Without an open surface, key geochemical cycles, including the supply of carbon and phosphorus to ocean reservoirs from continental weathering, would be inaccessible.
The six planets of the TRAPPIST-1 system can contain huge oceans, and the amount of water on some of them is a thousand times greater than all the water reserves of the Earth. However, this abundance may diminish their chances of living, according to a study published in the journal Nature Astronomy.
“The worlds of TRAPPIST-1 are certainly interesting to us, but they are most likely lifeless, because they have too much water,” says Cayman Anteborn, lead author of the study at the University of Arizona (USA).
The planetary system of the dim red dwarf TRAPPIST-1, located just 40 light years from Earth, was discovered in 2016. Subsequent observations revealed in this system at least seven planets close in size to Earth. The exomers are designated TRAPPIST-1b, 1c, 1d, 1e, 1f, 1g, and 1h, in order of increasing distance from the central star.
TRAPPIST-1 is about 2000 times weaker than the Sun, so the habitable zone is located very close to the star. All of the planets in the system were detected using the "transit method": several different instruments noticed tiny dips in the brightness of the red dwarf that were caused by the passage of worlds between Earth and TRAPPIST-1. These data made it possible to establish the size of exoplanets, and subsequent calculations - to estimate their masses.
Based on known parameters, Cayman Anteborn and his team created a computer model of the system to better understand the composition of the six TRAPPIST-1 worlds. The outer planet TRAPPIST-1h was not included in the study as little is known about it.
Artistic representation of the TRAPPIST-1 system. Credit: NASA
As a result, the simulation showed that the planets of the system are water worlds. The closest to the star TRAPPIST-1b and TRAPPIST-1c are probably 10% water, and the outer ones TRAPPIST-1f and TRAPPIST-1g are 50%. If this is true, then the probability of finding life in the system is very small. For comparison, on Earth, the mass of water is only 0.2% of the total mass of the planet.
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“Without an open surface, key geochemical cycles, including the supply of carbon and phosphorus to ocean reservoirs from continental weathering, will not be available. The huge amount of water and its pressure on the planet's mantle, in fact, will become an obstacle to key geological processes that could contribute to the development of life,”explained Cayman Anteborn.
The new study also sheds light on the formation and evolution of the TRAPPIST-1 system. All seven planets currently lie within the former "snow line", outside of which, during the era of the formation of worlds, water was frozen. But the results suggest that the three outer planets actually formed outside this boundary and migrated inward over time.
An artistic representation of a line of snow. Credit: ESO.
Overall, the study suggests that red dwarf systems like TRAPPIST-1 should not be viewed as miniature versions of our own solar system, as their planets may form in slightly different ways and on different time scales.
Roman Zakharov