Hubble finds a world that behaves like the ghostly “Planet 9”


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In the last five years several astronomers have suggested an option that would change our conception of the solar system: that up there, on the outskirts, there is a ninth and gigantic planet, too far away as to have detected so far: “Planet 9”. The orbits of some trans-Neptunian objectsBodies located beyond Neptune may fit the bill if a world comparable in size to Neptune were exerting its gravitational influence on them. Also, some astronomers believe that in the sun’s vicinity there are planets larger than Jupiter, sometimes thought of as brown dwarfs and something like non-glowing stars, also hidden in the dark.

Artistic representation of Planet 9
Artistic representation of Planet 9 – ESA / Hubble, M. Grain Knives

Now, an investigation that has focused on a point very far from the solar system, 336 light years from Earth, has made some inquiries that may be interesting to unravel the mystery of Planet 9. A team of astronomers, led by Meiji Nguyen, a researcher at the University of California at Berkeley (USA), has been able to measure the orbit of a gigantic exoplanet, 11 times more massive than Jupiter, and by name HD106906 b. Furthermore, the novelty is that this was the first time that the motion of a gaseous planet so far from its star has been studied. Their conclusions have been published in « The Astronomical Journal»

HD106906 b is the name of a world discovered in 2013 by the Magellan Telescope, at the Las Campanas Observatory, in Chile. Thanks to the presence of a peculiar disk of debris and gas in the environment of its star, several astronomers focused their attention on the area and ended up discovering the presence of an exoplanet by direct imaging. However, at first nothing was known about its orbit.

After 14 years of very precise measurements, compiled by NASA’s legendary Hubble space telescope, this has changed. Now we know that HD106906 b is very far from its host star, a binary system (that is, a double star), located at 730 Astronomical Units (UAs), when one AU is the distance that separates the Earth from the Sun, and is equivalent to about 150 million kilometers. The distance is such that the planet takes 15,000 years to travel its orbit, at a very low speed and very far from the gravitational influence of its stars.

A small portion of the sky where HD106906 b is located
A small portion of the sky where HD106906 b is located – ESA/Hubble, Digitized Sky Survey 2/Davide De Martin

Most surprising to astronomers is that the orbit of this distant world is very inclined and very elongated, extending well beyond the disk of debris that surrounds its two stars.

«To underline why this is rare – Nguyen has commented in a statement – we simply have to look towards our solar system, and see that all the planets are in the same plane.

But 336 light years from Earth, at some point in the constellation Crux, the same is not true. ‘It would be weird if, for example, Jupiter was tilted 30 degrees in relation to the plane that the other planets orbit. So, we have all kinds of questions about how HD106906 b ended up in an orbit like this».

What pushed HD106906 b?

The most likely explanation is that HD106906 b was formed just 3 AUs from its stars, but that friction with the disk of gas and debris caused it to slow down and slowly approach its suns. Then, there came a time when gravitational forces threw him into the vastness of space.

This world I could have become a wandering planet, without any sun attracting it with its gravity, but some nearby star stabilized it and prevented it from doing so. In fact, data from the large survey of the European Space Agency’s (ESA) Gaia satellite has already provided several candidate stars.

Something like this could have happened in the solar system. Planet 9 could have formed in the inner solar system, but would have been expelled to the outskirts, beyond Pluto, for its interactions with the gigantic planet Jupiter. Again, the interaction of other neighboring stars would have prevented this planet 9 from becoming a wanderer.

The past of the solar system

“This is as if we had a time machine to see what our solar system looked like 4.6 billion years ago,” he said. Paul Kalas, a co-author of the paper and also a researcher at Berkeley — and to study what could happen when our planetary system was dynamically active and everything was being shaken and repositioned.

So far, however, the evidence for the existence of a Planet 9 is limited to the presence of trans-Neptunian objects with difficult-to-explain and unusual orbits compared to the rest of the solar system. They point in the direction that they ended up like this after receiving the gravitational pull of a gigantic planet, but until it is discovered it will not be possible to know if it was.

“Despite not having detected Planet 9 to date, its orbit can be inferred, based on its effects on various objects on the outskirts of the solar system,” he commented. Robert De Rosa, co-author of the work and researcher at the European Southern Observatory (ESO). These effects presage that this world “would have an eccentric and inclined orbit (…) similar to what we are seeing with HD 106906b”.

The authors of this work hope that the James Webb Space Telescope, Hubble’s successor with incredible capabilities, will be able to collect more data on HD106906 b to learn more about how and where it formed, as well as to improve estimates of its orbit.

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