how many planets have been discovered upto this time?

Answer 1

That won't be decided until the International Astromonical Union comes up with a definition of "planet". However, the answer is likely to be much more than ten as extrasolar planets have been observed.

Answer 2

10

Answer 3

I would actually say that only three planets were discovered in this solar system. Can you say that a planet was "discovered" when everyone knew it was there? Mercury, Venus, Mars, Jupiter, and Saturn were known to be special and separate from the stars thousands of years ago. The word planet comes from the Greek word that means "wanderer," because these objects moved among the supposedly fixed stars.

On the other hand, Uranus was discovered with a telescope, and the existence of Neptune and Pluto were calculated due to perturbances in the orbits of Uranus (Neptune) and Neptune (Pluto). I would say that these objects were truly discovered.

Now some people have argued that Pluto isn't a planet, but some sort of captured object. And this is the same argument that they are applying to Sedna now. Part of this is an issue of size. Pluto is smaller than Titan, one of the moons of Saturn. But on the other hand, so is Mercury, and no one questions Mercury's status as a planet. Or do we grandfather it in, because, hey, Aristotle knew it was a planet? I mean look at the rest of his track record.

Then you have to wonder what qualifies as having been discovered in other ways. For example, if we photograph an object around another star, I think we can say that we have discovered it. But what if we know the planet is there in other ways? For example, the nearest star to Earth after the alpha-Centauri group (and the Sun, of course) is Barnard's Star (MCC 799). In 1963, it was "discovered" that Barnard's Star had a planet, based on a wobble in the star's proper motion. It turns out that there was an error in the postulated position, and when that was corrected, it was found that there was no wobble, so it is now believed that there is no planet, but had that not in error, would you count this "planet" as discovered?

In 1983, the Infra-Red Astronomical Satellite discovered that in a cloud of gas orbitting beta-Pictoris exhibited Keplerian motion. Now a real gas cloud will orbit like a disc, with particles on the edge displaying the same angular velocity as particles close to the center. But separate objects, like those of our solar system, display Keplerian motion, meaning that objects at the edge have a slower angular velocity, so that Mercury can go around the Sun in 87 days, while Pluto takes 248.5 years. Keplerian motion is indicative of planets.

Now the Hubble Space Telescope has photographed that cloud and detected a "hump" that suggests that a planet about the size of Jupiter is orbiting in there. Has this "planet" been discovered? Think about Barnard's Star before you answer.

I'm not going to bring in Bode's Law, which suggests that you are going to find planets at certain distances from the star, since it hasn't been proven because it's only got one incident (our solar system). A Jupiter-sized planet around beta-Pictoris is suggestive of smaller terrestrial ones closer in. But there's no way you could claim to discover planets based on that.

Anywho, the Barnard's Star page listed below says that as of 2001, 74 planets had been found orbiting 66 stars. The paper on the Observatatoire de Paris-Meudon-Nancay site says 119 stars as of 2004. The PlanetQuest site is the most current and says 172 planets around 97 stars, but also says that this only includes planets around main sequence stars. If Barnard's Star was still thought to have a planet, it would be excluded from this count. I guess that makes sense; if you are hoping to find life, you are not going to find it around some neutron star or red dwarf. Still, it makes it pretty difficult to give a definitive answer to your question.

Answer 4

9 - Mercury, Venus, The Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Sedna, is not officially declared as a planet.
90377 Sedna is a trans-Neptunian object, discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. At the time of its discovery it was the most distant observed natural solar system body, though this has now been exceeded by 2003 UB313. Sedna is described as a cold planetoid, perhaps as large as two-thirds the size of Pluto.

Answer 5

well according to the lame sites on the internet it says 20 to 30 I have read before that over 50 have been discovered and I'd imagine the numbers are more likely in the hundreds, sorry I don't have an accurate answer for you, these being around others suns other than our own of course, if that is what you were looking for

Answer 6

10 in this solar system and 131 orbiting other stars.

Answer 7

i think so ten only