The thread on active SETI — broadcasting messages from Earth in a targeted way to other star systems — has been an active and fruitful one. Unfortunately, I’m getting a few reports that recent attempts to post new comments haven’t been successful. This may involve a size limit on comments to a single post; in any case, I haven’t yet figured it out. So to continue any comments on the active SETI thread, please use the comment area for this post. And let me know if you have any problems posting, or if any comments you make don’t appear.
In the meantime, if any of you have any knowledge of size limits on WordPress comments to individual posts, please let me know. Sometimes software seems more mysterious than the interstellar realm; at least, it does to me after spending a couple of hours this morning trying to figure out what was going on in the depths of WordPress. My spam filter’s behavior is also under active investigation.
The disks of gas, dust and debris that surround young stars are breeding grounds for planets, a premise that every new exoplanet detection seems to confirm. But we know little about the disks themselves, and a key area of uncertainty continues to be the nature of disks around stars more massive than the Sun. What effect, for example, does their luminosity have on the disk, and how do the processes of large star formation affect planetary systems?
The European Southern Observatory’s Very Large Telescope is providing data that will shape a more refined view of these disks. At the heart of these new studies is HD 97048, a star some 600 light years away in the stellar spawning ground known as the Chameleon 1 dark cloud. HD 97048 is two and a half times as massive as the Sun, and fully forty times more luminous, making it ideal for such study.
Image: Artist’s impression of a flared proto-planetary disc, similar to what has been deduced from VISIR observations on ESO’s Very Large Telescope around the 2.5 solar mass star HD 97048. Credit: ESO.
Infrared mapping of this star’s disk with ESO’s VISIR (VLT Imager and Spectrometer for the InfraRed) instrument shows a huge, flared disk, reaching twelve times further than the orbit of Neptune. “This is,” says Pierre-Olivier Lagage (CEA Saclay, France), leader of the team that carried out the observations, “the first time such a structure, predicted by some theoretical models, is imaged around a massive star.”
Unclear of the meaning of the word ‘flared’ in this context, I checked with Dr. Lagage. His answer: “A flared disk is a disk whose thickness increases rapidly when going further away from the star, so that any point at the surface from the disk is in direct view from the star.”
Astronomers on Lagage’s team estimate the disk must contain a large amount of gas, amounting to ten times the mass of Jupiter, and perhaps 50 Earth masses worth of dust. That would make for a dust mass about a thousand times larger than what we’ve yet seen around older stars like Beta Pictoris, Fomalhaut and Vega. Lagage again: “From the structure of the disc, we infer that planetary embryos may be present in the inner part of the disc.”
In other words, the older stars mentioned contain dusty disks filled with debris thought to be the result of larger bodies colliding. We can do measurements on the dust but we have yet to detect the parent bodies that spawned it. Add up the mass of the dust and the presumed bodies that produced it and you get a mass similar to what is being seen around HD 97048. The young star’s disk, then, is simply much less evolved, a precursor for later planet formation.
Follow-up observations using the European Southern Observatory’s VLT interferometer are planned. A report on this work appears as Lagage et al., “Anatomy of a Flaring Proto-Planetary Disk Around a Young Intermediate-Mass Star” in the September issue of Science Express, with abstract available here.
The transit method has now bagged its 13th and 14th planets, both of them ‘hot Jupiters’ so close to their stars that their orbits are two and two and one-half days respectively. That makes for temperatures well over 1800 degrees Celsius, and adds more data points in our improbable collection of massive planets that all but skim their stars as they race around their orbits. One of the new planets, called WASP-1b, is in the constellation Andromeda, and is thought to be 1000 light years distant. WASP-2b, in Delphinius, is some 500 light years away.
Behind the discovery is the UK consortium called SuperWASP — Wide Angle Search for Planets. The astronomers involved are surveying millions of stars from robotic observatories in the Canary Islands and in South Africa. Each observatory uses eight wide-angle cameras, with a field of view 2000 times greater than a conventional astronomical telescope. The goal is to detect the faint dimming of starlight that flags a planetary transit, visible in the ‘light curve’ of stars with a clear transit. In the case of WASP-1b and WASP-2b, the discoveries were later confirmed by radial velocity measurements.
Image: The transit detection process. As the planet passes in front of the star it produces a characteristic ‘light-curve’ whose shape is affected by the size and orbital distance (and hence orbital period) of the planet. SuperWASP constantly monitors the brightness of the stars in its field of view and alerts astronomers to any variations that may be due to the presence of a planet. Credit: SuperWASP.
I see that the SuperWASP team is still working with 2004 data (although its Web site doesn’t make it clear when the data on these new planets were gathered), but they seem to have enough interesting light-curves to feel confident that their transit effort will produce big results. The work was announced at the Transiting Extrasolar Planets Workshop at the Max Planck Institute for Astronomy in Heidelberg on September 26. The paper, available as a preprint, is Cameron et al., “WASP-1b and WASP-2b: Two new transiting exoplanets detected with SuperWASP and SOPHIE,” which has been submitted to the Monthly Notices of the Royal Astronomical Society.
An operating run at Fermilab involving the Tevatron, the world’s highest-energy particle accelerator, has produced an experimental result of extraordinary precision, one that has measured transitions between matter and antimatter that occur three trillion times a second. Tevatron Run 2, from February of 2002 to January of this year, produced trillions of collisions between protons and antiprotons to achieve the discovery, a measurement sought for two decades.
Making the fast change is the B_s meson (pronounced B-sub-s), whose behavior is predicted by the Standard Model that describes our understanding of fundamental particles and forces in the universe. The finding thus reinforces that model in the world of the exquisitely small. The B_s meson is made up of a bottom quark bound by the strong nuclear interaction to a strange antiquark. These exotic particles, present in abundance in the early universe, can only be produced and studied at particle accelerator installations like Fermilab’s.
Earlier measurements of the matter-antimatter transitions in the B_s meson did not reach the level of accuracy of this latest work, in which the probability for a false observation has been shown to be less than about eight in 100 million. And the discoveries from this impressive run of data may not be over yet:
“Everyone in Fermilab’s Accelerator Division has worked hard to create the number of collisions that were required to reach this impressive result,” said Fermilab Director Pier Oddone. “We’re glad that CDF has been able to put these efforts to such good effect. This is one of the signature measurements for Run II, and as we collect several times the data already on hand, I have great expectations for future discoveries.”
CDF refers to the Collider Detector at Fermilab collaboration, an experiment in high energy particle collisions that involves 700 physicists from 61 institutions in 13 countries. MIT’s Christoph Paus presented the discovery in a talk at Fermilab on Friday September 22; a paper on this work has been submitted to Physical Review Letters.
Centauri Dreams‘ take: The behavior of exotic particles like the quarks under study and their interactions with matter and antimatter may tell us a good deal about how the early universe evolved. It may also push physics into a more complete Standard Model, and that, in turn, should help us understand just how matter and antimatter are entwined. The sense here is that for breakthroughs in antimatter production to occur — and for propulsion purposes we must hope some day they will — they must emerge with the underpinning of work like CDF’s, which may yet tease out phenomena the Standard Model does not predict.
Centauri Dreams admits to troubling new doubts about a variant of SETI called METI — Messaging to Extraterrestrial Intelligence. The notion, also known as ‘active SETI,’ is backed by some members of the SETI community and is especially strong in Russia. Its premise is that rather than listening passively for signs of extraterrestrials, we should actively try to achieve contact through messages of our own. This would constitute a ‘brightening’ of our civilization in the radio sky, making us more noticeable by many orders of magnitude.
A number of intentional signals besides the famous Arecibo message of 1974 have already been sent. The so-called ‘Cosmic Call 1’ message was transmitted from the Evpatoria Planetary Radar site in the Crimea in 1999, targeting four Sun-like stars and sending an overview of terrestrial life written in a code called Lexicon. Cosmic Call 2, sent to five Sun-like stars, followed in 2003. Based on the target list and the distances involved, the window for a possible response to these messages opens in sixty years.
Is this a good idea? We are only beginning to have some understanding of how many planetary systems are out there and to learn about the properties of their largest planets. Knowing what we know now about the tenacity of life on Earth even in the most extreme environments, and knowing that there may well be Earth-like worlds in solar systems throughout the galaxy, we face the real possibility of alerting other civilizations to our presence before we know anything whatsoever about them. This may or may not prove dangerous, but it seems like something that deserves wide discussion.
But the conversations now going on in the SETI community focus on the work of a small committee of the International Academy of Astronautics (IAA), one chaired by the SETI Institute’s Seth Shostak. You may know of this committee from its earlier work, as it developed the so-called ‘First SETI Protocol’ that outlines a rational response to the detection of an extraterrestrial intelligence. Such protocols are highly productive, for they bring the scientific community together before such a paradigm-changing event can occur, allowing for a thoughtful look at the issues and encouraging debate.
But there is a second protocol under discussion, one that asks METI proponents to hold back from deliberate transmissions until their plans can be examined in open gatherings by a broad community of experts in various disciplines. What is now under debate is whether such restraint is sensible or simply represents a paranoid response to a non-existent threat. The IAA meeting this October in Valencia may well ratify a protocol that accepts METI transmissions without requiring any further discussions to occur.
It is striking to me that there is only one science fiction author — astrophysicist David Brin — on the IAA committee that will decide these things. I would argue that writers like Brin, Gregory Benford, Greg Bear and others have spent years pondering the possibilities of interstellar contact and its ramifications. Their contribution would broaden this debate, which seems from my perspective to be focused on a tightly defined group of SETI proponents whose work could nonetheless have serious repercussions for the human future.
It would be useful to find out what readers think about this issue. Some have argued that it is already too late, that the broadening sphere of our radio and television transmissions is already well past numerous star systems and in any case cannot be called back. But such signals are far less visible than the beacon-like effects contemplated by some proponents of active SETI. METI proposes a genuine change in tactics, one that seems to cry out for sustained and highly visible debate before we raise Earth’s visibility.