[Rockhounds] Researchers Revise Recipe for Building a Rocky Planet Like Earth

[Kreigh Tomaszewski]

Bob O’Dell wasn’t quite sure what he was looking at. It was 1992, and he
had just got his hands on new images from the Hubble Space Telescope that
zoomed in on young stars in the Orion Nebula. O’Dell had been hoping to
study the nebula itself, an interesting region of star formation relatively
close to Earth. Yet something else caught his attention. Several of the
stars didn’t look like stars at all, but were instead enveloped by a dim
shroud. They seemed to form a “silhouette against the nebula,” said O’Dell.

At first O’Dell and his colleagues thought they might be seeing an image
artifact resulting from Hubble’s warped primary mirror, which had been
molded ever so slightly into the wrong shape and would be fixed by a space
shuttle mission in 1993. “We really wondered if this was a residual effect
of the flawed primary mirror,” said O’Dell
<https://www.vanderbilt.edu/AnS/physics/cv/odell.html>, who had been
Hubble’s project scientist. Soon, however, they saw more and more of the
phenomena <https://esahubble.org/images/opo9229c/> in the images, even after
the mirror was fixed
<https://hubblesite.org/contents/news-releases/1994/news-1994-24.html>, and
realized it wasn’t a flaw at all. They were actually seeing infant disks of
dust and gas surrounding young stars. They were, for the first time,
witnessing the birth of planets.

O’Dell’s discovery of protoplanetary disks sparked a transformation in our
understanding of planet formation. In the following decades, astronomers
would realize that our classical idea of how planets form — small rocks
clump into bigger rocks, which then clump further — might not be correct.
For the gas giants, such as Jupiter and Saturn, a model called pebble
accretion, where a dominant object gobbles up smaller rocks — would come to
replace the old views of how such monstrous worlds come to be.

https://www.quantamagazine.org/scientists-debate-if-cosmic-pebbles-create-rocky-planets-like-earth-20211103/