Adieu Titan: So Long & Thanks For All The Hydrocarbons

Artist's conception of Cassini winging by Saturn's moon Titan (right) with the planet in the background. Credit: NASA/JPL-Caltech

The Cassini spacecraft has done some amazing things since it arrived in the Saturn system in 2004. In addition to providing valuable information on the gas giant and its system of rings, it has also provided us with extensive data and photographs of Saturn’s many moons. Nowhere has this been more apparent than with Saturn’s largest moon, the hydrocarbon-rich satellite known as Titan.

And with just a few hours left before Cassini makes its final plunge between Saturn and its innermost ring (something that no other spacecraft has ever done), we should all take this opportunity to say goodbye to Titan. In the past few years, it has dazzled us with its methane lakes, dense atmosphere, and potential for hosting life. And it shall be sorely missed!

Cassini’s last encounter with Titan – where it passed within 979 km (608 mi) of the moon’s surface – took place on April 21st, at 11:08 p.m. PDT (April 22nd, 2:08 a.m. EDT). The probe also used this opportunity to take some radar images of the moon’s northern polar region. While this area has been photographed before, this was the first time that radar images were acquired.

*Unprocessed image of Saturn’s moon Titan, captured by NASA’s Cassini spacecraft during its final close flyby on April 21st, 2017. Credit: NASA/JPL-Caltech/Space Science Institute*

Over the course of the next week, Cassini’s radar team hopes to pour over theses images, which provide a detailed look at the methane seas and lakes in the northern polar region. It is hoped that this data will allow scientists to shed more light on the depths and compositions of some of the small lakes in the area, as well as provide more information on the evolving surface feature known as “magic island“.

With this last pass complete (its 127th in total), Cassini is now beginning the final phase of its mission – known as the Grand Finale. This will consist of the spacecraft making a final set of 22 orbits around the ringed planet between April 26th and September 15th. The maneuver will allow Cassini to go where no other probe has gone before and get the closest look ever at Saturn’s outer rings.

The final pass over Titan was part of this maneuver, using the moon’s gravity to bend and reshape the probe’s orbit so that it would be able to pass through Saturn’s ring system – instead of passing just beyond the main rings. As Earl Maize, Cassini project manager at JPL, said in a NASA press release:

“With this flyby we’re committed to the Grand Finale. 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.”

*Some key numbers for Cassini’s Grand Finale and final plunge into Saturn. Credit: NASA/JPL-Caltech*

Cassini’s final pass with Titan allowed it to acquire a boost in velocity, increasing its speed by 860.5 meters per second (3098 km/h; 1,925 mph). It then reached its farthest point in its orbit around Saturn (apoapse) on April 22nd, :46 p.m. PDT (11:46 p.m. EDT). This effectively began the Grand Finale orbits, with the first dive coming on April 26th, at 02:00 a.m. PDT (05:00 a.m. EDT).

This orbit will provide Cassini with its best look to date at Saturn’s north pole, which it will be studying with both its Visible and Infrared Mapping Spectrometer (VIMS) and Composite Infrared Spectrometer (CIRS). These studies will lead to the creation of the sharpest movies to date in the near-infrared band, which will also allow the science team to study the motions of the hexagon pattern around Saturn’s north pole in more detail.

Between now and September, when the mission will end, the probe will provide information that is expected to improve our understanding of how giant planets form and evolve. Things will finally wrap on September 15th, 2017, when the probe will plunge into Saturn’s atmosphere. But even then, the probe will be sending back information until its very last seconds of operation.

Safe journeys Cassini! And so long Titan! We hope to be exploring you again someday soon, preferably with something that can float or fly around inside your dense atmosphere, or perhaps investigate your methane seas in serious depth!

In the meantime, be sure to check out this narrated, 360-degree animated video from NASA. As you can see, it simulates what a ride on the Cassini spacecraft might look like as it makes its Grand Finale:

Further Reading: NASA, Cassini – The Grand Finale

April 25, 2017April 28, 2017 by Evan Gough

Another Strange Discovery From LHC That Nobody Understands

New results from ALICE at the Large Hadron Collider show so-called strange hadrons being created where none were expected. As the number of proton-proton collisions (the blue lines) increase, the more of these strange hadrons are seen (as shown by the red squares in the graph). (Image: CERN)

There are some strange results being announced in the physics world lately. A fluid with a negative effective mass, and the discovery of five new particles, are all challenging our understanding of the universe.

New results from ALICE (A Large Ion Collider Experiment) are adding to the strangeness.

ALICE is a detector on the Large Hadron Collider (LHC). It’s one of seven detectors, and ALICE’s role is to “study the physics of strongly interacting matter at extreme energy densities, where a phase of matter called quark-gluon plasma forms,” according to the CERN website. Quark-gluon plasma is a state of matter that existed only a few millionths of a second after the Big Bang.

In what we might call normal matter—that is the familiar atoms that we all learn about in high school—protons and neutrons are made up of quarks. Those quarks are held together by other particles called gluons. (“Glue-ons,” get it?) In a state known as confinement, these quarks and gluons are permanently bound together. In fact, quarks have never been observed in isolation.

A cut-away view of the ALICE detector at CERN’s LHC. Image: By Pcharito – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31365856

The LHC is used to collide particles together at extremely high speeds, creating temperatures that can be 100,000 times hotter than the center of our Sun. In new results just released from CERN, lead ions were collided, and the resulting extreme conditions come close to replicating the state of the Universe those few millionths of a second after the Big Bang.

In those extreme temperatures, the state of confinement was broken, and the quarks and gluons were released, and formed quark-gluon plasma.

So far, this is pretty well understood. But in these new results, something additional happened. There was increased production of what are called “strange hadrons.” Strange hadrons themselves are well-known particles. They have names like Kaon, Lambda, Xi and Omega. They’re called strange hadrons because they each have one “strange quark.”

If all of this seems a little murky, here’s the dinger: Strange hadrons may be well-known particles, because they’ve been observed in collisions between heavy nuclei. But they haven’t been observed in collisions between protons.

“Being able to isolate the quark-gluon-plasma-like phenomena in a smaller and simpler system…opens up an entirely new dimension for the study of the properties of the fundamental state that our universe emerged from.” – Federico Antinori, Spokesperson of the ALICE collaboration.

“We are very excited about this discovery,” said Federico Antinori, Spokesperson of the ALICE collaboration. “We are again learning a lot about this primordial state of matter. Being able to isolate the quark-gluon-plasma-like phenomena in a smaller and simpler system, such as the collision between two protons, opens up an entirely new dimension for the study of the properties of the fundamental state that our universe emerged from.”

Enhanced Strangeness?

The creation of quark-gluon plasma at CERN provides physicists an opportunity to study the strong interaction. The strong interaction is also known as the strong force, one of the four fundamental forces in the Universe, and the one that binds quarks into protons and neutrons. It’s also an opportunity to study something else: the increased production of strange hadrons.

In a delicious turn of phrase, CERN calls this phenomenon “enhanced strangeness production.” (Somebody at CERN has a flair for language.)

Enhanced strangeness production from quark-gluon plasma was predicted in the 1980s, and was observed in the 1990s at CERN’s Super Proton Synchrotron. The ALICE experiment at the LHC is giving physicists their best opportunity yet to study how proton-proton collisions can have enhanced strangeness production in the same way that heavy ion collisions can.

According to the press release announcing these results, “Studying these processes more precisely will be key to better understand the microscopic mechanisms of the quark-gluon plasma and the collective behaviour of particles in small systems.”

I couldn’t have said it better myself.

April 24, 2017May 8, 2017 by Tammy Plotner

Messier 40 – the Winnecke 4 Double Star

The double star Messier 40 (Winnecke 4), along with PGC 39934, NGC 4290 and NGC 4284. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the double star known as Messier 40. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is Messier 40, this double star is now known to be an optical double star (i.e. two independent stars at different distances that appear aligned based on our perspective). It is also included in the Winnecke Catalogue of Double Stars as number 4, and is located in the constellation of Ursa Major (aka. the Big Dipper).

Description:

At roughly 500 light years away from us, no one is quite sure if this pair of stars is truly a binary system or an optical double star. According to Richard Nugent’s 2002 data, “The observed relative proper motion, as measured in separation and position angle, is consistent with a straight, independent motion of the two stars, one crossing between us and the other.”

The two stars are nearly the same brightness as each other, with the primary star being magnitude 9 and the secondary being magnitude 9.3 and they are separated by about 49 arc seconds – a wide gap. At one time, the angular separation of the pair was measured at 49.2″, but has gradually changed to about 52.8″ in more recent years.

History of Observation:

Messier 40 was discovered by Charles Messier in 1764 while he was searching for a nebula that had been reported in the area by Johann Hevelius. As he wrote at the time:

“The same night on October 24-25, [1764], I searched for the nebula above the tail of the Great Bear [Ursa Major], which is indicated in the book Figure of the Stars, second edition: it should have, in 1660, the right ascension 183d 32′ 41″, and the northern declination 60d 20′ 33″. I have found, by means of this position, two stars very near to each other and of equal brightness, about the 9th magnitude, placed at the beginning of the tail of Ursa Major: one has difficulty to distinguish them with an ordinary refractor of 6 feet. Here are their position: right ascension, 182 deg 45′ 30″, and 59 deg 23′ 50″ northern declination. There is reason to presume that Hevelius mistook these two stars for a nebula.”

History often credits Messier for being a little bit crazy for cataloging a double star, but upon having read Messier’s report, I feel like he was an astronomer doing his job. If Hevelius reported a nebula here – then he was bound to look and write down what he saw. He didn’t just stumble on a double star and catalog it for no reason!

*Close-up of the double star Messier 40. Credit: Wikisky*

Later astronomers would also search for M40 and report a double star, and it was cataloged by such as by Friedrich August Theodor Winnecke at Pulkovo Observatory in 1863 as WNC 4. However, to give the good Hevelius credit, John Mallas reports, “the Hevelius object is the 5th-magnitude star 74 Ursae Majoris, more than one degree away, as reference to his star catalogue will show.”

In 1991, the separation between the stars was measured at 52.8 arcseconds, which represented an increase since 1966, when it was measured at 51.7. In 2001 and 2002, studies conducted by Brian Skiff and Richard L. Nugent suggested that the stars comprising the double star (HD 238107 and HD 238108) were in fact an optical double star, rather than a double star system.

In 2016, by using parallax measurements from the Gaia satellite, this theory was proven for the first time. Distance estimates were also produced, indicating that the two components are 350±30 and 140±5 parsecs (~1141±98 and 456±16 light years).

Locating Messier 40:

Finding Messier 40 isn’t very difficult for fairly large binoculars and small telescopes – but you need to remember that it’s a double star. First locate the easily recognized constellation of Ursa Major and focus on the ‘Big Dipper’ and look for the two stars that form the edge that connect to the handle – Gamma and Delta.

*The location of Messier 40 in Ursa Major, above and to the left of MegrezCredit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

Aim your telescope’s finderscope at Delta – the point where the ‘handle’ would connect. In the finder, you will see a fainter star to the northeast. Hop there. Now, using a low power eyepiece, scan slightly further northeast and you will locate M40. Once located, you may go to higher magnification to more closely examine this Messier catalog curiosity.

While this pair of stars will show easily in binoculars, you must remember that binoculars give such a wide field that it will be difficult to distinguish them from surrounding stars. However, this is a great object for light-polluted skies and moonlit nights!

Enjoy the controversy… and this pair! And here are the quick facts on M40 to help you get started:

Object Name: Messier 40
Alternative Designations: M40, WNC 4
Object Type: Double Star
Constellation: Ursa Major
Right Ascension: 12 : 22.4 (h:m)
Declination: +58 : 05 (deg:m)
Distance: 0.51 (kly)
Visual Brightness: 8.4 (mag)
Apparent Dimension: 0.8 (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, M8 – The Lagoon 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:

April 24, 2017April 8, 2018 by Matt Williams

What is the Average Surface Temperature of Mercury?

MESSENGER image of Mercury from its third flyby (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Of all the planets in the Solar System, Mercury is the closest to our Sun. As such, you would think it is the hottest of all the Solar planets. But strangely enough, it is not. That honor goes to Venus, which experiences an average surface temperature of 750 K (477 °C; 890 °F). Not only that, but Mercury is also cold enough in some regions to maintain water in ice form.

Overall, Mercury experiences considerable variations in temperatures, ranging from the extremely hot to the extremely cold. All of this arises from the fact that Mercury has an extremely thin atmosphere, as well as the nature of its orbit. Whereas the side facing the Sun experiences temperatures hot enough to melt lead, the darkened areas are cold enough to freeze water.

Orbital Characteristics:

Mercury has the most eccentric orbit of any planet in the Solar System (0.205). Because of this, its distance from the Sun varies between 46 million km (29 million mi) at its closest (perihelion) to 70 million km (43 million mi) at its farthest (aphelion). And with an average orbital velocity of 47.362 km/s (29.429 mi/s), it takes Mercury a total 87.969 Earth days to complete a single orbit around the Sun.

With an average rotational speed of 10.892 km/h (6.768 mph), Mercury also takes 58.646 days to complete a single rotation. This means that Mercury has a spin-orbit resonance of 3:2, which means that it completes three rotations on its axis for every two orbits around the Sun. This does not, however, mean that three days last the same as two years on Mercury.

In fact, its high eccentricity and slow rotation mean that it takes 176 Earth days for the Sun to return to the same place in the sky (aka. a solar day), which means that one day is twice as long as a single year on Mercury. The planet also has the lowest axial tilt of any planet in the Solar System – approximately 0.027° compared to Jupiter’s 3.1°, (the second smallest). This means that there is virtually no seasonal variation in surface temperature.

Exosphere:

Another factor that affects Mercury’s surface temperatures is its extremely thin atmosphere. Mercury is essentially too hot and too small to retain anything more than a variable “exosphere”, one which is made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor.

The Fast Imaging Plasma Spectrometer on board MESSENGER has found that the solar wind is able to bear down on Mercury enough to blast particles from its surface into its wispy atmosphere. Credit: Carolyn Nowak/Media Academica, LLC

These trace gases have a combined atmospheric pressure of about 10^-14 bar (one-quadrillionth of Earth’s atmospheric pressure). It is believed this exosphere was formed from particles captured from the Sun, volcanic outgassing and debris kicked into orbit by micrometeorite impacts.

Surface Temperatures:

Because it lacks a viable atmosphere, Mercury has no way to retain the heat from the Sun. As a result of this and its high eccentricity, the planet experiences considerable variations in temperature between its light side and dark side. Whereas the side that faces the Sun can reach temperatures of up to 700 K (427° C; 800 °F), the side in shadow dips down to 100 K (-173° C: -279 °F).

Despite its extreme highs in temperature, the existence of water ice and even organic molecules has been confirmed on Mercury’s surface, specifically in the cratered northern polar region. Since the floors of these deep craters are never exposed to direct sunlight, temperatures there remain below the planetary average.

*View of Mercury’s north pole. based on MESSENGER probe data, showing polar deposits of water ice. Credit: NASA/JHUAPL/Carnegie/National Astronomy and Ionosphere Center, Arecibo Observatory.*

These icy regions are believed to contain about 10¹⁴–10¹⁵ kg of frozen water, and may be covered by a layer of regolith that inhibits sublimation. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by the impacts of comets. There are thought to be craters at the south pole as well, where temperatures are similarly cold enough to sustain water in ice form.

Mercury is a planet of extremes. It has an extremely eccentric orbit, an extremely thin-atmosphere, and experiences extremely hot and cold surface temperatures. Little wonder then why there is no life on the planet (at least, that we know about!) But perhaps someday, human beings may live there, sheltered in the cratered regions and using the water ice to create a habitat.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Sources:

April 24, 2017April 28, 2017 by Evan Gough

Into The Submillimeter: The Early Universe’s Formation

A new study looked at 52 submillimeter galaxies to help us understand the early ages of our Universe. Image: University of Nottingham/Omar Almaini

In order to make sense of our Universe, astronomers have to work hard, and they have to push observing technology to the limit. Some of that hard work revolves around what are called sub-millimeter galaxies (SMGs.) SMGs are galaxies that can only be observed in the submillimeter range of the electromagnetic spectrum.

The sub-millimeter range is the waveband between the far-infrared and microwave wavebands. (It’s also called Terahertz radiation.) We’ve only had the capability to observe in the sub-millimeter range for a couple decades. We’ve also increased the angular resolution of telescopes, which helps us discern separate objects.

The submillimter wavelength is also called Terahertz Radiation, and is between Infrared and Microwave Radiation on the spectrum. Image: By Tatoute, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6884073

SMGs themselves are dim in other wavelengths, because they’re obscured by dust. The optical light is blocked by the dust, and absorbed and re-emitted in the sub-millimeter range. In the sub-millimeter, SMGs are highly luminous; trillions of times more luminous than the Sun, in fact.

This is because they are extremely active star-forming regions. SMGs are forming stars at a rate hundreds of times greater than the Milky Way. They are also generally older, more distant galaxies, so they’re red-shifted. Studying them helps us understand galaxy and star formation in the early universe.

ALMA is an array of dishes located at the Atacama Desert in Chile. Image: ALMA (ESO/NAOJ/NRAO), O. Dessibourg

A new study, led by James Simpson of the University of Edinburgh and Durham University, has examined 52 of these galaxies. In the past, it was difficult to know the exact location of SMGs. In this study, the team relied on the power of the Atacama Large Millimeter/submillimeter array (ALMA) to get a much more precise measurement of their location. These 52 galaxies were first identified by the Submillimeter Common-User Bolometer Array (SCUBA-2) in the UKIDSS Ultra Deep Survey.

There are four major results of the study:

48 of the SMGs are non-lensed, meaning that there is no object of sufficient mass between us and them to distort their light. Of these, the team was able to constrain the red-shift (z) for 35 of them to a median range of z-2.65. When it comes to extra-galactic observations like this, the higher the red-shift, the further away the object is. (For comparison, the highest red-shift object we know of is a galaxy called GN-z11, at z=11.1, which corresponds to about 400 million years after the Big Bang.
Another type of galaxy, the Ultra-Luminous Infrared Galaxy (ULIRG) were thought to be evolved versions of SMGs. But this study showed that SMGs are larger and cooler than ULIRGs, which means that any evolutionary link between the two is unlikely.
The team calculated estimates of dust mass in these galaxies. Their estimates suggest that effectively all of the optical-to-near-infrared light from co-located stars is obscured by dust. They conclude that a common method in astronomy used to characterize astronomical light sources, called Spectral Energy Distribution (SED), may not be reliable when it comes to SMGs.
The fourth result is related to the evolution of galaxies. According to their analysis, it seems unlikely that SMGs can evolve into spiral or lenticular galaxies (a lenticular galaxy is midway between a spiral and an elliptical galaxy.) Rather, it appears that SMGs are the progenitors of elliptical galaxies.

The Pinwheel Galaxy (M101, NGC 5457) is a stunning example of a spiral galaxy. This study determines that there likely is no evolutionary link between sub-millimeter galaxies and spiral galaxies. Image: European Space Agency & NASA. CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=36216331

This study was a pilot study that the team hopes to extend to many other SMGs in the future.

April 23, 2017April 23, 2017 by Fraser Cain

Join Fraser and Friends for a COSMOS Marathon on Monday

Viking Lander — In 1976, two Viking spacecraft landed on Mars. The image is of a model of the Viking lander, along with astronomer and pioneering astrobiologist Carl Sagan. Each lander was equipped with life detection experiments designed to detect life based on its metabolic activities. Credits: NASA/Jet Propulsion Laboratory, Caltech

Click here on Monday, April 24th at 12:00 pm PST to join the livestream.

Remember COSMOS, with Carl Sagan? Of course you do. If you’re fascinated with space and astronomy like me, then the original COSMOS must have had a pivotal impact on your enthusiasm for all things space. And not just space, but all things science. I don’t think it’s an understatement to say that Carl Sagan completely changed the paradigm for what it means to be a science communicator. He revealed the discoveries made by astronomers, and made them accessible to a general audience – and he took a lot of heat for it.

Unfortunately, Carl Sagan died of cancer in 1996, years too early. He changed the world, but he never got to stick around and see his impact echoing through the Internet as it has today. When I started Universe Today in 1999, it was because the ideas in Pale Blue Dot resonated so deeply with me. I wanted to dedicate my life to understanding and teaching the world about space. And I’m always sad that I never got a chance to meet with him, and tell him how much of an influence he had on my career. Demon Haunted World taught me to be a skeptic.

I’ve had an idea kicking around for years now. I’ve always wanted to watch the entire COSMOS series with a bunch of my space friends, and do a live commentary. Partly to update the science, partly to reflect on Sagan’s influence, and partly to just hang out with a bunch of friends and be silly. But I could never figure out how I could navigate the copyright issues to be able to broadcast something based on COSMOS. And Ann Druyan would kill me.

Well, my friends at Twitch.tv have decided to grant my wish, and they’re going to be running a COSMOS marathon on Monday, April 24, 2017 at 12:00 pm PST. Not only that, but they’re encouraging other livestreamers to co-stream the show, and do exactly what I’ve always wanted to do – provide a commentary.

The challenge is that it’s a marathon, which means they’re going to run all 13 episodes back to back. 13 hours of watching COSMOS with my friends, chatting about the show, answering questions, and having fun. I’m up for it. But then, I’m a glutton for punishment.

So, if you’re interested in the raw Twitch stream and all the other cool events that Twitch has planned over the next week, check out their announcement.

And if you want to join me for some or all of the COSMOS marathon, follow fcain on Twitch. I’ll be starting up my livestream when the main feed goes live. And in theory, I’ll be sticking around until the whole thing ends 13 hours later.

Over the course of the livestream, I’ll be joined by many of my space and astronomy journalist friends. Like Dr. Ian O’Neill, Morgan Rehnberg, Nancy Atkinson, Dr. Brian Koberlein, and Dr. Paul Matt Sutter.

Hang out with us, ask questions, chat about your memories and experiences with Carl Sagan’s COSMOS.

I’ll see you on Monday!

April 21, 2017April 28, 2017 by Matt Williams

First Detailed Image Of Accretion Disk Around A Young Star

An illustration of an accretion disk feeding a central young star, or protostar, and the gaseous jet ejected from the protostar. Credit: Yin-Chih Tsai/ASIAA

According to the Nebula Hypothesis, stars and their systems of planets form from giant clouds of dust and gas. After undergoing gravitational collapse at the center (which creates the star), the remaining matter then forms an accretion disk in orbit around it. Over time, this matter is fed to the star – allowing it to become more massive – and also leads to the creation of a system of planets.

And until this week, the Nebula Hypothesis was just that. Given the distance involved, and the fact that the formation of star systems takes billions of years, being able to witness the process at various stages is quite difficult. But thanks to the efforts of team of researchers from the U.S. and Taiwan, astronomers have now captured the first clear image of a young star surrounded by an accretion disk.

As they explained in their paper – “First Detection of Equatorial Dark Dust Lane in a Protostellar Disk at Submillimeter Wavelength“, which was recently published in the journal Science Advances – these disks are difficult to resolve spatially because of their small sizes. However, by using the Atacama Large Millimeter/submillimeter Array (ALMA) – which offers unprecedented resolution – they were able to resolve a star’s disk and study it in detail.

*This artist’s concept shows a young stellar object and the whirling accretion disk surrounding it. NASA/JPL-Caltech*

The protostellar system in question is known as HH 212, a young star system (40,000 years old) located in the Orion constellation, roughly 1300 light-years from Earth. This star system is noted for its powerful bipolar jet – i.e. the continuous flows of ionized gas from its poles – which is believed to cause it to accrete matter more efficiently. Due to its age and its position relative to Earth, this protostar system has been a popular target for astronomers in the past.

Basically, the fact that it is still in an early phase of formation (and the fact that it can be viewed edge-on) make the star system ideal for studying the evolution of low-mass stars. However, previous searches had a maximum resolution of 200 AU, which meant astronomers were only able to get a hint of a small dusty disk. This disk appeared as a flattened envelope, spiraling towards the protostar at the center.

But with ALMA’s resolution (8 AU, or 25 times higher), the research team was not only able to detect the accretion disk, but also able to spatially resolve its dust emissions at submillimeter wavelength. As Chin-Fei Lee – a research fellow at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan and the lead author on the paper – said in an ALMA press release:

“It is so amazing to see such a detailed structure of a very young accretion disk. For many years, astronomers have been searching for accretion disks in the earliest phase of star formation, to determine their structure, how they are formed, and how the accretion process takes place. Now using the ALMA with its full power of resolution, we not only detect an accretion disk but also resolve it, especially its vertical structure, in detail.”

Jet and disk in the HH 212 protostellar system: (a) A composite image of the jet, produced by combining images from different telescopes. (b) Close-up of the center of the dusty disk at 8 AU resolution. (c) An accretion disk model that can reproduce the observed dust emission in the disk. Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.

What they observed was a disk that has a radius of roughly 60 astronomical units, which is slightly greater than the distance from the Sun and the outer edge of the Kuiper Belt (50 AU). They also noted that the disk was compromised of silicate minerals, iron and other interstellar matter, and consisted of a prominent equatorial dark layer that was sandwiched between two brighter layers.

This contrast between light and dark sections was due to relatively low temperatures and high optical depth near the central plane of the disk. Meanwhile, the layers above and below the central plane showed greater absorption in both the optical and near-infrared light wavelengths. Because of this layered appearance, the research team described it as looking like “a hamburger”.

These observations are exciting news for the astronomical community, and not just because they are a first. In addition, they also represent a new opportunity to study small disks around the youngest protostars. And with the kinds of high-resolution imaging made possibly by ALMA and other next-generation telescopes, astronomers will be able to place new and stronger constraints on theories pertaining to disk formation.

As Zhi-Yun Li from University of Virginia (the co-author on the study) put it:

“In the earliest phase of star formation, there are theoretical difficulties in producing such a disk, because magnetic fields can slow down the rotation of collapsing material, preventing such a disk from forming around a very young protostar. This new finding implies that the retarding effect of magnetic fields in disk formation may not be as efficient as we thought before.”

A chance to watch stars and planetary systems in their earliest phase of formation and a chance to test our theories about how it’s all done? Definitely not something that happens every day!

And be sure to enjoy this video of the observation, courtesy of ALMA and narrated by Dr. Lee:

Further Reading: Science Advances, ALMA

April 21, 2017April 28, 2017 by Evan Gough

Are Drylanders The Minority On Habitable Worlds?

Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)

If we want to send spacecraft to exoplanets to search for life, we better get good at building submarines.

A new study by Dr. Fergus Simpson, of the Institute of Cosmos Sciences at the University of Barcelona, shows that our assumptions about exo-planets may be wrong. We kind of assume that exoplanets will have land masses, even though we don’t know that. Dr. Simpson’s study suggests that we can expect lots of oceans on the habitable worlds that we might discover. In fact, ocean coverage of 90% may be the norm.

At the heart of this study is something called ‘Bayesian Statistics’, or ‘Bayesian Probability.’

Normally, we give something a probability of occurring—in this case a habitable world with land masses—based on our data. And we’re more confident in our prediction if we have more data. So if we find 10 exoplanets, and 7 of them have significant land masses, we think there’s a 70% chance that future exoplanets will have significant land masses. If we find 100 exoplanets, and 70 of them have significant land masses, then we’re even more confident in our 70% prediction.

Is Earth in the range of normal when it comes to habitable planets? Or is it an outlier, with both large land masses, and large oceans? Image: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC

But the problem is, even though we’ve discovered lots of exoplanets, we don’t know if they have land masses or not. We kind of assume they will, even though the masses of those planets is lower than we expect. This is where the Bayesian methods used in this study come in. They replace evidence with logic, sort of.

In Bayesian logic, probability is assigned to something based on the state of our knowledge and on reasonable expectations. In this case, is it reasonable to expect that habitable exoplanets will have significant landmasses in the same way that Earth does? Based on our current knowledge, it isn’t a reasonable expectation.

According to Dr. Simpson, the anthropic principle comes into play here. We just assume that Earth is some kind of standard for habitable worlds. But, as the study shows, that may not be the case.

“Based on the Earth’s ocean coverage of 71%, we find substantial evidence supporting the hypothesis that anthropic selection effects are at work.” – Dr. Fergus Simpson.

In fact, Earth may be a very finely balanced planet, where the amount of water is just right for there to be significant land masses. The size of the oceanic basins is in tune with the amount of water that Earth retains over time, which produces the continents that rise above the seas. Is there any reason to assume that other worlds will be as finely balanced?

Dr. Simpson says no, there isn’t. “A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected.” says Simpson.

Simpson’s statistical model shows that oceans dominate other habitable worlds, with most of them being 90% water by surface area. In fact, Earth is very close to being a water world. The video shows what would happen to Earth’s continents if the amount of water increased. There is only a very narrow window in which Earth can have both large land masses, and large oceans.

Dr. Simpson suggests that the fine balance between land and water on Earth’s surface could be one reason we evolved here. This is based partly on his model, which shows that land masses will have larger deserts the smaller the oceans are. And deserts are not the most hospitable place for life, and neither are they biodiverse. Also, biodiversity on land is about 25 times greater than biodiversity in oceans, at least on Earth.

Simpson says that the fine balance between land mass and ocean coverage on Earth could be an important reason why we are here, and not somewhere else.

“Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life,” Simpson concludes.

April 21, 2017April 21, 2017 by Bob King

Earth Beams From Between Saturn’s Rings in New Cassini Image

NASA’s Cassini spacecraft captured the view on April 13, 2017 at 12:41 a.m. CDT. The probe was 870 million miles (1.4 billion km) away from Earth when the image was taken. The part of Earth facing toward Cassini at the time was the southern Atlantic Ocean. Look closely to the left of Earth; that pinprick of light is the Moon. Credit: NASA/JPL Caltech

Look at us. Packed into a gleaming dot. The entire planet nothing more than a point of light between the icy rings of Saturn. The rings visible here are the A ring (top), followed by the Keeler and Encke gaps, and finally the F ring at bottom. During this observation, Cassini was looking toward the backlit rings with the sun blocked by the disk of Saturn.

Cassini first photographed Earth from Saturn in July 2013. Credit: NASA/JPL-Caltech

Seen from Saturn, Earth and the other inner solar system planets always appear close to the sun much like Venus and Mercury do from Earth. All orbit interior to Saturn; even at maximum elongation, they never get far from the Sun. Early this month, as viewed from Saturn, Earth was near maximum elongation east of the sun, thus an “evening star,” making it an ideal time to take a picture.

In this cropped view of the April 13 image, you can better see the Moon, located a short distance to the left of the Earth. Credit: NASA/JPL-Caltech

Opportunities to capture Earth from Saturn have been rare in the 13 years Cassini has spent orbiting the ringed planet. The only other photo I’m aware of was snapped on July 19, 2013. Each is a precious document with a clear message: we are all tiny, please let’s be kind to one another.

This graphic shows Cassini’s flight path during the final two phases of its mission. The 20 Ring-Grazing Orbits are in gray (completed) and the 22 Grand Finale Orbits are in blue. The final partial orbit is colored orange. The first of the Grand Finale orbits begins on April 22 at 10:46 p.m. CDT. Credit: NASA/JPL-Caltech/Space Science Institute

We’ll soon miss the steady stream of artistic images of Saturn, its rings and moons by the Cassini team. The probe will make its final close flyby of the planet’s largest moon, fog-enshrouded Titan, at 1:08 a.m. April 22, at a distance of just 608 miles (979 km). That night at 10:46 p.m. CDT, Cassini will enter the first of its Grand Finale orbits, a series of 22 weekly dives between the planet and the rings. The first ring plane crossing is slated for midnight CDT April 25-26.

Cassini at Saturn and the Grand Finale

The coming week will be a busy one for Cassini. On each orbit, the probe will draw closer and closer to the butterscotch ball of Saturn until it finally tears across the cloud tops and burns up as a spectacular fireball on September 15. Scientists would rather see the craft burn up in Saturn’s atmosphere instead crash into a moon and possibly contaminate it.

Cassini will become a brilliant fireball streaking over Saturn’s cloud tops on the last day of its operation on September 15. Credit: NASA/JPL-Caltech

After nearly 20 years in space, seven of them spent traveling to the ringed planet, Cassini feels like family. It won’t be easy to say goodbye, but thanks to the probe, Saturn’s family album is bursting with remarkable images that will forever remind us the tenacity of this amazing machine and the vision and work of those who kept it operating for so many years.

April 20, 2017April 21, 2017 by Matt Williams

Is This The Exoplanet Where Life Will First Be Found?

Using data obtained by Kepler and numerous observatories around the world, an international team has found a Super-Earth that orbits its orange dwarf star in just 14 hours. Credit: M. Weiss/CfA

It is good time to be an exoplanet hunter… or just an exoplanet enthusiast for that matter! Every few weeks, it seems, new discoveries are being announced which present more exciting opportunities for scientific research. But even more exciting is the fact that every new find increases the likelihood of locating a potentially habitable planet (and hence, life) outside of our Solar System.

And with the discovery of LHS 1140b – a super-Earth located approximately 39 light years from Earth – exoplanet hunters think they have found the most likely candidate for habitability to date. Not only does this terrestrial (i.e. rocky) planet orbit within its sun’s habitable zone, but examinations of the planet (using the transit method) have revealed that it appears to have a viable atmosphere.

Credit for the discovery goes to a team of international scientists who used the MEarth-South telescope array – a robotic observatory located on Cerro Tololo in Chile – to spot the planet. This project monitors the brightness of thousands of red dwarf stars with the goal of detecting transiting planets. After consulting data obtained by the array, the team noted characteristic dips in the star’s brightness that indicated that a planet was passing in front of it.

*The MEarth-South telescope array, located on Cerro Tololo in Chile, searches for planets by monitoring the brightness of nearby, small stars. Credit: Jonathan Irwin*

These findings were then followed up using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the ESO’s La Silla Observatory, located on the outskirts of Chile’s Atacama Desert. According to the their study – which appeared in the April 20th, 2017, issue of the journal Nature – the team was able to make estimates of the planet’s age, size, mass, distance from its star, and orbital period.

They estimate that the planet is at least five billion years old – about 500 million years older than Earth. It is also slightly larger than Earth – 1.4 times Earth’s diameter – and is considerably more massive, weighing in at a hefty 6.6 Earth masses. Since they were able to view the planet almost edge-on, the team was also able to determine that it orbits its sun at a distance of about 0.1 AU (one-tenth the distance between Earth and the Sun) with a period of 25 days.

However, since its star is a red dwarf, this proximity places it in the middle of the system’s habitable zone. But what was most exciting was the fact that the team was able to look for evidence of an atmosphere since the planet was passing in front of its star – something that has not been possible with many exoplanets. Because of this, they were able to conduct transmission spectroscopy measurements that revealed the presence of an atmosphere.

As Jason Dittmann – of the Harvard-Smithsonian Center for Astrophysics (CfA) and the lead author of the study – said in a CfA press release:

“This is the most exciting exoplanet I’ve seen in the past decade. We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

*This artist’s impression shows the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth. Credit: ESO/spaceengine.org*

Granted, this exoplanet is not as close as Proxima b, which orbits Proxima Centauri – just 4.243 light years away. And it certainly isn’t as robust a find as the TRAPPIST-1 system, with its seven rocky planets, three of which are located within its habitable zone. But compared to these candidates, the researchers were able to place solid constraints on the planet’s mass and density, not to mention the fact that they were able to observe an atmosphere.

The discovery of an exoplanet that orbits a red dwarf star and has an atmosphere is also encouraging in a wider context. Low-mass red dwarf stars are the most common star in the galaxy, accounting for 75% of stars in our cosmic neighborhood alone. They are also long-lived (up to 10 trillion years), and recent research indicates that they are capable of hosting large numbers of planets.

But given their variability and unstable nature, astronomers have expressed doubts as to whether or not planet orbiting them could retain their atmospheres for very long. Knowing that a terrestrial planet that orbits a red dwarf, is five billion years old, and still has an atmosphere is therefore a very good sign. But of course, simply knowing there is an atmosphere doesn’t mean that it is conducive to life as we know it.

“Right now we’re just making educated guesses about the content of this planet’s atmosphere,” said Dittman. “Future observations might enable us to detect the atmosphere of a potentially habitable planet for the first time. We plan to search for water, and ultimately molecular oxygen.”

This chart shows the location of the faint red star LHS 1140 in the faint constellation of Cetus (The Sea Monster). This star is orbited by a super-Earth exoplanet called LHS 1140b, which may be best place to look for signs of life beyond the Solar System. The star is too faint to be seen in a small telescope.

Hence, additional studies will be needed before this planet can claim the title of “best place to look for signs of life beyond the Solar System”. To that end, future space-based missions like the James Webb Space Telescope (which will launch in 2018), and ground-based instruments like the Giant Magellan Telescope and the ESO’s Extremely Large Telescope, will be especially well-suited!

In the meantime, the NASA/ESA Hubble Space Telescope will be conducting observations of the star system in the near future. These observations, it is hoped, will indicate exactly how much high-energy radiation LHS 1140b receives from its sun. This too will go a long way towards determining just how habitable the Super-Earth is.

And be sure to enjoy this video of the LHS 1140 star system, courtesy of the European Southern Observatory and spaceengine.org:

Further Reading: ESO, CfA