April 25, 2017

Cassini Completes Final - and Fateful - Titan Flyby

Saturn's moon TitanSaturn's moon Titan

NASA's Cassini spacecraft has had its last close brush with Saturn's hazy moon Titan and is now beginning its final set of 22 orbits around the ringed planet.

The spacecraft made its 127th and final close approach to Titan on April 21 at 11:08 p.m. PDT (2:08 a.m. EDT on April 22), passing at an altitude of about 608 miles (979 kilometers) above the moon's surface.

Cassini transmitted its images and other data to Earth following the encounter. Scientists with Cassini's radar investigation will be looking this week at their final set of new radar images of the hydrocarbon seas and lakes that spread across Titan's north polar region. The planned imaging coverage includes a region previously seen by Cassini's imaging cameras, but not by radar. The radar team also plans to use the new data to probe the depths and compositions of some of Titan's small lakes for the first (and last) time, and look for further evidence of the evolving feature researchers have dubbed the "magic island."

"Cassini's up-close exploration of Titan is now behind us, but the rich volume of data the spacecraft has collected will fuel scientific study for decades to come," said Linda Spilker, the mission's project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

Gateway to the Grand Finale

The flyby also put Cassini on course for its dramatic last act, known as the Grand Finale. As the spacecraft passed over Titan, the moon's gravity bent its path, reshaping the robotic probe's orbit slightly so that instead of passing just outside Saturn's main rings, Cassini will begin a series of 22 dives between the rings and the planet on April 26. The mission will conclude with a science-rich plunge into Saturn's atmosphere on September 15.

"With this flyby we're committed to the Grand Finale," said Earl Maize, Cassini project manager at JPL. "The spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn's atmosphere on Sept. 15 no matter what."

Cassini received a large increase in velocity of approximately 1,925 mph (precisely 860.5 meters per second) with respect to Saturn from the close encounter with Titan.

After buzzing Titan, Cassini coasted onward, reaching the farthest point in its orbital path around Saturn at 8:46 p.m. PDT (11:46 p.m. EDT) on April 22. This point, called apoapse, is where each new Cassini lap around Saturn begins. Technically, Cassini began its Grand Finale orbits at this time, but since the excitement of the finale begins in earnest on April 26 with the first ultra-close dive past Saturn, the mission is celebrating the latter milestone as the formal beginning of the finale.

The spacecraft's first finale dive will take place on April 26 at 2 a.m. PDT (5 a.m. EDT). The spacecraft will be out of contact during the dive and for about a day afterward while it makes science observations from close to the planet. The earliest time Cassini is scheduled to make radio contact with Earth is 12:05 a.m. PDT (3:05 a.m. EDT) on April 27. Images and other data are expected to begin flowing in shortly after communication is established.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://www.nasa.gov/feature/jpl/cassini-completes-final-and-fateful-titan-flyby

Cascading Post-coronal Loops

Cascading Post-coronal Loops

An active region that had just rotated into view blasted out a coronal mass ejection, which was immediately followed by a bright series of post-coronal loops seeking to reorganize that region's magnetic field (April 19, 2017). We have observed this phenomenon numerous times, but this one was one of the longest and clearest sequences we have seen in years. The bright loops are actually charged particles spinning along the magnetic field lines. The action was captured in a combination of two wavelengths of extreme ultraviolet light over a period of about 20 hours.

Image Credit: NASA/GSFC/Solar Dynamics Observatory
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21598

Martian Gullies

Martian Gullies

Gullies eroded into the steep inner slope of an impact crater at this location appear perfectly pristine in this image captured by NASA's Mars Reconnaissance Orbiter (MRO). Although at first glance it may appear that there are craters superimposed on the gully fans, inspection of HiRISE stereo coverage shows that the craters lie only on the pre-gully terrain.

Distinctive colors in the gully channels and alcoves offer another indication of youth and recent activity. The pre-gully landscape is covered by secondary craters from nearby Gasa Crater, estimated to be about 1 million years old. Although some have suggested that the Martian gullies are also about a million years old and formed in a different environment, we now know that they are continuing to form today.

Image Credit: NASA/JPL-Caltech/Univ. of Arizona
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21599

Red Panda

Red PandaRed PandaRed PandaRed PandaRed PandaRed PandaRed PandaRed PandaRed Panda

The red panda is a mammal native to the eastern Himalayas and southwestern China. It has reddish-brown fur, a long, shaggy tail, and a waddling gait due to its shorter front legs; it is slightly larger than a domestic cat. It is arboreal, feeds mainly on bamboo, but also eats eggs, birds, and insects. It is a solitary animal, mainly active from dusk to dawn, and is largely sedentary during the day.

The red panda has been classified as Endangered by the IUCN because its wild population is estimated at less than 10,000 mature individuals and continues to decline due to habitat loss and fragmentation, poaching, and inbreeding depression, although red pandas are protected by national laws in their range countries.

The red panda is the only living species of the genus Ailurus and the family Ailuridae. It has been previously placed in the raccoon and bear families, but the results of phylogenetic analysis provide strong support for its taxonomic classification in its own family Ailuridae, which, along with the weasel, raccoon and skunk families is part of the superfamily Musteloidea. Two subspecies are recognized. It is not closely related to the giant panda.

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

The Far Side of the Moon

The Far Side of the Moon

Because the Moon is tidally locked (meaning the same side always faces Earth), it was not until 1959 that the farside was first imaged by the Soviet Luna 3 spacecraft (hence the Russian names for prominent farside features, such as Mare Moscoviense). And what a surprise -­ unlike the widespread maria on the nearside, basaltic volcanism was restricted to a relatively few, smaller regions on the farside, and the battered highlands crust dominated. A different world from what we saw from Earth.

Of course, the cause of the farside/nearside asymmetry is an interesting scientific question. Past studies have shown that the crust on the farside is thicker, likely making it more difficult for magmas to erupt on the surface, limiting the amount of farside mare basalts. Why is the farside crust thicker? That is still up for debate, and in fact several presentations at this week's Lunar and Planetary Science Conference attempt to answer this question.

The Clementine mission obtained beautiful mosaics with the sun high in the sky (low phase angles), but did not have the opportunity to observe the farside at sun angles favorable for seeing surface topography. This WAC mosaic provides the most complete look at the morphology of the farside to date, and will provide a valuable resource for the scientific community. And it's simply a spectacular sight!

The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) is a push-frame camera that captures seven color bands (321, 360, 415, 566, 604, 643, and 689 nm) with a 57-km swath (105-km swath in monochrome mode) from a 50 km orbit. One of the primary objectives of LROC is to provide a global 100 m/pixel monochrome (643 nm) base map with incidence angles between 55°-70° at the equator, lighting that is favorable for morphological interpretations. Each month, the WAC provides nearly complete coverage of the Moon under unique lighting. As an added bonus, the orbit-to-orbit image overlap provides stereo coverage. Reducing all these stereo images into a global topographic map is a big job, and is being led by LROC Team Members from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). Several preliminary WAC topographic products have appeared in LROC featured images over the past year (Orientale basin, Sinus Iridum).

Image Credit: NASA/Goddard/Arizona State University.
Explanation from: https://www.nasa.gov/mission_pages/LRO/news/lro-farside.html

Airglow and the Milky Way Galaxy

Airglow and the Milky Way Galaxy

The skies above ESO’s Paranal Observatory resemble oil on water in this picture, as greens, yellows, and blues blend to create an iridescent skyscape.

The rocky, barren landscape below evokes an image of an alien world, perfectly complementing the shimmering cosmic display occurring above. The main feature is our beautiful home galaxy, the Milky Way, arching across the Chilean night sky and framing the awestruck observer on the left. The light from billions of stars combines to create the Milky Way’s glow, with huge clouds of dark dust blocking the light here and there and creating the dark and mottled pattern we observe. A natural effect known as airglow is responsible for the swathes of green and orange light that appear to be emanating from the horizon.

ESO’s Very Large Telescope can be seen as a speck in the distant background to the right atop Cerro Paranal. Its neighbour, slightly lower down, is the Visible and Infrared Survey Telescope for Astronomy (VISTA).

Image Credit: ESO/P. Horálek
Explanation from: https://www.eso.org/public/images/potw1715a/

April 24, 2017

Earth at Night: Asia and Australia

Earth at Night: Asia and Australia

Suomi NPP satellite
2016

Image Credit: NASA

Iceberg near Ferryland

Iceberg near Ferryland

Ferryland, Newfoundland and Labrador, Canada
April 16, 2017

Image Credit: Jody Martin/Reuters

Star TYC 3203-450-1 and Galaxy NGC 7250

Star TYC 3203-450-1 and Galaxy NGC 7250

In space, being outshone is an occupational hazard. This NASA/ESA Hubble Space Telescope image captures a galaxy named NGC 7250. Despite being remarkable in its own right — it has bright bursts of star formation and recorded supernova explosions — it blends into the background somewhat thanks to the gloriously bright star hogging the limelight next to it.

This bright object is a single and little-studied star named TYC 3203-450-1, located in the constellation of Lacerta (The Lizard), much closer than the much more distant galaxy. Only this way a normal star can outshine an entire galaxy, consisting of billions of stars. Astronomers studying distant objects call these stars “foreground stars” and they are often not very happy about them, as their bright light is contaminating the faint light from the more distant and interesting objects they actually want to study.

In this case TYC 3203-450-1 million times closer than NGC 7250 which lies over 45 million light-years away from us. Would the star be the same distance as NGC 7250, it would hardly be visible in this image.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1717a/

Detecting Life in the Ultra-dry Atacama Desert

Atacama Desert
Chile's Atacama Desert is the driest non-polar desert on Earth -- and a ready analog for Mars' rugged, arid terrain.

Few places are as hostile to life as Chile's Atacama Desert. It's the driest non-polar desert on Earth, and only the hardiest microbes survive there. Its rocky landscape has lain undisturbed for eons, exposed to extreme temperatures and radiation from the sun.

If you can find life here, you might be able to find it in an even harsher environment -- like the surface of Mars. That's why a team of researchers from NASA and several universities visited the Atacama in February. They spent 10 days testing devices that could one day be used to search for signs of life on other worlds. That group included a team from NASA's Jet Propulsion Laboratory in Pasadena, California, working on a portable chemistry lab called the Chemical Laptop.

With just a small water sample, the Laptop can check for amino acids, the organic molecules that are widespread in our solar system and considered the building blocks of all life as we know it. Liquid-based analysis techniques have been shown to be orders of magnitude more sensitive than gas-based methods for the same kinds of samples. But when you scoop up a sample from Mars, the amino acids you're looking for will be trapped inside of or chemically bonded to minerals.

To break down those bonds, JPL has designed another piece of technology, a subcritical water extractor that would act as the "front end" for the Laptop. This extractor uses water to release the amino acids from a soil sample, leaving them ready to be analyzed by the Chemical Laptop.

"These two pieces of technology work together so that we can search for biosignatures in solid samples on rocky or icy worlds," said Peter Willis of JPL, the project's principal investigator. "The Atacama served as a proving ground to see how this technology would work on an arid planet like Mars."

To find life, just add water

Willis' team revisited an Atacama site he first went to in 2005. At that time, the extractor he used was manually operated; in February, the team used an automated extractor designed by Florian Kehl, a postdoctoral researcher at JPL.

The extractor ingests soil and regolith samples and mixes them with water. Then, it subjects the samples to high pressure and temperature to get the organics out.

"At high temperatures, water has the ability to dissolve the organic compounds from the soil," Kehl said. "Think of a tea bag: in cold water, not much happens. But when you add hot water, the tea releases an entire bouquet of molecules that gives the water a particular flavor, color and smell."

To remove the amino acids from those minerals, the water has to get much hotter than your ordinary cup of tea: Kehl said the extractor is currently able to reach temperatures as high as 392 degrees Fahrenheit (200 degrees Celsius).

Liquid samples would be more readily available on ocean worlds like Jupiter's moon Europa, Kehl said. There, the extractor might still be necessary, as amino acids could be bonded to minerals mixed into the ice. They also may be present as part of larger molecules, which the extractor could break into smaller building blocks before analyzing them with the Chemical Laptop. Once the extractor has prepared its samples, the Laptop can do its work.

NASA's own tricorder

The Chemical Laptop checks liquid samples for a set of 17 amino acids -- what the team refers to as "the Signature 17." By looking at the types, amounts and geometries of these amino acids in a sample, it's possible to infer the presence of life.

"All these molecules 'like' being in water," said Fernanda Mora of JPL, the Chemical Laptop's lead scientist. "They dissolve in water and they don't evaporate easily, so they're much easier to detect in water."

The Laptop mixes liquid samples with a fluorescent dye, which attaches to amino acids and makes it possible to detect them when illuminated by a laser.

Then, the sample is injected onto a separation microchip. A voltage is applied between the two ends of the channel, causing the amino acids to move at different speeds towards the end, where the laser is shining. Amino acids can be identified by how quickly they move through the channel. As the molecules pass through the laser, they emit light that is used to quantify how much of each amino acid is present.

"The idea is to automate and miniaturize all the steps you would do manually in a chemistry lab on Earth," Mora said. "That way, we can do the same analyses on another world simply by sending commands with a computer."

The near-term goal is to integrate the extractor and Chemical Laptop into a single, automated device. It would be tested during future field campaigns to the Atacama Desert with a team of researchers led by Brian Glass of NASA's Ames Research Center in Mountain View, California.

"These are some of the hardest samples to analyze you can get on the planet," Mora said of the team's work in the Atacama. She added that in the future, the team wants to test this technology in icy environments like Antarctica. Those could serve as analogs to Europa and other ocean worlds, where liquid samples would be more readily plentiful.

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/feature/jpl/detecting-life-in-the-driest-place-on-earth

Gravitationally Lensed Supernova

Gravitationally Lensed SupernovaGravitationally Lensed Supernova

A Swedish-led team of astronomers used the NASA/ESA Hubble Space Telescope to analyse the multiple images of a gravitationally lensed type Ia supernova for the first time. The four images of the exploding star will be used to measure the expansion of the Universe. This can be done without any theoretical assumptions about the cosmological model, giving further clues about how fast the Universe is really expanding. The results are published in the journal Science.

An international team, led by astronomers from the Stockholm University, Sweden, has discovered a distant type Ia supernova, called iPTF16geu — it took the light 4.3 billion years to travel to Earth. The light from this particular supernova was bent and magnified by the effect of gravitational lensing so that it was split into four separate images on the sky. The four images lie on a circle with a radius of only about 3000 light-years around the lensing foreground galaxy, making it one of the smallest extragalactic gravitational lenses discovered so far. Its appearance resembles the famous Refsdal supernova, which astronomers detected in 2015. Refsdal, however, was a core-collapse supernova.

Gravitationally Lensed Supernova
The galaxy SDSS J210415.89-062024.7 is located 2.5 billion light years away. It acted as a lens for a supernova at an even greater distance, creating four distinct images of the explosion — an effect created by strong gravitational lensing.

Type Ia supernovae always have the same intrinsic brightness, so by measuring how bright they appear astronomers can determine how far away they are. They are therefore known as standard candles. These supernovae have been used for decades to measure distances across the Universe, and were also used to discover its accelerated expansion and infer the existence of dark energy. Now the supernova iPTF16geu allows scientists to explore new territory, testing the theories of the warping of spacetime on smaller extragalactic scales than ever before.

“Resolving, for the first time, multiple images of a strongly lensed standard candle supernova is a major breakthrough. We can measure the light-focusing power of gravity more accurately than ever before, and probe physical scales that may have seemed out of reach until now,” says Ariel Goobar, Professor at the Oskar Klein Centre at Stockholm University and lead author of the study.

Gravitationally Lensed Supernova
The Palomar Observatory, located on Palomar Mountain, California, created this wide-field view of the night sky. In the lower central part of the image scientists discovered a supernova explosion, being lensed by a foreground galaxy.

The critical importance of the object meant that the team instigated follow-up observations of the supernova less than two months after its discovery. This involved some of the world’s leading telescopes in addition to Hubble: the Keck telescope on Mauna Kea, Hawaii, and ESO’s Very Large Telescope in Chile. Using the data gathered, the team calculated the magnification power of the lens to be a factor of 52. Because of the standard candle nature of iPTF16geu, this is the first time this measurement could be made without any prior assumptions about the form of the lens or cosmological parameters.

Currently the team is in the process of accurately measuring how long it took for the light to reach us from each of the four images of the supernova. The differences in the times of arrival can then be used to calculate the Hubble constant — the expansion rate of the Universe — with high precision. This is particularly crucial in light of the recent discrepancy between the measurements of its value in the local and the early Universe.

Gravitationally Lensed Supernova
Astronomers used the Sloan Digital Sky Survey (SDSS), carried out by a 2.5-metre wide-angle optical telescope at Apache Point Observatory in New Mexico, USA, to look for supernovae. The explosion named iPTF16geu can be seen left of the centre of the image as a tiny red dot.

As important as lensed supernovae are for cosmology, it is extremely difficult to find them. Not only does their discovery rely on a very particular and precise alignment of objects in the sky, but they are also only visible for a short time. “The discovery of iPTF16geu is truly like finding a somewhat weird needle in a haystack,” remarks Rahman Amanullah, co-author and research scientist at Stockholm University. “It reveals to us a bit more about the Universe, but mostly triggers a wealth of new scientific questions.”

Studying more similarly lensed supernovae will help shape our understanding of just how fast the Universe is expanding. The chances of finding such supernovae will improve with the installation of new survey telescopes in the near future.

Image Credit: ESA/Hubble, NASA, Sloan Digital Sky Survey, Palomar Observatory/California Institute of Technology
Explanation from: https://www.spacetelescope.org/news/heic1710/

NASA’s Cassini Mission Prepares for 'Grand Finale' at Saturn

NASA’s Cassini Mission Prepares for 'Grand Finale' at Saturn
This illustration shows NASA’s Cassini spacecraft above Saturn's northern hemisphere prior to one of its 22 grand finale dives.

NASA's Cassini spacecraft, in orbit around Saturn since 2004, is about to begin the final chapter of its remarkable story. On Wednesday, April 26, the spacecraft will make the first in a series of dives through the 1,500-mile-wide (2,400-kilometer) gap between Saturn and its rings as part of the mission’s grand finale.

"No spacecraft has ever gone through the unique region that we'll attempt to boldly cross 22 times," said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "What we learn from Cassini’s daring final orbits will further our understanding of how giant planets, and planetary systems everywhere, form and evolve. This is truly discovery in action to the very end."

During its time at Saturn, Cassini has made numerous dramatic discoveries, including a global ocean that showed indications of hydrothermal activity within the icy moon Enceladus, and liquid methane seas on its moon Titan.

Now 20 years since launching from Earth, and after 13 years orbiting the ringed planet, Cassini is running low on fuel. In 2010, NASA decided to end the mission with a purposeful plunge into Saturn this year in order to protect and preserve the planet's moons for future exploration – especially the potentially habitable Enceladus.

But the beginning of the end for Cassini is, in many ways, like a whole new mission. Using expertise gained over the mission's many years, Cassini engineers designed a flight plan that will maximize the scientific value of sending the spacecraft toward its fateful plunge into the planet on Sept. 15. As it ticks off its terminal orbits during the next five months, the mission will rack up an impressive list of scientific achievements.

"This planned conclusion for Cassini's journey was far and away the preferred choice for the mission's scientists," said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. "Cassini will make some of its most extraordinary observations at the end of its long life."

The mission team hopes to gain powerful insights into the planet's internal structure and the origins of the rings, obtain the first-ever sampling of Saturn's atmosphere and particles coming from the main rings, and capture the closest-ever views of Saturn's clouds and inner rings. The team currently is making final checks on the list of commands the robotic probe will follow to carry out its science observations, called a sequence, as it begins the finale. That sequence is scheduled to be uploaded to the spacecraft on Tuesday, April 11.

Cassini will transition to its grand finale orbits, with a last close flyby of Saturn's giant moon Titan, on Saturday, April 22. As it has many times over the course of the mission, Titan's gravity will bend Cassini's flight path. Cassini's orbit then will shrink so that instead of making its closest approach to Saturn just outside the rings, it will begin passing between the planet and the inner edge of its rings.

"Based on our best models, we expect the gap to be clear of particles large enough to damage the spacecraft. But we're also being cautious by using our large antenna as a shield on the first pass, as we determine whether it's safe to expose the science instruments to that environment on future passes," said Earl Maize, Cassini project manager at JPL. "Certainly there are some unknowns, but that's one of the reasons we're doing this kind of daring exploration at the end of the mission."

In mid-September, following a distant encounter with Titan, the spacecraft's path will be bent so that it dives into the planet. When Cassini makes its final plunge into Saturn's atmosphere on September 15, it will send data from several instruments – most notably, data on the atmosphere's composition – until its signal is lost.

"Cassini's grand finale is so much more than a final plunge," said Spilker. "It's a thrilling final chapter for our intrepid spacecraft, and so scientifically rich that it was the clear and obvious choice for how to end the mission."

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/press-release/nasa-s-cassini-mission-prepares-for-grand-finale-at-saturn

April 23, 2017

Earth at Night: Africa and Europe

Earth at Night: Africa and Europe

Suomi NPP satellite
2016

Image Credit: NASA

Interacting Galaxies NGC 4302 • NGC 4298

Interacting Galaxies NGC 4302 • NGC 4298

This stunning cosmic pairing of the two very different looking spiral galaxies NGC 4302 and NGC 4298 was imaged by the NASA/ESA Hubble Space Telescope. The image brilliantly captures their warm stellar glow and brown, mottled patterns of dust. As a perfect demonstration of Hubble’s capabilities, this spectacular view has been released as part of the telescope’s 27th anniversary celebrations.

Since its launch on 24 April 1990, Hubble has been nothing short of a revolution in astronomy. The first orbiting facility of its kind, for 27 years the telescope has been exploring the wonders of the cosmos. Astronomers and the public alike have witnessed what no other humans in history have before. In addition to revealing the beauty of the cosmos, Hubble has proved itself to be a treasure chest of scientific data that astronomers can access.

ESA and NASA celebrate Hubble’s birthday each year with a spectacular image. This year’s anniversary image features a pair of spiral galaxies known as NGC 4302 — seen edge-on — and NGC 4298, both located 55 million light-years away in the northern constellation of Coma Berenices (Berenice’s Hair). The pair, discovered by astronomer William Herschel in 1784, form part of the Virgo Cluster, a gravitationally bound collection of nearly 2000 individual galaxies.

The edge-on NGC 4302 is a bit smaller than our own Milky Way Galaxy. The tilted NGC 4298 is even smaller: only half the size of its companion.

At their closest points, the galaxies are separated from each other in projection by only around 7000 light-years. Given this very close arrangement, astronomers are intrigued by the galaxies’ apparent lack of any significant gravitational interaction; only a faint bridge of neutral hydrogen gas — not visible in this image — appears to stretch between them. The long tidal tails and deformations in their structure that are typical of galaxies lying so close to each other are missing completely.

Astronomers have found very faint tails of gas streaming from the two galaxies, pointing in roughly the same direction — away from the centre of the Virgo Cluster. They have proposed that the galactic double is a recent arrival to the cluster, and is currently falling in towards the cluster centre and the galaxy Messier 87 lurking there — one of the most massive galaxies known. On their travels, the two galaxies are encountering hot gas — the intracluster medium — that acts like a strong wind, stripping layers of gas and dust from the galaxies to form the streaming tails.

Even in its 27th year of operation, Hubble continues to provide truly spectacular images of the cosmos, and even as the launch date of its companion — the NASA/ESA/CSA James Webb Space Telescope — draws closer, Hubble does not slow down. Instead, the telescope keeps raising the bar, showing it still has plenty of observing left to do for many more years to come. In fact, astronomers are looking forward to have Hubble and James Webb operational at the same time and use their combined capabilities to explore the Universe.

Image Credit: NASA, ESA, and M. Mutchler (STScI)
Explanation from: https://www.spacetelescope.org/news/heic1709/

Earthrise

Earthrise

LRO experiences twelve earthrises every day, however LROC is almost always busy imaging the lunar surface so only rarely does an opportunity arise such that LROC can capture a view of the Earth. On February 1, 2014 LRO pitched forward while approaching the north pole allowing the LROC WAC to capture the Earth rising above Rozhdestvenskiy crater (180-km diameter).

The LROC Wide Angle Camera (WAC) is very different than most digital cameras. Typically resolution is reported as the number pixels in a single image, a cell phone camera today has more than 5 million pixels (5 megapixels). A single WAC frame has only 9856 pixels, however the WAC builds up a much larger image by exposing a series of images (or frames) as LRO progresses in its orbit; this type of imaging is called "push-frame". Over a full month as the LRO orbit track progresses around the Moon the WAC builds up a collection of images that covers the entire globe.

Occasionally LRO points off into space to acquire observations of the exosphere and perform instrument calibration measurements. During these slews sometimes the Earth (and other planets) pass through the WAC's field of view and dramatic images such as the one shown here are acquired. In the opening image the Moon is a greyscale composite of the first six frames of the WAC observation (while the spacecraft was still actively slewing), using visible bands 604 nm, 643 nm, and 689 nm. The Earth is a color composite of later frames, using the 415 nm, 566 nm, and 604 nm bands as blue, green, and red, respectively. These wavelengths were picked as they match well the response of the human eye, so the colors are very close to true, that is what the average person might see. Also, in this image the relative brightness between the Earth and the Moon is correct, note how much brighter the Earth is relative to the Moon.

Image Credit: NASA/GSFC/Arizona State University
Explanation from: http://lroc.sese.asu.edu/posts/764

Solar Eruption

Solar Eruption

A solar eruption on September 26, 2014, seen by NASA's Solar Dynamics Observatory. If erupted solar material reaches Earth, it can deplete the electrons in the upper atmosphere in some locations while adding electrons in others, disrupting communications either way.

Image Credit: NASA

Pingualuit and Couture craters

Couture Crater
Pingualuit Crater

When NASA’s Aqua satellite passed over northern Quebec on November 25, 2012, winter snow and ice had transformed the pockmarked landscape of Ungava Peninsula into a seemingly endless expanse of white. However, two areas—both near-perfect circles—remained stubbornly free of ice. Those ice-free areas, seen in the top image above, are Pingualuit and Couture craters. The lower image shows just Pingualuit as seen from an airplane on October 12, 2007.

Both craters were formed millions of years ago by meteorites striking the surface, and today they hold deep lakes. Couture is approximately 8 kilometers (5 miles) wide and has a water depth of 150 meters (490 feet); Pingualuit’s lake is about 3 kilometers (2 miles) across and has a depth of 246 meters (807 feet).

“The crater lakes hold such huge volumes of water in comparison to the surrounding glacial lakes that they’re slower to respond to temperature changes,” explained Reinhard Pienitz, a fresh water lake expert who recently led an expedition to Pingualuit to collect sediment cores. “Pingualuit Crater Lake is always the last to freeze in the winter and the last to melt in the spring.”

Still, Pienitz found it surprising that the crater lakes were ice-free so late in November. Pingualuit usually has open water for just six-to-eight weeks in August and September. Pienitz suspects the unseasonably warm summer has played a role in keeping the lakes ice-free so late this year.

Hot summer temperatures in the Arctic made headlines when satellites observed widespread melting across Greenland in July 2012. Meteorological records from Environment Canada show that average temperatures at weather stations near the lakes have been above normal for every month since July.

Temperature isn’t the only factor that influences when the lakes freeze. Wind-driven mixing and late-season overturning of the water column probably also helped keep the two crater lakes free of ice longer than others in the area. During the short open water periods, the lake’s water column is slightly warmer at the top than at the bottom. When the lake freezes, the situation reverses such that the warmest water is at the bottom of the lake.

“This means the whole water column turns over during the end of the open water season—a process that is exacerbated by strong descending westerly wind gusts that cross the rim and plunge into the crater during the fall,” explained Pienitz. “This mixing in the fall and early winter likely contributes to Pingualuit’s enormous thermal inertia and helps keep waters above the freezing temperature.”

Image Credit: NASA/Jeff Schmaltz
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=79743

Lunar Topography

Lunar TopographyLunar Topography

The science team that oversees the imaging system on board NASA’s Lunar Reconnaissance Orbiter (LRO) has released the highest resolution near-global topographic map of the Moon ever created.

This new topographic map, from Arizona State University in Tempe, shows the surface shape and features over nearly the entire Moon with a pixel scale close to 100 meters (328 feet). A single measure of elevation (one pixel) is about the size of two football fields placed side-by-side.

Although the Moon is our closest neighbor, knowledge of its morphology is still limited. Due to instrumental limitations of previous missions, a global map of the Moon’s topography at high resolution has not existed until now. With the LRO Wide Angle Camera and the Lunar Orbiter Laser Altimeter (LOLA) instrument, scientists can now accurately portray the shape of the entire Moon at high resolution.

“Our new topographic view of the Moon provides the dataset that lunar scientists have waited for since the Apollo era,” says Mark Robinson, Principal Investigator of the Lunar Reconnaissance Orbiter Camera (LROC) from Arizona State University in Tempe. “We can now determine slopes of all major geologic terrains on the Moon at 100 meter scale. Determine how the crust has deformed, better understand impact crater mechanics, investigate the nature of volcanic features, and better plan future robotic and human missions to the Moon.”

Called the Global Lunar DTM 100 m topographic model (GLD100), this map was created based on data acquired by LRO’s WAC, which is part of the LROC imaging system. The LROC imaging system consists of two Narrow Angle Cameras (NACs) to provide high-resolution images, and the WAC to provide 100-meter resolution images in seven color bands over a 57-kilometer (35-mile) swath.

The WAC is a relatively small instrument, easily fitting into the palm of one’s hand; however, despite its diminutive size it maps nearly the entire Moon every month. Each month the Moon's lighting has changed so the WAC is continuously building up a record of how different rocks reflect light under different conditions, and adding to the LROC library of stereo observations.

The LROC (WAC) has a pixel scale of about 75 meters (246 feet), and at the average altitude of 50 km (31 miles) a WAC image swath is 70 km (43 miles) wide across the ground-track. Since the equatorial distance between orbits is about 30 km (18 miles) there is complete overlap all the way around the Moon in one month. The orbit-to-orbit WAC overlap provides a strong stereo effect. Using digital photogrammetric techniques, a terrain model can be computed from the stereo overlap.

The near-global topographic map was constructed from 69,000 WAC stereo models and covers the latitude range 79°S to 79°N, 98.2% of the entire lunar surface. Due to persistent shadows near the poles it is not possible to create a complete stereo based map at the highest latitudes. However, another instrument onboard LRO called LOLA excels at mapping topography at the poles. Since LOLA ranges to the surface with its own lasers, and the LRO orbits converge at the poles, a very high resolution topographic model is possible, and can be used to fill in the WAC “hole at the pole.” The WAC topography was produced by LROC team members at the German Aerospace Center.

“Collecting the data and creating the new topographic map was a huge collaborative effort between the LRO project, the LOLA team, the LROC team at ASU and in Germany at the DLR,” says Robinson. “I could not be more pleased with the quality of the map – it’s phenomenal! The richness of detail should inspire lunar geologists around the world for years to come.”

Shaded relief images can be created from the GLD100 by illuminating the “surface” (in this case the shape model) from a given Sun direction and elevation above the horizon. To convey an absolute sense of height the resulting grayscale pixels are painted with colors that represent the altitude. Visualizations like these allow scientists to view the surface from very different perspectives, providing a powerful tool for interpreting the geologic processes that have shaped the Moon.

Image Credit: NASA's Goddard Space Flight Center/DLR/ASU
Explanation from: https://www.nasa.gov/mission_pages/LRO/news/lro-topo.html

April 22, 2017

Megalodon and Platybelodon

Megalodon and Platybelodon

Megalodon is an extinct species of shark that lived approximately 23 to 2.6 million years ago, during the Cenozoic Era (early Miocene to end of Pliocene).

The taxonomic assignment of C. megalodon has been debated for nearly a century, and is still under dispute. The two major interpretations are Carcharodon megalodon (under family Lamnidae) or Carcharocles megalodon (under the family Otodontidae). Consequently, the scientific name of this species is commonly abbreviated C. megalodon in the literature.

Regarded as one of the largest and most powerful predators in vertebrate history, C. megalodon probably had a profound impact on the structure of marine communities. Fossil remains suggest that this giant shark reached a length of 18 metres (59 ft), and also indicate that it had a cosmopolitan distribution. Scientists suggest that C. megalodon looked like a stockier version of the great white shark, Carcharodon carcharias.


Platybelodon was a genus of large herbivorous mammal related to the elephant (order Proboscidea). It lived during the late Miocene Epoch in Asia and the Caucasus.

Platybelodon was very similar to Amebelodon, another, closely related gomphothere genus. Due to the shape of the two lower teeth, in common with many gomphothere genera (such as Platybelodon, Archaeobelodon, Konobelodon, and Amebelodon), they are popularly known as "shovel tuskers."

Platybelodon was previously believed to have fed in the swampy areas of grassy savannas, using its teeth to shovel up aquatic and semi-aquatic vegetation. However, wear patterns on the teeth suggest that it used its lower tusks to strip bark from trees, and may have used the sharp incisors that formed the edge of the "shovel" more like a modern-day scythe, grasping branches with its trunk and rubbing them against the lower teeth to cut it from a tree. Adult animals in particular might have eaten coarser vegetation more frequently than juveniles.

Image Credit & Copyright: Julius Csotonyi
Explanation from: https://en.wikipedia.org/wiki/Megalodon and https://en.wikipedia.org/wiki/Platybelodon

Earth at Night: the Americas

Earth at Night: the Americas

Suomi NPP satellite
2016

Image Credit: NASA

Earth and the Moon seen between the Rings of Saturn by Cassini spacecraft

Earth and the Moon seen between the Rings of Saturn by Cassini spacecraftEarth and the Moon seen between the Rings of Saturn by Cassini spacecraft

This view from NASA's Cassini spacecraft shows planet Earth as a point of light between the icy rings of Saturn.

The spacecraft captured the view on April 12, 2017 at 10:41 p.m. PDT (1:41 a.m. EDT). Cassini was 870 million miles (1.4 billion kilometers) away from Earth when the image was taken. Although far too small to be visible in the image, the part of Earth facing toward Cassini at the time was the southern Atlantic Ocean.

Earth's moon is also visible to the left of our planet in a cropped, zoomed-in version of the image.

The rings visible here are the A ring (at top) with the Keeler and Encke gaps visible, and the F ring (at bottom). During this observation Cassini was looking toward the backlit rings, making a mosaic of multiple images, with the sun blocked by the disk of Saturn.

Seen from Saturn, Earth and the other inner Solar System planets are all close to the Sun, and are easily captured in such images, although these opportunities have been somewhat rare during the mission. The F ring appears especially bright in this viewing geometry.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21445

April 21, 2017

Earth Day 2017

Mosasaurs

Mosasaurs

Mosasaurs are an extinct group of large marine reptiles. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-T event at the end of the Cretaceous period, about 66 million years ago.

Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow inland seas prevalent during the Late Cretaceous period. Mosasaurs were so well adapted to this environment that they gave birth to live young, rather than returning to the shore to lay eggs as sea turtles do.

The smallest-known mosasaur was Dallasaurus turneri, which was less than 1 m (3.3 ft) long. Larger mosasaurs were more typical, with many species growing longer than 4 m (13 ft). Mosasaurus hoffmannii, the largest known species may have reached up to 17 m (56 ft) in length. Currently, the largest publicly exhibited mosasaur skeleton in the world is on display at the Canadian Fossil Discovery Centre in Morden, Manitoba. The specimen, nicknamed "Bruce", is just over 13 m (43 ft) long.

Mosasaurs had a body shape similar to those of modern-day monitor lizards (varanids), but were more elongated and streamlined for swimming. Their limb bones were reduced in length and their paddles were formed by webbing between their long finger and toe bones. Their tails were broad, and supplied their locomotive power. Until recently, mosasaurs were assumed to have swum in a method similar to the one used today by conger eels and sea snakes, undulating their entire bodies from side to side. However, new evidence suggests that many advanced mosasaurs had large, crescent-shaped flukes on the ends of their tails, similar to those of sharks and some ichthyosaurs. Rather than use snake-like undulations, their bodies probably remained stiff to reduce drag through the water, while their tails provided strong propulsion. These animals may have lurked and pounced rapidly and powerfully on passing prey, rather than chasing after it.

Early reconstructions showed mosasaurs with dorsal crests running the length of their bodies, which were based on misidentified remains of tracheal cartilage. By the time this error was discovered, depicting mosasaurs with such crests in artwork had already become a trend.

Mosasaurs had double-hinged jaws and flexible skulls (much like those of snakes), which enabled them to gulp down their prey almost whole. A skeleton of Tylosaurus proriger from South Dakota included remains of the diving seabird Hesperornis, a marine bony fish, a possible shark, and another, smaller mosasaur (Clidastes). Mosasaur bones have also been found with shark teeth embedded in them.

One of the food items of mosasaurs were ammonites, molluscs with shells similar to those of Nautilus, which were abundant in the Cretaceous seas. Holes have been found in fossil shells of some ammonites, mainly Pachydiscus and Placenticeras. These were once interpreted as a result of limpets attaching themselves to the ammonites, but the triangular shape of the holes, their size, and their presence on both sides of the shells, corresponding to upper and lower jaws, is evidence of the bite of medium-sized mosasaurs. Whether this behaviour was common across all size classes of mosasaurs is not clear.

Virtually all forms were active predators of fish and ammonites; a few, such as Globidens, had blunt, spherical teeth, specialized for crushing mollusk shells. The smaller genera, such as Platecarpus and Dallasaurus, which were about 1–6 m (3.3–19.7 ft) long, probably fed on fish and other small prey. The smaller mosasaurs may have spent some time in fresh water, hunting for food. The larger mosasaurs, such as Tylosaurus, and Mosasaurus, reached sizes of 10–15 m (33–49 ft) long and were the apex predators of the Late Cretaceous oceans, attacking other marine reptiles, as well as preying on large fish and ammonites.

Based on features such as the double row of pterygoid ("flanged") teeth on the palate, the loosely hinged jaw, modified/reduced limbs and probable methods of locomotion, many researchers believe that snakes share a common marine ancestry with mosasaurs, a suggestion advanced in 1869 by Edward Drinker Cope, who coined the term Pythonomorpha to unite them. The idea lay dormant for more than a century, to be revived in the 1990s. Recently, the discovery of Najash rionegrina, a fossorial snake from South America, cast doubt on the marine origin hypothesis.

The skeleton of Dallasaurus turneri, described by Bell and Polcyn (2005), has a mixture of features present in the skeletons of derived mosasaurs and in the skeletons of mosasaurid ancestors, such as aigialosaurids. Dallasaurus retains facultatively terrestrial limbs similar in their structure to the limbs of aigialosaurids and terrestrial squamates (plesiopedal limb condition), unlike derived mosasaurids, which evolved paddle-like limbs (hydropedal limb condition). However, the skeleton of Dallasaurus simultaneously had several characters that linked it with derived members of the subfamily Mosasaurinae; the authors of its description listed "invasion of the parietal by medial tongues from the frontal, teeth with smooth medial enamel surface, high coronoid buttress on surangular, interdigitate anterior scapulo-coracoid suture, humeral postglenoid process, elongate atlas synapophysis, sharp anterodorsal ridge on synapophyses, vertically oriented vertebral condyles, elongate posterior thoracic vertebrae, and fused haemal arches" as the characters uniting Dallasaurus with Mosasaurinae. The phylogenetic analysis conducted by Bell and Polcyn indicated that hydropedal mosasaurids did not form a clade that wouldn't also include plesiopedal taxa, such as Dallasaurus, Yaguarasaurus, Russellosaurus, Tethysaurus, Haasiasaurus and Komensaurus (in 2005 only informally known as "Trieste aigialosaur"); the analysis indicated that hydropedal limb condition evolved independently in three different groups of mosasaurs (Halisaurinae, Mosasaurinae and the group containing the subfamilies Tylosaurinae and Plioplatecarpinae). The result of this phylogenetic study was subsequently mostly confirmed by the analyses conducted by Caldwell and Palci (2007) and Leblanc, Caldwell and Bardet (2012); the analysis conducted by Makádi, Caldwell and Ősi (2012) indicated that hydropedal limb condition evolved independently in two groups of mosasaurs (in Mosasaurinae and in the clade containing Halisaurinae, Tylosaurinae and Plioplatecarpinae). Conrad et al. (2011), on the other hand, recovered hydropedal mosasaurs forming a clade that excluded their plesiopedal relatives. If the hypothesis of Bell and Polcyn (2005) is correct, then mosasaurs in the traditional sense of the word, i.e. "lizards that evolved paddle-like limbs and radiated into aquatic environments in the late Mesozoic, going extinct at the end of that era", are actually polyphyletic; Bell and Polcyn (2005) maintained monophyletic Mosasauridae by including Dallasaurus and other aforementioned plesiopedal taxa in the family as well, while Caldwell (2012) suggested (though explicitly stated that it was not "a formal proposal of new nomenclature") to restrict Mosasauridae only to the genus Mosasaurus and its closest hydropedal relatives.

The exact phylogenetic position of the clade containing mosasaurids and their closest relatives (aigialosaurids and dolichosaurs) within Squamata remains uncertain. Some cladistic analyses recovered them as the closest relatives of snakes, taking into account similarities in jaw and skull anatomies; however, this has been disputed and the morphological analysis conducted by Conrad (2008) recovered them as varanoids closely related to terrestrial monitor lizards instead. Subsequent analysis of anguimorph relationships conducted by Conrad et al. (2011) based on morphology alone recovered mosasaurids, aigialosaurids and dolichosaurs as anguimorphs lying outside the least inclusive clade containing monitor lizards and helodermatids; the analysis based on combined datasets of morphological and molecular data, on the other hand, found them more closely related to monitor lizards and the earless monitor lizard than to helodermatids and the Chinese crocodile lizard. The large morphological analysis conducted by Gauthier et al. (2012) recovered mosasaurids, aigialosaurids and dolichosaurids in an unexpected position as basal members of the clade Scincogekkonomorpha (containing all taxa sharing a more recent common ancestor with Gekko gecko and Scincus scincus than with Iguana iguana) that didn't belong to the clade Scleroglossa. The phylogenetic position of these taxa turned out to be highly dependent on which taxa were included in or excluded from the analysis. When mosasaurids were excluded from the analysis, dolichosaurs and aigialosaurids were recovered within Scleroglossa, forming a sister group to the clade containing snakes, amphisbaenians, dibamids and the American legless lizard. When mosasaurids were included in the analysis, and various taxa with reduced or absent limbs other than snakes (such as dibamids or amphisbaenians) were excluded, mosasaurids, aigialosaurids and dolichosaurs were recovered inside Scleroglossa forming the sister group to snakes. Longrich, Bhullar and Gauthier (2012) conducted a morphological analysis of squamate relationships using a modified version of the matrix from the analysis of Gauthier et al. (2012); they found the phylogenetic position of the clade containing mosasaurs and their closest relatives within Squamata to be highly unstable, with the clade "variously being recovered outside Scleroglossa (as in Gauthier et al., 2012) or alongside the limbless forms".

Image Credit & Copyright: Matte FX
Explanation from: https://en.wikipedia.org/wiki/Mosasaur

Europe and Africa at Night

Europe at Night

Suomi NPP satellite
2016

Image Credit: NASA

April 20, 2017

Valley of the Dinosaurs

Valley of the Dinosaurs

The Valley of the Dinosaurs is an area in the state of Paraíba, Brazil, that contains many fossilized dinosaur tracks. It contains the Valley of the Dinosaurs Area of Relevant Ecological Interest, a sustainable use area of relevant ecological interest. This in turn contains the smaller and fully protected Valley of the Dinosaurs Natural Monument. In 2015–16 there was concern that renovations to the tourist attraction, which had been delayed through lack of funding, might not be respecting the integrity of the site.

The Valley of the Dinosaurs is an area in the sedimentary basin of the Peixe River that holds over 50 types of ancient animal tracks, including those of stegosaurus, allosaurus and iguanodons. The valley covers an area of about 700 square kilometres (270 sq mi) that includes the city of Sousa, Paraíba, and ten other municipalities. It is in a Caatinga biome. Tracks have been found in about 30 locations in the valley, with fossilized footprints of over 80 species at about 20 different stratographic levels. Most of the tracks are of carnivorous dinosaurs.

The tracks the dinosaurs made in the damp earth beside ponds and rivers in rainy periods hardened over long periods of drought, gained new layers of sand and clay from floods, and fossilized. Footprints are as small as 5 centimetres (2.0 in), perhaps from dinosaurs the size of modern chickens, up to 40 centimetres (16 in) long, such as that of a four-ton iguanodon. The most visited site is the island called the Passagem das Pedras (Crossing of Stones) in the bed of the Peixe River. This is about 7 kilometres (4.3 mi) from the urban centre of Sousa.

Explanation from: https://en.wikipedia.org/wiki/Valley_of_the_Dinosaurs,_Para%C3%ADba

Europe at Night

Europe at Night

Suomi NPP satellite
2016

Image Credit: NASA

Supermassive Black Hole in Elliptical Galaxy NGC 4696

Supermassive Black Hole in Elliptical Galaxy NGC 4696

  • A black hole has been "beating" about every 5 to 10 million years, pumping material and energy into its environment.
  • This black hole is at the center of a large elliptical galaxy located within the core of the Centaurus Cluster of galaxies.
  • Data from Chandra and other telescopes show evidence for repeated bursts, or eruptions, from the black hole.
  • These bursts created cavities within the hot, X-ray emitting gas that pervades the cluster.

At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.

New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.

In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.

Supermassive Black Hole in Elliptical Galaxy NGC 4696Supermassive Black Hole in Elliptical Galaxy NGC 4696Supermassive Black Hole in Elliptical Galaxy NGC 4696
Data from Chandra and other telescopes have provided evidence for repeated bursts of energetic particles generated by the supermassive black hole at the center of the Centaurus Cluster. These images show X-ray data from Chandra that reveals the hot gas in the cluster, and radio data from the VLA that shows high-energy particles produced by jets powered by the black hole. Visible light data from Hubble show galaxies in the cluster as well as galaxies and stars outside the cluster.
By examining the details of the X-ray data from Chandra, scientists have found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

This composite image contains X-ray data from Chandra (red) that reveals the hot gas in the cluster, and radio data from the NSF's Karl G. Jansky Very Large Array (blue) that shows high-energy particles produced by the black hole-powered jets. Visible light data from the Hubble Space Telescope (green) show galaxies in the cluster as well as galaxies and stars outside the cluster.

Supermassive Black Hole in Elliptical Galaxy NGC 4696
Astronomers employed special processing to the Chandra X-ray data of NGC 4696 to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.

Astronomers employed special processing to the X-ray data (shown above) to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.

Supermassive Black Hole in Elliptical Galaxy NGC 4696
A different type of processing of the Chandra X-ray data of NGC 4696 reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole's repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate.

The researchers estimate that these black hole bursts, or "beats", have occurred every five to ten million years. Besides the vastly differing time scales, these beats also differ from typical human heartbeats in not occurring at particularly regular intervals.

A different type of processing of the X-ray data (shown above) reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole's repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate. (Note that both images showing the labeled cavities and this image are rotated slightly clockwise to the main composite.)

The features in the Centaurus Cluster are similar to the ripples seen in the Perseus cluster of galaxies. The pitch of the sound in Centaurus is extremely deep, corresponding to a discordant sound about 56 octaves below the notes near middle C. This corresponds to a slightly higher (by about one octave) pitch than the sound in Perseus. Alternative explanations for these curved features include the effects of turbulence or magnetic fields.

Supermassive Black Hole in Elliptical Galaxy NGC 4696
By examining the details of the X-ray data from Chandra, scientists found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

The black hole bursts also appear to have lifted up gas that has been enriched in elements generated in supernova explosions. The authors of the study of the Centaurus cluster created a map showing the density of elements heavier than hydrogen and helium. The brighter colors in the map show regions with the highest density of heavy elements and the darker colors show regions with a lower density of heavy elements. Therefore, regions with the highest density of heavy elements are located to the right of the black hole. A lower density of heavy elements near the black hole is consistent with the idea that enriched gas has been lifted out of the cluster's center by bursting activity associated with the black hole. The energy produced by the black hole is also able to prevent the huge reservoir of hot gas from cooling. This has prevented large numbers of stars from forming in the gas.

Image Credit: X-ray: NASA/CXC/MPE/J.Sanders et al.; Optical: NASA/STScI; Radio: NSF/NRAO/VLA
Explanation from: http://chandra.harvard.edu/photo/2017/ngc4696/

Exoplanet LHS 1140b

Exoplanet LHS 1140b

This planet is located in the liquid water habitable zone surrounding its host star, a small, faint red star named LHS 1140. The planet weighs about 6.6 times the mass of Earth and is shown passing in front of LHS 1140. Depicted in blue is the atmosphere the planet may have retained.

Image Credit: M. Weiss/CfA