A Neptune-like exoplanet has been discovered in an area previously though “forbidden”. The planet is so rare that astronomers have called it “The Forbidden Planet”.
A team of astronomers recently announced the discovery of an exoplanet evolving in the Neptunian desert of its system. But it should not be here. Details of the study are published in the Monthly Notices of the Royal Astronomical Society.
The Neptunian desert is the region close to the stars where no planet of Neptunian size can evolve. The area, highly irradiated, is indeed hostile to giant planets who can not keep their gaseous atmosphere. In general, these worlds evaporate, leaving behind only their rocky nuclei. At least, that’s what the theory suggests. But as always, the Universe is full of surprises.
A team of astronomers from the University of Warwick (UK), led by Dr. Richard West, announced that they have discovered one of these “forbidden” worlds. The so-called NGTS-4b is about three times larger than the Earth, 20 times more massive, and its radius is about 20% less than that of Neptune. The planet goes around its star every 1.3 days, and its surface temperature is around 1000 degrees Celsius. But despite these conditions, NGTS-4b still retains its atmosphere.
It is simply the first exoplanet of this type evolving in a “Neptune desert”. But then, how is this possible? The researchers propose two hypotheses. The first is that the planet has moved very recently within its orbit, perhaps over the last million years. Or, its atmosphere would be really thick and would continue to evaporate today.
It is noted that this planet has been identified through the Next-Generation Transit Survey (NGTS) program, available at the Paranal facilities of the European Southern Observatory in the Atacama Desert. The principle is to rely on the transit method. In other words, scientists look for distortion in the light coming from a star, indicating the presence of a planet. As a general rule, ground-based telescopes can not detect brightness dips up to 1%. But the more sensitive NGTS program can record declines as low as 0.2%.
“It’s really remarkable that we found a planet in transition in front of a star only decreasing 0.2% of its brightness. It has never been done with telescopes on the ground, explains the researcher. We are now looking at our data to see if we can find more planets in these Neptunian deserts. Maybe the desert is greener than previously thought. “