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Since its discovery in 2016, planetary scientists have been wrapped up by TRAPPIST-1, a system where seven rocky planets the size of the Earth revolve around a cold star. Three of the planets are in the habitable zone, the region of the space where liquid water can flow to the surface of the planets. Two new studies by scientists at the Lunar and Planetary Laboratory of the University of Arizona could bring astronomers to redefine the habitable area of TRAPPIST-1.
The three planets of the habitable zone are probably confronted with a formidable opponent of life: high energy particles spewed by the star. For the first time, Federico Fraschetti and a team of scientists from the Center for Astrophysics | Harvard & Smithsonian have calculated how much these particles hit the planets.
Hamish Hay, a graduate student at the Lunar and Planatary Laboratory, discovered that the gravitational armor that the TRAPPIST-1 planets play between them raises tides on the surface, possibly causing volcanic activity or warming ice. oceans isolated on planets too cold to support life.
The article by Fraschetti and Hay, "Tides between the planets TRAPPIST-1", have recently been published in Astrophysical Journal.
Punchy Protons
The system star, TRAPPIST-1A, is smaller, less massive, and colder at 6,000 degrees Fahrenheit than our 10,000-degree sun. It is also extremely active, which means that it emits huge amounts of high energy protons – the same particles that cause auroras on the Earth.
Fraschetti and his team simulated the travels of these high energy particles in the star's magnetic field. They discovered that the fourth planet – the deepest world in the TRAPPIST-1 habitable zone – was perhaps undergoing a powerful proton bombardment.
"The flux of these particles in the TRAPPIST-1 system can be up to 1 million times greater than the flux of particles on Earth," said Fraschetti.
This surprised the scientists, even though the planets are much closer to their star than the Earth is to the sun. The high energy particles are transported in space along magnetic fields and the magnetic field of TRAPPIST-1A is tightly wrapped around the star.
"You expect the particles to become trapped in these tightly wrapped magnetic field lines, but if you introduce turbulence, they can escape, moving perpendicular to the average stellar field," Fraschetti said.
The eruptions on the surface of the star cause turbulence in the magnetic field, allowing the protons to move away from the star. The location of the particles depends on the inclination of the magnetic field of the star with respect to its axis of rotation. In the TRAPPIST-1 system, the most likely alignment of this field will bring energetic protons directly to the face of the fourth planet, where they could break down the complex molecules needed for life – or could perhaps serve as catalysts At the creation. of these molecules.
While the Earth's magnetic field protects most of the planet from energetic protons emitted by our sun, a field strong enough to deflect the protons of TRAPPIST-1 should be incredibly powerful – hundreds of times more powerful than Earth's . But that does not necessarily mean death for life in the TRAPPIST-1 system.
The TRAPPIST-1 planets are probably locked, on the one hand, which means that the same hemisphere of each planet is always facing the star, while perpetual night embraces the other.
"Maybe the night side is still hot enough for life and that it's not being bombarded by radiation," said Benjamin Rackham, research associate at the astronomy department of the United States. AU, who did not participate in any of these studies.
The oceans could also protect against high energy destructive protons, just as deep waters could absorb the particles before they destroy the building blocks of life. The tides lifted in these oceans and even in the rocks of the planets could have other interesting implications for life.
Pulling the tides
On Earth, the moon does not lift the tides in the oceans – tidal forces also deform the spherical shape of the mantle and the earth's crust. In the TRAPPIST-1 system, the planets are close enough to each other to allow scientists to think that the worlds could ride the tides on top of each other, as does the moon on Earth.
"When a planet or a moon is deformed because of the tides, friction inside will create a warm up," said Hay, lead author of the second study.
By calculating how the gravity of the TRAPPIST-1 planets would pull and deform each other, Hay explored how much heat the tides bring to the system.
TRAPPIST-1 is the only known system where planets can lift each other as the worlds are so tight around their star.
"It's such a unique process that nobody has thought about in detail before, and it's pretty amazing that it's something that's happening," Hay said. In the past, scientists had only considered the tides raised by the star.
Hay discovered that the two inner planets of the system are close enough to each other to create powerful tides. It is possible that the subsequent tidal warming is powerful enough to fuel the volcanic activity, which can in turn support the atmospheres. Although the deepest planets in TRAPPIST-1 are probably too hot the day of their lives to stay alive, an atmosphere powered by volcanoes could help move heat to their otherwise cold night side. warm enough to prevent living things from freezing.
The sixth planet in the system, called TRAPPIST-1g, undergoes tidal contractions due to both stars and other planets. It is the only planet in the system where tidal warming from other planets is as powerful as that caused by the central star. If TRAPPIST-1g is an oceanic world, like Europa or Enceladus in our own solar system, tidal heating could keep its waters warm.
The M-dwarf star systems such as TRAPPIST-1 offer astronomers the best opportunity to search for life outside the solar system, and the studies of Fraschetti and Hay can help scientists choose how to explore this system at home. l & # 39; future.
"We really need to understand the adequacy of these systems to life, and energy particle fluxes and tidal heating are important factors in limiting our ability to do so," Rackham said.
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