A new study has shown that all the planets in the Trappist-1 system are very similar to Earth. And also that there is more water on some of these planets than on Earth.
Trappist-1 is a system of planets 39 light years away. It is called the twin of the solar system. It is a dim, ultracold dwarf. At a short distance from it, as many as seven small terrestrial planets. In 2018, scientists clarified the size of the planets in the system and the properties of the Trappist-1 star itself. It is also known that the system is much older than the solar system, which is 4.6 billion years old. For Trappist-1, scientists estimate it to be between 5.4 and 9.8 billion years.
A new study has been published in the journal Astronomy & Astrophysics that focuses on the density of worlds in the Trappist-1 system. It showed the most accurate results to date. Thanks to him, it was discovered that some of the planets in this system contain 5% water - this is 250 times more than water on Earth.
Here is what Simon Grimm, an exoplanetologist at the University of Bern, said in a letter to Space.com: “All the planets in the Trappist-1 system are very similar to Earth: they have a solid core surrounded by an atmosphere. Trappist-1 is the planet most similar to Earth in terms of mass, radius and energy from a star.”
Grimm and his colleagues became interested in the system in 2016, immediately after its discovery, and decided to study it using the transit time variation (TTV) method. By observing small variations in the periods in which the planet passed in front of the star from our point of view, this method allows researchers to conduct perhaps the most accurate studies of planetary masses and densities.
“TTV is now the only method for determining the masses, and hence the density of planets like the Trappist-1 system,” says Grimm.
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Scientists used data from the Spitzer space telescope, as well as several devices from the European Southern Observatory, located in Chile, to make detailed observations that would help study variations in planetary orbits.
If the planet revolved around its star alone, then it would be exposed only to the gravitational effect of the star. But if there are two or more worlds in the system, the planets interact gravitationally, acting on each other with a force corresponding to their masses. These changes depend on planetary masses, distance and other orbital parameters.
At the same time, "overcrowded systems" like Trappist-1 make it difficult to determine the effects of individual planets, since each of them affects its neighbors. It is easier to measure the planets of this system directly, since they rotate synchronously. Together, the seven exoplanets form a resonant chain that connects them all and suggests a slow, calm evolution.
“The Trappist-1 system is special because all its planets are in resonance,” explains Grimm.
The scientist used a simulation that he adapted to the TTV analysis. Previously it was used to calculate planetary orbits. To model the masses and densities of the planets, the team required more than 200 transits. They simulated their orbits until the simulated transits matched exactly with the research.
The researchers found that planetary densities range from 0.6 to 1.0 Earth's. Seven of them are rich in water, and on some it makes up as much as 5% of the total mass. For comparison: water on Earth is only 0.02% of the planet's mass.
Trappist-1b and c are the closest to the star - most likely they have rocky cores and are surrounded by high-density atmospheres.
Trappist-1d is the lightest of the seven planets. Its mass is about 30% of the mass of the Earth. Its low mass can be due to the expanded atmosphere, the ocean, or a layer of ice.
Trappist-1f, g, and h are far enough away from their star that the water on their entire surface is completely frozen. Thin atmospheres are unlikely to be able to contain heavier molecules like Earth.
In addition, there is Trappist-1e, which is the most Earth-like of the group. It is somewhat denser than our planet and, most likely, has a denser iron core. It may also lack a dense atmosphere, ocean, or ice sheet.
Scientists warn that these results say nothing about planetary habitability. However, the work could help researchers better understand the conditions at work in crowded systems and determine if life can exist on the worlds of the Trappist-1 system today.