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Dialogo di Galileo Galilei Linceo : matematico sopraordinario dello studio di Pisa. E filosofo e matematico primario del serenissimo gr. duca di Toscana, doue ne i congressi di quattro giornate si discorre sopra i due massimi sistemi del mondo tolemaico e copernicano, proponendo indeterminatamente le ragioni filosofiche e naturali tanto per l'una quanto per l'altra parte
The Dialogue Concerning the Two Chief World Systems was an attempt by Galileo to promote the heliocentric theory of the universe. In the Copernican system the Earth and other planets revolved around the sun, while in the Ptolemaic system everything in the universe circles around the Earth. The Dialogue, published in Florence under a formal license from the Inquisition, attempted to skirt the controversy by couching the discussion in a fictional dialogue between Aristotle, Copernicus, and Ptolemy. The ruse was unsuccessful, and in 1633 Galileo was convicted of grave suspicion of heresy. Galileo was imprisoned, and the Dialogo was placed on the Index of Forbidden Books, from which it was not removed until 1835.
Rare Book
The unexpected surface of asteroid (101955) Bennu
NASA’S Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at the near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth1. Bennu is a low-albedo B-type asteroid2 that has been linked to organic-rich hydrated carbonaceous chondrites3. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine—that is, not affected by these processes4. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu’s global properties, support the selection of a sampling site and document that site at a sub-centimetre scale5,6,7,8,9,10,11. Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid’s properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu’s thermal inertia12 and radar polarization ratios13—which indicated a generally smooth surface covered by centimetre-scale particles—resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres4. We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success.
Journal Article
Dialogue by Galileo Galilei Linceo
The Dialogue Concerning the Two Chief World Systems was an attempt by Galileo to promote the heliocentric theory of the universe. In the Copernican system the Earth and other planets revolved around the sun, while in the Ptolemaic system everything in the universe circles around the Earth. The Dialogue, published in Florence under a formal license from the Inquisition, attempted to skirt the controversy by couching the discussion in a fictional dialogue between Aristotle, Copernicus, and Ptolemy. The ruse was unsuccessful, and in 1633 Galileo was convicted of grave suspicion of heresy. Galileo was imprisoned, and the Dialogo was placed on the Index of Forbidden Books, from which it was not removed until 1835.
Rare Book
Martian moons exploration MMX: sample return mission to Phobos elucidating formation processes of habitable planets
Martian moons exploration, MMX, is the new sample return mission planned by the Japan Aerospace Exploration Agency (JAXA) targeting the two Martian moons with the scheduled launch in 2024 and return to the Earth in 2029. The major scientific objectives of this mission are to determine the origin of Phobos and Deimos, to elucidate the early Solar System evolution in terms of volatile delivery across the snow line to the terrestrial planets having habitable surface environments, and to explore the evolutionary processes of both moons and Mars surface environment. To achieve these objectives, during a stay in circum-Martian space over about 3 years MMX will collect samples from Phobos along with close-up observations of this inner moon and carry out multiple flybys of Deimos to make comparative observations of this outer moon. Simultaneously, successive observations of the Martian atmosphere will also be made by utilizing the advantage of quasi-equatorial spacecraft orbits along the moons’ orbits.
Journal Article
An evaporite sequence from ancient brine recorded in Bennu samples
Evaporation or freezing of water-rich fluids with dilute concentrations of dissolved salts can produce brines, as observed in closed basins on Earth
1
and detected by remote sensing on icy bodies in the outer Solar System
2
,
3
. The mineralogical evolution of these brines is well understood in regard to terrestrial environments
4
, but poorly constrained for extraterrestrial systems owing to a lack of direct sampling. Here we report the occurrence of salt minerals in samples of the asteroid (101955) Bennu returned by the OSIRIS-REx mission
5
. These include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine that existed early in the history of Bennu’s parent body. Discovery of diverse salts would not be possible without mission sample return and careful curation and storage, because these decompose with prolonged exposure to Earth’s atmosphere. Similar brines probably still occur in the interior of icy bodies Ceres and Enceladus, as indicated by spectra or measurement of sodium carbonate on the surface or in plumes
2
,
3
.
Samples from the asteroid (101955) Bennu, returned by the OSIRIS-REx mission, include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine.
Journal Article
A 4,565-My-old andesite from an extinct chondritic protoplanet
The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun’s photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.
Journal Article
Highly porous nature of a primitive asteroid revealed by thermal imaging
Carbonaceous (C-type) asteroids
1
are relics of the early Solar System that have preserved primitive materials since their formation approximately 4.6 billion years ago. They are probably analogues of carbonaceous chondrites
2
,
3
and are essential for understanding planetary formation processes. However, their physical properties remain poorly known because carbonaceous chondrite meteoroids tend not to survive entry to Earth’s atmosphere. Here we report on global one-rotation thermographic images of the C-type asteroid 162173 Ryugu, taken by the thermal infrared imager (TIR)
4
onboard the spacecraft Hayabusa2
5
, indicating that the asteroid’s boulders and their surroundings have similar temperatures, with a derived thermal inertia of about 300 J m
−2
s
−0.5
K
−1
(300 tiu). Contrary to predictions that the surface consists of regolith and dense boulders, this low thermal inertia suggests that the boulders are more porous than typical carbonaceous chondrites
6
and that their surroundings are covered with porous fragments more than 10 centimetres in diameter. Close-up thermal images confirm the presence of such porous fragments and the flat diurnal temperature profiles suggest a strong surface roughness effect
7
,
8
. We also observed in the close-up thermal images boulders that are colder during the day, with thermal inertia exceeding 600 tiu, corresponding to dense boulders similar to typical carbonaceous chondrites
6
. These results constrain the formation history of Ryugu: the asteroid must be a rubble pile formed from impact fragments of a parent body with microporosity
9
of approximately 30 to 50 per cent that experienced a low degree of consolidation. The dense boulders might have originated from the consolidated innermost region or they may have an exogenic origin. This high-porosity asteroid may link cosmic fluffy dust to dense celestial bodies
10
.
Thermal imaging data obtained from the spacecraft Hayabusa2 reveal that the carbonaceous asteroid 162173 Ryugu is an object of unusually high porosity.
Journal Article
Probable detection of an eruptive filament from a superflare on a solar-type star
Solar flares are often accompanied by filament/prominence eruptions (~10
4
K and ~10
10−11
cm
−3
), sometimes leading to coronal mass ejections that directly affect the Earth’s environment
1
,
2
. ‘Superflares’ are found on some active solar-type (G-type main-sequence) stars
3
–
5
, but the filament eruption–coronal mass ejection association has not been established. Here we show that our optical spectroscopic observation of the young solar-type star EK Draconis reveals evidence for a stellar filament eruption associated with a superflare. This superflare emitted a radiated energy of 2.0 × 10
33
erg, and a blueshifted hydrogen absorption component with a high velocity of −510 km s
−1
was observed shortly afterwards. The temporal changes in the spectra strongly resemble those of solar filament eruptions. Comparing this eruption with solar filament eruptions in terms of the length scale and velocity strongly suggests that a stellar coronal mass ejection occurred. The erupted filament mass of 1.1 × 10
18
g is ten times larger than those of the largest solar coronal mass ejections. The massive filament eruption and an associated coronal mass ejection provide the opportunity to evaluate how they affect the environment of young exoplanets/the young Earth
6
and stellar mass/angular momentum evolution
7
.
An energetic eruptive filament on EK Draconis most probably launched a coronal mass ejection with a mass ten times larger than the largest solar coronal mass ejection. Studying such ejections provides insight into stellar angular momentum loss and the habitability of orbiting planets.
Journal Article