassmann-Wachmann 1, another Centaur at a similar heliocentric distance,
which may be explained by thermal processing of 39P's surface during its
previous Jupiter-family comet orbit. To help contextualize the JWST data we
also acquired visible CCD imaging data on two dates in July (Gemini North) and
September (Lowell Discovery Telescope) 2022. Image analysis and photometry
based on these data are consistent with a point source detection and an
estimated effective nucleus radius of 39P in the range of 2.21 to
2.49~km
Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space Telescope
The asteroid (21) Lutetia is the target of a planned close encounter by the
Rosetta spacecraft in July 2010. To prepare for that flyby, Lutetia has been
extensively observed by a variety of astronomical facilities. We used the
Hubble Space Telescope (HST) to determine the albedo of Lutetia over a wide
wavelength range, extending from ~150 nm to ~700 nm. Using data from a variety
of HST filters and a ground-based visible light spectrum, we employed synthetic
photometry techniques to derive absolute fluxes for Lutetia. New results from
ground-based measurements of Lutetia's size and shape were used to convert the
absolute fluxes into albedos. We present our best model for the spectral energy
distribution of Lutetia over the wavelength range 120-800 nm. There appears to
be a steep drop in the albedo (by a factor of ~2) for wavelengths shorter than
~300 nm. Nevertheless, the far ultraviolet albedo of Lutetia (~10%) is
considerably larger than that of typical C-chondrite material (~4%). The
geometric albedo at 550 nm is 16.5 +/- 1%. Lutetia's reflectivity is not
consistent with a metal-dominated surface at infrared or radar wavelengths, and
its albedo at all wavelengths (UV-visibile-IR-radar) is larger than observed
for typical primitive, chondritic material. We derive a relatively high FUV
albedo of ~10%, a result that will be tested by observations with the Alice
spectrograph during the Rosetta flyby of Lutetia in July 2010.Comment: 14 pages, 2 tables, 8 figure
- …