WASHINGTON – They are the most commonly observed type of planet in our Milky Way galaxy. Its size is two to three times the diameter of Earth but smaller than Neptune. They orbit closer to their stars than the innermost planet Mercury in our solar system does to the sun.
Called “sub-Neptunians,” they do not exist in our solar system and their basic nature remains an enigma. But the discovery of six of them in synchronized orbits announced Wednesday around a star about 20% less massive than the sun gives astronomers hope that answers will soon emerge.
The researchers determined that the six planets are in a rare state called orbital resonance, with their synchronized orbits around the stars apparently unchanged since they formed about 4 billion years ago. This shows that there were no chaotic events such as giant impacts that disrupted its orbit.
“Aspects of the resonance are very interesting – one of them is its mathematical beauty,” said astronomer Hugh Osborn of the University of Bern in Switzerland, one of the authors of the study published in the journal Nature.
“The main thing about this system is its potential to reveal the secrets of mysterious sub-Neptune planets about which we know little,” Osborn added. “This is definitely not an Earth-like planet.”
Hundreds of sub-Neptunes have been discovered.
“The materials that make up these sub-Neptunes are an active research topic in the field because there are various combinations of rock, water, and atmospheric compositions that can reproduce the bulk properties – mass, radius, and density – of these planets,” said University of Chicago astronomer Rafael Luque, lead author of this study.
Scientists wonder whether sub-Neptune might be a rocky planet with a thick atmosphere of hydrogen and helium gas, a planet made of rock and ice that has a warm, water-rich atmosphere – or something else.
Earth, the largest of the four rocky planets in our solar system, has a diameter of about 7,900 miles (12,750 km). Neptune, the smallest of the four gas planets, has a diameter of about 30,600 miles (49,250 km), about four times that of Earth.
The newly discovered sub-Neptune ranges from 1.9 to 2.9 times the diameter of Earth. They all seem to have a great atmosphere. They and their stars are located about 100 light years from Earth. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). Their star, called HD110067, is visible in Earth’s night sky in the northern constellation Coma Berenices.
The planets are detected by observing the small dip in the star’s brightness as they pass in front of it from our perspective.
The innermost planet takes about nine days to orbit its star. The outermost planet takes about 54 days. The planets orbit the star between 6% and 20% of the distance between Earth and the sun. However, because the star is smaller and less luminous than the Sun, the radiation level is not the same as if it were orbiting a larger star.
Scientists refer to the “habitable zone” around a star – a distance considered neither too close nor too far for a rocky planet to harbor life. Earth is within the sun’s “habitable zone.” But what about these six sub-Neptunes?
“None of them are in the habitable zone for terrestrial planets. However, for sub-Neptunes, the definition of a habitable zone may include a much larger set of orbits because they have atmospheres that can warm or cool the planet’s surface. how close or far they are from their star,” Luque said.
Researchers hope the James Webb Space Telescope (JWST), which began operating last year, can provide answers about the six planets and sub-Neptunes in general.
“The potential for sub-Neptune habitability is also an active research topic in the field, and promising results are expected to come from JWST, most likely this planetary system,” Luque said.
2023-12-01 06:01:00
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