It turns out that planets can indeed live a long time.
Around one of the oldest stars in the galaxy, an orange dwarf named TOI-561 just 280 light-years away, astronomers have discovered three orbiting exoplanets – one of which is a 1.5 times the size of the Earth’s rocky world, which flies around the star on a 10.5-hour Orbit breakdown.
In fact it is unlikely to be able to exoplanet as close to its star, even though it is rocky like Earth, Venus and Mars. It would have a temperature of 2,480 Kelvin, quickly locked by a magma ocean on the permanent side of the day.
But the TOI-561 system, planets and all, is one of the oldest ever seen, at an estimated age of around 10 billion years.
That is more than twice the age of the Solar System, almost as old as the Universe itself, and evidence that rocky exoplanets can remain stable for a very long time.
“TOI-561 b is one of the oldest rocky planets yet to be discovered,” said astronaut Lauren Weiss of the University of Hawai’i.
“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 looks at sections of the sky, looking for occasional doses in the light of distant stars. These are the motions, when a planet passes between us and its star.
From these data, and from follow-up studies, astronomers were able to determine the orbital times and sizes of the three exoplanets.
TOI-561 d, the outermost, is about 2.3 times the size of Earth, with an orbital time of 16.3 days. TOI-561 c is 2.9 times the size of Earth, with an orbital time of 10.8 days. And TOI-561 b is 1.45 times the size of the Earth, with an orbital time of just over 10.5 hours.
The team also did a radial distance measurement. As planets move to a star, that star will not sit still. Each exoplanet exerts its own gravitational pull on the star, resulting in a complex little dance that strains and stretches the star’s light as it moves in and out. away from us as we look at it.
If we know the mass of the star, we can see how much the star is moving in response to the gravity pull of an exoplanet and work out the mass of the exoplanet. From this, the researchers found that TOI-561b is about three times the mass of the Earth.
But the density is about the same as the Earth, about five grams per cubic centimeter.
“This is surprising because you would expect the density to be higher,” said planetary astronaut Stephen Kane of the University of California, Riverside. “This is consistent with the idea that the planet is very old.”
That’s because the heaviest elements in the Earth – metals heavier than iron – are formed in the hearts of stars, in the supernovae at the end of the life of a big star, and collisions between large dead stars. Only once stars have died and these elements are released into space can they be taken up to other objects.
So the oldest stars in the Universe are very poor in metals. TOI-561, for example, is low in metallurgy. And any planets created in the previous Universe should have low metallicity.
Previous research has suggested that there is a lower limit of metallization for the formation of a rocky planet, since heavier elements are less likely to be evacuated by stellar radiation, the grains that live long enough in the circumellar disk to accumulate and create planets.
Finding planets like TOI-561 b can help limit these models, which may help us find old rocky rocks.
“While humans are unlikely to inhabit this particular planet today,” Kane said, “it may be a sign of much of a rocky world that has not yet been discovered around the oldest stars. in our galaxy. “
And this can help us find a world of agriculture. The Earth is about 4.5 billion years old; the earliest signs of life are estimated to be around 3.5 billion years old. And yet backbones did not appear on the fossil record until about 500 million years ago, give or take.
A complex life as we know it will take time to emerge. So if we want to find life more complex than archaea or microbes, scientists will think that long-lived and relatively stable planets are most likely to be hostile.
So while TOI-561 b may not be a good place to visit, it does provide another insight that may help us in our quest for another life. out there in the Universe.
The team’s research was presented at the 237th meeting of the Astronomical Society of America. It was also accepted The Astronomical Journal, and is available on arXiv.