Combining photography and computed tomography to make three dimensional models of the Blaschka Glass Marine Invertebrates.

An increasing number of museums are using 3D imaging both for archival recording and to allow the global public to experience objects in collections that they would otherwise never be able to get close to. Photogrammetry, optical scanning and X-ray computed tomography scanning are all being used. These efforts benefit from steadily improving technology and abundant software options, and they build on extensive earlier work done primarily in archaeological, zoological and biomedical applications. Notable efforts are those at the Smithsonian Institution and the British Museum. However, rendering 3D images that are faithful to the original object remains difficult for many specimens. Fine detail or lack of detail, thin structures, hidden or glossy surfaces, and transparent or semi-transparent volumes are a few of the challenges. Intricate antique glasswork, while especially challenging for 3D imaging, also benefits tremendously from it because the specimens are typically very fragile; for conservation reasons, they should be handled as little as possible, if at all.

In a paper published in the journal Digital Applications in Archaeology and Cultural Heritage in September 2020, Peter Fried of the Department of Applied Physics at the New York University Tandon School of Engineering, Jonathan Woodward of the Museum of Comparative Zoology at Harvard University, David Brown of the Herbert F. Johnson Museum of Art at Cornell University, Drew Harvell of the Department of Ecology and Evolutionary Biology at Cornell University, and James Hanken, also of the Museum of Comparative Zoology at Harvard University, present the results of a project which for the last three years has been making 3D images of the intricate and beautiful glass models of Marine Invertebrates created between 1863 and 1890 by the father and son team of Leopold and Rudolf Blaschka.

The Blaschkas made thousands of these models, principally as teaching aids. They were shipped from the Blaschkas’ workshop in Dresden, Germany, to universities, schools and museums around the world. The Blaschkas made their models based on their own extensive observations of living Animals in aquaria and during several ocean voyages, and also based on drawings by contemporary taxonomists. The glass models of soft Marine Invertebrates were especially valuable because the shape and color of live specimens did not preserve well after death in fixatives used at that time. These models serve as a record of ocean life 100 or more years ago, and therefore are valuable to studies of evolution and the impacts of climate change.

Today, the principal collections of Blaschka Marine Invertebrate models are at Cornell University, the Harvard Museum of Comparative Zoology, the Corning Glass Museum, and University College, Dublin. Many smaller collections exist at institutions around the world. Fried et al. have imaged models at Cornell University and the Harvard Museum of Comparative Zoology.

Fried et al.'s imaging work began with glass models that are relatively simple in form and completely painted, so as to develop the basic photogrammetry workflow required, e.g. the minimum numbers of photographs and angles needed to yield high-resolution images. They then optimised control of the lighting, especially polarisation, using somewhat more complicated models that include sections of bare glass and/or glossy paint. Finally, there are some models with substantial transparent areas and/or intricate detail for which photogrammetry alone is inadequate. For these models, Fried et al. generated meshes with both photogrammetry and X-ray computed tomography scanning, which were then combined to create the final reconstruction.

 

European Squid, Loligo berthelotii. Model B-560 of the Cornell University Collection of Blaschka Marine Invertebrates (length about 6.4 cm). Fried et al. (2020).

The photogrammetry involved between 250 and 700 photographs of each glass model, which were taken against a black background on a turntable using 2–4 different camera angles. When possible, the model was arranged on the turntable in several different orientations to achieve 2–3 more or less orthogonal axes of rotation. A large number of photographs is needed both to insure good inter-photo registration, or 'alignment', and to insure adequate coverage of the entire complex geometry of the models. To further insure proper alignment, distinct coloured targets were mounted on the turntable, away from the glass model, near the edge of the field of view.

 

Fontaine’s Octopus, Robsonella fontanianus. Model SC-380 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates (spanning 13 cm from arm to arm). Fried et al. (2020).

Traditionally, specular reflections are minimized by applying a powder or spray coating to the subject. Such treatment, however, is not possible for the Blaschka models, especially in view of the fragile organic paints used to manufacture many of them. Controlling the polarisation of incident light by applying filters to the lens and/or the lights themselves can also be used to minimize (or maximize) specular reflections.

 

Stout Bobtail Squid, Rossia macrosoma. Model B-588 of the Cornell University Collection of Blaschka Marine Invertebrates (length about 15 cm). Fried et al. (2020).

The final position of the camera and lights was a compromise among the polarisation control and additional issues: The need for high resolution; the need to maximize relative depth of field; the need to minimise exposure time; and available resources, including lenses and controllable polarisers.

 

Sea Anemone, Phymactis pustulata. Model SC-51 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates (width about 10 cm). Fried et al. (2020).

For the 3D models illustrated here, Fried et al. used a 55 W, 1400- diameter ring light and a Nikon 7100 DSLR camera with an 80- or 90-mm macro lens. Lights and lens were located between one and three feet from the turntable. Apertures of f11–f20 were generally used. The camera, mounted on a firm tripod, was usually operated by remote control and typically set at a high ISO value (1600–2500). Excessive sensor noise can sometimes degrade inter-image alignment, but this did not appear to be the case at these ISO values. For some models, Fried et al were able to operate the turntable continuously at 1 rpm while making 1/50- or 1/25-second exposures every 0.5–1.0 seconds. However, crossed polarisers on the lens and ring light were used when necessary to control specular reflections, and this procedure required longer exposures (e.g. ¼–1/10 seconds) and, hence, manual stepping of the turntable.

 

Greater Argonaut, Argonauta argo. Model SC-363 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates (length about 7 cm). Fried et al. (2020).

Among the many different software packages currently available, Fried et al. used Agisoft Photoscan (recently updated and renamed Metashape). This software is affordable, completes the processing locally and has a good user interface that allows the user to control the separate processing steps in a manner suitable for this work. The software is used on a Dell Precision Mobile Workstation M4800 with 32 GB of RAM, an Intel Core i7-4910MQ Processor running at 2.9 GHz, and an NVIDIA Quadro K2100M Graphics card with a clock rate of 666 MHz.

 

Blue Button Jellyfish, Porpita porpita. Model SC-138 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates (diameter about 7 cm). Fried et al. (2020).

Key factors that affect processing time are the number of photos, the number of pixels in the unmasked portion of each photo, and the required accuracy level. The most challenging step in the photogrammetry, but not necessarily the most time-consuming, was always the inter-photo alignment. For several models, Fried et al. included alignment targets off the model at the edge of the turntable. These were useful as long as the model’s orientation on the turntable remained unchanged. To align photos of a given model in multiple orientations, in one case Fried et al. created separate partial digital models 'chunks' in the Agisoft nomenclature, for each orientation and then merged the chunks. In other cases, Fried et al. used the off-model alignment targets in one orientation and masked them in others to achieve a successful alignment. In any event, the software occasionally failed to align or created erroneous alignments due to accumulated small errors. Solving these cases involved various combinations of (a) adding more photos, (b) removing selected photos, (c) reordering photos, and (d) sequential re-alignments of subsets of photos. The highest-accuracy mode, which also is the most time-consuming, was usually required to successfully align the large number of photographs.

 

Football Sea Squirt, Diazona violacea. Model SC-418 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates (width about 9 cm). The high definition of the digital model results from a mesh made from a computerised tomography scan. This was aligned and merged in Agisoft Metashape with a mesh made from 699 photographs. The combined mesh was then textured from the photos. Fried et al. (2020).

There were some glass models for which even the techniques described above would not yield satisfactory results. Typically, these combine complex design with hidden or partially hidden surfaces, transparent or semi-transparent sections, and/or significant specular reflecting surfaces. For these glass models, Fried et al.  generated an X-ray computed-tomography scan that would be combined with a photogrammetry scan of the same specimen. 3D reconstruction from computed-tomography data has been extensively developed for metrology and biomedical applications.

 

Partial reconstructions of the Football Sea Squirt, Diazona violacea. (a) The reconstruction created by using only X-ray data, and (b) the reconstruction created by using only photographic data. Fried et al. (2020).

For computed-tomography scanning, Fried et al. mounted the glass model on an archival foam block, stabilizing it with Parafilm strips wrapped around archival cotton pads. We scanned the model using a Bruker Skyscan 1173 Micro-Computed Tomography Scanner, with a source voltage of 105 kV and a source current of 60 μA. Fried et al. interposed a 1.0 mm aluminum filter to reduce scatter artifacts in the final model.

 

Blaschka Sea Cucumber. Model SC174 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates. This is a roughly 7-inch glass model of a Sea Cucumber, Sporadipus tremula. The glass model is one of thousands done by the father-and-son team Rudolf and Leopold Blaschka in the late 1800s. Peter Fried/Sketchfab.

For reconstruction of the computed-tomography scan (creating slice images) and 3D model building, Fried et al. used NRecon and CTAn, respectively (each is part of the Bruker '3D.SUITE' software package). The slice images went through an initial thresholding step to separate the model from the background, a de-speckling step aimed at further reducing noise, and a model-creation step that resulted in an STL surface model file. Finally, in Meshlab, Fried et al. manually removed islands of artifact noise before downsampling (for ease of use) using Quadric Edge Collapse Decimation.

 

Blaschka Nudibranch, Red-Finger Aeolis, swimming. Model B-370, the Red-Finger Aeolis, Flabellina veruccosa, a Nudibranch, of the Cornell University Collection of Blaschka Marine Invertebrates. The Red-Finger Aeolis has been spotted in the Salish Sea (off Washington State). This is a roughly 4-inch glass model of a similar-sized Marine Invertebrate. The glass model is one of thousands done by the father-and-son team Rudolf and Leopold Blaschka in the late 1800s. Originally made as educational models, they are now in collections in over 50 institutions around the world. Peter Fried/Sketchfab.

The greatest challenges encountered during the micro-computed-tomography scan and reconstruction were attributable to the very thin and relatively radiotransparent glass of the Blaschka models. Several scanning attempts were required to achieve a set of slice images in which the model could be cleanly thresholded from the background. After even the best of these attempts, several levels of noise reduction were necessary.

 

Blaschka Vilella – By-the-wind Sailor. Model B-221, By-the-wind Sailor, of the Cornell University Collection of Blaschka Marine Invertebrates. The classification is: Phylum: Cnidaria, Class: Hydrozoa, Order: Anthoathecata, Family: Porpitidae, Genus: Vilella, species: vilella. By-the-wind Sailor is a free-floating colony of |Hydroids that, with a stiff upright 'sail', is blown about on the surface of the open ocean. They eat plankton and often are found stranded on the Northwest coasts of North America. This roughly 4-inch glass model is one of thousands done by the father-and-son team Rudolf and Leopold Blaschka in the late 1800s. Originally made as educational models, they are now in collections in over 50 institutions around the world. Major collections are at Cornell, the Corning Glass Museum, Harvard and University College, Dublin. The model was made from 310 photographs. Photogrammetry with Agisoft Photoscan and touch-up applied in Blender. Peter Fried/Sketchfab.

For some complex models, the mesh can be defined entirely by the X-ray computed-tomography data. Any surface coloring, however, such as that in the texture file, must be provided by photographic data. For other models, certain parts of the structure are made of paint and other filler materials, which are radiotransparent. These parts must be defined with photogrammetry meshes that are then merged with the X-ray-generated sections.

 

Blaschka Sea Anemone. Model SC64 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates. This is an approximately 3.5-inch glass model of a Sea Anemone, Tealia crassicornis var. purpurea. The glass model is one of thousands done by the father-and-son team Rudolf and Leopold Blaschka in the late 1800s. Originally made as educational models, they are now in collections in over 50 institutions including Cornell, the Corning Glass Museum, Harvard and University College, Dublin. The model was made from 312 photographs with processing by Agisoft Photoscan and touch-up in Blender. The white arms were a challenge, both due to their frosted, semi-transparent glass and also to the thick cross sections which hid many of the surfaces. Peter Fried/Sketchfab.

Some models required no additional work after the mesh and texture files were completed. Others, however, required post-processing, which was done with Blender. The 'Sculpt' mode in Blender provides tools for smoothing portions of the mesh, removing distortions and improving the definition of narrow crevices. Blender can also be used to divide the mesh into sections of different materials (defined by the.mtl files). This allows for different levels of transparency and translucence, albedo, roughness and surface gloss.

 

Blaschka Nudibranch. Model SC-308 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates. This is a glass model (length about 3.5 inches) of a Nudibranch (originally listed as Pterogasteron marginata, currently known as Elysia marginata). The Nudibrancia, an order in the subclass of sea slugs, include more than 3000 species, of widely varying appearance and colour. This model is one of thousands made by Rudolf and Leopold Blaschka as educational models in the late 1800s. The light-colored material on the bottom of the model is residual epoxy, used to affix a mounting wire for exhibit in decades past. The thin dorsal fins were a challenge to mesh, requiring 528 photographs shot in 7 orientations. The processing was done with Agisoft Photoscan and the surface was post-processed with Blender. Peter Fried/Sketchfab.

Once post-processing was complete the 3D files were uploaded to the SketchFab viewer where, after adding a background and appropriate lighting, Fried et al. adjusted surface qualities of the model. 

Fried et al.'s objective is to demonstrate archival capture of challenging 3D subjects, specifically glossy, translucent and highly detailed and delicate glass models. Much of their workflow optimises well-known techniques of light and polarisation control and photogrammetric processing. Significantly, we have also merged photogrammetry and computed-tomography data to create meshes of intricate structures made of multiple materials including glass.

 

Blaschka Cuttlefish. Model SC-369 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates. This glass model is one of thousands made by Rudolf and Leopold Blaschka in the late 1800s as educational models. This species of Cuttlefish (labeled by the Blaschkas as Sepia bisserialis, but currently known as Sepia elegans), never larger than about 3.5 inches, is found in the Mediterranean and in the Eastern Atlantic from Scotland in the north to the west coast of Africa in the south. The 3D model was made from 365 photographs using Agisoft Photoscan. In addition to glass the Blaschkas used other materials. For this Cuttlefish the dorsal surface was made of painted paper. This thin surface posed a challenge for the photogrammetry alignment and required careful masking of the photos prior to processing. Blender was used to assign four sets of material properties to the dorsal area, the remainder of the body, the tentacle and the eyes. Peter Fried/Sketchfab.

Recently, software and cameras have become available with automated focus stacking. This feature holds promise for some combination of higher resolution, larger effective depth of field and shorter individual exposures, but only if the processing load  for 250–700 separate photos is manageable.

 

Blaschka Sea Cucumber. Model SC168 of the Harvard Museum of Comparative Zoology Collection of Blaschka Marine Invertebrates. This is a roughly 5-inch glass model of a Sea Cucumber, Holothuria maculata. The glass model is one of thousands done by the father-and-son team Rudolf and Leopold Blaschka in the late 1800s. Originally made as educational models, they are now in collections in over 50 institutions around the world. Major collections are at Cornell, the Corning Glass Museum, Harvard and University College, Dublin. The 3D model was made from about 200 photographs taken at the Museum of Comparative Zoology. The photogrammetry processing was done with Agisoft Photoscan and minor touch-up was applied in Blender. Peter Fried/Sketchfab.

Future work should (a) identify ways to improve efficiency and resolution through focus stacking; (b) develop further use of computed-tomography scanning, especially for imaging highly transparent glassworks (e.g. Blaschka Jellyfish); and (c) explore the utility of voxel-based processing for digitising such objects. The use of these additional techniques, as well as those demonstrated so far, should expand the universe of objects suitable for 3D digitisation.

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Sollasina cthulhu: A new species of Ophiocistioid Echinoderm from the Silurian Herefordshire Lagerstätte.

The living Echinoderm groups Echinoidea (Sea Urchins) and Holothuroidea (Sea Cucumbers) are united into the larger group Echinozoa, allong with an extinct group, the Ophiocistioidea, which first appeared in the Ordovician and died out in the Triassic. The Ophiocistioids shared some traits seem in modern Echinozoans, such as complex jaw apparatus of the Sea Urchins and the body-wall skeleton mostly reduced to small spicules of the Sea Cucumbers, with traits uniquely their own, most notably a dome-shaped body similar to half the test of a Sea Urchin, with five ambulacra on the outside, radiating out from a mouth at the centre, each of which ends with three enlarged, tentacle-like tube feet. Because of the easily fragmented nature of the skeletons of these Echinoderms, they are only found in deposits with exceptional preservation.

In a paper published in the journal Proceedings of the Royal Society Series B Biological Sciences on 10 April 2019, Imran Rahman of the Oxford University Museum of Natural History, Jeffrey Thompson of the Department of Earth Sciences at the University of Southern California, Derek Briggs of the Department of Geology and Geophysics and Yale Peabody Museum of Natural History at Yale University, David Siveter of the School of Geography, Geology and the Environment, at the University of Leicester, Derek Siveter also of the Oxford University Museum of Natural History, and of the Department of Earth Sciences at the University of Oxford, and Mark Sutton of the Department of Earth Sciences and Engineering at Imperial College London, describe a new species of Ophiocistioid Echinoderm from the Silurian Herefordshire Lagerstätte of England.

The Herefordshire Lagerstätte comprises a large number of small (at most centimetres) organisms from the Middle Silurian (about 425 million years ago). The organisms are preserved in three dimensions within calcareous nodules within a layer of volcaniclastic sediments (i.e. a volcanic ashfall in a marine environment), many of which can only be accessed using computerised tomography or similar scanning techniques. Brachioods, Polychaete Worms, Gastropods, Aplacophorans, Chelicerates, Marrellomorphs, Mandibulates, Barnacles, Phyllocarids, Ostracods, Starfish and Sponges have all been found in the Herefordshire Lagerstätte; together these are known as the Herefordshire Biota.

The new species is placed in the genus Sollasina, and given the specific name cthulhu, in reference to the tentacled monster from the writings of HP Lovecraft. The species is described from thirteen fossils, all preserved three-dimensionally as calcite void-fill in calcareous concretions. One exceptionally well-preserved specimen was selected for detailed study by physical–optical tomography. The specimen was cut into seven pieces, serially ground at 30 μm intervals, and the exposed surfaces were imaged using a Leica digital camera attached to a Wild binocular microscope. The resulting sets of slice images were digitally reconstructed as a three-dimensional (3-D) virtual model using the SPIERS software suite.

Sollasina cthulhu. (a)–(m) Virtual reconstructions (stereo-pairs), (n), (o) specimen in rock. (a) Oral view. (b) Lateral view. (c) Aboral view. (d) Non-peristomial tube foot (unpaired). (e) Non-peristomial tube foot (paired). (f) Peristomial tube feet. (g) Oral view showing the peristome, madreporite and gonopore (peristomial tube feet omitted). (h) Oral view showing the madreporite and gonopore (peristomial tube feet removed). (i) Aboral view showing the periproct. (j) Lateral view showing plating in the interambulacral area containing the madreporite and gonopore (tube feet removed). Interambulacral plates are shown in green. (k) Oral view showing ambulacral plating at the margin of the theca (tube feet removed). (l) Oral view showing the internal ring (all other features transparent). (m) Aboral view showing ambulacral plating at the margin of the theca (tube feet removed). (n) Section through the theca showing the tube feet. (o) Section through the theca showing the internal ring. Abbreviations: cp, circular pore; go, gonopore; ir, internal ring; jp, jaw plates; ma, madreporite; pe, peristome; pr, periproct; pt, peristomial tube feet; st, small adoral non-peristomial tube foot; tf, non-peristomial tube feet; ut, unpaired non-peristomial tube feet. In k and m, perradial plates are shown in purple, adradial plates in red, and interambulacral plates in green. Scale bars: (a)-(c), (l ) 5 mm; (d), (e), (g), (k), (l), (n), (o) 2 mm; (f), (h), (i), (j), (m) 1 mm. Rahman et al. (2019).

Sollasina cthulhu has a theca approximately 15 mm in diameter and pentagonal in outline, with thin, imbricate plates. The oral (lower) surface is slightly concave; the aboral (upper) surface is partly collapsed, but was presumably convex in life. The oral surface of the theca consists of five wide ambulacral areas, composed of columns of perradial and adradial plates, which alternate with five narrow interambulacral areas. The aboral surface of the theca consists of numerous irregularly arranged plates. The peristome occupies the middle of the oral surface. It is subcircular in outline and approximately 6 mm in diameter. Five thick, rhomboidal, interradially positioned plates form the jaw apparatus, which occupies about half the peristome diameter. 

In each ambulacral area, the plates are divided into one central column of six alternating perradial plates and two lateral columns of four adradial plates each. There are nine plated tube feet within each ambulacral area. The first pair is located within the peristome, close to the outer edge of the jaw apparatus. These peristomial tube feet are covered in tiny plates and are smaller than the other tube feet, measuring approximately 3 mm in length and 0.8 mm in diameter. The other tube feet are located outside the peristome, occurring as three slightly offset pairs, with an additional solitary tube foot at the aboral end of each ambulacral area. The non-peristomial tube feet increase in size aborally (reaching a maximum of approximately 14 mm in length and 2 mm in diameter), with the exception of the unpaired tube foot which is shorter than its adoral neighbour. Within one of the ambulacral areas, the most adoral of the tube feet outside the peristome is much smaller than all others . The tube feet are preserved hollow. They consist of thin plates arranged in longitudinal rows, overlapping distally. There are at least eight rows of about 20–30 plates each in the paired tube feet and four rows of about 13 plates each in the unpaired ones.

Reconstruction of Sollasina cthulhu. Elissa Martin/Division of Invertebrate Paleontology/Yale Peabody Museum of Natural History in Rahman et al. (2019).

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Architeuthis dux: Giant Squid captured on video for the second time ever.

The Giant Squid, Architeuthis dux, is a deep-sea Cephalopod Mollusc found in oceans around the world. Reaching about 10 m in length, it is the second largest known Cephalopod, the second largest Mollusc, and the second largest Invertebrate Animal of any type, being exceeded in size only by the even larger Colossal Squid, Mesonychoteuthis hamilton, which can reach about 14 m and is only known from the waters around Antarctica. Despite its large size, the Giant Squid is very poorly understood by marine biologists, with very few recorded sightings of living animals, and most of what is known about the species based upon the study of specimens recovered from the stomachs of Sperm Whales.

The US National Oceanic and Atmospheric Administration this week published footage of a Giant Squid filmed at a depth of 759 m in the Gulf of Mexico about 160 km to the southeast of New Orleans, which was captured by the Medusa camera system on Wednesday 19 June 2019, using an electronic 'Jellyfish' lamp to mimic a bioluminescent Coronate Medusa Jellyfish, Atolla wyvilleias, thought to be one of the Giant Squid's main prey items.

Footage of a Giant Squid captured by the NOAA's Medusa System in the Gulf of Mexico this week. NOAA.

This is only the second time that video footage of a Giant Squid has been captured, the first time having been in 2012, when the same camera system filmed another member of the species, off the coast of Japan. Both videos were captured at similar depths, and show the Squid to be active animals deliberately seeking out prey, rather than being passive drifters, as had preciously been suggested by some Marine Biologists.

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Laser-Stimulated Fluorescence reveals previously unseen plumage in a hatchling Enantiornithine Bird from the Las Hoyas Deposits of Spain.

Specimen MPCM-LH-26189 is a hatchling Enantiornithine Bird described from the Early Cretaceous Las Hoyas Deposits of Spain, first described in 2018. Like other Enantiornithine Birds preserved in the Las Hoyas Deposits, specimen MPCM-LH-26189 is preserved in an articulated state, with some soft tissue preservation. However the specimen has no apparent plumage (feathers), which led the scientists describing it to conclude that, like many modern Birds, MPCM-LH-26189 was featherless when it hatched, implying that it was also likely to be altricial (completely dependent on its parents for food and shelter), rather than precocious (able to fend for itself with minimal parental supervision) in nature.

In a paper published in the journal Scientific Reports on 21 March 2019, Thomas Kaye of the Foundation for Scientific Advancement, Michael Pittman of the Vertebrate Palaeontology Laboratory at the University of Hong Kong, and Jesús Marugán-Lobón, Hugo Martín-Abad, José Luis Sanz, and Angela Buscalioni of the Facultad de Ciencias at the Universidad Autónoma de Madrid, re-examine specimen MPCM-LH-26189 using Laser-Stimulated Fluorescence imaging.

Kaye et al. used a 405 nm laser diode to cause the specimen to fluoresce, then imaged it with a Nikon D810 DSLR camera and a 425 nm laser blocking filter, then processed the pictures in Photoshop CS6, using a technique in which the equalisation, saturation and colour balance was adjusted across the entirety of the image, in order to prevent inadvertently manufacturing features.

Specimen MPCM-LH-26189 is surrounded by yellowish stains in several places, which when subjected to Laser-Stimulated Fluorescence imaging revealed filamentous structures, which Kaye et al. interpret as feathers. They further reason that if the hatchling Bird did in fact have feathers, then it is less likely to have been completely altricial at the time of hatching, as in modern Birds species which hatch with feathers are far more likely to be precocious.

Spanish Enantiornithine hatchling MPCM-LH-26189. (A) White light image of the counterslab. (B) Laser-Stimulated Fluorescence image of the slab and counterslab combined (composite image) reveals brown patches around the specimen. These comprise of clumps of elongate feathers associated with the neck and wings (upper arrows) as well as a single long pennaceous feather associated with the left wing (lower arrow). (C) White light image of the slab. Scale bar is 5 mm. Kaye et al. (2019).

Feathers are present in patches across the body, with the best preservation seen on the left side of the neck and on the left wing. The feathers of the left side of the neck are elongate, with bands of darker and lighter colour, with a generally bushy appearance. On the right wing feathers can be seen associated with the radius and ulna, with those on the ulna seeming obliquely in multiple thin filaments. The best preserved feather is associated with the left wing, and is about 3 cm in length, with barbs deriving from the rachis at an angle of about 30°.

Preserved feathering of Spanish Enantiornithine hatchling MPCM-LH-26189 under LSF and white light. Elongate feathers preserving bushy dorsal tips are found near the neck and appear to be cover feathers: (A) under Laser-Stimulated Fluorescence, (B) under white light. Scale bar is 1 mm. Suspected feather clumps are associated with the right wing (C) under Laser-Stimulated Fluorescence, (D) under white light. Scale bar is 3 mm. A long pennaceous feather associated with the left wing is very similar to an Enantiornithine embryo specimen from China (E) under Laser-Stimulated Fluorescence, (F) under white light. Scale bar is 4 mm. Kaye et al. (2019).

The presence of feathers in very young Birds has been seen in other Enantiornithines, and the newly discovered plumage of MPCM-LH-26189 shows that the specimen conforms to this wider pattern. Interestingly the presence of bushy feathers on the neck of the hatchling shows that it possessed cover, as well as flight, feathers, something which has not previously been demonstrated in an Enantiornithine Bird, and the discovery of which adds to our understanding of the biology of the group.

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Investigating a meteoroid impact on the Moon during the 21 January 2019 Lunar eclipse.

On 21 January 2019 the only total Lunar eclipse of 2019 was watched by millions of observers across the Americas, North Africa and Europe. A few minutes after totality was reached (i.e. after the Moon was completely covered by the Earth’s shadow), witnesses across this area began to report a flash on the east side of the Moon, presumably caused by a meteoroid impact. Such impacts are thought to be extremely common on the Moon, which lacks an atmosphere to protect its surface from impacts as the Earth does (indeed a second impact, on the brighter western side of the Moon, was reported a few minutes later by the Royal Observatory in the UK, though this has not been confirmed by other observers), but few are witnessed by quite as many observers, both amateur and professional, as this event, opening the potential for it to b studied in detail in ways that are not possible for most Lunar impacts.

In a paper published on the arXiv database at Cornell University on 28 January 2019, and submitted to the journal Icarus, Jorge Zuluaga and Pablo Cuartas-Restrepo of the Solar, Earth and Planetary Physics Group at the University of Antioquia, and the Sociedad Antioqueña de Astronomía, Jonathan Ospina, also of the Sociedad Antioqueña de Astronomía, Fritz Pichardo of the Sociedad Astronómica Dominicana, Sergio López, again of the Sociedad Antioqueña de Astronomía, Karls Peña, also of the Sociedad Astronómica Dominicana, and Mauricio Gaviria-Posada of the Observatorio LaLoma, present an examination of the 21 January 2019 Lunar meteoroid impact, based upon observations by amateur and professional astronomers in Morocco, the Dominican Republic and Colombia.

The first set of observations come from the Mobile Observatory of the Time and Date Astronomy Portal, which at the time of the eclipse was located at Ouarzazate in Morocco, and which broadcast the entire eclipse on the Time and Date website. Zuluaga et al. extracted six frames from this video, and used them to estimate the duration of the flash.

From left to right, frames of the video taken at Ouarzazate, Morocco by Time and Date mobile observatory. The 21 January 2019 Lunar impact flash, which is visible close to the lower dark limb, appeared in four of the six frames. Zuluaga et al. (2019).

The second observation used was made by Fritz Pichardo in Santo Domingo, the Dominican Republic, who used a Canon T3i DSLR camera mounted on a 8 inch Celestron CPC 800 SchmidtCassegrain telescope to take an image of the eclipsed Moon with a 20 minute exposure, between 4.41 and 5.01 am GMT.

20 minute exposure of the total lunar eclipse at the time of the impact flash taken in Santo Domingo, the Dominican Republic. Impact site is labelled as L1-21-J. Fritz Pichardo in Zuluaga et al. (2019).

The third observation used came from the 25 inch telescope of the LaLoma Observatory at San Vicente Ferrer in Antioquia; the largest telescope in Colombia, with a focal length of 2700 m. This much larger aperture telescope was able to take images of the Moon with a much lower exposure time, enabling Zuluaga et al. to extract a single image taken at 37 seconds past 4.41 am GMT, the exact time recorded for the flash by the Moon Impacts Detection and Analysis System, a Spanish project which has constantly monitored the Moon for such impacts for the past two decades.

Picture of the total lunar eclipse at the time of the impact flash taken the observatory LaLoma, Colombia. Jonathan Ospina, Mauricio Gaviria and Sergio López in Zuluaga et al. (2019).

Zuluaga et al. were able to use the high resolution image from the LaLoma telescope in combination with maps produced by the Lunar Reconnaissance Orbiter Camera to determine the precise location of the impact, determining it to have happened within an ellipse measuring 18 km along its east-west axis and 15 km along its north-south axis, centred on a point at a latitude of -29.428816° and a longitude of -68.167435°, close to the Byrgius crater to the southeast of Mare Humoris. The Lunar Reconnaissance Orbiter has been surveying the Moon for six years, at a resolution of one metre per pixel, during which time it has covered 70% of the Moon’s surface, with 3% having been covered moor than once. The calculated area within which the impact occurred should be small enough that this, or other Lunar surveying satellites, should potentially be able to detect the impact site directly in the future.

 

Impact estimated location. (Upper panel) Original picture taken at LaLoma Observatory in Colombia. (Middle panel) Superposition of the original picture and a Lunar Reconnaissance Orbiter Camera ortographic map. (Bottom panel) Flash image and location on top of a high-resolution Lunar Reconnaissance Orbiter Camera cylindrical map of the impact area. Zuluaga et al. (2019). 

Determining the original orbit of an asteroid based upon a simple observation of a flash is impossible, but Zuluaga et al. were able to use Gravitational Ray Tracing, a technique developed by Jorge Zuluaga and Mario Sucerquia, also of the Solar, Earth and Planetary Physics Group at the University of Antioquia, to determine the most likely origin of the body. Gravitational Ray Tracing works by using a computer model to create a large number of random incoming trajectories, each separated by at least 5°, and then tracing them backwards for a calendar year at regularly spaced speeds, through the gravitational fields of the Solar System, to determine which paths are possible and how likely these are. Zuluaga et al. generated 997 random incoming trajectories, and ran each of these at 100 different speeds.

82% of the hypothetical objects generated by this process survived a year into the past, and impactors travelling at shallow angles relative to the surface of the Moon were found to be more probable, with the object most likely to have hit the Lunar surface at an angle of less than 35°, and almost zero chance that it was on a trajectory close to the vertical. The object was also found to be travelling quite slowly relative to the Moon, probably hitting the surface at about 13.8 km per second (most such impactors are calculated to be in the 16-22 km per second range). The object was probably on an orbital path consistent with it being an Aten Group Asteroid (a body that spends most of its time closer to the Sun than the Earth, but which does cross the Earth’s orbit), though it does not appear to have been on a trajectory close to that of any known asteroid or meteor shower.

The data produced by the Time and Date telescope suggests that the flash was 0.30 seconds in duration and did not vary significantly in duration during this time. This means that all of the light that contributed to the visible point of light in the image taken by Fritz Pichardo in Santo Domingo must have been emitted during that time, while the images of stars in the background of that photograph must reflect the light emitted from those stars over the full 20 minutes of the exposure. Therefore if the brightness of the flash can be compared to the brightness of any stars can be found in the image, then the light reaching the Earth from those over 20 minutes must have a direct ratio to the light reaching Earth from the impact flash over 0.30 seconds, and since the distance to the Moon and that to all nearby stars is known, as well as the brightness of those stars, then this can be used to calculate the actual energy released during the impact.

Zuluaga et al. (2019). used nine stars to calibrate this method, HD 67564, BD+20 2009, BD+20 2007, BD+20 2005, BD+21 1766, BD+21 1779, BD+21 1777, TYC 1385-899-1, and TYC 1385-939-1. This led to the calculation that the impact released energy equivalent to that released by 0.3-0.5 tons of TNT, which in turn suggests an object 10-27 cm in diameter, with a mass of 7-40 kg, which would leave an impact crater 5-10 m in diameter, well within the detection range of lunar prospecting satellites.

Picture of the total lunar eclipse at the time of the impact  ash taken in Santo Domingo, the Dominican Republic with the moon removed, highlighting the background stars. 9 stars were identi ed and used for the photometry. Fritz Pichardo in Zuluaga et al. (2019).

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