It turns out that planets can live a long time.
Around one of the galaxy’s oldest stars, an orange dwarf named TOI-561, just 280 light-years away, astronomers have found three orbiting exoplanets, one of which is a 1.5-fold rocky world. the size of the Earth, whipping the star on a vertigo. Bitrbita of 10.5 hours.
Viously, obviously an exoplanet so close to its star is unlikely to be habitable, even if it is rocky like Earth, Venus, and Mars. It would have a temperature of 2,480 Kelvin, closed with an ocean of magma on the permanent side of the day.
But the TOI-561 system, the planets and all, is one of the oldest ever seen, with an estimated age of about 10 billion years.
It is more than double the solar system, almost as old as the Universe itself, and evidence that rocky exoplanets can remain stable for a long time.
“TOI-561 b 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 been forming rocky planets almost since its inception 14 billion years ago.”
The three planets, named TOI-561 b, TOI-561 c and TOI-561 d, were identified by NASA’s planetary space hunting telescope, TESS. TESS observes sections of the sky, looking for periodic, faint falls in the light of distant stars. These are transits, when a planet passes between us and its star.
From these follow-up data and observations, astronomers were able to determine the orbital periods and sizes of the three exoplanets.
TOI-561 d, the outermost, 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 the Earth, with an orbital period of 10.8 days. And 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 does not stand still. Each exoplanet exerts its own gravitational pull on the star, resulting in an uncomplicated dance that compresses and stretches the star’s light as it moves toward us and away from us as we observe it.
If we know the mass of the star, we can observe how much the star moves in response to the gravitational pull of an exoplanet and calculate the mass of the exoplanet. From this, the researchers calculated that TOI-561b is about three times the mass of Earth.
But its density is about the same as that of the Earth, about five grams per cubic centimeter.
“This is surprising because the density is expected to be higher,” said planetary astrophysicist Stephen Kane of the University of California, Riverside. “This is consistent with the idea that the planet is extremely ancient.”
This is because the heaviest elements in the Universe (metals heavier than iron) are forged in the heart of stars, supernovae at the end of a massive star’s life, and collisions between stars. mass deaths. Only once the stars have died and spread these elements into space can they be captured by other objects.
Therefore, the oldest stars in the Universe are very poor in metals. The TOI-561, for example, has little metallicity. And all the planets that formed in the previous Universe should also have a low metallization.
Previous research has suggested that there is a lower metallicity limit for the formation of rocky planets, as heavier elements are less likely to be evaporated by stellar radiation, the grains surviving long enough in the circumstellar disk. lar to agglutinate and form planets.
Finding planets like TOI-561 b can help restrict these models, which in turn could help us locate older rocky exoplanets.
“While this particular planet is unlikely to be inhabited today,” Kane said, “it may be a harbinger of many rocky worlds yet to be discovered around the oldest stars in our galaxy.”
And this can help us in the search for habitable worlds. The Earth is about 4.5 billion years old; the first signs of life are believed to be about 3.5 billion years old. And yet vertebrates did not appear in the fossil record until about 500 million years ago.
The complex life as we know it takes time to emerge. Therefore, if we want to find life more complex than archaea or microbes, planets with a long and relatively stable life will be, according to scientists, the most likely to be hospitable.
So while the TOI-561 b would not be a good place to visit, it is another clue that can help us in our eager search for other lives out there outside the Universe.
The team’s research was presented at the 237th meeting of the American Astronomical Society. It has also been accepted in The Astronomical Journal, and is available at arXiv.