by Paul Gilster | Sep 25, 2007 | Deep Sky Astronomy & Telescopes |
By Larry Klaes
Tau Zero journalist Larry Klaes here offers a look at a revolutionary telescope that will soon take our vision of the universe into new domains.
In the early half of the next decade, an instrument called the Cornell Caltech Atacama Telescope (CCAT) is planned to examine the Universe through a less-studied region of the electromagnetic spectrum from an observatory in the remote deserts of Chile higher than any current major ground-based facility.
CCAT is the culmination of plans by Cornell University and the California
Institute of Technology (Caltech) initiated in 2004 to jointly conduct submillimeter astronomy with the largest telescope ever conceived for such an endeavor. The 25-meter (82-foot) wide mirror of the CCAT will allow astronomers to see the Cosmos in the area between the infrared and radio realms of the electromagnetic spectrum, an area well beyond the region that is visible to human eyes.
The moisture in Earth’s atmosphere normally blocks light waves coming at our planet from the submillimeter region. This is why CCAT will be built at 18,400 feet atop a dormant volcano named Cerro Chajnantor in Chile’s Atacama Desert. This region of South America is so dry and desolate that robotic Mars rovers have been tested there to approximate conditions on the Red Planet – nearly ideal for a telescope studying the submillimeter wavelengths.
Among the celestial objects astronomers want to study in this realm are
galaxies, especially the ones which formed not long after the Big Bang which created our Universe 13.7 billion years ago, and stars in our Milky Way galaxy with encircling debris disks that may be forming new planets. Even icy bodies in the Kuiper Belt of our outer Solar System will be explored by CCAT to understand how Earth and our neighboring worlds came to be five billion years in the past.
Image: An artist’s rendering of the proposed Cornell Caltech Atacama Telescope that will be built in the Cerro Chajnantor in the Atacama Desert region in Chile. Credit: Cornell University/CCAT.
CCAT will also investigate the mysterious dark matter that makes up the vast majority of the mass in the Universe. Understanding what this material is and how it interacts with clusters of galaxies is of paramount importance to science. The telescope will also look at the equally mysterious dark energy that is apparently causing our reality to expand at an ever-increasing rate.
What will become of our Universe as the galaxies recede from each other is another major goal of understanding for science. For example, the vast islands of stars we call galaxies formed from major clouds of dust and gas. Radiation from these new galaxies was absorbed by all the dust and later re-emitted at longer wavelengths on the electromagnetic spectrum. The radiation was “stretched” to even longer wavelengths as the Universe expanded and galaxies moved further apart from each other until it reached Earth in the submillimeter range. Until recent years and advances in technology, this wavelength was mostly invisible to ground-based telescopes due to its absorption by the aforementioned water that permeates our atmosphere.
The current crop of smaller submillimeter telescopes observe objects in
space a few hundred pixels at one time. CCAT, operating thirty times faster and with a mirror twice as large as its brethren, will observe tens of thousands and eventually millions of pixels at once, creating a clearer picture in the submillimeter realm of the denizens of our Cosmos than ever before.
Complementing CCAT is what will become a collection of eighty large antennae currently being built two thousand feet below the submillimeter telescope’s projected site on Cerro Chajnantor. The Atacama Large Millimeter Array (ALMA) is an interferometer to be operated as a public facility by the National Radio Astronomy Observatory (NRAO) to study the Universe in spectra that include the submillimeter. ALMA will make highly detailed maps of particular regions of space. An image made by CCAT will cover an area of the sky thousands of times larger. Objects of special interest imaged by CCAT will later be examined by ALMA to discern them in finer detail.
The construction of CCAT is expected to begin next year. The first
observations with the telescope are hoped to begin in 2012, with CCAT
becoming fully operational by 2014, about the same time as ALMA.
For more information on CCAT, go here to read the paper presented at the 18th International Symposium on Space Terahertz Technology.
by Paul Gilster | Sep 24, 2007 | Exoplanetary Science |
Our assumptions about terrestrial planets seem pretty straightforward. We’re only now reaching the level where detecting such worlds becomes a possibility, with advances in ground- and space-based telescopes imminent that will begin to give us an idea how common such planets are. Hoping for the best, we assume Earth-sized worlds in relatively comfortable places are common and even extend our search from G and K-type stars to the much dimmer (and more numerous) M-dwarfs.
But what do we mean by a terrestrial planet? Size is an obvious criterion, but so is placement in the kind of habitable zone we would find conducive to our kind of life. That means liquid water at the surface. So far so good, but keep a sharp eye on the wild card in all this: Orbital ecccentricity. It’s a measure of how far the orbit of a planet deviates from a circle, and we need to know more about it. Obviously a highly eccentric orbit could swing a planet through the habitable zone and right back out again, never allowing a stable and benign environment for life to develop.
Many of the planets already discovered show fairly eccentric orbits. A short but intriguing paper by Daniel Malmberg (Lund Observatory, Sweden) and team now asks a provocative question: Is there a mechanism that ensures high values of orbital eccentricity, and if so, what does it tell us about planet formation in other solar systems? The assumption is that because most stars form in clusters, close encounters between young stars are fairly common. And that poses real problems.
For one thing, the orbits of planets in a given system could be profoundly altered by a close stellar pass, with some of them being ejected entirely. The planets remaining would then be left with significantly more eccentric orbits. A major question to ask is whether our Sun has ever had such a close encounter with another star. If not, that could explain the nearly circular orbits we see in our Solar System, and might also have something to do with the placement of the more massive planets far from the Sun, not the scenario in many of the exoplanetary systems we’ve examined.
These considerations mean that planetary systems that were once much like ours have been made into the kind of systems we have often observed, with planets on orbits so eccentric as to make the emergence of life problematic at best. Consider, for example, what can happen when a single star encounters not just one other star but a binary system:
If a single star instead encounters a binary system, it can be exchanged into it. When this occurs, the orientation of the orbital plane of the planets with respect to that of the companion star is completely random. This means that in about 70 per cent of the cases, the inclination between the two will be larger than 40?. When that happens, the Kozai Mechanism will operate… Given that the binary is not too wide, the Kozai Mechanism will cause the eccentricities of the planets to oscillate. If the planetary system contains multiple planets, this eccentricity pumping can cause strong planet-planet interactions, causing the orbits of the planets to change signi?cantly and sometimes also ejecting one or more planets.
If so-called ‘singletons,’ formed singly and with no history of close stellar interactions, are the only places where Solar Systems like our own can form, we have placed a constraint on habitable terrestrial worlds. How much of one? We begin by ruling out a vast range of multiple star systems. As to solitary stars with Sun-like masses, the authors have numerically simulated a range of stellar clusters like those in which our Sun formed. They conclude that five to ten percent of all planetary systems around such stars have been altered by dynamical interactions as well, most likely to the detriment of life’s chances there.
A history of isolation, then, may play a role in the habitability of any terrestrial world around a Sun-like star. But note: The ‘if’ in the above paragraph is called into question by a good deal of recent work on the stability of planetary orbits in binary systems. The paper is Malmberg, Davies et al., “Is our Sun a Singleton?” to be published in the proceedings of IAUS246 “Dynamical Evolution of Dense Stellar Systems” (abstract).
by Paul Gilster | Sep 22, 2007 | Culture and Society |
Apropos of our recent speculations about planets without stars, this short podcast from Earth & Sky discusses dark planets within our galaxy able to sustain life, at least for a while. The scenario, developed by John Debes (Carnegie Institution) and Steinn Sigurðsson (Pennsylvania State): A planet with a large moon passes near a giant world like Jupiter. The team’s simulations show the Earth-moon system ejected into interstellar space, with the possibility of a thick atmosphere and large tidal forces keeping the place warm for more than a hundred million years.
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ESA’s latest backgrounder on the Don Quijote candidate mission lays out a plan to rendezvous with an asteroid and orbit it, monitoring its shape, mass and gravitational field. A second spacecraft would then be sent to impact the asteroid at about 10 km/s, while the first vehicle monitors the result, looking for changes in the asteroid’s trajectory. Mission planners have considered oft-mentioned Apophis as one of several potential targets. Even if approved, Don Quijote wouldn’t launch until early in the next decade. The recent impact in Peru reminds us of the need to learn more about space debris, though Tunguska left a far starker testament.
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Anticipating the next generation of ground and space-based telescopes, astronomers convene at the Astrophysics in the Next Decade conference on September 24 in Tucson. The rapidly expanding pace of exoplanetary investigation will only be accelerated as equipment ranging from the European Extremely Large Telescope to the James Webb Space Telescope comes online, not to mention what we’ll learn from earlier space missions like Kepler. We may know within the next twenty years (via spectroscopic studies) whether one or more terrestrial exoplanets are likely candidates for life. Ironically, the demonstration of such may well come before we know for sure whether places much closer to home, like Mars or Europa, are themselves life-bearing.
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HD 74156 becomes the eighth star known to be orbited by three or more planets, thanks to recent work using data from the Hobby-Eberly Telescope. The star is a G0 some 65 parsecs from the Sun, its two previously discovered planets being 6.2 and 1.9 Jupiter masses respectively. The lower mass world is known to be in a short-period orbit (51.7 days), the larger in a much wider 2477 day orbit. The new planet has an orbital period of 347 days and a minimum mass of 0.4 Jupiter masses; all three orbits show significant orbital eccentricity. The paper is “Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope,” accepted by The Astrophysical Journal (abstract).
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Imagine Isaac Newton working with a slightly different apparatus than the one he used to study the nature of light. Here’s Astounding/Analog editor John Campbell on the matter, as found recently on Crowlspace:
Literally, by a hairline Newton missed the spectroscope. Had he used a slit, the spectrum of the Sun would have been bright colors crossed by mysterious black bands and lines. He could not have left that mystery untouched. He would have found that sodium thrown on a candlewick would produce bright-yellow lines matching exactly two powerful dark lines in the mysterious solar spectrum. Calcium would have given him red lines, copper and other metals…
The result: A jump start on basic chemistry and spectroscopy. Would Newton, discovering the absorption lines in the spectrum go on to influence others to deliver the goods on distant planetary atmospheres? If so, as Adam Crowl speculates, a possible downside might have been a slowdown in the birth of spaceflight, the Solar System early on being seen as devoid of life. A fascinating speculation indeed.
by Paul Gilster | Sep 21, 2007 | Deep Sky Astronomy & Telescopes |
Speaking of absorbing views from a planetary surface, as we’ve been doing recently when discussing the Magellanic Clouds and what an observer there might see of the Milky Way, consider a much darker scenario. A galaxy called ESO 137-001 is in headlong flight toward the center of the galactic cluster Abell 3627. It is leaving in its wake a trail of gas that extends for more than 200,000 light years and is forming stars.
Bear in mind that the Milky Way itself is 100,000 light years across and you’ll get an idea of the magnitude of this tail, which Michigan State’s Ming Sun calls one of the longest of its kind his team has ever seen. Millions of stars have now come to life in the tail, apparently forming within the last ten million years. Adding to optical studies are Chandra X-ray data that show additional regions thought to be star-bearing.
Give these stars a few billion years to produce planets bearing intelligent life and you have a civilization coming into its own with skies that would be, by our standards, remarkably dark. The day will come when the gas that has produced the orphan stars is completely stripped from its parent galaxy, stopping further star formation, and the stragglers will be left out on a very long limb indeed.
Image: The comet-like tail behind the galaxy ESO 137-001 is clearly shown in this Chandra X-ray Observatory image. The 70,000 light year long tail was created as gas was stripped from ESO 137-001 while it plunges toward the center of Abell 3627, a giant cluster of galaxies. Cool gas from the galaxy – only seen in optical images – is mixed in with hot gas from the cluster as seen in X-rays. Credit: X-ray: NASA/CXC/MSU/M. Sun et al.; Optical: SOAR (MSU/NOAO/UNC/CNPq-Brazil)/M.Sun et al.
Thus we look at the inverse of the famous Isaac Asimov story ‘Nightfall.’ The good doctor postulated a planet in a system with six suns, keeping the surface always illuminated save for one day every 2049 years. Astounding‘s John Campbell proposed the story to Asimov by citing a Ralph Waldo Emerson quote: “If the stars should appear one night in a thousand years, how would men believe and adore and preserve for many generations the remembrance of the city of God!” Asimov took the idea and ran, producing one of science fiction’s classic works.
I’m not aware of a fictional equivalent to the situation postulated by the straggler stars of ESO 137-001, but there may be more orphans than we think. If, as some believe, galactic tails were not uncommon billions of years ago in an era of richer star-forming materials, then there may be hosts of planets experiencing the deep darkness of intergalactic space. We’ll know more about that idea when the paper on this work appears in The Astrophysical Journal, an event slated for December.
by Paul Gilster | Sep 20, 2007 | Astrobiology and SETI |
Tau Ceti has always been an interesting star, one of two (the other being Epsilon Eridani) that Frank Drake chose as targets for his pioneering Project Ozma SETI observations. The astrobiological interest is understandable. We’re dealing with a Sun-like star relatively close (11.9 light years) to Earth. But recent thinking downplays Tau Ceti as a potential home for life. Ponder this: The dust disk around the star seems vastly larger than what we find in our own Kuiper Belt, with deadly implications.
Or are they? Let’s look more closely. A model of Tau Ceti’s disk shows that the mass of small objects up to ten kilometers in size may total 1.2 Earth masses. Compared to our Kuiper Belt’s 0.1 Earth masses, this is one massive disk, with ten times the amount of cometary and asteroidal material found in our own system. This despite the fact that Tau Ceti seems to be twice the age of Sol. You might reasonably assume that any Earth-like planet in this system has been bombarded far more often than Earth itself.
Image: Does severe bombardment rule out intelligent life around Tau Ceti? Hint: Be careful what assumptions you bring to bear. Credit: PPARC/David Hardy.
The question is whether this is a valid indicator, another feather in the cap of those who favor the ‘rare Earth’ hypothesis. The reasoning, as Milan ?irkovi? (Astronomical Observatory of Belgrade) points out in a recent paper, would go something like this: Our Earth was hit by an object just large enough to kill off the dinosaurs (or, at least, to assist in their destruction), the Chicxulub impact of some 65 million years ago.
A little larger and even the mammals might not have survived. Smaller and the mammals might not have become ascendant. Here’s how ?irkovi? puts it:
…micrometeorites bombard Earth all the time, and larger particles create beautiful meteor showers apparently without threatening the biosphere or in any known way influencing the evolutionary processes. On the other hand, studies of early history of the Solar System suggested that collisions with bodies hundreds of kilometers in size remaining at that epoch had caused repeated meltdown of the entire planetary crust and perhaps even complete atmosphere blow-off…Thus, only a finite — and quite small—range of impactors at the fixed epoch of K-T boundary could have caused the evolution of modern humans.
Our emergence as an intelligent species, then, seems predicated on the Chicxulub strike being of a rather precise size. But as the author points out, we must be cautious about this ‘fine-tuned catastrophism.’ Rather than saying that our emergence is contingent upon a particular type of impact (and thus a vanishingly rare occurrence), we should be saying that our emergence in the present epoch is contingent upon that impact.
And that has wide implications. For what we are now doing is removing a bit of anthropocentrism from our thinking. We simply cannot know what forms of life might have emerged had the Chicxulub impact occurred at a different time, or been of a different magnitude. ?irkovi? goes on to apply Bayesian methods to the question of our understanding of catastrophic risk. Interestingly, we tend to underestimate the chances of catastrophe:
It is intuitively clear why: the symmetry between past and future is broken by the existence of an evolutionary process leading to our emergence as observers at this particular epoch in time. We can expect a large catastrophe tomorrow, but we cannot — even without any empirical knowledge — expect to find traces of a large catastrophe which occured yesterday, since it would have preempted our existence today.
This is interesting stuff, noting our reliance on Earth-specific records that cannot be translated into analysis of catastrophe in other systems. And its look at observation-selection effects leads to the conclusion that only continued astrobiological study will help us understand what biospheres and potentially intelligent communities might be out there, on Tau Ceti or elsewhere in the Milky Way. The author’s conclusion: “No amount of armchair theorizing can escape the observation selection effects related to the evolutionary development of intelligent observers on Earth.”
Life amidst the debris around Tau Ceti? Maybe so. This is a short but densely argued paper; I’ve only managed to summarize a subset of its major points. For more, the reference is ?irkovi?, “Evolutionary Catastrophes and the Goldilocks Problem,” accepted for publication in the International Journal of Astrobiology (abstract).
