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2 hours ago, DShomshak said:

As the article notes, the probe would be moving so fast that the crash would create an explosion of nuclear intensity. Nothing could survive that!

 

(Except maybe a cosmically-irradiated tardigrade-turned kaiju.)

 

Dean Shomshak

... That is irate. An irate ingrate irradiated tardigrade kaiju.

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I actually looked into it a bit more. I only knew about their Resistance from Micheal Burnham. But apparently that was based in reality. You think Cockroaches inherit the earth? Only if they manage to kill the Tardigrades first!

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Tardigrades (/ˈtɑːrdɪˌɡrd/; also known colloquially as water bears, space bears, or moss piglets)[2][3][4][5] are water-dwelling, eight-legged, segmented micro-animals.[2][6] They were first discovered by the German zoologist Johann August Ephraim Goeze in 1773. The name Tardigrada (meaning "slow stepper") was given three years later by the Italian biologist Lazzaro Spallanzani.[7] They have been found everywhere: from mountaintops to the deep sea and mud volcanoes;[8] from tropical rain forests to the Antarctic.[9]

Tardigrades are one of the most resilient animals known.[10][11] Individual species of tardigrades can survive extreme conditions that would be rapidly fatal to nearly all other known life forms, including complete global mass extinction events due to astrophysical events, such as supernovae, gamma-ray bursts, or large meteorite impacts.[10][11] Some tardigrades can withstand temperatures down to 1 K (−458 °F; −272 °C) (close to absolute zero) while others can withstand 420 K (300 °F; 150 °C)[12] for several minutes, pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space.[13] They can go without food or water for more than 30 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce.[3][14][15][16] Tardigrades, living in harsh conditions, undergo an annual process of cyclomorphosis.[further explanation needed]

They are not considered extremophilic because they are not adapted to exploit these conditions. This means that their chances of dying increase the longer they are exposed to the extreme environments,[7] whereas true extremophiles thrive in a physically or geochemically extreme environment that would harm most other organisms.[3][17][18]

Usually, tardigrades are about 0.5 mm (0.02 in; 19.69 thou) long when they are fully grown.[2] They are short and plump with four pairs of legs, each with four to eight claws also known as "disks".[2] The first three pairs of legs are directed ventrolaterally and are the primary means of locomotion, while the fourth pair is directed posteriorly on the terminal segment of the trunk and is used primarily for grasping the substrate.[19] Tardigrades are prevalent in mosses and lichens and feed on plant cells, algae, and small invertebrates. When collected, they may be viewed under a very low-power microscope, making them accessible to students and amateur scientists.[20]

Tardigrades form the phylum Tardigrada, part of the superphylum Ecdysozoa. It is an ancient group, with fossils dating from 530 million years ago, in the Cambrian period.[21] About 1,150 species of tardigrades have been described.[22][23] Tardigrades can be found throughout the world, from the Himalayas[24] (6,000 m; 20,000 ft, above sea level) to the deep sea (−4,000 m; −13,000 ft) and from the polar regions to the equator.

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

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5 hours ago, Christopher said:

I actually looked into it a bit more. I only knew about their Resistance from Micheal Burnham. But apparently that was based in reality. You think Cockroaches inherit the earth? Only if they manage to kill the Tardigrades first!

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

 

Pfft. Bacteria still have them stone cold. Tardigrades do alright for big critters, but as the late, great Stephen Jay Gould always used to point out, we are still in and always have been in the Age of Bacteria. By any measure they are the dominant life form on Earth (variety, biomass, numbers, resilience etc).

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

 

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Not sure that "more stable" is really the right term.

 

I've never heard of tidal locking where the satellite has any tilt at all. I think the effects that result in tidal lock tend to result in the same end result (i.e. satellite rotates with the same periodicity as its orbit).

 

But happy to hear from qualified astronomers, physicists and/or planetary scientists.

 

Edit:

You may also have tidal locking that's in other ratios than 1:1 - Mercury is in a 3:2 spin/orbit resonance

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

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11 hours ago, mrinku said:

I've never heard of tidal locking where the satellite has any tilt at all. I think the effects that result in tidal lock tend to result in the same end result (i.e. satellite rotates with the same periodicity as its orbit).

 

I had to do a bit of library searching to find this, but when synchronous rotation develops, the orientation of the spin axis also undergoes a forced change.   Exactly what happens depends on what other masses are in the system and where those are.  I have found decent discussions of this only in papers dealing with known systems with more than two bodies, for example Earth's Moon (considering the Earth-Moon-Sun system) and the satellite system of Jupiter (the planet plus three or four of the Galilean satellites).  For Earth's Moon, there are small but constant-in-magnitude-but-not-direction differences between the orientation of the Moon's spin axis and the orientation lines perpendicular to Moon's orbit around Earth and Earth's orbit around the Sun.  Put another way,  the spin axis and the normal to Moon's orbit plane around Earth precess around the normal to Earth's orbit around the Sun, and the three are always coplanar.

 

If the moon were perfectly spherically symmetric, or fluid, then the orbit also would be driven to circular.  But with a solid and rigid body, it may end up in a state close to but distinctly and persistently different from circular.  This is true, e.g., for Earth's Moon, which has an orbit eccentricity around Earth of 0.055 (compare the eccentricity of Earth's orbit around the Sun, 0.0167, a perfect circle is exactly zero).

 

The most comprehensible discussion of this that I've found is in one chapter (chapter 19, "Europa" by Chyba and Phillips) of a team-written book Planets and Life, edited by Sullivan and Baross, published 2007 by Cambridge U Press.  While some chapters from that book can be found separately and downloaded for free, I haven't found this one in that form.  It's written as a graduate-level textbook for students coming from a variety of disciplines, which means it's a bit more approachable.  See if you can find it in a library.

 

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19 hours ago, mrinku said:

Edit:

You may also have tidal locking that's in other ratios than 1:1 - Mercury is in a 3:2 spin/orbit resonance

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

I've designed a couple planets in 3:2 resonance, ever since I read about it in a book on SF world-building. I never had a chance to use them in games, though.

 

What I find cool: Very long day/night cycle leads to extreme temperature swings. I imagine ecosystems radically changing through the day and night as different creatures emerge or go into hibernation as their preferred temperature range comes and goes. Also, frickin' enormous tides, since the planet is so close to its star, such that the shape of continents might change through the day. (The ecosystem change might be especially pronounced in the intertidal zone, if the vast sweep of water in and out doesn't scour them too severely.)

 

Oh, and earthquakes. Lots of earthquakes. And the sun seeming to change speed, reverse direction, and otherwise behave in a far more complicated way than we experience on Earth. So much potential for strangeness.

 

Dean Shomshak

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The Dec. '17 issue of Discover has a couple articles relating to the Kuiper Belt. One is about the little Kuiper Belt object that's the next port of call for the New Horizons space probe. The other is about Pluto and Ceres. A few planetologists wonder if there's a connection: Ceres isn't much like other asteroids, what with its unusually large mass and evidence that it has a lot of ice under the surface. These guys suggest that if you took Pluto, moved it to the asteroid belt and let the nitrogen, methane and other volatiles evaporate, you'd end up with something like Ceres. This could have happened early in the Solar System, when the planets were shuffling around. As Uranus and Neptune's orbits move outward (and maybe switched), a lot of the icy outer planetesimals were scattered outward to become Pluto and the rest of the Kuiper Belt; but some surely would have been scattered inward, too.

 

Dean Shomshak

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[url=https://www.nature.com/articles/nature25020]More on that interstellar visitor[/url] (could well be behind a subscriber wall)

 

From the abstract:

Quote

Here we report observations and subsequent analysis of 1I/2017 U1 (‘Oumuamua) that demonstrate the extrasolar trajectory of ‘Oumuamua. Our observations reveal the object to be asteroidal, with no hint of cometary activity despite an approach within 0.25 au of the Sun. Spectroscopic measurements show that the object’s surface is consistent with comets or organic-rich asteroid surfaces found in our own Solar System. Light-curve observations indicate that the object has an extreme oblong shape, with a 10:1 axis ratio and a mean radius of 102±4 m, assuming an albedo of 0.04. Very few objects in our Solar System have such an extreme light curve. The presence of ‘Oumuamua suggests that previous estimates of the density of interstellar objects were pessimistically low.

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