The exoplanet GJ 436b has a strange orbit

Artist's concept of the planet GJ 436b with its tail (Image courtesy Mark Garlick/University of Warwick)
Artist’s concept of the planet GJ 436b with its tail (Image courtesy Mark Garlick/University of Warwick)

An article published in the journal “Nature” describes a research on the planet GJ 436b, whose orbit around its star turned out to be almost polar instead of equatorial. A team of researchers led by the University of Geneva (UNIGE)Switzerland, discovered this strange new characteristic of this exoplanet’s orbit, already known because its orbit is very eccentric and above all because it has a huge tail similar to a comet’s.

The planet GJ 436b, also known as Gliese 436b, is of the hot Neptune type, which means that it’s similar in size to Uranus and Neptune but close to its star. In the case of GJ 436b, the distance is such that its orbital period is just over 2.5 Earth’s days. The star GJ 436, or Gliese 436, is a red dwarf about 33 light-years from Earth whose size and mass are less than half the Sun’s.

Discovered in 2004, the planet GJ 436b turned out to be stranger and stranger for a number of reasons. Its orbit is very eccentric and this means that its distance from its star varies greatly. In June 2015, a previous article published in the journal “Nature” described the traces of the enormous tail that makes it similar to a gigantic comet. David Ehrenreich of the Swiss Observatory of the University of Geneva, who led that research, is part of the team that discovered the strange alignment of GJ 436b’s orbit.

The general idea of ​​a solar system is that of a star with various planet orbiting it on its equatorial plane. However, a planet’s orbit can be modified by a more massive neighbor or by the close passage of another star. Over the last few years, various models have been developed to try to understand the phenomenon of planets’ migration closer or farther from their star depending on the type of forces they’re subjected to.

In the planet GJ 436b’s case, it’s possible that originally its orbit was farther from its star but that in that system there’s a more massive and distant planet that altered it considerably. If that’s the case, this must have happened in recent times from an astronomical point of view because that exoplanet is subjected to considerable tidal forces due to its current proximity to its star. In these cases, the orbit tends to become circular while GJ 436b’s is still a very elongated ellipse.

At this point, to really understand what happened in the star GJ 436’s system finding that other planet is needed. The possibility of investigating the characteristics of this still unknown planet and its influence on GJ 436b will improve our models regarding the possible dynamics among the planets in solar systems.

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