by Paul Gilster | Apr 15, 2008 | Astrobiology and SETI |
Larry Klaes tackles the METI question — do we intentionally broadcast to the stars? — in Athena Andreadis’ Astrogator’s Logs today, looking at the pros and cons of an issue that continues to bedevil the scientific community. Of METI advocate Alexander Zaitsev (Russian Academy of Science), for example, Klaes writes this:
In a paper Zaitsev published in 2006, the scientist notes that “SETI is meaningless if no one feels the need to transmit.” Zaitsev also feels that if there are advanced cultures bent on harming humanity, they will find us eventually, so it is in our best interests to seek them out first. Zaitsev sees the great distances between stars and the physical limits imposed by attempting to attain light speed serve as a natural protective barrier for our species and any other potentially vulnerable beings in the galaxy.
David Brin among others takes the other side of the debate in an article tuned for newcomers to these issues. And that’s an important audience. Most scientifically literate people know that we are listening for signals from extraterrestrial civilizations, with varying thoughts on the possibilities for success. But many don’t yet realize that powerful messages have already gone out, not only the Arecibo signal of 1974, but more recent broadcasts from the Evpatoria planetary radar site in the Crimea, and NASA’s Deep Space Network facility in Spain. The more public awareness the issue can generate, the better for balanced discussion.
by Paul Gilster | Apr 15, 2008 | Deep Sky Astronomy & Telescopes |
The death of a star fifty times more massive than our Sun may well result in a hypernova, far more powerful than a supernova and, if you’re in line with the concentrated beam of its energies, far more luminous. Such events are hypothesized to be associated with long-duration gamma ray bursts (GRBs). We’ve just had a spectacular example of an apparent hypernova/GRB combination in the form of GRB 080319B, the record-holder for brightest naked eye object ever seen from Earth.
The image shows the fading light of this event as seen by the Hubble spacecraft on April 7. Bear in mind that the flash of gamma rays and other radiation was detected on March 19, at which point the GRB could be viewed at 5th magnitude in the constellation Boötes. The kicker is that a full three weeks after the explosion, the light of the galaxy in which this event originated is still drowned out by the light of the GRB.
Image: The gamma ray burst GRB 080319B leaves us with an optical remnant and a puzzle. What forces drive an explosion of this size, still glowing halfway across the visible universe? Credit: NASA, ESA, N. Tanvir (University of Leicester), A. Fruchter (STScI), A. Levan (University of Warwick), and E. Rol (University of Leicester).
Could such an explosion happen right here in our own galaxy, possibly threatening life on Earth? Probably not, according to Andrew Fruchter (Space Telescope Science Institute) and colleagues. Back in 2006 Fruchter’s team published work in Nature studying the environment of 42 long-duration bursts and 16 supernovae with Hubble. They were able to show that most long-duration GRBs occurred in small, irregular galaxies of the kind usually deficient in higher elements. Gamma ray bursts like this are therefore unlikely to occur in galaxies like the Milky Way. Fruchter noted the significance of the find:
“The discovery that long-duration gamma-ray bursts lie in the brightest regions of their host galaxies suggests that they come from the most massive stars – 20 or more times as massive as our Sun. Their occurrence in small irregulars implies that only stars that lack heavy chemical elements tend to produce long-duration GRBs.”
The implication is that long-duration events like GRB 080319B happened more often long ago, when galaxies were largely lacking in such elements. An accompanying theory is that a massive star rich in heavy elements loses too much material through its own stellar wind to house the mass needed to trigger a long-duration burst. The collapse of such a star might lead to a neutron star rather than a black hole, with no accompanying jet. So our own galaxy is unlikely to see an explosion like this one in the future, but we still have much to learn about the factors at work in keeping this particular afterglow so bright.
The 2006 paper is Fruchter et al., “Long gamma-ray bursts and core-collapse supernovae have different environments,” Nature Vol. 441 (2006), pp. 463-468 (available online).
by Paul Gilster | Apr 14, 2008 | Asteroid and Comet Deflection |
Do we have a good idea how many impact events have affected life on Earth? New work on ocean sediments offers the chance to expand our knowledge, helping to flag the distinctive signature of an impact and even to tell us how large the incoming object was. We may find more historical impacts than have previously been identified, reminding us yet again that our habitable zone is an active and sometimes dangerous place to be.
True, the issues involved in mass extinctions are complicated, but major impacts clearly played a role in some, including the death of the dinosaurs. François Paquay and team estimate the impactor that struck 65 million years ago at the Cretaceous-Tertiary (K-T) boundary was between four and six kilometers in diameter. While other factors, including volcanism, can’t be ruled out, the meteorite certainly didn’t help matters.
Paquay (University of Hawaii at Manoa) analyzed samples of ocean sediments to study osmium levels therein. The element is useful because, as this news release explains, meteorites carry a distinct osmium isotope ratio that differs from that normally found in Earth’s oceans. Read properly, the osmium levels can provide a record of ancient impacts:
“The vaporization of meteorites carries a pulse of this rare element into the area where they landed,” says Rodey Batiza of the National Science Foundation (NSF)’s Division of Ocean Sciences, which funded the research along with NSF’s Division of Earth Sciences. “The osmium mixes throughout the ocean quickly. Records of these impact-induced changes in ocean chemistry are then preserved in deep-sea sediments.”
The critical issue is to verify how the impact changes the osmium levels, which is why Paquay has been focused on samples from the late Eocene, itself the time of the extinction event called the Grande Coupure, which may have been affected by impacts in Siberia and Chesapeake Bay. In any case, the period is known to have been marked by a number of impacts and thus offers the opportunity to observe the osmium signature related to these. Such studies led to the estimates of the K-T boundary event and may uncover the signs of previously unknown strikes.
The paper is Paquay et al., “Determining Chondritic Impactor Size from the Marine Osmium Isotope Record,” Science Vol. 320, No. 5873, pp. 214-218 (April 11, 2008). Abstract available.
by Paul Gilster | Apr 12, 2008 | Culture and Society |
The 49th Carnival of Space is up at Will Gater’s site, and this week I’ll point you in particular to Alan Boyle’s entry on black hole simulations. The mathematics of black hole collisions are not for the faint of heart, but the Rochester Institute of Technology’s supercomputer cluster seems up to the task, even if the work demanded a week to complete. Interesting stuff, as an actual triple black hole collision as simulated here should generate gravity waves of the sort being sought by the Laser Interferometer Gravitational Wave Observatory (LIGO). But LIGO scientists need to know what to look for amidst the incoming tsunami of data, which is where supercomputer modeling comes into play. Boyle’s presentation of this work is thorough and, as always, admirably clear.
There are actually not one but two space carnivals at play this week, the other being Fraser Cain’s at Universe Today. But rather than drawing on already written weblog entries, Fraser solicited comments from bloggers on a key question: What is the value of space exploration? Numerous writers weighed in. Here’s Robert Pearlman from collectSPACE:
Many of the problems we have on Earth are rooted in a our need for new ideas. From medical advancements to political diplomacy, it often takes a new perspective to find the answer. Space exploration offers the rare opportunity to look inwards while pushing out. The photographs sent back of the Earth as a “fragile blue marble”, a whole sphere for the first time, gave birth to the environmental movement. Astronauts, regardless of their home nation, have returned to Earth with a new world view, without borders. But the perspective isn’t limited to those who leave the planet. When Neil Armstrong and Buzz Aldrin walked on the Moon, “mankind” took on a new appreciation for all of humanity. It was “we” who went, even if “we” were not living in the United States. That sense of unity was recognized by the Apollo 11 crew upon their return to the planet: Buzz turned to Neil and commented, “We missed the whole thing…”
Nicely put. The whole collection is worth keeping for those times when you know you’re about to be challenged on why we don’t just keep ‘all that money’ here on Earth (this seems to be the theme of numerous dinner parties I’ve attended lately). The problem with rationales for the space program is that those of us who come up with them all tend to agree on them in the first place, while the general public is a much harder sell, as I am reminded every time I talk about preserving the species by building the infrastructure needed to divert incoming asteroids or comets. The lesson, I suppose, is keep trying, which is what these writers do day after day in their own weblogs, and more power to the attempt.
by Paul Gilster | Apr 11, 2008 | Astrobiology and SETI |
Although I suspect that intelligent life is rare in the cosmos, I’m playing little more than a hunch. So it’s interesting to see that Andrew Watson (University of East Anglia) has analyzed the chances for intelligence elsewhere in the universe by looking at the challenges life faced as it evolved. Watson believes that it took specific major steps for an intelligent civilization to develop on Earth, one of which, interestingly enough, is language. Identifying which steps are critical is tricky, but in the aggregate they reduce the chance of intelligence elsewhere.
A linguist at heart, I wasn’t surprised with the notion that the introduction of language marks a crucial transition as intelligence develops. But what are the other steps, and how do they feed into the possibility of life elsewhere? These interesting questions relate to how long the biosphere will be tenable for life as we know it. If, as was thought until relatively recently, Earth might support life for another five billion years, we would have emerged early in the history of our biosphere. But it is now believed that in perhaps a billion years, the era of complex macroscopic life will be ending, the victim of decreasing CO2 and increasing temperatures.
Startlingly, we’re faced with the fact that the Earth’s biosphere is even now in its old age. Here’s Watson’s take on the matter:
The question of the future life span of the biosphere has relevance to estimates of the likelihood that complex, perhaps intelligent, life evolves on a given planet. At present, Earth is the only example we have of a planet with life, and the fact that our own existence depends on Earth having developed complexity and intelligence introduces an anthropic “self-selection” bias into our sample of one… If we learned that the planet would be habitable for a set period and if we had evolved early in this period, then even with a sample of one, we might suspect that this suggested evolution from simple to complex and intelligent life was relatively likely to occur. By contrast, however, it is now believed that we evolved late in the habitable period; this suggests that our evolution is a comparatively unlikely occurrence.
The model Watson analyzes assumes that on planets where intelligence arises, its evolution is governed by the need to pass through a number of critical transitions, each of which are unlikely to occur in the time available. Critical steps might be events like the transition from unlinked replicators to chromosomes, or the differentiation of the eukaryotic kingdoms of plants, animals and fungi in the late Proterozoic. A number of essential evolutionary steps are suggested, the common thread being that they all involve increases in structural and genetic complexity.
An alternative to the critical step model would suggest that the evolution of intelligence is simply long and slow. The problem with that idea is our old friend Fermi, whose paradox would force us to ask why we see no signs of intelligent activity around us in the cosmos. For intelligence under the alternative model should have evolved on planets somewhat older than ours, whereas if the critical step model is right, then the passage through the steps becomes a tremendous roadblock to intelligence. The transition from biogenesis to observerhood is tightly constrained.
Why? Back to Watson, who uses the lottery analogy, explaining that each step in the process conditions what follows:
In terms of the lottery analogy, we need to condition our observations on winning not just the lottery of biogenesis, but several subsequent lotteries as well, in which tickets are only issued to those who have won in the previous round. In such a model, the constraint on absolute probability given by an early win in the first round becomes rapidly less useful as further rounds are added.
Is evolution a predictable movement toward intelligence? Watson doubts it:
There are numerous examples where complex traits have apparently been lost from organisms, and the question of whether increases in complexity are in fact any more intrinsically likely than decreases remains unresolved… From the perspective adopted here, this appearance of evolution as a monotonic “progress” toward ourselves results from “anthropic self-selection bias”… In this case, there is no need to postulate any directionality to evolution; and, in general, the kind of outcome seen on Earth may be vanishingly unlikely.
That, of course, has major implications for what we might expect to find around other stars. Vanishingly rare intelligence is the result of the evolutionary lottery taken through its repeated cyclings, and it’s noteworthy that in this model, even where intelligence does arise, it comes late in the history of the planet on which it appears. Thus civilizations find themselves in senescent biospheres, surrounded by other systems that may have some forms of life, but probably not intelligence.
The paper is Watson, “Implications of an Anthropic Model of Evolution for Emergence of Complex Life and Intelligence,” Astrobiology Volume 8, No. 1 (2008).
