In the many years that astronomers have been watching the skies, they’ve hoped to get a glimpse of the moment a new planet is formed. Now, a new study published in the journal Astronomy and Astrophysics has confirmed the first ever image of the birth of a new planet.
The image of the forming planet shows a blob of light surrounded by bright gas and dust, which are orbiting a young star dubbed PDS70 by astronomers. The black circle seen in the image is a filter that blocks the light from the star and allows other parts of the star system to been glimpsed. The star is surrounded by a layer of gas and dust called a “protoplanetary disk”. The planet was discovered within this disk, which means the planet is still close to where it was initially born and is presumably still growing through the accumulation of material.
The image was captured by the European Southern Observatory’s Very Large Telescope, specifically by a device called the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. SPHERE was able to take measurements of the planet’s brightness at different wavelengths, which lets the researchers determine the likely properties of the planet’s atmosphere. The young planet was found thanks to two separate space survey programmes called DISK and SHINE. SHINE’s (SpHere INfrared survey for Exoplanets) goal is to gather more information about the evolutionary process of planets, while DISK’s (sphere survey for circumstellar DISK) goal is to examine young planetary systems and their protoplanetary discs to determine the initial conditions needed for planetary formation.
The planet is a gas giant with a mass much greater than that of Jupiter and the newly formed planet is thought to be approximately as far from its own star as the distance between our sun and Uranus. The current theory of planet formation is that young stars frequently suck up nearby gas, meaning that most of the planets close to stars are made out of rock, just like the Earth and Mars. The farther out a planet is, the easier it is for it to become a gas giant, just like Jupiter.
Analyses of the planet revealed that it probably has a surface temperature of around 1000 degrees Celsius and a cloudy atmosphere. The star that the new planet orbits around is likely only five to six million years old, and the planet itself is likely even younger. Even though SPHERE utilized a coronagraph to block out the light from PDS70, the researchers still had to verify the planet’s signals in multiple ways, a process that was quite difficult.
Miriam Keppler, from the Max Planck Institute for Astronomy in Germany, was one of the lead authors on the study. Keppler explains that the discs of gas and dust that surround young stars are where planets are born, yet only a few observations have detected even hints of the formation of planets within these regions. Keppler was part of a secondary team of astronomers who studied the new planet after its discovery, examining wavelengths of light to infer that the planet possesses a cloudy atmosphere. According to Keppler, until now it was difficult to conclusively say that the candidates for planets were indeed planets. The observations made by astronomers in the past could simply have been features within the disc of dust. To ensure that the detection of the newly formed planet was legitimate, the astronomers used several different instruments with different filter bands to make observations.
The orbiter Kepler telescope has previously been used to identify possible young planets, but Keppler says that method has its own limitations as it relies on the dimming of a star’s light as a space body moves between the telescope and the star. Keppler says that the new planet can be imaged directly with their new imaging equipment. Keppler explains:
In this case we now have a direct image [of the planet] in its “birthplace”, which is the circumstellar disc. This is especially important because people have been wondering [for a long time], how these planets actually form and how the dust and the material in this disc forms [into] a planet, and now we can directly observe this.
Keppler explains that astronomers will now have to make further observations of the planet to determine how the planet will likely develop and to trace the orbit of the planet around the star. It’s currently thought that the planet will need around 120 years to complete a revolution around PDS70.
Other scientists, such as astrophysicist Zoe Leinhardt, from the University of Bristol (not involved in the research), have reacted enthusiastically to the discovery. Leinhardt explains that PDS70 is a relatively young star that had all the right indicators of having new planets around it and that the discovery of the new planet very likely confirms this theory. The discovery seems to support the current theory of how planets form. The way planets form means that a large planet similar in size to Jupiter would be the easiest to see, and those planets would also be the ones which form more quickly. There could even be neighboring planets surrounding the star that are newly formed as well.
While the discovery is exciting and has astronomers looking to keep doing research on the planet, it does raise a few important questions. It’s currently a mystery as to how such a large planet could form at such a great distance from its parent star, as the current planet formation theory has difficulty accounting for this distance.
The image of the planet orbiting PDS70 comes just a few weeks after the discovery of three probably newborn planets by the Atacama Large Millimetre/submillimetre Array (ALMA), located in Chile. Three planets were discovered orbiting a rather young star called HD163296. Astrophysicist Christophe Pinte and colleagues discovered a baby planet while examining the structure of the protoplanetary disc around HD163296, with an odd kink in the generally smooth trajectory of carbon monoxide gas flow matching directly with what a computer simulation of what a newly formed planet in a disc would look like.