How do they know that Pluto is the smallest planet - have they ever been there?

Answer 1

It is no longer a planet. It was reassigned as a dwarft planet. Thats blows.

There's this great discovery...called a telescople...it enables people to see planets and judge their size....amazing! (tongue in cheek)
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Once known as the smallest, coldest, and most distant planet from the Sun, Pluto has a dual identity, not to mention being enshrouded in controversy since its discovery in 1930. On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet. According to the new rules a planet meets three criteria: it must orbit the Sun, it must be big enough for gravity to squash it into a round ball, and it must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto and 2003UB313 (Eris), which orbit among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.

(1) A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

(3) All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".



Discovered by American astronomer Clyde Tombaugh in 1930, Pluto takes 248 years to orbit the Sun. Pluto's most recent close approach to the Sun was in 1989. Between 1979 and 1999, Pluto's highly elliptical orbit brought it closer to the Sun than Neptune, providing rare opportunities to study this small, cold, distant world and its companion moon, Charon.

Most of what we know about Pluto we have learned since the late 1970s from Earth-based observations, the Infrared Astronomical Satellite (IRAS), and the Hubble Space Telescope. Many of the key questions about Pluto, Charon, and the outer fringes of our solar system await close-up observations by a robotic space flight mission.

No spacecraft have yet visited Pluto. However, NASA launched a mission called New Horizons that will explore both Pluto and the Kuiper Belt region

Answer 2

Well, it's no longer classified a planet -- it's a dwarf planet.

But anyway...we can measure Pluto's size directly, from images taken by, for example, the Hubble Space Telescope. We know exactly how far away Pluto is at any particular time (by it's orbit, and by our own orbit, around the sun). We know the scale of images taken by Hubble. That's all you need -- an image, a known image scale, and the distance to the object, and you have the size. Pretty simple :)

By the way, there's a robotic spacecraft on its way to Pluto now, it'll be there in another 7 years or so (it's a long way). That will give us our first good close-up pictures.

Answer 3

I think it has to do with science and stuff... And supposedly the scientists who make things 'better' for everyone use math to determine stuff like that. They can compare the distance of an object in space to similiar objects and determine it's size... THey can use a spectragraph machine which can determine the elemental composition, ( make-up) of Pluto. Sadly though, the scientists decided Pluto is no longer a planet, or a moon, but chunk of rock floating in space. You MOTHER FATHERS!!! Oh well the aliens should take over the planet and change that... yeah, what ever.

Answer 4

Since when is Pluto a planet? But I don't imagine it looks very smaller the closer you get to it!

Answer 5

Well because it has gravity you can figure out its mass by the way it orbits the sun and the effect it has on the other nearby planets. There is another rock about the same size just a little further out. We knew about it only from the effect of its gravity for quite a while.

Answer 6

Pluto's not a planet.

Answer 7

Pluto is not even a planet anymore because it is so small. They don't have to go there to know that it is small, they use their eyes and look.

Answer 8

Telescope + Math

(you can calculate a planet's mass n size with its orbit structure)