Milky Way Galaxy seen over Joshua Tree National Park

Joshua Tree National Park, California, USA

Image Credit & Copyright: Ian Norman and Diana Southern

Hubble Witnesses Massive Comet-Like Object Pollute Atmosphere of a White Dwarf

For the first time, scientists using NASA’s Hubble Space Telescope have witnessed a massive object with the makeup of a comet being ripped apart and scattered in the atmosphere of a white dwarf, the burned-out remains of a compact star. The object has a chemical composition similar to Halley’s Comet, but it is 100,000 times more massive and has a much higher amount of water. It is also rich in the elements essential for life, including nitrogen, carbon, oxygen, and sulfur.

These findings are evidence for a belt of comet-like bodies orbiting the white dwarf, similar to our Solar System’s Kuiper Belt. These icy bodies apparently survived the star’s evolution as it became a bloated red giant and then collapsed to a small, dense white dwarf.

As many as 25 to 50 percent of white dwarfs are known to be polluted with infalling debris from rocky, asteroid-like objects, but this is the first time a body made of icy, comet-like material has been seen polluting a white dwarf’s atmosphere.

The results also suggest the presence of unseen, surviving planets which may have perturbed the belt and worked as a “bucket brigade” to draw the icy objects into the white dwarf. The burned-out star also has a companion star, which may disturb the belt, causing objects from the belt to travel toward the burned-out star.

Siyi Xu of the European Southern Observatory in Garching, Germany, led the team that made the discovery. According to Xu, this was the first time that nitrogen was detected in the planetary debris that falls onto a white dwarf. “Nitrogen is a very important element for life as we know it,” Xu explained. “This particular object is quite rich in nitrogen, more so than any object observed in our Solar System.”

Our own Kuiper Belt, which extends outward from Neptune’s orbit, is home to many dwarf planets, comets, and other small bodies left over from the formation of the Solar System. Comets from the Kuiper Belt may have been responsible for delivering water and the basic building blocks of life to Earth billions of years ago.

The new findings are observational evidence supporting the idea that icy bodies are also present in other planetary systems, and have survived throughout the history of the star’s evolution.

To study the white dwarf’s atmosphere, the team used both Hubble and the W. M. Keck Observatory. The measurements of nitrogen, carbon, oxygen, silicon, sulfur, iron, nickel, and hydrogen all come from Hubble, while Keck provides the calcium, magnesium, and hydrogen. The ultraviolet vision of Hubble’s Cosmic Origins Spectrograph (COS) allowed the team to make measurements that are very difficult to do from the ground.

This is the first object found outside our Solar System that is akin to Halley’s Comet in composition. The team used the famous comet for comparison because it has been so well studied.

The white dwarf is roughly 170 light-years from Earth in the constellation Bootes, the Herdsman. It was first recorded in 1974 and is part of a wide binary system, with a companion star separated by 2,000 times the distance that the Earth is from the Sun.

Image Credit: NASA, ESA, and Z. Levy (STScI)
Explanation from: https://www.nasa.gov/feature/goddard/2017/hubble-witnesses-massive-comet-like-object-pollute-atmosphere-of-a-white-dwarf

Artist's impression of the view from a hypothetical moon in orbit around planet in a triple-star system

A NASA-funded astronomer has discovered a world where the sun sets over the horizon, followed by a second sun and then a third. The new planet, called HD 188753 Ab, is the first known to reside in a classic triple-star system.

"The sky view from this planet would be spectacular, with an occasional triple sunset," said Dr. Maciej Konacki (MATCH-ee Konn-ATZ-kee) of the California Institute of Technology, Pasadena, Calif., who found the planet using the Keck I telescope atop Mauna Kea mountain in Hawaii. "Before now, we had no clues about whether planets could form in such gravitationally complex systems."

The finding, reported in this week's issue of Nature, suggests that planets are more robust than previously believed.

"This is good news for planets," said Dr. Shri Kulkarni, who oversees Konacki's research at Caltech. "Planets may live in all sorts of interesting neighborhoods that, until now, have gone largely unexplored." Kulkarni is the interdisciplinary scientist for NASA's planned SIM PlanetQuest mission, which will search for signs of Earth-like worlds.

Systems with multiple stars are widespread throughout the universe, accounting for more than half of all stars. Our Sun's closest star, Alpha Centauri, is a member of a trio.

"Multiple-star systems have not been popular planet-hunting grounds," said Konacki. "They are difficult to observe and were believed to be inhospitable to planets."

The new planet belongs to a common class of extrasolar planets called "hot Jupiters," which are gas giants that zip closely around their parent stars. In this case, the planet whips every 3.3 days around a star that is circled every 25.7 years by a pirouetting pair of stars locked in a 156-day orbit.

The circus-like trio of stars is a cramped bunch, fitting into the same amount of space as the distance between Saturn and our Sun. Such tight living quarters throw theories of hot Jupiter formation into question. Astronomers had thought that hot Jupiters formed far away from their parent stars, before migrating inward.

"In this close-knit system, there would be no room at the outskirts of the parent star system for a planet to grow," said Konacki.

Previously, astronomers had identified planets around about 20 binary stars and one set of triple stars. But the stars in those systems had a lot of space between them. Most multiple-star arrangements are crowded together and difficult to study.

Konacki overcame this challenge using a modified version of the radial velocity, or "wobble," planet-hunting technique. In the traditional wobble method, a planet's presence is inferred by the gravitational tug, or wobble, it induces in its parent star. The strategy works well for single stars or far-apart binary and triple stars, but could not be applied to close-star systems because the stars' light blends together.

By developing detailed models of close-star systems, Konacki was able to tease apart the tangled starlight. This allowed him to pinpoint, for the first time, the tug of a planet on a star snuggled next to other stars. Of 20 systems examined so far, HD 188753, located 149 light-years away, was the only one found to harbor a planet.

Hot Jupiters are believed to form out of thick disks, or "doughnuts," of material that swirl around the outer fringes of young stars. The disk material clumps together to form a solid core, then pulls gas onto it. Eventually, the gas giant drifts inward. The discovery of a world under three suns contradicts this scenario. HD 188753 would have sported a truncated disk in its youth, due to the disruptive presence of its stellar companions. That leaves no room for HD 188753's planet to form, and raises a host of new questions.

The masses of the three stars in HD 188753 system range from two-thirds to about the same mass as our Sun. The planet is slightly more massive than Jupiter.

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/vision/universe/newworlds/threesun-071305a.html

The Moon seen over Lake Mattamuskeet

Lake Mattamuskeet, North Carolina, USA

Image Credit & Copyright: George Grall

Globular Cluster NGC 6642

The compact nature of globular clusters is a double-edged sword. On the one hand, having so many stars of a similar age in one bundle gives astronomers insights into the chemical makeup of our galaxy in its early history. But, at the same time, the high density of stars in the cores of globulars also makes it difficult for astronomers to resolve individual stars.

The core of NGC 6642, shown here in this Hubble Space Telescope image, is particularly dense, making this globular a difficult observational target for most telescopes. Furthermore, it occupies a very central position in our galaxy, which means that images inadvertently capture many stars that don’t belong to the cluster — these “field stars” just get in the way.

However, using Hubble’s powerful Advanced Camera for Surveys (ACS), astronomers can identify and remove such distracting field stars, and resolve the cluster’s dense core in unprecedented detail. Using Hubble’s ACS, astronomers have already made many interesting finds about NGC 6642. For example, many “blue stragglers” (stars which seemingly lag behind in their rate of aging) have been spotted in this globular, and it is known to be lacking in low-mass stars.

This picture was created from visible and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys. The field of view is approximately 1.6 by 1.6 arcminutes.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1150a/

Jupiter at Opposition

During April 2017 Jupiter is in opposition: it is at its closest to Earth and the hemisphere facing Earth is fully illuminated by the Sun. The NASA/ESA Hubble Space Telescope used this special configuration to capture an image of what is by far the largest planet in the Solar System. This image adds to many others made in the past, and together they allow astronomers to study changes in the atmosphere of the gas giant.

On 7 April Jupiter will come into opposition, the point at which the planet is located directly opposite the Sun in the sky. This means that the Sun, Earth and Jupiter line up, with Earth sitting in between the Sun and the gas giant.

Opposition also marks the planet’s closest approach to Earth — about 670 million kilometres — so that Jupiter appears brighter in the night sky than at any other time in the year. This event allows astronomers using telescopes in space and on the ground to see more detail in the atmosphere of Jupiter.

On 3 April Hubble took advantage of this favourable alignment and turned its sharp eye towards Jupiter to add to the collection of images of our massive neighbour. Hubble observed Jupiter using its Wide Field Camera 3 (WFC3), which allows observations in ultraviolet, visible and infrared light. The final image shows a sharp view of Jupiter and reveals a wealth of features in its dense atmosphere. As it is so close, Hubble can resolve features as small as about 130 kilometres across.

The surface of Jupiter is divided into several distinct, colourful bands, running parallel to the equator. These bands are created by differences in the opacity of the clouds which have varying quantities of frozen ammonia in them; the lighter bands have higher concentrations than the darker bands. The differing concentrations are kept separate by fast winds which can reach speeds of up to 650 kilometres per hour.

The most recognisable feature on Jupiter is the huge anticyclonic storm, called the Great Red Spot — this storm is large enough to engulf a whole Earth-sized planet at once. However, as with the last images of Jupiter taken by Hubble and telescopes on the ground, this new image confirms that the huge storm which has raged on Jupiter’s surface for at least 150 years continues to shrink. The reason for this is still unknown. So Hubble will continue to observe Jupiter in the hope that scientists will solve this stormy riddle.

Next to the famous Great Red Spot a much smaller storm can be seen at farther southern latitudes. Because of its similar appearance but much smaller size it was dubbed “Red Spot Junior”.

The observations of Jupiter form part of the Outer Planet Atmospheres Legacy (OPAL) programme, which allows Hubble to dedicate time each year to observing the outer planets. This way scientists have access to a collection of maps, which helps them to understand not only the atmospheres of the giant planets in the Solar System, but also the atmospheres of our own planet and of the planets that are being discovered around other stars. The programme began in 2014 with Uranus, and has been studying Jupiter and Neptune since 2015. In 2018, it will begin viewing Saturn.

Image Credit: NASA, ESA, and A. Simon (GSFC)
Explanation from: https://www.spacetelescope.org/news/heic1708/

Earth and the International Space Station

Backdropped by a blue and white Earth, the International Space Station is seen from Space Shuttle Discovery as the two spacecraft begin their relative separation. Earlier the STS-119 and Expedition 18 crews concluded 9 days, 20 hours and 10 minutes of cooperative work onboard the shuttle and station. Undocking of the two spacecraft occurred at 2:53 p.m. (CDT) on March 25, 2009.

Space Shuttle Discovery, Orbit of the Earth

March 25, 2009

Image Credit: NASA

NuSTAR Spots Temperature Swings of Black Hole Winds

This artist's concept illustrates a supermassive black hole with X-ray emission emanating from its inner region (pink) and ultrafast winds (light purple lines) streaming from the surrounding disk.

For the first time, scientists have measured rapidly varying temperatures in hot gas emanating from around a black hole. These ultrafast "winds" are created by disks of matter surrounding black holes.

The winds, according to new measurements of a nearby supermassive black hole obtained with NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) telescope, can heat up and cool down in the span of just a few hours. The black hole is located in the active galaxy IRAS 13224-3809 in the constellation Centaurus. Scientists report these findings, using data from NuSTAR and European Space Agency's XMM-Newton telescope, in the journal Nature.

"We know that supermassive black holes affect the environment of their host galaxies, and powerful winds arising from near the black hole may be one means for them to do so," says NuSTAR Principal Investigator Fiona Harrison, professor at Caltech in Pasadena. "The rapid variability, observed for the first time, is providing clues as to how these winds form and how much energy they may carry out into the galaxy."

Image Credit: ESA
Explanation from: https://www.nasa.gov/feature/jpl/nustar-spots-temperature-swings-of-black-hole-winds

Supernova 1987A

Three decades ago, astronomers spotted one of the brightest supernovae in more than 400 years. The stellar explosion, SN 1987A, blazed with the power of 100 million suns for several months after its discovery on 23 February 1987.

Located in the Large Magellanic Cloud, one of the Milky Way’s satellite galaxies, SN 1987A was the nearest supernova explosion observed in centuries and it quickly became the best studied supernova of all time. Over the last thirty years, detailed follow-up observations with telescopes both in space and on the ground have allowed astronomers to study the death throes of a massive star in unprecedented detail, from star to supernova to supernova remnant, revolutionising our understanding of these explosive events.

With its superb sensitivity at millimetre and submillimetre wavelengths, the Atacama Large Millimeter/submillimeter Array (ALMA) has been exploring previously unstudied aspects of SN 1987A since 2013. Astronomers are using ALMA to observe the glowing remains of the supernova in high resolution, studying how the remnant is making vast amounts of dust from the new elements created in the progenitor star. A portion of this dust will make its way into interstellar space and may one day be the material from which future planets around other stars are made. These observations suggest that dust in the early Universe was created by similar supernova explosions.

The composite image presented here combines observations made with ALMA, the NASA/ESA Hubble Space Telescope and NASA’s Chandra X-Ray observatory.

Image Credit: ALMA: ESO/NAOJ/NRAO/A. Angelich, Hubble: NASA, ESA, R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation) and P. Challis (Harvard-Smithsonian Center for Astrophysics), Chandra: NASA/CXC/Penn State/K. Frank et al.
Explanation from: https://www.eso.org/public/images/potw1709a/

Aurora and the International Space Station

This is one of a series of night time images photographed by one of the Expedition 29 crew members from the International Space Station. It features Aurora Australis, seen from a point over the southeast Tasman Sea near southern New Zealand. The station was located at 46.65 degrees south latitude and 169.10 degrees east longitude.

ISS, Orbit of the Earth

September 17, 2011

Image Credit: NASA

VVV BD001

This image, from ESO’s VISTA telescope, shows a newly-discovered brown dwarf nicknamed VVV BD001, which is located at the very centre of this image. It is the first new brown dwarf spotted in our cosmic neighbourhood as part of the VVV Survey. VVV BD001 is located about 55 light-years away from us, towards the very crowded centre of our galaxy.

Brown dwarfs are stars that never quite managed to grow up into a star like our Sun. They are often referred to as “failed stars”; they are larger in size than planets like Jupiter, but smaller than stars.

This dwarf is peculiar in two ways; firstly, it is the first one found towards the centre of our Milky Way, one of the most crowded regions of the sky. Secondly, it belongs to an unusual class of stars known as “unusually blue brown dwarfs” — it is still unclear why these stars are bluer than expected.

Brown dwarfs are born in the same way as stars, but do not have enough mass to trigger the burning of hydrogen to become normal stars. Because of this they are much cooler and produce far less light, making them harder to find. Astronomers generally look for these objects using near and mid-infrared cameras and special telescopes that are sensitive to these very cool objects, but usually avoid looking in very crowded regions of space — such as the central region of our galaxy, for example.

VISTA (the Visible and Infrared Survey Telescope for Astronomy) is the world’s largest survey telescope and is located at ESO’s Paranal Observatory in Chile. It is performing six separate surveys of the sky, and the VVV (VISTA Variables in the Via Lactea) survey is designed to catalogue a billion objects in the centre of our own Milky Way galaxy. VVV BD001 was discovered by chance during this survey.

Scientists have used the VVV catalogue to create a 3 dimensional map of the central bulge of the Milky Way. The data have also been used to create a monumental 108 200 by 81 500 pixel colour image containing nearly nine billion pixels, one of the biggest astronomical images ever produced.

Image Credit: ESO, and D. Minniti and J. C. Beamín
Explanation from: https://www.eso.org/public/images/potw1338a/

Comet ISON

This view of Comet C/2012 S1 (ISON) was taken with the TRAPPIST–South national telescope at ESO's La Silla Observatory on the morning of Friday 15 November 2013. Comet ISON was first spotted in our skies in September 2012, and will make its closest approach to the Sun in late November 2013.

TRAPPIST–South has been monitoring comet ISON since mid-October, using broad-band filters like those used in this image. It has also been using special narrow-band filters which isolate the emission of various gases, allowing astronomers to count how many molecules of each type are released by the comet.

Comet ISON was fairly quiet until 1 November 2013, when a first outburst doubled the amount of gas emitted by the comet. On 13 November, just before this image was taken, a second giant outburst shook the comet, increasing its activity by a factor of ten. It is now bright enough to be seen with a good pair of binoculars from a dark site, in the morning skies towards the East. Over the past couple of nights, the comet has stabilised at its new level of activity.

These outbursts were caused by the intense heat of the Sun reaching ice in the tiny nucleus of the comet as it zooms toward the Sun, causing the ice to sublimate and throwing large amounts of dust and gas into space. By the time ISON makes its closest approach to the Sun on 28 November (at only 1.2 million kilometres from its surface — just a little less than the diameter of the Sun!), the heat will cause even more ice to sublimate. However, it could also break the whole nucleus down into small fragments, which would completely evaporate by the time the comet moves away from the Sun's intense heat. If ISON survives its passage near the Sun, it could then become spectacularly bright in the morning sky.

The image is a composite of four different 30-second exposures through blue, green, red, and near-infrared filters. As the comet moved in front of the background stars, these appear as multiple coloured dots.

TRAPPIST–South (TRAnsiting Planets and PlanetesImals Small Telescope–South) is devoted to the study of planetary systems through two approaches: the detection and characterisation of planets located outside the Solar System (exoplanets), and the study of comets orbiting around the Sun. The 60-cm national telescope is operated from a control room in Liège, Belgium, 12 000 km away.

Image Credit: TRAPPIST/E. Jehin/ESO
Explanation from: https://www.eso.org/public/images/potw1346a/

Saturn's F Ring

When seen up close, the F ring of Saturn resolves into multiple dusty strands. This Cassini view shows three bright strands and a very faint fourth strand off to the right.

The central strand is the core of the F ring. The other strands are not independent at all, but are actually sections of long spirals of material that wrap around Saturn. The material in the spirals was likely knocked out from the F ring's core during interactions with a small moon.

This view looks toward the unilluminated side of the rings from about 38 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on December 18, 2016.

The view was acquired at a distance of approximately 122,000 miles (197,000 kilometers) from Saturn and at a Sun-Ring-spacecraft, or phase, angle of 47 degrees. Image scale is 0.7 miles (1.2 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA20519

Sun Emitted Trio of Solar Flares

NASA's Solar Dynamics Observatory captured this image of a solar flare peaking at 4:02 a.m. EDT on April 2, 2017, as seen in the bright flash near the Sun’s upper right edge. The image shows a subset of extreme ultraviolet light that highlights the extremely hot material in flares and which is typically colorized in blue.

NASA's Solar Dynamics Observatory captured this image of a solar flare peaking at 4:33 p.m. EDT on April 2, 2017, as seen in the bright flash near the Sun’s upper right edge. The image shows a subset of extreme ultraviolet light that highlights the extremely hot material in flares and which is typically colorized in blue.

NASA's Solar Dynamics Observatory captured this image of a solar flare peaking at 10:29 a.m. EDT on April 3, 2017, as seen in the bright flash near the Sun’s upper right edge. The image shows a subset of extreme ultraviolet light that highlights the extremely hot material in flares and which is typically colorized in teal.

The Sun emitted a trio of mid-level solar flares on April 2-3, 2017. The first peaked at 4:02 a.m. EDT on April 2, the second peaked at 4:33 p.m. EDT on April 2, and the third peaked at 10:29 a.m. EDT on April 3. NASA’s Solar Dynamics Observatory, which watches the Sun constantly, captured images of the three events. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.

The first April 2 flare was classified as an M5.3 flare, while the second April 2 was an M5.7 flare. The April 3 flare was classified as an M5.8 flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.

Image Credit: NASA/SDO
Explanation from: https://www.nasa.gov/feature/goddard/2017/nasa-s-solar-dynamics-observatory-captured-trio-of-solar-flares-april-2-3

Mysterious flash of X-rays: Chandra Deep Field South X-ray Transient 1

• A mysterious X-ray source became 1,000 times brighter over a few hours before fading dramatically in about a day.

• This source was discovered in Chandra Deep Field-South data, giving the deepest X-ray image ever made.

• Hubble and Spitzer data indicate this source is likely located in a small galaxy about 10.7 billion light years from Earth.

• Evidence points to this being some sort of destructive event but perhaps unlike any ever seen before.

Scientists have discovered a mysterious flash of X-rays using NASA's Chandra X-ray Observatory, in the deepest X-ray image ever obtained. The X-ray source is located in a region of the sky known as the Chandra Deep Field-South (CDF-S), which is shown in the main panel of this graphic. Over the 17 years Chandra has been operating, the telescope has observed this field many times, resulting in a total exposure time of 7 million seconds, equal to two and a half months. In this CDF-S image, the colors represent different bands of X-ray energy, where red, green, and blue show the low, medium, and high-energy X-rays that Chandra can detect.

 

The mysterious source that scientists discovered, shown in the inset box, has remarkable properties. Prior to October 2014, this source was not detected in X-rays, but then it erupted and became at least a factor of 1,000 brighter in a few hours. After about a day, the source had faded completely below the sensitivity of Chandra.

Thousands of hours of legacy data from the Hubble and Spitzer Space Telescopes helped determine that the event came from a faint, small galaxy about 10.7 billion light years from Earth. For a few minutes, the X-ray source produced a thousand times more energy than all the stars in this galaxy.

While scientists think this source likely comes from some sort of destructive event, its properties do not match any known phenomenon. This means this source may be of a variety that scientists have never seen before.

The researchers do, however, have some ideas of what this source could be. Two of the three main possibilities to explain the X-ray source invoke gamma-ray burst (GRB) events, which are jetted explosions triggered either by the collapse of a massive star or by the merger of a neutron star with another neutron star or a black hole. If the jet is pointing towards the Earth, a burst of gamma-rays is detected. As the jet expands, it loses energy and produces weaker, more isotropic radiation at X-ray and other wavelengths.

Possible explanations for the CDF-S X-ray source, according to the researchers, are a GRB that is not pointed toward Earth, or a GRB that lies beyond the small galaxy. A third possibility is that a medium-sized black hole shredded a white dwarf star.

Thousands of hours of legacy data from the Hubble and Spitzer Space Telescopes helped determine that the event came from a faint, small galaxy about 10.7 billion light years from Earth. For a few minutes, the X-ray source produced a thousand times more energy than all the stars in this galaxy.

The mysterious X-ray source was not seen at any other time during the two and a half months of exposure time Chandra has observed the CDF-S region. Moreover, no similar events have yet been found in Chandra observations of other parts of the sky.

This X-ray source in the CDF-S has different properties from the as yet unexplained variable X-ray sources discovered in the elliptical galaxies NGC 5128 and NGC 4636 by Jimmy Irwin and collaborators. In particular, the CDF-S source is likely associated with the complete destruction of a neutron star or white dwarf, and is roughly 100,000 times more luminous in X-rays. It is also located in a much smaller and younger host galaxy, and is only detected during a single, several-hour burst.

Additional highly targeted searches through the Chandra archive and those of ESA's XMM-Newton and NASA's Swift satellite may uncover more examples of this type of variable object that have until now gone unnoticed. Future X-ray observations by Chandra and other X-ray telescopes may also reveal the same phenomenon from other objects.

Image Credit: X-ray: NASA/CXC/F.Bauer et al.
Explanation from: http://chandra.harvard.edu/photo/2017/cdfsxt1/

Puyehue-Cordón Caulle Volcano Eruption

Osorno, Los Lagos, Chile

Image Credit: Ivan Alvarado

Protoplanetary Disk HD 169142

This image depicts the dusty disc encircling the young, isolated star HD 169142. The Atacama Large Millimeter/submillimeter Array (ALMA) imaged this disc in high resolution by picking up faint signals from its constituent millimetre-sized dust grains. The vivid rings are thick bands of dust, separated by deep gaps.

Optimised to study the cold gas and dust of systems like HD 169142, ALMA’s sharp eyes have revealed the structure of many infant solar systems with similar cavities and gaps. A variety of theories have been proposed to explain them — such as turbulence caused by magnetorotational instability, or the fusing of dust grains — but the most plausible explanation is that these pronounced gaps were carved out by giant protoplanets.

When solar systems form gas and dust coalesce into planets. These planets then effectively spring clean their orbits, clearing them of gas and dust and herding the remaining material into well-defined bands. The deep gaps seen in this image are consistent with the presence of multiple protoplanets — a finding that agrees with other optical and infrared studies of the same system.

Observing such dusty protoplanetary discs with ALMA allows scientists to investigate the first steps of planet formation in a bid to unveil the evolutionary paths of these infant systems.

Image Credit: ALMA (ESO/NAOJ/NRAO)/ Fedele et al.
Explanation from: https://www.eso.org/public/images/potw1714a/

Comet 41P/Tuttle-Giacobini-Kresák

In this image taken March 24, 2017, comet 41P/Tuttle-Giacobini-Kresák is shown moving through a field of faint galaxies in the bowl of the Big Dipper. On April 1, the comet will pass by Earth at a distance of about 13 million miles (0.14 astronomical units), or 55 times the distance from Earth to the moon; that is a much closer approach than usual for this Jupiter-family comet.

On April 1, 2017, comet 41P will pass closer than it normally does to Earth, giving observers with binoculars or a telescope a special viewing opportunity. Comet hunters in the Northern Hemisphere should look for it near the constellations Draco and Ursa Major, which the Big Dipper is part of.

Whether a comet will put on a good show for observers is notoriously difficult to predict, but 41P has a history of outbursts, and put on quite a display in 1973. If the comet experiences similar outbursts this time, there’s a chance it could become bright enough to see with the naked eye. The comet is expected to reach perihelion, or its closest approach to the Sun, on April 12.

Officially named 41P/Tuttle-Giacobini-Kresák to honor its three discoverers, the comet is being playfully called the April Fool’s Day comet on this pass. Discovery credit goes first to Horace Tuttle, who spotted the comet in 1858. According to the Cometography website, 41P was recognized at the time as a periodic comet — one that orbits the Sun — but astronomers initially were uncertain how long the comet needed to make the trip. The comet was rediscovered in 1907 by Michael Giacobini but not immediately linked to the object seen in 1858.

Later, the astronomer Andrew Crommelin determined that the two observations had been of the same object and predicted that the comet would return in 1928 and 1934, according to the Cometography entry for the comet. However, the object was not seen then and was considered lost. In 1951, L’ubor Kresák discovered it again and tied it to the earlier observations.

A member of the Jupiter family of comets, 41P makes a trip around the Sun every 5.4 years, coming relatively close to Earth on some of those trips. On this approach, the comet will pass our planet at a distance of about 13 million miles (0.14 astronomical units), or about 55 times the distance from Earth to the moon. This is the comet’s closest approach to Earth in more than 50 years and perhaps more than a century.

For scientists, 41P’s visit is an opportunity to fill in details about the comet’s composition, coma and nucleus.

“An important aspect of Jupiter-family comets is that fewer of them have been studied, especially in terms of the composition of ices in their nuclei, compared with comets from the Oort cloud,” said Michael DiSanti of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. He and his team will be observing 41P on April 1 using NASA’s Infrared Telescope Facility in Hawaii.

Astronomers will try to determine characteristics such as how quickly 41P’s nucleus rotates, which provides clues about how structurally sound the nucleus is, and whether any changes can be documented in the coma and tail. Observers also will look for outbursts, which are an indication of how active a comet is.

By cataloging the subtle, and sometimes not-so-subtle, differences among comets, researchers can construct a family tree and trace the history of how and where these objects formed as the solar system was taking shape.

“Comets are remnants from the early solar system,” said DiSanti. “Each comet that comes into the neighborhood of Earth gives us a chance to add to our understanding of the events that led to the formation of our own planet.”

Image Credit & Copyright: Chris Schur
Explanation from: https://www.nasa.gov/feature/goddard/2017/comet-that-took-a-century-to-confirm-passes-by-earth

Earth and the International Space Station

ISS, Orbit of the Earth

September 2016

Image Credit: NASA/ESA

New Horizons Halfway from Pluto to Next Flyby Target

A KBO among the Stars: In preparation for the New Horizons flyby of 2014 MU69 on Jan. 1, 2019, the spacecraft’s Long Range Reconnaissance Imager (LORRI) took a series of 10-second exposures of the background star field near the location of its target Kuiper Belt object (KBO). This composite image is made from 45 of these 10-second exposures taken on Jan. 28, 2017. The yellow diamond marks the predicted location of MU69 on approach, but the KBO itself was too far from the spacecraft (544 million miles, or 877 million kilometers) even for LORRI’s telescopic “eye” to detect. New Horizons expects to start seeing MU69 with LORRI in September of 2018 – and the team will use these newly acquired images of the background field to help prepare for that search on approach.

How time and our spacecraft fly – especially when you’re making history at 32,000 miles (51,500 kilometers) per hour.

Continuing on its path through the outer regions of the solar system, NASA’s New Horizons spacecraft has now traveled half the distance from Pluto – its storied first target – to 2014 MU69, the Kuiper Belt object (KBO) it will fly past on Jan. 1, 2019. The spacecraft reached that milestone at midnight (UTC) on April 3 – or 8 p.m. ET on April 2 – when it was 486.19 million miles (782.45 million kilometers) beyond Pluto and the same distance from MU69.

“It’s fantastic to have completed half the journey to our next flyby; that flyby will set the record for the most distant world ever explored in the history of civilization,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute in Boulder, Colorado.

Later this week – at 21:24 UTC (or 5:24 p.m. ET) on April 7 – New Horizons will also reach the halfway point in time between closest approaches to Pluto, which occurred at 7:48 a.m. ET on July 14, 2015, and MU69, predicted for 2 a.m. ET on New Year’s Day 2019. The nearly five-day difference between the halfway markers of distance and time is due to the gravitational tug of the sun. The spacecraft is actually getting slightly slower as it pulls away from the sun’s gravity, so the spacecraft crosses the midpoint in distance a bit before it passes the midpoint in time.

Ready for a Rest

New Horizons will begin a new period of hibernation later this week. In fact, the spacecraft will be sleeping through the April 7 halfway timing marker to MU69, because mission operators at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, will have put the spacecraft into hibernation two hours beforehand.

The scheduled 157-day hibernation is well-deserved; New Horizons has been “awake” for almost two and a half years, since Dec. 6, 2014. Since then, in addition to its historic Pluto encounter and 16 subsequent months of relaying the data from that encounter back to Earth, New Horizons has made breakthrough, distant observations of a dozen Kuiper Belt objects (KBOs), collected unique data on the dust and charged-particle environment of the Kuiper Belt, and studied the hydrogen gas that permeates the vast space surrounding the sun, called the heliosphere.

“The January 2019 MU69 flyby is the next big event for us, but New Horizons is truly a mission to more broadly explore the Kuiper Belt,” said Hal Weaver, New Horizons project scientist from APL, in Laurel, Maryland. “In addition to MU69, we plan to study more than two-dozen other KBOs in the distance and measure the charged particle and dust environment all the way across the Kuiper Belt.”

New Horizons is currently 3.5 billion miles (5.7 billion kilometers) from Earth; at that distance, a radio signal sent from the operations team – and traveling at light speed – needs about five hours and 20 minutes to reach the spacecraft. All spacecraft systems are healthy and operating normally, and the spacecraft is on course for its MU69 flyby.

Image Credit: NASA/JHUAPL/SWRI
Explanation from: https://www.nasa.gov/feature/new-horizons-halfway-from-pluto-to-next-flyby-target

Auroras on Uranus

Ever since Voyager 2 beamed home spectacular images of the planets in the 1980s, planet-lovers have been hooked on extra-terrestrial aurorae. Aurorae are caused by streams of charged particles like electrons, that come from various origins such as solar winds, the planetary ionosphere, and moon volcanism. They become caught in powerful magnetic fields and are channelled into the upper atmosphere, where their interactions with gas particles, such as oxygen or nitrogen, set off spectacular bursts of light.

The alien aurorae on Jupiter and Saturn are well-studied, but not much is known about the aurorae of the giant ice planet Uranus. In 2011, the NASA/ESA Hubble Space Telescope became the first Earth-based telescope to snap an image of the aurorae on Uranus. In 2012 and 2014 a team led by an astronomer from Paris Observatory took a second look at the aurorae using the ultraviolet capabilities of the Space Telescope Imaging Spectrograph (STIS) installed on Hubble.

They tracked the interplanetary shocks caused by two powerful bursts of solar wind travelling from the Sun to Uranus, then used Hubble to capture their effect on Uranus’ aurorae — and found themselves observing the most intense aurorae ever seen on the planet. By watching the aurorae over time, they collected the first direct evidence that these powerful shimmering regions rotate with the planet. They also re-discovered Uranus’ long-lost magnetic poles, which were lost shortly after their discovery by Voyager 2 in 1986 due to uncertainties in measurements and the featureless planet surface.

This is a composite image of Uranus by Voyager 2 and two different observations made by Hubble — one for the ring and one for the aurorae.

Image Credit: ESA/Hubble & NASA, L. Lamy / Observatoire de Paris
Explanation from: https://www.spacetelescope.org/images/potw1714a/