Astronomers discover the first signature of magnetic field on a planet outside our solar system

Exoplanet HAT-P-11b

The artist’s impression of HAT-P-11b, an exoplanet orbiting its host star at only one-twentieth the distance from Earth to the sun. Credit: Denis Bajram / University of Geneva

Scientists have identified the first signature of a magnetic field that surrounds a planet outside our solar system. The Earth’s magnetic field acts as a shield against energetic particles from the sun known as the solar wind. Magnetic fields can play similar roles on other planets.

An international team of astronomers used data from The Hubble Space Telescope to discover the signature of a magnetic field in a planet outside our solar system. Found, described in a paper in the journal Nature astronomy, marks the first time such a feature has been viewed on one exoplanet.

A magnetic field best explains the observations of an extended region of charged carbon particles that surround the planet and flow away from it in a long tail. Magnetic fields play a crucial role in protecting planetary atmospheres, so the ability to detect the magnetic fields on exoplanets is a significant step towards better understanding what these alien worlds might look like.

The team used Hubble to observe the exoplanet HAT-P-11b, a NeptuneA planet 123 light-years from Earth passes directly over its host star six times in what is known as a “transit”. The observations were made in the ultraviolet light spectrum, which is just beyond what the human eye can see.

Hubble discovered carbon ions – charged particles that interact with magnetic fields – that surround the planet in what is known as a magnetosphere. A magnetosphere is an area around a celestial body (such as Earth) formed by the object’s interaction with the solar wind emitted by its host star.

Charged carbon particles Exoplanet HAT-P-11b

Hubble’s observations of an extended region of charged carbon particles surrounding the exoplanet HAT-P-11b and flowing away in a long tail are best explained by magnetic fields, the first discovery of this kind on a planet outside our solar system. The planet is depicted as the small circle near the center. Carbon ions fill a huge area. In the magneto tail, which is not shown in its full extent, ions escape at the observed average speeds of about 100,000 mph. 1 AU is equal to the distance between the Earth and the sun. Credit: Lotfi Ben-Jaffel / Institute of Astrophysics, Paris

“This is the first time that the signature of an exoplanet’s magnetic field has been detected directly on a planet outside our solar system,” said Gilda Ballester, an adjunct research professor at the University of Arizona Lunar and Planetary Laboratory and one of the newspaper’s co-authors. authors. “A strong magnetic field on a planet like Earth can protect its atmosphere and surface from the direct bombardment of the energetic particles that make up the solar wind. These processes greatly affect the evolution of life on a planet like Earth because the magnetic field protects organisms from them. energetic particles. “

The discovery of the magnetosphere of the HAT-P-11b is a significant step towards an improved understanding of the habitability of an exoplanet. Not all planets and moons in our solar system have their own magnetic fields, and the connection between magnetic fields and the habitability of a planet requires more and more research, according to researchers.

“HAT-P-11 b has proven to be a very exciting target because Hubble’s UV transit observations have revealed a magnetosphere, seen as both an extended ion component around the planet and a long tail of escaping ions,” Ballester said, adding that this general method could be used to detect magnetospheres on a number of exoplanets and to assess their role in potential habitability.

Ballester, a principal investigator of one of the Hubble Space Telescope programs that observed HAT-P-11b, contributed to the selection of this specific target for UV studies. A key discovery was the observation of carbon ions, not only in an area around the planet, but also in a long tail that flowed away from the planet at average speeds of 100,000 mph. The tail reached out into space for at least 1 astronomical unit, the distance between the Earth and the sun.

Scientists led by the paper’s first author, Lotfi Ben-Jaffel at the Institute of Astrophysics in Paris, then used 3D computer simulations to model interactions between the planet’s upper atmospheric regions and magnetic fields with the incoming solar wind.

“Just as the Earth’s magnetic field and its immediate space environment interact with the incident solar wind, which consists of charged particles moving at about 900,000 mph, there are interactions between the HAT-P-11bs magnetic field and its immediate space environment with the solar wind from its host star, and they are very complex, ”Ballester explained.

The physics of the Earth’s magnetospheres and HAT-P-11b are the same; however, the exoplanet’s proximity to its star – just one – twentieth the distance from Earth to the Sun – causes its upper atmosphere to heat up and essentially “boil out” in space, resulting in the formation of magnetohale.

Researchers also found that the metallicity of HAT-P-11b’s atmosphere – the number of chemical elements in an object heavier than hydrogen and helium – is lower than expected. In our solar system are the icy gas planets, Neptune and Uranus, are rich in metals but have weak magnetic fields, while the much larger gas planets, Jupiter and Saturn, has low metallicity and strong magnetic fields. HAT-P-11bs low atmospheric metallicity challenges current models of exoplanet formation, the authors say.

“Although the mass of HAT-P-11b is only 8% of Jupiter, we think the exoplanet is more like a mini-Jupiter than a Neptune,” Ballester said. “The atmospheric composition we see on HAT-P-11b suggests that further work needs to be done to refine current theories on how certain exoplanets form in general.”

Reference: “Signatures of strong magnetization and a metal-poor atmosphere for a Neptune-sized exoplanet” by Lotfi Ben-Jaffel, Gilda E. Ballester, Antonio García Muñoz, Panayotis Lavvas, David K. Sing, Jorge Sanz-Forcada, Ofer Cohen, Tiffany Kataria, Gregory W. Henry, Lars Buchhave, Thomas Mikal-Evans, Hannah R. Wakeford and Mercedes López-Morales, 16 December 2021, Nature astronomy.
DOI: 10.1038 / s41550-021-01505-x

The Hubble Space Telescope is a project for international collaboration between NASA and the European Space Agency. The observations were made through the following programs: Small HST Program # 14625 dedicated to HAT-P-11b (Chief Investigator Gilda E. Ballester) and HST Treasury Program # 14767 called PanCET: The Panchromatic Comparative Exoplanetary Treasury Program (co-principal investigators) David K. Sing and Mercedes López-Morales).

The newspaper, “Signatures of Strong Magnetization and a Metal-Poor Atmosphere for a Neptune-Size Exoplanet” is published in the December 16 issue of Nature astronomy. Co-authors besides Ballester and Ben-Jaffel are Antonio García Muñoz, Panayotis Lavvas, David K. Sing, Jorge Sanz-Forcada, Ofer Cohen, Tiffany Kataria, Gregory W. Henry, Lars Buchahave, Thomas Mikal-Evans, Hannah R Wakeford and Mercedes López -Morales.

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