30 Nov 2016

The astronomy program for December 2016

Running time: 33 minutes

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THE ORION NEBULA is a fine target for astro-photographers, and is known worldwide.

In this program we learn all about the white hot Trapezium stars, Star birth in the nebula, Brown dwarfs, and star so small they are classed as planets. 

You also learn how to use the constellation of Orion as a signpost to nearby constellations this Winter.

YearbookAcknowledgements: The European Southern Observatory, and Hubble Telescope science team for providing further educational items for Richard Pearson’s outreach work.

The bright comet 45P/Honda-Markos-Pajdusa which will be easily visible in binoculars from February 2017 onwards. The star chart shows you where to look for the comet through December 206 to March 2017.

Astronomy & Space is now in its 4th year, and remains a very popular program.

When book publishers Pan McMillan decided not to continue publishing Patrick Moore’s Yearbook of Astronomy, it looked as though the annual book would be lost entirely after 60 years. I am pleased to announce that  after contacting author Brian Jones, and working together, we have found a new publisher to save this splendid book for future generations. This is one legacy left for all of us by Patrick Moore; you to can ensure that Patrick Moore’s Yearbook of Astronomy is safe by buying it when it goes into book shops in 2017.

26 Nov 2016

NASA’s Cassini space probe images Prometheus

PIA20508Prometheus is an inner satellite of Saturn. It was discovered in 1980 (some time before October 25) from photos taken by the Voyager 1 probe, and was provisionally designated S/1980 S 27. In late 1985 it was officially named after Prometheus, a Titan in Greek mythology

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Surface features are visible on Saturn's moon Prometheus in this view from NASA's Cassini spacecraft. Most of Cassini's images of Prometheus are too distant to resolve individual craters, making views like this a rare treat.

Saturn's narrow F ring, which makes a diagonal line beginning at top centre, appears bright and bold in some Cassini views, but not here. Since the sun is nearly behind Cassini in this image, most of the light hitting the F ring is being scattered away from the camera, making it appear dim. Light-scattering behaviour like this is typical of rings comprised of small particles, such as the F ring.

This view looks toward the unilluminated side of the rings from about 14 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 24, 2016.

The view was acquired at a distance of approximately 226,000 miles (364,000 kilometres) from Prometheus and at a sun-Prometheus-spacecraft, or phase, angle of 51 degrees. Image scale is 1.2 miles (2 kilometres) per pixel.

The November program: The Clouds of Magellan

Running time 30 Minutes

ALSO SEE OUR PAST SHOWS RUNNING DOWN THE SIDE COLUMNS

Visible primarily in the southern hemisphere the Magellanic clouds are an attraction for astronomers because they are at the same distance from the observer, and the large variety of exotic objects they contain. Supernova remnants, star clusters, globular clusters, Cepheid-variables and some stars that are record breakers like S-Doradus that is a million times more luminous than our Sun.

The astronomers at the Armagh Observatory in northern ireland has a long history of observing the clouds from the Boyden Observatory in South Africa before the founding of the European Southern Observatory in northern Chile.

In this program Richard Pearson FRAS takes us on a guided tour of the Armagh Observatory and the clouds themselves.

For foreign viewers, the Program Script is below, click on the document to open and read. This will help you to follow the program …

Did a solar storm damage Earth’s magnetic field?

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A review of data, relating to the summer of 2015, suggests a solar storm struck the Earth’s magnetic field. This unprecedented event lasted a couple of hours, and it could have shrunk the Earth’s magnetosphere.

The collected data, reported this month by astrophysicists and highlighted by Wired, indicated that a giant cloud of fast-moving plasma from the Sun struck the Earth’s magnetic field (or ‘magnetosphere’) shrunk from 11 times the Earth’s radius to just four for the two hour period.

The magnetosphere is the region of space surrounding an astronomical object (in this case, our planet) where charged particles are controlled by that object's magnetic field. To give an idea of the strength of the field, NASA scientists have suggested the Earth's magneto tail may cause "dust storms" on the Moon. The storms are created through the potential magnetic difference between the day side and the night side of the moon.

The review of the 2015 event suggests a solar storm of such intensity passed Earth’s magnetosphere (which provides a natural defence against cosmic radiation). The impact of this storm was to hit technology in several regions of the Northern hemisphere through electromagnetic pulses. A solar storm (or solar flare) is a sudden flash of brightness observed near the Sun's surface. It involves a very broad spectrum of energy emissions.

Scientists, Laboratory Roots reports, are concerned the event has put a permanent dent in the Earth’s magnetic field. This is concerning should further events of this magnitude occur in the future, since the magnetic field is our main protection against solar radiation. This doesn’t mean immediate harm to life but such events could further damage electrical equipment and there is a risk, in some areas, of increased skin cancer. And this is all dependent upon future solar storms of a similar magnitude.

The research indicates humanity must be mindful of our magnetic field and the role it plays. However, there isn’t much we can do to protect the planet other than continue to monitor.

The event has been described in the journal Physical Review Letters. The paper is titled “Transient Weakening of Earth’s Magnetic Shield Probed by a Cosmic Ray Burst.”

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The GRAPES-3 tracking muon telescope in Ooty, India measures muon intensity at high cutoff rigidities (15–24 GV) along nine independent directions covering 2.3 sr. The arrival of a coronal mass ejection on 22 June 2015 18:40 UT had triggered a severe G4-class geomagnetic storm (storm). Starting 19:00 UT, the GRAPES-3 muon telescope recorded a 2 h high-energy (   ) burst of galactic cosmic rays (GCRs) that was strongly correlated with a 40 nT surge in the interplanetary magnetic field (IMF). Simulations have shown that a large ( ) compression of the IMF to 680 nT, followed by reconnection with the geomagnetic field (GMF) leading to lower cutoff rigidities could generate this burst. Here, 680 nT represents a short-term change in GMF around Earth, averaged over 7 times its volume. The GCRs, due to lowering of cutoff rigidities, were deflected from Earth’s day side by   in longitude, offering a natural explanation of its night-time detection by the GRAPES-3. The simultaneous occurrence of the burst in all nine directions suggests its origin close to Earth. It also indicates a transient weakening of Earth’s magnetic shield, and may hold clues for a better understanding of future superstorms that could cripple modern technological infrastructure on Earth, and endanger the lives of the astronauts in space.

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24 Nov 2016

Two-year extensions confirmed for ESA's science missions

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ESA's Science Programme Committee (SPC) has today confirmed two-year mission extensions for nine scientific missions in which the Agency is participating. This secures their operations until the end of 2018.

After a comprehensive review of their current operational status and the likely scientific return from each mission, the SPC decided to extend the operation of six ESA-led missions (Cluster, INTEGRAL, Mars Express, PROBA-2, SOHO and XMM-Newton) from 1 January 2017 to 31 December 2018.

The go-ahead was also given to continue ESA's contributions to the operations of three international collaborative missions: the Hubble Space Telescope and the Interface Region Imaging Spectrograph (IRIS), which are both led by NASA, as well as Hinode, which is a Japanese-led mission.

Every two years, all missions whose approved operations end within the following four years are subject to review by the advisory structure of the Science Directorate. Extensions are granted to missions that satisfy the established criteria for operational status and science return, subject to the level of financial resources available in the science programme. These extensions are valid for the following four years, subject to a mid-term review and confirmation after two years.

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For the current cycle, the committee deferred any decision for the period 2019-2020 until after the meeting of the ESA Council at Ministerial Level, which is being held in Lucerne, Switzerland, 1–2 December. Among many decisions to be taken, the ESA Council will decide the longer-term budget of the science programme.

Science enabled

Extensions for SOHO, PROBA-2 and Hinode, and the continued contribution to IRIS, will ensure that our Sun is closely observed as it continues to head towards an unusually weak minimum of sunspot and flare activity.

Meanwhile, the Cluster quartet will measure the effects of this changing activity nearer to home, as they visit new regions of Earth's magnetosphere and operate simultaneously with other solar-terrestrial missions.

Mars Express has been in operation since December 2003 and it continues to study many different aspects of the Red Planet's atmosphere, surface and moons. Its data will complement measurements made by ESA's Trace Gas Orbiter, which arrived at Mars in October 2016.

XMM-Newton, the Hubble Space Telescope and INTEGRAL will continue to provide complementary observations of the Universe at many different wavelengths. These will include studies of the Solar System, planets orbiting distant stars, exploding stars, black holes, and the evolution of galaxies and the Universe.

23 Nov 2016

It turns out the Sun is more cooler than we previously thought

Ashampoo_Snap_2016.11.23_21h24m04s_001_Article: The Mount Wilson Observatory S-index of the Sun

Authors: Ricky Egeland, Willie Soon, Sallie Baliunas, Jeffrey C. Hall, Alexei A. Pevtsov, and Luca Bertello

First author’s institutions: High Altitude Observatory; Montana State University

One of the few certainties that we have as humans is that the Sun always comes and goes, always in intervals of 24 hours, and will continue to do so for the next 5 billion years or so. Owing to this familiar cycle, we sometimes take for granted that our host star is not itself completely stable. It is active, and this activity shapes the evolution the solar system and life on Earth. Because we use the Sun as a reference for other stars, it is thus crucial that we measure its activity as accurately and precisely as possible.

Blame magnetic fields

Stars are big balls of hot gas with lots of moving parts. The ones that are similar to the Sun (i.e., solar-type stars) have large convective atmospheres, which act just like boiling water inside a cooking pot. The convective circulation of plasma generates magnetic fields, and the stellar rotation, in turn, makes field lines wrap around the star, creating a stellar dynamo. When the magnetic field lines concentrate, they produce dark spots in the stellar surface and spectacular mass ejections; the activity of a star is measured by the strength of these episodes.

Ashampoo_Snap_2016.11.23_21h24m44s_002_One precise and accurate way of assessing stellar activity uses the features in stellar spectrum known as the Ca II H & K lines. Their strength can be easily measured with spectrometers, and are then translated into a ratio called the S-index (the higher it is, the more active the star). The most famous survey of stellar activity is the HK Project at Mount Wilson Observatory (MWO), which consisted on assessing S-index of many stars in the sky, and ended up becoming the standard calibration for current studies on activity. The problem is that not all observations are carried out with the same instrument, and hence systematic errors start to become a serious problem.

Context is key

In order to understand the role of activity in the physics of stellar and planetary evolution, it is important to place the Sun, the one star we know best, in the same context as the others. In today’s paper, the authors aim to precisely and accurately measure its activity using spectroscopic observations of the Moon — which reflects sunlight — obtained with the same instrument employed at the MWO.

Sun-like stars have activity cycles with periods of the order of a few years. The solar cycle has an 11-year period, encompassing a minimum and a maximum. The authors directly measured the minimum, maximum and mean S-index of the solar cycle 23 (1996 – 2007, although the MWO data goes only up to 2003), and found that they were significantly lower than previous estimates of the same cycle. This result shows that, when using different instruments, systematic errors plague the measurements of activity, but the good news is that now we can correct them by applying a better calibration with results from today’s paper.

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Well, now that we have dealt with accuracy, what about precision? As it turns out, there is no lack of solar activity data in the literature, which are now correctly calibrated. The authors used them to constrain the solar activity minimum, maximum and mean values within less than 1% for all indexes.

Effects on future studies

So, the Sun is slightly less active than we previously measured, and this impacts our understanding of solar-type stars the most. By correctly placing our star in the context of others, we can better assess how common it is, which helps us answer questions about the conditions necessary for life to emerge and how it evolves along with the star. These results also rectify some inconsistencies previously observed in the activity of solar-type stars, and again reminds us of a critical aspect of science: systematics matter. The article itself will serve as a guide on measuring stellar activity, paving the way towards better practices in the field.

22 Nov 2016

Mars ice deposit holds as much water as Lake Superior

Ashampoo_Snap_2016.11.22_22h53m07s_003_Frozen beneath a region of cracked and pitted plains on Mars lies about as much water as what's in Lake Superior, largest of the Great Lakes, researchers using NASA's Mars Reconnaissance Orbiter have determined.

Scientists examined part of Mars' Utopia Planitia region, in the mid-northern latitudes, with the orbiter's ground-penetrating Shallow Radar (SHARAD) instrument. Analyses of data from more than 600 overhead passes with the on-board radar instrument reveal a deposit more extensive in area than the state of New Mexico. The deposit ranges in thickness from about 260 feet (80 meters) to about 560 feet (170 meters), with a composition that's 50 to 85 percent water ice, mixed with dust or larger rocky particles.

At the latitude of this deposit -- about halfway from the equator to the pole -- water ice cannot persist on the surface of Mars today. It sublimes into water vapour in the planet's thin, dry atmosphere. The Utopia deposit is shielded from the atmosphere by a soil covering estimated to be about 3 to 33 feet (1 to 10 meters) thick.

"This deposit probably formed as snowfall accumulating into an ice sheet mixed with dust during a period in Mars history when the planet's axis was more tilted than it is today," said Cassie Stuurman of the Institute for Geophysics at the University of Texas, Austin. She is the lead author of a report in the journal Geophysical Research Letters.

Mars today, with an axial tilt of 25 degrees, accumulates large amounts of water ice at the poles. In cycles lasting about 120,000 years, the tilt varies to nearly twice that much, heating the poles and driving ice to middle latitudes. Climate modelling and previous findings of buried, mid-latitude ice indicate that frozen water accumulates away from the poles during high-tilt periods.

Martian Water as a Future Resource

The name Utopia Planitia translates loosely as the "plains of paradise." The newly surveyed ice deposit spans latitudes from 39 to 49 degrees within the plains. It represents less than one percent of all known water ice on Mars, but it more than doubles the volume of thick, buried ice sheets known in the northern plains. Ice deposits close to the surface are being considered as a resource for astronauts.

"This deposit is probably more accessible than most water ice on Mars, because it is at a relatively low latitude and it lies in a flat, smooth area where landing a spacecraft would be easier than at some of the other areas with buried ice," said Jack Holt of the University of Texas, a co-author of the Utopia paper who is a SHARAD co-investigator and has previously used radar to study Martian ice in buried glaciers and the polar caps.

Ashampoo_Snap_2016.11.22_22h52m44s_002_The Utopian water is all frozen now. If there were a melted layer -- which would be significant for the possibility of life on Mars -- it would have been evident in the radar scans. However, some melting can't be ruled out during different climate conditions when the planet's axis was more tilted. "Where water ice has been around for a long time, we just don't know whether there could have been enough liquid water at some point for supporting microbial life," Holt said.

Utopia Planitia is a basin with a diameter of about 2,050 miles (3,300 kilometres), resulting from a major impact early in Mars' history and subsequently filled. NASA sent the Viking 2 Lander to a site near the centre of Utopia in 1976. The portion examined by Stuurman and colleagues lies southwest of that long-silent lander.

Use of the Italian-built SHARAD instrument for examining part of Utopia Planitia was prompted by Gordon Osinski at Western University in Ontario, Canada, a co-author of the study. For many years, he and other researchers have been intrigued by ground-surface patterns there such as polygonal cracking and rimless pits called scalloped depressions -- "like someone took an ice-cream scoop to the ground," said Stuurman, who started this project while a student at Western.

Clue from Canada

In the Canadian Arctic, similar landforms are indicative of ground ice, Osinski noted, "but there was an outstanding question as to whether any ice was still present at the Martian Utopia or whether it had been lost over the millions of years since the formation of these polygons and depressions."

The large volume of ice detected with SHARAD advances understanding about Mars' history and identifies a possible resource for future use.

Why do massive stars lose gas as they evolve? Mira supercomputer may provide answers

Ashampoo_Snap_2016.11.22_22h05m15s_001_Scientists believe they're close to understanding why massive stars lose mass in the form of gas as they evolve. The only problem: a lack of computing power.

The processing power required to run models simulating the evolution of massive stars is immense. But scientists with the Kavli Institute for Theoretical Physics, at the University of California, Santa Barbara, have been gifted a solution.

Officials with the Innovative and Novel Computational Impact on Theory and Experiment, a Department of Energy program, have granted astrophysicists Matteo Cantiello and Yan-Fei Jiang 120 million CPU hours on the world's sixth-fastest computer. The researchers will get two years of access to the supercomputer Mira.

"Access to Mira means that we will be able to run calculations that otherwise would take about 150,000 years to run on our laptops," Cantiello said in a news release.

Unlike smaller one-dimensional stellar simulations, the model developed by Cantiello and Jiang will generate 3D simulations of the insides of massive stars, exploring the interactions of gas, radiation and magnetic fields. The researchers hope a better understanding of these interactions will yield insights into the nature of the episodic eruptions that bleed gas into space over the lifetime of a star.

The ways in which massive stars lose gas also have implications for the study of stellar structures created by supernovae, such as black holes and neutron stars. Scientists are hopeful revelations offered by their work with Mira will inform analysis of black hole systems like that one credited with producing the gravitational waves recorded by LIGO earlier this year.

640px-Mira_-_Blue_Gene_Q_at_Argonne_National_Laboratory_-_Skin"Understanding how these black hole binary systems formed in the first place requires a better understanding of the structure and mass loss of their stellar progenitors," said Jiang.

Mira is a pet scale Blue Gene/Q supercomputer. As of June 2013, it is listed on TOP500 as the fifth-fastest supercomputer in the world. It has a performance of 8.59 petaflops (LINPACK) and consumes 3.9 MW. The supercomputer was constructed by IBM for Argonne National Laboratory's Argonne Leadership Computing Facility with the support of the United States Department of Energy, and partially funded by the National Science Foundation.Mira will be used for scientific research, including studies in the fields of material science, climatology, seismology, and computational chemistry. The supercomputer is being utilized initially for sixteen projects, selected by the Department of Energy.

Interview: Helen Sedgwick, Author of ‘The Comet Seekers’

Ashampoo_Snap_2016.11.22_12h23m20s_002_In her novel The Comet Seekers, Helen Sedgwick presents an astounding narrative, which uses multiple points of views to weave a story that reaches across time and ultimately throws together two broken and lonely people in the middle of Antarctica. Sedgwick admits that The Comet Seekers didn’t initially start out as a full-fledged novel.  “I first had the idea for a story combining comets and history (back) in 2011, Sedgwick said. “I wrote it as a short story to begin with, but the characters kept calling me back for more.”

 Róisín and François are both running away from a past that haunts them, escaping feelings of guilt and regret. Róisín, an astronomer of Irish roots but with great ambition, and François who has lived all his life in a small northern French town has seldom left it, but finds solace and catharsis in cooking, encounter each other at a research base in Antarctica. Unbeknownst to each other they have shared a fascination for comets their entire lives and even as they develop a tentative closeness, Róisín and François are unaware that their paths are coincidentally joined by the lives and choices of their ancestors.

Sedgwick weaves multiple comet sightings and different points of view that begin in 2017 and trail back to the first glimpse of Halley’s Comet in 1066. But instead of finding it daunting, Sedgwick admits that it wasn’t as difficult as it seems. “I found the (different) points of view helpful in the writing process and in a way they directed the novel”, Sedgwick explained. “I knew that I wanted to write about people making different choices, and the multiple points of view allowed me to show why each of the characters make the decisions they do. It felt like the natural way to write a book about choice, and the ways in which we are both individual and connected.”

Ashampoo_Snap_2016.11.22_12h22m55s_001_But it’s not just the unique way how Sedgwick manoeuvres multiple POVs and navigates through different centuries. It’s that we see François and Róisín’s ancestors interact across time, living out their own fascinating and tragic stories. The groundwork is laid out for Róisín and François to meet in a way that almost seems preternaturally planned. Sedgwick however, doesn’t quite see it that way.

“I’d say the opposite (of preternaturally)”, she stated. “Their encounter was pure chance. Searching through history over a thousand years will show that we are all linked, and similar connections as those between Róisín and François can be found between all the people in our lives. It is not just that we are all related, though we are, but also that we all share something in common, and if we look for those similarities we will find them.” Indeed Sedgwick proposes an interesting theory. If in fact we are linked and bound together in a sort of “six degrees of separation”, is it then inevitable to repeat the history of our ancestors over and over again because it is engraved in our DNA?

In the opening scene of the novel, Róisín watches as a group of people run a marathon around the base that has temporarily become their home in Antarctica, while they await for the arrival of Comet Giacobini, the main reason they are there. Róisín  prefers to stand in the side-lines and observe, only joining the others as they run the final lamp in temperatures of minus ten degrees. It’s at that moment that she first encounters François, her first impression of him is that he seems so young but she is nevertheless intrigued by him.

Their first conversation takes place a while after the run, as they are drawn towards one another, even as Róisín is flooded with uncertainty about wanting his company:

❝One hour, forty minutes of darkness, and someone is behind her. Five days she has been here, five days she has searched the sky alone. Róisín turns around.

What are you looking for?

François is here, wanting to see what she’s doing, to join in. She’s not sure how she feels about that; she did not come here to make friends. Róisín thinks about telling him so, asking him to leave, but for some reason she decides to make him stay. Beside her, François looks at the sky and exhales.

There’s a comet predicted, she says. It’s going to be very bright. But it’s too early. I mean, we’re too soon.

Because it’s not dark enough yet?

Yes. Well, that and other things.

It’s beautiful isn’t it?

Above them, colours swirl like sea mist.

François stays where he is, doesn’t ask any more questions. He doesn’t take his eyes from the sky.

Róisín’s initial apprehension towards engaging with François in conversation may be better understood by observing her heart-breaking past. She lost not only the first man she ever loved but also the man she abandoned for her promising future as an astronomer, her cousin Liam. Róisín and Liam’s relationship, was complicated because of a perceived incestuous tinge and their completely different live paths. While Róisín moves to the city in her search for scientific developments in her field, Liam is dead-set on running his late father’s farm. This ultimately tears their relationship apart, and their breakup is later further tinted with tragedy.

Ashampoo_Snap_2016.11.22_12h28m00s_003_ Sedgwick writes her dialogues with no quotation marks, which initially can take some getting used to, even though she is by no means the first to do this. Cormac McCarthy, James Joyce, Jose Saramago, and Cynan Jones are only a few who have sought to abolish the conventionality of traditional punctuation seeking to challenge the reader, particularly in Jones’s case, to go beyond the well-known layout of how a dialogue is perceived.

Was Sedgwick afraid that readers would find this lack of speech marks intimidating? She says no. “I didn’t use speech marks because I enjoy the flow of prose without them, and I’m interested in the questions it raises about what we think and what we say, the internal and the external, she stated. “I must admit I didn’t worry about confusing the reader at all – I think readers are able to cope with pretty much anything, and I love them for it.”

Although Róisín is presented as a complex character whose life has been broken, François is no stranger to painful situations. Living with a mother who loves him dearly, but who is constantly plagued by the ghosts of her ancestors, François seeks solace in his ability to create recipes that help him imagine the many exotic places where he’s never been. Sedgwick admits that the character of François was for her the one that posed a complex task.  “Adult François was the most challenging character to write, because he had existed as a young boy in my mind for so long”, she said. “I (think) I had trouble getting him to grow up.”

As Róisín and François slowly come towards each other and begin telling their stories, Sedgwick’s astounding ability for description and engaging narrative through heart-felt dialogues between the characters really shines through. Róisín and François’s destiny is sketched not only by their individual actions and decisions, but also by those of their ancestors, who like them, were brought together by the magic and cosmic pull of comets. The Comet Seekers is a fascinating character and philosophical study that poses thought-provoking questions: Is our future decided solely by our actions? Or is our destiny somehow tied to those that came before us?

OSIRIS-REx Spacecraft Check Out and Early Cruise Phase Activities

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It has been awhile since I posted anything to this site. The launch of OSIRIS-REx was such an amazing, emotional experience; it took me about a month to come back down to Earth (pun intended). I have now settled into a normal work routine in Tucson and the team has been busy operating the spacecraft and planning for the encounter with Bennu in 2018. We are now in the Outbound Cruise phase of the mission.

We Have a Healthy Spacecraft

Outbound Cruise began soon after the spacecraft separated from the Atlas V launch vehicle as planned. The spacecraft post-separation activities were all nominal and the spacecraft quickly transitioned to the “Outbound Cruise” operating mode. I studied the separation video quite a bit and noticed what appeared to be a plume originating from the lower portion of the spacecraft. After talking with the spacecraft engineers, we realized that the out-gassing was the result of the initialization of the propulsion system. This out-gassing was also evident in the DSN tracking data since we could see small forces slightly changing the spacecraft trajectory.

After launch-vehicle separation, the spacecraft was placed into the “Sun point” attitude (+X spacecraft axis toward the sun) with the solar arrays off-pointed from the sun by 45 degrees. This attitude ensures that the spacecraft will collect sufficient power to remain power positive at all times while keeping the other components from experiencing direct solar heating.

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Propulsion System Performance

The propulsion system has been performing well. Momentum dumps using the Attitude Control System (ACS) thrusters are occurring as planned. During these manoeuvres, reaction wheel momentum is unloaded by firing the ACS thrusters. Reaction wheels are flywheels that use electric motors to change their rotation speed. As the wheels rotate, the spacecraft counter-rotates as a result of the conservation of angular momentum.  Wheel speeds are generally maintained below 3000 RPM which requires desaturation of the built-up angular momentum approximately once every seven days.

We also executed our first Trajectory Correction Manoeuvre (TCM-1) using the TCM thrusters. This manoeuvre was placed into the mission plan to clean up any errors introduced by the Atlas V launch vehicle. However, since the Atlas V performance was nearly perfect, we re-designed TCM-1 as a minimal engineering burn, just to check out the TCM thruster performance. Our first major manoeuvre using the spacecraft main engines is Deep Space Manoeuvre #1 (DSM-1), which will be executed on December 28th, 2016. The preliminary design cycle for this manoeuvre has begun, with a DSM-1 Readiness Review planned for December 1st.

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Science Instrument Checkouts

As part of checking out the flight system, we turned on all of the science instruments and ran them through some basic functional check outs. I am happy to report that OCAMS, OVIRS, OTES, OLA, and REXIS all completed post-launch aliveness checkouts with no major issues.  OCAMS is investigating stray light effects which appear to be due to sunlight reflecting off PolyCam and OTES protruding from the +Z deck. We don’t expect this stray light to be an issue in operations but we are building a detailed optical model of the science deck and planning a follow-on characterization campaign later in Outbound Cruise. This model will allow us to maximize the science value of our imaging campaigns and ensure that stray light does not degrade our science data.

We also switched on the Touch and Go Camera System (TAGCAMS) and successfully acquired 19 images of star fields and spacecraft hardware. TAGCAMS is not part of the science payload; it is considered a component of the spacecraft Guidance, Navigation, and Control system. The purpose of TAGCAMS is to provide imagery during the mission to facilitate navigation to the target asteroid, acquisition of the asteroid sample and confirmation of asteroid sample stowage. The cameras were designed and built by Malin Space Science Systems (MSSS) based on requirements developed by Lockheed Martin and the OSIRIS-REx project.

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Near-term Activities

Right | The StowCam views the Sample Return Capsule in flight. This view will be critical as we stow the TAGSAM head with the collected Bennu sample for Earth return.

We still have many activities planned for Outbound Cruise. We will perform a thorough instrument calibration campaign at Launch + 6 months. We are busy planning for an extensive instrument check out and characterization during the Earth Gravity Assist in September 2017. We also have some tricks up our sleeves, with a science observing campaign planned for February 2017. Stay tuned for more details about this exciting activity in future blog posts.

Overall, the launch and early checkout of the OSIRIS-REx flight system has gone flawlessly. We have an amazing spacecraft and an extremely talented operations team. There is a lot of work to do to get ready for the encounter with Bennu in August 2018. However, we have the right equipment and the right team to get this job done successfully. With sample acquisition nominally scheduled for July 2020, OSIRIS-REx promises to be a highlight of planetary exploration over the next four years.

21 Nov 2016

Large number of dwarf galaxies discovered in the early universe

VST image of the Fornax Galaxy ClusterA team of researchers, led by University of California, Riverside astronomers, found for the first time a large population of distant dwarf galaxies that could reveal important details about a productive period of star formation in the universe billions of years ago.

The findings, just published in The Astrophysical Journal, build on a growing body of knowledge about dwarf galaxies, the smallest and dimmest galaxies in the universe. Though diminutive, they are incredibly important for understanding the history of the universe.

It is believed that dwarf galaxies played a significant role during the reionization era in transforming the early universe from being dark, neutral and opaque to one that is bright, ionized and transparent.

Despite their importance, distant dwarf galaxies remain elusive, because they are extremely faint and beyond the reach of even the best telescopes. This means that the current picture of the early universe is not complete.

However, there is a way around this limitation. As predicted by Einstein's general theory of relativity, a massive object such as a galaxy located along the line of sight to another distant object, can act as a natural lens, magnifying the light coming from that background source.

This phenomenon, known as gravitational lensing, causes the background object to appear brighter and larger. Therefore, these natural telescopes can allow us to discover unseen distant dwarf galaxies.

As a proof of concept, in 2014, the UC Riverside team, including Brian Siana, an assistant professor in UC Riverside's Department of Physics and Astronomy who is the principal investigator of the observing programs, targeted one cluster of galaxies that produce the gravitational lensing effect and got a glimpse of what appeared to be a large population of distant dwarf galaxies.

The just-published paper, whose lead author was Anahita Alavi, a post-doctoral scholar working with Siana, builds on that work.

The team used the Wide Field Camera 3 on the Hubble Space Telescope to take deep images of three clusters of galaxies. They found the large population of distant dwarf galaxies from when the universe was between two to six billion years old. This cosmic time is critical as it is the most productive time for star formation in the universe.

In addition, the team took advantage of the spectroscopic data from Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) on the W.M. Keck Observatory, to confirm that the galaxies belonged to this important cosmic period.

These dwarf galaxies are 10 to 100 times fainter than galaxies that have been previously observed during these periods of time. Though faint, these galaxies are far more numerous than their brighter counterparts.

This study demonstrates that the number of these dwarf galaxies evolves during this important time period such that they are even more abundant at earlier times. Therefore, the researchers unveiled a population of dwarf galaxies that are the most numerous galaxies in the universe during these time periods.

Despite their faintness, these dwarf galaxies produce more than half of the ultraviolet light during this era. As ultraviolet radiation is produced by young hot stars, dwarf galaxies host a significant fraction of newly-formed stars at these cosmic times.

These results suggest that dwarf galaxies played a prominent role in the reionization era. These galaxies will be the primary targets of the next generation of telescopes, particularly the James Webb Space Telescope, scheduled to launch in October 2018.

New Horizons prepares for distant encounter beyond Pluto

Ashampoo_Snap_2016.11.21_11h44m33s_002_When we last visited with Alan Stern, principal investigator for NASA’s New Horizons, it was 2009, and the little probe was barely halfway to its planned encounter with Pluto. I asked him then, in the context of a terrible recession and assuming we got any images back at all, what taxpayers were getting for their money.

Paraphrasing, he replied rather presciently, ”Jobs for starters—and good, high tech ones at that. But more importantly: we are expanding human knowledge to the edge of our solar system. This is what great nations do, they make great history ... [Y]ears from now, when today’s politicians are forgotten ... a student or teacher who opens a textbook and sees Pluto will be looking at images and data from New Horizons. I think that’s worth a lot, because it is a legacy for our nation and our civilization.”

Since then, New Horizons delivered on every one of those predictions. The encounter was breath-taking, the incredible high resolution images of Pluto and its moons are exquisite, and the data will fuel several fields of study for a generation or more. So we caught up with a very busy Alan Stern, who took the time to get us caught up on where New Horizons is now, and more importantly, what it will do next.

Come below for some space exploration Q & A, and a free-ranging discussion in the comments.

DS: Before looking ahead, I wanted to ask, what has surprised you the most about the New Horizons mission overall, or any data it returned specifically?

AlanSternPlutophileAlan Stern: The public reaction. You know, we haven’t had a fly-by of a totally new planet and moon system since the late 80s and the Voyagers, since Voyager Two’s encounter with Neptune in 1989, so we expected some interest. We did not expect to get over one billion page views in a day or two! The team and I get something like 10 requests a week for presentations. Even a year-and-a-half a later, after encounter, people recognize me in airports and come up and shake my hand, kids send letters asking for autographs.

The one feature that surprised me the most? There are so many to choose from … maybe the heart-shaped plain now called Tombaugh Regio. Who could have possibly guessed that Pluto would have a heart the size of the American Midwest!

DS: New Horizons will make a pass by a classical Kuiper Belt Object or KBO dubbed MU69 beginning in late December 2018, with encounter set for Jan. 1, 2019. What can we learn from that relatively drab little snow-ball that we didn’t learn from big beautiful Pluto and its colourful moons?

MU69 as seen by HST attribution: NASA/SwRI/APLMU69 is barely visible to Hubble under extreme zoom, shown in circles as it moves over time. The background “snow” is random noise, the two brighter objects are faint stars.  Alan Stern: Well, it’s not just a drab little snowball. It’s between 25 and 50 kilometres across, orders of magnitude more massive than comet 67P that Rosetta just landed on, and we have no idea what it will look like. You remember how I told you years ago that when I was growing up and starting to study astronomy, there were four gas giants and four rocky terrestrial worlds, and that little Pluto was the lone oddball? And then we learned later on that there are at least half a dozen small planets like Pluto and probably hundreds if not more, meaning Pluto and its cohorts actually represents the most common kind of planet-sized object in the solar system?

Studying Pluto and its moons gave us a window into what that class of worlds might be like, it was a new class of planet seen close up for the very first time.

MU69 is whole new classes of objects seen close up for the first time, the Kuiper Belt Objects, the trans-Neptunian Objects. That alone is exciting.

But think about this: Up to now we could mostly see our planetary targets as disks before visiting them, in the case of Pluto a very small, very mysterious disk, but we knew a little bit about it before New Horizons. We knew it would be a sphere, we knew it would have a wisp of an atmosphere, we had a few hints on the colour and contrasts, that kind of thing. Now we can literally write the textbook on Pluto.

Ashampoo_Snap_2016.11.21_11h44m06s_001_Until we see MU69 close up, objects like it -- and there are billions of them! — they only show up as tiny specks of light in our most powerful telescopes. We know almost nothing about them at all. We believe these kinds of objects represent the basic building blocks for planets like Pluto and probably the rest of the planets as well, including possibly even Earth. And out there, where its so cold so far from the Sun, we believe they’re in the most pristine state. That they look like they did billions of years ago when the solar system was first forming. That can teach us a lot, we can't even guess how much until we see it and get data from it.

DS: Lastly, at the risk of being political, there are many people here and and around the world who would like to see more missions like this one. What can we do to convey that effectively to a new Congress and president?

Alan Stern: Tell your reps and your senators and the president that you support space exploration. Remind them how important space exploration is not just to science, but to developing other fields like engineering and technology, and even to national pride.

Remind politicians that a lot of today’s most successful entrepreneurs got hooked on science and technology as kids because of NASA. That’s what feeds innovation, and innovation is what feeds our economy. Tell our representatives and the new administration that you support more planetary exploration missions and all the other wonderful other things NASA does for our nation and our species.

Remember how much planning and preparation New Horizons took. If we started urging for and designing another mission like it, into far deep space, it might not launch for a decade. And it could take at least another decade or more to get out there beyond Pluto. So, it would be the 2030s before we got to see anything completely new. But if we wait too long to start, we might not be in that distant neighborhood again for the rest of this century!

The interview was conducted by phone and represents my notes and best recollection of what we discussed. Any remaining errors are solely mine — DS

19 Nov 2016

NASA's Physics-Defying EM Drive Passes Peer Review

figure15The reactionless thruster known as the EM Drive has stirred heated debate over the past few years. If successful it could provide a new and powerful method to take our spacecraft to the stars, but it has faced harsh criticism because the drive seems to violate the most fundamental laws of physics. One of the biggest criticisms has been that the work wasn’t submitted for peer review, and until that happens it shouldn’t be taken seriously. Well, this week that milestone was reached with a peer-reviewed paper. The EM Drive has officially passed peer review.

Ashampoo_Snap_2016.11.19_22h16m50s_002_It’s important to note that passing peer review means that experts have found the methodology of the experiments reasonable. It doesn’t guarantee that the results are valid, as we’ve seen with other peer-reviewed research such as BICEP2. But this milestone shouldn’t be downplayed either. With this new paper we now have a clear overview of the experimental setup and its results. This is a big step toward determining whether the effect is real or an odd set of secondary effects. That said, what does the research actually say?

The basic idea of the EMDrive is an asymmetrical cavity where microwaves are bounced around inside. Since the microwaves are trapped inside the cavity, there is no propellant or emitted electromagnetic radiation to push the device in a particular direction, standard physics says there should be no thrust on the device. And yet, for reasons even the researchers can’t explain, the EM Drive does appear to experience thrust when activated. The main criticism has focused on the fact that this device heats up when operated, and this could warm the surrounding air, producing a small thrust. In this new work the device was tested in a near vacuum, eliminating a major criticism.

Paper: Harold White, et al. Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum. Journal of Propulsion and Power. DOI: 10.2514/1.B36120 (2016)

What the researchers found was that the device appears to produce a thrust of 1.2 ± 0.1 millinewtons per kilowatt of power in a vacuum, which is similar to the thrust seen in air. By comparison, ion drives can provide a much larger 60 millinewtons per kilowatt. But ion drives require fuel, which adds mass and limits range. A functioning EM drive would only require electric power, which could be generated by solar panels. An optimized engine would also likely be even more efficient, which could bring it into the thrust range of an ion drive.

While all of this is interesting and exciting, there are still reasons to be sceptical. As the authors point out, even this latest vacuum test doesn’t eliminate all the sources of error. Things such as thermal expansion of the device could account for the results, for example. Now that the paper is officially out, other possible error sources are likely to be raised. There’s also the fact that there’s no clear indication of how such a drive can work. While the lack of theoretical explanation isn’t a deal breaker (if it works, it works), it remains a big puzzle to be solved.  The fact remains that experiments that seem to violate fundamental physics are almost always wrong in the end.

I’ve been pretty critical of this experiment from the get go, and I remain highly sceptical. However, even as a sceptic I have to admit the work is valid research. This is how science is done if you want to get it right. Do experiments, submit them to peer review, get feedback, and revaluate. For their next trick the researchers would like to try the experiment in space. I admit that’s an experiment I’d like to see.

Is Physical Law an Alien Intelligence?

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What if dark matter is really just aliens?

An astrophysicist has put forward an interesting thought experiment this week: what if a civilisation of extra-terrestrial life was advanced enough, it's possible that we might confuse its presence with the laws of physics.

In other words, what we think might be the effects of mysterious forces such as dark energy and dark matter in the Universe, could actually be the influence of alien intelligence - or maybe even aliens themselves.

Let's be clear - we're way outside the realms of evidence here, and this isn't an hypothesis that can easily be tested. And no one is actually suggesting that aliens are at work in the force of gravity of dark energy.

But what Caleb Scharf, director of astrobiology at Columbia University, is suggesting in a new article in Nautilus, is that, in theory at least, it's possible for an alien civilisation to become so advanced, it's indistinguishable from the laws of physics.

And there are already a few cosmic phenomena that could potentially be explained that way - or, at the very least, are so weird that we couldn't rule the possibility out.

Before you write this all off as crazy, this idea is basically an expansion of science fiction writer Arthur C. Clarke's three laws: that any sufficiently advanced technology is indistinguishable from magic.

Ashampoo_Snap_2016.11.18_23h31m04s_003_

Clarke was a writer, not a scientist, so we have to take that into account, but when you imagine someone from today being sent back in time to the Stone Age with their hover board, iPhone, and wi-fi connection, it doesn't seem too out there. Even electricity seemed like magic when it was first invented.

But at least our Stone Age ancestors would recognise us as being somehow related to them. Scharf's thought experiment takes things one step further.

"What if life has moved so far on that it doesn’t just appear magical, but appears like physics?" he asks in Nautilus.

"After all, if the cosmos holds other life, and if some of that life has evolved beyond our own waypoints of complexity and technology, we should be considering some very extreme possibilities."

Scharf isn't the first person to suggest that we need to look for aliens beyond our idea of 'life'.

While life on Earth is based on carbon, astrobiologists have argued for decades that there might be life "not as we know it" out there in the Universe that use, say, methane instead.

Ashampoo_Snap_2016.11.18_23h39m00s_004_

It's also been suggested that advanced alien life could have long ago done away with their mortal bodies and uploaded themselves into some other, unrecognisable kind of technology.

There's even a group of scientists out there who are convinced we actually live in an alien simulation.

All of these claims might sound whacky, but they could explain one of the biggest questions in science, known as the Fermi Paradox: where are all the aliens?

So how does all this tie in with the laws of physics?

As Scharf explains, if we're willing to admit that aliens might not look the way do, and could be far more advanced than we can comprehend, then we should also consider the possibility that they could be behind some of the stranger phenomena we see in the Universe.

Take dark matter, for example. All the visible matter out there in the Universe, the stars, and planets, and cosmic gas, can't explain the amount of gravity that holds together our galaxies.

So scientists came up with the concept of dark matter - a mysterious kind of matter that doesn't interact with electromagnetic radiation - to explain this inconsistency.

Dark matter is thought to make up around 27 percent of the mass and energy in the known Universe, but there are inconsistencies in our observations of the phenomena, and we're yet to find a way to properly explain it within the laws of physics.

But what if what we consider dark matter is actually an advanced extra-terrestrial civilisation that learnt to encode themselves in this strange type of subatomic particle that's essentially invisible to the rest of the Universe?

"What better way to escape the nasty vagaries of supernova and gamma-ray bursts than to adopt a form that is immune to electromagnetic radiation?" Scharf writes.

"Perhaps the mismatch of astronomical models and observations is evidence not just of self-interacting dark matter, but of dark matter that is being artificially manipulated."

If that's not mind-melting enough, Scharf's ideas about dark energy are even freakier.

mW59sNDark energy is the hypothetical force responsible for speeding up the expansion of the Universe. But the Universe didn't actually begin expanding at an accelerated rate until about 5 billion years ago, and researchers aren't too sure why.

Scharf suggests that maybe dark energy was created by an advanced alien civilisation who wanted to avoid the crowded Universe from getting too hot by spreading things out a little more.

"Any very early life in the universe would have already experienced 8 billion years of evolutionary time by the time expansion began to accelerate," he writes.

"It’s a stretch, but maybe there’s something about life itself that affects the cosmos, or maybe those well-evolved denizens decided to tinker with the expansion."

None of these ideas have been peer-reviewed, and they're just the opinion of one astrophysicist pushing the boundaries of what's theoretically possible.

But while we can't test any of these ideas just yet, we also can't really rule them out. The reality is, there's a lot about physics that we still don't understand.

Yes, it's unlikely that the explanation for the mysterious things we see in the cosmos will be aliens, but at the very least, scientists need to be open to the possibility that there could be other forces at play we can't yet even begin to imagine.

18 Nov 2016

Astronomers have confirmed that a force of nature in a distant galaxy is the same as on Earth

BlueQuasar_web_1024

Astronomers have successfully measured one of the four fundamental forces of nature – electromagnetism – using the light from a quasar known as HE 0515-4414, which passed through a series of distant galaxies on its way to reaching us some 8.5 billion years ago.

By examining the strength of electromagnetism inside these galaxies and comparing it to the strength here on Earth, the team found evidence that electromagnetism is the same everywhere in our Universe, suggesting that it is, indeed, a constant of nature.

A quasar is the area around a supermassive black hole that produces extremely bright and powerful jets of energy as mass from its surrounding galaxy falls into the black hole.

The quasar HE 0515-4414 is one of the brightest anyone has ever seen, and that means researchers can use it like a torch - or, more accurately, a cosmic barcode scanner - to shine through galaxies between it and Earth and reveal insights about how they work.

One thing researchers are particularly interested in is how the four fundamental forces of nature work in the far reaches of space. Those four forces are gravity, electromagnetism, and the strong and weak nuclear force.

The precise values of those fundamental forces are crucial to life being able to exist here on Earth, and it's generally assumed that they're the same across the Universe. But it's hard to say for sure, because we can only study them properly here on Earth.

For the new study, the team from Swinburne University in Australia and the University of Cambridge in the UK used a quasar to peer into a galaxy 8.5 billion light-years away, and see if works the same way as on our own planet.

cosmicbarcod

"Electromagnetism determines almost everything about our everyday world, like the light we receive from the Sun, how we see that light, how sound travels through the air, the size of atoms and how they interact," explains one of the team, Michael Murphy from Swinburne University.

"But no one knows why electromagnetism has the strength it has and whether it should be constant, or vary, and why."

The team used spectrographs – 'light rulers', as they are commonly known – on board the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT) and 3.6-m Telescope in Chile to measure patterns of colours inside the quasar’s light.

"The VLT's spectrograph is a little inaccurate: it's a high-quality ruler for measuring light, but the numbers on that ruler are a little offset," said lead author Srđan Kotuš, also from Swinburne University.

"So, to make the best measurement, we also used the 3.6-m Telescope's spectrograph to provide very accurate numbers."

The team was able to use these tools to measure how the light from the quasar changes as it passed through galaxies on its way to Earth, showing how strong electromagnetism is in these distant galaxies.

They then compared that number to the one commonly found in the Milky Way - just like cross-checking a couple of barcodes.

To better visualise this, check out this quick video the team made:

Inside view of a VLT unit telescopeAs you can see, the light from the quasar is filtered by the galaxy, providing insights into how strong electromagnetism is there.

"The pattern of colours tells us how strong electromagnetism is in this galaxy, and because the quasar is one of the brightest ones known, we were able to make the most precise measurement so far," explains Kotuš.

In the end, they found that the electromagnetic force in the distant galaxy is the same as here on Earth, suggesting that researchers have been correct in their suspicions that electromagnetism is a constant of nature.

"We found electromagnetism in this galaxy was the same as here on Earth within just one part per million – about the width of a human hair compared to the size of a sports stadium," says Kotuš.

While the finding definitely helps us better understand a fundamental force, the team still has many questions, such as why is it a constant in the first place? How did it come to be this way?

"For me, finding that electromagnetism is constant over more than half the Universe's age just deepens the mystery – why is it that way? We still don't know," says Murphy.

"It's remarkable that distant galaxies provide such a precise probe of such a fundamental question. With even larger telescopes now being built, we'll be able to test it even better in the near future."

Hopefully, as astronomers gain access to more sophisticated and precise tools, they will be able to answer some of these fundamental questions, giving all of us a better understanding of our own planet, Solar System, and the Universe at large.

The team’s work was published in Monthly Notices of the Royal Astronomical Society.

Brightest Radio Burst Contains Cosmic Clue

Ashampoo_Snap_2016.11.17_23h17m00s_001_There’s a long list of scientific discoveries that continue to puzzle researchers around the world, and one of the most mysterious comes in the form of something called Fast Radio Bursts, or FRBs.

Scientists suspect that these extremely bright flashes of light originate from outside of the Milky Way Galaxy, but they still aren’t entirely sure where in the universe they’re coming from, or what kind of event causes them.

Up until last year only 17 had been detected. That changed when the brightest FRB ever discovered was seen by two different telescopes at Parkes Observatory in Australia on August 5, 2015. Published today in the journal Science, a team of researchers from the California Institute of Technology, Curtin University, and CSIRO Astronomy and Space Science centre in Australia announced not only that they’d observed the 18th FRB, but it’s also the brightest ever seen.

Until this 18th discovery, the very first FRB ever observed also held the position for the brightest.

When FRB 010621 was seen in 2001 at the Parkes Radio Observatory, astronomer Duncan Lorimer had no idea what to make of the signal. The 5-millisecond burst was a new kind of cosmic phenomenon, and one that sparked more questions than the field was ready for.

Vikram Ravi of Caltech and Ryan Shannon at CSIRO and their team discovered the newest burst named FRB 150807 using the Parkes Radio telescope in New South Wales Australia. The burst was so bright that it actually pinged two of the radio telescopes, marking the first time an FRB showed up in more than one instrument.

Antennae_galaxies_xl“By having the signal hit two telescopes it helped us narrow down a specific patch of sky that this signal could be coming from,” says Shannon.

There are 13 telescopes at Parkes Observatory, each working like a 1 pixel camera.  By picking up on this signal with two pixels, it allowed the team to examine that area of the sky, and what they found were six galaxies and three stars. Ultimately the team ruled out the stars since they were located in the Milky Way, and after examining the six other candidates, they decided to put their money on a sizeable galaxy 1 billion light years away called VHS7.

Scientists expect these FRBs to be the product of large cosmic explosions like supernovae, colliding black holes, pulsars, magnetars or even gamma ray bursts. One reason why scientists are desperate to understand these anomalies is that the FRBs actually carry evidence about their origins and the medium in which they travelled. By understanding more about FRBs cosmologists could understand more about our universe.

Perhaps the most interesting thing is what these FRBs can tell scientists based on their individual imprints. The data for this particular burst points to a smoother journey than maybe some others that have been discovered.

“FRBs carry the imprint of the medium that they’ve travelled through. The radio waves from the burst interact with the ionized gas between us and it’s source,” explains Shannon. “With this FRB we saw an imprint of a very diffuse galaxy and a diffuse intergalactic medium.” Because of the brightness of this particular burst and showing up on two telescopes, it gives the team more clues about the cosmic web — the vast space that exists between all objects in the universe.

After a radio wave travels for millions and millions of years, its shape can become altered on the journey. Often times what we’ve seen from FRBs is a by-product called Faraday rotation which morphs the radio wave into a corkscrew shape. This happens when a radio wave travels through a thick intergalactic medium that’s heavily magnetized.

The newest FRB actually had little evidence of Faraday rotation, leading the team to believe that the area that the radio wave travelled through wasn’t very magnetic, and that the “space” was thinner in that region. The intergalactic medium or what we think about as “space” is made up of plasma, an ionized gas, but it’s not a uniform consistency. Shannon explains, “this burst was scintillating, so the brightness varies if you look at different wavelengths of light. Not unlike when a star twinkles in the sky, that light is traveling through diffuse gas in the intergalactic medium. What this tells us is that there’s a bit of turbulence churning around, but not that much.”

By better knowing each bursts unique signature, scientists can rectify their theories on the makeup of the universe. As more telescopes are built and go online surely more FRBs will be observed and eventually scientists will begin to decipher their messages. Astronomers expect that if the technology was available and the telescopes were built to scan the sky at all times, that there would be anywhere from 2500 to 10,000 FRBs hitting Earth every single day. Luckily there are more telescopes planned to begin surveying wider swaths of sky with the hopes of picking up more bright flashes of light from any number of places in our universe. For now though the illusive fast radio burst will continue to be a source of intrigue for astronomers and cosmologists who will continue waiting to find the answers of what lies between us and everything else.

17 Nov 2016

How can we slow down planet migration?

superearths_formation-001Authors: Kévin Baillié, Sébastien Charnoz, Éric Pantin
First Author’s Institution: University Paris Diderot

Walking the Snow Line

Planets can move – or “migrate” – inward and outward. When a planet forms in a protoplanetary disk, it excites two spiral density waves — places where excess mass collects in the disk. (This movie shows what that looks like!) The inner spiral moves ahead of the planet and speeds it up, increasing the planet’s angular momentum and propelling it outwards. Meanwhile, the outer spiral lags behind the planet and slows it down, stripping the planet of some of its angular momentum and forcing it inwards towards the star.  In the simplest models, the outer wave exerts a torque that is just barely stronger than the inner wave. Although that difference is small, it should be enough to cause a planet to spiral into its star and die long before the disk dissipates in a few million years!

Thankfully, we know from our own solar system and countless exo-solar systems that planets are more than capable of surviving disk migration. This motivates Baillié et al. to ask: What secondary effects in a disk are responsible for preventing planets from migrating too quickly?

An idea: Simple disk models are not enough. Density and temperature are not smooth!

When astronomers create models – whether with pencil and paper (analytic) or with simulations (computational) – we try to incorporate only the simplest, relevant laws of physics that are needed to adequately represent the phenomena that we study. In protoplanetary disk models, most studies assume smooth power-law profiles to describe the density and temperature as they drop off at larger and larger radii. For modelling migration, this is not enough. Previous work has shown that generic bumps and discontinuities in these profiles can slow migration – but only if such features can survive for long periods of time.

superearths_formation-002The authors in this study want to further validate that idea by focusing on more realistically modelling the evolution of “bump-causing” features that appear naturally in protoplanetary disks. They focus on two features in particular:

•Planet Traps – narrow annuli where any material just outside of the trap gets pushed towards it, causing a build-up. If a planet migrates into a trap, it will stop migrating and get stuck here. However, if the disk structure changes, the trap will disappear and the planet will continue to migrate (usually inward towards its star).

•The H2O Snow Line – the dividing line between where small rocky planets can or cannot grow into larger gas giants. Beyond this line, water is at a low enough temperature that it can de-sublimate into solid ice grains, greatly increasing the density of solids in this region. With more ice grains and other volatiles, smaller planet cores can accrete more material and grow much more quickly into larger cores. This gives the cores enough time to accrete large amounts of gas from the disk and become gas giants before that gas dissipates away.

Developing a More Realistic Model: Consider the disk composition.

No model is perfectly realistic, but the authors feel they can improve on other models by considering not just the disk density, but also the disk composition – something that is often neglected in similar studies. They start with the standard choice of a density profile – the Minimum Mass Solar Nebula (the minimum mass distribution that could make all 8 planets and still have started with the same composition as the Sun). Then, they go an extra step by accounting for the fact that the temperature is set by how well different materials can absorb and transfer heat through the disk (as quantified by their opacities). They use the opacities of the different materials in the disk to construct the initial temperature profile and continue to take these materials into account when simulating how the temperature profile evolves over time.

Results: Snow lines widen into snow regions. Planets can be trapped near this region.


Ashampoo_Snap_2016.11.17_13h10m45s_002_Figure 1: The width and location of the snow region during the disk lifetime (5×106 yr) and beyond. (Fig. 11 of the paper.)

When the authors simulate the disk’s evolution, they find that the temperature flattens into a “plateau” near the water snow line. In a smooth decaying temperature profile, there is only one point in the disk that has the exact temperature at which water de-sublimates – the so-called “snow line.” However, with these plateaus, that point widens into a region sometimes as wide as 1 AU – a “snow region.” If snow lines are actually snow regions, then “walking the line” is not saying much if you are walking a snow line.

Figure 2: The temperature profile flattens at the snow line. It also shows the location of traps where the total torque is pointing outward (right arrow above zero) on the left and pointing inward (left arrow below zero) immediately on the right. There is a trap (dashed line) very close to the H2O snow region (purple lines) near 1.7 AU. Adapted from Fig. 14 of the paper.

The plateau in the temperature profile creates a planet trap near the water snow region. Normally, traps that are not in any special part of the disk dissipate relatively quickly. However, the authors find that the trap associated with the snow region stays with it.

Since there must always be some location in the disk that has the temperature at which water de-sublimates from gas to solid, the snow region always exists somewhere in the disk. Since the snow region is able to survive the lifetime of the disk, the associated planet trap also survives (unlike the other traps in the disk). Therefore, this trap should be able to slow the migration of any planet that it captures.

The authors warn that a planet in the trap might be able to escape when the trap is migrating (which happens at a slower rate than the planet usually migrate). Naturally, they expect the planet to migrate with the trap, but they worry that a real planet might be able to start migrating closer to its usual rate, which would be faster than the trap. The authors hope to investigate if that occurs in a follow-up study. Regardless, the traps make the density and temperature profiles much less smooth throughout the disk – showing that the traps and snow lines are viable mechanisms for slowing down migration.