Jim Benford's study of 'lurkers' -- possibly ancient probes that may have been placed here by extraterrestrial civilizations to monitor our planet's development -- breaks into two parts. The first, published Friday, considered stars passing near our Sun in the lifetime of the Solar System. Today Dr. Benford looks at the Drake Equation and sets about modifying it to include the lurker possibility. Along the way, he develops a quantitative way to compare conventional SETI with the strategy called SETA -- the search for extraterrestrial artifacts. Both articles draw on recently published work, the first in JBIS, the second in Astrobiology. The potential of SETA and the areas it offers advantages over traditional SETI argue for close observation of a number of targets close to home. by James Benford Introduction “To think in a disciplined way about what we may now be able to observe astronomically is a serious form of science.” –Freeman Dyson I propose a version of the Drake Equation for...

Jim Benford is continuing his research into the still nascent field known as SETA, the Search for Extraterrestrial Artifacts. A plasma physicist and CEO of Microwave Sciences, as well as a frequent Centauri Dreams contributor, Benford became intrigued with recent discoveries about Earth co-orbital objects -- there is even a known Earth Trojan -- and their possibilities in a SETI context. If we accept the possibility that an extraterrestrial civilization may at some point in Earth’s 4.5 billion year history have visited the Solar System, where might we find evidence of it? Two papers grew out of this, one in Astrobiology, the other in the Journal of the British Interplanetary Society (citations below). In the first of two posts here, Jim explains where his work has led him and goes through the thinking behind these recent contributions. by James Benford Part 1: How Many Alien Probes Could Have Come From Stars Passing By Earth? 1. Searching for Extraterrestrial Artifacts Alien...

Just how useful is oxygen as a biosignature? It’s a question we’ve examined before, always with the cautionary note that there are non-biological mechanisms for producing oxygen which could make any detected biosignature ambiguous. But let’s go deeper into this, thanks to a new paper on ‘oxygen false positives’ out of the University of California at Santa Cruz. The paper, produced by lead author Joshua Krissansen-Totton and team, offers scenarios that can place an oxygen detection in the broader context that would distinguish any such find as biological. Let’s begin with the fact that in addition to its obvious interest because of Earth’s history, photosynthesis involving oxygen requires the likely ubiquitous carbon dioxide and water we would expect on habitable zone planets. Helpfully, oxygen should be readily detectable on exoplanets because of its absorption features, which are prominent not only in visible light but in the near infrared and thermal infrared, if we include ozone....

Interesting news out of CNRS (the French National Center for Scientific Research) renews our attention to the mechanisms for supplying the early Earth with water and carbonaceous molecules. We've looked at comets as possible water sources for a world forming well inside the snow line, and asteroids as well. What the CNRS work reminds us is that micrometeorites also play a role. In fact, according to the paper just out in Earth and Planetary Science Letters, 5,200 tons of extraterrestrial materials -- dust particles from space -- reach the ground yearly. Image: From the paper's Figure 1, although not the complete figure. The relevant part of the caption: Fig. 1. Left: Location of the CONCORDIA station (Dome C, Antarctica). Centre: View of a trench at Dome C. Credit: Rojas et al. This conclusion comes from a study spanning almost twenty years, conducted by scientists in an international collaboration involving laboratories in France, the United States and the United Kingdom. CNRS...

Let's take a look at how Earth's carbon came to be here, through the medium of two new papers. This is a process most scientists have assumed involved molecules in the original solar nebula that wound up on our world through accretion as the gases cooled and the carbon molecules precipitated. But the first of the papers (both by the same team, though with different lead authors) points out that gas molecules carrying carbon won't do the trick. When carbon vaporizes, it does not condense back into a solid, and that calls for some explanation. University of Michigan scientist Jie Li is lead author of the first paper, which appears in Science Advances. The analysis here says that carbon in the form of organic molecules produces much more volatile species when it is vaporized, and demands low temperatures to form solids. Moreover, says Li, it does not condense back into organic form. "The condensation model has been widely used for decades. It assumes that during the formation of the...

I've used the discovery of 'Oumuamua as a learning opportunity. I knew nothing about the Local Standard of Rest (LSR) when the analysis of the object began, but soon learned that it measured the mean motion of interstellar materials in the Milky Way near the Sun. The Sun moves clockwise as viewed from galactic north, with an orbital speed that has been measured, through interferometric techniques, at 255.2 kilometers per second, give or take 5.1 km/s. Invoking the LSR in this connection calls for a quote from Eric Mamajek (JPL/Caltech) in his paper "Kinematics of the Interstellar Vagabond 1I/'Oumuamua (A/2017 U1)" (abstract here): 'Oumuamua's velocity is within 5 km/s of the median Galactic velocity of the stars in the solar neighborhood (<25 pc), and within 2 km/s of the mean velocity of the local M dwarfs. Its velocity appears to be statistically "too" typical for a body whose velocity was drawn from the Galactic velocity distribution of the local stars (i.e. less than 1 in 500...