Understanding the plasma environment around Mercury.

As the closest planet to the Sun, has the most direct exposure to the solar winds of any planet in the Solar System. The planet has a weak magnetic field, with a magnetosphere strongly linked to the surface and exosphere (a zone around its solid surface within which individual atoms and molecules can be found moving freely, but seldom, if ever, interacting) by a range of processes. These are largely driven by the exchange of energy with the solar winds, and loss of material from the planetary surface. The magnetosphere contains a mixture of ions derived from the solar winds, primarily hydrogen⁺ and helium²⁺ ions, and others derived from the planet's surface via ionization of material in the exosphere. 

The Mariner 10 spacecraft made three flybys of Mercury in 1974 and 1975, detecting heavy ions thought to be derived from the planet's exosphere. Subsequent observations of Mercury by Earth-based telescopes were able to identify ions such as sodium⁺, potassium⁺, and calcium⁺. Between 2011 and 2015 the MESSENGER spacecraft orbited Mercury, during which time its Fast Imaging Particle Spectrometer was able to detect a variety of ions in the planet's magnetosphere, including hydrogen⁺ and helium²⁺ derived  from the solar winds, as well as heavier ions such as helium⁺, oxygen⁺, water group ions (hydroxide⁺, water⁺, and hydrogen peroxide⁺), sodium⁺, magnesium⁺, aluminium⁺, and silicon⁺, derived from the planet. The helium⁺ ions showed a relatively even distribution around the planet, but the other planetary-derived ions were concentrated around the planetary cusp (i.e. directly facing the Sun) and in the equatorial band of the nightside of the planet, although it was not possible to further define the distribution of individual types of ion.

The BepiColombo spacecraft is a joint project by the European Space Agency and the Japan Aerospace Exploration Agency which was launched in 2018, on aa trajectory which would lead it to make close flybys of Mercury in October 2021, June 2022, June 2023, September 2024, December 2024, and January 2025, before finally entering the planet's orbit in November 2026. 

In a paper published in the journal Communications Physics on 3 October 2024, a team of scientists led by Lina Hadid of the Observatoire de Paris, Sorbonne Université, Université Paris Saclay, École polytechnique, and Institut Polytechnique de Paris, present the result of a study of ion plasma observations made by BepiColombo's Mercury Plasma Particle Experiment instruments, during the flyby of Mercury made on 19 June 2023.

The 19 June 2023 flyby took BepiColombo to about 235 km above the surface of Mercury, enabling sampling of ions within the magnetosphere plasma at low altitudes along the spacecraft's trajectory. During the flyby BepiColombo approached Mercury from its dusk-nightside, passing through the post-midnight magnetosphere close to the equator of the planet, and moving away towards dawn-dayside. 

BepiColombo’s journey through Mercury’s magnetosphere. European Space Agency.

BepiColombo crossed the bow-shock of the planet inbound at 6.44 pm GMT, and outbound at 7.52 pm. Outside of this bowshock region, both before and after the crossing, ions with energies of about 10 and about 20 electronvolts were constantly observed, with mass-per-charge ratios of 1 and 16. This is consistent with hydrogen⁺ and oxygen⁺ ions, derived from water molecules outgassed from the planet.

Projections of BepiColombo’s third Mercury flyby trajectory in the aberrated Mercury–Sun magnetospheric (aMSM) coordinate system. (a) X'–Z' and (b) X'–Y' planes, all expressed in Mercury radii (The radius of Mercury is 2440 km). Note the displacement in (a) of the magnetopause relative to the planetary centre because of the northward offset of the magnetic dipole by approximately 0.2 of the radius of Mercury. In traditional MSM coordinates, the X-axis and Z-axis point to the sun and north pole, respectively, and the Y-axis completes a right-hand system. In the aberrated coordinates, Mercury’s orbital velocity is considered. The X-axis is anti-parallel to the solar wind direction in the rest of the reference frame of Mercury. The aberration angle varies between about 5.5° and about 8.4° assuming a solar wind speed of 400 km per second. The black arrows indicate the viewing direction of instrument during this flyby. The magenta and cyan crosses represent the observed inbound (and outbound) bow shock and magnetopause crossings, respectively. The red dot highlights the closest approach of BepiColombo to Mercury. The black solid and dashed lines represent the modelled dayside bow shock and magnetopause that are obtained from the statistical distribution of observed crossing points, respectively. Hadid et al. (2024).

As BepiColombo entered the dusk magnetosphere of Mercury, it encountered ions with energies of around 20 000 electronvolts, but following this the energy of the ions fell to a few tens of electronvolts. Hadid et al. interpret this area as the low latitude boundary layer, the area along the magnetospheric side of a planet's low-latitude magnetopause where plasmas form the magnetosheath and magnetosphere are mixed. This kind of energy dispersion within the plasma mantle is typically seen at high latitudes; its presence close to the equator of Mercury suggests a relationship between the plasma mantle and the low latitude boundary layer, with convection carrying ions deep into the magnetosphere. 

Hydrogen⁺ ions were detected in the low latitude boundary layer region which Hadid et al. interpret as having derived from the duskside magnetosphere (i.e. the part of the magnetosphere where the Sun is setting). The low latitude boundary layer region is also likely to contain heavy ions derived from the dayside exosphere of the planet and transported over the polar caps, although Hadid et al. are careful to emphasise that determining the origin of the low latitude boundary layer is beyond the scope of the current study.

Model of the hydrogen⁺ ion trajectories. (a) Shows various particle trajectory projections in the equatorial plane traced backward in time. (b) Shows the particle kinetic energy versus time. The ions are launched from different locations (closed circles) along BepiColombo’s orbit, and their trajectories are traced backward in time. The colour code depicts the different magnetospheric regions, viz., the Low- Latitude Boundary Layer in green, the umbra in blue, the Plasma Sheet Horns in yellow, and ring current in red. The test hydrogen⁺ ion trajectories were computed using a modified Luhmann–Friesen model for the magnetic field combined with a two-cell convection pattern for the electric field. The full equation of motion was integrated backward in time using a fourth-order Runge–Kutta technique. Hadid et al. (2024).

As BepiColombia enetered the umbra (shadow) of Mercury and inner part of the low latitude boundary layer at 7.24 pm it encountered 'cold' ions with energies as low as 30-100 electronvolts. Hadid et al. suggest that this might be because negatively charged, causing low-energy ions from the exosphere to become attracted towards it. The ions encountered around the low latitude boundary layer include oxygen⁺ and calcium⁺ and/or potassium⁺ ions thought to have originated from the dayside of the planet and lighter hydrogen⁺ and helium²⁺ ions, probably of solar origin.

At 7.28 pm, shortly after leaving the low latitude boundary layer, BepiColombo began to encounter 'hot' ions with energies in the kiloelectronvolt range, in an area corresponding to the 'plasma sheet horns' detected by the MESSENGER spacecraft a decade previously. These ions are thought to originate from the tail of the magnetosphere, and to be accelerated towards the planet by convection currents.

After passing through this region at 7.32pm, BepiColombo encountered a region with intense ion fluxes, with ion energies in the 5-40 kiloelectronvolt range. Because this layer is present at low altitudes in the equatorial region, Hadid et al. interpret this as a tenuous ring current, in which charged particles could become trapped in orbits of the planet at altitudes of 1.3-1.5 times its radius. At this altitude a hydrogen⁺ could orbit Mercury in about four minutes, bouncing back and forth on either side of the equatorial plane throughout its motion around the planet. The presence of such a ring current had been suggested from the MESSENGER data, but the data was rather limited, with particles with energies of no more than 13 kiloelectronvolts being detected. The greater energy range detected in the BepiColombo data provides much better support for the presence of such a ring current, although again it is not sufficient to state definitively that this is what is being detected. 

The high energy particles within this band appear to be hydrogen⁺ and helium²⁺ ions, but BepiColombo also encountered larger particles. The most common of these have energies of around 2 kiloelectronvolts, and are interpreted as oxygen⁺ ions, while more energetic particles, with energies of around 10 kiloelectronvolts, and are interpreted as being predominantly calcium⁺ and potassium⁺ ions, with some sodium⁺ ions also present. BepiColombo also encountered cold ions, with energies of about 15 electronvolts. These cold ions are presumed to have originated from the surface of Mercury, and peaked at the closest to the planet, an altitude of 332 km.

After passing through the post-midnight magnetosphere of Mercury, BepiColombo re-entered the planet's magnetosheath and then moved back into the solar wind. This solar wind comprises a compressed and heated stream of hydrogen⁺ and helium²⁺ ions, although outgasses water group ions could again be detected in this region.

Mercury’s magnetosphere during BepiColombo’s third flyby. European Space Agency.

The 19 June 2023 flyby of BepiColombo has provided us with our first reasonably detailed view of the structure of Mercury's magnetosphere, demonstrating that it is not greatly different from that of the Earth. Both low and high energy ions were observed in the planet's magnetosphere, including the deepest parts encountered, suggesting that ion sputtering (the dislodging of low energy ions from the surface of the planet by the impact of high energy ions from the Sun) plays a significant role in the system. The evidence collected by the spacecraft supports the presence of a ring current encircling Mercury, and for the first time demonstrate the presence of a low latitude boundary layer. 

The magnetosphere of Mercury will remain a subject of study for the remainder of the BepiColombo mission, including the planned further flybys and orbital stage, which should serve to greatly enhance our understanding of the planet's magnetic environment.

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Outbreak of Marburg Virus reported in Rwanda.

On 27 September 2024 the  Rwanda Ministry of Health confirmed that an outbreak of Marburg Virus Disease was present in the country, following the detection of the Virus in the blood of two patients by real-time reverse transcription polymerase chain reaction analysis at the National Reference Laboratory of the Rwanda Biomedical Center, according to a press release issued by the World Health Organization on 30 September 2024.

As of 29 September 2024, 26 cases of the disease have been reported in seven of the country's thirty districts (Gasabo, Gatsibo, Kamonyi, Kicukiro, Nyagatare, Nyarugenge and Rubavu), with eight people having died of the disease, a case fatality rate of 31%. The majority of the patients are healthcare workers from two health facilities in Kigali; this is not uncommon with outbreaks of the Marburg and Ebola viruses, with the highly transmittable nature of these diseases often resulting in aa high mortality rate in healthcare workers around the initial locus of the outbreak.

Contract tracing has led to the screening of about 300 contacts of diagnosed patients, one of whom had travelled to Belgium, with all found to be healthy and not a threat to public health. The initial source of the outbreak is still under investigation.

Marburg Virus Disease is a haemorrhagic fever, similar to the closely related Ebola Virus Disease. Both are caused by single-strand negative-sense RNA viruses of the Filoviridae family. Both are easily spread though contact with bodily fluids, and can also spread by contaminated clothing and bedding. 

Negative stained transmission electron micrograph of a number of filamentous Marburg Virions, which had been cultured on Vero cell cultures, and purified on sucrose, rate-zonal gradients. Erskine Palmer/Russell Regnery/Centers for Disease Control and Prevention/Wikimedia Commons.

Marburg Virus has an incubation period of between two and 21 days, manifesting at first as a high fever, combined with a severe headache and a strong sense of malaise. This is typically followed after about three days by severe abdominal pains, with watery diarrhoea and vomiting. In severe cases the disease develops to a haemorrhagic stage after five-to-seven days, manifesting as bleeding from some or all bodily orifices. This typically leads to death on day eight or nine, from severe blood loss and shock. There is currently no treatment or vaccine available for Marburg Virus, although a number of teams are working on trying to develop vaccines. 

Previous outbreaks of Marburg Virus have been reported in Rwanda, as well as the neighbouring Democratic Republic of Congo and Tanzania. The Virus has also been reported in a number of other African countries, including Angola, Equatorial Guinea, Ghana, Guinea, Kenya, and South Africa. The most recent outbreaks occurred in January 2023, with unrelated epidemics in Tanzania and Equatorial Guinea. 

The high rate of infection of healthcare workers seen in Marburg Virus is particularly alarming, as this tends to weaken communities ability to resist the Virus. The Virus can spread quickly in healthcare settings, infecting people whose immune systems are already stressed by other conditions, and creating aa reserve which can feed infections in the wider community. This makes it important to screen all people potentially infected with the disease as quickly as possible, and to arrange for patients to be treated in isolation, as well as quickly tracing all known contacts of any cases, and screening them for infection too.

Marburg Virus is a zoonotic infection (disease transferred from Animals to Humans), with a wild-reserve of the Virus known to be present in Egyptian Fruit Bats, Rousettus aegyptiacus, which are found across much of Africa, the Mediterranean region, the Middle East, and South Asia. These Bats form large colonies in caves or sometimes mines. They are frugivores, and can be major pests of farmed fruits, bringing them into conflict with Humans, and are sometimes hunted for food, all of which create potential avenues for the Marburg Virus to pass from a Bat host to a Human one.

A colony of Egyptian Rousette Bats, Rousettus aegyptiacus. Giovanni Mari/Flikr/iNaturalist.

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Tomb of Twelth Dynasty noblewoman discovered in Asyut, Egypt.

Archaeologists from Sohag University in Egypt and Freie Universität Berlin in Germany have uncovered the tomb of a Twelfth Dynasty noblewoman while carrying out excavations at Asyut. The tomb has been identified as that of Edi, the daughter of Jifai-Hapi, who was governor of Asyut during the reign of the Twelfth Dynasty Pharaoh Senusret I. The tomb was connected to that of Jifai-Hapi, which in turn is the largest known non-royal tomb from the Twelfth Dynasty.

The entrance to the burial chamber of Edi. Ministry of Tourism and Antiquities of Egypt.

The tomb was located to the north of that of Jifai-Hapi and was about fifteen metres deep, containing an ornate, highly decorated wooden sarcophagus with a similar inner coffin. The tomb had been looted in antiquity, with the lid of the outer sarcophagus displaced. The body of the occupant had been removed from her coffin and ripped apart, but was still present within the tomb. Examination of her remains suggests that she died before the age of forty, and had a congenital deformation of one foot. Also present in the tomb were a box of utensils and another of statues.

The sarcophagus of Edi. Ministry of Tourism and Antiquities of Egypt.

The Twelfth Dynasty was the second dynasty of the Egyptian Middle Kingdom, and was a time of military expansion and relative prosperity. Senusret I was the second Pharaoh of this dynasty, ruling from 1971-1926 BC, during which time he waged two successful wars against Nubia to the south, expanding Egyptian rule to the Second Cataract of the Nile (close to Aswan in modern Egypt), as well as building more peaceful trading relationships with the kingdoms of the near east, such as Canaan and Syria. 

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At least 148 dead amid flooding and landslides in Nepal.

At least 148 people have died and more than fifty are still missing in a series of flood and landslide events which hit Nepal driven by heavy rains which have fallen across the country since Friday 27 September 2024. The worst of the flooding has occurred in the densely populated Kathmandu Valley in the central part of the country, where 322 mm of rain fell within 24 hours between Friday and Saturday mornings, the largest amount of rain ever recorded within 24 hours in Nepal.

Flooding on the Bagmati River in Kathmandu on Saturday 28 September 2024. Anadolu Ajansi/Getty Images.

Thirty four people are known have died in Kathmandu, and at least 35 more in a series of landslides on the Prithvi Highway, outside the city, which buried two busses and several other vehicles. In the city Bhaktapur, 15 km to the east of Kathmandu, five people, including a pregnant woman and a four-year-old girl died when a house collapsed, and six people died when a landslide hit the All Nepal Football Association's training centre in Makwanpur. 

Flooding in Lalitpur, to the south of Kathmandu, on 28 September 2024. Gopen Rai/Nepal Times.

The annual monsoon in Nepal claims a large number of lives each year, with at least 170 known to have died this year between the onset of the monsoon season in June and the onset of Friday's rains. However, this rainfall typically ends towards the middle of September. This year's extended monsoon is thought to have been caused by a low pressure system over India, in turn caused by this year's exceptionally high global temperatures. Late rains such as these bring with them additional problems, as by September the ground in lowlying areas of Nepal is often waterlogged, and the waters rivers and lakes high, if not actually overflowing. This means that even if the rains stop soon, their effects are likely to be felt for some time yet, with the waters in the Koshi River recorded as running at a rate of over 12 700  cubic metres per second, compared to a seasonal average of 4200 cubic metres per second. Such high flow rates on the Koshi River almost invariably lead to significant flood events in Bihar State, India.

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Fossil pinnate Palm leaves from the Island Lagoon Flora, in the arid zone of South Australia.

Palms are an important part of the flora of the wet tropical and subtropical forests of eastern Australia, but are almost absent from the drier areas of the Australian interior, with only two species known from this area today, Livistona mariae from central Australia, and Livistona alfredii from the Pilbara region of Western Australia. Despite its large area, Australia is relatively species-poor in Palms compared with nearby landmasses, with only 54 species in 17 genera, compared to about 250 species on the island of New Guinea. 

The Palm flora of Australia contains a mixture of groups with different biogeographical regions, including Gondwanan groups, such as the Archontophoenicinae, Calamoideae, and Nypoideae, with fossil records in Australai which pre-date the Miocene, and Laurasian groups, such as Livistona spp., thought to have migrated from Southeast Asia since the Miocene, when monsoonal climates became prevalent across the region. Although of Gondwanan origin, the Archontophoenicinae are thought to have reached Australia from New Guinea in the Eocene, and subsequently dispersed from Australia to New Guinea in the Miocene. Beyond this, however, our understanding of the biogeographical origins of modern Australian Palms is severely limited by a paucity of fossils, particularly compared to the numerous fossil Palms of the Northern Hemisphere.

In a paper published in the journal Historical Biology on 25 September 2024, David Greenwood of the Department of Biology at Brandon University, and John Conran of rhe Environment Institute at the University of Adelaide, describe a new Palm species from fossil pinnate leaves from the Island Lagoon Flora for South Australia.

The Island Lagoon Flora is one of a number of ‘silcrete floras’ known the arid zone of South Australia, which produce a Plant fossils, which appear to have been species adapted to arid environments, with a smaller proportion of broad-leaved and Coniferous tree fossils. Age estimates for these floras have varied considerably since they were first recorded in the 1890s, with current estimates suggesting that different localities may reflect Eocene, Miocene, and Miocene-Pliocene assemblages. The Island Lagoon Flora is thought most likely to be of Miocene origin, probably contemporaneous with the Stuart Creek Silcrete Macroflora, though it is possible that it is older, possibly Eocene or Late Oligocene-Early Miocene.

The new Palm species is placed in the genus Phoenicites and given the specific name insula-lacuna, which is a Latin translation of 'Island Lagoon'. The species is described from two specimens, P14209 and P14467, both in the collection of the South Australian Museum. Both are incomplete portions of pinnate leaves, P14209 measuring 29.5 cm long and 27.7 cm wide, and P14467 measuring  23.9 cm long and 9.8 cm wide, with both showing at least 11 pinnae per side.

Phoenicites insula-lacuna. (A) Holotype P14209 showing whole specimen. (B) Paratype (P14467) with midvein at arrow. (C) Detail showing asymmetry of pinnae base (P14209). (D), (E) Detail of mid-pinnae showing midvein and secondary veins (P14209). (F) Rachis (P14209) showing patterned surface corresponding to ‘brown spots’ similar to those of extant Archontophoenix spp. (G) Detail of mid-pinnae with arrow showing midvein (P14467). John Conran in Greenwood & Conran (2024).

Greenwood and Conran note that there is little to differentiate the fossil genus Phoenicites from the living genus Archontophoenix, although they have chosen to use Phoenicites as the limited material available does not contain all of the diagnostic features for inclusion in the extant genus. This is a common situation in palaeontology, where all fossil species are morphospecies (species defined by their morphological appearance) rather than true biological species (which are defined by their ability to breed with other members of the species - something which fossils are incapable of doing).

(A)–(F) Extant Archontophoenix in the Adelaide Botanical Gardens and Waite Arboretum, University of Adelaide, or in habitat ((E) only). (A), (C) Archontophoenix alexandrae, whole leaf (A) and partial view of abaxial side (B) showing pinnae with prominent veins and pinnae rachis attachment. (B), (D) Archontophoenix cunninghamiana, partial view of abaxial side showing pinnae venation and rachis attachment, and (D) rachis showing brown spots that dry as ‘tuberculae’. (E) Archontophoenix purpurea and (F) Archontophoenix tuckerii showing pinnae venation and rachis attachment. John Conran and John Dowe in Greenwood & Conran (2024).

Modern members of the genus Archontophoenix are found in wet environments, such as freshwater swamps, rainforests, under monsoonal to seasonally dry climates. This is different from the drier climate generally recorded in the silcrete floras of South Australia. However, Greenwood and Conran note that one of the environments in which these Palms are found is rainforest gullies within (dry) tall Eucalypt forests, possibly providing a setting for the other more moisture-loving Plants found in these floras.

Map of Australia showing the Island Lagoon fossil locality, other South Australian Silcrete Flora sites, the arid zone (where the annual rainfall is less than 250 mm), the extant distribution of Archontophoenix (green circles) and the two extant species of Palm endemic in the arid zone (orange squares; Livistona alfredii in Western Australia and Livistona mariae in the Northern Territory).Abbreviations: NSW, New South Wales; NT, Northern Territory; Qld, Queensland; SA, South Australia; Tas, Tasmania; Vic, Victoria; WA, Western Australia. Greenwood & Conran (2024).

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