There's no known tractable way to solve chess. There's something like 10^120 move orders [0], and no known way to find perfect play without brute-forcing (almost) all of them. Chess engines can't solve to to the end of a game to see which moves are certain to win; they can only explore to a very shallow depth, and evaluate the horizon nodes by very human-like [1] approximate heuristics.

It looks perfect from a human PoV (the best human players have no chance of winning); but there's still an unimaginably large gulf between chess engines and mathematically perfect chess.

[0] https://en.wikipedia.org/wiki/Shannon_number

[1] https://github.com/official-stockfish/Stockfish/blob/master/...

https://chess24.com/en/read/news/chess24-win-moscow-case-ann...

https://www.youtube.com/channel/UCkTCNuQ2mGfW6-SpHpaze_g (direct link to livestream)

If you're looking for live computer engine lines, Steinar Gunderson offers that here, with 38 cores running Stockfish:

http://analysis.sesse.net/

As well as PGN files (live-updated):

http://pgn.sesse.net/

http://spectrum.ieee.org/aerospace/space-flight/titan-callin...

http://descanso.jpl.nasa.gov/seminars/abstracts/viewgraphs/H...

This was an extremely serious bug in NASA/ESA's Cassini-Huygens probe, in the S-band link between Huygens (landing on Saturn's moon Titan) and Cassini (acting as radio relay).

It was a timing bug. There'd be a very high relative velocity between Cassini and Huygens, creating a significant (~2e-5) Doppler shift in the link. This shifted the frequency of the 2 GHz carrier (by 38 kHz). Likewise, it shifted the symbol rate of the 16 kbps bit stream (by 0.3 bps). The second effect was overlooked. On the demodulating end (Cassini), the bit-synchronizer expected the nominal bit rate, not the Doppler-shifted bit rate. Since its bandwidth was narrower than the 0.3 bps Doppler shift, it was unable to recognize frame syncs; this was proven in experiments post-launch. The parameter that set the bitrate was stored in non-modifiable firmware.

As it was when launched, Huygens would be unable to return any instrument data. For some context, this was the only probe that's ever visited Titan, at a cost of about $400 million.

The workaround

[spoiler]

The workaround was a major change in the orbit trajectory of Cassini (a $3 billion probe). Details aside, it set up an orbit geometry with this feature: at the time Huygens was descending in Titan's atmosphere, Cassini would be flying at a ~90° angle to their separation. The relative velocity was still 20,000 kph, but tangential velocity doesn't contribute to Doppler shift.

http://www.cosmos.esa.int/web/gaia/dr1

    ...tidally locked, possibly losing their water and
    atmosphere in tens or hundreds of millions of years.

    Can we directly image the planet from earth?

    1. "The planet/star contrast is 10^-7 " This basically means
    for every 10,000,000 photons from the star, we would measure
    ~ one from the planet.
    
    2. "Current instrumentation using adaptive optics and
    coronography on 10 m class telescopes (like Sphere on VLT or
    Gemini Planetary Imager) aims at achieving a contrast of
    10^-6 to 10^-7 at an angular resolution of 100-200 mas"
    
    3. "The planet has a separation of 38 mas".
    
    4. Therefore with the best planet imagers we cannot
    currently directly image the planet. Our best hope is the
    E-ELT which should have first light in 2024.

http://www.eso.org/public/archives/releases/sciencepapers/es...

(PDF)

    However, there is reason to hope that the even larger
    European Extremely Large Telescope will have enough
    resolution (about 5e-8 radians? hard to tell from their
    official publications)

[0] https://www.eso.org/public/usa/teles-instr/e-elt/e-elt-instr...

[1] https://www.eso.org/sci/facilities/eelt/fp7-elt-pub/wfi_work...

https://en.wikipedia.org/wiki/Proxima_Centauri

    The planet is about 0.05 AU from Proxima Centauri, meaning
    we need an angular resolution of about 1.9e-7 radians to
    even distinguish it from its host star. Is that realistic?

This is why coronagraphs will be so useful.

[0] https://en.wikipedia.org/wiki/Airy_disk#Mathematical_details

[1] a log-log graph shows the envelope is close to inverse-cubic (x^-3)

[2] http://nexsci.caltech.edu/workshop/2016/NIRCam_Planets_and_B...

Proxima Centauri has a luminosity of 0.0017 suns [1], so Earth-like conditions would occur at ~sqrt(0.0017) au = 0.04 au, an apparent angular separation of arcsin(0.04 au / 4.2 light years) = 0.03". JWST wants star-planet separations at least an order of magnitude larger [0], ideally with very hot, infrared-bright planets.

E-ELT should be able to resolve them, according to [2]. Page 7 gives values for a very similar scenario: an Earth-like planet around an M dwarf (like Proxima), 6 pc away (5 times farther), at an angular separation of 0.015" (half as wide). In this scenario, E-ELT could image the star and planet as separate points, and take useful spectroscopic measurements of the planet's light. For it example it could detect a spectral line of oxygen (O2) in 4 hours of exposure time.

[0] http://nexsci.caltech.edu/workshop/2016/NIRCam_Planets_and_B...

[1] https://en.wikipedia.org/wiki/Proxima_Centauri

[2] https://www.eso.org/sci/meetings/2014/exoelt2014/presentatio...

    can it be easily ruled out?

At 2 light years for instance, that spacecraft would trace an apparent ellipse 3.3" in diameter, while Tabby's star (1,480 ly) would be stationary (0.004" parallax). In comparison, the star's apparent disk is just 30 μas wide (0.00003").

At 2 light years for instance, that spacecraft would trace an apparent ellipse 3.3" in diameter, while Tabby's star (1,480 ly) would be stationary (0.004" parallax). In comparison, the star's apparent disk is just 30 μas wide (0.00003").

Comments URL: https://news.ycombinator.com/item?id=12233164

Points: 6

# Comments: 1

https://www.lsst.org/science/solar-system/potentially-hazard...

https://en.wikipedia.org/wiki/Large_Synoptic_Survey_Telescop...

Comments URL: https://news.ycombinator.com/item?id=11950583

Points: 1

# Comments: 0

    ListPlay@ Flatten@ NestList[
       0.996*#& /@ MovingAverage[# ~Join~ {First[#]}, 2]&,
       RandomReal[1.0, {80}], 100]

    If you are the first almost live form, you have plenty of
    time, and can evolved in an environment that has plenty of
    food. Something like the brown goo of Titan, with lots of
    hydrocarbons and other small molecules that you can pick up
    for free.

That's likely generic for pre-biotic environments. Planets don't naturally form redox gradients; if there's a large redox potential, that's reactive chemistry, which will react away to equilibrium over geologic time. It takes work to maintain such a gradient; for example, Earth's oxidizing atmosphere is actively maintained by life. Oxygen is geologically removed from atmospheres, reacting with exposed rock surfaces (oxygen weathering). It takes active expenditure of work (solar energy) to keep it existing.

There is some chemical energy in abiotic planets, but only small amounts, at very low power levels compared to Earth's aerobic biosphere (which eats something like 10^14 watts!). There's photochemistry caused by solar UV light, and there's atmospheric lightning (which is a major player in the Earth's N2 cycle). Most important is geochemical energy; i.e. primordial chemical gradients that aren't yet at equilibrium, because the two reactants are physically separated by rock layers. On Europa for example, a very slow process brings rocks into contact with the ocean, where slow serpentinization reactions can occur: oxidation of Fe++ to Fe+++ by water, with the production of H2. This would be the food source of Europa life, if it's there.

    I think what will really help us to get at a better estimate
    is to answer the question whether there exists life in our
    solar system that evolved independently of that on Earth.

There's no hard reason why another, orthogonal family of life couldn't coexist with DNA/RNA life. We have 10^7 extant species of DNA/RNA life; that's an existence proof that hostile, competing "types" of life can coexist. Suppose we found terrestrial "XNA life" with a biochemistry totally unrelated to anything else, with no possible common origin or lateral gene transfer. Then we would know life on Earth developed independently N >= 2 times, instead of N >= 1. That would change a lot; we could update P(life | Earth-like planet) from the subjective probability range [10^-Graham's number, 1) to something more like [10^-4, 1).

What's really surprising is that this is completely untested! We genuinely don't know if there's "alien" life on Earth, because we don't know how to look for it. There's no black-box tool to approach unknown biochemistry:

    Some have postulated the existence of a 'shadow biosphere'
    on Earth, teeming with life that has gone undiscovered
    because scientists simply don't know where to look. It could
    contain life that relies on a fundamentally different
    biochemistry, using different forms of amino acids or even
    entirely novel ways of storing, replicating and executing
    inherited information that do not rely on DNA or
    proteins. [...] The trick is deciding what to look for and
    how to detect it. The usual way that researchers search for
    new organisms — by sequencing DNA or RNA — will not pick up
    life that does not depend on them.

    ...We could even be oblivious to unfamiliar forms of life
    right under our noses...