Seeing a planet form is harder than watching a plant grow: it can take hundreds of thousands of years for specks of space dust to snowball into a single meter-size rock. It takes many more eons for such a rock to reach the size of a small asteroid or planet. But scientists say they have now witnessed the very first stages of planet formation in the Orion Nebula. Science published the results electronically today.

Using visible and infrared data from the Hubble Space Telescope, the researchers estimated the size of dust particles orbiting several young sun-like stars in Orion and confirmed that the particles are clumping together and expanding. "The dust we are seeing in the visible light observations appears gray, which we haven't seen in astronomy before," says Henry Throop, formerly at the University of Colorado at Boulder and now at Southwest Research Institute. "Small particles in space usually cause the light behind them to appear slightly red. That isn't happening here at all, and these dust grains are gigantic compared to what we expected to see."

Another mystery is whether these embryonic bodies will survive in Orion's womb, which is filled with violent and powerful type O and type B stars. "UV light comes streaming off these large stars like a blowtorch, evaporating the gases and removing the dust from the circumstellar dust rings of the smaller stars," remarks John Bally of CU-Boulder's Center for Astrophysics and Space Astronomy. "Thus, massive stars are hazardous to planets forming around nearby, lower mass stars." If they do survive, however, the planets won't resemble Earth. "I think we can safely conclude that planetary systems, wherever they form, will be unique," Throop adds.