Carey Lisse and Ralph McNutt from Johns Hopkins University Applied Physics Laboratory and a team of colleagues detected the X-rays by pointing the Chandra X-Ray Obervatory telescope in Pluto’s direction four different times between February 2014 and August 2015. Seven photons of X-ray light were detected during these observations, confirming the team’s hypothesis that the dwarf planet is detectable on the X-ray spectrum, potentially due to the presence of an atmosphere. Their findings have been published in the scientific journal, Icarus.
Why is this such a big deal? First of all, it would challenge what scientists have previously believed to be true of Pluto’s nature. Until now, the popular description of the dwarf planet is as a tiny ball of frozen rock slowly meandering around the sun some 3.6-billion miles away.
The recent fly-by done by the New Horizons space probe began to call this idea of Pluto into question, as data from the spacecraft’s approach of the dwarf planet indicated the presence of an atmosphere. That atmosphere is likely a result of Pluto’s icy surfaces slowly melting when it is closer to the sun along certain points of its orbit. The loose atmosphere then trails from Pluto, much like a comet’s tail.
One of the possible explanations for why Pluto is emanating X-rays would be that the high energy particles emitted by the sun are stripping away and reacting with Pluto’s atmosphere, producing the X-rays that are visible to Chandra. Such interactions have been witnessed in the interaction between the sun’s high-energy particles and the cold material that trails off of comets, but this would mark the first time an object past Saturn was visible on the X-ray spectrum. It also makes sense given that Pluto, like many comets, is part of the Kuiper Belt and produces a tail.
So, instead of just being a frozen, dead orb floating beyond Neptune, Pluto might actually be a frozen, dead orb that is being very slowly boiled away by solar winds like a giant comet.
There are other potential explanations, such as haze particles in Pluto’s atmosphere scattering the sun’s X-rays are possible, though unlikely given the temperature of the X-rays observed. It is also possible that these X-rays are actually bright auroras produced by the atmosphere, but that would require Pluto to have a magnetic field — something that would have been detected during New Horizon’s flyby, yet no evidence of one was found.
The other aspect of this discovery that could bring about major changes to the way we see the universe is how we might now explain all that background X-ray radiation scientists are always observing. Instead of background X-rays simply being a characteristic of the universe, it is possible that some of that radiation — or even all of it — is a result of similar interactions happening throughout the universe.
In a way, it seems like poetic justice that the little once-planet of Pluto continues to be the very thing that challenges our classifications and beliefs about the way the universe works.
