Giant Protoplanet Directly Observed For First Time

The planet formation process, until now only known from computer simulation, was possibly observed directly for the first time in a not too far away system by Swiss astronomers using ESO’s Very Large Telescope. A protoplanet candidate, similar to the gas giant Jupiter, was detected to be embedded in a thick disc of gas and dust surrounding the young star HD 100546 located 335 light-years from Earth.

“So far, planet formation has mostly been a topic tackled by computer simulations,” says Sascha Quanz at the Swiss Federal Institute of Technology Zurich (ETH Zurich), who led an international team for the study. “If our discovery is indeed a forming planet, then for the first time scientists will be able to study the planet formation process and the interaction of a forming planet and its natal environment empirically at a very early stage.”

The star system HD 100546 is quite well known and believed to contain a giant planet that orbits about six times further from the star than the Earth is from the Sun. The newly found planet candidate is located in the outer regions of the system, about ten times further out--which actually runs counter to some current theories about planet formation and exoplanets because it is a bit too far out for a forming planet.

The planet candidate around HD 100546 was detected as a faint blob located in the circumstellar disc revealed thanks to the NACO adaptive optics instrument on ESO’s VLT, combined with pioneering data analysis techniques. By using a special coronagraph in NACO which operates at near-infrared wavelengths the brilliant light coming from the star could be blocked exactly at the location of the protoplanet candidate to obtain the observation.

According to current theory, giant planets grow by mopping up some of the gas and dust that remains after the formation of a star, and the astronomers have indeed spotted several features in the new image of the disc around HD100546 that support this protoplanet hypothesis.

There is a second hypothesis about the current find, since it could also be a planet being ejected from the system instead of a forming one. There is a very good way to confirm one of the options though: with more observation. If the point source moves away from the star radially in the next decade, this would support the ejection theory. If it is a protoplanet, it would have to move in an orbit around HD100546. In one year, that would mean roughly a one-degree deviation from its present location. "If we observe the object regularly, we'll soon be able to prove which hypothesis is correct," says Quanz.

Adam Amara, another member of the team, is enthusiastic about the finding. “Exoplanet research is one of the most exciting new frontiers in astronomy, and direct imaging of planets is still a new field, greatly benefiting from recent improvements in instruments and data analysis methods. In this research we used data analysis techniques developed for cosmological research, showing that cross-fertilisation of ideas between fields can lead to extraordinary progress.”

The ESO will carry out further research, and in the next decade it should be able to take a much closer look using its planned European Extremely Large Telescope (E-ELT), which is currently in the design phase.

Study:

Quanz SP et al.: A Young Protoplanet Candidate Embedded in the Circumstellar disc of HD 100546, Astrophysical Journal Letters, 2013.