A Stolen Exoplanet That Will Kill Us All? Here’s What We Do Know About ‘Planet Nine’

Artist’s impression of Planet Nine. Tomruen, nagualdesign; background taken from File:ESO , CC BY-SA

While this is entirely possible, the research assumes that Neptune-sized objects were relatively common in this region – something we simply don’t know. The study also suggest that further observations and modelling of the positions and orbits of minor objects in the solar system beyond Neptune now may provide further clues as to the origin of the proposed Planet Nine – whether this is core expulsion as originally proposed or exoplanet capture.

At the moment, the lack of direct observations of Planet Nine and the whole range of objects which may be affected by it mean that the explanations are poorly constrained. In the meantime, this kind of work provides interesting ideas – but ultimately we need proof. Excitingly, if it does exist and turns out to be a captured exoplanet, it is likely to be our best bet for visiting an exoplanet in the near future.

It Could Be Made Up Of Iron And Ice

Planet Nine could be similar to Uranus. NASA, ESA, and M. Showalter

Other computer simulations assume that Planet Nine was a distant ice giant similar to Neptune and Uranus. They calculate the evolution of the size, temperature, luminosity and colour of such a body, having moved from its possible formation point nearer the sun to its distant position at about 700 AU.

This research suggests Planet Nine is like a “mini-Uranus”, with an iron core, silicate mantle, water ice shell and hydrogen/helium outer layers. Its temperature would be about -226°C (or 47 Kelvin) – and most of this would be internal heat rather than absorbed sunlight, which means it would be difficult to see with optical telescopes. In fact, the planet would reflect very little sunlight, which means it would be visible in infrared wavelengths (heat) instead of visible light.

The research is useful for scientists modelling and searching for the planet, as it helps them to know what they should look for.

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