It’s up… Carnival of Space #77 at Tomorrow Is Here Blog…
…Paul Gilster scooped me with a better discussion piece on the Benfords’ papers. I chucked in a comment about my favourite star HD 157881 or Gliese 673 as it is otherwise known. In 1990 – according to an interview I saw on an ABC Science Doco in 1992 – a Western Australian radio telescope picked up a really strong signal (like the “Wow!” signal of 1978) from Gliese 673 but didn’t get another ‘scope on it before it faded. According to the Benfords that’s exactly what we should expect from economically practical beacons. Not saying it really was a signal from ETIs, but it’d be so cool if it was. The star itself is a K7V, with an absolute visual magnitude of 8.1 and an effective temperature of 4020 K. A planet could easily exist in its habitable zone – the extended habitable zone of James Kasting, not Michael Hart’s ultra-tight hab-zone that is.
Addendum
Data on stars to 30 parsecs (about 100 ly) can be found HERE… and our star in question is #76 in Tables 1 & 2 (dwarf Main Sequence stars). According to their computations the Teff is 4115 K – for “cool” stars it’s really hard for computations to get closer than ~100 K working from different empirical formulae. The luminosity is ~0.11, so the HabZone is between 0.32 AU and 0.64 AU. Tidally locked planets have issues keeping an even temperature, so how far out does an Earth-sized planet have to be to avoid tide-lock? For the Sun it’s about 0.5 AU. Assuming stellar mass is ~1/4 power of the luminosity we get ~ 0.58 Msol for GJ 673. The tide-lock scales to the 1/3 power of the mass, thus ~0.41 is the new tide-lock radius, which HD 157881 dodges neatly. It really could host an exo-earth with ETIs… could…
At 25.2 ly away that’s 50.4 years round trip for signalling. Since high-powered RADAR were used extensively during the “Battle of Britain” in 1940 what’s the minimum time-span for ETIs to signal back with what they received? Just like Ron Bracewell first suggested – send back the signal you receive to get noticed. Well 1940 plus 50.4 is… 1990!
