A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and – according to the International Astronomical Union but not all planetary scientists – has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Apart from Earth itself, five planets in the Solar System are often visible to the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the current definition, some celestial bodies, such as Ceres, Pallas, Juno and Vesta (each an object in the solar asteroid belt), and Pluto (the first trans-Neptunian object discovered), that were once considered planets by the scientific community, are no longer viewed as planets under the current definition of planet.
The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions. Although the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. About the same time, by careful analysis of pre-telescopic observational data collected by Tycho Brahe, Johannes Kepler found the planets' orbits were elliptical rather than circular. As observational tools improved, astronomers saw that, like Earth, each of the planets rotated around an axis tilted with respect to its orbital pole, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology.
Planets in the Solar System are divided into two main types: large low-density giant planets, and smaller rocky terrestrials. There are eight planets in the Solar System according to the IAU definition. In order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites, the two exceptions being Mercury and Venus.
Several thousands of planets around other stars ("extrasolar planets" or "exoplanets") have been discovered in the Milky Way. As of 22 June 2021, 4,768 known extrasolar planets in 3,527 planetary systems (including 783 multiple planetary systems), ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter, have been discovered, out of which more than 100 planets are the same size as Earth, nine of which are at the same relative distance from their star as Earth from the Sun, i.e. in the circumstellar habitable zone. On 20 December 2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A 2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way.
Around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone.
to the earth. I will arrive at Earth a little over 5 years from the time I depart, correct? How many years will I have aged as a passenger on the spaceship and how long will someone on Earth have aged during my journey?
I had this nice cute idea about a small inhabitable planet that is, say, 1km around equator (that's about 320m in diameter).
Is it possible that such planet has gravity the strength of the Earth's gravity? (or, to rephrase the question, from what matter should that 320m diameter planet be made...
It's on the Discovery channel right now and it's official. Deep Sea Creatures scare the hell out of me.
This is really an amazing program with the best video of freaky creatures I've ever seen. I highly recommend it to anyone who doesn't frighten easily.
Hi!
I saw the definition of a planet -- basically anything differentiated that has cleared everything in the area and orbits the central star.
Pluto doesn't count because it's in the middle of a belt.
Ceres doesn't count because it's in the middle of a belt.
Sedna -- well...
http://www.cnn.com/2006/TECH/space/08/24/pluto.ap/index.html
"PRAGUE, Czech Republic (AP) -- Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight."
... :rofl:
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_resolution.html"
I'm ok with Pluto and Charon being a planet and 2003 UB313but crers? what were they thinking!
In a recent theological discussion, I came to realize that there is a point in question regarding planet formation in the current model of the origins of the Solar System. The question itself is not theological, but has some theological ramifications. It goes like this:
Planets are believed...
Why doesn't this force give the gravitational acceleration on the surface of the earth?
a = G \cdot \frac{m}{r^2}
I would think that it could be derived from the law of universal gravitation:
F = G \cdot \frac{m_1 \cdot m_2}{r^2}
Since F = m_2 a
I'd be grateful if someone can help me with this problem -
Zero, a hypothetical planet, has a mass of 4.4 × 10^23 kg, a radius of 3.2 × 10^6 m, and no atmosphere. A 2.4 kg space probe is to be launched vertically from its surface. (a) If the probe is launched with an initial energy of 7.4 ×...
my question is for example if we have a commet,asteroid in an impact collision with a planet, can the planet gravitational force can stop it from colliding, and bound it so the commet,asteroid will orbit the planet?
i think the answer is yes, but what minimal velocity should the the commet...
Can anybody help me find informations about the mathematical discovery of planet neptune ?
I would like to know how Leverrier and Adams calculated the position of neptune and all this stuff...
Thanks in advance..
Jack
can u help me to explain the role of gravity in the equilibrium of stars in their production of enegry , and an explanation of the role of gravity in the formation of planets.
thankssssssss
Ive been wondering about this for a while. i read in the newspaper about jupiters new red spot, but anyways they mentioned that it was a gas planet. does this mean that if you were to fly to Jupiter and keep going, eventually you'd go right through it and out the other side? or is it so dense...
2 part question
The density of a certain planet varies with radial distance as: D(r) = Do*[1-(a*r/Ro)], where Ro= 3.1623×106 m is the radius of the planet, Do = 3160 kg/m3 is its central density, and a = 0.160. Calculate the total mass of this planet.
Calculate the weight of a one kilogram...
Drake equation and planet finding
I've just finished reading a Discover mag article on the Drake equation. It suggests that - despite the 45 year difference wherein many terms have been changed or anchored with more precision - the final number is about the same as it always was; there should...
If there was a planet and there was no real energy source near it (say like our sun) would a few stars around 100million light years away on all sides of the planet(like our stars) be enought to keep atoms on the planet moving enough to stop BEC, or would BEC occur. Also if there was only one...
So I heard a theory once that a planet, gaining mass through collisions, could over time become a feelble star (if it gained about 10x the mass of jupiter), through adding kinetic energy and pressure, etc., and that this would create nuclear ignition.
My question is this: If somehow we could...
http://arxiv.org/abs/astro-ph/0601469
Comparative Planetology and the Search for Life Beyond the Solar System
Charles A. Beichman, Malcolm Fridlund, Wesley A. Traub, Karl R. Stapelfeldt, Andreas Quirrenbach, Sara Seager
To Appear in Protosars and Planets V
"The study of planets beyond...
It is said that high massive planets can eject small planets in planetary forming systems. I don't understand that since gravitation is supposed to attrack things. Do you know of any article that expains that kind of phenomenum?
Life on a brown dwarf or a fissioning rogue planet?
Is life on a brown dwarf or a rogue planet with a fissioning core any less feasible than life in a solar system?
I was thinking about this while reading the thread about destroying a star, I thought well what would you have to do to simply annihilate a planet? Note I am not simply talking about making it devoid of life but actually destroying it utterly.:devil:
The former is a hypothesis that originated with observations of (apparent) periodicity in the extinction record, and has had its share of fame and controversy; the latter began as an innocent follow-on to the discovery of Pluto ('that puny little thing, a planet??') but in the late 20th century...
Hi,
I need to find the density \rho(r) of an ideal gas at constant temperature T surrouding a planet of mass M and radius R. The gas is attrated by the planet and is also self-attracting. First, I used the hydrostatic equilibirum equation...
Does anyone know anything about this?
http://tv.yahoo.com/news/wwn/20050912/112653720001.html
I'd love to hear what people who know what they're talking about, physics-wise, have to say about this.
\phi
The Rev
I have heard of terrestrial, gas giant, liquid and (speculatively) crystal planets. It seems to me that the conditions for forming a glass planet would be relatively common (more than those for their crystal cousins) - enough so that such bodies might eventually be detectable in our galactic...
From last week's Science Daily headlines:
Underlying Cause Of Massive Pinyon Pine Die-off Revealed
http://www.sciencedaily.com/releases/2005/10/051011073510.htm
The article says nothing about man's contribution to warming; it is merely another datapoint of the changing face of the planet.
my evil teacher is making me and my friend to do a 12 page report. and the question is "how does the distance of a planet from the sun affect the temperature?" i would really apperciate it. thanks.
I think I have done this problem correctly,
The mass of a robot is 6680 kg. This robot weighs 3070 N more on planet A than it does on planet B. Both planets have the same radius of 4.00 x 10^8. What is the difference Ma - Mb in the masses of these plantes?
I used this equation F = G *...
Alright I am obviously retarded since I am unable to figure this question out.
The question is:
You have just landed on Planet X. You take out a ball of mass m, release it from rest from a height of h and measure that it takes a time of t to reach the ground. You can ignore any force on...
Hello everyone, I'm a physics/astronomy noob, actually I don’t even begin my curricula till later this 2006.Yes, the credibility of this source is well umm… it’s a tabloid! But my friend who studies astronomy sent me this and this is the debunking thread afterall. :biggrin...
"10th Planet" resonance with Neptune
The "10th Planet" is locked in resonance with Neptune. 2003 UB313 is in a 17:5 resonance with Neptune. I've never seen a number as high as 17 be part of a resonance before . 2005 FY9 is in an 11:6 resonance with Neptune. Here's a page I made...
A new solar system object past Pluto and Neptune's object with a moon, which is smaller than Pluto has been discovered. (This is also very delicate wording. The sensational way to word it would be: "New Planet Discovered Past Pluto!", but given that Pluto just barely qualifies to be a planet...
http://news.yahoo.com/s/space/20050713/sc_space/triplesunsetplanetdiscoveredin3starsystem :cool: Awesome!
A newly discovered planet has bountiful sunshine, with not one, not two, but three suns glowing in its sky.
It is the first extrasolar planet found in a system with three stars...
The idea popped into my head today of building an extreme telescope (larger than hubble) to orbit an outer planet such as Jupiter etc.. I'm thinking that with it being past the asteroid belt, we would be able to see farther and clearer than with the hubble. Is this an accurate assumption? The...
Q:
Your starship, the Aimless Wanderer, lands on the mysterious planet Mongo. As chief scientist-engineer, you make the following measurements: a 2.50-kg stone thrown upward from the ground at 15.0 m/s returns to the ground in 7.00 s; the circumference of Mongo at the equator is 1×10^5 km; and...
Intelligent beings on the plantet Xeno have developed a unit of distance called the xen.
The number of square xens in the surface area of Xeno is exactly the number of cubic zens in its volume.
If Xeno is a spherical planet with a diameter of 2160 Kms, how many km are there in one Xen...
An atlas of environmental change compiled by the United Nations reveals some of the dramatic transformations that are occurring to our planet. It compares and contrasts satellite images taken over the past few decades with contemporary ones.
These highlight in vivid detail the striking...
A planet with mass m, and radius r...
what is the acceleration due to gravity on the surface of the planet?
a = Gm/r^2
correct?
I'm pretty sure I'm right, but I will sleep better if someone can confirm this :smile:
thanks
A planet has mass Mplanet = 4.46e24 Kg and a radius Rplanet = 5900 Km
Some space explorer lands on the equator of this planet and he weighs 161lbs, whereas he weight 185lbs on Earth. He journeys over to the North pole and he finds himself weight only 95% of what he did at the equator. Now the...
There's a planet with a moon that orbits the plant in 30 days and moves at a distance of 370million meters from the center of the planet. i need to find the mass of the planet and I've used the following equation that was derived from the keplers laws: P = 2pi(a^(3/2))/(GM)^(1/2). P is the time...
Q:
The residents of a small planet have bored a hole straight through its center as part of a communications system. The hole has been filled with a tube and the air has been pumped out of the tube to virtually eliminate friction. Messages are passed back and forth by dropping packets through...