September 24, 2016

Hadean: the first eon in Earth's history

Hadean: the first eon in Earth's history

The Hadean is a geologic eon of the Earth, and lies before the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the ICS, 4 billion years ago. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term: the "Priscoan period". Other, older texts simply refer to the eon as the Pre-Archean. Nonetheless, in 2015, traces of carbon minerals interpreted as "remains of biotic life" were found in 4.1-billion-year-old rocks in Western Australia.

In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada, and Western Australia.

The oldest dated zircon crystals, enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss Terrane of Western Australia, date to 4.404 ± 0.008 Ga. This zircon is a slight outlier, with the oldest consistently-dated zircon falling closer to 4.35 Ga—around 200 million years after the hypothesized time of the Earth's formation.

A sizeable quantity of water would have been in the material that formed the Earth. Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. Hydrogen and helium are expected to continually escape (even to the present day) due to atmospheric escape. Part of the ancient planet is theorized to have been disrupted by the impact that created the Moon, which should have caused melting of one or two large areas. Earth's present composition suggests that there was not complete remelting as it is difficult to completely melt and mix huge rock masses. However, a fair fraction of material should have been vaporized by this impact, creating a rock vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a heavy CO2 atmosphere with hydrogen and water vapor. Liquid water oceans existed despite the surface temperature of 230 °C (446 °F) because water is still at an atmospheric pressure of above 27 atmospheres, caused by the heavy CO2 atmosphere, water is still liquid. As cooling continued, subduction and dissolving in ocean water removed most CO2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles appeared.

Study of zircons has found that liquid water must have existed as long ago as 4,400 million years ago, very soon after the formation of the Earth. This requires the presence of an atmosphere. The Cool Early Earth theory covers a range from about 4,400 to 4,000 million years ago.

A September 2008 study of zircons found that Australian Hadean rock holds minerals pointing to the existence of plate tectonics as early as 4,000 million years ago. If this is true, the time when Earth finished its transition from having a hot, molten surface and atmosphere full of carbon dioxide, to being very much like it is today, can be roughly dated to about 4.0 billion years ago. The actions of plate tectonics and the oceans trapped vast amounts of carbon dioxide, thereby eliminating the greenhouse effect and leading to a much cooler surface temperature and the formation of solid rock, and possibly even life.

Image Credit: Tim Bertelink via wikipedia.org
Explanation from: https://en.wikipedia.org/wiki/Hadean

Clouds over South Pacific Ocean seen from the International Space Station

Clouds over South Pacific Ocean seen from the International Space Station

ISS, Orbit of the Earth
August 2016

Image Credit: ESA/NASA

Planetary Nebula NGC 2440

Planetary Nebula NGC 2440

The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the center. Our Sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years.

Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers named them planetary nebulae because through small telescopes they resembled the disks of the distant planets Uranus and Neptune. The planetary nebula in this image is called NGC 2440. The white dwarf at the center of NGC 2440 is one of the hottest known, with a surface temperature of nearly 400,000 degrees Fahrenheit (200,000 degrees Celsius). The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bow tie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.

The image was taken February 6, 2007 with Hubble's Wide Field Planetary Camera 2. The colors correspond to material expelled by the star. Blue corresponds to helium; blue-green to oxygen; and red to nitrogen and hydrogen.

Image Credit: NASA, ESA, and K. Noll (STScI)
Explanation from: http://hubblesite.org/newscenter/archive/releases/2007/09/image/a/

September 23, 2016

Early Earth

Early Earth

The early Earth is loosely defined as Earth in its first one billion years, or gigayear. On the geologic time scale, this comprises all of the Hadean eon (starting with the formation of the Earth about 4.6 billion years ago), as well as the Eoarchean (starting 4 billion years ago) and part of the Paleoarchean (starting 3.6 billion years ago) eras of the Archean eon.

This period of Earth's history involved the planet's formation from the solar nebula via a process known as accretion. This time period included intense meteorite bombardment as well as giant impacts, including the Moon-forming impact, which resulted in a series of magma oceans and episodes of core formation. After formation of the core, delivery of meteoritic or cometary material in a "late veneer" may have delivered water and other volatile compounds to the Earth. Although little crustal material from this period survives, the oldest dated specimen is a zircon mineral of 4.404 ± 0.008 Ga enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss Terrane of Western Australia. The earliest supracrustals (such as the Isua greenstone belt) date from the latter half of this period, about 3.8 gya, around the same time as peak Late Heavy Bombardment.

According to evidence from radiometric dating and other sources, Earth formed about 4.54 billion years ago. Within its first billion years, life appeared in its 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 emerge, develop photosynthesis, and, later, evolve further and thrive. The earliest life on Earth arose at least 3.5 billion years ago. Earlier possible evidence of life include graphite, which may have a biogenic origin, in 3.7-billion-year-old metasedimentary rocks discovered in southwestern Greenland, as well as 4.1-billion-year-old zircon grains in Western Australia.

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

Moon seen from the International Space Station

Moon seen from the International Space Station

ISS, Orbit of the Earth
August 2016

Image Credit: ESA/NASA

Hubble Finds Planet Orbiting Pair of Stars

Planet Orbiting Pair of Stars
This artist's illustration shows a gas giant planet circling a pair of red dwarf stars. The Saturn-mass planet orbits roughly 300 million miles from the stellar duo. The two red dwarf stars are a mere 7 million miles apart.

Astronomers using NASA's Hubble Space Telescope, and a trick of nature, have confirmed the existence of a planet orbiting two stars in the system OGLE-2007-BLG-349, located 8,000 light-years away towards the center of our galaxy.

The planet orbits roughly 300 million miles from the stellar duo, about the distance from the asteroid belt to our Sun. It completes an orbit around both stars roughly every seven years. The two red dwarf stars are a mere 7 million miles apart, or 14 times the diameter of the Moon's orbit around Earth.

The Hubble observations represent the first time such a three-body system has been confirmed using the gravitational microlensing technique. Gravitational microlensing occurs when the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The particular character of the light magnification can reveal clues to the nature of the foreground star and any associated planets.

The three objects were discovered in 2007 by an international collaboration of five different groups: Microlensing Observations in Astrophysics (MOA), the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-up Network (MicroFUN), the Probing Lensing Anomalies Network (PLANET), and the Robonet Collaboration. These ground-based observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify.

"The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star," explained David Bennett of the NASA Goddard Space Flight Center in Greenbelt, Maryland.

The sharpness of the Hubble images allowed the research team to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our Sun. "So, the model with two stars and one planet is the only one consistent with the Hubble data," Bennett said.

Bennett's team conducted the follow-up observations with Hubble's Wide Field Planetary Camera 2. "We were helped in the analysis by the almost perfect alignment of the foreground binary stars with the background star, which greatly magnified the light and allowed us to see the signal of the two stars," Bennett explained.

Kepler has discovered 10 other planets orbiting tight binary stars, but these are all much closer to their stars than the one studied by Hubble.

Now that the team has shown that microlensing can successfully detect planets orbiting double-star systems, Hubble could provide an essential role in this new realm in the continued search for exoplanets.

Image Credit: NASA, ESA, and G. Bacon (STScI)
Explanation from: http://hubblesite.org/newscenter/archive/releases/2016/32/full/

September 22, 2016

Earth Formation

Earth Formation

The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago (Gya). By 4.54±0.04 Gya the primordial Earth had formed. The formation and evolution of the Solar System bodies occurred along with those of the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk along with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 Ma to form.

An subject of on-going research is the formation of the Moon, some 4.53 billion years ago. A working hypothesis is that it formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, impacted Earth. In this scenario, the mass of Theia was approximately 10% of that of Earth, it impacted Earth with a glancing blow, and some of its mass merged with Earth. Between approximately 4.1 and 3.8 Gya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon, and by inference, to that of Earth.

Earth's atmosphere and oceans were formed by volcanic activity and outgassing that included water vapor. The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, protoplanets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Gya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.

A crust formed when the molten outer layer of Earth cooled to form a solid as the accumulated water vapor began to act in the atmosphere. The two models that explain land mass propose either a steady growth to the present-day forms or, more likely, a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. On time scales lasting hundreds of millions of years, the supercontinents have assembled and broken apart. Roughly 750 mya (million years ago), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which also broke apart 180 mya.

The present pattern of ice ages began about 40 mya and then intensified during the Pleistocene about 3 mya. High-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 40 000–100000 years. The last continental glaciation ended 10,000 years ago.

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

Typhoon Lionrock seen from the International Space Station

Typhoon Lionrock seen from the International Space Station

ISS, Orbit of the Earth
August 2016

Image Credit: NASA/ESA

Sirius - the brightest star in the Earth's night sky

Sirius - the brightest star in the Earth's night sky

This Hubble Space Telescope image shows Sirius A, the brightest star in our nighttime sky, along with its faint, tiny stellar companion, Sirius B. Astronomers overexposed the image of Sirius A [at centre] so that the dim Sirius B [tiny dot at lower left] could be seen. The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system. The two stars revolve around each other every 50 years. Sirius A, only 8.6 light-years from Earth, is the fifth closest star system known.

Sirius B, a white dwarf, is very faint because of its tiny size, only 12,000 kilometres in diameter. White dwarfs are the leftover remnants of stars similar to our Sun. They have exhausted their nuclear fuel sources and have collapsed down to a very small size. Sirius B is about 10,000 times fainter than Sirius A. The white dwarf's feeble light makes it a challenge to study, because its light is swamped in the glare of its brighter companion as seen from telescopes on Earth. However, using the keen eye of Hubble's Space Telescope Imaging Spectrograph (STIS), astronomers have now been able to isolate the light from Sirius B and disperse it into a spectrum. STIS measured light from Sirius B being stretched to longer, redder wavelengths due to the white dwarf's powerful gravitational pull. Based on those measurements, astronomers have calculated Sirius B's mass at 98 percent that of our Sun. Analysis of the white dwarf's spectrum also has allowed astronomers to refine the estimate for its surface temperature to about 25,000 C.

Accurately determining the masses of white dwarfs is fundamentally important to understanding stellar evolution. Our Sun will eventually become a white dwarf. White dwarfs are also the source of Type Ia supernova explosions, which are used to measure cosmological distances and the expansion rate of the universe. Measurements based on Type Ia supernovae are fundamental to understanding "dark energy" , a dominant repulsive force stretching the universe apart. Also, the method used to determine the white dwarf's mass relies on one of the key predictions of Einstein's theory of General Relativity: that light loses energy when it attempts to escape the gravity of a compact star.

This image was taken 15 Oct., 2003, with Hubble's Wide Field Planetary Camera 2. Based on detailed measurements of the position of Sirius B in this image, astronomers were then able to point the STIS instrument exactly on the white dwarf and make the measurements to determine its gravitational redshift and mass.

Image Credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester)
Explanation from: https://www.spacetelescope.org/images/heic0516a/

September 21, 2016

Earth

Earth

Earth (otherwise known as the world, in Greek: Gaia, or in Latin: Terra) 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 radiometric dating and other sources of evidence, Earth 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 within a period of one tropical year (365.24 solar days). The Moon is the Earth's only permanent natural satellite; their gravitational interaction 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. The remaining 29% is land mass—consisting of continents and islands—that together has many lakes, rivers, and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in 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 Earth's magnetic field, and a convecting mantle that drives plate tectonics.

Within the first billion years of Earth history, life appeared in the oceans and began to affect the atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive. Life had certainly arisen on Earth 3.5 billion years ago, though some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. In the history of the Earth, biodiversity has gone through long durations of expansion, but occasionally punctuated by mass extinction events. Over 99% of all species of life that ever lived on Earth are today extinct. Estimates of the number of species on Earth today vary widely; most species have not been described. Over 7.3 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humanity has developed diverse societies and cultures; politically, the world is divided into about 200 sovereign states.

Image Credit: NASA/DSCOVR EPIC
Explanation from: https://en.wikipedia.org/wiki/Earth

Cassiopeia A

Cassiopeia A

This image taken with the NASA/ESA Hubble Space Telescope provides a detailed look at the tattered remains of a supernova explosion known as Cassiopeia A (Cas A). It is the youngest known remnant from a supernova explosion in the Milky Way. The Hubble image shows the complex and intricate structure of the star's shattered fragments.

The image is a composite made from 18 separate images taken using Hubble's Advanced Camera for Surveys (ACS), and it shows the Cas A remnant as a broken ring of bright filamentary and clumpy stellar ejecta. These huge swirls of debris glow with the heat generated by the passage of a shockwave from the supernova blast. The various colours of the gaseous shards indicate differences in chemical composition. Bright green filaments are rich in oxygen, red and purple are sulphur, and blue are composed mostly of hydrogen and nitrogen.

A supernova such as the one that resulted in Cas A is the explosive demise of a massive star that collapses under the weight of its own gravity. The collapsed star then blows its outer layers into space in an explosion that can briefly outshine its entire parent galaxy. Cas A is relatively young, estimated to be only about 340 years old. Hubble has observed it on several occasions to look for changes in the rapidly expanding filaments.

In the latest observing campaign, two sets of images were taken, separated by nine months. Even in that short time, Hubble's razor-sharp images can observe the expansion of the remnant. Comparison of the two image sets shows that a faint stream of debris seen along the upper left side of the remnant is moving with high speed - up to 50 million kilometres per hour (fast enough to travel from Earth to the Moon in 30 seconds!).

Cas A is located ten thousand light-years away from Earth in the constellation of Cassiopeia. Supernova explosions are the main source of elements more complex than oxygen, which are forged in the extreme conditions produced in these events. The analysis of such a nearby, relatively young and fresh example is extremely helpful in understanding the evolution of the Universe.

Image Credit: NASA, ESA, and the Hubble Heritage STScI/AURA)-ESA/Hubble Collaboration, Robert A. Fesen (Dartmouth College, USA) and James Long (ESA/Hubble)
Explanation from: https://www.spacetelescope.org/news/heic0609/

Martian Sand Dune

Martian Sand DuneMartian Sand DuneMartian Sand DuneMartian Sand Dune

Two sizes of wind-sculpted ripples are evident in this view of the top surface of a Martian sand dune. Sand dunes and the smaller type of ripples also exist on Earth. The larger ripples -- roughly 10 feet (3 meters) apart -- are a type not seen on Earth nor previously recognized as a distinct type on Mars.

The Mast Camera (Mastcam) on NASA's Curiosity Mars rover took the multiple component images of this scene on December 13, 2015, during the 1,192nd Martian day, or sol, of the rover's work on Mars. That month, Curiosity was conducting the first close-up investigation ever made of active sand dunes anywhere other than Earth.

The larger ripples have distinctive sinuous crest lines, compared to the smaller ripples.

The location is part of "Namib Dune" in the Bagnold Dune Field, which forms a dark band along the northwestern flank of Mount Sharp.

The component images were taken in early morning at this site, with the camera looking in the direction of the Sun. This mosaic combining the images has been processed to brighten it and make the ripples more visible. The sand is very dark, both from the morning shadows and from the intrinsic darkness of the minerals that dominate its composition.

Image Credit: NASA/JPL-Caltech/MSSS
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA20755

September 20, 2016

Gale Crater Lake on Mars, 3 billion years ago

Gale Crater Lake on Mars, 3 billion years ago
Gale Crater Lake on Mars, 3 billion years ago

This illustration depicts a lake of water partially filling Mars' Gale Crater, receiving runoff from snow melting on the crater's northern rim. Evidence of ancient streams, deltas and lakes that NASA's Curiosity Mars rover mission has found in the patterns of sedimentary deposits in Gale Crater suggests the crater held a lake such as this more than three billion years ago, filling and drying in multiple cycles over tens of millions of years.

Gale Crater is 96 miles (154 kilometers) in diameter. This view is looking toward the southeast. The land surface in this illustration is the area's modern shape. Three billion years ago, the rim would have been higher and less eroded. A large layered mountain, Mount Sharp, now stands in the middle of Gale Crater. Accumulation of sediments in lakes, deltas, streams and wind-blown deposits is proposed to have formed the layers making up the lower portion of the mountain. When the crater first held a lake, it might have had central peak, much smaller than Mount Sharp, formed as a rebound from the impact that excavated the crater. Such a peak might have appeared as an island in the lake.

This illustration incorporates portions of a simulated oblique view of Gale Crater based on elevation data from the High Resolution Stereo Camera on the European Space Agency's Mars Express orbiter, image data from the Context Camera on NASA's Mars Reconnaissance Orbiter, and color information from Viking Orbiter imagery. The appearance of snow is added as part of the simulation of conditions from billions of years ago. The lake is depicted filling the crater approximately to the elevation where Curiosity found lakebed sediments in the "Pahrump Hills" outcrop at the base of Mount Sharp.

Image Credit: NASA/JPL-Caltech
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA19080

Aurora, Milky Way Galaxy, Large Magellanic Cloud Galaxy and Small Magellanic Cloud Galaxy seen over Queenstown

Aurora, Milky Way Galaxy, Large Magellanic Cloud Galaxy and Small Magellanic Cloud Galaxy seen over Queenstown

Queenstown, New Zealand
October 14, 2015

Image Credit & Copyright: Minoru Yoneto

The Egg Nebula

Egg Nebula

The NASA/ESA Hubble Space Telescope has been on the forefront of research into the lives of stars like our Sun. At the ends of their lives, these stars run out of nuclear fuel in a phase that is called the preplanetary or protoplanetary nebula stage. This Hubble image of the Egg Nebula shows one of the best views to date of this brief, but dramatic, phase in a star's life.

During the preplanetary nebula phase, the hot remains of an aging star in the center of the nebula heat it up, excite the gas and make it glow over several thousand years. The short lifespan of preplanetary nebulae means there are relatively few of them in existence at any one time. Moreover, they are very dim, requiring powerful telescopes to be seen. This combination of rarity and faintness means they were only discovered comparatively recently. The Egg Nebula, the first to be discovered, was first spotted less than 40 years ago, and many aspects of this class of object remain shrouded in mystery.

At the center of this image, and hidden in a thick cloud of dust, is the nebula's central star. While scientists can't see the star directly, four searchlight beams of light coming from it shine out through the nebula. Researchers hypothesize that ring-shaped holes in the thick cocoon of dust, carved by jets coming from the star, let the beams of light emerge through the otherwise opaque cloud. The precise mechanism by which stellar jets produce these holes is not known, but one explanation is that a binary star system, rather than a single star, exists at the center of the nebula.

The onion-like layered structure of the more diffuse cloud surrounding the central cocoon is caused by periodic bursts of material being ejected from the dying star. The bursts typically occur every few hundred years.

This image is produced from exposures in visible and infrared light from Hubble's Wide Field Camera 3.

Image Credit: ESA/Hubble, NASA
Explanation from: https://www.nasa.gov/multimedia/imagegallery/image_feature_2235.html

September 19, 2016

Proto-Earth May Have Been Significant Source of Lunar Material

Proto-Earth May Have Been Significant Source of Lunar Material

A giant impact between the proto-Earth and a Mars-sized impactor named Theia is the best current theory for the formation of the Moon. Scientists believe that Theia collided with the early Earth and that the Moon was created from the rubble left over from the collision. Researchers have estimated that more than 40% of the Moon-forming debris should have been derived from left over pieces of Theia, but new research by a team of geochemists led by Junjun Zhang at the University of Chicago suggests that the Moon is made mostly of material from early Earth instead. The team analyzed Oxygen isotopes and found that terrestrial and lunar samples were almost identical, which is inconsistent with earlier models.

The researchers measured ratios in lunar samples measured by mass spectrometry. After correcting for secondary effects associated with cosmic-ray exposure at the lunar surface, they found that the ratio of the Moon is identical to that of the Earth within about four parts per million, which is only 1/150 of the isotopic range documented in meteorites.

The isotopic homogeneity of this highly refractory element suggests that lunar material was derived from the proto-Earth mantle, an origin that could be explained by efficient impact ejection, by an exchange of material between the Earth’s magma ocean and the proto-lunar disk, or by fission from a rapidly rotating post-impact Earth.

However, it remains uncertain whether more refractory elements, such as titanium, show the same degree of isotope homogeneity as oxygen in the Earth–Moon system.

Scientists still believe the general idea of having an impact forming disk that coalesced into the Moon is probably right, but this paper shows that scientists still don’t fully understand exactly what the mechanisms were. There is a lot of exciting research still to be done in this field!

Image Credit: NASA
Explanation from: http://sservi.nasa.gov/articles/the-proto-earth-may-have-been-significant-source-of-lunar-material/

Star-Forming Region NGC 6611

Star-Forming Region NGC 6611

The NASA/ESA Hubble Space Telescope has once more turned its attention towards the magnificent Eagle Nebula (Messier 16). This picture shows the northwestern part of the region, well away from the centre, and features some very bright young stars that formed from the same cloud of material. These energetic toddlers are part of an open cluster and emit ultraviolet radiation that causes the surrounding nebula to glow.

The star cluster is very bright and was discovered in the mid-eighteenth century. The nebula, however, is much more elusive and it took almost a further two decades for it to be first noted by Charles Messier in 1764. Although it is commonly known as the Eagle Nebula, its official designation is Messier 16 and the cluster is also named NGC 6611. One spectacular area of the nebula (outside the field of view) has been nicknamed “The Pillars of Creation” ever since the Hubble Space Telescope captured an iconic image of dramatic pillars of star-forming gas and dust.

The cluster and nebula are fascinating targets for small and medium-sized telescopes, particularly from a dark site free from light pollution. Messier 16 can be found within the constellation of Serpens Cauda (the Tail of the Serpent), which is sandwiched between Aquila, Sagittarius, and Ophiuchus in the heart of one of the brightest parts of the Milky Way. Small telescopes with low power are useful for observing large, but faint, swathes of the nebula, whereas 30 cm telescopes and larger may reveal the dark pillars under good conditions. But a space telescope in orbit around the Earth, like Hubble — which boasts a 2.4-metre diameter mirror and state-of-the-art instruments — is required for an image as spectacular as this one.

This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a near-infrared filter (F775W) are coloured red and images through a blue filter (F475W) are blue. The exposures times were one hour and 54 minutes respectively and the field of view is about 3.3 arcminutes across.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1033a/

Aurora and the Milky Way Galaxy

Aurora and the Milky Way Galaxy

Ifjord, Finnmark, Norway
September 26, 2011

Image Credit & Copyright: Tommy Eliassen

September 18, 2016

Ocean on Mars, 4 billion years ago

Ocean on Mars, 4 billion years ago

A primitive ocean on Mars held more water than Earth’s Arctic Ocean, according to NASA scientists who, using ground-based observatories, measured water signatures in the Red Planet’s atmosphere.

Scientists have been searching for answers to why this vast water supply left the surface.

“Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “With this work, we can better understand the history of water on Mars.”

Perhaps about 4.3 billion years ago, Mars would have had enough water to cover its entire surface in a liquid layer about 450 feet (137 meters) deep. More likely, the water would have formed an ocean occupying almost half of Mars’ northern hemisphere, in some regions reaching depths greater than a mile (1.6 kilometers).

The new estimate is based on detailed observations made at the European Southern Observatory’s Very Large Telescope in Chile, and the W.M. Keck Observatory and NASA Infrared Telescope Facility in Hawaii. With these powerful instruments, the researchers distinguished the chemical signatures of two slightly different forms of water in Mars’ atmosphere. One is the familiar H2O. The other is HDO, a naturally occurring variation in which one hydrogen is replaced by a heavier form, called deuterium.

By comparing the ratio of HDO to H2O in water on Mars today and comparing it with the ratio in water trapped in a Mars meteorite dating from about 4.5 billion years ago, scientists can measure the subsequent atmospheric changes and determine how much water has escaped into space.

The team mapped H2O and HDO levels several times over nearly six years, which is equal to approximately three Martian years. The resulting data produced global snapshots of each compound, as well as their ratio. These first-of-their-kind maps reveal regional variations called microclimates and seasonal changes, even though modern Mars is essentially a desert.

The research team was especially interested in regions near Mars’ north and south poles, because the polar ice caps hold the planet’s largest known water reservoir. The water stored there is thought to capture the evolution of Mars’ water during the wet Noachian period, which ended about 3.7 billion years ago, to the present.

From the measurements of atmospheric water in the near-polar region, the researchers determined the enrichment, or relative amounts of the two types of water, in the planet’s permanent ice caps. The enrichment of the ice caps told them how much water Mars must have lost – a volume 6.5 times larger than the volume in the polar caps now. That means the volume of Mars’ early ocean must have been at least 20 million cubic kilometers (5 million cubic miles).

Based on the surface of Mars today, a likely location for this water would be in the Northern Plains, considered a good candidate because of the low-lying ground. An ancient ocean there would have covered 19 percent of the planet’s surface. By comparison, the Atlantic Ocean occupies 17 percent of Earth’s surface.

“With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting it might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard.

NASA is studying Mars with a host of spacecraft and rovers under the agency’s Mars Exploration Program, including the Opportunity and Curiosity rovers, Odyssey and Mars Reconnaissance Orbiter spacecraft, and the MAVEN orbiter, which arrived at the Red Planet in September 2014 to study the planet’s upper atmosphere.

In 2016, a Mars lander mission called InSight will launch to take a first look into the deep interior of Mars. The agency also is participating in ESA’s (European Space Agency) 2016 and 2018 ExoMars missions, including providing telecommunication radios to ESA’s 2016 orbiter and a critical element of the astrobiology instrument on the 2018 ExoMars rover. NASA’s next rover, heading to Mars in 2020, will carry instruments to conduct unprecedented science and exploration technology investigations on the Red Planet.

NASA’s Mars Exploration Program seeks to characterize and understand Mars as a dynamic system, including its present and past environment, climate cycles, geology and biological potential. In parallel, NASA is developing the human spaceflight capabilities needed for future round-trip missions to Mars in the 2030s.

Image Credit: NASA/GSFC
Explanation from: http://www.nasa.gov/press/2015/march/nasa-research-suggests-mars-once-had-more-water-than-earth-s-arctic-ocean

Spiral Galaxy NGC 6217

Spiral Galaxy NGC 6217

The barred spiral galaxy NGC 6217 was photographed on 13 June and 8 July 2009, as part of the initial testing and calibration of Hubble’s ACS. The galaxy lies up to 90 million light-years away in the north circumpolar constellation Ursa Major.

Image Credit: NASA, ESA and the Hubble SM4 ERO Team

Planetary Nebula NGC 7027

Planetary Nebula NGC 7027

This visible and infrared light picture of NGC 7027 provides a more complete view of how this planetary nebula is being shaped, revealing steps in its evolution.

Image Credit: William B. Latter (SIRTF Science Center/Caltech) and NASA/ESA