Earth-like Planets Near Dim Stars May Have Magnetic Fields and Life

Earth-like plants may actually have magnetic fields, which may aid chances for life. Scientists have discovered that these planets orbiting close to small stars have magnetic fields that protect them from stellar radiation and help maintain safe surface conditions.

A planet's magnetic field emanates from its core and is thought to deflect the charged particles of the stellar wind, protecting the atmosphere from being lost to space. Magnetic fields, born from the cooling of a planet's interior, could also protect life on the surface from harmful radiation, as the Earth's magnetic field protects us.

Low-mass stars are among the most common in the universe. In addition, planets that orbit near these stars are easier for astronomers to target for study because when they transit their host star, they block a larger fraction of the light than if they transited a more massive star. Yet because these small stars are dim, the habitable zone lies relatively close in.

A planet that's close to its star, though, is subject to the star's powerful gravitational pull. This can cause the planet to become tidally locked so the same side is forever facing its host star-just like the moon is with Earth. This same pull creates tidally generated heat inside the planet, or tidal heating. This heating is responsible for driving the most volcanically active body in our solar system, Jupiter's moon, Io.

In this latest study, the researchers combined models of orbital interactions and heating. The simulations ranged from one stellar mass-stars the size of our sun-down to about one-tenth of that size. By merging their models, they were able to create a more realistic picture of what occurs inside these planets.

So what did they find? Tidal heating processes are more extreme for planets in the habitable zone around very small stars. Yet for planets in eccentric orbits around low mass stars, these orbits become more circular during the time of extreme tidal heating, and then the planet stops experiencing any tidal heating at all.

"I was excited to see that tidal heating can actually save a planet in the sense that it allows cooling of the core," said Rory Barnes, one of the researchers, in a news release. "That's the dominant way to form magnetic fields."

The findings are published in the journal Astrobiology.

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