Innumerable as the Starrs of Night,
Or Starrs of Morning, Dew-drops, which the Sun Impearls on every leaf and every flouer Milton |
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Impearls | ||
NGC3132 © |
Beauty is truth, truth beauty,
— that is all Ye know on earth, and all ye need to know. Keats
E = M
Energy is eternal delight.
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What wailing wight
© Copyright 2002 – 2009
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Impearls: 2009-07-19 Archive Earthdate 2009-07-20
As a Board member of the Friends of the U.C. Santa Cruz Library, I was invited this year to assist in judging UCSC's annual Graduate Research Symposium, in which the university's graduate students present personal or poster presentations concerning their thesis research for prestige, prizes, and trophies.
The winner of this year's entire event was a female graduate student, Javiera Guedes of the Astronomy and Astrophysics department at UCSC, who presented a talk on “The Earths of Alpha Centauri,” concerning the likelihood that both principal stars of the binary Alpha Centauri system possess planets, which we should be able to start discovering (as detection technology has steadily improved, and given a determined search) within the next several years.
I wrote up a brief report on Guedes' talk for a mailing list, only to be subsequently invited by editor Kevin Langdon (also endorsed by Javiera) to expand that piece for the Mega Society's online journal Noesis's upcoming special issue on Astronomy and Space.
University of California at Santa Cruz astronomy and astrophysics graduate student Javiera Guedes (first author), together with her coauthors, have published a fascinating piece in The Astrophysical Journal titled the “Formation and Detection of Terrestrial Planets around α [Alpha] Centauri B” 1 — which in my view deserves far wider audience and consideration than it can receive in that journal, however prestigious and renowned a scientific journal it assuredly is. The subject of that paper, the binary Alpha Centauri star system (also known as Rigil Kentaurus or Toliman), at some 4.4 light years (or about 1.3 parsecs) distant from the Sun, is the closest extrasolar stellar system to our own Solar System and Earth. The brightest star in that system Alpha Centauri A is quite similar to our Sun in mass (at ∼1.105 solar masses), and extremely similar in color and thus temperature (classed like the Sun as a spectral type G2 V, a so-called “yellow dwarf”), whilst its companion Alpha Centauri B is only slightly smaller (∼0.934 times the Sun's mass) and a bit redder and therefore cooler (spectral type K1 V) than the Sun. One might note that the Alpha Centauri system (at about 5.6–5.9 Gyr) is between 1 and 1.3 billion years older than our Sun and Solar System, while it's about half again as rich in “metals” (as astronomers regard them: i.e., elements heavier than hydrogen and helium) as our own system. Though it has a third, much smaller (∼0.1 solar mass) spectral type M “red dwarf” companion star known as Proxima Centauri — swinging at an enormous distance (perhaps a fifth of a light year) away from its principals — however ignoring Proxima, Alpha Centauri is essentially a close binary star system; and thus one might imagine that Alpha Centauri's two principal stars A and B's gravitational interference on each other would forestall prospects for any stable planets circling either star. As it happens, however, those primary components of Alpha Centauri are not actually all that close, orbiting each other some 23 astronomical units (23 times the distance between the Earth and the Sun, abbreviated AU) apart from each other — equivalent to B (or A) circling between the orbits of Uranus and Neptune (in our Solar System) with regard to the other — and as a result planets orbiting beyond what would be the orbit of Mars here, up to some 3 AU away from its primary (or well into our asteroid belt) are not ruled out around either star; moreover any planets (if they exist) are computed with high probability to be stable for the requisite billions of years time. Moreover, planets have already been discovered orbiting other roughly similar binary stars (e.g., γ [Gamma] Cephei, HD 41004, and Gliese 86) having basically equivalent separations from each other. Indeed, Alpha Centauri A and B would probably even have performed a positive perturbative role with regard each other's incipient planetary systems, similar to that which the gas giants Jupiter, Saturn, and beyond are thought to have played in planetary evolution here in our Solar System, to wit providing “perturbations allow[ing] for the accretion of a large number of planetary embryos into a final configuration containing 3–4 bodies.” (Note that we omit end-note references in all quotes from The Astrophysical Journal article.) Alpha Centauri B, as a cooler, “quieter,” less variable and flare-prone star than Alpha Centauri A (or the Sun for that matter), as a result is somewhat easier than A to detect any planets circling round. Thus it is on B that the authors concentrate their attention, estimating that after only about three years of “high cadence” observations (watching B on basically every night that there's good seeing, which could be close to 300 days a year), one could detect (using the so-called Doppler or radial-shift detection method) a planet of only some 1.8 Earth-masses circling within B's so-called “habitable zone,” while somewhat smaller worlds ought to become apparent in only a couple of years more. Whilst it's also sometimes possible to detect extrasolar planets by observing their transit (or eclipse) across the disk of their primary star as seen from Earth, that method requires that the plane of any planets' orbits be closely aligned with the direction of our Sun with respect to that system — which is obviously extremely unlikely when attempting to locate worlds circling any particular star — and thus such an approach is suitable only for statistical surveys of a great many stars, not for finding the planets of any specific suns. In addition to evaluating how Alpha Centaurian planets could be observed from the perspective of Earth, the authors conducted a number of computed simulations (eight in all) of possible routes to planetary system formation, starting from initial circumstances “mimic[ing] conditions at the onset of the chaotic growth phase of terrestrial planet formation in which collisions of isolated embryos, protoplanets of approximately lunar mass, dominate the evolution of the disk. During this phase, gravitational interactions among planetary embryos serve to form the final planetary system around the star and clear out the remaining material in the disk. At the start of this phase, several hundred protoplanets were presumed to orbit the star on nearly circular orbits.” Each run of the simulation “populate[d] the disk with N = 400 to N = 900 embryos of lunar mass […].” Simulation number 7 (see Figure 3), specially exemplified herein and in The Astrophysical Journal article (known as r600_1 there), started with 600 embryos. All bodies in the simulations interact only through gravity and the evolution of their positions and velocities with time were calculated using the MERCURY code, designed for the presence of a binary companion and allowing planetary embryos to collide and stick together to form larger planets. The investigators “focus[ed] on terrestrial planet formation around α Cen B […].” As they note, “[P]lanet formation around α Cen A is expected to be qualitatively similar.” Figure 2 illustrates how simulations of the evolution of a planetary system surrounding Alpha Centauri B typically progressed (using simulation 7):
The authors describe the foregoing figure thusly:
Figure 3 illustrates the results of all eight Alpha Centauri B system evolution simulations that the authors performed. The especially illustrated simulation used herein appears as number seven near the bottom, whilst for comparison our Solar System is shown to scale at top.
We see that realistic astrophysical simulations predict that planets surrounding Alpha Centauri B (as well as a similar system circling A) are quite likely. What will it take to actually find such worlds, if they do exist? As noted earlier, due to the extreme unlikelihood of any specific stellar planetary system's equivalent of our “plane of the ecliptic” (the plane in which its planets' orbits generally circle) exactly lining up on edge as seen from Earth, the transit method for detecting extrasolar planets cannot be applied (other than by the remotest chance) for locating worlds orbiting specific suns — leaving only the “Doppler wobble” approach available for finding planets in more particular circumstances. Even for that method to work, the plane of a given star's planetary orbits must not directly face the Sun (i.e., the axis of that plane mustn't be oriented directly toward or away from the Sun), as there has to be some planetary radial velocity toward or away from the Earth for us to detect. Inasmuch as theoretical considerations imply that the orbital plane of planets circling either star of a close binary system should in general be aligned with the orbits of the stars themselves as they revolve about each other — and since in the case of the Alpha Centauri system, its two stars' orbital plane can be observed to be inclined to the line of view from here in the Sol System by a mere 11 degrees (the axis of that plane being almost perpendicular to the line of sight from the Earth) — thus planets circling either A or B are nearly ideal for detection from Earth using the radial-velocity technique. Indeed, as the authors of this study conclude: “α Cen B is overwhelmingly the best star in the sky for which one can contemplate mounting a high-cadence [nightly] search” for extant terrestrial worlds, among other things because “α Cen B is exceptionally quiet, both in terms of acoustic p-wave mode oscillations and chromospheric activity.” They note that “[t]he radial velocity [Doppler] detection of Earth-mass planets near the habitable zones of solar-type stars requires cm s−1 [centimeter per second velocity] precision,” whereas Alpha Centauri A exhibits (rather Sun-like) oscillatory noise on the order of 1 to 3 m s−1 (meters per second), which would effectively swamp attempts to detect planets circling A using near-term technology. Alpha Centauri B, on the other hand, as a fundamentally quieter star, displays peak amplitude noise on the order of 0.08 m s−1 (8 cm/second), which is also far higher in frequency than the periods of any potential terrestrial planets to be detected. As a result, a “focused high cadence approach involving year-round, all-night observations would effectively average out the star's p-mode oscillations.” Observations also reveal that Alpha Centauri B exhibits much less chromospheric variability associated with stellar flares than does A (the former modifying its x-ray brightness only within a factor of two over a couple of years time whilst A could be observably seen to vary by an order-of-magnitude factor of ten). The paper further points out that:
Moreover, Alpha Centauri A and B being so close to each other in space as well as physically similar to one another allows parallel observations of the two stars to reveal concurrent variations which, seen in both, allow identification of systematic artifacts in the observational process, that can thus be filtered out of any meaningful results. Furthermore, as the study notes, the position of Alpha Centauri at about −60° declination in our southern sky is nearly perfect for virtually continuous night-by-night (“high cadence”) observations from two existing vantage points, the Las Campanas Observatory together with the Cerro Tololo Inter-American Observatory, both in Chile, either of which ought to provide up to almost 300 viewing days a year (60 days a year being basically unavailable while Alpha Centauri annually passes behind the Sun, plus a few more days lost as a result of bad weather). Inasmuch as the proportionate density of binary, roughly solar-mass component star systems in this part of the galaxy is only about 0.02 per cubic parsec (1 cubic parsec = ∼35 cubic light years), since at this time the Alpha Centauri system hovers a mere 1.33 parsecs away from us, we're very lucky here in the Solar System having α Cen proceeding so close nearby during this era for us to perform this highly desirable search upon. As The Astrophysical Journal paper concludes: “All these criteria make α Cen B the ideal host and candidate for the detection of a planetary system that contains one or more terrestrial planets.” Indeed, “our current understanding of the process of terrestrial planet formation strongly suggests that both principal components of the α Cen system should have terrestrial planets.” Given that extremely tantalizing possibility, what will it take to find at least those worlds orbiting Alpha Centauri B, if they exist? As the authors make note:
At this point well over three hundred planets have been discovered circling other stars beyond the Sun — all thus far found, due to hitherto operative technical limitations, necessarily being much larger than Earth and thus far from being really terrestrial in type. The Alpha Centauri system offers the opportunity to refine those limits downward towards worlds much closer in size, and thus potentially in habitability, to the Earth. Figures 4 and 5 below illustrate how such a high-cadence search over a period of several years could zero in closer and closer towards identifying any planets of Alpha Centauri B that are truly terrestrial in scale.
As the capability for detecting truly terrestrial-type planets circling round nearby stars approaches, we're on the cusp of an adventure grander by far than Columbus's voyages to the New World or other great discoveries of the age of exploration, not only for its tremendous scientific value (finding what variety of worlds so-called “terrestrial” planets can form, not to speak of the enormous significance of possibly discovering other independently evolved organisms inhabiting them), but also for the sake of the future history of mankind, along with the ultimate fate of all life dwelling on — but presently restricted to this single egg-basket of — our planet Earth. In a discussion such as this of potential planets circling the component stars of the Alpha Centauri system, special recognition is due the late biochemist and most prolific science fiction and fact writer Isaac Asimov, for it was he who, just a half-century ago (in June, 1959), penned his far-sighted essay “The Planet of the Double Sun” 2 concerning the possibility of just such worlds existing. A quarter-century later, in 1985 he wrote another essay on the subject of life near Alpha Centauri called “The Double Star&rdquo 3; whilst in 1976 Asimov published an entire book on Alpha Centauri, The Nearest Star. 4 In regard to the intrinsic value of such planets, it's worth noting the ending of Asimov's affecting science fiction novel The End of Eternity 5, which serves as the introduction to his famous Galactic Empire and Foundation series of stories. In the context of this tale, when it is realized that ready access to the universe is at hand for humanity (provided they take a critical step, namely make a certain change to the past), the principal protagonist wonders aloud what good it would really do if they should indeed accomplish it:
Whereupon his erstwhile enemy, more recent ally, and soon to be spouse replies:
Now, on the cusp of the fortieth anniversary of mankind's (as representative of all life on Earth) first visit in all the billions of years history of Earthly life to another planet, it's time to get on with it.
Let's find those worlds!
Glossary
Acknowledgments and References
Many thanks to talented astronomy and astrophysics graduate student Javiera Guedes for her support and suggestions as well as permission to use the figures (indeed her own modifications to one of the figures) from her and her coauthors' article in The Astrophysical Journal. One might note that Ms. Guedes herself will personally be conducting observations of Alpha Centauri later on this year. Kudos to her and the other investigators in this study, and best wishes in the great search! 1 J. M. Guedes, E. J. Rivera, E. Davis, and G. Laughlin (all at the University of California at Santa Cruz, Astronomy and Astrophysics department), E. V. Quintana (SETI Institute, Mountain View, CA), and D. A. Fischer (San Francisco State University, Physics and Astronomy department), “Formation and Detection of Terrestrial Planets around α Centauri B,” The Astrophysical Journal, Vol. 679, Issue No. 2 (2008), pp. 1581-1587; doi: 10.1086/587799. 2 Isaac Asimov, “The Planet of the Double Sun,” The Magazine of Fantasy and Science Fiction, 1959-06, Mercury Press, New York. Collected in Fact and Fancy, Doubleday & Co., Garden City, NY, 1962; also in Asimov on Astronomy, Anchor Press, Garden City, NY, 1975. 3 Isaac Asimov, “The Double Star,” American Way, American Airlines, 1985-09-03. Collected in The Dangers of Intelligence And Other Science Essays, Houghton Mifflin, Boston, 1986. 4 Isaac Asimov, Alpha Centauri, The Nearest Star, Lothrop, Lee & Shepard Co., New York, 1976. 5
Isaac Asimov, The End of Eternity, Doubleday & Co., Garden City, NY, 1955, p. 187.
UPDATE: 2009-07-19 19:40 UT: Version 2: Updated via suggestions from Javiera Guedes. UPDATE: 2009-07-28 06:00 UT: Version 3: At the time of submission for publication in Noesis. UPDATE: 2009-08-03 19:00 UT: Version 4: Further updates to the Noesis publication version, including adding the Glossary. UPDATE: 2009-08-04 15:30 UT: Version 5: A few corrections. UPDATE: 2009-08-05 03:40 UT: Version 6: Minor fix. Labels: Alpha Centauri, Apollo 11, Apollo Program, astronomy, extrasolar planet, planet Impearls: 2009-07-19 Archive Earthdate 2009-07-04
Fourth of July, 2008, aboard the W.W. II aircraft carrier the U.S.S. Hornet There was concern arriving in the area that day that it would be thoroughly socked in (and thus cold and dreary) with San Francisco's famous fog, but even though great tongues of fog had pushed via the considerable onshore breeze some distance to the north and south of the U.S.S. Hornet's permanent home (at the Naval Air Station on the island of Alameda, California, along the eastern shore of San Francisco Bay) — and while the city of San Francisco to be seen across the bay was almost completely enveloped in it, fortunately however the day actually experienced in the environs of the Hornet itself was beautifully sunny; though with the typical stiff cold onshore breeze emerging out of that fog bank (I wore an overcoat and was glad of it, many others there that day did too). (In these shots, as usual, simply click on an image to link to a substantially larger version of it….)
Even considering that there are much more substantial (and nuclear-powered) aircraft carriers operating these days, it's still amazing seeing, not to speak of hoofing it from one end to the other and back again (several times) on, this historic old warship: basically several city blocks' of artificial territory placed end-to-end, several high decks deep bearing huge aircraft-carrying elevators, mounting massive engines (wish I could have seen them), thereafter set afloat to steam as an artificial steel island mounting a powerful mobile naval airfield (the pinnacle in military technology during its heyday) round the world's oceans and seas. Impressive isn't the word for it.
The U.S.S. Hornet (CV-12) had an illustrious career. Its namesake predecessor, the seventh American Hornet (CV-8), fought in the Pacific war's desperate turning-point Battle of Midway, afterwards going down to the bottom in the Battle of Santa Cruz later in 1942. Launched in 1943, its replacement, the eighth, now Essex-class Hornet, the instance before us, as the ship's museum web site notes, accomplished the following:
“A HERITAGE OF EXCELLENCE” is the ship's creed:
The Hornet's extensive resume is also presented graphically within the carrier's high-rising hanger deck:
The kind of extreme action the Hornet and its sisters and kin experienced during World War II makes fond illusions about a “quagmire” in the present war in Iraq seem badly misplaced (especially now that the war there is winding down and nearly won). [Written in July of 2008; now of course that prognosis has simply been confirmed by an additional year's events.]
After such notable and terrific service during World War II, the Hornet entered into a second life during the fifties and sixties (performing antisubmarine-warfare carrier duty during that period, for instance), then directly supporting the Gemini and Apollo Moon program, ultimately retrieving the first two expeditions to visit surface of the Moon — Apollos 11 and 12 — from the sea, following their fireball return to this planet.
Following their return from visiting the surface of the Moon, the Apollo astronauts spent a preplanned few weeks in a quarantine facility, as a precaution against the very remote eventuality that some dread malady could have been acquired by the astronauts during their visit to the (with little doubt) sterile surface of the Moon. As expected there was no such contagion.
It looks like a modified “Airstream” trailer, actually — I wonder if that's what NASA did? (A fellow can be seen examining a display of a moon rock just in front of the entrance.)
In the relaxed atmosphere of the Hornet's hanger deck (where the hectic though pleasant vibes of the band up atop the flight deck seemed far away), Kids enjoyed playing at hamming it up on the Hornet's flag-draped stage — while their doting parents oftentimes stood out in the “audience” videotaping them against the starry-striped backdrop. As a result of various instances of blurred motion, one can see that no was flash used anywhere during this visit to the Hornet — even in quite low-light situations — though the Panasonic DMC-FZ8 camera employed does possess a built-in flash, which generally works adequately well. Didn't turn out too bad, I'd have to say, though in retrospect I might have used the flash on a couple of occasions (such as for the fireworks -- just joking; actually what the fireworks could have used was turning off autofocus, while setting manual focus to infinity; along with mounting the camera on a tripod.)
For those occupying the stern end of the great aircraft carrier's hanger deck, folks enjoyed a relaxing (if bracing) view overlooking San Francisco Bay….
Thereafter, whilst angling through various narrow passageways and clambering up and down steep ship's stairs aboard the old steel warcraft, one closely encounters the antiaircraft cannon glimpsed from dockside before….
Ah, just the thing for an American gun-lover's back (or maybe front) yard! That ought to deal with all those naggling drive-by shootings! (/attempted humor) One might note that in the recent U.S. Supreme Court decision issued just the other day concerning the Constitution's Second (gun rights) Amendment, all nine Justices (including those appointed by liberal presidents) affirmed (with some variance from the majority 5-4 opinion concerning the extent of resulting legal protections, but unanimously as to) the basic individual rights interpretation of the original intent of the American founding fathers in composing the Second Amendment. As a result, the “collective rights” interpretation — whereby for decades legal “experts” solemnly intoned that when it said “the right of the people” it really meant “the right of the state(s)” — is now officially dead as a doornail. It is an individual right to keep and bear arms that the U.S. Constitution guarantees — though admittedly (and thankfully) that right does not extend to such things as personal WMD.
Once up on the flight deck, the aircraft carrier's commanding “Island” rises like an arcane metallic crag + treehouse, or vertical mandala, above the flattop “plateau.” (We're viewing the sternward-facing side of the island, opposite the bridge per se. The windowed area visible on this side isn't the ship's bridge proper but rather, I believe, controlled flight operations.) Hanging off the tower above, flags flap, and radar antennae rotate, like watchful eyes. On the left, today, kiosks provide refreshments.
My ex-wife Tamara appears in the shot above, at lower right with her TV production camera, wearing my Ecuadorian poncho for warmth….
The bow of the aircraft carrier's flight deck, at the exact opposite end from where the band was set up, was a bit lonely during the celebration — until, later, the city of Oakland's fireworks commenced, that is!
Ascending into the Island into the Hornet's Bridge, one obtains great views looking down on the flight deck and surrounding terrain….
“Captain James Cook,” er… “Kirk” issues an order on his communicator — “Warp factor eight, Scotty…!” (or should that be, “Full steam ahead!”).
In the bridge, the pilothouse receives some special armor protection, but the outer area, ringed by windows, does not:
Descending from the bridge, the sun was close to setting at that point in the bank of fog, whilst near the stern of the flattop, the band played on….
As the sun set behind the fog bank and lights began coming on across the bay, the final band, the “Unauthorized Rolling Stones” — not a military or marching band, one might note, like the other bands playing that day — finished up its set. As their name implies, specializing in Rolling Stones compositions, and not doing too bad a job on them I'd say, they performed a number of oldies from other groups as well. (I don't recall them doing the Stones' “20,000 light years from home” though, which this ship certainly makes me think of — as an analogy to the “Starship Enterprise” in Star Trek — indeed, there is an in-commission U.S. nuclear-powered aircraft carrier today called the U.S.S. Enterprise ….)
Notice in the background of the last shot above how the Transamerica Pyramid skyscraper pokes up out of the top of the fog bank, above San Francisco's foggy cityscape.
Behind the band, at the stern end of the flight deck facing San Francisco Bay, a remembered flag flaps in the breeze…. Note the number and pattern of stars. This is the 48-star flag that the Hornet fought under during World War II — and in the fifties, during the Korean War.
The evening ended with spectacular fireworks in several directions — except the direction of San Francisco, whose own fireworks were lost in the fog — with just an occasional flash, like distant lightning, visible from that direction. Other points of the compass held greater wonders:
That one kind of looks like a Hubble Space Telescope photo, no? The Orion Nebula….
After that there was nothing to do but join the hour-long traffic jam getting off Alameda island and onto the freeway heading towards home. Labels: aircraft carrier, Alameda, Apollo Program, Fourth of July, San Francisco, San Francisco Bay, US Navy, USS Hornet, World War II
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