If Planet Nine Really Is Out There, It May Be 'Invisible' To Our Telescopes

Although the evidence to support the existence of Planet Nine has only been circumstantial so far, astronomers continue the search for this mysterious world hypothetically lurking in the outer regions of the solar system.

Thought to hide out somewhere beyond the orbit of Neptune and the Kuiper belt, the elusive Planet Nine was first theorized in 2016 by Konstantin Batygin and Mike Brown, two planetary astrophysicists with the California Institute of Technology (Caltech).

As reported by The Inquisitr, Batygin and Brown proposed that this enigmatic planet, known as the "missing super-Earth," is the reason behind the peculiar orbit of a handful of small objects in the Kuiper belt, which exhibit a bizarre tilt in relation to the plane of the solar system.

The scientists speculate that these objects, called trans-Neptunian objects or TNOs, are being pulled by the gravity of Planet Nine, an ice giant believed to weigh between five and 20 times the mass of Earth.

Although a recent study offers a different explanation for the tilted orbit of the TNOs — arguing that Planet Nine doesn't actually exist, as The Inquisitr recently reported — Brown remains "eternally optimistic" that someone will eventually find the elusive giant.

According to the Washington Post, the astrophysicist says that one major impediment hindering our efforts to detect it is that Planet Nine is too distant to spot, its location rendering it "essentially invisible to our observatories."

Astronomers believe that this remote frozen world lies hundreds and up to 1,000 times farther from the sun than Earth. Since it's so far away, Planet Nine would appear extremely dim to an Earth-based observatory, which is why our telescopes are having a hard time picking up its trail in the darkness of space.

If Planet Nine was located 600 times farther away from the sun than Earth — in other words, at a distance of 600 astronomical units (AU), where 1 AU is the distance between Earth and the sun, or about 93 million miles — it would look 160,000 times dimmer than Neptune, which orbits at 30 AU.

At a presumed distance of 1,000 AU, Planet Nine would appear more than 1 million times weaker, explains the media outlet, citing Quanta Magazine.

Planet Nine
3D illustration of the hypothetical Planet Nine in front the Milky Way galaxy.

Another thing to consider is the wavelength of light that should be coming from Planet Nine. Scientists anticipate that this hypothetical planet shines in the millimeter part of the spectrum, which is between infrared light and microwaves, notes the Washington Post.

This means that our millimeter telescopes in Antarctica and Chile might be able to pick up its glow if Planet Nine happens to cross their search field.

"Every time we take a picture, there is this possibility that Planet Nine exists in the shot," says Surhud More, an astronomer at the University of Tokyo.

At the moment, two separate teams are searching for Planet Nine with the Subaru telescope in Hawaii. This highly potent instrument has a very wide field of view and is able to examine massive swaths of sky big enough to fit 4,000 full moons. One team is led by Brown himself, while the other is being helmed by astronomer Scott Sheppard of the Carnegie Institution for Science in Washington.

Sheppard is convinced that Planet Nine is out there. In 2014, the scientist took part in the discovery of a planetoid orbiting the sun at 80 AU, well beyond the Kuiper belt (which stretches from Neptune's orbit to 50 AU). This discovery ultimately revealed the situation of the TNOs.

"If things are in the same orbit, then something's pushing them," said Sheppard.

But even if we manage to zero in on the exact swath of sky where Planet Nine is nestled, there are a number of things that could obscure it from out sight, points out the Washington Post. For instance, the planet could be hidden by the glare of a bright star or the light pollution in the Milky Way.

The worst-case scenario is that we might glance over to its location when the planet has already moved to a more distant point in its elliptical orbit, slipping beyond the 1,000 AU-limit. This would make it entirely invisible for at least a thousand years, notes Advocator.