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

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

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.