Artist's illustration of the supernova remnant known as 1993J, which came from a double-star system.

Credit: NASA, ESA, G. Bacon (STScI)

A faraway supernova explosion may have contributed to a minor mass extinction here on Earth 2.59 million years ago, a new study suggests.

Fast-moving, charged particles called cosmic rays that were blasted out by asupernova may have played a role in the climatic changes that apparently led to a die-off at the end of the Pliocene epoch and the start of the Pleistocene, researchers said.

"Africa dried out, and a lot of the forest turned into savannah. Around this time and afterwards, we started having glaciations — ice ages — over and over again, and it's not clear why that started to happen," study co-author Adrian Melott, of the University of Kansas, said in a statement. "It's controversial, but maybe cosmic rays had something to do with it." [Wipe Out: History's Most Mysterious Extinctions]

**How is a supernova different from a hypernova? Learn about the different types of exploding stars that astronomers have identified in this infographic.**
**Credit: by Karl Tate, Infographics artist**

Melott and his colleagues — led by Brian Thomas, of Washburn University in Kansas — conducted computer simulations that modeled how supernovas might affect Earth's climate and biosphere. (Supernovas can occur in two ways: when a star much more massive than the sun runs out of fuel and dies, or when a superdense stellar corpse called a white dwarf steals so much matter from a nearby companion star that it crosses a mass threshold and explodes.)

The researchers were particularly interested in supernovas that occur about 300 light-years from Earth, because scientists think such events flared up twice relatively recently — once 6.5 million to 8.7 million years ago, and again 1.7 million to 3.2 million years ago. (This latter supernova is the one that may be tied to the Pliocene-Pleistocene extinction.)

"I was expecting there to be very little effect at all," Melott said, noting that 300 light-years is not very close.

The results were therefore surprising. The team's simulations suggest, for example, that such supernovas bathed the night sky in blue light so bright that it disrupted animals' sleep patterns for weeks. And, more importantly, a surge of radiation probably hit organisms on land and in the shallower parts of the ocean.

"The big thing turns out to be the cosmic rays," Melott said. "The really high-energy ones are pretty rare. They get increased by quite a lot here — for a few hundred to thousands of years, by a factor of a few hundred. The high-energy cosmic rays are the ones that can penetrate the atmosphere. They tear up molecules. They can rip electrons off atoms, and that goes on right down to the ground level. Normally, that happens only at high altitude."

Did Supernova Explosion Contribute to Earth Mass Extinction?

https://youtu.be/NE52c67-Xcg

The end result was likely a tripling of the overall radiation dose at ground level, the researchers found. This may have been enough to increase cancer and mutation rates, "but not enormously," Melott said. "Still, if you increased the mutation rate, you might speed up evolution."

This radiation may also have affected Earth's climate, the study said. The team's simulations suggest that the increased flux of cosmic rays caused many of the atoms and molecules in the lowest layer of Earth's atmosphere (known as the troposphere) to acquire a positive or negative charge.

This "tropospheric ionization" likely lasted for at least 1,000 years, the researchers said.

"It is possible that this could trigger climate change, especially if instability was already present," they wrote in the new study, which appears in The Astrophysical Journal Letters. (You can read it for free at the online preprint site arXiv.org here.)

The Pliocene-Pleistocene extinction was quite a minor one as far as these events go. Previous studies have suggested that a supernova would have to be quite close to Earth — within 25 light-years or so — to trigger a major mass extinction such as the one 65 million years ago that marked the end of the age of dinosaurs.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us@Spacedotcom, Facebook or Google+. Originally published on Space.com.

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New Dwarf Planet Discovered Far Beyond Pluto's Orbit

Pluto isn't quite as lonely as scientists had thought.

Astronomers have discovered another dwarf planet in the Kuiper Belt, the ring of icy objects beyond Neptune. But this newfound world, dubbed 2015 RR245, is much more distant than Pluto, orbiting the sun once every 700 Earth years, scientists said. (Pluto completes one lap around the sun every 248 Earth years.) You can see an animation of the new dwarf planet's orbit here.

"The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the sun," discovery team member Michele Bannister, of the University of Victoria in British Columbia, said in a statement. "They let us piece together the history of our solar system." [Meet the Solar System's Dwarf Planets]

"But almost all of these icy worlds are painfully small and faint; it's really exciting to find one that's large and bright enough that we can study it in detail," Bannister added.

**Rendering of the orbit of the newfound dwarf planet RR245 (orange line), which scientists say is the 18th largest object in the Kuiper Belt beyond Neptune.**
**Credit: Alex Parker/OSSOS team**

The exact size of 2015 RR245 is not yet known, but the researchers think it's about 435 miles (700 kilometers) wide. Pluto is the largest resident of the Kuiper Belt, with a diameter of 1,474 miles (2,371 km).

The research team first spotted 2015 RR245 in February of this year, while poring over images that the Canada-France-Hawaii Telescope in Hawaii took in September 2015 as part of the ongoing Outer Solar System Origins Survey (OSSOS).

"There it was on the screen — this dot of light moving so slowly that it had to be at least twice as far as Neptune from the sun," Bannister said.

OSSOS has discovered more than 500 objects beyond Neptune's orbit, but 2015 RR245 is the first dwarf planet that the survey has found, the scientists said.

**Discovery images of the dwarf planet RR245, showing the object’s slow motion across the sky over three hours.**
**Credit: OSSOS team**

Dwarf planets are massive enough to be crushed into spheres by their own gravity, but they have not "cleared their neighborhood" of other objects, which differentiates them from "normal" planets such as Earth and Saturn. This definition, which was devised by the International Astronomical Union in 2006, led to Pluto's controversial reclassification as a dwarf planet.

Astronomers are still working out the details of 2015 RR245's highly elliptical orbit, but the object appears to come as close to the sun as 34 astronomical units (AU), and farther away than 120 AU. (One AU is the average Earth-sun distance — about 93 million miles, or 150 million km.)

2015 RR245 — which will get a catchier, official name at some point — will make its closest approach to the sun in 2096, the researchers said.

Other confirmed dwarf planets in the Kuiper Belt region include Pluto, Eris, Haumea and Makemake. Several other objects in this distant realm, including Sedna, Quaoar and 2007 OR10, probably meet the dwarf-planet criteria as well, scientists have said.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us@Spacedotcom, Facebook or Google+. Originally published on Space.com.