An infant planet thought to have been born less than ten million years ago has been identified by astronomers.
The planet is the youngest yet discovered and is in a solar system still being formed from cosmic dust and gas. Despite being a baby, chronologically speaking, it is vast in comparison with Earth and has been classified as a giant planet. Astronomers reckon that it has a mass 3,115 times that of our own planet and 9.8 times that of Jupiter.
Previously the youngest planet to have been identified was an estimated 100 million years old. Earth is calculated to be 4.5 billion years old.
The new planet orbits an infant star, called TW Hydrae (TW Hya), which is thought to have formed between eight and ten million years ago.
The planet would have formed shortly after the birth of the star and it is possible that other planets are forming within the disc. The star is 180 million light years from Earth. On Earth at that time, chimpanzees were splitting from gorillas to form a branch of the ape family tree that led to the evolution of human beings. Dinosaurs had been extinct for 50 million years.
The new planet is 3.7 million miles from its parent star - compared with the 93 million miles between Earth and the Sun - and takes a mere 3.56 days to complete an orbit around TW Hya.
Star systems are thought to form amid clouds of dust and gas, and the discovery of the planet is expected to provide insights into the mechanisms.
The researchers demonstrated that the new planet, TW Hya b, had formed within the first ten million years of the star system's formation, before stellar winds and radiation could dissipate the clouds.
The process of formation of TW Hya is still continuing and is thought to be nearly complete. There is a gap of 5.6 million miles between the star and the inside edge of the disc of clouds surrounding it.
The planet lies between the disc and the star and it was the absence of gas or dust in the gap where it orbits that helped to alert astronomers. Vast discs of dust and as are thought to form stars and planets because microscopic specks of matter bump into each other to create lumps that eventually become big enough to form cores.
Researchers from the Max Planck Institute for Astronomy, in Germany, reported their discovery in the journal Nature. They said: "There is a general consensus that planets form within discs of dust and gas around newly born stars. Details of their formation process, however, are a matter of debate. The timescale of planet formation remains unclear, so the detection of planets around young stars with protoplanetary discs is potentially of great interest. Hitherto, no such planet has been found."
An alternative theory is that gravitational anomalies within the disc of dust and gas cause giant planets to form.