The strongest evidence to date for planets beyond our solar system magnetic fields, like Earth and five more planets, astronomers now have in their hands, based on the behavior of the winds in seven large exoplanets with atmospheres in which high temperatures are recorded.
The findings, which resulted from the observations with telescopes in Chile and Hawaiideepen our understanding of exoplanets by demonstrating that at least some have an important characteristic seen in six of the eight planets in the solar system. This is none other than the magnetic field, an invisible field of force produced by the movement of an electrically conductive material deep inside a planet—a molten metal core—combined with the planet’s rotation.
And despite that none of the exoplanets in the survey are candidates to host life as we know it, the magnetic field could be one of the contributing factors in making a rocky planet like Earth habitable.
These exoplanets each orbit very close to a large and hot star, with one side permanently facing the star and the other permanently facing the dark, as is the case with the Moon and Earth.
This type of planet is called a “hot Jupiter” because it has a size and composition comparable to that of the largest planet in our solar system, except that it has a much higher temperature. As for their mass, it was comparable to that of Jupiter – up to three times greater.
Strong winds blow from the hemisphere facing their warm star (dayside) to the hemisphere facing away from the star (nightside). The orbital proximity of the planets to their host stars creates extremely high temperatures on the side facing the star. All of them are closer to their host star than Mercury is to the sun.
“What you would expect is that planets with higher temperatures would have stronger winds. The more energy a system has, the more violent the winds become. But we see the opposite”the astronomer said Julia Seidel of the Lagrange Laboratory of the Côte d’Azur Observatory in Nice, France, lead author of the study published Tuesday in the journal Nature Astronomy.
“The hottest planets have the least strong winds (…) and that’s really strange from what we know about how atmospheres behave,” Seidel said. “This means that all that energy that the star pours into the planet’s atmosphere has to be dissipated in a different way. And the only possibility (…) is through the magnetic field and its interaction with the moving charged particles of the atmosphere”.
Wind speeds on the seven exoplanets were many times those recorded on Jupiter.
Considering that most planets in our solar system have magnetic fields, the researchers said it is not surprising that the same is true of exoplanets. However, scientists have so far struggled to find convincing evidence.
“We’re not looking at a single exoplanet, but we’re looking at a multitude and we’re seeing a trend emerging,” Seidel said.
Jupiter’s magnetic field is the largest and strongest in our solar system. The seven exoplanets had magnetic fields smaller than Jupiter’s, but comparable to the rest of the solar system’s planets.
Mercury, Saturn, Uranus, Neptune, Earth, and Jupiter all have planetary-scale magnetic fields. Venus and Mars, in contrast, have no magnetic field, while Ganymede, a large moon of Jupiter, produces its own magnetic field. Earth’s moon, long ago, also had its own magnetic field.
The magnetic field is one of the factors that determine whether a planet is able to maintain its atmosphere for long periods of time. For example, Mars once had a magnetic field, but lost it billions of years ago, after its interior cooled, and now its atmosphere is fragile and its environment inhospitable.
“Although the notion that magnetic fields directly determine whether a planet is habitable is wrong, they can indeed play an important role in how a planet evolves over time,” said astronomer and study co-author Bibiana Prinoth of the European Southern Observatory in Germany. “Life as we know it is based on the existence of an atmosphere. The atmosphere helps maintain surface pressure, regulate temperature and, on Earth, allows liquid water to exist on the surface.”
Source: Reuters
