How do planets form? For many years, scientists believed they understood this process by studying the one example we had access to: our own solar system.
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New research has identified a hot gas giant similar to our own Jupiter, in the process of forming around a star about 500 light-years from Earth.
This rare “baby Jupiter” in the solar system that is in the process of forming, drawing matter from a huge disk of dust and gas swirling around its also infant sun, has opened a window into mysteries that have puzzled astronomers for years and into the question: How do planets form?
Scientific research into the origins of Earth and the other planets in our solar system began in the mid-17th century.
When the first planetary systems orbiting distant stars were discovered in the mid-1990s, there was immediate controversy and concern. The new planets didn't fit the model at all.
Since then, there has been a realization that there may be different paths for a planetary system to form. Among the thousands of planets orbiting other stars that now populate our catalogs, our sun's family of planets is starting to look somewhat unusual.
However, one of the most basic physical components of the planet-building mechanism we believe is responsible for the formation of giant gas planets like Jupiter and Saturn has stood the test of time: the idea of "core accretion.".
Core accretion begins with the gases and tiny dust grains that are thought to form the typical Kantian cloud (which is shaped like a flattened rotating disk with the infant star at its center). The dust grains coalesce into successively larger grains, then pebbles, rocks, and then a cascade of baby planets or "planetoids.".
When such a cluster becomes large enough, it reaches a tipping point. Gravitational pull now helps the embryonic planet quickly pull in gas, dust, and other clumps, clearing its orbital path and carving a circular gap in the disk.
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It is one of the characteristic triumphs of modern astronomy that precisely the kinds of "empty disks" predicted by theory are now seen and studied in the world.
Last year, a massive planet was detected, in the process of forming, around a star about 500 light-years from Earth.
This star, called AB Aurigae, has become famous in astronomy circles for the beautiful, intricate, spiral disk that surrounds it.
The clumps and waves seen in this disk are consistent with what one would see if gravitational collapse were occurring. But until now, evidence for planet formation has been lacking.
This newly discovered planet – named AB Aurigae b – is embedded in a thick, swirling halo of dust and gas, amidst telltale spirals and waves that suggest gravitational collapse. The planet is about 93 times farther from its star than Earth is from the sun, far outside the region where the traditional core-accretion theory could explain its formation.
This discovery thus provides strong evidence for the alternative theory of gravitational collapse.
The discovery was made using observations from the Subaru Telescope on Mauna Kea , Hawaii, as well as the Hubble.
Fueled by energy from the violent, rapid formation process, the planet is hot enough to glow (about 2000 degrees Celsius). It is this glow that gives the planet its presence. At the same time, the swirling gas and dust around the forming planet appear illuminated by the blue light of AB Aurigae's central star.
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This new discovery in the solar system provides a crucial piece of the planet formation puzzle, but the case is by no means closed.
As the science and technology at our disposal evolve, so does our ability to ultimately discover how the planets that make up our universe are formed.
