Did Fomalhaut, HR 8799, and HL Tauri Form Planets via the Gravitational Instability? Placing Limits on the Required Disk Masses

Disk fragmentation resulting from the gravitational instability has been proposed as an efficient mechanism for forming giant planets. We use the planet Fomalhaut b, the triple-planetary system HR 8799, and the potential protoplanet associated with HL Tau to test the viability of this mechanism. We choose the above systems since they harbor planets with masses and orbital characteristics favored by the fragmentation mechanism. We do not claim that these planets must have formed as the result of fragmentation, rather the reverse: if planets can form from disk fragmentation, then these systems are consistent with what we should expect to see. We use the orbital characteristics of these recently discovered planets, along with a new technique to more accurately determine the disk cooling times, to place both lower and upper limits on the disk surface density--and thus mass--required to form these objects by disk fragmentation. Our cooling times are over an order of magnitude shorter than those of Rafikov (2005),which makes disk fragmentation more feasible for these objects. We find that the required mass interior to the planet's orbital radius is ~0.1 Msun for Fomalhaut b, the protoplanet orbiting HL Tau, and the outermost planet of HR 8799. The two inner planets of HR 8799 probably could not have formed in situ by disk fragmentation.Comment: 5 pages, 1 figure, accepted for publication in ApJ

Geodynamics and Rate of Volcanism on Massive Earth-like Planets

We provide estimates of volcanism versus time for planets with Earth-like composition and masses from 0.25 to 25 times Earth, as a step toward predicting atmospheric mass on extrasolar rocky planets. Volcanism requires melting of the silicate mantle. We use a thermal evolution model, calibrated against Earth, in combination with standard melting models, to explore the dependence of convection-driven decompression mantle melting on planet mass. Here we show that (1) volcanism is likely to proceed on massive planets with plate tectonics over the main-sequence lifetime of the parent star; (2) crustal thickness (and melting rate normalized to planet mass) is weakly dependent on planet mass; (3) stagnant lid planets live fast (they have higher rates of melting than their plate tectonic counterparts early in their thermal evolution) but die young (melting shuts down after a few Gyr); (4) plate tectonics may not operate on high mass planets because of the production of buoyant crust which is difficult to subduct; and (5) melting is necessary but insufficient for efficient volcanic degassing - volatiles partition into the earliest, deepest melts, which may be denser than the residue and sink to the base of the mantle on young, massive planets. Magma must also crystallize at or near the surface, and the pressure of overlying volatiles must be fairly low, if volatiles are to reach the surface. If volcanism is detected in the Tau Ceti system, and tidal forcing can be shown to be weak, this would be evidence for plate tectonics.Comment: Revised version, accepted by Astrophysical Journa

Evolutionary Tracks of Trapped, Accreting Protoplanets: the Origin of the Observed Mass-Period Relation

The large number of observed exoplanets ($\gtrsim$ 700) provides important constraints on their origin as deduced from the mass-period diagram of planets. The most surprising features in the diagram are 1) the (apparent) pile up of gas giants at a period of $\sim 500$ days ($\sim1$ AU) and 2) the so-called mass-period relation which indicates that planetary mass is an increasing function of orbital period. We construct the evolutionary tracks of growing planets at planet traps in evolving protoplanetary disks and show that they provide a good physical understanding of how these observational properties arise. The fundamental feature of our model is that inhomogeneities in protoplanetary disks give rise to multiple (up to 3) trapping sites for rapid (type I) planetary migration of planetary cores. The viscous evolution of disks results in the slow radial movement of the traps and their cores from large to small orbital periods. In our model, the slow inward motion of planet traps is coupled with the standard core accretion scenario for planetary growth. As planets grow, type II migration takes over. Planet growth and radial movement are ultimately stalled by the dispersal of gas disks via photoevaporation. Our model makes a number of important predictions: that distinct sub-populations of planets that reflect the properties of planet traps where they have grown result in the mass-period relation; that the presence of these sub-populations naturally explains a pile-up of planets at $\sim 1$ AU; and that evolutionary tracks from the ice line do put planets at short periods and fill an earlier claimed "planet desert" - sparse population of planets in the mass-semi-major axis diagram.Comment: 20 pages, 11 figures, 9 tables; accepted for publication in ApJ. No change in our conclusions while more discussion is added for supporting the importance of planet trap

The Growth & Migration of Jovian Planets in Evolving Protostellar Disks with Dead Zones

The growth of Jovian mass planets during migration in their protoplanetary disks is one of the most important problems that needs to be solved in light of observations of the exosolar planets. Studies of the migration of planets in standard gas disk models routinely show that migration is too fast to form Jovian planets, and that such migrating planetary cores generally plunge into the central stars in less than a Myr. In previous work, we have shown that a poorly ionized, less viscous region in a protoplanetary disk called a dead zone slows down the migration of fixed-mass planets. In this paper, we extend our numerical calculations to include dead zone evolution along with the disk, as well as planet formation via accretion of rocky and gaseous materials. Using our symplectic-integrator-gas dynamics code, we find that dead zones, even in evolving disks wherein migrating planets grow by accretion, still play a fundamental role in saving planetary systems. We demonstrate that Jovian planets form within 2.5 Myr for disks that are ten times more massive than a minimum mass solar nebula (MMSN) with an opacity reduction and without slowing down migration artificially. Our simulations indicate that protoplanetary disks with an initial mass comparable to the MMSN only produce Neptunian mass planets. We also find that planet migration does not help core accretion as much in the oligarchic planetesimal accretion scenario as it was expected in the runaway accretion scenario. Therefore we expect that an opacity reduction (or some other mechanisms) is needed to solve the formation timescale problem even for migrating protoplanets, as long as we consider the oligarchic growth. We also point out a possible role of a dead zone in explaining long-lived, strongly accreting gas disks.Comment: 16 pages, 15 figures, accepted for publication in Ap

ESPRESSO Mass determination of TOI-263b: An extreme inhabitant of the brown dwarf desert

The TESS mission has reported a wealth of new planetary systems around bright and nearby stars amenable for detailed characterization of the planet properties and their atmospheres. However, not all interesting TESS planets orbit around bright host stars. TOI-263b is a validated ultra-short period substellar object in a 0.56-day orbit around a faint (V=18.97) M3.5 dwarf star. The substellar nature of TOI-263b was explored using multi-color photometry, which determined a true radius of 0.87+-0.21 Rj, establishing TOI-263b's nature ranging from an inflated Neptune to a brown dwarf. The orbital period-radius parameter space occupied by TOI-263b is quite unique, which prompted a further characterization of its true nature. Here, we report radial velocity measurements of TOI-263 obtained with 3 VLT units and the ESPRESSO spectrograph to retrieve the mass of TOI-263b. We find that TOI-263b is a brown dwarf with a mass of 61.6+-4.0 Mj. Additionally, the orbital period of the brown dwarf is found to be synchronized with the rotation period of the host star, and the system is found to be relatively active, possibly revealing a star--brown dwarf interaction. All these findings suggest that the system's formation history might be explained via disc fragmentation and later migration to close-in orbits. If the system is found to be unstable, TOI-263 is an excellent target to test the migration mechanisms before the brown dwarf becomes engulfed by its parent star.Comment: Accepted for Publication in Astronomy and Astrophysic

Mutational Profile and Pathological Features of a Case of Interleukin-10 and RGS1-Positive Spindle Cell Variant Diffuse Large B-Cell Lymphoma

Diffuse large B-cell lymphoma with spindle cell morphology is a rare variant. We present the case of a 74-year-old male who initially presented with a right supraclavicular (lymph) node enlargement. Histological analysis showed a proliferation of spindle-shaped cells with narrow cytoplasms. An immunohistochemical panel was used to exclude other tumors, such as melanoma, carcinoma, and sarcoma. The lymphoma was characterized by a cell-of-origin subtype of germinal center B-cell-like (GCB) based on Hans’ classifier (CD10-negative, BCL6-positive, and MUM1-negative); EBER negativity, and the absence of BCL2, BCL6, and MYC rearrangements. Mutational profiling using a custom panel of 168 genes associated with aggressive B-cell lymphomas confirmed mutations in ACTB, ARID1B, DUSP2, DTX1, HLA-B, PTEN, and TNFRSF14. Based on the LymphGen 1.0 classification tool, this case had an ST2 subtype prediction. The immune microenvironment was characterized by moderate infiltration of M2-like tumor-associated macrophages (TMAs) with positivity of CD163, CSF1R, CD85A (LILRB3), and PD-L1; moderate PD-1 positive T cells, and low FOXP3 regulatory T lymphocytes (Tregs). Immunohistochemical expression of PTX3 and TNFRSF14 was absent. Interestingly, the lymphoma cells were positive for HLA-DP-DR, IL-10, and RGS1, which are markers associated with poor prognosis in DLBCL. The patient was treated with R-CHOP therapy, and achieved a metabolically complete response

Discovering the Growth Histories of Exoplanets: The Saturn Analog HD 149026b

The transiting "hot Saturn" HD 149026b, which has the highest mean density of any confirmed planet in the Neptune-Jupiter mass range, has challenged theories of planet formation since its discovery in 2005. Previous investigations could not explain the origin of the planet's 45-110 Earth-mass solid core without invoking catastrophes such as gas giant collisions or heavy planetesimal bombardment launched by neighboring planets. Here we show that HD 149026b's large core can be successfully explained by the standard core accretion theory of planet formation. The keys to our reconstruction of HD 149026b are (1) applying a model of the solar nebula to describe the protoplanet nursery; (2) placing the planet initially on a long-period orbit at Saturn's heliocentric distance of 9.5 AU; and (3) adjusting the solid mass in the HD 149026 disk to twice that of the solar nebula in accordance with the star's heavy element enrichment. We show that the planet's migration into its current orbit at 0.042 AU is consistent with our formation model. Our study of HD 149026b demonstrates that it is possible to discover the growth history of any planet with a well-defined core mass that orbits a solar-type star.Comment: 20 pages, including 3 figures. Accepted for publication in ApJ letters. Discussion updated to include new NICMOS transit photometry (Carter et al. 2009

Sclerosing mesenteritis affecting the small and the large intestine in a male patient with non-Hodgkin lymphoma: a case presentation and review of the literature

<p>Abstract</p> <p>Introduction</p> <p>Sclerosing mesenteritis is a rare disease resembling a mesenteric tumour. We present here a case of sclerosing mesenteritis that affected both the large and the small intestine of the patient. Therapeutic and diagnostic issues are discussed.</p> <p>Case presentation</p> <p>A 62-year-old man with a history of non-Hodgkin lymphoma presented with fatigue, a palpable tender abdominal mass and clinical signs of progressing intestinal obstruction. The preoperative evaluation failed to prove recurrence of the lymphoma or any other definite diagnosis. A laparotomy was performed through a midline incision. The mesentery resembled a tumour-like thickened and fibrotic mass. Abundant, rigid intestinal loop adhesions were observed. Diffuse fibrotic infiltration of the ileum and of the sigmoid colon, which obviously affected the intestinal vascular supply, were identified. A right colectomy and partial sigmoidectomy were performed. Pathological evaluation revealed extensive myofibroblastic reaction of the mesentery with accompanying loci of fat necrosis and areas of inflammation. A diffuse fibrotic infiltration that focally showed a ground-glass appearance was observed. The post-operative course was complicated by respiratory insufficiency and infections and the patient died 2 months after the operation.</p> <p>Conclusion</p> <p>Sclerosing mesenteritis that affects both the small and the large intestine is extremely rare. The disease is characterized by myofibroblastic reaction, fat necrosis and diffuse fibrosis of the mesentery. Pathological confirmation may be required for definite diagnosis. If the disease is characterized by severe and diffuse fibrosis, then the application of surgical therapy may be problematic.</p

Formation of Super-Earths

Super-Earths are the most abundant planets known to date and are characterized by having sizes between that of Earth and Neptune, typical orbital periods of less than 100 days and gaseous envelopes that are often massive enough to significantly contribute to the planet's overall radius. Furthermore, super-Earths regularly appear in tightly-packed multiple-planet systems, but resonant configurations in such systems are rare. This chapters summarizes current super-Earth formation theories. It starts from the formation of rocky cores and subsequent accretion of gaseous envelopes. We follow the thermal evolution of newly formed super-Earths and discuss their atmospheric mass loss due to disk dispersal, photoevaporation, core-cooling and collisions. We conclude with a comparison of observations and theoretical predictions, highlighting that even super-Earths that appear as barren rocky cores today likely formed with primordial hydrogen and helium envelopes and discuss some paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio Belmonte and Hans Deeg, Ed