148 votes
Accepted

Could we breathe an atmosphere that is not nitrogen based?

We can breathe pure oxygen for unlimited time if the pressure is not too high; about 0.4 bar is okay. Breathing pure oxygen at 1 bar is possible for some hours, but a longer time may damage the lungs. ...
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  • 47.3k
122 votes
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What will be the effect if we stand on Jupiter?

(*) Jupiter, for all intents and purposes, doesn't have a solid surface to stand on. Not any more than you could say that Earth's atmosphere has it, before you hit Terra Firma. It's an enormous ball ...
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  • 75.6k
98 votes

Is it possible for a moon to have a higher surface gravity than the planet it is attached to?

Given a pair of objects that are gravitationally bound to each other, they will orbit around their common barycenter (center of mass of the system). The object to be most logically deemed the moon ...
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  • 17.1k
82 votes
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Is it true that NASA is hiring a new 'planetary protection officer'?

You're observing shamefully bad journalism. The "protect Earth from aliens" bullet point in the "Highlights" section of the article was put there by an editor who either ignorantly ...
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74 votes

Is it possible for a moon to have a higher surface gravity than the planet it is attached to?

Gravity isn't just about mass, but about distance, too. Our moon has a surface gravity of about 1/6th of Earth, because it is small and less dense than the Earth is. Surface gravity of a body is ...
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58 votes
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Did the Mars rovers actually confirm the gravity of Mars?

The "gravity of Mars" is not a number but rather a complex field. The most recent is remarkably detailed, made up to spherical harmonics degree and order 120, described by 29,512 coefficients: These ...
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  • 57.7k
51 votes
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Why are probes that tend to explore outer system always launched to go outwards instead of straight upwards or downwards?

Starting out from Earth, you have the free 30 km/s from Earth's movement around the Sun, which is in the plane of the ecliptic. To get far out of the plane you either have to boost a similar amount "...
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48 votes

Do scientist who study martian geology typically use the term areology?

Good question. I work on the Curiosity team, and I hear "geology" all the time, but never "areology." Too bad, really, since it's a great word, and I love the R/G/B Mars series.
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  • 1,223
40 votes
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What is the deepest we have penetrated a terrestrial body other than Earth?

In July 2005, the Deep Impact mission released an impactor that excavated a crater, estimated to be 100 meters wide and 30 meters deep, into comet Tempel 1.
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  • 911
39 votes

Why are probes that tend to explore outer system always launched to go outwards instead of straight upwards or downwards?

We've had 5 flyby missions to the outer solar system so far. All of them had primary missions at one or more planets. That set the main constraints for their trajectories. Anything after the last ...
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  • 122k
38 votes
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Could the Moon keep an atmosphere?

It can keep an atmosphere, and in fact does. The atmosphere is something akin to a high grade Earth-based vacuum. But that's probably not what you are looking for. Okay, so what would happen with, ...
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  • 119k
36 votes

If there's nothing special about Pluto, why was it discovered so early?

There are a few special things about Pluto, as compared to the other dwarf planets in the Kuiper belt. These include: It is the largest dwarf planet known, by diameter. (Note, this was only ...
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  • 119k
31 votes

If there's nothing special about Pluto, why was it discovered so early?

Pluto was discovered by a manual search of the sky using a blink comparator. This is an extremely laborious process. For Pluto, it made sense to go to all this trouble, because there were indications ...
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  • 122k
31 votes
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Why was Titan the first celestial body beyond Mars to be landed on?

Simple. It was the easiest to land on. Titan has an atmosphere, which makes landing there quite a bit easier than landing on Europa, which does not. In addition, Europa has only been known as an ...
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  • 119k
30 votes

Do other planets and moons share Earth’s mineral diversity?

We turn to Mars, which we have studied for decades now. And we do see plenty of mineral diversity on the surface of the Red Planet, it's not just rust by any means. Curiosity's CheMin analyzer has ...
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  • 7,630
29 votes
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Is water on Mars the same as Earth water?

Fundamentally, water is water. In its purest form, it is the same anywhere, except perhaps for the isotopes. However, one of the wonderful things about water is the fact that it's a good solvent, and ...
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  • 119k
29 votes

Why are probes that tend to explore outer system always launched to go outwards instead of straight upwards or downwards?

It is important to realize that space probes aren't really useful for finding objects in deep space. Space is so empty that a probe sent in a random "exploratory" direction would have a negligible ...
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  • 7,051
28 votes

Is it possible for a moon to have a higher surface gravity than the planet it is attached to?

Yes, it is possible. As James K observed in a comment, the surface gravity of Uranus is slightly less than that of Earth, but its mass is 14 times larger. If Earth were orbiting Uranus, it would be a ...
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  • 7,051
28 votes

How does a planet's gravity push away smaller bodies that would otherwise intersect its orbit?

I feel the need to correct some issues that were brought up in the other answers. Yes, gravity is an attraction-only force. But due to its relative weakness, objects in space can attain large ...
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24 votes

What defines the radius of a ball of gas like Jupiter?

The radius of Jupiter and the other gas giants is defined, somewhat arbitrarily, to be the radius at which the atmosphere has a pressure of 1 bar. As your question points out, they had to pick ...
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  • 57.7k
23 votes
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Do scientist who study martian geology typically use the term areology?

A search on arXiv for "areology" produces no results. A search on ADS produces two results (one of which has the subtitle "The Geological Environment of Mars"). So the term is ...
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  • 4,820
22 votes

Which of the four inner planets has the strongest magnetic field, Mars, Mercury, Venus, or Earth?

Which of the four terrestrial planets has the strongest magnetic field, Mars, Mercury, Venus, or Earth? The Earth, by far. The four giant planets have rather strong magnetic fields. Amongst the ...
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  • 65.6k
21 votes

BBC: "In 2009 Prof McDowell & other astronomers performed an experiment in which a similar-sized rocket was crashed into the Moon." Really? Which one?

"2009 impact" would probably be when the LCROSS/LRO upper stage was crashed into a crater at the Moon's south pole. The LCROSS Centaur upper stage had a mass at impact of around 2300 kg; an ...
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  • 11.6k
20 votes
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How tall are Pluto's mountains? Are they the tallest ice features in the Solar System?

How tall are these things? Are they made of ice? Are they the tallest things on Pluto? Are these the tallest ice features in the Solar System? "New close-up images of a region near Pluto’s ...
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  • 1,270
20 votes

Do other planets and moons share Earth’s mineral diversity?

They do not! The reasons for this are simple: minerals are semi-stable configurations of elements formed in certain pressure-temperature-redox conditions. A planet in the possession of active plate ...
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  • 10.1k
19 votes
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What is the mysterious "Ball of Mars"?

As called2voyage♦ pointed out in a comment, this looks like a concretion. It is not the first concretion observed on Mars, and it was most likely formed back when Mars had liquid water. More ...
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  • 11.2k
19 votes

What is the mysterious "Ball of Mars"?

Curiosity photographs thousands of rocks every week. It does that for years. You will find rocks with almost any shape you can think of. This one happens to be somewhat round in one direction. From ...
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19 votes
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When is the next Outer Planet lineup (Voyager)

The lineup occurs once every 175 years. The launch window the last time this alignment occurred was from 1976 to 1980 [1], so the next time it would open would be around 2151-2154. Another Voyager-...
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  • 2,174
19 votes
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Is Mohs scale of mineral hardness applicable for rocks and minerals of terrestrial planets other than Earth?

Yes, because for the vast majority of minerals you can find in space, they are the same as those you can find (or synthesize) on Earth. A pyrite in space is a pyrite just like on Earth. A wollastonite ...
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