"So far, planet formation has mostly been a topic tackled by computer simulations," said lead scientist Sascha Quanz, an astronomer at Swiss university ETH Zurich.
"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 astronomers said several features of the image support the theory that giant planets grow by picking up gas and dust remaining after a star forms.
Scientists detected the protoplanet using a high-resolution camera linked to the European Southern Observatory's telescope in Chile's Atacama desert.
The ESO, a collaboration involving 15 mainly European countries, operates a number of high-powered telescopes in Chile, including the Very Large Telescope array (VLT), the world's most advanced telescope.