154 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. ...
  • 48.2k
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 ...
  • 17.3k
82 votes
Accepted

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 ...
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 ...
58 votes
Accepted

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 ...
  • 58.1k
51 votes
Accepted

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 "...
  • 19.2k
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.
  • 1,243
40 votes
Accepted

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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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 ...
  • 123k
38 votes
Accepted

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, ...
  • 120k
37 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 ...
  • 120k
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 ...
  • 123k
31 votes
Accepted

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 ...
  • 120k
31 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 ...
  • 8,205
29 votes
Accepted

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 ...
  • 120k
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 ...
  • 8,094
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 ...
  • 8,094
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 ...
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 ...
  • 58.1k
23 votes
Accepted

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 ...
  • 4,960
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 ...
  • 71.3k
21 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 ...
  • 10.3k
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 ...
  • 12.4k
20 votes

Could we breathe an atmosphere that is not nitrogen based?

Yes, we don't require nitrogen to breathe. For example, NASA astronauts used to use a pure oxygen environment. The complication with this environment was the risk of fire. For more information: Why ...
  • 23.9k
20 votes
Accepted

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 ...
  • 1,270
19 votes
Accepted

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 ...
  • 10.3k
18 votes
Accepted

Is there a map or list of all the lava tube skylights the LRO has detected on the Moon?

There is a map of lunar pits, created by R. V. Wagner and M. S. Robinson of the School of Earth and Space Exploration, Arizona State University, in 2014. From Distribution, Age, and Formation ...
  • 76.1k
18 votes

Is Mohs scale of mineral hardness applicable for rocks and minerals of terrestrial planets other than Earth?

Yes, but with a couple modifications. On some planets, notably Venus within our Solar Systen, different conditions from those on Earth, especially temperature, can affect mineral hardness. Pyrite is ...
  • 8,205
16 votes
Accepted

What causes moonquakes?

You are correct about some of the sources of moon quakes. NASA states there are are least four types of moon quakes: There are at least four different kinds of moonquakes: (1) deep moonquakes ...
  • 12k

Only top scored, non community-wiki answers of a minimum length are eligible