Hot answers tagged

45

Jupiter being a gas giant is not about its appearance, as another answer stated. It's only about the mass distribution of a planet. Jupiter's mass is 320 Earth masses, while we know from the Juno mission that the rock/ice in the core account for 5–25 of these Earth masses. So the rest of about 300 Earth masses is gas. Thus Jupiter is a gas giant. It is ...


25

Yes, certainly, around 6 of 8 planets in the Solar System, the oldest of which, The 2001 Mars Oddessey orbiter has been in orbit around another planet longer than any other satellite. A key thing to note is that artificial satellites are defined as anything man-made that orbits another celestial body, the difference with a space probe being that a satellite ...


21

I was actually just reading a great What If? article on this found here. Flight on other planets is possible. I think the included comic strip summarizes it wonderfully: As for each valid body in our solar system (barring Earth of course), I'm going to paraphrase a bit: The Sun: Attempting flight on the sun is more or less useless as any vessel close ...


21

Saturn has co-orbital moons, Epimetheus and Janus. They orbit in the same direction and swap orbits approximately every four years as the inner body catches up with the outer body.


19

This topic is actually pretty nicely covered in the Planets beyond Neptune Wikipedia page, so I recommend reading it, if for nothing else then for a convenient collection of references. But to quote the most relevant part on Harrington's Planet X (beyond Pluto) of that Wiki page: Planet X disproved Harrington died in January 1993, without having found ...


19

In 1989, Voyager 2 did a fly-by of the planet Neptune. The orignal plan for the Grand Tour would have included Pluto, but the Voyager series was reduced from four craft to just two. The New Horizons craft, launched in 2006, made it's closes approach to Pluto on July 14, 2015, at 11:49 UTC (2,500 km/7,800 mi). Technically, Neptune is still be the most ...


16

It is not coincidence and it does not apply to just the Earth. The Sun, Earth, Jupiter, Saturn, Uranus, and Neptune all have sizable magnetic fields. Mercury and Ganymede have smaller but still noticeable magnetic fields. All of these bodies have one thing in common: They have a sizable amount of rotating, electrically conductive fluid somewhere beneath the ...


16

It's just a coincidence, and officially, the dates aren't that close. The IAU (International Astronomical Union) General Assembly in Prague, Czech Republic where the new definition of a planet was endorsed and with it Pluto losing its planetary status, happened in late August, 2006. Final draft that was voted on states: A planet is a celestial body that ...


16

The official trigger for what caused Pluto's demotion as a planet was the discovery of Eris, in October 2005. For a number of years, starting with the discovery of non-Pluto Kuiper Belt Objects (KBOs), and later with the discovery of other large objects in the Kuiper Belt. When Eris was discovered, the IAU decided that it needed to decide what a planet was. ...


16

The term for bodies sharing an orbit in this manner is co-orbital configuration. It is technically possible for two objects of planetary size to share an orbit like this, and we may have even found an example in an extrasolar system. It is speculated that early in Earth's history that it shared an orbit with a Mars-sized planet named Theia which later ...


15

One reason they are called gas giants is because they are mostly composed of elements that are gaseous at Earth like temperatures and pressures. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium, though helium comprises only about a tenth of the number of molecules. Jupiter's upper atmosphere is about 88–92% hydrogen ...


14

None of the TRAPPIST-1 planets are "considered habitable"; we don't know nearly enough about them to say that (any news article which referred to the planets themselves as "habitable" needs firm correction). Three of them are within the habitable zone of the star, which is defined as the region around the star where liquid water could potentially be found on ...


13

This is a simple calculation in the conservation of angular momentum. The angular momentum of uniform sphere is ${2\over 5}MR^2\omega$. We will assume that Earth is a uniform sphere (close enough for this question), so $M=5.972\times 10^{24}\,\mathrm{kg}$, $R=6371\,\mathrm{km}$ (mean), and $\omega=7.292\times 10^{-5}\,\mathrm{s}$. So the angular momentum ...


13

Getting hard numbers about how accurate measures we can get from current systems, adapted to the Sun instead of far away stars is difficult, bordering to impossible. But we can get data about the relative difficulty of the solar system planets. First off, we can do some cheating for Mercury and Venus, as they occasionally go in front of the Sun. Given your ...


12

The key thing to doing this is to accelerate some of the mass of Venus outside of the planet, or alternatively bringing in some mass. Thus, there are 2 main things that could be done to alter the rotation speed. These ideas are explained in Wikipedia. Carefully plan a series of asteroid impacts in a direction where they can increase the rotational energy of ...


12

I'll have to dig through the decadal survey and LPI proceedings a few times, so I decided I have to make this answer a community wiki anyway. As soon as there is a decent answer by anybody else, I'll accept it. Three basic mission modes: getting inside the ocean getting onto the surface doing research from low orbit The main goal: determining habitability ...


12

You can parse and use those ascii JPL ephemeris files. Warning: This is an exercise for people who like to torture themselves. If you aren't into self-flagellation, you should do what Mark Adler wrote and use the SPICE toolkit. I went through this self-flagellation over a decade ago, when SPICE was closed and wasn't what it is now. Now people are thinking ...


12

I would argue that it is disproven already. There have been studies done with Extrasolar planets, and it has been found to only apply in a very small number of instances. There might be some that follow the law, but the number is quite small. There are instances where it lines up nicely, but it seems like ultimately it fails most of the time.


11

This could be off-topic here, but I have an answer, so I might as well post it. Yes and No According to Wikipedia, decomposition occurs due to two factors: the body's own chemicals and the effects of bacteria. Autolysis Autolysis is the process of a bit of organic matter breaking itself down. The lysosomes in a cell use digestive enzymes that normally ...


11

No, the first step is to download the SPICE Toolkit. It will read the ephemeris and generate the data you need for you, as well as do much, much more. There are many formats used in SPICE kernel files, not just the particular one you're looking at, which is probably a Chebyshev position-only array (type 2). There are 16 types. The values can be stored ...


10

Centrifuges with long tethers (or airbeams) could be used also on the ground. Below is an illustration where the crewed part of the carousel is below ground for protection against radiation. According to the source the centrifugal radius would be 33 meter long to achieve 0.5 g (with 0.17 g given naturally on the Moon). From www.cislunarone.com by Dr. Doug ...


10

No. A planet of significant mass would cause detectable perturbations in the orbits of the other planets. This is how Neptune's existence was postulated. Deviations from predictions in Uranus' orbit suggested where an 8th planet must be located. A focused search in the projected area led to its discovery.


9

From basic physics if there is one it cannot be massive, or must be incredibly far away, as we would see the perturbations in the orbits of the other planets. Additionally, if it was massive but very low density, for some reason, so we couldn't see it's effect on the orbits of the other planets, we would expect to see something with a regular orbit from ...


9

This is not only relevant to the off chance, distant future human colonisation or otherwise long term stay on celestial bodies with larger than Earth surface gravity, but also constant acceleration space travel at over 1 g. It's a fair question, and to be fair in return, as far as adaptation to hypergravity conditions goes, we haven't a clue to what degree ...


9

There is no generally agreed upon naming convention that I'd know of. Since the prefixes for the closest (peri-) and farthest (apo-) orbital point to the parent body are of ancient Greek origins, most commonly found forms use ancient Greek names for celestial bodies. Either ancient Greek gods that are equivalent to Roman gods that the celestial bodies were ...


9

There have been several sample return missions: NASA mission Genesis collected samples of the solar wind comet Wild 2 was visited by NASA mission Stardust asteroid 25143 Itokawa was visited by JAXA spacecraft Hayabusa 2 more asteroid sample return missions are currently active: Hayabusa 2 was launched in 2014, Osiris-REX is being built. Plans for more ...


9

You can try for yourself how bright it is on Pluto. High noon on Pluto is as bright as a certain point during dusk/dawn on Earth. I tried this, at that point it's bright enough to make out details. My conclusion is that you can see the daylight side of every planet incl. Pluto with the naked eye if you're close enough. This does depend on the planet's ...


9

Yes, any planet within a sufficient distance from the parent sun is assumed to be tidally locked. Proxima Centauri B, the nearest exo-planet to the Earth, is believed to be tidally locked. Pluto and its moon Charon, are believed to be tidally locked to each other. Your thoughts are exactly correct - life would be tough and probably confined to the, ahem, ...


9

The period $T$ of some satellite in orbit is determined by its semi-major axis $a$, so for a given $a$ (and central body), the orbital period will always be the same: $$T = 2\pi \sqrt{\frac{a^{3}}{GM}}$$ However, the angular rate of the orbit will change over time depending on the eccentricity of the orbit, but the mean motion $n$ will remain the same, ...


8

Yes, it is possible to detect rogue planets by observing distant stars and measuring the microlensing effect when a big enough object passes in front of them and increases their apparent brightness. If the rogue planet passes one of the observed stars, this microlensing effect will be a lot shorter than when any of the planets orbiting the star would pass ...


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