M. F. A'Hearn's research while affiliated with University of Maryland, College Park and other places
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Publications (524)
The Alice far-UV imaging spectrograph (700-2050 A) acquired over 70,000 spectral images during Rosetta's 2-year escort mission, including over 20,000 in the months surrounding perihelion when the comet activity level was highest. We have developed automated software to fit and remove ubiquitous H, O, C, S, and CO emissions from Alice spectra, along...
Following our previous detection of ubiquitous H2O and O2 absorption against the far-UV continuum of stars located near the nucleus of Comet 67P/Churyumov-Gerasimenko, we present a serendipitously observed stellar occultation that occurred on 2015 September 13, approximately one month after the comet's perihelion passage. The occultation appears in...
This report continues the practice where the IAU Working Group on Cartographic Coordinates and Rotational Elements revises recommendations regarding those topics for the planets, satellites, minor planets, and comets approximately every 3 years. The Working Group has now become a “functional working group” of the IAU, and its membership is open to...
We directly measure twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimate the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around one Pa or less (one to five Pa, when scaled to a metre length)....
Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain. Aims. Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Obser...
On 3 July 2016, several instruments on board ESA's Rosetta spacecraft detected signs of an outburst event on comet 67P, at a heliocentric distance of 3.32 AU from the sun, outbound from perihelion. We here report on the inferred properties of the ejected dust and the surface change at the site of the outburst. The activity coincided with the local...
Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain. Aims. Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Obser...
We report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, using images acquired by the OSIRIS camera onboard Rosetta between August 2014 and March 2015. They are found in consolidated terrains and grouped in localized networks. They are present at all latitudes (from...
The ESA Rosetta spacecraft has been tracking its target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, in close vicinity for over two years. It hosts the OSIRIS instruments: the Optical, Spectroscopic, and Infrared Remote Imaging System composed of two cameras, see e.g. Keller et al. (2007). In some imaging sequences dedicated to observe dust...
We collect observational evidence that supports the scheme of mass transfer on the nucleus of comet 67P/Churyumov-Gerasimenko. The obliquity of the rotation axis of 67P causes strong seasonal variations. During perihelion the southern hemisphere is four times more active than the north. Northern territories are widely covered by granular material t...
We present a statistical analysis of the distribution of large scale topographic features on comet 67P/Churyumov-Gerasimenko. We observe that the cumulative cliff height distribution across the surface follows a power law with a slope equal to -1.69 +- 0.02. When this distribution is studied independently for each region, we find a good correlation...
The Rosetta spacecraft was launched in 2004 and, after several planetary and two asteroid fly-bys, arrived at comet 67P/Churyumov-Gerasimenko in August 2014. After escorting the comet for two years and executing its scientific observations, the mission ended on 30 September 2016 through a touch down on the comet surface. This paper describes how th...
By using the imagery acquired by the OSIRIS-WAC camera, we prepare a high resolution morphological map of the Rosetta Sais final landing site, characterised by an outcropping consolidated terrain unit, a coarse boulder deposit and a fine particle deposit. Thanks to the 0.014 m resolution images, we derive the pebbles/boulders size-frequency distrib...
We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov–Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-sca...
On approach to comet 9P/Tempel 1, Deep Impact observed about a dozen natural outbursts. One of the largest occurred on 2 July 2005 and was also captured by Deep Impact's infrared spectrometer, HRI-IR. HRI-IR operates between 1.05 and 4.86 microns, allowing it to detect H2O (2.67 microns) and CO2 (4.27 microns) emission bands simultaneously. In the...
Observations from Earth-based ground and orbiting telescopes indicate that the Ceres's exosphere has a time-varying water component. Evidence of a transient atmosphere was also detected by Dawn upon its arrival, inferred from the response on the Gamma Ray and Neutron Detector. That atmosphere appeared shortly after the passage of a large enhancemen...
Outbursts occur commonly on comets1 with different frequencies and scales2,3. Despite multiple observations suggesting various triggering processes4,5, the driving mechanism of such outbursts is still poorly understood. Landslides have been invoked6 to explain some outbursts on comet 103P/Hartley 2, although the process required a pre-existing dust...
Waypoints to indefinitely park a deep space SmallSat or CubeSat is a novel solution for opportunistic missions to explore new comets and circumvents mission risk due to launch system delays. Comet apparitions into the inner solar system (<0.4 AU from Earth) are accessible to CubeSat class missions that can return unique data not obtainable from gro...
Waypoints to indefinitely park a deep space SmallSat or CubeSat is a novel solution for opportunistic missions to explore new comets and circumvents mission risk due to launch system delays. Comet apparitions into the inner solar system (<0.4 AU from Earth) are accessible to CubeSat class missions that can return unique data not obtainable from gro...
During its two years mission around comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft had the unique opportunity to follow closely a comet in the most active part of its orbit. Many studies have presented the typical features associated to the activity of the nucleus, such as localized dust and gas jets. Here we report on series of more ene...
We present OSIRIS/NAC observations of decimetre-sized, likely ice-containing aggregates ejected from a confined region on the surface of comet 67P/Churyumov-Gerasimenko. The images were obtained in January 2016 when the comet was at 2 AU from the Sun out-bound from perihelion. We measure the acceleration of individual aggregates through a two-hour...
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and plasma instruments, and one dust collector. At 9:40 a dust cloud develo...
Beginning in March 2014, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the...
Our work focuses on the spectrophotometric analysis of selected terrain and bright patches in the Khonsu region on the comet 67P/Churyumov-Gerasimenko. Despite the variety of geological features, their spectrophotometric properties appear to indicate a similar composition. It is noticeable that the smooth areas in Khonsu possess similar spectrophot...
By using the images acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) and ROLIS (ROsetta Lander Imaging System) cameras, we derive the size- frequency distribution (SFD) of cometary pebbles and boulders covering the size range 0.05- 30.0 m on the Agilkia landing site. The global SFD measured on OSIRIS images, reflec...
The Deep Impact spacecraft observed comet C/2012 S1 (ISON) between 17 January and 10 March 2013 when the comet was ∼5 AU from the Sun. Continuous, high-cadence, images spanning as much as 6 days at a time, and high-cadence IR spectral scans spanning 2 days, represent the most intensive set of observations available from the early part of ISON's app...
Context. Since the orbital insertion of the Rosetta spacecraft, comet 67P/Churyumov-Gerasimenko (67P) has been mapped by OSIRIS camera and VIRTIS spectro-imager, producing a huge quantity of images and spectra of the comet’s nucleus. Aims. The aim of this work is to search for the presence of H2O on the nucleus which, in general, appears very dark...
Aims. The OSIRIS camera on board the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P)’s nucleus since August 2014. Starting in May 2015, the southern hemisphere gradually became illuminated and was imaged for the first time. Here we present the regional morphology of the southern hemisphere, which serves as...
Context. We investigate the formation and evolution of comet nuclei and other trans-Neptunian objects (TNOs) in the solar nebula and primordial disk prior to the giant planet orbit instability foreseen by the Nice model. Aims. Our goal is to determine whether most observed comet nuclei are primordial rubble-pile survivors that formed in the solar n...
The Wide Angle Camera of the OSIRIS instrument on board the Rosetta spacecraft is equipped with several narrowband filters that are centered on the emission lines and bands of various fragment species. These are used to determine the evolution of the production and spatial distribution of the gas in the inner coma of comet 67P with time and helioce...
Aims. We aim to characterize the circular depressions of comet 67P/Churyumov-Gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a Jupiter family comet (JFC). Methods. The images from the Rosetta/OSIRIS science camera experiment are used to construct size freq...
Aims. The OSIRIS camera on board the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P)'s nucleus since August 2014. Starting in May 2015, the southern hemisphere gradually became illuminated and was imaged for the first time. Here we present the regional morphology of the southern hemisphere, which serves as...
Data derived from the reconstruction of the nucleus shape of comet 67P/Churyumov-Gerasimenko (67P) from images of the OSIRIS camera onboard ROSETTA show evidence that the nucleus rotates in complex mode. First, the orientation of the spin axis is not fixed in an inertial reference frame, which suggests a precessing motion around the angular momentu...
The Rosetta spacecraft reached comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) in August 2014 at an heliocentric distance of 3.6 au and was then put in orbit around its nucleus to perform detailed observations. Among the collected data are the images acquired by the OSIRIS instrument up to the perihelion passage of the comet in August 2015, whi...
The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov–Gerasimenko, has been detecting individual dust particles of mass larger than 10−10 kg by means of the GIADA dust collector and the OSIRIS Wide Angle Camera and Narrow Angle Camera since 2014 August and will continue until 2016 September. Detections of single dust particles allow us to...
We analyze the physical properties and dynamical origin of a curved jet of comet 67P/Churyumov-Gerasimenko that was observed repeatedly in several nucleus rotations starting on May 30 and persisting until early August, 2015.Methods. We simulated the motion of dust grains ejected from the nucleus surface under the influence of the gravity and viscou...
Context. Dust jets (i.e., fuzzy collimated streams of cometary material arising from the nucleus) have been observed in situ on all comets since the Giotto mission flew by comet 1P/Halley in 1986, and yet their formation mechanism remains unknown. Several solutions have been proposed involving either specific properties of the active areas or the l...
Aims. The OSIRIS camera onboard the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P)’s nucleus at spatial resolutions down to ~0.17 m/px ever since Aug. 2014. These images have yielded unprecedented insight into the morphological diversity of the comet’s surface. This paper presents an overview of the region...
Context. One of the main aims of the ESA Rosetta mission is to study the origin of the solar system by exploring comet 67P/Churyumov-Gerasimenko at close range. Aims. In this paper we discuss the origin and evolution of comet 67P/Churyumov-Gerasimenko in relation to that of comets in general and in the framework of current solar system formation mo...
Context. Since August 2014, the OSIRIS Narrow Angle Camera (NAC) onboard the Rosetta spacecraft has acquired high spatial resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko, down to the decimeter scale. This paper focuses on the Imhotep region, located on the largest lobe of the nucleus, near the equator. Aims. We map, inventory, a...
The Rosetta mission of the European Space Agency has been orbiting the comet
67P/Churyumov-Gerasimenko (67P) since August 2014 and is now in its escort
phase. A large complement of scientific experiments designed to complete the
most detailed study of a comet ever attempted are onboard Rosetta. We present
results for the photometric and spectrophot...
During September and October 2014, the OSIRIS cameras onboard the ESA Rosetta mission detected millions of single particles. Many of these dust particlesappear as long tracks (due to both the dust proper motion and the spacecraft motion during the exposure time) with a clear brightness periodicity. We interpret the observed periodic features as a r...
Context. We present an investigation of the surface properties of areas on the nucleus of comet 67P/Churyumov-Gerasimenko. Aims. We aim to show that transport of material from one part of the cometary nucleus to another is a significant mechanism that influences the appearance of the nucleus and the surface thermal properties. Methods. We used data...
Context. On 12 November 2014 the European mission Rosetta succeeded in delivering a lander, named Philae, on the surface of one of the smallest, low-gravity and most primitive bodies of the solar system, the comet 67P/Churyumov-Gerasimenko (67P). Aims. The aim of this paper is to provide a comprehensive geomorphological and spectrophotometric analy...
Aims. We study the link between gravitational slopes and the surface morphology on the nucleus of comet 67P/Churyumov-Gerasimenko and provide constraints on the mechanical properties of the cometary material (tensile, shear, and compressive strengths). Methods. We computed the gravitational slopes for five regions on the nucleus that are representa...
Context. During the most recent perihelion passage in 2009 of comet 67P/Churyumov–Gerasimenko, ground–based observations showed an anisotropic dust coma where jet–like features were detected at ∼ 1.3 AU from the Sun. The current perihelion passage is exceptional as the Rosetta spacecraft is monitoring the nucleus activity since March 2014, when a c...
Aims. The Alice far-ultraviolet (FUV) spectrograph onboard Rosetta has, for the first time, imaged the surface of a comet, 67P/Churyumov-Gerasimenko (67P), in the FUV. With spatially resolved data, the nucleus properties are characterized in the FUV, including phase dependence, albedo, and spectral slope. Regional measurements across the nucleus ar...
The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) experiment onboard the Rosetta spacecraft currently orbiting comet 67P/Churyumov-Gerasimenko has yielded unprecedented views of a comet's nucleus. We present here the first ever observations of meter-scale fractures on the surface of a comet. Some of these fractures form polygo...
The complex shape of comet 67P and its oblique rotation axis cause pronounced seasonal effects. Irradiation and hence activity vary strongly. Aims. We investigate the insolation of the cometary surface in order to predict the sublimation of water ice. The strongly varying erosion levels are correlated with the topography and morphology of the prese...
One of the main aims of the ESA Rosetta mission is to study the origin of the
solar system by exploring comet 67P/Churyumov-Gerasimenko at close range. In
this paper we discuss the origin and evolution of comet
67P/Churyumov-Gerasimenko in relation to that of comets in general and in the
framework of current solar system formation models. We use da...
We used the Alice spectrograph onboard the Rosetta comet orbiter spacecraft to observe the surface of comet 67P/Churyumov-Gerasimenko in the extreme and far ultraviolet (EUV/FUV) from 700-2050 Å in mid-August 2014. These observations were before significant EUV/FUV coma signatures were observed by Alice. The resulting coadded spectrum has high sign...
Measurements by ROSINA imply that 67P/ formed very cold. Thus JF comets formed in a much wider region, but one containing the formation of Oort cloud comets.
Context. On 12 November 2014 the European mission Rosetta succeeded in deploying a lander, named Philae, on the surface of one of the smallest, low-gravity and more primitive bodies of the Solar System, the comet 67P/Churyumov-Gerasimenko (67P). Aims. The aim of this paper is to provide a comprehensive geomorphological and spectrophotometric analys...
Context. The complex shape of 67P and its oblique rotation axis cause pronounced seasonal effects. Irradiation and hence activity vary strongly. Aims. We investigate the insolation of the cometary surface in order to predict the sublimation of water ice. The strongly varying erosion levels are correlated with the topography and morphology of the pr...
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...
We performed ultraviolet spectroscopy of Comet ISON with the Hubble Space Telescope.
Comets provide a very different but well understood environment in which to search for DIBs. Observations of occultations by cometary comae have not detected DIBs, but none were very near the nucleus, where the column density of dust is highest. We report here unidentified emission bands, centered at λ4430, very near the nucleus of comet Hyakutake....
C/2012 S1 (ISON) is a dynamically new comet with a sungrazing perihelion
only 1.7 solar radii from the Sun's surface, which makes it unique among
the known comets. The discovery of C/ISON in September 2012 at a
heliocentric distance of ~6 AU is more than one year before its
perihelion in November 2013, allowing a detailed characterization as the
co...
In addition to an unprecedented number of Kreutz sungrazing comets, the
LASCO coronagraphs have discovered some 238 unrelated "sunskirting"
comets over the 12 years from 1996 to 2008. This new class is organized
in several groups, and at least two comets have further been found
periodic. This article presents the photometry and the heliocentric
lig...
Comet C/2012 S1 (ISON) is a dynamically new comet on a sungrazing orbit.
As such, C/ISON represents a unique opportunity to study both the
cosmic-ray-irradiated surface, produced during the comet's long
residence in the Oort cloud, and much deeper layers in the nucleus,
exposed when the comet passes 1.7 solar radii from the Sun's surface at
perihel...
The Deep Impact flyby spacecraft (DI) is currently operating as a remote
observatory, studying bright comets from a different perspective than
can be achieved from Earth. Images are obtained with the Medium
Resolution Imager (MRI) using a broadband CLEAR filter to capture the
continuum, and narrowband filters to capture OH, CN and C2 gas bands
(Far...
The set of comets observed by SOHO and STEREO provides us with a large
(>2500 comets) and unique database for studying cometary properties.
Sungrazing comets are discovered in SOHO or STEREO images on average
every few days, with individual comets typically observable for up to a
few days. We compiled photometry of 23 comets observed simultaneously...
Deep Impact acquired a unique rotational data set during its close flyby
of comet 103/P Hartley 2 (DIXI mission, November 4, 2010). The HRI-IR
spectrometer (1.05-4.85 microns) monitored the coma throughout the
encounter acquiring infrared scans every 2 hr over the 18 hr period
prior to closest approach and every 30 min for 2 days after closest
appr...
In February 2013, the Deep Impact Flyby (DIF) spacecraft observed comet
C/2012 S1 ISON when the comet was ~4.7 AU from the Sun. As expected, the
High Resolution Instrument Infrared Spectrometer (HRI-IR) did not detect
the comet between 1.05 and 4.85 microns, a wavelength range where
ro-vibrational bands of H2O, CO2, and CO, can be
measured simultan...
We present results from SEPPCoN, an on-going Survey of the Ensemble Physical
Properties of Cometary Nuclei. In this report we discuss mid-infrared
measurements of the thermal emission from 89 nuclei of Jupiter-family comets
(JFCs). All data were obtained in 2006 and 2007 with the Spitzer Space
Telescope. For all 89 comets, we present new effective...
CBET 3496 available at Central Bureau for Astronomical Telegrams.
Comet 85P/Boethin was selected as the original comet target for the Deep Impact extended mission, EPOXI. Because this comet had been only observed at two apparitions in 1975 and 1986 and consequently had a large ephemeris error, an early intense recovery effort similar to that of 1P/Halley was undertaken beginning in 2005 using the ESO Very Large T...
Comet missions are changing the paradigm for understanding comet
activity, composition, and the formation of planetesimals in the
protoplanetary disk. Each encounter has shown the diversity of surface
morphologies and new insights into comet chemistry, formation scenarios,
activity mechanisms and geology. Prior to the comet 103P/Hartley 2 EPOXI
enc...
Recent space missions (such as Deep Impact & EPOXI) have provided
spectra from comets of unprecedented spatial resolution of the regions
of the coma nearest the nucleus and demonstrate the need for better
modeling of comae with optical depth effects included. We have developed
a coma model that includes radiative transfer to model comets including...
The target of the NASA DIXI mission, comet 103P/Hartley 2 is in a
non-principal-axis (NPA) rotational state that was observed to be
varying with time. However, there is still no consensus on the specific
NPA rotational state during the 103P/Hartley 2 encounter by DIXI. We
analyze the continuum features observed in ground-based images
bracketing the...
The Deep Impact spacecraft observed comet C/2009 P1 Garradd with the
Medium Resolution Instrument at ∼hourly intervals from 2012 Feb 20
to Mar 7, with additional observations between Mar 25 and Apr 8. Images
were obtained with the broadband CLEAR filter and narrowband CN, OH, C2
and Green Continuum filters. During the time of the observations, the...
We have built a coma model that includes radiative transfer to model
comets including optical depth effects. Recent space missions (e.g. Deep
Impact & EPOXI) have provided spectra from comets of unprecedented
spatial resolution of the regions of the coma near the nucleus and
demonstrate the need for better modeling of comae with optical depth
effec...
The Deep Impact eXtended Investigation (DIXI) to comet 103P/Hartley 2
culminated in a closest approach (CA) of 700 km on November 4th, 2010,
when the comet was at 1.064 astronomical units (AU) from the Sun. In
visible images at closest approach, comet Hartley 2 displays jets off
the end of the smaller lobe of the nucleus and beyond the terminator
a...
We report on space-borne observations of comet C/2009 P1 (Garradd) using
Swift’s UV-Optical Telescope (UVOT). C/2009 P1 is a dynamically
new comet and this is likely its first journey to the inner solar system
since its emplacement in the Oort cloud. It was discovered in 2009 and
clearly exhibited a dust coma as far as 8.5 AU from the Sun. We obser...
In addition to an unprecedented number of Kreutz sungrazing comets, the
LASCO coronagraphs aboard SOHO have discovered some 238 unrelated
"sunskirting" comets from 1996 to 2008. This new family is organized in
several groups, and two comets have further been found periodic. We
present the photometry and the heliocentric light curves of these
sunski...
On 10th July 2010 the Rosetta spacecraft passed within 3160 km of
asteroid 21 Lutetia during which seven instruments attempted to detect
an exosphere. A comparison of the sensitivity is made between the
different instruments based on a simple spherical out-gassing point
source model, which was used to infer that the Lutetia exosphere
production rat...
We have adapted the Coupled Escape Probability method of radiative
transfer calculations for use in asymmetrical spherical situations and
applied it to modeling molecular emission spectra of potentially
optically thick cometary comae.
Recent space missions (e.g. Deep Impact & EPOXI) have provided
spectra from comets of unprecedented spatial resolu...
Comet 103P/Hartley 2 had a very close approach to Earth and was
successfully encountered by the EPOXI mission in 2010. We observed the
comet with the Kitt Peak 2.1m telescope September 1-3, September 30 -
October 4, November 2-8, and December 11-15 with broadband R and
narrowband HB comet filters. Results on the structures seen in the CN
coma were...
We present observations of a statistically-significant number of
Jupiter-family cometary nuclei as part of SEPPCoN (Survey of the
Ensemble Physical Properties of Cometary Nuclei). We present preliminary
results on distributions of albedos and shapes.
The NASA Planetary Data System contains a large range of asteroid,
comet, and other small bodies data obtained from spacecraft and
ground-based facilities. The Small Bodies Data Ferret is a tool for
searching and accessing this data.
We present and analysis of the excited spin state of comet 103P/Hartley
and show how the total angular momentum varies through the DIXI
encounter.
We present the Coupled Escape Probability method of radiative transfer
which we have adapted to Asymmetric Spherical situations and some
results of applying it to modeling molecular emission spectra of
optically thick cometary comae e.g. near nuclei.
We present observations of the gas-rich comet C/2009 P1 (Garradd) made
in January 2012 with two of the spectrographs on the Hubble Space
Telescope. Our preliminary analysis gives an abundance of CO relative
to water of ~20%.
CBET 3090 available at Central Bureau for Astronomical Telegrams.
CBET 3090 available at Central Bureau for Astronomical Telegrams.
Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which...
Citations
... High resolution OSIRIS images and the VIRTIS spectroscopic analysis show small-scale areas holding ice-containing material (icy and ice-rich patches) which can be localized on the spatial scale of metres up to several tens of metres. 27,50,51,53 With areas between 4 × 10 5 m 2 and 1.6 × 10 6 m 2 , the consideration Figure 15: Observed gas production P s (integrated emission rates) over the entire 2015 apparition for the 10 patches in Table 2. Mass-fraction of a species P s / P r is reflected by the segment size in the bar. On top of each bar, the sum (over the species) per area P r /|A| [kg/m 2 ] is given. ...
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... Structurally, the head is thought to contain some inner layering, whose signature is given by the 900-m-high vertical cliff characterized by horizontal lineaments aligned with small terraces, called the region Hathor [269]. The minimum tensile strength needed to support overhanging cliffs on the surface is very small (1-5 Pa, when scaled to a meter length) and relatively homogeneous [270] if considering only static stresses and not dynamic stresses owing to cometary activities or impacts. The presence of some eroded material at the base of most overhangs and the observed/implied collapse suggest that the true material strength is close to these lower limits. ...
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... For that purpose, we use the open-source PlanetProfile framework (Vance et al. 2018b;Styczinski et al. 2023a) to generate a Europa interior model, denoted E1. The model has a solid metallic core, rocky mantle, subsurface ocean, and ice shell fitting the bulk properties inferred from Galileo data: a planetary radius of 1560.8 km (Archinal et al. 2018), mass of 4.8 × 10 22 kg (Hussmann et al. 2006), and moment of inertia of 0.346 ± 0.005 (Anderson et al. 2019). We create a Europa liquid core model, denoted E2, by adjusting the E1 model to mimic a liquid core. ...
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... An overview of measurements of tensile and compressive strengths for cometary materials can be found in Biele et al. (2022). The analysis of a cliff collapse on comet 67P/Churyumov-Gerasimenko (hereafter comet 67P) derived tensile strength values on the order of 1 Pa (Attree et al. 2018b). From the observation of breakups of cometary meteors with a size of millimetres in Earth's atmosphere, the tensile strength on small length scale can be estimated. ...
... 67P displayed numerous localized dust and gas jet features (e.g. Agarwal et al. 2017 ;Bockel ée-Morvan et al. 2017 ;Lin et al. 2017 ;Schmitt et al. 2017 ), offering a unique opportunity to investigate these outburst phenomena across extended time frames and in exceptional detail. Skorov et al. ( 2016 ) formulated a physical model to explain outbursts observed within fractured terrains on comet 67P near perihelion. ...
![[object Object]](https://i1.rgstatic.net/ii/profile.image/939280109162502-1600953237886_Q64/Paul-Feldman-5.jpg)
... On comet 67P, several cracks on the metre scale were observed (El-Maarry et al. 2015). They could be attributed to sintering processes, combined with thermal fracturing (Auger et al. 2018;Höfner et al. 2017). Attree et al. (2018a) modelled the stresses induced by temperature changes and found that stresses can penetrate to typical depths of ∼ 25 cm. ...
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... Actually, similar processes, but on a much larger scale, could play a role in 67P's web of surface fractures. They gain higher temperatures and sublimation rates compared to flat terrains (Höfner et al. 2017). It is worth mentioning that, higher ice abundances would result in increased albedo (Fornasier et al. 2017), which could reduce the insolation absorbed by the nucleus. ...
... Solar System long-period comets, that is, comets with an orbital period greater than hundreds or even thousands of years, are particularly interesting from a scientific point of view [4]. Indeed, it is well known how repeated passages of a comet near the Sun can alter the surface of its nucleus (or even destroy the comet [5]), as was demonstrated in the case of comet 67P/Churyumov-Gerasimenko [6]. Long-period comets, on the other hand, are not contaminated by these natural effects because they have ideally never previously entered the inner region of the Solar System and, therefore, are likely to retain internally unaltered information about the formation and evolution of our planetary system [7]. ...
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... In recent years, asteroid detection is becoming an attractive research field. Human-made spacecraft have visited many asteroids by flying inspection (Brownlee et al., 2003), surrounding (Rayman and Patel, 2010), or landing (Barthelemy et al., 2018). Compared with the previous two methods, landing detection could utilize the drilling method, which is widely used in existing probes, to obtain soil/rock samples on a particular location for in situ analysis or sample return (Chen et al., 2016). ...
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... To alleviate this issue, automated methods can be considered to serve as initial guidance and obtain the first assessment of the surface morphology. Examples of automated determination of morphological units on comet 67P/Churyumov-Gerasimenko can be found in Vincent et al. (2017) (cliffs) and Thomas et al. (2018) (smooth units). Both studies are based on the analysis of the tri-dimensional mesh of the comet's shape model. ...
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