# Tag Info

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No habitable zones at all. Consider a habitable zone. It receives enough radiation from its star (or star pair) such that water does not freeze or evaporate. From OP "one habitable zone is deep inside another." I take it that this is the habitable zone of the yellow stars which is deep inside the zone of the reds. The habitable zone of the ...

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I think they'll be okay. Let's start by figuring out what we're up against. Neutron stars can produce high-energy radiation through two means: thermal and non-thermal emission. Thermal emission is just the light emitted by a black body. Young neutron stars that have begun cooling (a couple of years old - younger than this one) have temperatures of $\sim10^6$ ...

17

We can calculate the effect on Earth's orbit by applying conservation of angular momentum. Earth's orbital angular momentum is $$\ell=mvr=mr\sqrt{GM/r}=m\sqrt{GMr}$$ with $M$ the mass of the Sun, $m$ the mass of Earth, $v$ Earth's orbital velocity at any given point and $r$ the distance from Earth to the Sun at any given point. As angular momentum is a ...

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The "Habitable zone" concept becomes "The collection of all habitable orbits" The habitable zone is a simplification depicting 2 circles around a sun (or barycentre of N suns) representing the boundaries on the possible orbits that could sustain life: By defining the red and green circles, all those blue orbits (and infinitely more) are ...

15

Star Lifting Gone Wrong There are very few natural phenomena that are big enough to wipe out a solar system, but also small enough to not kill everyone just a few light weeks away. The only real candidate for this would probably be a nova (not to be confused with a supernova). Smaller novas can cause a star to flare up its energy output somewhere in the ...

13

For a naturally evolving planetary system, it is very unlikely. But if you hire even a novice planetary system engineer, s/he will arrange for you a system with as many planets as you want (more than two, though) so "that, to an observer standing on one of the planets, only the stars themselves seem to be moving along the night sky." The trick is ...

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Boatloads of Uranium! It works for Earth. It can work for your world too! https://en.wikipedia.org/wiki/Decay_heat#Natural_occurrence Naturally occurring decay heat is a significant source of the heat in the interior of the Earth. Radioactive isotopes of uranium, thorium and potassium are the primary contributors to this decay heat, and this radioactive ...

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In general, you want to compare some characteristic thermal velocity $v_{\mathrm{th}}$ of a gas molecule with the escape velocity of the planet. There are different choices you can make, all within a factor of 2 or so of each other. I tend to take $$v_{\mathrm{th}}=\sqrt{\frac{3k_BT}{m}}$$ where $k_B$ is Boltzmann's constant, $T$ is the atmospheric ...

11

No. The moon is simply too small to be useful as a mirror. As you're no doubt aware, moonlight is already reflected light from the sun. Lunar dust is fairly dark, with an albedo of about 11-12%. In other words, about 8/9ths of the light that falls on the moon doesn't reach Earth. With a perfect mirror, you could deliver all of that. The problem is, the moon ...

10

All you need is to flatten the orbits and make them circular The reason total eclipses do not happen more often on Earth is that the orbit of Luna around Earth, and Earth around Sol, are elliptical and inclined. All you need to make eclipses happen more frequently in this configuration is to... Flatten the orbit, make Luna's orbit be in plan with Earth's ...

10

You're doing it wrong First, bear in mind that optics used to be a normal branch of physics where you had to learn all the impossible things you can't do. Now, well, this is by no means the strangest thing I've read recently: Anti-Solar Cells: A Photovoltaic Cell That Works At Night Next, well, if you want to bounce light off the Moon to a point on Earth, ...

9

Without offering any proof for my assertions... Electromagnetic emissions that don't belong. Should your aliens use EM transmissions (optical or radiometric), then it's possible to detect them here on Earth using current tech. After all, we're still detecting both Voyagers, and they're a honking lot further away than Europa. Heat. This one is a little less ...

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Probes! Yeh, Fish suggested this in the comments. But here is a sweet image! This close-up view of the icy surface of Europa, a moon of Jupiter, was obtained on Dec. 20, 1996, by the Solid State Imaging system on board the Galileo spacecraft during its fourth orbit around Jupiter. The view is about 7 miles by 10 miles (11 kilometers by 16 kilometers) and ...

9

how would the red giant binary's habitable zone affect the yellow-dwarf binary's habitable zone? I think you should go with a superposition of the amount of received energy to determine the habitable zone in the system as a whole. Let me explain my reasoning with a simplification: if an habitable zone is defined as the region of space where the total amount ...

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When you get to the scale of "wiping out solar systems" there aren't many phenomena capable of producing power on the insane levels we're talking about. The most likely option is to have a rogue black hole hurtle through the system and rip it apart. Detecting a rogue black hole might be incredibly difficult, as the only thing you can see is the ...

9

This is a great question; I hope I can write a half-decent answer. Some of these points have already been made by others, but I wanted to go into more detail. Atmospheric escape I actually don't think that the atmospheric composition will change significantly, because the solar wind isn't the primary driver of atmospheric escape. Rather, photons - ...

9

Of course it can. You need not look further than out next neighbour outwards. The moons Phobos and Deimos of Mars are distinctly asymmetrical: All that is required is that it is not massive enough to be formed into a globe by its own gravity, the so called hydrostatic equilibrium.

8

Alogrithm outline So like L. Dutch said, if you assume the volume or average density of the planet you can do this. But the volume and average density aren't first principles values-- they themselves depend on the material and composition in a way that I'll describe shortly. As a word of warning-- I'm going to assume you understand calculus for this-- if you ...

7

I think that a planet that can hold an Earth like atmosphere can keep two spherical moons with no big issues. Let's break down your question in sub-problems. First: what is the smallest a body can be while becoming spherical? For a body to become a sphere, it has to have sufficient self-gravity to pull it into a spherical shape. This depends on what the ...

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Jupiter at 0.02AU will lose about 5%-7% via hydrodynamic escape From Wikipedia (source) If the atmosphere of a hot Jupiter is stripped away via hydrodynamic escape, its core may become a chthonian planet. The amount of gas removed from the outermost layers depends on the planet's size, the gases forming the envelope, the orbital distance from the star, and ...

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This is what Hubble can see from Europa, as published by NASA This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position off the limb of Jupiter’s moon Europa. The plumes, photographed by NASA’s Hubble’s Space Telescope Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter. Hubble’s ...

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Give it a really big moon. Or you could have it be a moon (rather than a planet) like Io orbiting a larger planet, though with that option it's liable to be tidally locked which can cause it's own issues. The tidal forces generated by the body orbiting it will push & pull it helping to keep it warm longer. Io is a good example of how it works, the most ...

7

Strangelet Strangelets are fragments of matter made of strange matter. I.E. matter composed by roughly equal numbers of up, down and strange quarks. So, the alien civilization is running an experiment for generating a high-density fuel by exploring the energetic possibilities of quark-gluon plasma. The strange* experiment needs copious amount of power, so ...

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Handwavium, right? Like, lotsa handwavium, but with a plausible mechanism. IK Pegasi is a binary with a secondary 1.15 M☉ white dwarf and A-type main-sequence star primary. They circle each other in a close enough orbit with only 21.72168 days as period. Moreover, the primary is a Delta-Scuti variable, with an actual metallicity ratio of 1.17, about 17% ...

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Regarding, "... would it be more likely picked up by someone with a (big) telescope in their back yard?", the Hubble Space Telescope is among the highest resolution telescopes in existence. According to https://hubblesite.org/contents/media/images/2009/12/2508-Image.html, "Hubble can see details as small as 190 miles (300 km) across on Saturn....

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How does this work? If the core of the star were made of 50/50 matter and antimatter, it would supernova immediately, so we know that's not what's happening. You must have a star that is mostly one type of matter, and is steadily supplied with the other. Lets talk about that. When anti-protons encounter protons they self annihilate and produce gamma rays. If ...

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Why not? We have several examples. Neptune, at 30.1 AU from the Sun has a considerable atmosphere - indeed, it's mostly atmosphere. Its moon Triton also has a bit of an atmosphere, as does Pluto, at an average 38.5 AU.

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We recently had a question very similar to this about a relativistic asteroid impacting the Sun. I made the argument that the asteroid would not survive because the high speed would translate to quite a lot of ablation, as the intense drag forces in the photosphere tore it apart. Even if it penetrated to any reasonable depth, the high temperatures in the ...

6

You could definitely have a longer winter. https://www.windows2universe.org/physical_science/physics/mechanics/orbit/ellipse.html You mandate an orbital period similar to earth and also an irregular orbit, which I take to mean an elliptical orbit. Seasons would definitely depend on how close the planet was to the star. The planet is moving fastest when it ...

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