Scientists Find a 'Forbidden Planet' That Shouldn't Exist

How can a gaseous planet exist amidst intense radiation? Scientists aren't sure, but it does.

warwick forbidden planet
University of Warwick

Exoplanet discoveries—finding a planet outside of the solar system—have become a regular scientific occurrence, but they can still manage to surprise scientists. A new Neptunian planet, for example, has been discovered amidst what was previously described as a "Neptunian desert." Scientists on the international team that made the discovery have taken to calling it the "Forbidden Planet" as it defies expectations.

A Neptunian desert is a region of space where no planets around the size of Neptune, the fourth-largest planet in the solar system by diameter, can be found. At 15,299 miles diameter, Neptune is around 388 percent bigger than Earth. A Neptunian desert signifies that the region receives powerful radiation, strong enough to disseminate any gaseous atmosphere. That radiation leaves planet that normally be gaseous, like Neptune, as rocky cores.

Or at least, that's the theory.

“This planet must be tough - it is right in the zone where we expected Neptune-sized planets could not survive," says Dr. Richard West, from the Department of Physics at the University of Warwick, in a . "It is truly remarkable that we found a transiting planet via a star dimming by less than 0.2 percent—this has never been done before by telescopes on the ground, and it was great to find after working on this project for a year."

The team of scientists, which included members from Queen's University Belfast, Observatoire de Genève, DLR Berlin and Universidad de Chile, discovered the planet with the state-of-the-art (NGTS) observing facility in the Chilean Atacama Desert. The NGTS is designed to detected planetary transits, when a planet orbits around its star and the camera is able to detect the shadow. Officially known as NGTS-4b, the planet is so small that other ground surveys would have missed it.

atacama desert telescope
Scientists at the Next-Generation Transit Survey in Atacama Desert.
University of Warwick

NGTS-4b has a mass of 20 Earth masses and a radius 2o percent smaller than Neptune. It orbits its parent star in a mere 1.3 days, equivalent to the Earth’s orbit around the sun in one year. The planet's speedy orbit made it difficult to track in transit. Normally transitory dips, or where the planet is blocking the sun, of 1 percent and more are needed to be picked up by ground-based searches. But the NGTS telescopes can pick up a dip of just 0.2 percent, which allowed the planet to be found.

Now that this Neptunian desert is proving to be more filled than previously thought, the team is eager for further exploration. “We are now scouring out data to see if we can see any more planets in the Neptune Desert," says Dr. West. "Perhaps the desert is greener than was once thought.”


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