Hunting for Brown Dwarf Planets

Brown dwarfs fascinate me because they’re the newest addition to the celestial menagerie, exotic objects about which we know all too little. The evidence suggests that brown dwarfs can form planets, but so far we’ve found only a few. Two gravitational microlensing detections on low mass stars have been reported, one of which is a 3.2 Earth-mass object orbiting a primary with mass of 0.084 that of the Sun, putting it into the territory between brown dwarfs and stars. The MEarth project has uncovered a planet 6.6 times the mass of the Earth orbiting a 0.16 solar mass star.

Now a new proposal to use the Spitzer Space Telescope to hunt for brown dwarfs planets is available on the Net, one that digs into what we’ve found so far, with reference to the discoveries I just mentioned:

Accounting for their low probabilities, such detections indicate the presence of a large, mostly untapped, population of low mass planets around very low mass stars (see also Dressing & Charbonneau (2013)). Arguably the most compelling discovery is that of the Kepler Object of Interest 961, a 0.13 [solar mass] star, orbited by a 0.7, a 0.8 and a 0.6 Rearth on periods shorter than two days (Muirhead et al. 2012). The KOI-961 system, remarkably, appears like a scaled-up version of the Jovian satellite system. This is precisely what we are looking for.

The plan is to use the Spitzer instrument to discover rocky planets orbiting nearby brown dwarfs, the idea being that the upcoming mission of the James Webb Space Telescope will need a suitable target list, and soon, for it to be put to work on probing the atmospheres of exoplanets. A 5400 hour campaign is the objective, the goal being to detect a small number of planetary systems with planets as small as Mars. Interestingly, the team is advocating a rapid release of all survey data to up the pace of exoplanet research and compile a database for further brown dwarf studies.


Image: The stellar menagerie: Sun to Jupiter, via brown dwarfs. Credit: Space Telescope Science Institute.

Brown dwarfs turn out to be excellent targets as we try to learn more about rocky planets around other stars. Studying the photons emitted by an atmosphere during an occultation requires relatively close targets, and as the paper on this work points out, the fainter the primary, the better the contrast between the central object and the planet. And around brown dwarfs we can expect deep transits that allow us to detect objects down to Mars size with Spitzer’s equipment. The paper also notes that brown dwarfs older than half a billion years show a near constant radius over their mass range, making it easier to estimate the size of detected planets.

Spitzer is the only facility that can survey a sufficient number of brown dwarfs, long enough, with the precision and the stability required to credibly be able to detect rocky planets down to the size of Mars, in time for JWST. We estimate that about 8 months of observations would be needed to complete the survey. Once candidates are detected, large ground-based facilities will confirm the transits, find the period (if only one event was captured by Spitzer) and check for the presence of additional companions. This program will rapidly advance the search for potentially habitable planets in the solar neighborhood and transmit to JWST a handful of characterizable rocky planet atmospheres.

This is a survey that not only probes a fascinating kind of object but one that should offer what the paper calls “the fastest and most convenient route to the detection and to the study of the atmospheres of terrestrial extrasolar planets.” It goes public at a time when 76 new brown dwarfs have been discovered by the UKIRT Infrared Deep Sky Survey, including two potentially useful ‘benchmark’ systems. The authors of the Spitzer proposal argue that observing the atmospheres of Earth-sized transiting worlds around M-Dwarfs with JWST will be much more challenging than equivalent work using brown dwarfs, assuming we get to work identifying the best targets.

The white paper is Triaud et al., “A search for rocky planets transiting brown dwarfs,” available online. The UKIRT Infrared Deep Sky Survey paper is Burningham et al., “Seventy six T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density,” accepted at Monthly Notices of the Royal Astronomical Society (abstract).


Starship Congress Registration Opens

Our friends at Icarus Interstellar continue working on this summer’s conference. Just in from my son Miles is news about the opening of registration for the Dallas event.

Registration for the 2013 Starship Congress, hosted by Icarus Interstellar, is now open. The registration fee is $100; however, the first 25 paid registrations receive a $25 discount. This discount is also available to individuals who sign up by May 2nd, 2013. Students can register for a reduced rate of $50. Students must present a valid student I.D. at the Starship Congress to take advantage of the student rate. The $25 discount does not apply to student registrations. Group rates are also available. An optional lunch is offered for August 15, 16 and 17 for $25.

The Starship Congress will be held August 15-18 at the Hilton Anatole in Dallas, Texas. A discounted rate for Starship Congress attendees is available at the Hilton Anatole from August 12-20. To book a room at the special rate, click here.

Richard Obousy, President and Senior Scientist for Icarus Interstellar, provided Centauri Dreams readers with a preview of the Starship Congress, which you can read here. For any questions, contact


Robotic Replicators

Centauri Dreams regular Keith Cooper gives us a look at self-replication and the consequences of autonomous probes for intelligent cultures spreading into the universe. Is the Fermi paradox explained by the lack of such civilizations in the galaxy, or is there a far more subtle reason? Keith has been thinking about these matters for some time as editor of both Astronomy Now and Principium, which has just published its fourth issue in its role as the newsletter of the Institute for Interstellar Studies. Intelligent robotic probes, as it turns out, may be achievable sooner than we have thought.

by Keith Cooper


There’s a folk tale that you’ll sometimes hear told around the SETI or physics communities. Back in the 1940s and 50s, at the Los Alamos National Labs, where the first nuclear weapons were built, many physicists of Hungarian extraction worked. These included such luminaries in the field as Leó Szilárd, Eugene Wigner, Edward Teller and John Von Neumann. When in 1951 their colleague, the Italian physicist Enrico Fermi, proposed his famous rhetorical paradox – if intelligent extraterrestrial life exists, why do we not see any evidence for them? – the Hungarian contingent responded by standing up and saying, “We are right here, and we call ourselves Hungarians!”

It turns out that the story is apocryphal, started by Philip Morrison, one of the fathers of modern SETI [1]. But there is a neat twist. You see, one of those Hungarians, John Von Neumann, developed the idea of self-replicating automata, which he presented in 1948. Twelve years later astronomer Ronald Bracewell proposed that advanced civilisations may send sophisticated probes carrying artificial intelligence to the stars in order to seek out life and contact it. Bracewell did not stipulate that these probes had to be self replicating – i.e able to build replicas of themselves from raw materials – but the two concepts were a happy marriage. A probe could fly to a star system, build versions of itself from the raw materials that it finds there, and then each daughter probe could continue on to another star, where more probes are built, and so on until the entire Galaxy has been visited for the cost of just one probe.

The combination of Von Neumann machines and Bracewell’s probes made Fermi’s Paradox all the more puzzling. There has been more than enough time throughout cosmic history for one or more civilisations to send out an army of self-replicating probes that could colonise the Galaxy in anywhere between three million and 300 million years [2] [3]. By all rights, if intelligent life elsewhere in the Universe does exist, then they should have colonised the Solar System long before humans arrived on the scene – the essence of Fermi’s Paradox. The conundrum it is about to be compounded further, because human civilisation will have its own Von Neumann probes within the next two to three decades, tops. And if we can do it, so can the aliens, so where are they?

To Build a Replicator

A self-replicator requires four fundamental components: a ‘factory’, a ‘duplicator’, a ‘controller’ and an instruction program. The latter is easy – digital blueprints that can be stored on computer and which direct the factory in how to manufacturer the replica. The duplicator facilitates the copying of the blueprint, while the controller is linked to both the factory and the duplicator, first initiating the duplicator with the program input, then the factory with the output, before finally copying the program and uploading it to the new daughter probe, so it too can produce offspring in the future.

‘Duplicator’, ‘controller’, ‘factory’; these are just words. What are they in real life? In biology, DNA permits replication by following these very steps. DNA’s factory is found in the form of ribosomes, where proteins are synthesised. The duplicators are RNA enzymes and polymerase, while the controllers are the repressor molecules that can control the conveyance of genetic information from the DNA to the ribosomes by ‘messenger RNA’ created by the RNA polymerase. The program itself is encoded into the RNA and DNA, which dictates the whole process.

That’s fine for biological cells; how on earth can a single space probe take the raw materials of an asteroid and turn it into another identical space probe? The factory itself would be machinery to do the mining and smelting, but beyond this something needs to do the job of constructing the daughter probe down to the finest detail. Previously, we had assumed that nanotechnology would do the duplicating, reassembling the asteroidal material into metal paneling, computer circuits and propulsion drives. However, nanotechnology is far from reaching the level of autonomy and maturity where it is able to do this.

Perhaps there is another way, a technology for which we are only now beginning to see its potential. Additive manufacturing or, as it is more popularly known, 3D printing, is being increasingly utilised in more and more areas of technology and construction. Additive manufacturing takes a digital design (the instruction program) and is able to build it up layer by layer, each 0.1mm thick. The factory, in this sense, is then the 3D printer as a whole. The duplicator is the part that lays down the layers while the controller is the computer. It’s not a pure replica in the Star Trek sense, but it can build practically anything, including moving parts, that can otherwise only be manufactured in a real factory.

Gathering Space Resources

3D printing is not the technology of tomorrow; it’s the technology of today. It’s not a suddenly disruptive technology either (well, not in the sense of how it has gradually evolved), having been around in its most basic form since the 1970s and in its current form since 1995. Rather, it is a transformative technology. The reason it is gaining traction in modern society now is because it is becoming affordable, with small 3D printers now costing under $2,000. Within a decade or so, we’ll all have one; they’ll be as ubiquitous as a VCR, cell phone or a microwave. This will have huge consequences for manufacturing, jobs and the economy, potentially destroying large swathes of the supply chains from manufacturing to the purchaser, but, whereas the factory production lines on Earth may dry up, in space new economic opportunities will open up.

As spaceflight transitions from the domain of national space agencies to a wider field of private corporations, economic opportunities in space are already being sought after, including the mineral riches of the asteroids. One company in particular, Deep Space Industries, has already patented a 3D printer that will work in the microgravity of space [4] and they intend to use additive manufacturing to construct communication and energy platforms, space habitats, rocket fuel stations and probes from material mined from asteroids and brought into Earth orbit. For now, they envisage factory facilities in orbit and the asteroids mined will be those that come close to Earth [5]. Nevertheless, it has already been mooted that astronauts on a mission to Mars will be able to take 3D printers with them and, as we utilise asteroids further afield, we’ll start to bundle in the 3D printers with automated probes, creating an industrial infrastructure in space, first across the inner Solar System and then expanding into the outer realms.

Archimedes concept

Image: A ‘fuel harvestor’ concept as developed by Deep Space Industries. Credit: DSI.

Here’s the key; these 3D printers that will sit in orbit and are designed to build habitats or communication platforms, could easily become part of a large probe and be programmed to just build more probes. All of a sudden, we’d have a population of Von Neumann probes on our hands.

Without artificial intelligence, the probes would just be programmed automatons. They’d spend their time flitting from asteroid to asteroid, following the simple programming we have given them, but one day someone is inevitably going to direct them towards the stars. This raises two vital points. One is that if we can build Von Neumann probes, then a technological alien intelligence could surely do the same and their absence is therefore troubling. And two, Von Neumann probes will soon no longer be a theoretical concept and we are going to have to start to decide what we want them to be: explorers, or scavengers.

A Future Beyond Consumption

It seems clear that self-replicating probes will first be used for resource gathering in our own Solar System. Gradually their sphere of influence will begin to edge out into the Kuiper Belt and then the Oort Cloud, halfway to the nearest stars. That may not be for some time, given the distances involved, but when we start sending them to other stars, do we really want them rampaging through another planetary system, consuming everything like a horde of locusts? How would we feel if someone else’s Von Neumann probes entered our Solar System to do the same? Once they are let loose, we need to take responsibility for their behaviour, lest we be considered bad parents for not supervising our creations. That would not be the ‘first contact’ situation we’ve been dreaming of.

On the other hand, Bracewell’s probes were designed for contact, for communication, for the storage and conveyance of information – a far more civilised task. But standards, however low, can be set early. If our Von Neumann probes are only ever used for mining, will we be wise enough to have the vision in the future to appropriate them for other means too? It seems we need to think about how we are going to operate them now, rather than later after the horse has bolted.

And perhaps there lies the answer to Fermi’s Paradox. Maybe intelligent extraterrestrials are more interested in making a good first impression than the incessant consumption of resources. Perhaps that is why the Solar System wasn’t scoured by a wave of Von Neumann probes long ago. The folly of our assumption is that we see all before us as resources to be utilised, but why should intelligent extraterrestrial life share that outlook? Maybe they are more interested in contact than consumption – a criticism that can be levelled at other ideas in SETI, such as Kardashev civilisations and Dyson spheres that have been discussed recently on Centauri Dreams. Perhaps instead there is a Bracewell probe already here, lurking in in a Lagrange point, or in the shadow of an asteroid, watching and waiting to be discovered. If that’s the case, it may be one our own Von Neumann probes that first encounters it – and we want to make sure that we make the right impression with our own probe the day that happens.


[1] H Paul Schuch’s edited collection of SETI essays, SETI: Past, Present and Future, published by Springer, 2011.

[2] Birkbeck College’s Ian Crawford has calculated that the time to colonise the Galaxy could be as little as 3.75 million years, as described in an article in the July 2000 issue of Scientific American.

[3] Frank Tipler’s estimate for the time to colonise the Galaxy was 300 million years, as written in his famous 1980 paper “Extraterrestrial Intelligent Beings Do Not Exist,” that appeared in the Royal Astronomical Society’s Quarterly Journal.

[4] Deep Space Industries 22 January 2013 press announcement.

[5] Private correspondence with Deep Space Industries’ CEO, David Gump.


The Alpha Centauri Angle

Apropos of yesterday’s article on the discovery of Proxima Centauri, it’s worth noting that Murray Leinster’s story “Proxima Centauri,” which ran in Astounding Stories in March of 1935, was published just seven years after H. A. Alden’s parallax findings demonstrated beyond all doubt that Proxima was the closest star to the Sun, vindicating both Robert Innes and J. G. E. G. Voûte. Leinster’s mile-wide starship makes the first interstellar crossing only to encounter a race of intelligent plants, the first science fiction story I know of to tackle the voyage to this star.


The work surrounding Proxima Centauri was intensive, but another fast-moving star called Gamma Draconis in Draco, now known to be about 154 light years from Earth thanks to the precision measurements of the Hipparcos astrometry satellite, might have superseded it. About 70 percent more massive than the Sun, Gamma Draconis has an optical companion that may be an M-dwarf at about 1000 AU from the parent. Its bid for history came from the work of an astronomer named James Bradley, who tried without success to measure its parallax. Bradley was working in the early 18th Century on the problem and found no apparent motion.

Stellar parallax turned out to be too small an effect for Bradley’s instruments to measure. Most Centauri Dreams readers will be familiar with the notion of observing the same object from first one, then the other side of the Earth’s orbit, looking to determine from the angles thus presented the distance to the object. It’s no wonder that such measurements were beyond the efforts of early astronomers and the apparent lack of parallax served as an argument against heliocentrism. A lack of parallax implied a far greater distance to the stars than was then thought possible, and what seemed to be an unreasonable void between the planets and the stars.

It would fall to the German astronomer Friedrich Wilhelm Bessel to make the first successful measurement of stellar parallax, using a device called a heliometer, which was originally designed to measure the variation of the Sun’s diameter at different times of the year. As so often happens in these matters, Bessel was working on 61 Cygni at the same time that another astronomer — his friend Thomas Henderson — was trying to come up with a parallax reading for Alpha Centauri. Henderson had been tipped off by an observer on St. Helena who was charting star positions for the British East India Company that Alpha Centauri had a large proper motion.

Henderson was at that time observing at the Cape of Good Hope, using what turned out to be slightly defective equipment that may have contributed to his delays in getting the Alpha Centauri parallax into circulation. In any event, Bessel’s heliometer method proved superior to Henderson’s mural circle and Dollond transit (see this Astronomical Society of Southern Africa page for more on these instruments), and Bessel’s findings on 61 Cygni were accepted by the Royal Astronomical Society in London in 1842, while Henderson’s own figures were questioned.


Bessel thus goes down as the first to demonstrate stellar parallax. Henderson went on to tighten up his own readings on Alpha Centauri, using measurements taken by his successor at the Royal Observatory at the Cape of Good Hope, but it took several decades for the modern value of the parallax to be established. But both astronomers were on to the essential fact that parallax was coming within the capabilities of the instruments of their time, and by the end of the 19th Century, about 60 stellar parallaxes had been obtained. The parallax of Proxima Centauri, for the record, is now known to be 0.7687 ± 0.0003 arcsec, the largest of any star yet found.

Image: A portrait of the German mathematician Friedrich Wilhelm Bessel by the Danish portrait painter Christian Albrecht Jensen. Credit: Wikimedia Commons.

While the Hipparcos satellite was able to extend the parallax method dramatically, it falls to the upcoming Gaia mission to measure parallax angles down to an accuracy of 10 microarcseconds, meaning we should be able to firm up distances to stars tens of thousands of light years from the Earth. Indeed, working with stars down to magnitude 20 (400,000 times fainter than can be seen with the naked eye), Gaia will be able to measure the distance of stars as far away as the galactic center to an accuracy of 20 percent. The Gaia mission’s planners aim to develop a catalog encompassing fully one billion stars, producing a three-dimensional star map that will not only contain newly discovered extrasolar planets but brown dwarfs and thousands of other objects useful in understanding the evolution of the Milky Way.

One can only imagine what the earliest reckoners of stellar distance would have made of all this. Archimedes followed the heliocentric astronomer Aristarchus in calculating that the distance to the stars, compared to the Sun, was proportionally as far away as the ratio of the radius of the Earth was to the distance to the Sun (thanks to Adam Crowl for this reference). Using the figures he was working with, that works out to a stellar distance of 100 million Earth radii, a figure then all but inconceivable. If we translated into our modern values for these parameters, the stars Aristarchus was charting would be 6.378 x 1011 (637,800,000,000) kilometers away. The actual distance to Alpha Centauri is now known to be roughly 40 trillion (4 x 1013) kilometers.


Finding Proxima Centauri

It’s fascinating to realize how recent our knowledge of the nearest stars has emerged. A little less than a century has gone by since Proxima Centauri was discovered by one Robert Thorburn Ayton Innes (1861-1933), a Scot who had moved to Australia and went on to work at the Union Observatory in Johannesburg. Innes used a blink comparator to examine a photographic plate showing an area of 60 square degrees around Alpha Centauri, comparing a 1910 plate with one taken in 1915. Forty hours of painstaking study revealed a star with a proper motion similar to Alpha Centauri (4.87″ per year), and about two degrees away from it.


The question Innes faced was whether the new star was actually closer than Alpha Centauri, an issue that could be resolved only with better equipment. Ian Glass (South African Astronomical Observatory) tells the tale in a short paper written for the publication African Skies. Innes ordered a micrometer eyepiece that would be fitted to the observatory’s 9-inch telescope, an addition that was completed by May of 1916. In April of the following year he realized he was in a competition. A Dutch observer working at the Royal Observatory in Cape Town wrote to Innes to say that he had begun parallax studies on the new star in February of 1916.

Image: Robert Thorburn Ayton Innes, discoverer of Proxima Centauri. Credit: Wikimedia Commons.

Proxima did not yet have its name, of course, though there was suspicion that it was bound to Alpha Centauri and thus might be Centauri C (it’s worth noting that the question isn’t fully resolved even today, though the case for a bound Proxima seems strong). The Dutch observer, who bore the majestic name of Joan George Erardus Gijsbertus Voûte, published his results before Innes could get into print. There was not enough evidence to prove that the new star was closer than Alpha Centauri, but Voûte pointed out that its implied absolute magnitude made it the least luminous star then known. The soon to be christened Proxima was hardly a headliner.

According to Glass, Innes was concerned to establish his priority in the discovery — some things never change — and so he rushed his incomplete parallax results into a 1917 meeting of the South African Association for the Advancement of Science. Relying partly on Voûte’s data, Innes wound up with a parallax value of 0.759″. Says Glass: “…without a proper discussion of the probable error of the measurement, [Innes] drew the unjustifiable conclusion that his star was closer than α Cen and therefore must be the nearest star to the Solar System.”

Thus, based on as yet incomplete evidence, the new star was named, with Innes suggesting ‘Proxima Centaurus.’ It turns out that the preliminary value Voûte calculated for Proxima’s parallax in his paper was closer to the correct one than Innes’, but the latter would always be known for the discovery of Proxima. We didn’t really peg the accurate value of Proxima’s proper motion until H. A. Alden did so at Yale Southern Station in Johannesburg in 1928. Innes, as it turned out, had made a lucky guess forced by circumstance, one that proved to be correct.

Voûte (1879-1953) turned out to be an interesting figure in his own right. Having decided at an early age to make astronomy his life’s work, he developed a keen interest in double stars and parallaxes and published on the subject over a span of some fifty years. Born to Dutch parents in Java, he returned there to found the Nederlandsch-Indische Sterrekundige Vereeniging, whose express object was to set up an astronomical observatory. Voûte would use the observatory at Lembang, 1300 meters up on the side of the Tangkoebanl Prahoe volcano, to make numerous parallax determinations and photographic studies of variable stars, concentrating particularly on closely paired double stars. You can see where he got his interest in Alpha Centauri!


Image: From left to right: J.G.E.G. Voûte (the first director of Bosscha Observatory), K.A.R. Bosscha (the principal benefactor and chairman of the NISV), Ina Voûte (Voûte’s wife). Source: Private collection of Bambang Hidayat. Credit: Tri Laksmana Astraatmadja.

World War II destroyed Voûte’s health — he was imprisoned during the Japanese occupation of Java, and never fully recovered — but he remained interested in astronomy until his death. As to Innes (whom Glass mistakenly refers to as ‘Richard’ rather than ‘Robert’), his work on binary stars would lead to 1628 discoveries and the publication of the Southern Double Star Catalog in 1927. Innes was a self-taught amateur astronomer, a wine merchant in Sydney with a passion for the sky who, despite his lack of formal training, showed enough promise to be invited to the Cape Observatory by the astronomer royal Sir David Gill, moving on to Johannesburg in 1903. It seems appropriate that a small M-dwarf in Carina with a high proper motion — GJ 3618 — is today known as Innes’ Star after its discoverer.

For more, see Glass, “The Discovery of the Nearest Star,” African Skies Vol. 11 (2007), p. 39 (abstract).