SHARON SHANKS | The Cosmos Is Pluto a real planet? Experts still debate

Let's try a simple quiz to start your day: how many planets are there?
If you answered nine, you're right. If you answered eight, you're also right. And if you answered approximately 90, you're right, too.
Sorry about that -- it was a trick question.
The answer depends on how we define a planet and if we're talking about our solar system or planets around other stars. Both questions are hot topics right now.
First, are there nine planets in our solar system, or eight?
The debate over the status of Pluto is still going on. It's not a raging debate or one that will change the course of the universe, but an interesting one nonetheless because the changing view of Pluto is echoing changes in technology since the body was discovered in 1930.
Discoverer's work: Clyde Tombaugh relied heavily on tenacity and the equipment of his time to discover Pluto.
He used a blink comparitor, which allowed him to examine two images side by side, back and forth, and check for the tiniest of changes that would indicate that one spot of light out of thousands had moved, the surest indication of a planet. It was back-breaking, eye-straining work.
Today's computers can make the same comparisons in a fraction of a second.
The driving force behind the search for "Planet X" was Percival Lowell, the builder of the Lowell Observatory, who was convinced it existed.
Observational evidence at the time suggested that another large body beyond the orbit of Neptune was gravitationally disturbing the orbits of Neptune and Uranus.
The idea was a sound one -- after all, Neptune's gravitational pulls on Uranus led to the discovery of the eighth planet in 1846 -- but the apparent gravity pulls of a "Planet X" turned out to be errors in measurement.
It was a wonder that Pluto, whose gravity is so slight that it doesn't appreciably affect the orbit of Neptune, was discovered at all.
Better equipment: Since 1930 technology has improved to the point that the theoretical existence of the Kuiper Belt, an area of comets and icy asteroids beyond the orbit of Neptune, has been confirmed.
Within the past decade, large objects have been detected within the belt, a challenge because of their great distance (about 4 billion miles), small size, and extreme dimness.
Fittingly, astronomers from the Lowell Observatory were among those who recently discovered another large object within the Kuiper Belt, one that may rival Charon, Pluto's moon, in size. (Others working on the project are from MIT and the Large Binocular Telescope Observatory.)
The discovery adds more ammunition to the argument that Pluto isn't a planet, but a large object from the Kuiper Belt.
The object is called 2001 KX76 and appears to have a lot in common with Pluto and Charon: it is a rocky-cored body covered with a crust of ice.
Pluto and Charon are believed to be very large bodies from the inner fringes of the Kuiper Belt that were captured into orbit around the sun.
Pluto is about 2,275 km across (1,400 miles); Charon is 1,200 km (745 miles); and the new object is estimated at 1,270 km (789 miles), slightly larger than Charon. To compare, our moon is 3,476 km in diameter (2,160 miles).
Even with this new evidence, it's doubtful that Pluto will ever truly lose its planet status; sentiment sometimes is more powerful than science.
This means that today's children still have to learn the names of nine planets and the familiar rhyme "My Very Excellent Mother Just Served Us Nine Pizzas."
Meanwhile, planet discoveries around other stars is proceeding at a frantic pace and astronomers using the Hubble Space Telescope have detected the first atmosphere of an extra-solar planet.
Improving technology and enough time to observe longer orbits has changed the search for planets outside our solar system.
The first question was: Do they exist? Followed by: How do we find them? The question now is: How similar are they to Earth?
Early detection of extra-solar planets first found the literal "odd balls," the huge planets eight to 10 times the mass of Jupiter, our solar system's largest planet, that orbited closer to their stars than Mercury, our system's smallest and closest to the sun.
The short orbital periods of these planets (the time it takes them to go around their stars) made it easy for them to be spotted first.
Outside our system: Astronomers have spent enough years now observing nearby sunlike stars to begin finding more "normal" planets -- planets similar to the large planets of our own solar system.
The recent discovery of eight more planets outside our solar system was particularly exciting because three of those planets are about the same mass and distance from their stars as our Jupiter and Saturn and their orbits are nearly circular.
This brings the total of extra-solar planets to nearly 80; the number will certainly change quickly as planets in longer orbits are discovered. (And it brings the total of planets to nearly 90, when you add our solar system's eight or nine.)
At the same time that the new planets were being discovered, astronomers using the Hubble Space Telescope watched a known planet called "HD 209458 b" pass between us and its star and discovered evidence for an atmosphere.
The planet is one of the "hot Jupiters," big planets made mostly of gasses that orbit very close to their stars.
The size of the planet suggested that it was made mostly of gas; the spectroscopic evidence from the Hubble confirmed the suspicion when traces of sodium (the basic ingredient in salt) were found. The signs of sodium could only come from a planetary atmosphere.
The planet is about 150 light years away and orbits a star in the constellation of Pegasus. It takes only 3.5 days for the planet to complete one orbit.