An international team of scientists has discovered a small exoplanet in a region of the universe close to stars where no Neptune-sized worlds typically exist.

Astronomers from the University of Warwick and other organizations described a rogue planet that they spotted in the "Neptunian Desert," some 920 light-years away from Earth.

The newly discovered world, designated as NGTS-4b, is believed to be 20 percent smaller than Neptune but is about three times the size of Earth.

The researchers dubbed NGTS-4b as the "The Forbidden Planet" since it was located in an area of space not really known to have such kinds of worlds.

Looking For The Rogue Planet

Dr. Richard West of the University of Warwick led the team in finding NGTS-4b. He was joined by Prof. Peter Wheatley, Dr. Daniel Bayliss, and Dr. James McCormac, who were members of the university's Astronomy and Astrophysics Group.

The group also collaborated with colleagues at Cambridge, Leicester, Queen's University Belfast, and University of Warwick in the United Kingdom, as well as those at the Observatoire de Genève in Switzerland, DLR Berlin in Germany, and the Universidad de Chile in Santiago, Chile.

To determine the location of the Forbidden Planet, the researchers used a state-of-the-art observing facility known as the Next-Generation Transit Survey. The NGTS is found at the European Southern Observatory's Paranal Observatory at the Atacama Desert in Chile.

Researchers often look for a dip in the light of stars when trying to find new planets beyond the galaxy. A dip usually means a planet orbiting a star is blocking its light.

Ground-based searches are known to detect only dips in light of about 1 percent or more. However, the telescopes at the NGTS facility can pick up dips even as small as 0.2 percent. These helped West and his team get a fix on where NGTS-4b is.

NGTS-4b, The Forbidden Planet

West and his colleagues discovered that NGTS-4b has roughly the mass of 20 Earths and a radius about 20 percent smaller compared to Neptune. It is also considered extremely hot even for such a small exoplanet, with temperatures reaching about 1,000 degrees Celsius. This makes it a lot hotter than Mercury.

NGTS-4b can complete an entire orbit around its host star in just 1.3 days. This is relatively short compared to the Earth's orbit around the sun, which takes one full year.

What makes the Forbidden Planet such a unique find is because it is the only Neptune-sized world ever to be found in the Neptunian Desert so far. The region is known to receive high levels of radiation from its host star, which causes gaseous atmosphere from planets to eventually evaporate and leave only a rocky core.

NGTS-4b is currently the only planet to retain its atmosphere of gas despite being in such an inhospitable environment in space.

The researchers suspect that NGTS-4b may have only recently moved into the Neptunian Desert, perhaps over the last million years. It is also possible that the Forbidden Planet may have been a massive world and that its atmosphere of gas is still in the process of evaporating.

"This planet must be tough — it is right in the zone where we expected Neptune-sized planets could not survive," West explained.

"It is truly remarkable that we found a transiting planet via a star dimming by less than 0.2% — 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."

West added that they are still looking over data to find out whether there are more planets to discover in the Neptunian Desert. He said the region may even be a lot greener than scientists initially thought.

The findings of the international study are featured in the journal Monthly Notices of the Royal Astronomical Society.

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