A Third Exoplanet Discovered in the Beta Pictoris System, Among the Weakest Exoplanets Ever Detected
The search for exoplanets is just beginning, and despite everything, over 6,300 have already been identified (among those confirmed). The goal of the research is not to find an alternative to Earth but to understand what types of exoplanets are most common in the cosmos, what their characteristics are, and which could potentially be habitable, although this last point presents a greater challenge.
One of the latest developments in this area is the discovery of the exoplanet Beta Pictoris d, which orbits around the star Beta Pictoris (which names the planetary system) along with two other previously known planets. The interesting part is that Beta Pictoris d is a hundred times weaker than Beta Pictoris b, the first discovered in the same system, making it one of the lightest exoplanets ever observed from Earth.
The New Exoplanet in the Beta Pictoris System
The discovery was made possible thanks to the Very Large Telescope (VLT) of ESO, but the exoplanet turned out to be anything but easy to detect. This object was hidden in numerous archival observations dating back over a decade. As Ben Sutlieff (University of Edinburgh) recounts, "Initially, we wanted to better observe an already known planet in the system, Beta Pictoris b, to see how it evolved over time." However, while analyzing the images, the team noticed something unexpected.
Markus Bonse (ESO astronomer) added, "There’s something else there, did you see it?". The details of the discovery were included in the study titled Direct Imaging Discovery of Giant Exoplanet β Pictoris d: A Decade-Long Game of Hide-and-Seek. To verify the nature of this new object, the researchers consulted the ESO archive, finding traces of Beta Pictoris d in various images taken up to eleven years prior, including one in which it was barely distinguishable from the light of the larger Beta Pictoris b.
Although it is a particularly weak exoplanet, it is not actually that "small". Beta Pictoris d is a gas giant similar to Jupiter or Saturn, but with a much wider orbit. While the other two exoplanets in this planetary system have a mass about ten times that of Jupiter, the newly discovered one is only 2.4 times (± 0.6) more massive, which makes it one of the lightest planets ever directly photographed from Earth (its size is 1.26 Jupiter radii). Obtaining a direct image of such a weak object compared to its mother star represents a significant scientific achievement. The temperature of Beta Pictoris d is about 326°C, making it relatively cool compared to other gas giants.
The first clear observation of the exoplanet, located 63 light-years from Earth, was made using the ERIS (Enhanced Resolution Imager and Spectrograph) instrument of the Very Large Telescope. Simultaneously, an independent group led by Aidan Gibbs from the University of California identified the same planet using the James Webb Space Telescope, also publishing results on the same day. Confirmations also came from previous observations collected with the SPHERE instrument of the VLT and with NIRCam of the JWST, data that, once the search area was known, revealed the planet's presence from the beginning.
Thus, Beta Pictoris becomes the second planetary system, after HR 8799, in which more than two exoplanets are directly photographed. Sutlieff compares these multiple systems to a “Holy Grail” for research, as they allow understanding of how much exoplanets born in the same formation environment can differ. Additionally, the new planet helps to explain the unusual shape of the debris disk surrounding the star. Its orbit is about 26 AU and inclined at 89° (co-planar to the other two), while the dust disk is located about 40 AU away.
Beth Biller (co-author of the study) is already looking to the future: thanks to the upcoming Extremely Large Telescope (ELT) of ESO, many more low-mass planets, which currently remain hidden, could soon be discovered.