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August 2, 2017August 2, 2017 by Matt Williams

Kepler Spots the First Exomoon Candidate 4000 Light Years From Earth

Artist's impression of the view from a hypothetical moon around a exoplanet orbiting a triple star system. Credit: NASA

Ever since it was deployed in March of 2009, the Kepler mission has detected thousands of extra-solar planet candidates. In fact, between 2009 and 2012, it detected a total of 4,496 candidates, and confirmed the existence of 2,337 exoplanets. Even after two of its reaction wheels failed, the spacecraft still managed to turn up distant planets as part of its K2 mission, accounting for another 521 candidates and confirming 157.

However, according to a new study conducted by a pair of researches from Columbia University and a citizen scientist, Kepler may also have also found evidence of an extra-solar moon. After sifting through data from hundreds of transits detected by the Kepler mission, the researchers found one instance where a transiting planet showed signs of having a satellite.

Their study – which recently published online under the title “HEK VI: On the Dearth of Galilean Analogs in Kepler and the Exomoon Candidate Kepler-1625b I” – was by led Alex Teachey, a graduate student at Columbia University and a Graduate Research Fellow with the National Science Foundation (NSF). He was joined by David Kipping, an Assistant Professor of Astronomy at Columbia University and the Principal Investigator of The Hunt for Exomoons with Kepler (HEK) project, and Allan Schmitt, a citizen scientist.

*Artist’s impression of NASA’s Kepler spacecraft. Credit: NASA*

For years, Dr. Kipping has been searching the Kepler database for evidence of exomoons, as part of the HEK. This is not surprising, considering the kinds of opportunities that exomoons present for scientific research. Within our Solar System, the study of natural satellites has revealed important things about the mechanisms that drive early and late planet formation, and moons possess interesting geological features that are commonly found on other bodies.

It is for this reason that extending that research to the hunt for exoplanets is seen as necessary. Already, exoplanet-hunting missions like Kepler have turned up a wealth of planets that challenge conventional ideas about how planet formation and what kinds of planets are possible. The most noteworthy example are gas giants that have observed orbiting very close to their stars (aka. “Hot Jupiters”).

As such, the study of exomoons could yield valuable information about what kinds of satellites are possible, and whether or not our own moons are typical. As Teachey told Universe Today via email:

“Exomoons could tell us a lot about the formation of our Solar System, and other star systems. We see moons in our Solar System, but are they common elsewhere? We tend to think so, but we can’t know for sure until we actually see them. But it’s an important question because, if we find out there aren’t very many moons out there, it suggests maybe something unusual was going on in our Solar System in the early days, and that could have major implications for how life arose on the Earth. In other words, is the history of our Solar System common across the galaxy, or do we have a very unusual origin story? And what does that say about the chances of life arising here? Exomoons stand to offer us clues to answering these questions.”

*A montage of some of the potentially-habitable moons in our Solar System. From top to bottom, left to right, these include Europa, Enceladus, TItan and Ceres. Credit: NASA/JPL*

What’s more, many moons in the Solar System – including Europa, Ganymede, Enceladus and Titan – are thought to be potentially habitable. This is due to the fact that these bodies have steady supplies of volatiles (such as nitrogen, water, carbon dioxide, ammonia, hydrogen, methane and sulfur dioxide) and possess internal heating mechanisms that could provide the necessary energy to power biological processes.

Here too, the study of exomoons presents interesting possibilities, such as whether or not they may be habitable or even Earth-like. For these and other reasons, astronomers want to see if the planets that have been confirmed in distant star systems have systems of moons and what conditions are like on them. But as Teachey indicated, the search for exomoons presents a number of challenges compared to exoplanet-hunting:

“Moons are difficult to find because 1) we expect them to be quite small most of the time, meaning the transit signal will be quite weak to begin with, and 2) every time a planet transits, the moon will show up in a different place. This makes them more difficult to detect in the data, and modeling the transit events is significantly more computationally expensive. But our work leverages the moons showing up in different places by taking the time-averaged signal across many different transit events, and even across many different exoplanetary systems. If the moons are there, they will in effect carve out a signal on either side of the planetary transit over time. Then it’s a matter of modeling this signal and understanding what it means in terms of moon size and occurrence rate.”

To locate signs of exomoons, Teachey and his colleagues searched through the Kepler database and analyzed the transits of 284 exoplanet candidates in front of their respective stars. These planets ranged in size from being Earth-like to Jupiter-like in diameter, and orbited their stars at a distance of between ~0.1 to 1.0 AU. They then modeled the light curve of the stars using the techniques of phase-folding and stacking.

*An artist’s conception of a habitable exomoon. Credit: NASA*

These techniques are commonly used by astronomers who monitor stars for dips in luminosity that are caused by the transits of planets (i.e. the transit method). As Teachey explained, the process is quite similar:

“Basically we cut up the time-series data into equal pieces, each piece having one transit of the planet in the middle. And when we stack these pieces together we’re able to get a clearer picture of what the transit looks like… For the moon search we do essentially the same thing, only now we’re looking at the data outside the main planetary transit. Once we stack the data, we take the average values of all the data points within a certain time window and, if a moon is present, we ought to see some missing starlight there, which allows us to deduce its presence.”

What they found was a single candidate located in the Kepler-1625 system, a yellow star located about 4000 light years from Earth. Designated Kepler-1625B I, this moon orbits the large gas giant that is located within the star’s habitable zone, is 5.9 to 11.67 times the size of Earth, and orbits its star with a period of 287.4 days. This exomoon candidate, if it should be confirmed, will be the first exomoon ever discovered

The team’s results (which await peer review) also demonstrated that large moons to be a rare occurrence in the inner regions of star systems (within 1 AU). This was something of a surprise, though Teachey acknowledges that it is consistent with recent theoretical work. According to what some recent studies suggest, large planets like Jupiter could lose their moons as they migrate inward.

If this should prove to be the case, then what Teachey and his colleagues witnessed could be seen as evidence of that process. It could also be an indication our current exoplanet-hunting missions may not be up to the task of detecting exomoons. In the coming years, next-generations missions are expected to provide more detailed analyses of distant stars and their planetary systems.

*An artist’s conception of a distance exomoon blocking out a star’s light. Credit: Dan*

However, as Teachey indicated, these too could be limited in terms of what they can detect, and new strategies may ultimately be needed:

“The rarity of moons in the inner regions of these star systems suggests that individual moons will remain difficult to find in the Kepler data, and upcoming missions like TESS, which should find lots of very short period planets, will also have a difficult time finding these moons. It’s likely the moons, which we still expect to be out there somewhere, reside in the outer regions of these star systems, much as they do in our Solar System. But these regions are much more difficult to probe, so we will have to get even more clever about how we look for these worlds with present and near-future datasets.”

In the meantime, we can certainly be exited about the fact that the first exomoon appears to have been discovered. While these results await peer review, confirmation of this moon will mean additional research opportunities for Kepler-1625 system. The fact that this moon orbits within the star’s habitable zone is also an interesting feature, though its not likely the moon itself is habitable.

Still, the possibility of a habitable moon orbiting a gas giant is certainly interesting. Does that sound like something that might have come up in some science fiction movies?

Further Reading: arXiv

August 2, 2017 by David Dickinson

A Partial Lunar Eclipse Ushers in Eclipse Season

Live on the wrong continent to witness the August 21^st total solar eclipse? Well… celestial mechanics has a little consolation prize for Old World observers, with a partial lunar eclipse on the night of Monday into Tuesday, August 7/8^th.

A partial lunar eclipse occurs when the Moon just nicks the inner dark core of the Earth’s shadow, known as the umbra. This eclipse is centered on the Indian Ocean region, with the event occurring at moonrise for the United Kingdom, Europe and western Africa and moonset/sunrise for New Zealand and Japan. Western Australia, southern Asia and eastern Africa will see the entire eclipse.

The path of the Moon through the Earth’s shadow Monday night. Credit: adapted from NASA/GSFC/Fred Espenak

The penumbral phase of the eclipse begins on August 7^th at 15:50 Universal Time (UT), though you probably won’t notice a slight tea colored shading on the face of the Moon until about half an hour in. The partial phases begin at 17:23 UT, when the ragged edge of the umbra becomes apparent on the southeastern limb of the Moon. The deepest partial eclipse occurs at 18:22 UT with 25% of the Moon submerged in the umbra. Partial phase lasts 116 minutes in duration, and the entire eclipse is about five hours long.

The viewing prospects for the partial lunar eclipse. Credit: NASA/GSFC/Fred Espenak.

This also marks the start of the second and final eclipse season for 2017. Four eclipses occur this year: a penumbral lunar eclipse and annular solar eclipse this past February, and this month’s partial lunar and total solar eclipse.

Eclipses always occur in pairs, or very rarely triplets with an alternating lunar-solar pattern. This is because the tilt of the Moon’s orbit is inclined five degrees relative to the ecliptic, the plane of the Earth’s orbit around the Sun. The Moon therefore misses the 30′ wide disk of the Sun and the 80′ – 85′ wide inner shadow of the Earth on most passes.

Fun fact: at the Moon’s 240,000 mile distance from the Earth, the ratio of the apparent size of the Moon and the shadow is approximately equivalent to a basketball and a hoop.

When celestial bodies come into alignment, however, things can get interesting. For an eclipse to occur, the nodes – the point where the Moon’s orbit intersects the ecliptic – need to align with the position of the Moon and the Sun. There are two nodes, one descending with the Moon crossing the ecliptic from north to south, and one ascending. The time it takes for the Moon to return to the same node (27.2 days) is a draconitic month. Moreover, the nodes are moving around the Earth due to drag on the Moon’s orbit mainly by the Sun, and move all the way around the zodiac once every 18.6 years.

Got all that? Let’s put it into practice with this month’s eclipses. First, the Moon crosses its descending node at 10:56 UT on August 8th, just over 16 hours after Monday’s partial eclipse. Two weeks later, however, the Moon crosses ascending node just under eight hours from the central conjunction with the Sun, and a total solar eclipse occurs.

Tales of the Saros

The August 7^th lunar eclipse is member number 62 of the 83 lunar eclipses in saros series 119, which started on October 14^th, 935 AD and will end with a final shallow penumbral eclipse on March 25^th, 2396 AD. If you witnessed the lunar eclipse of July 28^th, 1999, then you saw the last lunar eclipse in the same saros. Saros 119 produced its last total lunar eclipse on June 15^th, 1927.

The next lunar eclipse, a total occurs on January 31^st, 2018, favoring the Pacific rim regions.

Partial lunar eclipses have occasionally work their way into history, usually as bad omens. One famous example is the partial lunar eclipse of May 22^nd, 1453 which preceded the Fall of Constantinople to the Ottoman Turks by a week. Apparently, a long standing legend claimed that a lunar eclipse would be the harbinger of the fall of Byzantium, and the partially eclipsed Moon rising over the besieged city ramparts seemed to fulfill the prophecy.

In our more enlightened age, we can simply enjoy Monday’s partial lunar eclipse as a fine celestial spectacle. You don’t need any special equipment to enjoy a lunar eclipse, just a view from the correct Moonward facing hemisphere of the Earth, and reasonably clear skies.

See the curve of the Earth’s shadow? This is one of the very few times that you can see that the Earth is indeed round (sorry, Flat Earthers) with your own eyes. And this curve is true for observers watching the Moon on the horizon, or high overhead near the zenith.

This month’s lunar eclipse occurs in the astronomical constellation of Capricornus. The Moon will also occult the +5^th magnitude star 29 Capricorni for southern India, Madagascar and South Africa shortly after the eclipse.

The viewing footprint for the 29 Capricorni occultation shortly after the eclipse. Credit: Occult 4.2.

Finally, anyone out there planning on carrying the partial lunar eclipse live, let us know… curiously, even Slooh seems to be sitting this one out.

Update: we have one possible broadcast, via Shahrin Ahmad (@shahgazer on Twitter). Updates to follow!

The final eclipse season for 2017 is now underway, starting Monday night. Nothing is more certain in this Universe than death, taxes and celestial mechanics, as the path of the Moon now sends it headlong to its August 21^st destiny and the Great American Total Solar Eclipse.

-We’ll be posting on Universe Today once more pre-total solar eclipse one week prior, with weather predictions, solar and sunspot activity and prospects for viewing the eclipse from Earth and space and more!

-Read more about this year’s eclipses in our 2017 Guide to 101 Astronomical Events.

-Eclipse… science fiction? Read our original eclipse-fueled tales Exeligmos, Shadowfall, Peak Season and more!

August 1, 2017August 1, 2017 by Matt Williams

Physicists Take Big Step Towards Quantum Computing and Encryption with new Experiment

Artist’s concept of the experiment in which two atoms are being entangled over a distance of 400 meters. Credit: Wenjamin Rosenfeld

Quantum entanglement remains one of the most challenging fields of study for modern physicists. Described by Einstein as “spooky action at a distance”, scientists have long sought to reconcile how this aspect of quantum mechanics can coexist with classical mechanics. Essentially, the fact that two particles can be connected over great distances violates the rules of locality and realism.

Formally, this is a violation of Bell’s Ineqaulity, a theory which has been used for decades to show that locality and realism are valid despite being inconsistent with quantum mechanics. However, in a recent study, a team of researchers from the Ludwig-Maximilian University (LMU) and the Max Planck Institute for Quantum Optics in Munich conducted tests which once again violate Bell’s Inequality and proves the existence of entanglement.

Their study, titled “Event-Ready Bell Test Using Entangled Atoms Simultaneously Closing Detection and Locality Loopholes“, was recently published in the Physical Review Letters. Led by Wenjamin Rosenfeld, a physicist at LMU and the Max Planck Institute for Quantum Optics, the team sought to test Bell’s Inequality by entangling two particles at a distance.

*John Bell, the Irish physicist who devised a test to show that nature does not ‘hide variables’ as Einstein had proposed. Credit: CERN\*

Bell’s Inequality (named after Irish physicist John Bell, who proposed it in 1964) essentially states that properties of objects exist independent of being observed (realism), and no information or physical influence can propagate faster than the speed of light (locality). These rules perfectly described the reality we human beings experience on a daily basis, where things are rooted in a particular space and time and exist independent of an observer.

However, at the quantum level, things do not appear to follow these rules. Not only can particles be connected in non-local ways over large distances (i.e. entanglement), but the properties of these particles cannot be defined until they are measured. And while all experiments have confirmed that the predictions of quantum mechanics are correct, some scientists have continued to argue that there are loopholes that allow for local realism.

To address this, the Munich team conducted an experiment using two laboratories at LMU. While the first lab was located in the basement of the physics department, the second was located in the basement of the economics department – roughly 400 meters away. In both labs, teams captured a single rubidium atom in an topical trap and then began exciting them until they released a single photon.

As Dr. Wenjamin Rosenfeld explained in an Max Planck Institute press release:

“Our two observer stations are independently operated and are equipped with their own laser and control systems. Because of the 400 meters distance between the laboratories, communication from one to the other would take 1328 nanoseconds, which is much more than the duration of the measurement process. So, no information on the measurement in one lab can be used in the other lab. That’s how we close the locality loophole.”

*The experiment was performed in two locations 398 meters apart at the Ludwig Maximilian University campus in Munich, Germany. Credit: Rosenfeld et al/American Physical Society*

Once the two rubidium atoms were excited to the point of releasing a photon, the spin-states of the rubidium atoms and the polarization states of the photons were effectively entangled. The photons were then coupled into optical fibers and guided to a set-up where they were brought to interference. After conducting a measurement run for eight days, the scientists were able to collected around 10,000 events to check for signs entanglement.

This would have been indicated by the spins of the two trapped rubidium atoms, which would be pointing in the same direction (or in the opposite direction, depending on the kind of entanglement). What the Munich team found was that for the vast majority of the events, the atoms were in the same state (or in the opposite state), and that there were only six deviations consistent with Bell’s Inequality.

These results were also statistically more significant than those obtained by a team of Dutch physicists in 2015. For the sake of that study, the Dutch team conducted experiments using electrons in diamonds at labs that were 1.3 km apart. In the end, their results (and other recent tests of Bell’s Inequality) demonstrated that quantum entanglement is real, effectively closing the local realism loophole.

As Wenjamin Rosenfeld explained, the tests conducted by his team also went beyond these other experiments by addressing another major issue. “We were able to determine the spin-state of the atoms very fast and very efficiently,” he said. “Thereby we closed a second potential loophole: the assumption, that the observed violation is caused by an incomplete sample of detected atom pairs”.

By obtaining proof of the violation of Bell’s Inequality, scientists are not only helping to resolve an enduring incongruity between classical and quantum physics. They are also opening the door to some exciting possibilities. For instance, for years, scientist have anticipated the development of quantum processors, which rely on entanglements to simulate the zeros and ones of binary code.

Computers that rely on quantum mechanics would be exponentially faster than conventional microprocessors, and would ushering in a new age of research and development. The same principles have been proposed for cybersecurity, where quantum encryption would be used to cypher information, making it invulnerable to hackers who rely on conventional computers.

Last, but certainly not least, there is the concept of Quantum Entanglement Communications, a method that would allow us to transmit information faster than the speed of light. Imagine the possibilities for space travel and exploration if we are no longer bound by the limits of relativistic communication!

Einstein wasn’t wrong when he characterized quantum entanglements as “spooky action”. Indeed, much of the implications of this phenomena are still as frightening as they are fascinating to physicists. But the closer we come to understanding it, the closer we will be towards developing an understanding of how all the known physical forces of the Universe fit together – aka. a Theory of Everything!

Further Reading: LMU, Physical Review Letters

August 1, 2017August 1, 2017 by Matt Williams

Impending Asteroid Flyby Will be a Chance to Test NASA’s Planetary Defense Network!

Artist's concept of a large asteroid passing by the Earth-Moon system. Credit: A combination of ESO/NASA images courtesy of Jason Major/Lights in the Dark.

This coming October, an asteroid will fly by Earth. Known as 2012 TC4, this small rock is believed to measure between 10 and 30 meters (30 and 100 feet) in size. As with most asteroids, this one is expected to sail safely past Earth without incident. This will take place on October 12th, when the asteroid will pass us at a closest estimated distance of 6,800 kilometers (4,200 miles) from Earth’s surface.

That’s certainly good news. But beyond the fact that it does not pose a threat to Earth, NASA is also planning on using the occasion to test their new detection and tracking network. As part of their Planetary Defense Coordination Office (PDCO), this network is responsible for detecting and tracking asteroids that periodically pass close to Earth, which are known as Potentially Hazardous Objects (PHOs)

In addition to relying on data provided by NASA’s Near-Earth Object (NEO) Observations Program. the PDCO also coordinates NEO observations conducted by National Science Foundation (NSF)-sponsored ground-based observatories, as well as space situational awareness facilities run by the US Air Force. Aside from finding and tracking PHOs, the PDCO is also responsible for coming up with ways of deflecting and redirecting them.

*On Oct. 12, 2017, asteroid 2012 TC4 will safely fly past Earth at an estimated distance of 6,800 km (4,200 mi). Credits: NASA/JPL-Caltech*

The PDCO was officially created in response to the NASA Office of Inspector General’s 2014 report, titled “NASA’s Efforts to Identify Near-Earth Objects and Mitigate Hazards.” Citing such events as the Chelyabinsk meteor, and how such events are relatively common, the report indicated that coordination, early warning and mitigation strategies were needed for the future:

“[I]n February 2013 an 18-meter (59 foot) meteor exploded 14.5 miles above the city of Chelyabinsk, Russia, with the force of 30 atomic bombs, blowing out windows, destroying buildings, injuring more than 1,000 people, and raining down fragments along its trajectory… Recent research suggests that Chelyabinsk-type events occur every 30 to 40 years, with a greater likelihood of impact in the ocean than over populated areas, while impacts from objects greater than a mile in diameter are predicted only once every several hundred thousand years.”

The PDCO was established in 2016, which makes this upcoming flyby the first chance they will have to test their network of observatories and scientists dedicated to planetary defense. Michael Kelley is the program scientist and the NASA Headquarters lead for the TC4 observation campaign, which has been monitoring 2012 TC4 for years. As he said in a recent NASA press statement:

“Scientists have always appreciated knowing when an asteroid will make a close approach to and safely pass the Earth because they can make preparations to collect data to characterize and learn as much as possible about it. This time we are adding in another layer of effort, using this asteroid flyby to test the worldwide asteroid detection and tracking network, assessing our capability to work together in response to finding a potential real asteroid threat.”

*Diagram showing the data gathered from 1994-2013, indicating daytime (orange) and nighttime (blue) impacts of small meteorites. Credit: NASA*

In addition, the flyby will be an opportunity to reacquire 2012 TC4, which astronomers lost track of in 2012 when it moved beyond the range of their telescopes. For this reason, people like Professor Vishnu Reddy of the University of Arizona are also excited. A member of the Lunar and Planetary Laboratory, Reddy also leads the campaign to reacquire the asteroid. As he indicated, this flyby will be a chance for collaborative observation.

“This is a team effort that involves more than a dozen observatories, universities and labs across the globe so we can collectively learn the strengths and limitations of our near-Earth object observation capabilities,” he said. “This effort will exercise the entire system, to include the initial and follow-up observations, precise orbit determination, and international communications.”

2012 TC4 was originally discovered on Oct. 5th, 2012, by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at the Haleakala Observatory in Hawaii. After it sped past Earth in that same year, it has not been directly observed since. And while it is slightly larger than the meteor that exploded in Earth’s atmosphere near Chelyabinsk, Russia, in 2013, scientists are certain that it will pass us by at a safe distance.

This is based on tracking data that was collected by scientists from NASA’s Center for Near-Earth Object Studies (CNEOS). After monitoring 2012 TC4 for a period of seven days after it was discovered in 2012, they determined that at its closest approach, the asteroid will pass no closer than 6,800 km (4,200 mi) to Earth. However, it is more likely that it will pass us at distance of about 270,000 km (170,000 mi).

*The Pan-Starrs telescope at dawn. The mountain in the distance is Mauna Kea, about 130 kilometers southeast. Credit: pan-starrs.ifa.hawaii.edu*

This would place it at a distance that is about two-thirds the distance between the Earth and the Moon. The last time this asteroid passed Earth, it did so at a distance that was one-quarter the distance between the Earth and the Moon. Therefore, the odds of it passing by without incident are even greater this time around. So rather than representing a threat, the passage of this asteroid represents a good chance for research.

As Paul Chodas, the manager of the CNEOS at NASA’s Jet Propulsion Laboratory, stated:

“This is the perfect target for such an exercise because while we know the orbit of 2012 TC4 well enough to be absolutely certain it will not impact Earth, we haven’t established its exact path just yet. It will be incumbent upon the observatories to get a fix on the asteroid as it approaches, and work together to obtain follow-up observations than make more refined asteroid orbit determinations possible.”

By monitoring 2012 TC4 as it flies by, astronomers will be able to refine their knowledge about the asteroid’s orbit, which will help them to predict and calculate future flybys with even greater precision. This will further mitigate the risk posed by PHOs down the road, and help the PDCO to develop and test strategies to address possible future impacts.

In short, remain calm! This flyby is a good thing!

Further Reading: NASA

July 31, 2017July 31, 2017 by Matt Williams

NASA Detects More Chemicals on Titan that are Essential to Life

Titan's atmosphere makes Saturn's largest moon look like a fuzzy orange ball in this natural-color view from the Cassini spacecraft. Cassini captured this image in 2012. Image Credit: NASA/JPL-Caltech/Space Science Institute — According to a study from UCLA, Titan experiences severe methane rainstorms, leading to a the alluvial fans found found in both hemispheres. Credit: NASA/JPL-Caltech/Space Science Institute

Saturn’s largest moon Titan may be the most fascinating piece of real-estate in the Solar System right now. Not surprising, given the fact that the moon’s dense atmosphere, rich organic environment and prebiotic chemistry are thought to be similar to Earth’s primordial atmosphere. As such, scientists believe that the moon could act as a sort of laboratory for studying the processes whereby chemical elements become the building blocks for life.

These studies have already led to a wealth of information, which included the recent discovery of “carbon chain anions” – which are thought to be building blocks for more complex molecules. And now, thanks to data from the the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, a team of NASA researchers have detected the presence of acrylonitrile, another chemical elements that could be the basis for life on that moon.

The study that details their findings – titled “ALMA detection and astrobiological potential of vinyl cyanide on Titan” – was published in the July 28th issue of the journal Science Advances. In it, the team explains how data from the ALMA array indicated that large quantities of acrylonitrile (C₂H₃CN) exist on Titan – most likely within the moon’s stratosphere.

As Maureen Palmer, a researcher with the Goddard Center for Astrobiology and the lead author on the paper, indicated in a NASA press release: “We found convincing evidence that acrylonitrile is present in Titan’s atmosphere, and we think a significant supply of this raw material reaches the surface.”

Also known as vinyl cyanide, acrylonitrile is used here on Earth in the manufacture of plastics. In the past, it has been speculated that this compound could be present in Titan’s atmosphere. However, it was only recently that scientists became aware of the possibility that it be the basis for living creatures within Titan’s rich organic environment – with its steady supply of carbon, hydrogen, and nitrogen.

This is based on a study that was conducted in 2015, where a team of Cornell scientists sought to determine if organic cells could form in Titan’s harsh environment. Given that the moon experiences average surface temperatures of -179 °C (-290 °F) and the atmosphere is predominantly nitrogen and hydrocarbons, lipid bilayer membranes (which are the foundation of life on Earth) could not survive there.

However, after conducting molecular simulations, the team determined that small organic nitrogen compounds would be capable of forming a sheet of material similar to a cell membrane. They also determined that these sheets could form hollow, microscopic spheres that they dubbed “azotosomes”, and that the best chemical candidate for this sheets would be acrylonitrile.

*Artist concept of Methane-Ethane lakes on Titan (Credit: Copyright 2008 Karl Kofoed). Click for larger version.*

Such a material would be capable of surviving in liquid methane and at extremely cold temperatures, and would therefore be the most likely basis for organic life on Titan. As Michael Mumma, the director of the Goddard Center for Astrobiology, explained:

“The ability to form a stable membrane to separate the internal environment from the external one is important because it provides a means to contain chemicals long enough to allow them to interact. If membrane-like structures could be formed by vinyl cyanide, it would be an important step on the pathway to life on Saturn’s moon Titan.”

For the sake of their study, the Goddard team combined 11 high-resolution data sets from ALMA, which they retrieved from an archive of observations that were used to calibrate the array. From the data, Palmer and her team determined that acrylonitrile is relatively abundant in Titan’s atmosphere, reaching concentrations of up to 2.8 parts per billion. They also determined that it would be most common in Titan’s upper atmosphere.

It is here that carbon, hydrogen and nitrogen could chemically bond from exposure to sunlight and energetic particles from Saturn’s magnetic field. Eventually, the acrylonitrile would make its way down through the cold atmosphere and condense to form rain droplets that would fall to the surface. The team also estimated how much of this material would accumulate in Ligeia Mare – Titan’s second-largest methane lake – over time.

Finally, they calculated that within every cubic centimeter (cm³) of its volume, Ligeia Mare could form as many as 10,000,000 azotosomes. That roughly ten times the amount of bacteria that exists in the waters along Earth’s coastal regions. As Martin Cordiner, one of the senior authors on the paper, indicated, these findings are certainly encouraging when it comes to the search for extra-terrestrial life in our Solar System.

“The detection of this elusive, astrobiologically relevant chemical is exciting for scientists who are eager to determine if life could develop on icy worlds such as Titan,” he said. “This finding adds an important piece to our understanding of the chemical complexity of the solar system.”

Granted, the study and the basis for its conclusions are quite speculative. But they do show that within certain established parameters, life could exist within our Solar System well-beyond the limits of our Sun’s “habitable zone”. This study could also have implications in the hunt for life in extrasolar systems. If scientists can say definitively that life does not need warmer temperatures and liquid water to exist, it opens up immense possibilities.

In the coming decades, several missions are expected to go to Titan, ranging from submarines that will explore its methane lakes to drones and aerial platforms that will study its atmosphere and surface. Already, it is expected that they will obtain valuable information about the formation of the Saturn system. But to also discover entirely new forms of life? That would truly be Earth-shattering!

Further Reading: NASA, Science Advances

July 31, 2017August 7, 2017 by Tammy Plotner

Messier 52 – the NGC 7654 Open Star Cluster

The location of the Messier 52 open star cluster, located in the direction of the southern constellation Cassiopeia. Credit: Wikisky

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the open star cluster of Messier 52. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is Messier 52, an open star cluster that can seen in proximity to the northern constellation Cassiopeia. Located about 5000 light years from Earth, this star cluster is easily spotted in the night sky because of its association with Cassiopeia’s familiar W-shape. It can viewed with binocular and telescopes, and will appears as a hazy, nebulous patch of light.

Description:

Located roughly 5000 light years away, this 35 million year old cluster of stars has around 200 members – one of which is a very peculiar Of star. According to A.K. Pandy (et al), M52 is an interesting cluster in which to study star formation history. As they stated in their 2001 study:

“The colour magnitude diagrams show a large age spread in the ages. Star formation was biased towards relatively higher masses during the early phase of star formation whereas most of the low mass stars of the cluster were formed during the later phase. The star formation seems to have been a gradual process that proceeded sequentially in mass and terminated with the formation of most massive stars.”

*The Messier 52 open star cluster. Credit: Wikisky*

Indeed, M52 has been very studied for its star structure, including a search for variables. As S.L. Kim (et al), wrote in a 2000 study:

“We have performed a long-term project of CCD photometry of open clusters. Its primary goal is to search for variable stars, in particular short-period (less than a few days) pulsating stars such as Delta Sct, Gamma Dor, and slowly pulsating B-type stars (SPBs). These pulsating stars are recognized as important objects in studying stellar structure and testing evolution theory of intermediate-mass main sequence stars. Thus these clusters are ideal targets to investigate whether Gamma Dor type variability occurs in old open clusters or not.”

And it’s not just the structure they’re looking at – but the time frame in which they formed. As Anil K. Pandey wrote in her 2001 study:

“The distribution of stars in NGC 7654 indicates that the star formation within the cluster is not coeval and has an age spread -50 Myr. We found that star formation took place sequentially in the sense that low mass stars formed first. The star formation history in NGC 7654 supports the conventional picture of star formation in cluster where ‘low mass stars’ form first and star formation continues over a long period of time. The star formation within the cluster terminates with the formation of most massive stars in the cluster.”

History of Observation:

M52 was an original discovery of Charles Messier, captured on the night of September 7th, 1774. As he wrote in his notes at the time:

“Cluster of very small stars, mingled with nebulosity, which can be seen only with an achromatic telescope. It was when he observed the Comet which appeared in this year that M. Messier saw this cluster, which was close to the comet on the 7th of September 1774; it is below the star d Cassiopeiae: that star was used to determine both the cluster of stars and the comet.”

*Atlas Image mosaic of Messier 52, as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/UPAC/Caltech/NASA/NSF*

Sir William Herschel would also observe M52, but he would keep his notes private. As he wrote on August 29th, 1873:

“All resolved into innumerable small stars without any suspicion of nebulosity. 7 ft., 57. In the sweeper, 30, shews nebulosity, the stars being too obscure to be distinguished with its light tho’ considerable.” and again on December 23, 1805: “Review. Large 10 feet. This is a cluster of pretty condensed stars of different sizes. It is situated in a very rich part of the heavens and can hardly be called insulated, it may only be a very condensed part of the Milky Way which is here much divided and scattered. It is however so far drawn together with some accumulation that it may be called a cluster of the third order.”

Herschel’s son John would also add it to the General Catalog a few years later with less descriptive narrative, but it was Admiral Smyth who described M52’s beauty best when he said:

“An irregular cluster of stars between the head of Cepheus and his daughter’s throne; it lies north-west-by-west of Beta Cassiopeiae, and one third of the way towards Alpha Cephei. This object assumes somewhat of a triangular form, with an orange-tinted 8th-mag star at its vertex, giving it the resemblance of a bird with outspread wings. It is preceded by two stars of 7th and 8th magnitudes, and followed by another of similar brightness; and the field is one of singular beauty under a moderate magnifying power. While these were under examination, one of those bodies called falling stars passed through the outliers. This phenomenon was so unexpected and sudden as to preclude attention to it; but it appeared to be followed by a train of glittering and very minute spangles.”

May it glitter and spangle for you!

*The location of Messier 52 in proximity to the constellation Cassiopeia. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

Locating Messier 52:

In the rich star cluster fields of Cassiopeia, M52 is distinctive for its size and brightness. It’s not hard to find! Begin by identifying the W-shape of Cassiopeia and focus on its two brightest stars – Alpha and Beta. Because this constellation is circumpolar, remembering to look at the side that has the brightest stars or the steepest angle, will help you remember how to find this great open cluster. Now, just draw a mental line between Alpha, the lower star, and Beta, the upper.

Extend that line into space about the same distance and aim your binoculars or finderscope there. In binoculars M52 will show clearly as a beginning to resolve star cloud and a hazy patch in a telescope finderscope. Even the smallest of telescopes can expect resolution from this multi-magnitude beauty and the more aperture you apply, the more stars you will see. M52 is well suited to urban or light polluted skies and stands up well to fairly moonlit conditions and hazy skies.

Object Name: Messier 52
Alternative Designations: M52, NGC 7654
Object Type: Open Galactic Star Cluster
Constellation: Cassiopeia
Right Ascension: 23 : 24.2 (h:m)
Declination: +61 : 35 (deg:m)
Distance: 5.0 (kly)
Visual Brightness: 7.3 (mag)
Apparent Dimension: 13.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, M1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

July 30, 2017August 1, 2017 by Ken Kremer

Veteran Multinational Trio Launches on Soyuz and Arrives at International Space Station

The Soyuz MS-05 rocket is launched with Expedition 52 flight engineer Sergei Ryazanskiy of Roscosmos, flight engineer Randy Bresnik of NASA, and flight engineer Paolo Nespoli of ESA (European Space Agency), Friday, July 28, 2017 at the Baikonur Cosmodrome in Kazakhstan. Photo Credit: (NASA/Joel Kowsky)

An all veteran multinational trio of astronauts and cosmonauts rocketed to orbit aboard a Russian Soyuz capsule and safely arrived at the International Space Station (ISS) after a fast track rendezvous on Friday, July 28.

NASA astronaut Randy Bresnik, Sergey Ryazanskiy of Roscosmos and Paolo Nespoli of ESA (European Space Agency) docked at the orbiting outpost at 5:54 p.m. EDT (2154 GMT) Friday just six hours after departing our Home Planet.

The three crewmates launched aboard the Russian Soyuz MS-05 spacecraft from the Baikonur Cosmodrome in Kazakhstan during a typically hot mid-summers night at 9:41 p.m. Baikonur time, or 11:41 a.m. EDT, 1541 GMT, as the booster and Baikonur moved into the plane of the space station’s orbit. They blasted to space from the same pad as Yuri Gagarin, the first man in space.

The entire launch sequence aboard the Soyuz rocket performed flawlessly and delivered the Soyuz capsule to its targeted preliminary orbit flowing by the planned opening of the vehicles solar arrays and antennas.

The Russian Soyuz MS-05 carrying NASA astronaut Randy Bresnik, Sergey Ryazanskiy of the Russian space agency Roscosmos, and Paolo Nespoli of ESA (European Space Agency) docked to the International Space Station at 5:54 p.m. on Friday, July 28, 2017. Credits: NASA Television

Following a rapid series of orbit raising maneuvers, the Soyuz reached the ISS after 4 orbits and six hours to successfully complete all the rendezvous and docking procedures.

The Soyuz docked at the Earth-facing Russian Rassvet module as the spaceships were flying some 250 mi (400 km) over Germany.

Following the standard pressurization and leak checks, the hatches between the spacecraft and station were opened from inside the ISS at about 9:45 p.m. EDT.

The new trio of Bresnik, Ryazanskiy and Nespoli then floated one by one from the Soyuz into the station and restored the outpost to a full strength crew of six humans.

The veteran space flyers join Commander Fyodor Yurchikhin of Roscosmos and Flight Engineers Peggy Whitson and Jack Fischer of NASA who are already serving aboard.

Thus begins Expedition 52 aboard the million pound orbiting science complex.

This is the second space flight for both Bresnik and Ryazanskiy and the third for Nespoli.

Bresnik previously flew to the space station as a member of the STS-129 space shuttle Atlantis mission in November 2009. The 10 day mission delivered two Express Logistics Carriers (ELC racks) to the space station as part of approximately 30,000 pounds of replacement parts.

Bresnik performed two spacewalks for a total of 11 hours and 50 minutes during the STS-129 mission. He is slated to take command of the ISS as a member of Expedition 53.

The six person crew of Space Shuttle Atlantis walk out from crew quarters at 10:38 AM to greet the cheering crowd of media and NASA officials and then head out to pad 39 A to strap in for space launch with hours. Randy Bresnik is third from left. Credit: Ken Kremer/kenkremer.com

The new Expedition 52 crew will spend a four and a half month stint aboard the station and continue over 250 ongoing science investigations in fields such as biology, Earth science, human research, physical sciences and technology development.

Bresnik, Ryazanskiy and Nespoli are slated to stay aboard until returning to Earth in December.

Whitson, Fischer and Yurchikhin are in the home stretch of their mission and will retun to Earth in September. Shortly after their departure, NASA astronauts Mark Vande Hei and Joseph Acaba and Russian cosmonaut Alexander Misurkin will launch on the next Soyuz from Kazakhstan to join the Expedition 53 crew.

Whitson is the most experienced US astronaut with time in space. Her record setting cumulative time in space will exceed 600 days and include a 9 month stay on this flight upon her return to Earth.

She most recently launched to the ISS last year on Nov 17, 2016 aboard a Russian Soyuz capsule from the Baikonur Cosmodrome. This is her 3rd long duration stay aboard the station.

Whitson also holds the record for most spacewalks by a female astronaut. Altogether she has accumulated 53 hours and 23 minutes of EVA time over eight spacewalks.

The newly-expanded Expedition 52 crew expect to welcome a pair of unmanned US cargo ships carrying new research experiments and supplies, namely the SpaceX Dragon as soon as August and Orbital ATK Cygnus a month or two later, on NASA-contracted commercial resupply missions.

The SpaceX CRS-12 mission will carry investigations ”the crew will work on including a study developed by the Michael J. Fox Foundation of the pathology of Parkinson’s disease to aid in the development of therapies for patients on Earth. The crew will use the special nature of microgravity in a new lung tissue study to advance understanding of how stem cells work and pave the way for further use of the microgravity environment in stem cell research. Expedition astronauts also will assemble and deploy a microsatellite investigation seeking to validate the concept of using microsatellites in low-Earth orbit to support critical operations, such as providing lower-cost Earth imagery in time-sensitive situations such as tracking severe weather and detecting natural disasters.”

Watch for Ken’s onsite space mission reports direct from the Kennedy Space Center and Cape Canaveral Air Force Station, Florida.

Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.

July 29, 2017July 29, 2017 by Fraser Cain

Where Will the Space Launch System Take Us? Preparing For The Most Powerful Rocket Ever Built

NASA is in an awkward in-between time right now. Since the beginning of the space age, the agency has had the ability to send its astronauts into space. The first American to go to space, Alan Shepard, did a suborbital launch on board a Mercury Redstone rocket in 1961.

Then the rest of the Mercury astronauts went on Atlas rockets, and then the Gemini astronauts flew on various Titan rockets. NASA’s ability to hurl people and their equipment into space took a quantum leap with the enormous Saturn V rocket used in the Apollo program.

It’s difficult to properly comprehend just how powerful the Saturn V was, so I’ll give you some examples of things this monster could launch. A single Saturn V could blast 122,000 kilograms or 269,000 pounds into low-Earth orbit, or send 49,000 kilograms or 107,000 pounds on a transfer orbit to the Moon.

Instead of continuing on with the Saturn program, NASA decided to shift gears and build the mostly reusable space shuttle. Although it was shorter than the Saturn V, the space shuttle with its twin external solid rocket boosters could put 27,500 kilograms or 60,000 pounds into Low Earth orbit. Not too bad.

And then, in 2011, the space shuttle program wrapped up. And with it, the United States’ ability to launch humans into the space. And most importantly, to send astronauts to the continuously inhabited International Space Station. That task has fallen to Russian rockets until the US builds back the capability for human spaceflight.

Space Shuttle Columbia launching on its maiden voyage on April 12th, 1981. Credit: NASA

Since the cancellation of the shuttle, NASA’s workforce of engineers and rocket scientists has been developing the next heavy lift vehicle in NASA’s line up: the Space Launch System.

The SLS looks like a cross between a Saturn V and the space shuttle. It has the same familiar solid rocket boosters, but instead of the space shuttle orbiter and its orange external fuel tank, the SLS has the central Core Stage. It has 4 of the space shuttle’s RS-25 Liquid Oxygen engines.

Although two shuttle orbiters were lost in disasters, these engines and their liquid oxygen and liquid hydrogen performed perfectly for 135 flights. NASA knows how to use them, and how to use them safely.

The very first configuration of the SLS, known as the Block 1, should have the ability to put about 70 metric tonnes into Low Earth Orbit. And that’s just the beginning, and it’s just an estimate. Over time, NASA will increase its capabilities and launch power to match more and more ambitious missions and destinations. With more launches, they’ll get a better sense of what this thing is capable of.

After the Block 1 is launching, NASA will develop the Block 1b, which puts a much larger upper stage on top of the same core stage. This upper stage will have a larger fairing and more powerful second stage engines, capable of putting 97.5 metric tonnes into low Earth orbit.

Graphic shows all the dome, barrel, ring and engine components used to assemble the five major structures of the core stage of NASA’s Space Launch System (SLS) in Block 1 configuration. Credits: NASA/MSFC

Finally, there’s the Block 2, with an even larger launch fairing, and more powerful upper stage. It should blast 143 tonnes into low Earth orbit. Probably. NASA is developing this version as a 130 tonne-class rocket.

With this much launch capacity, what could be done with it? What kinds of missions become possible on a rocket this powerful?

The main goal for SLS is to send humans out, beyond low Earth orbit. Ideally to Mars in the 2030s, but it could also go to asteroids, the Moon, whatever you like. And as you’ll read later on in this article, it could send some amazing scientific missions out there too.

The very first flight for SLS, called Exploration Mission 1, will be to put the new Orion crew module into a trajectory that takes it around the Moon. In a very similar flight to Apollo 8. But there won’t be any humans, just the unmanned Orion module and a bunch of cubesats coming along for the ride. Orion will spend about 3 weeks in space, including about 6 days in a retrograde orbit around the Moon.

If all goes well, the first use of the SLS with the Orion crew module will happen some time in 2019. But also, don’t be surprised if it gets pushed back, that’s the name of the game.

After Exploration Mission 1, there’s be EM-2, which should happen a few years after that. This’ll be the first time humans get into an Orion crew module and take a flight to space. They’ll spend 21 days in a lunar orbit, and deliver the first component of the future Deep Space Gateway, which will be the subject of a future article.

From there, the future is unclear, but SLS will provide the capability to put various habitats and space stations into cislunar space, opening up the future of human space exploration of the Solar System.

Now you know where SLS is probably headed. But the key to this hardware is that it gives NASA raw capability to put humans and robots into space. Not just here on Earth, but way across the Solar System. New space telescopes, robotic explorers, rovers, orbiters and even human habitats.

In a recent study called “The Space Launch System Capabilities for Beyond Earth Missions,” a team of engineers mapped out what the SLS should be capable of putting into the Solar System.

For example, Saturn is a difficult planet to reach, and it order to get there, NASA’s Cassini spacecraft needed to do several gravitational slingshots around Earth and one past Jupiter. It took almost 7 years to get to Saturn.

SLS could send missions to Saturn on more direct trajectory, cutting the flight time down to just 4 years. Block 1 could send 2.7 tonnes to Saturn, while Block 1b could loft 5.1 tonnes.

An artist’s interpretation of NASA’s Space Launch System Block 1 configuration with an Orion vehicle. Image: NASA

NASA is considering a mission to Jupiter’s Trojan asteroids. These are a collection of space rocks trapped in Jupiter’s L4/L5 Lagrange points, and could be a fascinating place to study. Once put into the Trojan region, a mission could visit several different asteroids, sampling a vast range of rocks that detail the Solar System’s early history.

The Block 1 could put almost 3.97 tonnes into these orbits, while the Block 1b could do 7.59 tonnes. That’s 6 times the capability of an Atlas V. A mission like this would have a cruise time of 10 years.

In a previous video, we talked about future Uranus and Neptune missions, and how a single SLS could send spacecraft to both planets simultaneously.

Another idea that I really like is an inflatable habitat from Bigelow Aerospace. The BA-2100 module would be a fully self-contained space habitat. No need for other modules, this monster would be 65 to 100 tonnes, and would go up in a single launch of SLS. Once inflated, it would contain 2,250 cubic meters, which is almost 3 times the total living space of the International Space Station.

One of the most exciting missions, to me, is a next generation space telescope. Something that would be the true spiritual successor to the Hubble Space Telescope. There are a few proposals in the works right now, but the idea I like best is the LUVOIR telescope, which would have a mirror that measures 16 meters across.

The SLS Block 1b could put 36.9 tonnes into Sun-Earth Lagrange Point 2. Really there’s nothing else out there that could put this much mass into that orbit.

Just for comparison, Hubble has a mirror of 2.4 meters across, and James Webb is 6.5. With LUVOIR, you would have 10 times more resolution than James Webb, and 300 times more power than Hubble. But like Hubble, it would be capable of seeing the Universe in visible and other wavelengths.

A telescope like this could directly image the event horizons of supermassive black holes, see right to the edge of the observable Universe and watch the first galaxies forming their first stars. It could directly observe planets orbiting other stars and help us determine if they have life on them.

An artist's illustration of a 16 meter segmented mirror space telescope. There are no actual images of LUVOIR because the design hasn't been finalized yet. Image: Northrop Grumman Aerospace Systems & NASA/STScI — An artist’s illustration of a 16 meter segmented mirror space telescope. There are no actual images of LUVOIR because the design hasn’t been finalized yet. Image: Northrop Grumman Aerospace Systems & NASA/STScI

Seriously, I want this telescope.

At this point, I know this is going to set off a big argument about NASA versus SpaceX versus other private launch providers. That’s fine, I get it. And the Falcon Heavy is expected to launch later this year, bringing heavy lift launch capabilities at an affordable price. It’ll be able to loft 54,000 kilograms, which is less than the SLS Block 1, and almost a third of the capability of the Block 2. Blue Origins has its New Glenn, there are heavier rockets in the works from United Launch Alliance, Arianespace, the Russian Space Agency, and even the Chinese. The future of heavy lift has never been more exciting.

If SpaceX does get the Interplanetary Transport Ship going, with 300 tonnes into orbit on a reusable rocket. Well then, everything changes. Everything.

Until then, I’m still looking forward to the SLS.

July 28, 2017July 28, 2017 by Matt Williams

What Is the Name Of Our Galaxy?

The band of light (the Milky Way) that is visible in the night sky, showing the stellar disk of our galaxy. Credit: Bob King

Since prehistoric times, human beings have looked up at at the night sky and pondered the mystery of the band of light that stretches across the heavens. And while theories have been advanced since the days of Ancient Greece as to what it could be, it was only with the birth of modern astronomy that scholars have come come to know precisely what it is – i.e. countless stars at considerable distances from Earth.

The term “Milky Way”, a term which emerged in Classical Antiquity to describe the band of light in the night sky, has since gone on to become the name for our galaxy. Like many others in the known Universe, the Milky Way is a barred, spiral galaxy that is part of the Local Group – a collection of 54 galaxies. Measuring 100,000 – 180,000 light-years in diameter, the Milky Way consists of between 100 and 400 billion stars.

Structure:

The Milky Way consists of a Galactic Center that is shaped like a bar and a Galactic Disk made up of spiral arms, all of which is surrounded by the Halo – which is made up of old stars and globular clusters. The Center, also known as “the bulge”, is a dense concentration of mostly old stars that measures about 10,000 light years in radius. This region is also the rotational center of the Milky Way.

*Illustration of the supermassive black hole at the center of the Milky Way. Credit: NRAO/AUI/NSF*

The Galactic Center is also home to an intense radio source named Sagittarius A*, which is believed to have a supermassive black hole (SMBH) at its center. The presence of this black hole has been discerned due to the apparent gravitational influence it has on surrounding stars. Astronomers estimate that it has a mass of between 4.1. and 4.5 million Solar masses.

Outside the barred bulge at the Galactic Center is the Galactic Disk of the Milky Way. This consists of stars, gas and dust which is organized into four spiral arms. These arms typically contain a higher density of interstellar gas and dust than the Galactic average, as well as a greater concentration of star formation. While there is no consensus on the exact structure or extent of these spiral arms, they are commonly grouped into two or four different arms.

In the case of four arms, this is based on the traced paths of gas and younger stars in our galaxy, which corresponds to the Perseus Arm, the Norma and Outer Arm, the Scutum-Centaurum Arm, and the Carina-Sagittarius Arm. There are also at least two smaller arms, which include the Cygnus Arm and the Orion Arm. Meanwhile, surveys based on the presence of older stars show only two major spirals arms – the Perseus arm and the Scutum–Centaurus arm.

Beyond the Galactic Disk is the Halo, which is made up of old stars and globular clusters – 90% of which lie within 100,000 light-years (30,000 parsecs) from the Galactic Center. Recent evidence provided by X-ray observatories indicates that in addition to this stellar halo, the Milky way also has a halo of hot gas that extends for hundreds of thousands of light years.

*Artist’s conception of the spiral structure of the Milky Way with two major stellar arms and a bar. Credit: NASA/JPL-Caltech/ESO/R. Hurt*

Size and Mass:

The Galactic Disk of the Milky Way Galaxy is approximately 100,000 light years in diameter and about 1,000 light years thick. It is estimated to contain between 100 and 400 billion stars, though the exact figure depends on the number of very low-mass M-type (aka. red dwarf) stars. This is difficult to determine because these stars also have low-luminosity compared to other class.

The distance from the Sun to the Galactic Center is estimated to be between 25,000 to 28,000 light years (7,600 to 8,700 parsecs). The Galactic Center’s bar (aka. its “bulge”) is thought to be about 27,000 light-years in length and is composed primarily of red stars, all of which are thought to be ancient. The bar is surrounded by the ‘5-kpc ring’, a region that contains much of the galaxy’s molecular hydrogen and where star-formation is most intense.

The Galactic Disk has a diameter of between 70,000 and 100,000 light-years. It does not have a sharp edge, a radius beyond which there are no stars. However, the number of stars drops slowly with distance from the center. Beyond a radius of roughly 40,000 light years, the number of stars drops much faster the farther you get from the center.

Location of the Solar System:

The Solar System is located near the inner rim of the Orion Arm, a minor spiral arm located between the Carina–Sagittarius Arm and the Perseus Arm. This arm measures some 3,500 light-years (1,100 parsecs) across, approximately 10,000 light-years (3,100 parsecs) in length, and is at a distance of about 25,400 to 27,400 light years (7.78 to 8.4 thousand parsecs) from the Galactic Center.

History of Observation:

Our galaxy was named because of the way the haze it casts in the night sky resembled spilled milk. This name is also quite ancient. It is translation from the Latin “Via Lactea“, which in turn was translated from the Greek for Galaxias, referring to the pale band of light formed by stars in the galactic plane as seen from Earth.

Persian astronomer Nasir al-Din al-Tusi (1201–1274) even spelled it out in his book Tadhkira: “The Milky Way, i.e. the Galaxy, is made up of a very large number of small, tightly clustered stars, which, on account of their concentration and smallness, seem to be cloudy patches. Because of this, it was likened to milk in color.”

Astronomers had long suspected the Milky Way was made up of stars, but it wasn’t proven until 1610, when Galileo Galilei turned his rudimentary telescope towards the heavens and resolved individual stars in the band across the sky. With the help of telescopes, astronomers realized that there were many, many more stars in the sky, and that all of the ones that we can see are a part of the Milky Way.

In 1755, Immanuel Kant proposed that the Milky Way was a large collection of stars held together by mutual gravity. Just like the Solar System, this collection would be rotating and flattened out as a disk, with the Solar System embedded within it. Astronomer William Herschel (discoverer of Uranus) tried to map its shape in 1785, but he didn’t realize that large portions of the galaxy are obscured by gas and dust, which hide its true shape.

It wasn’t until the 1920s, when Edwin Hubble provided conclusive evidence that the spiral nebulae in the sky were actually whole other galaxies, that the true shape of our galaxy was known. Thenceforth, astronomers came to understand that the Milky Way is a barred, spiral galaxy, and also came to appreciate how big the Universe truly is.

The Milky Way is appropriately named, being the vast and cloudy mass of stars, dust and gas it is. Like all galaxies, ours is believed to have formed from many smaller galaxies colliding and combining in the past. And in 3 to 4 billion years, it will collide with the Andromeda Galaxy to form an even larger mass of stars, gas and dust. Assuming humanity still exists by then (and survives the process) it should make for some interesting viewing!

We have written many interesting articles about the Milky Way here at Universe Today. Here’s 10 Interesting Facts About the Milky Way, How Big is the Milky Way?, Why is our Galaxy Called the Milky Way?, What is the Closest Galaxy to the Milky Way?, Where is the Earth in the Milky Way?, The Milky Way has Only Two Spiral Arms, and It’s Inevitable: Milky Way, Andromeda Galaxy Heading for Collision.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We’ve also recorded an episode of Astronomy Cast about the Milky Way. Listen here, Episode 99: The Milky Way.

Sources:

July 28, 2017July 28, 2017 by Tammy Plotner

The Crater Constellation

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at “The Cup” – the Crater constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age

One of these constellation is Crater (aka. “The Cup”), an asterism located in the Southern Hemisphere. This small constellation is located south of the ecliptic plane, with no bright marker stars. As part of the Hercules family, it is bordered by the constellations of Leo, Sextans, Hydra, Corvus and Virgo. Today, it is one of the 88 modern constellations recognized by the International Astronomical Union.

Name and Meaning:

In Greek mythology, Crater represents the Cup of Apollo – the god of the skies – which is due to its chalice-like configuration. The cup is being held up by the Raven – Corvus – another figure in Greek mythology. The tale, much like many mythological stories, is a sad one, and begins with the Raven being sent to fetch water for his master, Apollo.

Unfortunately, Corvus (the Raven) was distracted as he became tempted by a fig, and then waited too long for it to ripen. When he realized his mistake, he returned sorrowfully to Apollo with his cup (Crater) and brought along the serpent Hydra in his claws as well. Angry, Apollo tossed all three into the sky for all eternity, where they became part of the starry firmament.

Corvus, Crater and other constellations seen around Hydra. From Urania's Mirror (1825). Credit: US Library of Congress — *Corvus, Crater and other constellations seen around Hydra. From Urania’s Mirror (1825). Credit: US Library of Congress*

History of Observation:

The Crater constellation comes to us from Classical Antiquity and was recorded by Ptolemy in his 2nd-century CE tract the Almagest. However, it was also recognized by Chinese astronomers, where the stars associated with it were viewed as being part the Vermillion Bird of the South (Nan Fang Zhu Que). Along with the some of the stars from Hydra, they depict the Red Bird’s wings.

Notable Objects:

Crater has only a few bright stars associated with it and no Messier Objects. The brightest, Delta Crateris, is an orange giant located approximately 196 light yeas from Earth. The star is also known as Labrum (Latin for “the lip”), due to the fact that it was sometimes associated with the story of the Holy Grail.

Next is Alpha Crateris, an orange giant located approximately 174 light-years from Earth which is 80 times more luminous than our Sun. It is also known as Alkes, derived from the Arabic word alkas, which means “the cup”. Then there’s Beta Crateris, a white sub-giant that is located approximately 266 light years from Earth. This star is also known by the name Al Sharasif, which means “the ribs” in Arabic.

In terms of Deep Sky Objects, Crater has no associated Messier Objects, but a few galaxies can be found in its region of the night sky. These include the Crater 2 dwarf galaxy, a satellite galaxy of the Milky Way that is located approximately 380,000 light years from Earth. There’s also the spiral galaxy known as NGC 3511, which has a slight bar and is seen from Earth nearly edge-on.

*The spiral galaxy NGC 3887, located in the constellation Crater. Credit: NASA (Wikisky)*

There’s also the NGC 3887 and NGC 2981 spiral galaxies, and the RX J1131 quasar, which is located 6 billion light years away from Earth. Interestingly, the black hole at the center of this quasar was the first to have its spin directly measured by astronomers.

Finding Crater:

Crater is visible at latitudes between +65° and -90° and is best seen at culmination during the month of April. It is comprised of only 4 main stars, and 12 stars with Bayer/Flamsteed designations. In order to spot these stars, observers should begin by looking for the Alpha star (the “a” shape on their star map) with binoculars.

Situated some 174 light-years from Earth, Alpha Crateris (the star’s official designation) is a spectral class K1 star – an orange giant that’s a little different from the rest. This is because Alkes is a “high velocity” star, which means it moves far faster than the stars around it. Another thing that sets it apart is its high metal content, which according to some researchers, it may have picked up when it came from the inner, metal-rich part of the Galaxy.

Artist's impression of Alkes - aka. Alpha Crateris. Credit: constellation-guide.com — *Artist’s impression of Alkes – aka. Alpha Crateris – a K1 orange giant star in the Crater constellation. Credit: constellation-guide.com*

Next, observers should look to Beta Crateris (the “B” shape on the map) which also goes by the name of Al Sharasif. This star is not an ordinary one either. For starters, Al Sharasif is about 265 light-years from our solar system, and it’s a white sub-giant star. To boot, it also has a low mass, white dwarf companion – which is why astronomers classify it as a Sirius-like system.

Next up is Delta Crateris – the “8” symbol on the map – which is an orange giant, spectral class K0III star with an apparent magnitude of 3.56. In time, this star will become an even larger giant, eventually turning into a Mira-type variable star before ending its life as a white dwarf. Oddly enough, Labrum has a very low metal content compared to its Crater-neighbors, containing about 40% as much iron as our own Sun.

At this point, observers with telescopes and have a look at Gamma Crateris – the “Y” shape on the map. Gamma Crateris is a fixed binary white dwarf star with an easy separation of 5.2″. Gamma itself is 89 light-years for Earth, which is rather hard to believe when you try to seek out the 9.5 stellar magnitude companion that accompanies it.

Although this is a disparate double star, it is still quite fun and easy to spot with a small telescope. For a challenge, try Iota Crateris – a close binary star with an 11th magnitude companion that’s only separated by 1.4″. Psi Crateris is an even closer binary. Both stars are within a half magnitude of each other, but the separation is only 0.2″.

Artist's impression of white dwarf binary pair CSS 41177. Image: Andrew Taylor. — *Artist’s impression of white dwarf binary pair, a type of star system that describes Gamma Crateris. Credit: Andrew Taylor.*

Next up is R Crateris, a variable star that can be observed with binoculars, and which is located at RA 10 56 Dec -17 47. You will notice it by its lovely red color and its nice change of magnitude, which goes from 8 to 9.5 in a period of about 160 days. And then there’s SZ Crateris, a magnitude 8.1 variable star. It is a nearby star system located about 44 light years from the Sun and is known as Gliese 425 – which in the past was known as Abt’s Star.

While there’s no brighter deep sky objects for binoculars or small telescopes, there are a couple of challenging galaxies in the Crater constellation that are well suited to a large aperture. Let’s start with the brightest – elliptical galaxy NGC 3962 – which is easy to spot (like all elliptical galaxies), though there’s not much detail to be seen. Even if it is not terribly exciting to behold, it is on the Herschel 400 observing list.

And then there’s NGC 3887 (11h47.1 -16 51), a nice spiral galaxy that’s only slightly fainter. It has two faint stars which accompany it and a stellar nucleus which occasionally makes an appearance and provides an opportunity for some very interesting viewing. Both of these galaxies are in the slightly fainter range, both being just under magnitude 11.

Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg) — *List of the stars that appear in the Crater constellation. Credit: IAU and Sky & Telescope magazine/Roger Sinnott & Rick Fienberg*

Observers who are skilled with telescopes should also keep and eye out for NGC 3511 (11h03.4 -23 05), a spiral galaxy of magnitude 11.5. It is joined in the same field of view by NGC 3513, a barred spiral galaxy that is a full magnitude dimmer. People with larger telescopes should also take a crack at spotting NGC 3672 (11h25.0 -09 48), a faint spiral galaxy that nevertheless has nice halo and a bright, apparent nucleus.

And last, but not least, there is NGC 3981 (11h56.1 -19 54), a beautifully inclined, magnitude 12 spiral galaxy that has a bright nucleus, and which sometimes shows some spiral galaxy structure when observing conditions are right.

Drink up… the “Cup” is waiting!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?, What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

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