Planets can form before stars are fully grown

Scientists do not know whether early planet formation is an anomaly or common to very young stars.

Scientists have discovered evidence of planet formation in the disk of dust and gas surrounding a young star that is not fully grown.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), a network of 66 connected radio telescopes that covers nearly ten miles (16 km) in Chile’s Atacama Desert, a group of astronomers from the Netherlands, Denmark, and Sweden observed TMC1A, a star in the constellation Taurus that is still in the process of developing.

In one part of the protoplanetary disk surrounding the star, the researchers detected a lack of carbon monoxide radiation, which they attributed to large dust particles in the area.  To test the theory, they inputted the data into numerical computer models, which indicated rapid growth of dust particles from approximately one-thousandth of a millimeter to one millimeter in this region of the disk.

“The results indicate that planets already start forming while the star is still developing,” noted lead researcher Daniel Harsono of Leiden University in the Netherlands.

Major questions continue to puzzle scientists regarding the process of planet formation, especially how it produces such a wide variety of planet masses and numbers in different star systems. This discovery suggests planet formation begins significantly earlier than researchers expected, before parent stars are fully grown.

“Only early protoplanetary disks contain sufficient mass to form giant planets,” said Per Bjerkeli of Chalmers University in Sweden. Formation of giant planets may have already begun in this particular system.

Scientists will have to study protoplanetary disks surrounding other protostars to determine whether the start of planet formation around TMC1A is typical or an exception.

“Maybe this young disk is very special,” commented research team member Matthijs van der Wiel of the Netherlands Institute for Radio Astronomy (ASTRON).

Findings of the study have been published in the journal Nature Astronomy.

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