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ORIGINS

Mobile music rocked the record industry

Sony’s Walkman portable audio cassette player in 1979 improved on the transistor radio by allowing people to take their

preferred music wherever they went (engineer Nobutoshi Kihara supposedly invented the device so that Sony co-chairman Akio Morita could listen to operas during long fl ights). But the digital revolution in personal audio technology was another two decades in the making and had implications beyond both the personal and audio.

Portable music went digital in the 1980s with the rise of devices built around CDs, mini discs and digital audiotape. In the 1990s the Moving Picture Experts Group (MPEG) developed a standard that became the MP3, a format that highly condenses audio fi les by discarding imper-ceptible sounds (although discriminating audio-philes tend to disagree with that description).

The Eiger Labs MPMan F10, which hit the market in 1998, was the fi rst MP3 player to store music on digital fl ash memory—a whopping 32

megabytes, enough for about half an hour of audio. A slew of similar gadgets followed, some of which replaced the fl ash memory with com-pact hard drives capable of holding thousands of songs. The breakthrough product was Apple’s 2001 iPod. Technologically, it was nothing new, but the combination of its physical sleekness, its spacious fi ve-gigabyte hard drive and its thumbwheel-based interface proved compelling. Today digital players are as likely to hold photo-graphs, videos and games as music, and they are increasingly often bundled into mobile phones and other devices.

MP3s—immaterial and easily copied—freed music from the physical grooves in vinyl or plastic media. They also dealt a severe blow to the recording industry, which long resisted selling MP3s, prompting music lovers to distribute fi les on their own. Since 2000, CD sales plummeted from $13 billion to $5 billion, according to the Recording Industry Association of America.

Meanwhile digital downloads rose from $138 million in 2004 to $1 billion last year; however, says Russ Crupnick, a senior industry analyst at NPD Entertainment, peer-to-peer shared fi les outnumber legal downloads by at least 10 to one. Looking ahead, he believes music will not be something to possess at all: the industry’s salva-tion (if any) may come from paid access to songs streaming from the Web. —Christie Nicholson

DIGITAL AUDIO PLAYER

ASTEROIDSThe small fry of the solar system have troubled pasts

For many people, asteroids are big rocks that drift menacingly through space and are great places to have a laser cannon dogfi ght. Conventional scientifi c

wisdom holds that they are the leftover scraps of planet formation. Their full story, though, is rather more complex and still only dimly glimpsed. What planetary scientists lump together as asteroids are far too diverse—from boul-ders to fl oating heaps of gravel to mini planets with signs of past volcanic activity and even liquid water—to have a single common origin.

Only the largest, more than about 100 kilometers across, date to the dawn of our solar system 4.6 billion years ago. Back then, the system was basically one big swarm of asteroids or, as researchers call them at this early

stage, planetesimals. How it got that way is a puzzle, but the leading idea is that

primordial dust swirling around the nascent sun coagulated into pro-

gressively larger bodies.

Some of those bodies then agglomerated into planets; some, accelerated by the gravity of larger bodies, were fl ung into deep space; some fell into the sun; and a tiny few did none of the above. Those survivors linger in pockets where the planets have left them alone, notably the gap between the orbits of Mars and Jupiter. Gradually they, too, are being picked off. Fewer than one in 1,000, and perhaps as few as one in a million, of the asteroids original-ly in the main belt remain.

Smaller asteroids are not relics but debris. They come in an assortment of sizes that indicate they are products of a chain reaction of collisions: asteroids hit and shatter, the fragments hit and shatter, and so on. Some are rocky; some are metal—suggesting they came from different layers within the original bodies. About a third of asteroids be-long to families with similar orbits, which can be rewound in time to a single point in space, namely, the location of the collision that birthed them. Because families should disperse after 10 million to 100 million years, asteroid formation by collision must be an ongoing process.

Indeed, so is planet formation. Whenever an asteroid hits a planet, it helps to bulk it up. Asteroids are not the leftovers of planet formation so much as they are the fi nishing touches. —George Musser