36 votes
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Why is there so little nitrogen in the Martian and Venusian atmospheres?

Nitrogen, with a molecular mass of 28 atomic mass units, is too light to have remained in Mars's atmosphere. Carbon dioxide, with a molecular mass of 44 amu, could (and does) exist on Mars, but it is ...
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13 votes

Why is there so little nitrogen in the Martian and Venusian atmospheres?

3.5% of all atmosphere in Venus still accounts for more partial pressure of nitrogen than on Earth. Venus has ~90bar pressure at the surface, 3.5% of them are ~3.2 bar nitrogen. Earth has only 0.8 bar ...
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  • 1,770
13 votes
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Do some comets spin? If so, how fast?

Yes, comets spin although measuring it can be tricky due to the coma and outgassing from the nucleus. It's easiest to measure the rotation period when the comet is inactive near aphelion although this ...
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  • 7,135
10 votes

Is there a way to tell the difference between earth andesite from Mars

If this is something that you have found (rather than purchased as a meteorite) the chances are very small that it is a meteorite. Even if it is a meteorite, the chances it's a Martian one are even ...
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10 votes
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How fast is Neptune getting brighter? When was was this first noticed and reported?

TL;DR: There was apparent 11% increase of Neptune brightness during 1980 and 2000. This could be due to multiple reasons. Recent observation suggested the reason to be change in the amount and ...
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  • 3,226
10 votes

Which JWST instrument modes are compatible with observations of the bright trans-Earth planets Mars, Jupiter, and Saturn? Which aren't?

There are approved proposals for Cycle 1 to point the JWST at The Jovian system Jupiter's great red spot Mars Saturn and its moons and rings In those PDFs, they describe exactly what instruments ...
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9 votes

Do gas giants have a core?

Gas giants are believed to have a solid core. They first formed as icy planets, and were heavy enough to accrete hydrogen and helium from the protoplanetary cloud they were in. Saturn, for instance, ...
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9 votes

What is k2, how does it relate to Io's volcanism and how can Juno constrain its value?

It is called Tidal love number. The definition is as follows: In Newtonian gravitational theory, a tidal Love number relates the mass multipole moment created by tidal forces on a spherical body to ...
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8 votes
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How can it be known that Venus does not have plate tectonics?

There's much less data available from Venus. Some data exists. As mentioned in HDE 226868's answer, maps of Venus's surface exist. Like Earth's atmosphere, Venus's atmosphere is transparent to some ...
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8 votes

Caves traced in nine planets of solar system

A key requirement for caves is solid substance: while there may be rock cores inside the giant planets, the rest is liquid or gas. Metallic hydrogen may be solid or liquid in Jupiter, but presumably ...
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7 votes
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Why is Saturn invisible in this radar image of its rings?

The main issue is that there is relatively little material in Saturn's atmosphere that can efficiently scatter radar waves, so the radar basically just gets absorbed. The key point is that it's much ...
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7 votes
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Is the boulder on the peak of Tycho Crater the core of the impactor, or is it a random rock?

It is just a rock. A complex crater like Tycho is formed in several stages as the rock behaves like a fluid. The initial impact completely destroys the impactor and excavates a large cavity in the ...
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  • 87.7k
7 votes

Which JWST instrument modes are compatible with observations of the bright trans-Earth planets Mars, Jupiter, and Saturn? Which aren't?

All modes can be used. But for bright targets, observations are limited to specific filters, subarrays, regions of the target planet, or spectral intervals. James Norwood and colleagues wrote a paper ...
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6 votes

How many things are wrong in this "artist view" of the TRAPPIST-1 system?

The 2 big planets are probably f & g and they don't look up to scale to me. While f is the size of Earth, or almost 4 times bigger than the Moon, but it's also further away, ~ 1.3 million ...
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6 votes
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Could rocks from Earth have reached the Kuiper belt, or Neptune at least? If so, how?

(I have tracked down the reference that I made in my comment on the question.) Presumably earth rocks once blasted into space (by volcanism or meteorite impact) gain or lose energy primarily by ...
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  • 2,661
6 votes

How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter?

The lunar opposition surge has been well studied, likely because we can study it in detail, we have surface samples, and so it serves as a baseline for other bodies in the solar system (as it does for ...
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6 votes
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What is k2, how does it relate to Io's volcanism and how can Juno constrain its value?

$k_2$ is one of three tidal Love-Shida numbers related to how gravitation of another body (Jupiter in this case) changes a planet-like body's second degree spherical harmonics (Io in this case). Three ...
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6 votes

How do rocky planet break up? Would they fragment into "a gazillion" rocky pieces pieces, or crack open like an egg?

Energy Intro I think any good discussion of planetary destruction should start by talking about energy! Our SI base unit of energy is a Joule, which is defined as $\mathrm{J} = \mathrm{kg} \mathrm{m}^...
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5 votes

Why is Saturn invisible in this radar image of its rings?

The images you present aren't literal images of Saturn's rings. They're "Doppler-delay" plots: the vertical axis represents distance from Earth, while the horizontal axis represents speed towards or ...
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5 votes
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Wondering about a horseshoe orbit

A basic orbital rule is Kepler's third law, which states that the closer the moon is to the planet, the quicker is its orbit. A body that is close to the Earth will move in orbit faster than one which ...
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5 votes

How can it be known that Venus does not have plate tectonics?

Essentially, it boils down to the question of uniformity. Magellan reached Venus in the early 1990s, and was able to greatly improve on previous mapping attempts. The spacecraft was able to map ...
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5 votes

How many things are wrong in this "artist view" of the TRAPPIST-1 system?

Hominids in the neighborhood is probably the biggest mistake made by the artist. Sorry to be a little less optimistic than people at NASA, but a journey this far would probably take hundreds of ...
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  • 1,392
5 votes
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What is the underlying nature of the dark spot found on Uranus?

There is a science-based approach to explaining the dark spot on Uranus. In 2009 (the image and sighting of the spot in question are from 2006) a paper was published titled: The Dark Spot in the ...
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5 votes
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I have a question about the wording in a paper about a planetary system and comets

What they have done is take each of the 580 Jupiter-Family Comets (JFCs) from our solar system (from the JPL Small Body DataBase; set object kind=comets, ...
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  • 7,135
5 votes

Whether the comet is moving in an elliptical or hyperbolic orbit around the sun?

This might not be so hard after all. Below I show the math for the analytical solution for a Kelperian orbit; the catch is that it's only analytical for $t(\theta)$ and not $\theta(t)$ but that ...
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5 votes
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...but where did Mars' atmosphere actually GO?

Assuming most of the escaping Martian atmosphere is entrained in the solar wind, it will flow outward until it reaches the termination shock, and then slow down in the heliosheath until it reaches the ...
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  • 14.7k
5 votes

Could a magnetosphere be created for Venus by recreated by spinning-up the planet to a 24 hour day?

Planetary magnetic fields are not produced by their rotation, they are produced by convection in the core. The rotation has an effect on the patterns of convection through Coriolis forces, but is not ...
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4 votes

Is it plausible for a planet that is positioned in the habitable area of a solar system to have little extractable metals?

Interesting question, though probably a better fit for world-building. Firstly "metals" is often used by astronomers to refer to any element other than hydrogen or helium. That is clearly not the ...
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  • 9,893
4 votes
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Is it plausible for a planet that is positioned in the habitable area of a solar system to have little extractable metals?

I'm going to approach this question in two steps: what metals are you talking about, and could you have a planet where those metals are not easily extractable. What metals? I get the sense that you'...
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