The countless frustrated attempts to find Planet 9 , a hypothetical giant gas planet in the confines of our solar system, have sparked the ingenuity of some Taiwanese scientists.
Short. For years, astronomers have swept the sky in search of the weak reflection of sunlight that should reach us from Planet 9, a demonstrably ineffective task. Despite numerous searches, the elusive planet has remained hidden, making the quest a challenging endeavor.
Now, a team of researchers has changed the rules of the game with an ingenious idea: instead of looking for light, they have opted to detect the planet’s heat . Their innovative approach has led to the identification of two very promising candidates .
Context. Beyond the orbit of Neptune lies an icy and dark region known as the Kuiper Belt , where the orbits of several objects seem to be grouped in a way that defies random chance. The trajectories of these transneptunian objects (TNOs) align as if an invisible hand were guiding them, leading astronomers to postulate the existence of something significant lurking just out of sight.
The most accepted hypothesis to explain this behavior is the existence of a massive unknown planet , referred to as Planet 9. If it exists, this distant world could possess a mass between five and ten times that of Earth . However, its vast distance—more than 400 astronomical units away—renders its light extremely dim. For perspective, Neptune is “only” 30 AU away or approximately 4,496 million kilometers from Earth.
If we can’t see it, maybe we can feel its heat. A team from the National Tsing Hua University in Taiwan believes they may have the strongest lead in years regarding the existence of this elusive object. Although the results of their study are not yet final , the findings point to two promising candidates.
Every object with a temperature above absolute zero emits thermal radiation—essentially, heat. While light decreases with distance following an inverse fourth power relationship (1/d4), heat diminishes only with the square of the distance (1/d2). This significant difference is the basis for the researchers to focus their search on the heat signature potentially emitted by Planet 9.
A needle in a haystack. The team harnessed the data from the Akari Space Telescope of Japan. Launched in 2006, Akari dedicated its operational life to sweeping the entire sky in distant infrared light, the optimal range for detecting the thermal brightness of Planet 9. Conducted from space, this research was free from the interference typically caused by Earth’s atmosphere.
Astronomers started with over 5.2 million signals from unprocessed data, which included many false positives. After narrowing down the search area, eliminating known objects, filtering sources contaminated by galactic dust clouds, and excluding static objects that seemed to occupy the same point in observations made months apart, they managed to reduce the number to 393 candidates .
From 393 candidates to two. The researchers meticulously inspected the images of these 393 potential candidates. They discarded weak detections, artifacts at the edges of the sensor, and particularly the effects of cosmic rays that could be mistaken for sources of heat.
After this exhaustive methodical process, only two primary candidates remained. These two heat sources appeared in the expected region for Planet 9, exhibited the predicted brightness based on theoretical models, and demonstrated the anticipated movement: they were detected in the same location within a 24-hour period but left no trace in that spot six months later.
All to demonstrate. The two candidates were tentatively named FISSDL J0250422-15011 and FISSDL J0301112-164240 . To confirm whether these two heat points represent a single object moving in an orbit consistent with that of Planet 9, further observations in visible light will be necessary, utilizing powerful telescopes capable of detecting their faint optical signatures and accurately measuring their movement.
If verified, this discovery could not only resolve one of the greatest mysteries of modern astronomy but also revolutionize our understanding of how our solar system was formed and evolved. While everything is still to be validated, at least we have a hot trail to follow in our pursuit of this enigmatic celestial body.
Image | ESA, Hubble, M. Kornmesser, CC By 4.0