It turns out that planets can live for a very long time indeed.
Around one of the oldest stars in the galaxy, an orange dwarf called TOI-561 just 280 light-years away, astronomers have found three exoplanets orbiting one of them – one of which is a rocky world 1.5 times the size of Earth, orbiting the star in a state of collapse. 10.5 hours in orbit.
It is clear that an exoplanet so close to its star is unlikely to be habitable, even if it is rocky like Earth. Venus And the Mars. It would have a temperature of 2,480 Kelvin, gradually locking in with an ocean of magma on the perpetual daytime side.
But the TOI-561 system, and the planets and all, is one of the earliest systems ever seen, with an estimated age of about 10 billion years.
This is more than twice the age of the solar system, and nearly as old as the universe itself, and is evidence that the rocky outer planets can remain stable for a very long time.
TOI-561 b is one of the oldest rocky planets discovered so far. Astronomer Lauren Weiss said From the University of Hawaii.
„Its existence indicates that the universe has formed nearly rocky planets since its inception 14 billion years ago.“
The three planets, named TOI-561 b, TOI-561c, and TOI-561d, were identified by NASA’s TESS Planetary Hunting Space Telescope. TESS gazes at parts of the sky, looking for faint periodic dips in distant starlight. This is a transit, when a planet passes between us and its star.
From this data, and follow-up observations, astronomers were able to determine the orbital periods and sizes of the three exoplanets.
TOI-561 d, the farthest, is about 2.3 times the size of the Earth, with an orbital period of 16.3 days. TOI-561 c is 2.9 times the size of Earth, with an orbital period of 10.8 days. The TOI-561 b is 1.45 times the size of Earth, with an orbital period of just over 10.5 hours.
The team also performed radial velocity measurements. When planets orbit a star, that star is not sitting still. Each exoplanet exerts its own gravitational pull on the star, creating a small complex dance that compresses and expands the star’s light as it moves toward and away from us as we observe it.
If we know the mass of the star, we can observe how much the star has moved in response to the gravitational pull of an exoplanet and calculate the mass of an exoplanet. From this, the researchers calculated that TOI-561b’s mass is three times the mass of Earth.
But its density is roughly equal to that of the Earth, about five grams per cubic centimeter.
„This is surprising because you expect the density to be higher,“ Planetary astrophysicist Stephen Kane said From the University of California, Riverside. „This is consistent with the idea that the planet is very old.“
This is because the heaviest elements in the universe – minerals heavier than iron – form in star cores, in supernovae at the end of a massive star’s life, and the collision between massive dead stars. Once the stars die and these elements are spread into space, they can be transferred to other things.
So, the oldest stars in the universe are very poor in minerals. TOI-561, for example, is low in minerals. And any planets that formed in the previous universe must also have a low mineral content.
Previous search and it has been suggested There is a low mineral limit for rocky planets to form, because heavy elements are less likely to be evaporated by stellar radiation, the grains remain long enough in the surrounding disk of stars to clump together and form planets.
Finding planets like TOI-561 b could help constrain those models, which in turn could help us identify more ancient, rocky exoplanets.
„Although it is unlikely that this planet is inhabited today,“ Ken said, „It may be a harbinger of many as yet undiscovered rocky worlds about the oldest stars of our galaxy.“
This can help us search for habitable worlds. Earth is about 4.5 billion years old; The oldest signs of life are thought to be around 3.5 billion years old. However, vertebrates did not even appear in the fossil record About 500 million years ago, give or take.
Complex life as we know it takes time to emerge. So, if we were to find life more complex than archaea or microbes, long-lived and relatively stable planets would be, scientists believe, the most likely to be hospitable.
So while TOI-561 b wouldn’t be a pleasant place to visit, it is another clue that could aid us in our passionate search for another life that exists in the universe.
The team’s research is presented in The 237th meeting of the American Astronomical Society. It was also accepted in The Astronomical Journal, And available at arXiv.
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