All Attempts to Broadcast Our Presence to Nearby Stars Should Be Forbidden

Here you can find a list of when there might be a response to known prior contact attempts within a century, assuming immediate light-speed response, and whether there are known terrestrial planets around the stars. This is incredibly dangerous and reveals the presence of intelligence on Earth to anything that might be listening, and should be immediately stopped (see Stephen Hawking's take on this here.) Granted, astronomers' definition of habitable - "terrestrial planet orbiting in liquid water temperature zone" - leaves a lot to be desired.

Until now. Measurements of terrestrial planets can now show if there is an atmosphere and it contains hydrogen, oxygen, and N2, making at least some water quite likely (Konatham et al 2020.)

We can update the list of stars where we've already broadcast contact attempts, with these new stricter criteria. There are two planets with atmospheres and likely water that we have deliberately broadcast to: Teegarden's Star, a red dwarf (with two planets with likely water), with a response possible by 2036; and GJ273b (Luyten's Star), with a super Earth with likely water, responding at earliest 2043.

Two facts to modify our enthusiasm:

• Both are red dwarfs, which have a habit of flaring. However, Luyten's Star is quiet by these standards.
• Also, aliens looking at our solar system using the same definition would keep both Mars and Venus on this stricter habitable list. Both do have atmospheres and some water.

Proxima Centauri is the closest star but in this more-strict list of habitable planets, but we haven't deliberately targeted it. It's worth pointing out that even if there were a twin Earth there, we still wouldn't be able to hear them (the C-index - a rule of thumb, assuming that strength of a civilization's emissions and ability to detect increase in concert.)

(Encouraging to amateurs: Teegarden's Star was discovered by a group of non-professional astronomers poring over data online, without access to telescopes.)

Konatham S, Martin-Torres J, Zorzano M. Atmospheric composition of exoplanets based on the thermal escape of gases and implications for habitability. Published:09 September 2020https://doi.org/10.1098/rspa.2020.0148

Unexpected Ejection of Material from Asteroid Bennu

Of obvious interest to any panspermia hypotheses, especially those which favor replicators (Von Neumann probes or otherwise) using organics on low-gravity bodies as building blocks. Paper here. Abstract:

In early 2019, the OSIRIS‐REx spacecraft discovered small particles being ejected from the surface of the near‐Earth asteroid Bennu.sww Although they were seen to be ejected at slow speeds, on the order of tens of cm/s, a number of particles were surprisingly seen to orbit for multiple revolutions and days, which requires a dynamical mechanism to quickly and substantially modify the orbit to prevent re‐impact upon their first periapse passage. This paper demonstrates that, based on simulations constrained by the conditions of the observed events, the combined effects of gravity, solar radiation pressure, and thermal radiation pressure from Bennu can produce many sustained orbits for ejected particles. Furthermore, the simulated populations exhibit two interesting phenomena that could play an important role in the geophysical evolution of bodies such as Bennu. First, small particles (less than 1 cm radius) are preferentially removed from the system, which could lead to a deficit of such particles on the surface. Second, re‐impacting particles preferentially land near or on the equatorial bulge of Bennu. Over time, this can lead to crater in‐filling and growth of the equatorial radius without requiring landslides.

McMahon JW, Scheeres DJ, Chesley SR, French A, Brack D, Farnocchia D, Takahashi Y, Rozitis B, Tricarico P, Mazarico E, Bierhaus B, Emery JP, Hergenrother CW, Lauretta DS. JGR Planets. Dynamical Evolution of Simulated Particles Ejected From Asteroid Bennu. First published: 18 May 2020 https://doi.org/10.1029/2019JE006229

San Francisco 2020 With Blade Runner 2049 Score

H/T Mr. Black