The Absolute Cosmos: Hubble observes a strange exoplanet that behaves like the long-sought Planet Nine

This Hubble image shows one possible orbit (dashed ellipse) of the exoplanet HD 106906 b. Image Credit: NASA, ESA, M. Nguyen (University of California, Berkeley), R. De Rosa (European Southern Observatory), and P. Kalas (University of California, Berkeley and SETI Institute)

At about 336 ± 13 light years away from Earth, in the constellation of Crux lies exoplanet HD106906 b. The exoplanet revolves around a bright, young binary star system in an unusual, never seen before, orbit.

The exoplanet’s unexpected orbit could help scientists to solve a mystery much closer to us- a theoretical, distant object/body in our own Solar System, famously called Planet Nine.

This is the first time that scientists have measured the motion of massive Jupiter like planet orbiting too far from its parent stars and visible disk of debris. This disk is very much similar to our Solar System’s Kuiper Belt.

In our own Solar System, the theorised Planet Nine is also suspected to lie far beyond Kuiper Belt on a similar mystery orbit. The hunt for Planet Nine is still on but the discovery of HD106906 b is the strong evidence that such strange orbits are possible.

The whole system is just fifteen million years old, suggesting that our mystery Planet Nine could have also formed very early in the history of our Solar System.

This eleven Jupiter mass exoplanet was discovered in 2013 with the use of Magellan Telescopes at the Campanas Observatory in the Atacama Desert, Chile.

Up until now, anything about exoplanet’s orbit was not known. This is something which could have only been processed by Hubble Space Telescope: collect the precise measurements of the vagabond’s motion for over fourteen years.

HD106906 b lies exceptionally far at more than 730 times the Earth-Sun distance, from its host binary stars. For comparison average distance between Earth and Sun is 149,597,870 kilometres.

Determining the exoplanet’s 15,000 year long orbit in relatively short time span of Hubble observations was extremely challenging, given the massive separation of exoplanet from its parent stars.

The exoplanet is moving extremely slow along its orbit due to weak gravitational pull from its distant host stars.

Scientists studying the Hubble data were surprised to observe that the exoplanet is in extreme orbit which is very misaligned, elongated and external to the disk of debris that surrounds the exoplanet’s parent stars.

This debris disk is pretty unusual looking, probably due to the gravitational tug of the exoplanet.

How did exoplanet happen to arrive at such a far flung and inclined orbit? Scientists believe that the exoplanet was formed much closer to its parent stars, at about three times the distance of Earth from Sun.

However, the exoplanet’s orbit decayed due to drag within the system’s gas disk, pushing the planet to migrate inward towards its host pair. The gravitational forces from the spinning stars then pushed the exoplanet out on an eccentric orbit, almost throwing it in the interstellar space.

Then a passing star from outside the system happened to stabilised the exoplanet’s orbit, thus preventing it from leaving its home system.

In 2019 candidate passing stars were identified by scientists, using European Space Agency’s (ESA) Gaia survey satellite.

Exoplanet HD 106906 b’s strange orbit is somewhat similar to what may have forced the theorised Planet Nine to wind up in the outer reaches of our planetary system. Far beyond the orbits of other planets and Kuiper Belt.

Planet Nine may have formed in the inner solar system but later got flushed out due to gravitational interactions with gas giant Jupiter. The gas giant possibly have kicked Planet Nine far beyond Pluto.

Then passing stars may have stabilised this kicked out orbit of Planet Nine by pushing the orbit path away from gas giant and other inner planets of our Solar System.

According to scientists, it’s like travelling back in time and watching our young Solar System 4.6 billion years ago, when it was dynamically active and everything was being pushed around and re-arranged.

As of now, scientists just have circumstantial evidence of Planet Nine. They have observed a cluster of small objects beyond ice giant Neptune, moving in unusual orbits compared to rest of the Solar System.

These objects, according to scientists, were put together by gravitational pull from a huge unseen planet.

Another theory says that this clustering is not due to one huge planet, in-fact it is due to the combined gravitational effects from multiple much smaller bodies.

Yet another theory completely rules out the existence of Planet Nine and attributes the clustering of small bodies to just a statistical anomaly.

Scientists hope to gather more details of HD 106906 b by using upcoming international mission James Webb Space Telescope. Since Webb is sensitive to small, Saturn mass planets, it could possibly detect other exoplanets that may have been ejected from this system.

Research paper: First Detection of Orbital Motion for HD 106906 b: A Wide-separation Exoplanet on a Planet Nine-like Orbit

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