# Liquids/Liquid objects

A division of astronomical objects between rocky objects, liquid objects, gaseous objects (including gas giants and stars), and plasma objects may be natural and informative.

## Liquids

A liquid is made up of tiny vibrating particles of matter, such as atoms and molecules, held together by intramolecular bonds. Although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require a relatively narrow temperature/pressure range to exist.

## Theoretical liquid objects

Def. a "substance that is flowing, and keeping no shape, such as water; a substance of which the molecules, while not tending to separate from one another like those of a gas, readily change their relative position, and which therefore retains no definite shape, except that determined by the containing receptacle; an inelastic fluid" is called a liquid.
Def. any object consisting of at least 2 % by particle, or least divisible particle, number of liquids is called a liquid object.

## Petroleums

"The dawn of the oil age was fairly recent. Although the stuff was used to waterproof boats in the Middle East 6,000 years ago, extracting it in earnest began only in 1859 after an oil strike in Pennsylvania. ... It was used to make kerosene, the main fuel for artificial lighting after overfishing led to a shortage of whale blubber. Other liquids produced in the refining process, too unstable or smoky for lamplight, were burned or dumped."

## Custards

Def. any "type of sauce made from milk and eggs (and usually sugar, and sometimes vanilla or other flavourings) and thickened by heat, served hot poured over desserts, as a filling for some pies and cakes, or cold and solidified" is called a custard.
Def. a "type of dessert that has a texture similar to custard or mousse but using some kind of starch as the thickening agent" is called a pudding.
For the determination of the elemental composition of liquid proteins microPIXE can quantify the metal content of protein molecules with a relative accuracy of between 10% and 20%. In part by the X-ray emission from sulfur and the phosphate groups but excessive amounts of chlorine overlap with the sulfur peak; whereas KBr and NaBr do not.
In the image second down on the right, the top image is the plum pudding model of atoms undisturbed by penetrating protons. In the bottom image, some of the protons are deflected.

## Melts

Free electrons in vacuum can be influenced by electric and magnetic fields [so] as to form a fine beam. At the spot of collision of the beam with the particles of the solid-state matter, most portion of the kinetic energy of electrons is transferred into heat. The main advantage of this method is the possibility of very fast local heating, which can be precisely electronically (computer) controlled. The high concentration of power in a small volume of matter, which can be reached in this way results in very fast increase of temperature in the spot of impact causing the melting or even evaporation of any material, depending on working conditions. This makes the electron beam an excellent tool in many applications.
"Electron beams can be generated by thermionic emission, field emission or the anodic arc method. The generated electron beam is accelerated to a high kinetic energy and focused towards the [target]. When the accelerating voltage is between 20 kV – 25 kV and the beam current is a few amperes, 85% of the kinetic energy of the electrons is converted into thermal energy as the beam bombards the surface of the [target]. The surface temperature of the [target] increases resulting in the formation of a liquid melt. Although some of incident electron energy is lost in the excitation of X-rays and secondary emission, the liquid [target] material evaporates under vacuum."
Any material can be melted by an electron beam in vacuum. This source of heat is absolutely clean, as well as the vacuum environment, so the purest materials can be produced in electron beam vacuum furnaces. For the production or refinement of rare and refractory metals the vacuum furnaces are of smaller volume, but for steels large furnaces with capacity in metric tons and electron beam power of megawatts are operated in industrialized countries.
"[W]e did not at all anticipate the nearly perfect liquid behavior."
"Other physicists have now observed quite similar liquid behavior in trapped atom samples at temperatures near absolute zero, ten million trillion times colder than the quark-gluon plasma we create at RHIC".
The second image down on the right shows the use of magnetic field induction heating to melt metal.

## Cores

Reconstructions of seismic waves in the deep interior of the Earth show that there are no S-waves in the outer core. This indicates that the outer core is liquid, because liquids cannot support shear. The outer core is liquid, and the motion of this highly conductive fluid generates the Earth's field (see geodynamo).
"Radioactive potassium [...] appears also to be a substantial source of heat in the Earth's core"
"Radioactive potassium, uranium and thorium are thought to be the three main sources of heat in the Earth's interior, aside from that generated by the formation of the planet. Together, the heat keeps the mantle actively churning and the core generating a protective magnetic field."
Much "less potassium [occurs] in the Earth's crust and mantle than [is] expected based on the composition of rocky meteors that supposedly formed the Earth. If, as some have proposed, the missing potassium resides in the Earth's iron core, how did an element as light as potassium get there, especially since iron and potassium don't mix?"
At "the high pressures and temperatures in the Earth's interior, potassium can form an alloy with iron never before observed. During the planet's formation, this potassium-iron alloy could have sunk to the core, depleting potassium in the overlying mantle and crust and providing a radioactive potassium heat source in addition to that supplied by uranium and thorium in the core."
The "new alloy [is created] by squeezing iron and potassium between the tips of two diamonds [a diamond anvil] to temperatures and pressures characteristic of 600-700 kilometers below the surface - 2,500 degrees Celsius and nearly 4 million pounds per square inch, or a quarter of a million times atmospheric pressure."
"Our new findings indicate that the core may contain as much as 1,200 parts per million potassium -just over one tenth of one percent."
"This amount may seem small, and is comparable to the concentration of radioactive potassium naturally present in bananas. Combined over the entire mass of the Earth's core, however, it can be enough to provide one-fifth of the heat given off by the Earth."
"With one experiment, Lee and Jeanloz demonstrated that potassium may be an important heat source for the geodynamo, provided a way out of some troublesome aspects of the core's thermal evolution, and further demonstrated that modern computational mineral physics not only complements experimental work, but that it can provide guidance to fruitful experimental explorations,"
"More experiments need to be done to show that iron can actually pull potassium away from the silicate rocks that dominate in the Earth's mantle."
"They proved it would be possible to dissolve potassium into liquid iron."
"Modelers need heat, so this is one source, because the radiogenic isotope of potassium can produce heat and that can help power convection in the core and drive the magnetic field. They proved it could go in. What's important is how much is pulled out of the silicate. There's still work to be done."
"If a significant amount of potassium does reside in the Earth's core, this would clear up a lingering question - why the ratio of potassium to uranium in stony meteorites (chondrites), which presumably coalesced to form the Earth, is eight times greater than the observed ratio in the Earth's crust. Though some geologists have asserted that the missing potassium resides in the core, there was no mechanism by which it could have reached the core. Other elements like oxygen and carbon form compounds or alloys with iron and presumably were dragged down by iron as it sank to the core. But at normal temperature and pressure, potassium does not associate with iron."
"Early in Earth's history, the interior temperature and pressure would not have been high enough to make this alloy."
"But as more and more meteorites piled on, the pressure and temperature would have increased to the point where this alloy could form."
"The Earth is thought to have formed from the collision of many rocky asteroids, perhaps hundreds of kilometers in diameter, in the early solar system. As the proto-Earth gradually bulked up, continuing asteroid collisions and gravitational collapse kept the planet molten. Heavier elements - in particular iron - would have sunk to the core in 10 to 100 million years' time, carrying with it other elements that bind to iron."
"Gradually, however, the Earth would have cooled off and become a dead rocky globe with a cold iron ball at the core if not for the continued release of heat by the decay of radioactive elements like potassium-40, uranium-238 and thorium-232, which have half-lives of 1.25 billion, 4 billion and 14 billion years, respectively. About one in every thousand potassium atoms is radioactive."
"The heat generated in the core turns the iron into a convecting dynamo that maintains a magnetic field strong enough to shield the planet from the solar wind. This heat leaks out into the mantle, causing convection in the rock that moves crustal plates and fuels volcanoes."
Pure "iron and pure potassium [combined] in a diamond anvil cell [that] squeezed the small sample to 26 gigapascals of pressure while heating the sample with a laser above 2,500 Kelvin (4,000 degrees Fahrenheit), which is above the melting points of both potassium and iron. [Repeat] six times in the high-intensity X-ray beams of two different accelerators - Lawrence Berkeley National Laboratory's Advanced Light Source and the Stanford Synchrotron Radiation Laboratory - to obtain X-ray diffraction images of the samples' internal structure. The images confirmed that potassium and iron had mixed evenly to form an alloy, much as iron and carbon mix to form steel alloy."
"In the theoretical magma ocean of a proto-Earth, the pressure at a depth of 400-1,000 kilometers (270-670 miles) would be between 15 and 35 gigapascals and the temperature would be 2,200-3,000 Kelvin."
"At these temperatures and pressures, the underlying physics changes and the electron density shifts, making potassium look more like iron."
"At high pressure, the periodic table looks totally different."
"The work by Lee and Jeanloz provides the first proof that potassium is indeed miscible in iron at high pressures and, perhaps as significantly, it further vindicates the computational physics that underlies the original prediction."
"If it can be further demonstrated that potassium would enter iron in significant amounts in the presence of silicate minerals, conditions representative of likely core formation processes, then potassium could provide the extra heat needed to explain why the Earth's inner core hasn't frozen to as large a size as the thermal history of the core suggests it should."
There are three requisites for a dynamo to occur and subsequently operate:
* An electrically conductive fluid medium such as a plasma or liquid iron
* local magnetohydrodynamic instabilities
* An energy source to create the local magnetohydrodynamic instabilities and to drive mechanical turbulence, motion, or shear within the fluid.
In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core. A requirement for the induction of field is a rotating fluid. Rotation in the outer core is supplied by the Coriolis effect caused by the rotation of the Earth. The Coriolis force tends to organize fluid motions and electric currents into columns aligned with the rotation axis. Induction or creation of magnetic field is described by the induction equation:
    ${\frac {\partial \mathbf {B} }{\partial t}}=\eta \nabla ^{2}\mathbf {B} +\nabla \times (\mathbf {u} \times \mathbf {B} ),$
where u is a velocity, B is the magnetic field, t is time, and $\eta =1/\sigma \mu$ is the magnetic diffusivity with $\sigma$ electrical conductivity and $\mu$ permeability. The ratio of the second term on the right hand side to the first term gives the Magnetic Reynolds number, a dimensionless ratio of advection of a magnetic field to diffusion.
Tidal forces between celestial orbiting bodies causes friction that heats up the interiors of these orbiting bodies. This is known as tidal heating, and it helps create the liquid interior criteria, providing that this interior is conductive, that is required to produce a dynamo.

## Meteors

The image on the left uses a visual radiation detector to record a meteor collision with liquid water.
Def. "precipitation products of the condensation of atmospheric water vapour" are called hydrometeors.
"Condensation or sublimation of atmospheric water vapor produces a hydrometeor. It forms in the free atmosphere, or at the earth's surface, and includes frozen water lifted by the wind. Hydrometeors which can cause a surface visibility reduction, generally fall into one of the following two categories:
* Precipitation. Precipitation includes all forms of water particles, both liquid and solid, which fall from the atmosphere and reach the ground; these include: liquid precipitation (drizzle and rain), freezing precipitation (freezing drizzle and freezing rain), and solid (frozen) precipitation (ice pellets, hail, snow, snow pellets, snow grains, and ice crystals).
* Suspended (Liquid or Solid) Water Particles. Liquid or solid water particles that form and remain suspended in the air (damp haze, cloud, fog, ice fog, and mist), as well as liquid or solid water particles that are lifted by the wind from the earth’s surface (drifting snow, blowing snow, blowing spray) cause restrictions to visibility. One of the more unusual causes of reduced visibility due to suspended water/ice particles is whiteout, while the most common cause is fog."
Def. "growth of a cloud or precipitation particle by the collision and union of a frozen particle (ice crystal or snowflake) with a super-cooled liquid droplet which freezes on impact" is called accretion.

## Rains

On the left is a late-summer rainstorm in Denmark. The nearly black color of the cloud's base indicates the foreground cloud is probably cumulonimbus.
The falling rain consists of water droplets.

## Drops

"Apart from the scientific interest for fluid sciences and material sciences in space, the rotating liquid drops have high interest for cosmogony, geophysics and nuclear physics as well."

## Infrareds

The image at right shows liquid water using an infrared detector, but information confirming the presence of liquid water solely from the infrared image is inferred.

## Astrochemistry

Aqueous geochemistry studies the role of various elements in watersheds, including copper, sulfur, mercury, and how elemental fluxes are exchanged through atmospheric-terrestrial-aquatic interactions.

## Meteorites

"When solid or liquid objects formed in the early Solar System, either by condensation from the vapor phase or by melting and crystallization of preexisting material, each of these isotopic chronometers is expected to have been reset."

## Hydrology

Def. the "science of the properties, distribution, and effects of water on a planet's surface, in the soil and underlying rocks, and in the atmosphere" is called hydrology.

## Geohydrology

The discoveries of the locations of water on Earth may be thought of as geohydrology.

## Hydromorphology

Hydromorphology is the science of the shapes and forms of water on Earth and other astronomical objects.
At the right is an "aerial view [of] thermokarst lakes outside the town of Chersky in northeast Siberia [on] August 28, 2007."
Def. "a lake occupying a closed depression formed by settlement of the ground following thawing of ice-rich permafrost or the melting of massive ice" is called a thermokarst lake.

## Oceans

Def. On Earth one "of the five large bodies of water separating the continents" is called an ocean.

## Oceanography

Oceanography, also called oceanology or marine science, studies the ocean. It covers a wide range of topics, including marine organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries.

## Mercury

"This plot [at right] shows the measured magnitude of the magnetic field of Mercury as MESSENGER executed its first flyby of that planet. MESSENGER's Magnetometer (MAG) provided definitive identification of all boundaries of the Mercury magnetosphere system, consistent with the observations made with the Fast Imaging Plasma Spectrometer (FIPS) on the Energetic Particle and Plasma Spectrometer (EPPS) instrument, and revealed a much more quiescent system than was seen during the first Mariner 10 flyby. This state of the system was also consistent with the absence of energetic particles as documented by the Energetic Particle Spectrometer (EPS) portion of MESSENGER's EPPS instrument. Mercury lacks radiations belts similar to the Van Allen belts at the Earth discovered by James Van Allen with a simple particle experiment on Explorer I launched 50 years ago."
Mercury, despite its small size, has a magnetic field [see image and plot at right], because it has a conductive liquid core created by its iron composition and friction resulting from its highly elliptical orbit.
"Mercury’s core, already suspected to occupy a greater fraction of the planet's interior than do the cores of Earth, Venus, or Mars, is even larger than anticipated."
The "elevation ranges on Mercury are much smaller than on Mars or the Moon and documents evidence that there have been large-scale changes to Mercury’s topography since the earliest phases of the planet’s geological history."
“From Mercury’s extraordinarily dynamic magnetosphere and exosphere to the unexpectedly volatile-rich composition of its surface and interior, our inner planetary neighbor is now seen to be very different from what we imagined just a few years ago."
"MESSENGER’s radio tracking has allowed the scientific team to develop the first precise model of Mercury’s gravity field which, when combined with topographic data and the planet’s spin state, sheds light on the planet’s internal structure, the thickness of its crust, the size and state of its core, and its tectonic and thermal history."
"Mercury’s core occupies a large fraction of the planet, about 85% of the planetary radius, even larger than previous estimates. Because of the planet’s small size, at one time many scientists thought the interior should have cooled to the point that the core would be solid. However, subtle dynamical motions measured from Earth-based radar, combined with MESSENGER’s newly measured parameters of the gravity field and the characteristics of Mercury’s internal magnetic field that signify an active core dynamo, indicate that the planet’s core is at least partially liquid."
"Mercury’s core is different from any other planetary core in the Solar System. Earth has a metallic, liquid outer core sitting above a solid inner core. Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer, a deeper liquid core layer, and possibly a solid inner core. These results have implications for how Mercury’s magnetic field is generated and for understanding how the planet evolved thermally."
"Energetic and magnetostrophic balance arguments show that a dynamo source for Mercury's observed magnetic field is problematic if one expects an Earth-like partitioning of toroidal and poloidal fields."
But, a thin shell dynamo model is consistent with the observed weak magnetic field.
From "the ratio of the dipole field at the core-mantle boundary to the toroidal field in the core for various shell thicknesses and Rayleigh numbers[...] some thin shell dynamos can produce magnetic fields with Mercury-like dipolar field intensities. In these dynamos, the toroidal field is produced more efficiently through differential rotation than the poloidal field is produced through upwellings interacting with the toroidal field. The poloidal field is also dominated by smaller-scale structure which was not observable by the Mariner 10 mission, compared to the dipole field."

## Venus

"Venus and the Earth have similar radii and estimated bulk compositions, and both possess an iron core that is at least partially liquid. However, despite these similarities, Venus lacks an appreciable dipolar magnetic field."
This "absence is due to Venus’s also lacking plate tectonics for the past 0.5 b.y. (1 b.y.=10$^9$ yr). The generation of a global magnetic field requires core convection, which in turn requires extraction of heat from the core into the overlying mantle. Plate tectonics cools the Earth’s mantle; on the basis of elastic thickness estimates and convection models, [...] the mantle temperature on Venus is currently increasing. This heating will reduce the heat flux out of the core to zero over ~1 b.y., halting core convection and magnetic field generation. If plate tectonics was operating on Venus prior to ca. 0.5 Ga, a magnetic field may also have existed. On Earth, the geodynamo may be a consequence of plate tectonics; this connection between near-surface processes and core magnetism may also be relevant to the generation of magnetic fields on Mars, Mercury and Ganymede."
The lack of an appreciable Earth-like dipolar magnetic field "cannot be explained by the planet's slow rotation".
In "the absence of plate tectonics, the mantle on Venus cannot cool rapidly enough to drive core convection and a geodynamo."
"Planetary magnetic fields are produced by motion in a conductor, usually the planet’s iron core. Such motion may be due to either thermal convection or compositional convection, driven by core solidification".
"The maximum heat flux that can be extracted from the core without thermal convection is given by"
    $F_{c}=k\alpha gT/C_{p},$
"where k and α are the thermal conductivity and expansivity, g is the acceleration due to gravity, T is the core temperature, and C$_p$ is the specific hear capacity. [...] F$_c$ is in the range 11-30 mW·m$^{-2}$. Thermal convection will cease if the heat being extracted from the core is less than F$_c$; in the absence of core solidification, the geodynamo will halt. Compositional convection may continue [...], but will certainly halt if the heat flux out of the core drops to zero or below (i.e., the core starts heating up). The rate at which the core loses heat is controlled by the temperature difference between core and mantle and, thus, on the rate at which the mantle is cooling".

## Earth

The image on the right is a detailed, photo-like view of Earth based largely on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite.
"Viewed from space, the most striking feature of our planet is the water. In both liquid and frozen form, it covers 75% of the Earth’s surface. It fills the sky with clouds. Water is practically everywhere on Earth, from inside the rocky crust to inside our cells."
The bluish color of water is a composite of several contributing agents. Prominent contributors include dissolved organic matter and chlorophyll.
"Why are their essays and books about the endangered earth so monological -- that is, a conversation of a dominant group talking to itself?"
Referring to the second image down on the right, "Despite differences between coastal and pelagic waters, and the differences both in the isolation techniques used and in the scale, the same major phylogenetic groups have been identified as being dominant in both these environments; however, in the larger scale study, a total of 16 major taxa were detected and in the open ocean Cyanobacteria were a dominant group."

## Moon

"The "geodynamo" that generates Earth's magnetic field is powered by heat from the inner core, which drives complex fluid motions in the molten iron of the outer core. But the moon is too small to support that type of dynamo."
"This is a very different way of powering a dynamo that involves physical stirring, like stirring a bowl with a giant spoon."
"Early in its history, the moon orbited the Earth at a much closer distance than it does today, and it continues to gradually recede from the Earth. At close distances, tidal interactions between the Earth and the moon caused the moon's mantle to rotate slightly differently than the core. This differential motion of the mantle relative to the core stirred the liquid core, creating fluid motions that, in theory, could give rise to a magnetic dynamo."
"The moon wobbles a bit as it spins--that's called precession--but the core is liquid, and it doesn't do exactly the same precession. So the mantle is moving back and forth across the core, and that stirs up the core."
A "lunar dynamo could have operated in this way for at least a billion years. Eventually, however, it would have stopped working as the moon got farther away from the Earth."
"The further out the moon moves, the slower the stirring, and at a certain point the lunar dynamo shuts off."
"Rocks can become magnetized from the shock of an impact, a mechanism some scientists have proposed to explain the magnetization of lunar samples. But recent paleomagnetic analyses of moon rocks, as well as orbital measurements of the magnetization of the lunar crust, suggest that there was a strong, long-lived magnetic field on the moon early in its history."
"One of the nice things about our model is that it explains how a lunar dynamo could have lasted for a billion years."
"It also makes predictions about how the strength of the field should have changed over the years, and that's potentially testable with enough paleomagnetic observations."
"Only certain types of fluid motions give rise to magnetic dynamos."
"We calculated the power that's available to drive the dynamo and the magnetic field strengths that could be generated. But we really need the dynamo experts to take this model to the next level of detail and see if it works."

## Interplanetary medium

"For specific cosmogonic details the most important piece of Mesopotamian literature is the Babylonian epic story of creation, Enuma Elish (ibid., 60–72). Here, as in Genesis, the priority of water is taken for granted, i.e., the primeval chaos consisted of a watery abyss. The name for this watery abyss, part of which is personified by the goddess Tiamat, is the etymological equivalent of the Hebrew tehom (Gen. 1:2), a proper name that always appears in the Bible without the definite article. (It should be noted, however, that whereas "Tiamat" is the name of a primal generative force, tehom is merely a poetic term for a lifeless mass of water.) In both Genesis (1:6–7) and Enuma Elish (4:137–40) the creation of heaven and earth resulted from the separation of the waters by a firmament. The existence of day and night precedes the creation of the luminous bodies (Gen. 1:5, 8, 13, and 14ff.; Enuma Elish 1:38)."

## Mars

The shield volcano, Olympus Mons [shown in the second image at right] (Mount Olympus), at 27 km is the second highest known mountain in the Solar System. It is an extinct volcano in the vast upland region Tharsis, which contains several other large volcanoes. Olympus Mons is over three times the height of Mount Everest, which in comparison stands at just over 8.8 km.

## Europa

"This rendering [at the right] of Europa shows the temperature field in a simulation of the icy Jupiter moon's global ocean dynamics, where hot plumes (red) rise from the seafloor and cool fluid (blue) sinks down from the ice-ocean border. More heat is delivered to the ice shell near the equator, consistent with the distribution of chaos terrains on Europa."
"This rendering [at the left] of Jupiter's icy moon Europa shows so-called isosurfaces of warmer (red) and cooler (blue) temperatures in a simulation of Europa’s global ocean dynamics. More heat is delivered to the ice shell near the equator where convection is more vigorous, consistent with the distribution of chaos terrains on Europa."

## Enceladus

With "a diameter only slightly more than 300 miles, Enceladus just doesn’t have the bulk needed for its interior to stay warm enough to maintain liquid water underground."
"With temperatures around 324 degrees below zero Fahrenheit, the surface of Enceladus is indeed frozen. However, in 2005 NASA's Cassini spacecraft discovered a giant plume of water gushing from cracks in the surface over the moon's south pole, indicating that there was a reservoir of water beneath the ice. Analysis of the plume by Cassini revealed that the water is salty, indicating the reservoir is large, perhaps even a global subsurface ocean. Scientists estimate from the Cassini data that the south polar heating is equivalent to a continuous release of about 13 billion watts of energy."
"To explain this mysterious warmth, some scientists invoke radiation coupled with tidal heating. As it formed, Enceladus (like all solar system objects) incorporated matter from the cloud of gas and dust left over from our sun’s formation. In the outer solar system, as Enceladus formed it grew as ice and rock coalesced. If Enceladus was able to gather greater amounts of rock, which contained radioactive elements, enough heat could have been generated by the decay of the radioactive elements in its interior to melt the body."
"Enceladus' orbit around Saturn is slightly oval-shaped. As it travels around Saturn, Enceladus moves closer in and then farther away. When Enceladus is closer to Saturn, it feels a stronger gravitational pull from the planet than when it is farther away. Like gently squeezing a rubber ball slightly deforms its shape, the fluctuating gravitational tug on Enceladus causes it to flex slightly. The flexing, called gravitational tidal forcing, generates heat from friction deep within Enceladus."
"The gravitational tides also produce stress that cracks the surface ice in certain regions, like the south pole, and may be reworking those cracks daily. Tidal stress can pull these cracks open and closed while shearing them back and forth. As they open and close, the sides of the south polar cracks move as much as a few feet, and they slide against each other by up to a few feet as well. This movement also generates friction, which (like vigorously rubbing your hands together) releases extra heat at the surface at locations that should be predictable with our understanding of tidal stress."
"To test the tidal heating theory, scientists with the Cassini team created a map of the gravitational tidal stress on the moon's icy crust and compared it to a map of the warm zones created using Cassini's composite infrared spectrometer instrument (CIRS). Assuming the greatest stress is where the most friction occurs, and therefore where the most heat is released, areas with the most stress should overlap the warmest zones on the CIRS map."
"However, they don't exactly match."
"For example, in the fissure called the Damascus Sulcus, the area experiencing the greatest amount of shearing is about 50 kilometers (about 31 miles) from the zone of greatest heat."
"Enceladus' wobble, technically called "libration," is barely noticeable."
"Cassini observations have ruled out a wobble greater than about 2 degrees with respect to Enceladus' uniform rotation rate."
A "computer simulation [...] made maps of the surface stress on Enceladus for various wobbles, and found a range where the areas of greatest stress line up better with the observed warmest zones."
"Depending on whether the wobble moves with or against the movement of Saturn in Enceladus' sky, a wobble ranging from 2 degrees down to 0.75 degrees produces the best fit to the observed warmest zones,"
"The wobble also helps with the heating conundrum by generating about five times more heat in Enceladus’ interior than tidal stress alone, and the extra heat makes it likely that Enceladus' ocean could be long-lived, according to Hurford. This is significant in the search for life, because life requires a stable environment to develop."
"The wobble is probably caused by Enceladus' uneven shape."
"Enceladus is not completely spherical, so as it moves in its orbit, the pull of Saturn's gravity generates a net torque that forces the moon to wobble."
"Enceladus' orbit is kept oval-shaped, maintaining the tidal stress, because of the gravitational tug from a neighboring larger moon Dione. Dione is farther away from Saturn than Enceladus, so it takes longer to complete its orbit. For every orbit Dione completes, Enceladus finishes two orbits, producing a regular alignment that pulls Enceladus' orbit into an oval shape."

## Stars

"The influence of the reflection asymmetry degrees of freedom on the stability of rotating charged or gravitating liquid objects [shows] that the Poincaré instability can, indeed, appear in rotating gravitating objects, but is quite unlikely in rotating nuclei."
"The formation of liquid metallic hydrogen brings with it a new candidate for the interior of the Sun and the stars."

## VY Canis Majoris

"This is one of the early spectra obtained with the SPIRE fourier transform spectrometer on Herschel. Shown here is a portion of the SPIRE spectrum of VY Canis Majoris (VY CMa), a red supergiant star near the end of its life, which is ejecting huge quantities of gas and dust into interstellar space. The inset is a SPIRE camera map of VY CMa, in which it appears as a bright compact source near the edge of a large extended cloud."
"The VY CMa spectrum is amazingly rich, with prominent features from carbon monoxide (CO) and water (H$_2$O). More than 200 other spectral features have been identified so far in the full spectrum, and several unidentified features are being investigated. Many of the features are due to water, showing that the star is surrounded by large quantities of hot steam. Observations like these will help to establish a detailed picture of the mass loss from stars and the complex chemistry occurring in their extended envelopes. As in all of the SPIRE spectra, the underlying emission increases towards shorter wavelengths, and is due to the emission from dust grains. The shape of the dust spectrum provides information on the properties of the dust."
"VY Canis Majoris (VY CMa) is a red supergiant star located about 4900 light years from Earth in the constellation Canis Major. It is the largest known star, with a size of 2600 solar radii, and also one of the most luminous, with a luminosity in excess of 100 000 times that of the Sun. The mass of VY CMa lies in the range 30-40 solar masses, and it has a mass-loss rate of 2x10-4 solar masses per year."
"The shell of gas it has ejected displays a complex structure; the circumstellar envelope is among the most remarkable chemical laboratories known in the Universe, creating a rich set of organic and inorganic molecules and dust species. Through stellar winds, these inorganic and organic compounds are injected into the interstellar medium, from which new stars orbited by new planets may form. Most of the carbon supporting life on Earth was forged by this kind of evolved star. VY CMa truly is a spectacular object, it is close to the end of its life and could explode as a supernova at any time."

## Technology

Condensed noble gases, most notably liquid xenon and liquid argon, are excellent radiation detection media. They can produce two signatures for each particle interaction: a fast flash of light (scintillation) and the local release of charge (ionisation). In two-phase xenon – so called since it involves liquid and gas phases in equilibrium – the scintillation light produced by an interaction in the liquid is detected directly with photomultiplier tubes; the ionisation electrons released at the interaction site are drifted up to the liquid surface under an external electric field, and subsequently emitted into a thin layer of xenon vapour. Once in the gas, they generate a second, larger pulse of light (electroluminescence or proportional scintillation), which is detected by the same array of photomultipliers. These systems are also known as xenon 'emission detectors'.
The basic set-up consists of 1600 water tanks (water Cherenkov Detectors, similar to the Haverah Park experiment) distributed over 3,000 square kilometres (1,200 sq mi), along with four atmospheric fluorescence detectors (similar to the High Resolution Fly's Eye) overseeing the surface array.
The Pierre Auger Observatory is unique in that it is the first experiment that combines both ground and fluorescence detectors at the same site thus allowing cross-calibration and reduction of systematic effects that may be peculiar to each technique. The Cherenkov detectors use three large photomultiplier tubes to detect the Cherenkov radiation produced by high-energy particles passing through water in the tank. The time of arrival of high-energy particles from the same shower at several tanks is used to calculate the direction of travel of the original particle. The fluorescence detectors are used to track the particle shower's glow on cloudless moonless nights, as it descends through the atmosphere.
The bubble chamber reveals the tracks of subatomic particles as trails of bubbles in a superheated liquid, usually liquid hydrogen. Bubble chambers can be made physically larger than cloud chambers, and since they are filled with much-denser liquid material, they reveal the tracks of much more energetic particles.
The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources so far are the Sun and supernova SN1987A. Various detection methods have been used. Super Kamiokande is a large volume of water surrounded by phototubes that watch for the Cherenkov radiation emitted when an incoming neutrino creates an electron or muon in the water. The Sudbury Neutrino Observatory is similar, but uses heavy water as the detecting medium. Other detectors have consisted of large volumes of chlorine or gallium which are periodically checked for excesses of argon or germanium, respectively, which are created by neutrinos interacting with the original substance. Borexino uses a liquid pseudocumene scintillator also watched by phototubes while the proposed NOνA detector will use liquid scintillator watched by avalanche photodiodes.
Scintillation neutron detectors include liquid organic scintillators, crystals, plastics, glass and scintillation fibers.

## Hypotheses

* Liquid objects are more common by a factor of two than previously realized.