Many Billions of Rocky Planets in the Habitable Zones around Red Dwarfs in the Milky Way Galaxy

This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone.

A result from ESO’s HARPS planet finder shows that rocky planets not much bigger than Earth are very common in the habitable zones around faint red stars. The international team estimates that there are tens of billions of such planets in the Milky Way Galaxy alone, and probably about one hundred in the Sun’s immediate neighbourhood. This is the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of the stars in the Milky Way.

This first direct estimate of the number of light planets around red dwarf stars has just been announced by an international team using observations with the HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile. A recent announcement, showing that planets are ubiquitous in our galaxy, used a different method that was not sensitive to the important class of exoplanets that lie in the habitable zones around red dwarfs.

The HARPS team has been searching for exoplanets orbiting the most common kind of star in the Milky Way — red dwarf stars (also known as M dwarfs). These stars are faint and cool compared to the Sun, but very common and long-lived, and therefore account for 80% of all the stars in the Milky Way.

“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet,” says Xavier Bonfils (IPAG, Observatoire des Sciences de l'Univers de Grenoble, France), the leader of the team. “Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

The HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period. A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of Gliese 581 and Gliese 667 C respectively. The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are around red dwarfs. They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.

On the other hand, more massive planets, similar to Jupiter and Saturn in our Solar System, are found to be rare around red dwarfs. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1000 times that of the Earth).

As there are many red dwarf stars close to the Sun the new estimate means that there are probably about one hundred super-Earth planets in the habitable zones around stars in the neighbourhood of the Sun at distances less than about 30 light-years.

"The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun," says Stéphane Udry (Geneva Observatory and member of the team). "But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely."

One of the planets discovered in the HARPS survey of red dwarfs is Gliese 667 Cc. This is the second planet in this triple star system and seems to be situated close to the centre of the habitable zone. Although this planet is more than four times heavier than the Earth it is the closest twin to Earth found so far and almost certainly has the right conditions for the existence of liquid water on its surface. This is the second super-Earth planet inside the habitable zone of a red dwarf discovered during this HARPS survey, after Gliese 581d was announced in 2007 and confirmed in 2009.

“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet’s atmosphere and searching for signs of life,” concludes Xavier Delfosse, another member of the team..

Image Credit: ESO/L. Calçada
Explanation from: https://www.eso.org/public/images/eso1214a/ and https://www.eso.org/public/news/eso1214/

Coronal Rain

Coronal rain is a phenomenon that occurs in the Sun's corona. It occurs when hot plasma in the corona cools and condenses in strong magnetic fields, usually associated with regions that produce solar flares. The plasma is attracted to the magnetic fields where it condenses and slowly falls back to the solar surface.

Video Credit: NASA/SDO/NASA Goddard

Clathrus Ruber

Clathrus ruber is a species of fungus in the stinkhorn family, and the type species of the genus Clathrus. It is commonly known as the latticed stinkhorn, the basket stinkhorn, or the red cage, alluding to the striking fruit bodies that are shaped somewhat like a round or oval hollow sphere with interlaced or latticed branches.

The fungus is saprobic, feeding off decaying woody plant material, and is usually found alone or in groups in leaf litter on garden soil, grassy places, or on woodchip garden mulches. Although considered primarily a European species, C. ruber has been introduced to other areas, and now has a wide distribution that includes northern Africa, Asia, Australia, and North and South America. The species was illustrated in the scientific literature during the 16th century, but was not officially described until 1729.

The fruit body initially appears like a whitish "egg" attached to the ground at the base by cords called rhizomorphs. The egg has a delicate, leathery outer membrane enclosing the compressed lattice that surrounds a layer of olive-green spore-bearing slime called the gleba, which contains high levels of calcium that help protect the fruit body during development. As the egg ruptures and the fruit body expands, the gleba is carried upward on the inner surfaces of the spongy lattice, and the egg membrane remains as a volva around the base of the structure. The fruit body can reach heights of up to 20 cm (7.9 in).

The color of the fruit body, which can range from pink to orange to red, results primarily from the carotenoid pigments lycopene and beta-carotene. The gleba has a fetid odor, somewhat like rotting meat, which attracts flies and other insects to help disperse its spores. Although the edibility of the fungus is not known with certainty, its odor would deter most from consuming it. C. ruber was not regarded highly in tales in southern European folklore, which suggested that those who handled the mushroom risked contracting various ailments.

Explanation from: https://en.wikipedia.org/wiki/Clathrus_ruber

Comparison of the Earth to the Moon

The Earth

Earth is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.

According to evidence from radiometric dating and other sources, Earth was formed about 4.54 billion years ago. Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 solar days or one sidereal year. Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). The Moon is Earth's only permanent natural satellite. Its gravitational interaction with Earth causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.

Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. 71% of Earth's surface is covered with water, with the remainder consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere. Earth's polar regions are mostly covered with ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the magnetic field, and a convecting mantle that drives plate tectonics.

Within its first billion years, life appeared in Earth's oceans and began to affect its atmosphere and surface, promoting the proliferation of aerobic as well as anaerobic organisms. Since then, the combination of Earth's distance from the Sun, its physical properties and its geological history have allowed life to thrive and evolve. The earliest undisputed life on Earth arose at least 3.5 billion years ago. Earlier physical evidence of life includes biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland, as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia. Earth's biodiversity has expanded continually except when interrupted by mass extinctions. Although scholars estimate that over 99% of all species of life (over five billion) that ever lived on Earth are extinct, there are still an estimated 10–14 million extant species, of which about 1.2 million have been documented and over 86% have not yet been described. Over 7.3 billion humans live on Earth and depend on its biosphere and minerals for their survival. Earth's human population is divided among about two hundred sovereign states which interact through diplomacy, conflict, travel, trade and communication media.

The Moon

The Moon is Earth's only natural satellite. It is one of the largest natural satellites in the Solar System, and, among planetary satellites, the largest relative to the size of the planet it orbits (its primary). It is the second-densest satellite among those whose densities are known (after Jupiter's satellite Io).

The Moon is thought to have formed approximately 4.5 billion years ago, not long after Earth. There are several hypotheses for its origin; the most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia.

The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the second-brightest regularly visible celestial object in Earth's sky after the Sun, as measured by illuminance on Earth's surface. Although it can appear a very bright white, its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art, and mythology.

The Moon's gravitational influence produces the ocean tides, body tides, and the slight lengthening of the day. The Moon's current orbital distance is about thirty times the diameter of Earth, causing it to have an apparent size in the sky almost the same as that of the Sun, with the result that the Moon covers the Sun nearly precisely in total solar eclipse. This matching of apparent visual size will not continue in the far future. The Moon's linear distance from Earth is currently increasing at a rate of 3.82 ± 0.07 centimetres (1.504 ± 0.028 in) per year, but this rate is not constant.

The Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft in 1959; the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned over 380 kg (840 lb) of lunar rocks, which have been used to develop a geological understanding of the Moon's origin, the formation of its internal structure, and its subsequent history. After the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft.

Explanation from: https://en.wikipedia.org/wiki/Earth and https://en.wikipedia.org/wiki/Moon

Sharpest View Ever of Dusty Disc Around Aging Star

The Very Large Telescope Interferometer at ESO’s Paranal Observatory in Chile has obtained the sharpest view ever of the dusty disc around an aging star. For the first time such features can be compared to those around young stars — and they look surprisingly similar. It is even possible that a disc appearing at the end of a star’s life might also create a second generation of planets.

As they approach the ends of their lives many stars develop stable discs of gas and dust around them. This material was ejected by stellar winds, whilst the star was passing through the red giant stage of its evolution. These discs resemble those that form planets around young stars. But up to now astronomers have not been able to compare the two types, formed at the beginning and the end of the stellar life cycle.

Although there are many discs associated with young stars that are sufficiently near to us to be studied in depth, there are no corresponding old stars with discs that are close enough for us to obtain detailed images.

But this has now changed. A team of astronomers led by Michel Hillen and Hans Van Winckel from the Instituut voor Sterrenkunde in Leuven, Belgium, has used the full power of the Very Large Telescope Interferometer (VLTI) at ESO’s Paranal Observatory in Chile, armed with the PIONIER instrument, and the newly upgraded RAPID detector.

Their target was the old double star IRAS 08544-4431, lying about 4000 light-years from Earth in the southern constellation of Vela (The Sails). This double star consists of a red giant star, which expelled the material in the surrounding dusty disc, and a less-evolved more normal star orbiting close to it.

Jacques Kluska, team member from the University of Exeter, United Kingdom, explains: “By combining light from several telescopes of the Very Large Telescope Interferometer, we obtained an image of stunning sharpness — equivalent to what a telescope with a diameter of 150 metres would see. The resolution is so high that, for comparison, we could determine the size and shape of a one euro coin seen from a distance of two thousand kilometres.”

Thanks to the unprecedented sharpness of the images from the Very Large Telescope Interferometer, and a new imaging technique that can remove the central stars from the image to reveal what lies around them, the team could dissect all the building blocks of the IRAS 08544-4431 system for the first time.

The most prominent feature of the image is the clearly resolved ring. The inner edge of the dust ring, seen for the first time in these observations, corresponds very well with the expected start of the dusty disc: closer to the stars, the dust would evaporate in the fierce radiation from the stars.

“We were also surprised to find a fainter glow that is probably coming from a small accretion disc around the companion star. We knew the star was double, but weren’t expecting to see the companion directly. It is really thanks to the jump in performance now provided by the new detector in PIONIER, that we are able to view the very inner regions of this distant system,” adds lead author Michel Hillen.

The team finds that discs around old stars are indeed very similar to the planet-forming ones around young stars. Whether a second crop of planets can really form around these old stars is yet to be determined, but it is an intriguing possibility.

“Our observations and modelling open a new window to study the physics of these discs, as well as stellar evolution in double stars. For the first time the complex interactions between close binary systems and their dusty environments can now be resolved in space and time,” concludes Hans Van Winckel.

Image Credit: ESO/Digitized Sky Survey 2, Davide De Martin
Explanation from: http://www.eso.org/public/news/eso1608/

Supercell over Colorado

Julesburg, Colorado, USA

July 2013

Image Credit & Copyright: Marko Korošec

Solar Eclipse of March 9, 2016 seen from Space

The Deep Space Climate Observatory (DSCOVR) was built to provide a distinct perspective on our planet. Yesterday, it added another first to its collection of unique snapshots. While residents of islands and nations in the Western Pacific looked up in the early morning hours to observe a total eclipse of the Sun, DSCOVR looked down from space and captured the shadow of the Moon marching across Earth’s sunlit face.

The animation above was assembled from 13 images acquired on March 9, 2016, by NASA’s Earth Polychromatic Imaging Camera (EPIC), a four-megapixel charge-coupled device (CCD) and Cassegrain telescope on the DSCOVR satellite. Click on the link below the animation to download the individual images from the series.

“What is unique for us is that being near the Sun-Earth line, we follow the complete passage of the lunar shadow from one edge of the Earth to the other,” said Adam Szabo, NASA’s project scientist for DSCOVR. “A geosynchronous satellite would have to be lucky to have the middle of an eclipse at noon local time for it. I am not aware of anybody ever capturing the full eclipse in one set of images or video.”

In this, the only total solar eclipse of 2016, the shadow of the new Moon starts crossing the Indian Ocean and marches past Indonesia and Australia into the open waters and islands of Oceania (Melanesia, Micronesia, and Polynesia) and the Pacific Ocean. Note how the shadow moves in the same direction as Earth rotates. The bright spot in the center of each disk is sunglint—the reflection of sunlight directly back at the EPIC camera.

From its position about 1.6 million kilometers (1 million miles) from Earth and toward the Sun, DSCOVR maintains a constant view of the sunlit face of the planet. EPIC acquires images using ten different spectral filters—from ultraviolet to near infrared—to produce a variety of science products. Natural-color images are generated by combining three separate monochrome exposures (red, green, and blue channels) taken in quick succession.

According to Szabo, the satellite normally collects images at all ten wavelengths about once every 108 minutes (with just one image at full resolution). For this eclipse, the EPIC team collected full-resolution images every 20 minutes on just the red, green, and blue channels. This allowed the satellite to collect 13 images spanning the entire four hours and twenty minutes of the eclipse.

In addition to the EPIC camera, DSCOVR carries the National Institute of Standards and Technology Advanced Radiometer (NISTAR), an instrument that measures how much solar energy is being radiated back into space from Earth. In coming weeks, scientists will be analyzing NISTAR data to quantify how the eclipse changed the incoming and outgoing radiation for those few hours.

Image Credit: DSCOVR EPIC team. NASA Earth Observatory
Explanation from: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=87675

Saturn in Color

Saturn and its rings completely fill the field of view of Cassini's narrow angle camera in this natural color image taken on March 27, 2004. This is the last single 'eyeful' of Saturn and its rings achievable with the narrow angle camera on approach to the planet. From now until orbit insertion, Saturn and its rings will be larger than the field of view of the narrow angle camera.

Color variations between atmospheric bands and features in the southern hemisphere of Saturn, as well as subtle color differences across the planet's middle B ring, are now more distinct than ever. Color variations generally imply different compositions. The nature and causes of any compositional differences in both the atmosphere and the rings are major questions to be investigated by Cassini scientists as the mission progresses.

The bright blue sliver of light in the northern hemisphere is sunlight passing through the Cassini Division in Saturn's rings and being scattered by the cloud-free upper atmosphere.

Two faint dark spots are visible in the southern hemisphere. These spots are close to the latitude where Cassini saw two storms merging in mid-March. The fate of the storms visible here is unclear. They are getting close and will eventually merge or squeeze past each other. Further analysis of such dynamic systems in Saturn's atmosphere will help scientists understand their origins and complex interactions.

Moons visible in this image are (clockwise from top right): Enceladus (499 kilometers or 310 miles across), Mimas (398 kilometers or 247 miles across), Tethys (1060 kilometers or 659 miles across) and Epimetheus (116 kilometers or 72 miles across). Epimetheus is dim and appears just above the left edge of the rings. Brightnesses have been exaggerated to aid visibility.

The image is a composite of three exposures, in red, green and blue, taken when the spacecraft was 47.7 million kilometers (29.7 million miles) from the planet. The image scale is 286 kilometers (178 miles) per pixel.

Image Credit: NASA/JPL/Space Science Institute
Explanation from: http://photojournal.jpl.nasa.gov/catalog/pia05389

Comparison of the Earth to the Sun

The Earth

Earth is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.

According to evidence from radiometric dating and other sources, Earth was formed about 4.54 billion years ago. Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 solar days or one sidereal year. Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). The Moon is Earth's only permanent natural satellite. Its gravitational interaction with Earth causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.

Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. 71% of Earth's surface is covered with water, with the remainder consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere. Earth's polar regions are mostly covered with ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the magnetic field, and a convecting mantle that drives plate tectonics.

Within its first billion years, life appeared in Earth's oceans and began to affect its atmosphere and surface, promoting the proliferation of aerobic as well as anaerobic organisms. Since then, the combination of Earth's distance from the Sun, its physical properties and its geological history have allowed life to thrive and evolve. The earliest undisputed life on Earth arose at least 3.5 billion years ago. Earlier physical evidence of life includes biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland, as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia. Earth's biodiversity has expanded continually except when interrupted by mass extinctions. Although scholars estimate that over 99% of all species of life (over five billion) that ever lived on Earth are extinct, there are still an estimated 10–14 million extant species, of which about 1.2 million have been documented and over 86% have not yet been described. Over 7.3 billion humans live on Earth and depend on its biosphere and minerals for their survival. Earth's human population is divided among about two hundred sovereign states which interact through diplomacy, conflict, travel, trade and communication media.

The Sun

The Sun is the star at the center of the Solar System and is by far the most important source of energy for life on Earth. It is a nearly perfect spherical ball of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. Its diameter is about 109 times that of Earth, and it has a mass about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen; the rest is mostly helium, with much smaller quantities of heavier elements, including oxygen, carbon, neon and iron.

The Sun is a G-type main-sequence star (G2V) based on spectral class and it is informally referred to as a yellow dwarf. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became increasingly hot and dense, eventually initiating nuclear fusion in its core. It is thought that almost all stars form by this process.

The Sun is roughly middle aged and has not changed dramatically for over four billion years, and will remain fairly stable for more than another five billion years. However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes and become a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury, Venus, and possibly Earth.

The enormous effect of the Sun on Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity. Earth's movement around the Sun is the basis of the solar calendar, which is the predominant calendar in use today.

Explanation from: https://en.wikipedia.org/wiki/Earth and https://en.wikipedia.org/wiki/Sun

Comet ISON seen by NASA's SOHO

ISON made its closest approach to the Sun during the evening of  November 28, 2013, passing just 1.2 million kilometres from the Sun's visible surface. At first the comet was thought to have disintegrated during its fiery encounter, with just a remnant of its tail continuing along ISON's trajectory. But, the next day, it seemed clear that something had survived after all -- possibly a small chunk of ISON's nucleus, along with a lot of dust. This progressively faded as it edged towards SOHO's field of view on 30 November. Over the coming weeks scientists will be analysing the data collected during ISON's encounter with the Sun to decipher the nail-biting chain of events that took place.

Video Credit: NASA/SOHO
Explanation from: http://soho.nascom.nasa.gov/hotshots/2013_11_28/

Globular cluster 47 Tucanae

This NASA/ESA Hubble Space Telescope image shows a globular cluster known as NGC 104 — or, more commonly, 47 Tucanae, since it is part of the constellation of Tucana (The Toucan) in the southern sky. After Omega Centauri it is the brightest globular cluster in the night sky, hosting tens of thousands of stars.

Scientists using Hubble observed the white dwarfs in the cluster. These dying stars migrate from the crowded centre of the cluster to its outskirts. Whilst astronomers knew about this process they had never seen it in action, until the detailed study of 47 Tucanae.

Image Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, J. Mack (STScI) and G. Piotto (University of Padova, Italy)
Explanation from: https://www.spacetelescope.org/images/heic1510a/

Spiral Galaxy NGC 253

Measuring 70 000 light-years across and laying 13 million light-years away, the nearly edge-on spiral galaxy NGC 253 is revealed here in an image from the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at the La Silla Observatory. The image is based on data obtained through four different filters (R, V, H-alpha and OIII). North is up and East to the left. The field of view is 30 arcminutes.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/eso0902c/

Lava

Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is also called lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites. The source of the heat that melts the rock within the earth is geothermal energy. When first erupted from a volcanic vent, lava is a liquid at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F).

A lava flow is a moving outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock. The term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties.

Explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows. The word "lava" comes from Italian, and is probably derived from the Latin word labes which means a fall or slide. The first use in connection with extruded magma (molten rock below the Earth's surface) was apparently in a short account written by Francesco Serao on the eruption of Vesuvius between May 14 and June 4, 1737. Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain.

Video Credit & Copyright: Sam Cossman
Explanation from: https://en.wikipedia.org/wiki/Lava

The Milky Way Galaxy Contains at Least 100 Billion Planets

This artist's illustration gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits, and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one.

An international team, including three astronomers from the European Southern Observatory (ESO), has used the technique of gravitational microlensing to measure how common planets are in the Milky Way. After a six-year search that surveyed millions of stars, the team concludes that planets around stars are the rule rather than the exception. The results will appear in the journal Nature on 12 January 2012.

Over the past 16 years, astronomers have detected more than 700 confirmed exoplanets and have started to probe the spectra and atmospheres of these worlds. While studying the properties of individual exoplanets is undeniably valuable, a much more basic question remains: how commonplace are planets in the Milky Way?

Most currently known exoplanets were found either by detecting the effect of the gravitational pull of the planet on its host star or by catching the planet as it passes in front of its star and slightly dims it. Both of these techniques are much more sensitive to planets that are either massive or close to their stars, or both, and many planets will be missed.

An international team of astronomers has searched for exoplanets using a totally different method — gravitational microlensing — that can detect planets over a wide range of mass and those that lie much further from their stars.

Arnaud Cassan (Institut dʼAstrophysique de Paris), lead author of the Nature paper, explains: "We have searched for evidence for exoplanets in six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our galaxy. We also found that lighter planets, such as super-Earths or cool Neptunes, must be more common than heavier ones."

The astronomers used observations, supplied by the PLANET and OGLE teams, in which exoplanets are detected by the way that the gravitational field of their host stars, combined with that of possible planets, acts like a lens, magnifying the light of a background star. If the star that acts as a lens has a planet in orbit around it, the planet can make a detectable contribution to the brightening effect on the background star.

Jean-Philippe Beaulieu (Institut d'Astrophysique de Paris), leader of the PLANET collaboration adds: "The PLANET collaboration was established to follow up promising microlensing events with a round-the-world network of telescopes located in the southern hemisphere, from Australia and South Africa to Chile. ESO telescopes contributed greatly to these surveys.”

Microlensing is a very powerful tool, with the potential to detect exoplanets that could never be found any other way. But a very rare chance alignment of a background and lensing star is required for a microlensing event to be seen at all. And, to spot a planet during an event, an additional chance alignment of the planet’s orbit is also needed.

Although for these reasons finding a planet by microlensing is far from an easy task, in the six year's worth of microlensing data used in the analysis, three exoplanets were actually detected in the PLANET and OGLE searches: a super-Earth , and planets with masses comparable to Neptune and Jupiter. By microlensing standards, this is an impressive haul. In detecting three planets, either the astronomers were incredibly lucky and had hit the jackpot despite huge odds against them, or planets are so abundant in the Milky Way that it was almost inevitable .

The astronomers then combined information about the three positive exoplanet detections with seven additional detections from earlier work, as well as the huge numbers of non-detections in the six year's worth of data — non-detections are just as important for the statistical analysis and are much more numerous. The conclusion was that one in six of the stars studied hosts a planet of similar mass to Jupiter, half have Neptune-mass planets and two thirds have super-Earths. The survey was sensitive to planets between 75 million kilometres and 1.5 billion kilometres from their stars (in the Solar System this range would include all the planets from Venus to Saturn) and with masses ranging from five times the Earth up to ten times Jupiter.

Combining the results suggests strongly that the average number of planets around a star is greater than one. They are the rule rather than the exception.

“We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way,” concludes Daniel Kubas, co-lead author of the paper.

Image Credit: NASA, ESA, and M. Kornmesser (ESO)
Explanation from: http://hubblesite.org/newscenter/archive/releases/2012/07/image/a/ and https://www.eso.org/public/news/eso1204/

The remnant of the supernova SN 1006 seen at many different wavelengths

Just over a thousand years ago, the stellar explosion known as supernova SN 1006 was observed. It was brighter than Venus, and visible during the day for weeks. The brightest supernova ever recorded on Earth, this spectacular light show was documented in China, Japan, Europe, and the Arab world.

Ancient observers were treated to this celestial fireworks display without understanding its cause or implications. Astronomers now understand that SN 1006 was caused by a white dwarf star that captured mass from a companion star until the white dwarf became unstable and exploded. Recent observations of the remnant of SN 1006 reveal the liberation of elements such as iron that were previously locked up inside the star. Because no material falls back into a neutron star or black hole after this type of supernova explosion, the liberation of this star's contents is complete. It represents, therefore, a cosmic version of Independence Day for this star.

This is a composite image of the SN 1006 supernova remnant, which is located about 7000 light years from Earth. Shown here are X-ray data from NASA's Chandra X-ray Observatory (blue), optical data from the University of Michigan's 0.9 meter Curtis Schmidt telescope at the NSF's Cerro Tololo Inter-American Observatory (CTIO; yellow) and the Digitized Sky Survey (orange and light blue), plus radio data from the NRAO's Very Large Array and Green Bank Telescope (VLA/GBT; red).

This combined study of the Chandra, CTIO and VLA/GBT observations shows new evidence for the acceleration of charged particles to high energies in supernova shockwaves. An accompanying Hubble Space Telescope image of SN 1006 shows a close-up of the region on the upper right of the supernova remnant. The twisting ribbon of light seen by Hubble reveals where the expanding blast wave is sweeping into very tenuous surrounding gas.

Image Credit: X-ray: NASA/CXC/Rutgers/G.Cassam-Chenaï, J.Hughes et al.; Radio: NRAO/AUI/NSF/GBT/VLA/Dyer, Maddalena & Cornwell; Optical: Middlebury College/F.Winkler, NOAO/AURA/NSF/CTIO Schmidt & DSS
Explanation from: http://chandra.si.edu/photo/2008/sn1006c/

Aurora over Faskrudsfjordur

Faskrudsfjordur, Iceland

March 8, 2012

Image Credit & Copyright: Jónína Óskarsdóttir

Earth seen from the International Space Station

ISS, Orbit of the Earth

Video Credit: ESA/NASA

Cave of the Crystals

Cave of the Crystals or Giant Crystal Cave is a cave connected to the Naica Mine 300 metres (980 ft) below the surface in Naica, Chihuahua, Mexico.

The main chamber contains giant selenite crystals (gypsum, CaSO4·2 H2O), some of the largest natural crystals ever found. The cave's largest crystal found to date is 12 m (39 ft) in length, 4 m (13 ft) in diameter and 55 tons in weight. The cave is extremely hot, with air temperatures reaching up to 58 °C (136 °F) with 90 to 99 percent humidity. The cave is relatively unexplored due to these factors. Without proper protection, people can only endure approximately ten minutes of exposure at a time.

A group of scientists known as the Naica Project have been heavily involved in researching these caverns.

Naica lies on an ancient fault above an underground magma chamber below the cave. The magma heated the ground water which was saturated with sulfide ions (S2−). Cool oxygenated surface water contacted the mineral saturated heated water, but the two did not mix due to the difference in their densities. The oxygen slowly diffused into the heated water and oxidized the sulfides (S2−) into sulfates (SO42−). The hydrated sulfate gypsum crystallized at an extremely slow rate of over the course of at least 500,000 years forming the enormous crystals found today. The key to this process is the slow diffusion of oxygen from the cool, low density surface water into the hot, high density ground water.

Explanation from: https://en.wikipedia.org/wiki/Cave_of_the_Crystals

F5 tornado in Elie, Canada

The Elie, Manitoba Tornado was an F5 tornado that struck the town of Elie, Manitoba, Canada, (40 kilometres (25 mi) west of Winnipeg) on June 22, 2007. While several houses were leveled, no one was injured or killed by the tornado. A well-built home in the town was swept clean off of its foundation, justifying the F5 classification. This makes it one of the strongest twisters on record since 1999 and one of only nine to reach F5/EF5 intensity between 1999 and 2011 in North America. Four other tornadoes were also confirmed in the small outbreak. Because Environment Canada adopted the Enhanced Fujita Scale in 2013, there will be no more tornadoes with an F5 rating, making this tornado the first and only confirmed F5 tornado that Canada has ever seen.

Image Credit & Copyright: Justin Hobson
Explanation from: https://en.wikipedia.org/wiki/2007_Elie,_Manitoba_tornado

The Butterfly Nebula

This celestial object looks like a delicate butterfly. But it is far from serene.

What resemble dainty butterfly wings are actually roiling cauldrons of gas heated to more than 36,000 degrees Fahrenheit. The gas is tearing across space at more than 600,000 miles an hour—fast enough to travel from Earth to the Moon in 24 minutes!

A dying star that was once about five times the mass of the Sun is at the center of this fury. It has ejected its envelope of gases and is now unleashing a stream of ultraviolet radiation that is making the cast-off material glow. This object is an example of a planetary nebula, so-named because many of them have a round appearance resembling that of a planet when viewed through a small telescope.

The Wide Field Camera 3 (WFC3), a new camera aboard NASA's Hubble Space Telescope, snapped this image of the planetary nebula, catalogued as NGC 6302, but more popularly called the Bug Nebula or the Butterfly Nebula. WFC3 was installed by NASA astronauts in May 2009, during the servicing mission to upgrade and repair the 19-year-old Hubble telescope.

NGC 6302 lies within our Milky Way galaxy, roughly 3,800 light-years away in the constellation Scorpius. The glowing gas is the star's outer layers, expelled over about 2,200 years. The "butterfly" stretches for more than two light-years, which is about half the distance from the Sun to the nearest star, Alpha Centauri.

The central star itself cannot be seen, because it is hidden within a doughnut-shaped ring of dust, which appears as a dark band pinching the nebula in the center. The thick dust belt constricts the star's outflow, creating the classic "bipolar" or hourglass shape displayed by some planetary nebulae.

The star's surface temperature is estimated to be about 400,000 degrees Fahrenheit, making it one of the hottest known stars in our galaxy. Spectroscopic observations made with ground-based telescopes show that the gas is roughly 36,000 degrees Fahrenheit, which is unusually hot compared to a typical planetary nebula.

The WFC3 image reveals a complex history of ejections from the star. The star first evolved into a huge red-giant star, with a diameter of about 1,000 times that of our Sun. It then lost its extended outer layers. Some of this gas was cast off from its equator at a relatively slow speed, perhaps as low as 20,000 miles an hour, creating the doughnut-shaped ring. Other gas was ejected perpendicular to the ring at higher speeds, producing the elongated "wings" of the butterfly-shaped structure. Later, as the central star heated up, a much faster stellar wind, a stream of charged particles traveling at more than 2 million miles an hour, plowed through the existing wing-shaped structure, further modifying its shape.

The image also shows numerous finger-like projections pointing back to the star, which may mark denser blobs in the outflow that have resisted the pressure from the stellar wind.

The nebula's reddish outer edges are largely due to light emitted by nitrogen, which marks the coolest gas visible in the picture. WFC3 is equipped with a wide variety of filters that isolate light emitted by various chemical elements, allowing astronomers to infer properties of the nebular gas, such as its temperature, density, and composition.

The white-colored regions are areas where light is emitted by sulfur. These are regions where fast-moving gas overtakes and collides with slow-moving gas that left the star at an earlier time, producing shock waves in the gas (the bright white edges on the sides facing the central star). The white blob with the crisp edge at upper right is an example of one of those shock waves.

NGC 6302 was imaged on July 27, 2009, with Hubble's Wide Field Camera 3 in ultraviolet and visible light. Filters that isolate emissions from oxygen, helium, hydrogen, nitrogen, and sulfur from the planetary nebula were used to create this composite image.

These Hubble observations of the planetary nebula NGC 6302 are part of the Hubble Servicing Mission 4 Early Release Observations.

Image Credit: NASA, ESA, and the Hubble SM4 ERO Team
Explanation from: http://hubblesite.org/newscenter/archive/releases/2009/25/image/f/

Jupiter's Great Red Spot

The Great Red Spot is a persistent anticyclonic storm on the planet Jupiter, 22° south of the equator, which has lasted for at least 186 years and possibly as long as 351 years or more. The storm is large enough to be visible through Earth-based telescopes. It was probably first observed by Giovanni Domenico Cassini, who described it around 1665. The spot has been noticeably red at times throughout its observed history, yet has not been appreciably red in the visible spectrum since a rather brief period in the mid 1970s.

Storms such as this are not uncommon within the turbulent atmospheres of gas giants. Jupiter also has white ovals and brown ovals, which are lesser unnamed storms. White ovals tend to consist of relatively cool clouds within the upper atmosphere. Brown ovals are warmer and located within the "normal cloud layer". Such storms can last hours or centuries.

Before the Voyager missions, astronomers were highly uncertain of the Red Spot's nature. Many believed it to be a solid or liquid feature on Jupiter's surface.

Image Credit: NASA/JPL
Explanation from: https://en.wikipedia.org/wiki/Great_Red_Spot

Colourful stars galore inside the globular star cluster Omega Centauri

The NASA/ESA Hubble Space Telescope snapped this panoramic view of a colourful assortment of 100 000 stars residing in the crowded core of a giant star cluster.

The image reveals a small region inside the massive globular cluster Omega Centauri, which boasts nearly 10 million stars. Globular clusters, ancient swarms of stars united by gravity, are almost as old as our Milky Way galaxy. The stars in Omega Centauri are between 10 billion and 12 billion years old. The cluster lies about 16 000 light-years from Earth.

This is one of the first images taken by the new Wide Field Camera 3 (WFC3), installed aboard Hubble in May 2009, during Servicing Mission 4. The camera can snap sharp images over a broad range of wavelengths.

The photograph showcases the camera's colour versatility by revealing a variety of stars in key stages of their life cycles.

The majority of the stars in the image are yellow-white, like our Sun. These are adult stars that are shining by hydrogen fusion. Towards the ends of their normal lives, the stars become cooler and larger. These late-life stars are the orange dots in the image.

Even later in their life cycles, the stars continue to cool down and expand in size, becoming red giants. These bright red stars swell to many times larger than our Sun's size and begin to shed their gaseous envelopes.

After ejecting most of their mass and exhausting much of their hydrogen fuel, the stars appear brilliant blue. Only a thin layer of material covers their super-hot cores. These stars are desperately trying to extend their lives by fusing helium in their cores. At this stage, they emit much of their light at ultraviolet wavelengths.

When the helium runs out, the stars reach the end of their lives. Only their burnt-out cores remain, and they are called white dwarfs (the faint blue dots in the image). White dwarfs are no longer generating energy through nuclear fusion and have gravitationally contracted to the size of Earth. They will continue to cool and grow dimmer for many billions of years until they become dark cinders.

Other stars that appear in the image are known as "blue stragglers". They are older stars that acquire a new lease of life when they collide and merge with other stars. The encounters boost the stars' energy-production rate, making them appear bluer.

All of the stars in the image are cosy neighbours. The average distance between any two stars in the cluster's crowded core is only about a third of a light-year, roughly 13 times closer than our Sun's nearest stellar neighbour, Proxima Centauri. Although the stars are close together, WFC3's sharpness can resolve each of them as individual stars. If anyone lived in this globular cluster, they would behold a star-saturated sky that is roughly 100 times brighter than Earth's sky.

Globular clusters were thought to be assemblages of stars that share the same birth date. Evidence suggests, however, that Omega Centauri has at least two populations of stars with different ages. Some astronomers think that the cluster may be the remnant of a small galaxy that was gravitationally disrupted long ago by the Milky Way, losing stars and gas.

Omega Centauri is among the biggest and most massive of some 200 globular clusters orbiting the Milky Way. It is one of the few globular clusters that can be seen with the unaided eye. Named by Johann Bayer in 1603 as the 24th brightest object in the constellation of Centaurus, it resembles a small cloud in the southern sky and might easily be mistaken for a comet.

Hubble observed Omega Centauri on 15 July 2009, in ultraviolet and visible light. These Hubble observations of Omega Centauri are part of the Hubble Servicing Mission 4 Early Release Observations.

Image Credit: NASA, ESA and the Hubble SM4 ERO Team
Explanation from: https://www.spacetelescope.org/images/heic0910g/