From:http://www.sciam.com/article.cfm?chanID=sa003&articleID=000891F1-AEA2-14B6-ABEB83414B7F4945

“NASA去年7月4日的深度撞击其 能量大约等价于５吨TNT，有1000万千克的彗星物质扩散到天空中，为科学家们提供了观察彗星内部构成的机会。Johns Hopkins大学的Carey Lisse和他的同事利用Spitzer太空望远镜的观察显示彗星尘埃主要由冰，气体，碳酸盐，碳氢化合物，硅酸盐，硫化物和其它元素组成。这些混合物并 不与之前的彗星尘埃模型相匹配，一些发现的矿物质的产生需要很高的温度。科学杂志有详细的分析。”

The Fourth of July last year had some extra fireworks. NASA’s Deep Impact spacecraft sent a hefty projectile–more than 800 pounds–into the body of the comet known as Tempel 1. The collision delivered 19 gigajoules of energy–the equivalent of nearly five tons of explosive TNT–into the wandering comet and ejected a plume of its innermost secrets. Roughly 10 million kilograms of comet stuff (more than 22 million pounds) spread out into space, giving scientists a rare glimpse of the ingredients that go into making a comet. Now researchers observing with the Spitzer Space Telescope have revealed their findings: comets contain a mix of materials that formed under widely divergent conditions.

Carey Lisse of Johns Hopkins University and his colleagues studied the collision through 12 infrared spectrographs taken by Spitzer from July 2 through July 5. Prior to impact, Tempel 1 displayed the same streaming dust as any other comet, pushed back from the cometary body by the sun’s radiation. But after the early-morning impact, Tempel 1 revealed itself to be made of water ice and gas, carbonates, polyaromatic hydrocarbons, silicates, sulfides and other elements.

This mix of components does not match current models of comet dust. Some of the minerals detected require temperatures between 1,100 and 1,400 degrees Kelvin–only found as close to the sun as Mercury–as well as volatile gases such as methane that only remain stable at temperatures below 100 K. This means that there must have been some form of mixing over large distances going on in the nebula that gave birth to the sun billions of years ago.The spectra also hint that water must have been abundant in the area where the comet formed and that Tempel 1 is not as carbon-rich as some of its peers; carbon-based materials appear to make up only 20 percent of this comet compared to as much as 50 percent of others. Nevertheless, the material in Tempel 1 matches that ejected by Comet Hale-Bopp in 1995 and that means that these comets formed in broadly similar ways, the researchers argue. Science published the paper analyzing the spectra online yesterday. –David Biello

From:http://www.physorg.com/news70120085.html

“在八月的会议上，国际天文联合会（IAU)将作出决定是否将冥王星从行星中除名。 国际天文联合会将首次官方定义“行星”这个词，而它正在世界天文学界引起争议。也许现在唯一能够确定是太阳系不再是九大行星。这个争议开始于发现了潜在的 第十行星，2005年一月临时命名为2003 UB313，它比冥王星大。一些天文学家认为太阳系拥有八大行星，冥王星与2003 UB313都达不到行星的等级，其他天文学家则认为要重新定义行星。”

At its conference this August, the International Astronomical Union (IAU) will make a decision that could see Pluto lose its status as a planet.

For the first time, the organisation will be officially defining the word “planet”, and it is causing much debate in the world of astronomy.

There is only one thing that everyone seems to agree on: there are no longer nine planets in the Solar System.

The debate has been brought to a head by the discovery of a potential 10th planet, temporarily named 2003 UB313 in January 2005. This new candidate planet is bigger than Pluto.

The question now facing the IAU is whether to make this new discovery a planet.

Pluto is an unusual planet as it is made predominantly of ice and is smaller even than the Earth’s Moon.

There is a group of astronomers that are arguing for an eight-planet SolarSystem, with neither Pluto or 2003 UB313 making the grade as a planet; but a number of astronomers are arguing for a more specific definition of a planet.

One of these; Kuiper Belt researcher Dr Marc Buie, of the Lowell Observatory in Arizona, has come up with a clear planetary definition he would like to see the IAU adopt.

I believe the definition of planet should be as simple as possible, so I’ve come up with two criteria,” he said.

“One is that it can’t be big enough to burn its own matter - that’s what a star does. On the small end, I think the boundary between a planet and not a planet should be, is the gravity of the object stronger than the strength of the material of the object? That’s a fancy way of saying is it round?”

This definition could lead to our Solar System having as many as 20 planets, including Pluto, 2003 UB313, and many objects that were previously classified as moons or asteroids.

One possible resolution to the debate is for new categories of planet to be introduced. Mercury, Venus, the Earth and Mars would be “rocky planets”. The gas-giants Jupiter, Saturn, Uranus and Neptune would be a second category.

Whatever the outcome of this debate there is only one thing that we can be certain of; by September 2006 there will no longer be just nine planets in our Solar System.

Source: BNSC