by James Benford We recently looked at a paper by Duncan Forgan and Robert Nichol on the question of detecting extraneous emissions from an extraterrestrial civilization using technology like the Square Kilometer Array. James Benford (Microwave Sciences) has some thoughts on the issue growing out of his own work with brother Gregory on interstellar beacons and SETI reception in general. No one has put the question of interstellar beacons to tighter scrutiny than the Benfords, with particular regard to bringing the SETI discussion, as Jim puts it, "onto a quantitative basis, as opposed to rampant speculation, as is typical of the playing-tennis-without-a-net approach taken previously." The Benfords' work on interstellar beacons appears this month in Astrobiology. I give full citations at the end of this post. The Forgan & Nichol paper on detection of leakage radiation does neglect our continuing use of microwave beams not only for radar, but also for likely future beaming of power for...

Take a look at the frequency range of our SETI searches and you'll see that we are probing into new territory. Project Phoenix, which ran from 1995 to 2004, used radio telescopes at Arecibo, Parkes (NSW, Australia) and Green Bank (WV, USA), working in a frequency range of 1.2 to 3 GHz. The BETA project used a 26-meter radio telescope to examine the so-called 'waterhole' frequencies between 1400 and 1720 MHz, which seemed a likely place to look for an extraterrestrial beacon because this range covers an unusually quiet band of the electromagnetic spectrum between the hydrogen spectral line and the strongest hydroxyl line. With the Allen Telescope Array coming online, we can look forward to a search of 250,000 stars in the 'waterhole' region, but new facilities like LOFAR (Low-Frequency Array) are pushing into the megahertz area in pursuit not only of SETI but also astrophysical studies of the early universe. LOFAR makes me think back to my shortwave radio days, tuning around these...

We often speak in these pages about extinction events, and cite such examples as the Cretaceous-Tertiary event some 65.5 million years ago, when the mass extinction of dinosaurs and numerous animal and plant species occurred. Whether caused by an incoming asteroid or comet or through a series of catastrophes including volcanic eruptions (the Deccan traps), the K-T event is the classic reminder of the perils that confront life. But perhaps the largest extinction event of all was the so-called 'oxygen catastrophe,' an environmental change that caused oxygen to become widely available in the atmosphere and shallow ocean water. The oxygen catastrophe occurred around 2.4 billion years ago and doomed the bulk of Earth's anaerobic inhabitants. Astrobiologists are fascinated with how life adapts to changing environments, so we'd like to learn much more about how these events proceeded. Now comes news of fossils in black shale formations in Africa that are apparently 200 million years older...

Are planets common around brown dwarfs? We aren't yet in a position to say, but the question is intriguing because some models suggest that the number of brown dwarfs is comparable to the number of low-mass main sequence stars. That would mean the objects -- 'failed' stars whose masses are below the limit needed to sustain stable hydrogen fusion -- could be as plentiful as the M-dwarfs that far outnumber any other type of star in the galaxy. If planets form around brown dwarfs, then we have to add them to our list of possible abodes for life. Evidence for Brown Dwarf Planet Formation But first, to the planet question. We can find suggestive analogs to planet formation around brown dwarfs in nearby space. The star Gl 876, some fifteen light years away, is not a brown dwarf, but this M-dwarf is only 1.24 percent as luminous as the Sun, with most of its energy being released at infrared wavelengths. We now know that at least three planets, two of them gas giants similar to Jupiter,...

Long-term thinking means planning for the consequences of things that are beyond our current capacity. What happens on the farside of the Moon is a case in point. Getting humans back to the Moon is going to happen sooner or later, and one day we will have bases there, as well as a human or robotic presence at the L4 and L5 Lagrangian points of the Earth-Moon system. That means an ever growing blanket of electromagnetic radiation from our various activities. At the same time, we want to protect the farside, which is ideal for future radio telescope or phased array detectors. What to do? Italian physicist Claudio Maccone has brought this issue to Vienna, speaking before the United Nations Committee on the Peaceful Uses of Outer Space. Maccone is proposing a radio-quiet zone on the farside that will guarantee radio astronomy and SETI a defined area in which human radio interference is impossible. It's an idea with a pedigree, going back to 1994, when the French radio astronomer Jean...