Exocomets from a Solar System Perspective

Exocomets are small bodies releasing gas and dust which orbit stars other than the Sun. Their existence was first inferred from the detection of variable absorption features in stellar spectra in the late 1980s using spectroscopy. More recently, they have been detected through photometric transits from space, and through far-IR/mm gas emission within debris disks. As (exo)comets are considered to contain the most pristine material accessible in stellar systems, they hold the potential to give us information about early stage formation and evolution conditions of extra solar systems. In the solar system, comets carry the physical and chemical memory of the protoplanetary disk environment where they formed, providing relevant information on processes in the primordial solar nebula. The aim of this paper is to compare essential compositional properties between solar system comets and exocomets to allow for the development of new observational methods and techniques. The paper aims to highlight commonalities and to discuss differences which may aid the communication between the involved research communities and perhaps also avoid misconceptions. The compositional properties of solar system comets and exocomets are summarized before providing an observational comparison between them. Exocomets likely vary in their composition depending on their formation environment like solar system comets do, and since exocomets are not resolved spatially, they pose a challenge when comparing them to high fidelity observations of solar system comets. Observations of gas around main sequence stars, spectroscopic observations of “polluted” white dwarf atmospheres and spectroscopic observations of transiting exocomets suggest that exocomets may show compositional similarities with solar system comets. The recent interstellar visitor 2I/Borisov showed gas, dust and nuclear properties similar to that of solar system comets. This raises the tantalising prospect that observations of interstellar comets may help bridge the fields of exocomet and solar system comets

The Main Belt Comets and ice in the Solar System

We review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called Main Belt Comets (MBCs). We summarise the evidence for water throughout the Solar System, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. We review progress in the first decade of study of MBCs, including observations, modelling of ice survival, and discussion on their origins. We then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies

The Castalia mission to Main Belt Comet 133P/Elst-Pizarro

We describe Castalia, a proposed mission to rendezvous with a Main Belt Comet (MBC), 133P/Elst-Pizarro. MBCs are a recently discovered population of apparently icy bodies within the main asteroid belt between Mars and Jupiter, which may represent the remnants of the population which supplied the early Earth with water. Castalia will perform the first exploration of this population by characterising 133P in detail, solving the puzzle of the MBC's activity, and making the first in situ measurements of water in the asteroid belt. In many ways a successor to ESA's highly successful Rosetta mission, Castalia will allow direct comparison between very different classes of comet, including measuring critical isotope ratios, plasma and dust properties. It will also feature the first radar system to visit a minor body, mapping the ice in the interior. Castalia was proposed, in slightly different versions, to the ESA M4 and M5 calls within the Cosmic Vision programme. We describe the science motivation for the mission, the measurements required to achieve the scientific goals, and the proposed instrument payload and spacecraft to achieve these

Thermal evolution and differentiation of Edgeworth-Kuiper belt objects

The region beyond Neptune's orbit is populated by numerous bodies with semimajor axes from 31 to 48 AU. This region, known as the Kuiper belt, should contain primitive bodies, perhaps among the most primitive objects in the solar system. These bodies could be remnants of the solar system formation. They seem to be dark, volatile-rich objects showing a strong relationship with comets: the Kuiper belt is probably the source of most short-period comets and Centaurs. The Kuiper belt objects (KBOs) could still contain ices and organic compounds in unaltered proportions with respect to those of their formation. Thermal models of bodies moving in Kuiper belt orbits have been developed to follow their evolution and differentiation and to better understand the relations between them and the short-period comets and Centaurs. In these models, we assume that KBOs are porous bodies composed of ices and dust. The solar energy is very low, between 30 and 50 AU, and radiogenic heating becomes a nonnegligible source of energy for differentiation. The radioactive elements, if they exist in sufficient quantity, may modify the original composition of cometary nuclei. In the models reported here, we have assumed that the radiogenic elements stored in the refractory component are K-40, Th-232,U-235, and U-238, in meteoritic proportions. In some models, we have also included the short-lived radio nuclide Al-26. The aim of this work is to see how an undifferentiated Kuiper belt body can change its internal structure under the combined effect of radiogenic heating and solar irradiation. Moderate heating can permit the sublimation of the most volatile ices both from the interior and from the surface, depending on the dominant heat source. The main result is that Kuiper belt objects can be strongly volatile depleted. From the surface down to several hundred meters below the surface, the most volatile ices (like CO) can be completely absent

Comet P/Gehrels 3: spectroscopic observations and nucleus models

In the framework of an observational campaign for increasing the knowledge on the relationship between cometary nuclei and asteroids, we performed spectroscopic observations of P/Gehrels 3. The Jupiter family comet P/Gehrels 3 moves on a particular orbit, with a very high Tisserand invariant with respect to Jupiter, that makes the encounters with the planet very effective. This implies that the comet spends part of its life as a temporary satellite of Jupiter, on an orbit that shows similarity with those of Trojans. This comet has been observed when it was far from the Sun, with the aim to acquire data on the nucleus status. In order to study from a theoretical point of view the possible status and evolution of a body on this orbit we have developed different nucleus models using a numerical code for the thermal evolution of the nucleus

High dose idarubicine, busulphan e melphalan as conditioning for autilogous blood stem cell transplantation in multiple myeloma. A feasibility study

Extensive studies have tested the clinical impact of double and triple sequential transplants as front-line therapy in MM, following the suggestion that dose escalation can overcome the marked drug resistance characteristic of this disease, but the superiority of such approaches vs one single transplant has still to be demonstrated. The aim of our study was to evaluate the feasibility and efficacy of high-dose idarubicine intensification of a standard busulphan-melphalan conditioning regimen in MM. Twenty-eight patients (median age 55 years) with sensitive disease received PBSCT after high-dose idarubicine combined with busulphan and melphalan and followed by s.c. rhG-CSF until PMN recovery. The most severe toxicity was represented by oral mucositis which resolved with hemopoietic reconstitution. Overall response and CR rate were 52% and 40%, respectively. Currently, 36 patients are alive and 19 are progression-free a median of 20 months (12-36) from transplant. The 3-year projected probability of progression-free survival for patients transplanted after first-line treatment is 60%. The combination of Ida/Bu/Melph appears a promising alternative regimen for PBSCT in myeloma, with low transplant-related toxicity and fast hematological recovery. Long-term follow-up and a prospective randomized study, now ongoing, will probably clarify whether an idarubicine-intensified regimen will result in superior outcomes to conventional conditioning and even be comparable to a double consecutive transplant program

Simulations using terrestrial geological analogues to assess interpretability of potential geological feature of the Hermean surface restituted by the STereo imaging Camera of the SIMBIO-SYS package (BepiColombo mission).

The BepiColombo space mission is one of the European Space Agency\u2019s cornerstone projects; it is planned for launch in 2013 to study the planet Mercury. One of the imaging instruments of BepiColombo is a STereo Camera (STC), whose main scientific objective is the global stereo mapping of the entire surface of Mercury. STC will permit the generation of a Digital Terrain Model (DTM) of Mercury\u2019s surface, improving the interpretation of morphological features at different scales and clarifying the stratigraphic relationships between different geological units. To evaluate the effectiveness of the STC-derived DTM for geological purposes, a series of simulations has been performed to find out to what extent the errors expected in the DTM may prevent the correct classification and interpretation of geological features. To meet this objective, Earth analogues (a crater, a lava cone and an endogenous dome) of likely components of the Hermean surface, small enough to be near the detection limit of the STC, were selected and a photorealistic three-dimensional (3D) model of each feature was generated using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Stereoscopic pairs of synthetic images of each feature were then generated from the 3D model at different locations along the BepiColombo orbit. For each stereo pair, the corresponding Hermean DTM was computed using image correlation and compared to the reference data to assess the loss of detail and interpretability. Results show that interpretation and quantitative analysis of simple craters morphologies and small volcanic features should be possible all along the periherm orbit arc. At the apoherm only the larger features can be unequivocally distinguished, but they will be reconstructed to a poor approximation

VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: Spectral properties and color temperature variability with phase and elevation

We analyze 2&ndash;5&nbsp;&mu;m spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distances&nbsp;rh&nbsp;= 1.24&ndash;1.55 AU. The 2&ndash;2.5&nbsp;&mu;m color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained at&nbsp;&alpha;&nbsp;= 90&deg; solar phase angle show an increase in bolometric albedo (0.05&ndash;0.14) with increasing altitude (0.5&ndash;8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50&deg;&ndash;120&deg;, phase reddening is significant (0.031%/100 nm deg&minus;1) for a mean color of 2%/100 nm at&nbsp;&alpha;&nbsp;= 90&deg;, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg&minus;1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (&alpha;&nbsp;= 90&deg;), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow a&nbsp;rh&minus;0.6&nbsp;variation in the&nbsp;rh&nbsp;= 1.24&ndash;1.5 AU range, which is close to the expected&nbsp;rh&minus;0.5&nbsp;value.</p