Orbital mayhem around a red dwarf

December 18, 2017

In the collective imagination, planets of a solar system all circle around their star, in the same plane that is also the equatorial plane of the star. The star also spins, and its spin axis is aligned with the spin axes of the planetary orbits, giving the impression of a well-ordered system. But nature is capricious, as an international team led by researchers from the University of Geneva (UNIGE), Switzerland, just found out : they detected a planetary system turned upside down. This discovery is published this week in the prestigious journal Nature.

GJ436 is a star that has already made much ink to flow, as it hosts a planet nicknamed the hairy planet that evaporates like a comet. In this study, researchers at UNIGE showed that in addition to its huge cloud of gas, the planet GJ436b also has a very special orbit. It is "polar": instead of turning in the equatorial plane of the star, the planet passes almost above the stellar poles.

The orbital inclination of this planet as big as four times the Earth is the last piece of a puzzle that has baffled astronomers for 10 years: unlike the planets of the solar system whose orbits almost form perfect circles, that of GJ436 forms a very flat or strongly eccentric ellipse, that is, its distance to the star varies along its orbit. "This planet is under enormous tidal forces because it is incredibly close to its star, barely 3% of the Earth-Sun distance, explains Vincent Bourrier, researcher at the Department of Astronomy of the UNIGE Faculty of Science, first author of the study and a member of the European project FOUR ACES*. The star is a red dwarf whose lifespan is very long, the tidal forces it induces should have since circularized the orbit of the planet, but this is not the case!"

The history of each planet is written in its orbit

Orbital architectures of planetary systems are fossil records that tell us how they have formed and evolved. A planet disturbed by the passage of a nearby star or by the presence of other massive planets in the system will keep track of it in its orbit. "Even if we have already seen misaligned planetary orbits, we do not necessarily understand their origin, especially since here it is the first time we measure the architecture of a planetary system around a red dwarf", adds Christophe Lovis, a UNIGE researcher and co-author of the study. The existence of an unknown, more massive and more distant disturbing planet would explain why GJ436b is not on a circular orbit: "If that is true, then our calculations indicate that not only would the planet not move along a circle around the star, as we've known for 10 years, but it should also be on a highly inclined orbit. That's exactly what we just measured!", says with enthusiasm Hervé Beust, who did the orbital calculations.

These same calculations also predict that the planet has not always been so close to its star, but might have come near it recently (on a cosmic scale). Thus, the "evaporating planet" would not always have evaporated, but would have been pushed towards the star by the gravity of a yet-undetected companion. For Vincent Bourrier, the hunt continues: "Our next goal is to identify the mysterious planet that has upset this planetary system."
-end-
*FOUR ACES, Future of Upper Atmospheric Characterisation of Exoplanets with Spectroscopy, is a Consolidator project granted to David Ehrenreich by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme under grant agreement number 724427.

Université de Genève

Related Solar System Articles from Brightsurf:

Ultraviolet shines light on origins of the solar system
In the search to discover the origins of our solar system, an international team of researchers, including planetary scientist and cosmochemist James Lyons of Arizona State University, has compared the composition of the sun to the composition of the most ancient materials that formed in our solar system: refractory inclusions in unmetamorphosed meteorites.

Second alignment plane of solar system discovered
A study of comet motions indicates that the Solar System has a second alignment plane.

Pressure runs high at edge of solar system
Out at the boundary of our solar system, pressure runs high.

What a dying star's ashes tell us about the birth of our solar system
A UA-led team of researchers discovered a dust grain forged in a stellar explosion before our solar system was born.

What scientists found after sifting through dust in the solar system
Two recent studies report discoveries of dust rings in the inner solar system: a dust ring at Mercury's orbit, and a group of never-before-detected asteroids co-orbiting with Venus, supplying the dust in Venus' orbit.

Discovered: The most-distant solar system object ever observed
A team of astronomers has discovered the most-distant body ever observed in our solar system.

Discovery of the first body in the Solar System with an extrasolar origin
Asteroid 2015 BZ509 is the very first object in the Solar System shown to have an extrasolar origin.

First interstellar immigrant discovered in the solar system
A new study has discovered the first known permanent immigrant to our solar system.

A star disturbed the comets of the solar system in prehistory
About 70,000 years ago, when the human species was already on Earth, a small reddish star approached our solar system and gravitationally disturbed comets and asteroids.

Scientists detect comets outside our solar system
Scientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets -- comets outside our solar system -- orbiting a faint star 800 light years from Earth.

Read More: Solar System News and Solar System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.