Published on March 2nd, 2013 | by James Ayre
The Birth Of A Planet, Protoplanet Imaged In The Process Of Formation
The first direct observation of a exoplanet forming out of its thick proto-planetary disc of dust and gas has been made by researchers with the ESO’s Very Large Telescope. Once confirmed, the finding should help to considerably improve the scientific understanding of how planets form, and also to offer an observable object to test theories on.
A team of international researchers investigating the disc of gas and dust around the star HD 100546 were surprised to discover what appears to be a planet in the process of formation within the disc of material, while still being embedded in it. HD 100546 is a fairly-close neighbor to us, being located ‘only’ about 335 light-years from the Earth.
“So far, planet formation has mostly been a topic tackled by computer simulations,” says Sascha Quanz, lead researcher. “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.”
“HD 100546 is a well-studied object, and it has already been suggested that a giant planet orbits about six times further from the star than Earth is from the Sun. The newly found planet candidate is located in the outer regions of the system, about ten times further out.”
The extreme distance that the planet appears to be forming at from its star is inconsistent with currently popular theory, which supposes that planets form relatively close in before migrating outwards because of collisions and interactions.
“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. The observations were made using a special coronagraph in NACO, which operates at near-infrared wavelengths and suppresses the brilliant light coming from the star at the location of the protoplanet candidate.”
Based on currently popular theory, “giant planets grow by capturing some of the gas and dust that remains after the formation of a star. The astronomers have spotted several features in the new image of the disc around HD100546 that support this protoplanet hypothesis. Structures in the dusty circumstellar disc, which could be caused by interactions between the planet and the disc, were revealed close to the detected protoplanet. Also, there are indications that the surroundings of the protoplanet are potentially heated up by the formation process.”
Adam Amara, one of the members of the research team, says, “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.”
Even though “the protoplanet is the most likely explanation for the observations, the results of this study require follow-up observations to confirm the existence of the planet and discard other plausible scenarios.”
Some of these other explanations include: a mixed signal it is possible from a background source, the possibility that the newly discovery may not be a protoplanet, but actually a already formed planet ejected outwards from the star into a debris field. “When the new object around HD 100546 is confirmed to be a forming planet embedded in its parent disc of gas and dust, it will become an unique laboratory in which to study the formation process of a new planetary system.”
Some more information on planet formation:
“It is not known with certainty how planets are formed. The prevailing theory is that they are formed during the collapse of a nebula into a thin disk of gas and dust. A protostar forms at the core, surrounded by a rotating protoplanetary disk. Through accretion (a process of sticky collision) dust particles in the disk steadily accumulate mass to form ever-larger bodies. Local concentrations of mass known as planetesimals form, and these accelerate the accretion process by drawing in additional material by their gravitational attraction. These concentrations become ever denser until they collapse inward under gravity to form protoplanets. After a planet reaches a diameter larger than the Earth’s moon, it begins to accumulate an extended atmosphere, greatly increasing the capture rate of the planetesimals by means of atmospheric drag.”
“When the protostar has grown such that it ignites to form a star, the surviving disk is removed from the inside outward by photoevaporation, the solar wind, Poynting–Robertson drag and other effects. Thereafter there still may be many protoplanets orbiting the star or each other, but over time many will collide, either to form a single larger planet or release material for other larger protoplanets or planets to absorb. Those objects that have become massive enough will capture most matter in their orbital neighbourhoods to become planets. Meanwhile, protoplanets that have avoided collisions may become natural satellites of planets through a process of gravitational capture, or remain in belts of other objects to become either dwarf planets or small bodies.”
“The energetic impacts of the smaller planetesimals (as well as radioactive decay) will heat up the growing planet, causing it to at least partially melt. The interior of the planet begins to differentiate by mass, developing a denser core. Smaller terrestrial planets lose most of their atmospheres because of this accretion, but the lost gases can be replaced by outgassing from the mantle and from the subsequent impact of comets. (Smaller planets will lose any atmosphere they gain through various escape mechanisms.)”
“With the discovery and observation of planetary systems around stars other than our own, it is becoming possible to elaborate, revise or even replace this account. The level of metallicity – an astronomical term describing the abundance of chemical elements with an atomic number greater than 2 (helium) – is now believed to determine the likelihood that a star will have planets. Hence, it is thought that a metal-rich population I star will likely possess a more substantial planetary system than a metal-poor, population II star.”
Image Credits: ESO/L. Calçada; ESO/NASA/ESA/Ardila et al.