Donald Savage
Headquarters, Washington, DC                April 26, 2001
(Phone: 202/358-1547)

Nancy Neal
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-0039)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4514)

RELEASE: 01-84

HUBBLE CAPTURES GALATIC  EPISODE OF SURVIVOR

     A dramatic life-and-death struggle of planetary survival 
taking place inside a giant cloud of gas and dust, 1,500 
light-years from Earth, could hold the key to how many planets 
actually exist in our Milky Way galaxy.

The good news, published electronically tomorrow by the 
journal Science, is that NASA's Hubble Space Telescope got an 
inside look at Earth's closest large star-factory. The images 
provide the first direct visual evidence for growth of planet 
building blocks inside embryonic dust disks around dozens of 
stars in the giant Orion Nebula.

The bad news is that other observations suggest, as in many 
contests, fledgling planets face a time obstacle, having to 
quickly beat the clock by forming before they evaporate under 
a blistering flood of radiation from the nebula's brightest 
star, called Theta 1 Orionis C. 

In the new research, John Bally of the University of Colorado 
and Henry Throop of the Southwest Research Institute, both in 
Boulder, CO, and co-investigators used Hubble to assess if 
planets were beginning to grow in million-year-old dusty disks 
in Orion. 

"This is the first time that large growing grains, from the 
size of smoke particles to sand grains, have been seen in 
visible light in these protoplanetary disks," said Throop. 
"The dust we're seeing in the Hubble observations is large, 
completely unlike dust that we've seen in young star-forming 
regions like this before. We're seeing the very first stages 
of planetary formation happening before our eyes."

"We have two things happening in these systems: Dust grains 
are beginning to stick together as a first step toward making 
planets, but then these bright stars are trying to tear 
everything apart. Which one wins is really a big question," 
Throop continued. "It's like trying to build a skyscraper in 
the middle of a tornado."

These observations show for the first time that it may be easy 
to start building planets. According to conventional theory 
the grains will continue to clump together, and as they grow 
gravity pulls in more material until the grains become 
planets. This discovery bolsters the long-proposed scenario 
for how Earth and our solar system formed 4.5 billion years 
ago.

If planets are not able to form quickly it could mean that 
they are more rare in our galaxy than thought previously. The 
astronomers point out this is not inconsistent with extrasolar 
planet discoveries so far, showing about five percent of the 
stars in our solar neighborhood have Jupiter-sized planets in 
small orbits.

Protoplanetary disks in Orion were first discovered in 1992 
and dubbed "proplyds." At first their existence seemed to 
greatly improve the odds for abundant planets in the galaxy, 
because these disks appeared to confirm a common model of 
planet formation. However, subsequent Hubble pictures revealed 
proplyds being blowtorched away by a relentless blast of 
radiation from the nebula's largest star. The doomed systems 
look like hapless comets, with wayward tails of gas boiling 
off the withering pancake-shaped disks. 

The researchers predict that that within 100,000 years the 
vast majority of the youngest 
disks -- which started out stretching billions of miles across 
-- will be largely destroyed. But in the small number of 
proplyds that are shielded from the ultraviolet radiation, 
planet formation will be business as usual, with these stars 
probably becoming hosts to a variety of planets. "We're seeing 
that planet formation is a hazardous process," said Bally.

Bally believes that the gaseous component of a disk will 
largely vaporize away but will leave behind a residual 
"gravel" disk of rocky pebbles that may successfully build 
terrestrial planets like Earth out of the grains he's seeing 
form. 

If giant planets like Jupiter could collapse quickly out of a 
gas disk they might survive, according to a theory proposed by 
Alan Boss of Carnegie Institutions of Washington. "Only time 
will tell. If we find lots of Jupiters around other stars, 
then it means the planets have managed to grow rapidly in 
Orion-type environments," said Boss.
 
"This discovery goes a long way toward helping us answer one 
of the biggest questions in science: Are we alone?" said Dr. 
Anne Kinney, Director of NASA's Origins Program at NASA 
Headquarters, Washington, DC. "Understanding planet formation 
gets us a step closer to that goal, something we hope to 
answer with the Terrestrial Planet Finder, a large space-based 
telescope we're planning for the next decade." The Hubble 
Space Telescope is a project of international cooperation 
between NASA and the European Space Agency. 

                         -end-