Paul Gilster | Centauri Dreams

SETI, Astrobiology and Red Dwarfs

by Paul Gilster | Aug 8, 2016 | Astrobiology and SETI | 69 Comments

If you’ve been following the KIC 8462852 story, you’ll want to be aware of Paul Carr’s Dream of the Open Channel blog, as well as his Wow! Signal Podcast, both of which make for absorbing conversation. In his latest blog post, Carr offers sensible advice about how to look at anomalies in our astronomical data. Dysonian SETI tries to spot such anomalies in hopes of uncovering the activities of an extraterrestrial civilization, but as Carr makes clear, this is an enterprise that needs to be slowly and patiently done, without jumping to any unwarranted assumptions. Let me quote Carr on this important point: ...we will have to be patient, since we will be almost certainly be wrong at first, or perhaps just unlucky in our search. We don't need to nail it exactly, but we will need to develop rough models of ET activity that distinguishes it from nature. These models would more or less fit the data that we think anomalous, would make testable predictions, and would show how to rule out at...

KIC 8462852: Fading in the Kepler Data

by Paul Gilster | Aug 5, 2016 | Deep Sky Astronomy & Telescopes | 127 Comments

Those of you who have been following the controversy over the dimming of KIC 8462852 (Tabby's Star) may remember an interesting note at the end of Bradley Schaefer's last post on Centauri Dreams. Schaefer (Louisiana State University) had gone through his reasoning for finding a long-term dimming of the star in the DASCH (Digital Access to a Sky Century@Harvard) database. His third point about the star had to do with the work of Ben Montet (Caltech) and Joshua Simon (Carnegie Observatories). Montet and Simon's work relied on an interesting premise. Tabby's Star had been discovered because it was in the Kepler field, and thus we had high-quality data on its behavior, the unusual light curves that the Planet Hunters team brought to the attention of Tabetha Boyajian. As the researchers note in a new paper, Kepler found ten significant dips in the light curve over the timespan of the Kepler mission, dips that were not only aperiodic but irregular in shape, and that varied enormously, from...

Antimatter Acquisition: Harvesting in Space

by Paul Gilster | Aug 3, 2016 | Antimatter | 32 Comments

Talking about antimatter, as we've done in the past two posts, leads to the question of why the stuff is so hard to find. When we make it on Earth, we do so by smashing protons into targets inside particle accelerators of the kind found at the Fermi National Accelerator Laboratory in Batavia, IL and CERN (the European Organization for Nuclear Research). It's not exactly an efficient process from the antimatter production standpoint, as it produces a zoo of particles, anti-particles, x-rays and gamma rays, but it does give us enough antimatter to study. But there is another way to find antimatter, for it occurs naturally in the outer Solar System and even closer to home. James Bickford (Draper Laboratory, Cambridge MA) has looked at how we might trap antimatter that occurs in the Earth's radiation belts. In a report for NIAC back in 2006 (available here), Bickford laid out a strategy for using high temperature superconductors to form two pairs of RF coils with a radius of 100 meters,...

The Evolution of Antimatter Propulsion

by Paul Gilster | Aug 2, 2016 | Advanced Rocketry | 14 Comments

Thinking about Eugen Sänger's photon rocket concept inevitably calls to mind his Silbervogel design. The 'Silverbird' had nothing to do with antimatter but was a demonstration of the immense imaginative power of this man, who envisioned a bomber that would be launched by a rocket-powered sled into a sub-orbital trajectory. There it would skip off the upper atmosphere enroute to its target. The Silbervogel project was cancelled by the German government in 1942, but if you want to see a vividly realized alternate world where it flew, have a look at Allen Steele's 2014 novel V-S Day, a page-turner if there ever was one. I almost said that it was a shame we don't have a fictionalized version of the photon rocket, but as we saw yesterday, there were powerful reasons why the design wouldn't work, even if we could somehow ramp up antimatter production to fantastic levels (by today's standards) and store and manipulate it efficiently. Energetic gamma rays could not be directed into an...

Antimatter Propulsion: Birth of a Concept

by Paul Gilster | Aug 1, 2016 | Antimatter | 31 Comments

I spent this past weekend poking into antimatter propulsion concepts and in particular looking back at how the idea developed. Two scientists -- Les Shepherd and Eugen Sänger -- immediately came to mind. I don't know when Sänger, an Austrian rocket designer who did most of his work in Germany, conceived the idea he would refer to as a 'photon rocket,' but he was writing about it by the early 1950s, just as Shepherd was discussing interstellar flight in the pages of the Journal of the British Interplanetary Society. A few thoughts: Sänger talked about antimatter propulsion at the 4th International Astronautical Congress, which took place in Zurich in 1953. I don't have a copy of this presentation, though I know it's available in a book called Space-Flight Problems (1953), which was published by the Swiss Astronautical Society and bills itself as a complete collection of all the lectures delivered that year in Zurich. If you like to track ideas as much as I do, you'll possibly be...

An Unusual Pulsating Binary

by Paul Gilster | Jul 29, 2016 | Deep Sky Astronomy & Telescopes | 9 Comments

A large part of the fascination of astronomy is the discovery of objects that don't fit our standard definitions. KIC 8462852 -- 'Tabby's Star' -- is deeply mysterious and high on my watchlist. But yesterday we also looked at CX330, a so-called FUor of the kind that brightens enormously over years of observation. Today we have another strange one, a system called AR Scorpii, where a white dwarf star in a binary system is releasing a blast of radiation onto a nearby red dwarf. The entire system brightens and fades every 1.97 minutes, a phenomenon that has only recently been properly understood. "AR Scorpii was discovered over 40 years ago, but its true nature was not suspected until we started observing it in June 2015," says Tom Marsh (University of Warwick), lead author of the paper on this work. "We realised we were seeing something extraordinary the more we progressed with our observations." Those observations proceeded with data from the European Southern Observatory's Very Large...

CX330: Distant (and Isolated) Star Formation

by Paul Gilster | Jul 28, 2016 | Deep Sky Astronomy & Telescopes | 1 Comment

Given that we have fewer than a dozen examples, highly variable stars like the recently discovered CX330 have much to teach us. These stars have been nicknamed FUors, after FU Orionis, a pre-main sequence star that has shown huge variations in magnitude over the past century. Eruptions like these may be common, as Alan Boss argued last year (see A Disruptive Pathway for Planet Formation), but as we learn more about them, we have to account for dramatic changes, as when the star V1057 Cyg increased in brightness by 5.5 magnitudes over the course of a few years. What does this do to an associated circumstellar disk? As we ponder these questions, we also have to account for CX330, which comes into the news this week because of its odd isolation. Star-forming clouds packed with young stars are rich in gas and dust, and it is in these that we find all other examples in the FU Orionis category. But CX330 is a thousand light years away from the closest region of star formation, and because...

Jupiter’s Great Red Spot as Heat Source

by Paul Gilster | Jul 27, 2016 | Outer Solar System | 9 Comments

Speculating about what an advanced extraterrestrial civilization might do has kept us occupied for the last two days, with gas giants like Jupiter the primary topic of conversation. We don't know if it's possible to ignite a gas giant to provide new sources of energy. But with Juno getting ready to measure Jupiter's aurorae, we're looking at naturally produced energy today, and now we have interesting work on the planet's Great Red Spot that comes out of Earth-based observations. The enormous storm turns out to be a key factor in heating Jupiter's atmosphere. And what a storm it is. We knew about the Great Red Spot as early as the 17th Century because its span -- three Earth diameters -- qualifies this highly visible maelstrom as the largest hurricane we know of. Winds can take six days to complete one circuit of the Great Red Spot, which has varied in size and color ever since it was discovered. It is now observed to span 22,000 km by 12,000 km in longitude and latitude,...

SETI: Detecting ‘Stellified’ Objects

by Paul Gilster | Jul 26, 2016 | Astrobiology and SETI | 43 Comments

When Nikolai Kardashev looked into the question of where to find advanced extraterrestrial civilizations, he argued that the obvious starting point would be in the vicinity of extreme astrophysics. Active galactic nuclei (AGN) come to mind, or even the centers of comparatively quiet galaxies like our own. Clément Vidal picked up the same point in his The Beginning and the End (Springer, 2014), arguing persuasively that we should consider how black holes could be used, perhaps by manipulating the merger of such objects. And yes, this is astroengineering utterly beyond our skills, but possibly not those of an advanced ETI. Using black holes for energy is extreme, but Roger Penrose has imagined a super-civilization extracting black hole rotational energy by the injection of matter, and there are a number of other propositions on how such advanced engineering might work. Extracting energy from a black hole’s accretion disk might be the most efficient method, but lower-grade operations...

Making Jupiter into a Star

by Paul Gilster | Jul 25, 2016 | Astrobiology and SETI | 41 Comments

The SETI concepts now called ‘Dysonian’ are to my mind some of the most exhilarating ideas in the field. Dysonian SETI gets its name from the ‘Dyson spheres’ and ‘Dyson swarms’ analyzed by Freeman Dyson in a 1960 paper. This is a technology that an advanced civilization might use to harvest the energy of its star. You can see how this plays off Nikolai Kardashev’s classification of civilizations; Kardashev suggested that energy use is a way to describe civilizations at the broadest level. A Type II society is one that can use all the energy of its star. In the film 2010, director Peter Hyams’ 1984 adaptation of Arthur C. Clarke’s novel 2010: Odyssey Two (Del Rey, 1982), we see an instance of this kind of technology at work, though it has nothing to do with a Dyson sphere. In the film, a dark patch appearing on Jupiter signals the onset of what Martyn Fogg has called ‘stellification,’ the conversion of a gas giant into a small star. Rapidly replicating von Neumann machines -- the...

Kepler-80: Analysis of a Compact System

by Paul Gilster | Jul 22, 2016 | Exoplanetary Science | 10 Comments

It’s been a week for unusual planetary systems, and I’ll cap it off with Kepler-80, a star about 1100 light years away that features five planets in extraordinarily tight orbits. Such systems are now being referred to as STIPs (Systems with Tightly-spaced Planets), a nod to our apparently imperishable drive to create acronyms. Whatever we call them, though, systems like these make us realize that our own Solar System’s configuration is but one possibility in a sea of other outcomes. Yesterday’s post on ‘warm Jupiters’ is yet another confirmation of the thought. What we have in new work from Mariah MacDonald, Darin Ragozzine (Florida Institute of Technology) and colleagues is an analysis of transit timing variations (TTVs) of the planets around this star, all of which orbit inside 1/10 AU. Here the planets’ years are 1.0, 3.1, 4.6, 7.1 and 9.5 days, respectively, close enough that gravitational perturbations can create slight changes in transit times. Although the innermost planet has...

‘Warm Jupiters’ and Nearby Worlds

by Paul Gilster | Jul 21, 2016 | Exoplanetary Science | 5 Comments

Where exactly do ‘hot Jupiters’ come from? I usually see explanations involving planetary migration for Jupiter-class objects with tight orbital periods of 10 days or less, the thinking being that such planets are too close to their host stars to have accumulated a Jovian-style gaseous envelope there. Migration explains their placement, with gas giants forming much further out in their planetary systems and then migrating disruptively inward to become hot Jupiters. Does the scenario work? Consider the hot Jupiter WASP-47b, which has two low-mass planets nearby in its system. WASP-47b is a problem because a migrating gas giant should have produced profound gravitational issues for small worlds in the inner system, likely ejecting them entirely. A new paper from Chelsea Huang and Yanqin Wu (University of Toronto), working with Amaury Triaud (University of Cambridge), tries to explain the dilemma posed by WASP-47b. The answer turns out to be that, according to Kepler data used by the...

A Deeper Look at TRAPPIST-1

by Paul Gilster | Jul 20, 2016 | Exoplanetary Science | 9 Comments

Small red stars are drawing increased attention as we continue to discover interesting planets around them. The past two days we've looked at the four worlds around K2-72, a red dwarf about 225 light years out in the constellation Aquarius. That two of these worlds have at least the potential for liquid water on the surface makes the system a prime target for further study. Now we return to another recently discussed system of note, TRAPPIST-1. Designated 2MASS J23062928-0502285, this ultracool dwarf is also in Aquarius, though at forty light years, much the closer target. As with K2-72, we have multiple planets here (three), and also like the K2 discovery, TRAPPIST-1 orbits a star small and dim enough to make planet detection easier -- a transiting world presents a clear signature and the study of planetary atmospheres is possible through what is known as transmission spectroscopy, wherein light from the star that has passed through the planet's atmosphere is analyzed. Today we have...

Ravi Kopparapu: Looking at K2-72

by Paul Gilster | Jul 19, 2016 | Exoplanetary Science | 25 Comments

Is the K2-72 system, discussed yesterday as part of a recent exoplanet announcement from Ian Crossfield and colleagues, as intriguing as it looks? Ravi Kopparapu has some thoughts on the matter. Dr. Kopparapu's work on exoplanet habitability is well known to Centauri Dreams readers -- he offered an overview in these pages called How Common Are Potential Habitable Worlds in Our Galaxy?, which ran in 2014. An assistant research scientist at NASA GSFC and the University of Maryland, Dr. Kopparapu began his exoplanet career with James Kasting at Penn State following work on the LIGO collaboration enroute to his PhD from Louisiana State. Analyzing habitable zone possibilities around different kind of stars, as well as modeling and characterizing exoplanet atmospheres, plays a major role in his research interests. I was pleased to receive the following note on the recently announced K2-72 system and want to run his thoughts today given the interest this unusual system has already begun to...

Intriguing System in New Exoplanet Haul

by Paul Gilster | Jul 18, 2016 | Exoplanetary Science | 10 Comments

Today’s announcement of the confirmation of over 100 planets using K2 data reminds me of how much has gone into making K2 a success. You’ll recall that K2 emerged when the Kepler spacecraft lost function in two of its four reaction wheels. Three of these were needed for pointing accuracy, but ingenious pointing techniques and software updates have made K2 into a potent project of its own. The latest announcements demonstrate that certain benefits emerged from the changed mission parameters, especially in the ability of K2 to move away from the original field of view (toward Cygnus and Lyra) and focus on targets in the ecliptic plane. What we gain from that change is that working in the ecliptic allows more chances for observation from ground-based observatories in both northern and southern hemispheres as they perform the needed exoplanet follow-up. But there are other factors that make K2 potent. With all targets being chosen by the entire scientific community (not limited to the...

A New Dwarf Planet (and its Implications)

by Paul Gilster | Jul 15, 2016 | Outer Solar System | 15 Comments

A dwarf planet designated 2015 RR245 (and now in search of a name) has been found in an orbit that takes it out to at least 120 AU. It's a discovery made by the Outer Solar System Origins Survey (OSSOS), an international collaboration focused on the Solar System beyond Neptune. The goal is to test models of how the Solar System developed by studying the movements of icy objects, many of which may have been destroyed or ejected from the Solar System altogether through movements of the giant planets early in the formation process. Image: Rendering of the orbit of RR245 (orange line). Objects as bright or brighter than RR245 are labeled. The blue circles show the projected orbits of the major planets. The Minor Planet Center describes the object as the 18th largest in the Kuiper Belt. Credit: Alex Parker/OSSOS team. We've had a close look at one dwarf planet at the edge of the system when New Horizons flew past Pluto a year ago, and with a diameter of roughly 700 kilometers, 2015 RR245...

Updates from Jupiter and Ceres

by Paul Gilster | Jul 14, 2016 | Outer Solar System | 8 Comments

We don't have high-resolution pictures of Jupiter from the Juno mission yet, but we do have JunoCam in operation. It's a color camera working in visible light that has returned data following the spacecraft's arrival at Jupiter on July 4. This JPL news release tells us that JunoCam was folded into the mission as part of NASA's public outreach. It is not, in other words, considered a science instrument, and we'll need to wait until late August for the first high-resolution images. Still, it's satisfying to see that all is apparently well in Jupiter space. Image: This color view from NASA's Juno spacecraft is made from some of the first images taken by JunoCam after the spacecraft entered orbit around Jupiter on July 5th (UTC). The view shows that JunoCam survived its first pass through Jupiter's extreme radiation environment, and is ready to collect images of the giant planet as Juno begins its mission. Credit: NASA/JPL-Caltech/SwRI/MSSS. Here we're about 4.3 million kilometers from...

Viewing a Protoplanetary Snowline

by Paul Gilster | Jul 13, 2016 | Exoplanetary Science | 2 Comments

A team led by Lucas Cieza (Universidad Diego Portales, Santiago, Chile) has produced the first image directly showing the water snowline in a protoplanetary disk, using the Atacama Large Millimeter/submillimeter Array (ALMA). It's fascinating to actually see a mechanism we've long discussed in these pages when analyzing exoplanetary systems (or for that matter, our own). We have a young star called V883 Orionis to thank for the possibility. It's an FU Orionis star of the kind we recently looked at in FU Orionis: Implications of Sudden Brightening for Planet Formation. And here, too, the implications are rich. FU Orionis stars are young, pre-main sequence objects that can produce extreme changes in magnitude and spectral type. The eponymous FU Orionis itself, 1500 light years away in the constellation Orion, underwent an event in 1936 that took it from a visual magnitude of 16.5 to 9.6. In the case of V883 Orionis, a similar outburst in temperature and luminosity has heated the...

Into the Nebula: Low-Mass Objects in Orion

by Paul Gilster | Jul 12, 2016 | Deep Sky Astronomy & Telescopes | 4 Comments

Because we want to learn more about how stars form, we study the so-called Initial Mass Function, which tells us, for a given population of stars, the distribution of their initial masses. As one recent reference (the Encyclopedia of Astrobiology, Springer, 2011) puts it: "The initial mass function is the relative number of stars, as a function of their individual initial mass, that forms during a single star forming episode." Figuring out the IMF for places like the Orion Nebula, visible from Earth with the naked eye as a patch in Orion's sword, is a start in learning how this grouping of stars formed. About 1350 light years from Earth, the Orion Nebula is known as an H II region, a reference to the fact that it contains ionized hydrogen in its star-forming, gaseous depths. A surprise emerged when the European Southern Observatory put its HAWK-I infrared instrument on the Very Large Telescope to work on the nebula. What turned up were faint brown dwarfs and isolated objects of...

WISE 0855: Probing a Brown Dwarf’s Atmosphere

by Paul Gilster | Jul 11, 2016 | Exoplanetary Science | 9 Comments

A brown dwarf as a 'quieter' version of Jupiter? That's more or less the picture offered in a new paper on WISE 0855 from Andrew Skemer (UC-Santa Cruz) and colleagues. Here we're working in the Solar System's close neighborhood -- WISE 0855 is a scant 7.2 light years from Earth -- and we're observing an object that is the coldest known outside of the Solar System. That makes the observational task difficult, but it has yielded rich results in the discovery of clouds of water or water ice. We learn that WISE 0855 is about five times the mass of Jupiter, with a temperature in the range of 250 K (-23 Celsius). This is the nearest known object of planetary mass, but it is too faint to characterize with conventional spectroscopy -- separating light into its component wavelengths -- in the optical or near infrared. But it turns out the object can be studied through thermal emissions from deep in its atmosphere in the range of 5 µm (a range frequently used to study Jupiter's own deep...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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