by Paul Gilster | Mar 31, 2007 | Culture and Society
John Updike reviews Walter Isaacson’s new biography of Einstein in The New Yorker, from which this excerpt on why a job in the Swiss patent office was actually a good thing for the young genius:
“Had he been consigned instead to the job of an assistant to a professor,” Isaacson points out, “he might have felt compelled to churn out safe publications and be overly cautious in challenging accepted notions.” Special relativity has a flavor of the patent office; one of the theory’s charms for the fascinated public was the practical apparatus of its exposition, involving down-to-earth images like passing trains equipped with reflecting mirrors on their ceilings, and measuring rods that magically shrink with speed from the standpoint of a stationary observer, and clocks that slow as they accelerate — counterintuitive effects graspable with little more math than plane geometry.
Einstein would later say, upon taking his first professorship (at Zurich), that in doing so he had become “…an official member of the guild of whores.” So much for academe. This review moves the book up on my list (and I’ve always thought no biographer would ever equal Abraham Pais’ Subtle Is the Lord — maybe Isaacson will change my mind). The book is Einstein: His Life and Universe (Simon & Schuster, 2007), and you can read Updike’s review here. Thanks to Larry Klaes for the pointer to this one.
by Paul Gilster | Mar 31, 2007 | Culture and Society
Centauri Dreams believes profoundly in what I might call ‘realistic optimism.’ While an aggressive belief in the human future can be overstated, it’s important to remember that intellectual fashions come and go, leaving many a futurist trying to explain another failed prediction. The view here is that the vast problems that face our species are solvable through common sense and technology, and that somehow we will engage our tools to get us off-planet before we annihilate ourselves.
Playing into this notion is the work of David Haussler, cited recently by Freeman Dyson as one reason for his own deeply optimistic view of the future. Studying the human genome, Haussler and team at UC Santa Cruz discovered a section of DNA called Human Accelerated Region 1. HAR1 evidently shows up in the genomes of a wide range of species, from mouse to chicken to chimpanzee. It was apparently unchanged for about three hundred million years, as Dyson told Benny Peiser in a recent interview (see this New Scientist story for more on HAR1).
Dyson notes that this unusual patch of DNA is considerably modified in the human genome, with eighteen known mutations. That means that as we move from the common ancestor of chimpanzees and humans to our species today, HAR1 seems to represent a key difference between humans and other mammals. Dyson sees it as wrapped up in the evolution of the human brain, and that’s good news because the more we understand what drives us, the more we can do about it.
Listen to Dyson relating HAR1 to the work of a man he deeply admired:
I am optimistic because I see the discovery of HAR1 as a seminal event in the history of science, marking the beginning of a new understanding of human evolution and human nature. I see it as a big step toward the fulfilment of the dream described in 1929 by Desmond Bernal, one of the pioneers of molecular biology, in his little book, The World, the Flesh and the Devil: An Enquiry into the Future of the Three Enemies of the Rational Soul. Bernal saw science as our best tool for defeating the three enemies. The World means floods and famines and climate changes. The Flesh means diseases and senile infirmities. The Devil means the dark irrational passions that lead otherwise rational beings into strife and destruction. I am optimistic because I see HAR1 as a new tool leading us toward a deep understanding of human nature and toward the ultimate defeat of our last enemy.
My own optimism holds that we will develop the technologies to maintain a large human presence in space in a variety of habitats. And of course the hope is that we will gradually expand outwards — either as humans adapting to living in the vacuum (Dyson sees this happening) or through highly developed artificial intelligence — to the stars themselves. With more than enough external threats from our own environment and nearby space to keep us busy, losing the fear of annihilation from our flawed human nature would be a major step in this direction. If Dyson is right, such a goal may emerge from our studies of the genome.
by Paul Gilster | Mar 30, 2007 | Exoplanetary Science
The number of stars with possible planets keeps going up. The astronomy books I read as a kid operated under the assumption that we needed to look at Sun-like stars to find planets, and that meant single rather than double or triple systems. The tantalizingly close Alpha Centauri stars were all but ruled out because of their assumed disruptive effects on planetary orbits. No, find a nice G-class star all by itself and there you might have a solar system something like our own and, who knows, a second Earth.
Today we’re fitting binary stars into the planetary picture with ease. Astronomers see little reason to rule them out. Consider what David Trilling (University of Arizona) has to say about the matter in an upcoming paper: “There appears to be no bias against having planetary system formation in binary systems. There could be countless planets out there with two or more suns.” Just imagine the possible sunsets.
Image: Our solitary sunsets here on Earth might not be all that common in the grand scheme of things. New observations from NASA’s Spitzer Space Telescope have revealed that mature planetary systems — dusty disks of asteroids, comets, and possibly planets — are more frequent around close-knit twin, or binary, stars than single stars like our sun. That means sunsets like the one portrayed in this artist’s photo concept, and more famously in the movie Star Wars, might be quite commonplace in the universe. Credit: NASA/JPL-Caltech/R. Hurt (SSC).
Countless planets with two or more suns. I like that, evoking as it does the awestruck wonder I used to feel when looking at the Midwestern sky at night, the air crystalline and aswarm with stars that I was convinced sheltered planets. But that was conjecture. Today we have 200 confirmed exoplanets, of which some 50 orbit one member of a wide binary system. The work Trilling is involved in now looks at closer binaries and involves the hunt for the debris disks that indicate a possible planetary system.
Using the Spitzer Space Telescope, the team examined 69 binary systems between 50 and 200 light years from Earth. The results are heartening indeed: Forty percent of these systems have debris disks, a figure which is actually somewhat higher than the comparable number for single stars. The implication is that planetary systems are as common around binaries as they are around single stars.
Where the work really gets interesting is when you look at tight binaries, where stars are three or less AU apart. In cases like these, the Spitzer work finds debris disks even more frequent, with the disks orbiting both members of the stellar pair rather than just one. A planet orbiting a tight binary could have the kind of sunset Luke Skywalker saw in Star Wars, a video of which — interwoven with the Spitzer findings — can be seen here.
Where planets seem least likely to form is in binaries with intermediate spacing, defined here as between three and fifty AU. The Centauri stars show a mean separation of 23 AU, placing them squarely in this category. We’ve determined that stable planetary orbits exist around such stars, but the question now turns to whether planet formation is likely.
The Spitzer data from this study draw the matter into question, implying that the best scenario for planets is tight binaries or widely spaced ones. But be aware that an Italian study we’ll examine next week argues that there “…is no significant dependence of planet frequency on the binary separation, except for a lower value of frequency for close binaries.” Obviously, the issue of binary separation is still in play.
And note this interesting fact from the Trilling paper:
The incidence of debris disks around main-sequence A3–F8 binaries is marginally higher than that for single old AFGK stars. Whatever combination of nature (birth conditions of binary systems) and nurture (interactions between the two stars) drives the evolution of debris disks in binary systems, it is clear that planetesimal formation is not inhibited to any great degree.
There goes our old G-class Sun-centrism again (forgive the coinage). For in addition to finding them in binary systems, we’re seeing debris disks, clear markers of possible planet formation, occurring around stars in a wide range of spectral types. The paper is Trilling et al., “Debris Disks in Main-Sequence Binary Systems,” Astrophysical Journal 658 (April 1, 2007), pp. 1289-1311, with abstract here.
by Paul Gilster | Mar 29, 2007 | Exoplanetary Science
Sometimes I imagine an ancient place where a dim sun hangs unmoving at zenith, and a race of philosophers and poets works out life’s verities under an unchanging sky. Could a place like this, on a terrestrial world orbiting an M-class red dwarf, really exist? A new paper by Jack Lissauer (NASA Ames) casts doubt on the idea. Lissauer argues that planets inside an M dwarf’s habitable zone are probably lacking in water and other volatiles, and are thus unable to produce life as we know it.
The question is important because M dwarfs make up as much as 75 percent of the stars in our part of the galaxy. If we include them as candidates for life, we add a hundred billion or more potential habitats in the Milky Way alone. We’ve known for some time that although the proximity of such a terrestrial M dwarf planet to its star would cause it to be tidally locked — one side in constant light, the other in darkness — habitable regions might still occur on the dayside given a dense enough atmosphere to transport heat globally.
But ponder the water question. Remarkably, the Earth itself is volatile-poor, with oceans and other reservoirs of near-surface water accounting for less than 0.03 percent of our planet’s mass. Lissauer believes that most of Earth’s water probably came from planetesimals that originally condensed beyond 2.5 AU. Our planet needed, in other words, help from farther out in the Solar System, and it can be shown that primitive meteorites from the outer regions of the asteroid belt have over 100 times as much water as those closer in.
But if our terrestrial world relied on such sources, could an M dwarf planet have done the same? Lissauer sees problems with the scenario. Stars are more luminous when they’re forming than when they reach the main sequence. In the case of M dwarfs, the difference in luminosity is significant. The zones that could become habitable around these stars are hotter during the planet formation period than similar zones around Sun-like stars. The so-called ‘snow line,’ which separates regions where rocky planets form from regions of icy planet formation, is proportionately more distant from an M dwarf’s habitable zone than it would be around a star like the Sun.
Another problem: planets take less time to form in the habitable zone of an M dwarf than they would around more massive stars because orbital periods are shorter and planetesimals bang into each other more frequently and with higher impact speeds. If anything, these frequent impacts may cause the young planet to lose gases and water rather than gaining them.
In short, our would-be terrestrial world forms in a volatile-poor environment and seems unable to retain what water it does accumulate. Lissauer’s conclusion is clear, and it makes grim reading for my imaginary M dwarf civilization:
In sum, under nominal circumstances, planets in main sequence habitable zones around M stars are likely to be fully formed and in their ?nal orbits by the time the gaseous circumstellar disk has dissipated or several million years after planetesimal formation, whichever is later. If growth is in situ, dynamical and thermal factors imply that the planets are unlikely to have large volatile inventories, and planetary masses are likely to be small. The large collision speeds of impacting comets, as well as the high activity and luminosities of young M stars, may lead to substantial mass loss from planetary atmospheres, depleting any reservoirs of volatiles that planets within the HZs are able to accrete.
A bleak picture for living worlds indeed. Are there any mitigating factors? Perhaps. A water-rich world could conceivably migrate inwards to the habitable zone of an M dwarf while the gaseous protoplanetary disk was still present, retaining some water even during the star’s active youth. Eccentric orbits can also be found that could allow water worlds to attain stability within the habitable zone.
But on balance, these exceptions look to be few. Writes Lissauer, “…the number of such planets is probably small, and Sun-like stars, despite being considerably less numerous, may well be the hosts of far more habitable planets.”
The paper is Lissauer, “Planets Formed in Habitable Zones of M Dwarf Stars Probably are De?cient in Volatiles,” in press at Astrophysical Journal Letters. Abstract available.
by Paul Gilster | Mar 28, 2007 | Outer Solar System
Shrouded in the night of a 15-year winter, Saturn’s north pole demands specialized instruments to yield its secrets. Enter Cassini’s visual and infrared mapping spectrometer, whose data on the region have disappointed no one. A six-sided honeycomb-shaped feature has emerged that was first found by the Voyager 1 and 2 spacecraft over twenty years ago. Now Cassini has, for the first time, captured the entire hexagon in a single image.
What exactly is it? Think of Earth’s polar regions, where winds move in a circular pattern around the pole, but ponder this difference: Saturn’s vortex is a hexagon nearly 25,000 kilometers across. Four Earths would fit inside it. Click here for a QuickTime movie of the odd feature.
This makes Saturn possibly the Solar System’s most intriguing object when it comes to polar anomalies. The south pole sports an enormous hurricane, while the north is dominated by clouds moving along the hexagon at great rate. Indications are that the hexagon extends fully 100 kilometers below the cloud tops, leaving us with yet another outer system surprise.
Image: In the new infrared images, the strong brightness of the hexagon feature indicates that it is primarily a clearing in the clouds, which extends deep into the atmosphere, at least some 75 kilometers (47 miles) underneath the typical upper hazes and clouds seen in the daytime imagery by Voyager. Thick clouds border both sides of the narrow feature, as indicated by the adjacent dark lanes paralleling the bright hexagon. This and other images acquired over a 12-day period between Oct. 30 and Nov. 11, 2006, show that the feature is nearly stationary, and likely is an unusually strong pole-encircling planetary wave that extends deep into the atmosphere. Credit: NASA/JPL/University of Arizona.
Cassini team member Kevin Baines (JPL), who works on the spacecraft’s visual and infrared mapping spectrometer, has this to day:
“This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides. We’ve never seen anything like this on any other planet. Indeed, Saturn’s thick atmosphere where circularly-shaped waves and convective cells dominate is perhaps the last place you’d expect to see such a six-sided geometric figure, yet there it is.”
It’s clear by comparing the results of Cassini’s infrared mapping with what the Voyagers found that the hexagon has remained fixed with Saturn’s rotation rate and axis for the last 26 years. The waning northern hemisphere winter may bring the feature into visual camera range within about two years, helping us get a better read on the rotation rate of Saturn’s deep atmosphere. Whether that will unlock further clues as to the actual rotation rate of the planet remains to be seen.
