LHS 1140b, un esopianeta roccioso in orbita nella zona abitabile intorno a una nana rossa, potrebbe avere una atmosfera, composta almeno in parte di elio.
L’articolo su Science spiega come è stato ottenuto questo risultato.
Astronomers spot first atmosphere around a potentially habitable alien world
Leader Collin Cherubim, a planetary scientist at Harvard University, had built a computer model of how exoplanetary atmospheres evolve over time. In particular, the model looked at how lighter elements, such as hydrogen and helium, would tend to drift up to the planet’s outer atmosphere and be the first to be boiled off by the heat and outbursts of the host star. As a result, heavier gases such as nitrogen and oxygen—held more tightly by the planet’s gravity—become enriched lower down.
Cherubim applied the model to LHS 1140b, a well-studied planet 49 light-years away whose density is slightly lower than Earth’s. That means it likely has a substantial atmosphere or is wrapped in water or ice, or a mixture of all three. Earlier studies of the world firmly ruled out a dense hydrogen atmosphere, although inconclusive hints of heavier gases such as nitrogen were found. Cherubim’s model predicted that LHS 1140b would have an upper atmosphere dominated by helium. “I was just following the numbers,” he says. “My model predicted escaping helium and a lot of it.”
To find that helium, the team used the 6.5-meter Magellan Telescopes in Chile, which recently had a new high-resolution spectrometer installed. “It was sensitive to this helium line in the near infrared, so it was kind of perfect,” Cherubim says. In 2024, the team observed the LHS 1140 system on a night when LHS 1140b and another smaller and closer in planet, LHS 1140c, both passed in front of their star. When the larger planet transited, the researchers saw starlight dropping in brightness at a wavelength known to be absorbed by helium. When the smaller planet crossed, they saw no such signal.
Il paper su Science:
Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone
Un articolo più completo su space.com, contiene anche una intervista ai ricercatori.
“We have actually detected directly the helium present in the atmosphere itself, and that’s the first direct detection for any rocky exoplanet, which is really exciting … and then there’s this added bonus that it’s in the habitable zone, which is super exciting for astrobiology and habitability and searching for life,” lead author Collin Cherubim, who recently earned his Ph.D. from Harvard University, told Space.com. “It feels kind of surreal.”
“This planet was found like 10 years ago, and we’re just now saying, okay, that’s an atmosphere,” Dittman told Space.com. “We’re slowly narrowing the gap and checking these boxes … we’re finding a planet that’s rocky, a planet that’s of the right temperature and now … it’s like okay, we finally found one that has an atmosphere.” And being a rocky planet, “there’s definitely a surface … it’s made of rocks,” Dittman said. […]
“It probably also has a lot of water,” Cherubim said. “If it has some amount of atmosphere that can provide a bit of a greenhouse effect, which we know that it does now … it will very likely be what we consider to be habitable conditions on Earth, and conditions that would likely support liquid water.”
La notizia in breve in italiano su Media INAF.
Bonus. I risultati sono stati presentati a Exoplanets 6.