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Obviously, an exoplanet that is this close to its star is unlikely to be fit for life, even if it is as rocky as Earth, Venus, and Mars. Its temperature on the noon side would be 2,206 ºC.
But the TOI-561 system – the planet and everything else – is one of the oldest ever seen – around 10 billion years old.
It is more than twice as old as the solar system, almost as old as the Universe itself, and this proves that rocky exoplanets can remain stable for a long time.
“TOI-561b is one of the oldest rocky planets ever discovered,” said astronomer Lauren Weiss of the University of Hawaii.
Its existence shows that the Universe has formed rocky planets almost since its inception, beginning 14 billion years ago.
Three planets, named TOI-561b, TOI-561c, and TOI-561d, were identified by NASA’s TESS planetary hunting space telescope. TESS looks at stretches of the sky for periodic, faint dips in the light of distant stars. These are transits where the planet passes between us and our star.
Based on these data and other observations, astronomers were able to determine the orbital periods and magnitudes of the three exoplanets.
The furthest TOI-561d is about 2.3 times larger than Earth, and the orbital period is 16.3 days. TOI-561c is 2.9 times larger than Earth and has an orbital period of 10.8 days. While TOI-561b is 1.45 times larger than Earth’s, its orbital period is just over 10.5 hours.
The Earth is about 4.5 billion years old, it is estimated that the first signs of life are about 3.5 billion years old.
The team also made radial velocity measurements. When planets orbit a star, that star does not stay still. Each exoplanet moves closer to gravity due to gravity, resulting in a complex little dance that compresses and stretches the star’s light as it moves toward and away from us.
If we know the mass of a star, we can observe how much the star moves in response to the gravitational pull of the exoplanet and calculate the mass of the exoplanet. From this, the researchers estimated that TOI-561b is roughly three times the mass of Earth.
But its density is roughly the same as Earth’s: about five grams per cubic centimeter.
“It’s surprising because I expected the density to be higher,” said planetary astrophysicist Stephen Kane of the University of California. “It is in line with the idea that the planet is very old.”
This is because the heaviest elements in the Universe, metals heavier than iron, are imprisoned in the hearts of stars, in supernovae at the end of a massive star’s life, and in star collisions. massive deaths. Only when the stars die and these elements scatter through space can they reach other objects.
Therefore, the oldest stars in the Universe contain very few metals. TOI-561, for example, is low in metals. All previously formed planets in the Universe should also be low in metal content.
Previous studies have shown that rocky planet formation has a lower metallization threshold because heavier elements are evaporated less by stellar radiation and small fragments in the surrounding disk survive long enough to assemble and form planets.
Finding planets like TOI-561b can help build those models, which in turn could help find ancient rocky exoplanets.
“While this particular planet is unlikely to be inhabited today,” Kane said, “it may be a prophet of many jealous worlds yet to be discovered around the oldest stars in our galaxy.”
It can help us search for mansion worlds. The Earth is about 4.5 billion years old; The first signs of life are estimated to be around 3.5 billion years old. However, the earliest data on vertebrates dates back about 500 million years.
Complex life, as we know, takes time. So if we want to find a life that is more complex than archaic or microbial, planets that are long-lived and fairly stable will likely be hospitable to such life.
So while TOI-561b wouldn’t be a hospitable planet to visit, it provides another clue that could help us eagerly search for other life in the Universe.
The team’s study was presented at the 237th meeting of the American Astronomical Society. It is also published in The Astronomical Journal and is available on arXiv.
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