Jun 29, 2023 12:21:00

Astronomers discover 'planet that shouldn't exist'

It has become clear that

extrasolar planets exist in places where planets should not exist according to previous thinking.

A close-in giant planet escapes engulfment by its star | Nature
https://www.nature.com/articles/s41586-023-06029-0

Astronomers find a planet that shouldn't exist
https://phys.org/news/2023-06-astronomers-planet-shouldnt.html

Astronomers puzzled by 'planet that shouldn't exist'
https://theconversation.com/astronomers-puzzled-by-planet-that-shouldnt-exist-208649

The search for exoplanets is one of the fastest growing fields in astronomy, with over 5000 exoplanets discovered by humans in the last few decades. At the time of writing, astronomers estimate that there is at least one planet per star in the galaxy.

Much of the research activity in astronomy at the time of writing is aimed at detecting ``earth-like planets'' where life may exist. And these efforts are focused on discovering stars like the sun. This is because, as mentioned above, there are always planets in fixed stars. In fact, more than 90% of the exoplanets discovered so far have been detected in the vicinity of their stars.

An international team of astronomers who have been searching for such an extrasolar planet investigated a similar star several billion years after the sun, and found a planet that should not have originally existed around it, the scientific journal Nature is reported in

Just like humans, stars change over time. When a star uses up all the hydrogen in its core, the core shrinks and the outer shell expands as the star cools. This is the stage called

a red giant star , and there are cases where it expands to more than 100 times the original size of the star. It is said that the sun will become a red giant star in about 5 billion years, but it is estimated that the sun will swallow planets such as Mercury, Venus, and Earth when this happens.

Then, when the star's core gets hot enough to start fusing helium, the star shrinks to about 10 times its original size and burns steadily for tens of millions of years. is.

One of the extrasolar planets orbiting a star called

8 Ursa Minor is '8 Ursa Minor b '. This planet has about the same mass as Jupiter, but is only half the distance from Earth to the Sun.

Analysis of the latest data on 8 Ursa Minor, collected using NASA's space telescope TESS , reveals that the red giant 8 Ursa Minor has already started burning helium in its nucleus. became. The burning of helium in the core has been identified through the application of astroseismology , which analyzes the sound waves inside the star.

The fact that 8 Ursa Minor is burning helium means that 8 Ursa Minor was larger in the past than it is now, given the stellar cycle. And if 8 Ursa Minor was larger than it is now, it would have been so large that 8 Ursa Minor b, which is very close, would have been swallowed up.

In other words, Ursa Minor 8 star b is 'a planet that should not exist'.

One of the possible theories about 8 Ursa Minor b is that '8 Ursa Minor was once a binary star .' If it was a binary star, 8 Ursa Minor b might not have been swallowed by 8 Ursa Minor.

Another theory is that 8 Ursa Minor b is a relatively recently born planet. In other words, the theory is that 8 Ursa Minor b was born after 8 Ursa Minor burned helium and shrank.

Whichever theory is correct, the fact that there are planets orbiting helium-burning red giants shows that there are cases where nature creates planets in ways humans have never expected.