Credit: Denis Bajram
Researchers have identified the first signature of a magnetic field surrounding a planet outside our solar system. The earth’s magnetic field acts as a protective shield against high-energy particles from the sun, the so-called solar wind. Magnetic fields could perform similar functions on other planets.
An international team of astronomers have used data from the Hubble Space Telescope to discover the signature of a magnetic field on a planet outside of our solar system. The discovery, described in an article in the journal Nature Astronomy, marks the first time that such a feature has been observed on an exoplanet.
A magnetic field best explains observations of extended region of charged carbon particles that surrounding the planet & moving away from it in long-tail. Magnetic fields play a crucial role in protecting planetary atmospheres, so the ability to detect magnetic fields from exoplanets is an important step towards a better understanding of what these alien worlds might look like.
The team used Hubble to observe the exoplanet HAT-P-11b, a planet the size of Neptune 123 light years from Earth, pass-directly across the face of its host star 6 times in what is called a “transit.” The observations were made in ultraviolet light spectrum, which is just beyond what human eye can see.
Hubble has detected carbon ions – charged particles that interact with magnetic fields – surrounding the planet in what’s called the magnetosphere. A magnetosphere is a region around a celestial object (like the Earth) that is formed by object’s interaction with solar wind emitted by its host star.
“This is the first time that a magnetic field signature from an exoplanet has been detected directly on a planet outside of our solar system,” said Gilda Ballester, adjunct research professor at the University of Arizona Lunar & Planetary Laboratoire and one of the co-authors of the article.
“A strong magnetic field on a planet like Earth can protect its atmosphere & surface from direct bombardment of high-energy particles that make up the solar wind. These processes have a major impact on the evolution of life on a planet like Earth, as the magnetic field protects organisms from these energetic particles.
The discovery of the HAT-P-11b magnetosphere is an important step towards a better understanding of the habitability of an exoplanet. Not all planets & moons in our solar system have their own magnetic fields, and the link between magnetic fields & planet’s habitability still needs to be further investigated, the researchers say.
“HATP11b has turned out to be a very exciting target, as observations of Hubble’s UV transit revealed a magnetosphere, seen as both an ionic component extended 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 variety of exoplanets & to assess their role in potential habitability.
Ballester, a principal investigator on one of Hubble Space Telescope programs that observed HAT-P-11b, helped to select this specific target for UV studies. A key discovery was the observation of carbon ions not only in an area surrounding the planet, but also extending into a long tail that moved away from the planet at an average speed of 100,000 mph. The tail reached space for at least 1 astronomical unit, the distance between the Earth & the sun.
The researchers led by first author of the article, Lotfi Ben Jaffel of the Institute of astrophysique de Paris, then used 3D computer simulations to model the interactions between upper-most atmospheric regions of the planet and the magnetic field with incoming solar wind.
“Just as the Earth’s magnetic field & its immediate space environment interact with the impacting solar wind, which is made up of charged particles traveling at around 900,000 mph, there are interactions between HATP11b’s magnetic field & its immediate space environment with solar wind from its host star, and these are very complex, ”explained Ballester.
The physics in the Earth’s magnetospheres & HATP11b are the same; however, the exoplanet’s close proximity to its star – just 1/12th of the Earth’s distance from the sun – causes its upper atmosphere to heat up & “boil off” into space, causing formation of magnetotail.
The researchers also found that the atmospheric metallicity of HATP11b – the number of chemical elements in an object that are heavier than hydrogen & helium – is lower than expected. In our solar system, the frozen gas planets, Neptune & Uranus, are rich in metals but have weak magnetic fields, while the much larger gas planets, Jupiter & Saturn, have low metallicity & strong magnetic fields. The low atmospheric metallicity of HATP11b calls into question the current models of exoplanet formation, according to the authors.
“Although the mass of HATP11b is only 8% that of Jupiter, we believe the exoplanet looks more like a mini-Jupiter than Neptune,” Ballester said. “The atmospheric composition we see on HATP11b suggests that more work needs to be done to refine current theories on how certain exoplanets typically form.
