It’s a new planet! It’s an unknown star! It’s — oops!
Questions raised about claims of two new massive objects orbiting in our solar system
Reports of large, previously unknown planets wandering through the outer solar system have been exaggerated.
A few odd blips of radio waves from space hint at not one but two massive bodies far beyond the orbit of Neptune, researchers suggest in two papers posted online December 9 on arXiv.org. A dearth of follow-up observations and the sheer unlikelihood of stumbling across such beasts, however, are cause for a healthy dose of skepticism.
“The nature of the source [of these radio waves] has only become more confusing,” admits Wouter Vlemmings, an astronomer at Chalmers University of Technology and Onsala Space Observatory in Sweden and lead author of one of the papers. Based on feedback received less than 24 hours after posting the papers, “I would rule the chance for an outer solar system object extremely small,” he says. “It was just not something we could rule out on the data alone.”
Vlemmings and colleagues noticed one of the alleged interlopers zipping by W Aql, a star located about 1,290 light-years away in the constellation Aquila. A point of light darted across two images taken in March and April with the Atacama Large Millimeter/submillimeter Array, or ALMA, a collection of radio telescopes in northern Chile. By May, it was gone.
There were a few potential culprits. It could have been one moving object. Or the radio blasts could have come from two stationary objects, such as distant galaxies. Catching two coincidental galactic flares in the same narrow field of view is highly unlikely, though, the researchers say. The source was also moving too fast to be a star hurtling through the Milky Way. Assuming the object was real, that left the possibility that it was either a large planet less than 600 billion kilometers from the sun or a large icy body meandering between the orbits of Saturn and Uranus.
A second team, led by René Liseau, also at Chalmers University, noticed another wandering dot when ALMA was pointed at a different part of the sky. That team was looking for exoplanets around the triple star system Alpha Centauri, which at 4.2 light-years away, are the closest stars to the sun. Once in July 2014 and again in May 2015, the researchers saw a speck of radio energy moving along with Alpha Centauri. They reasoned that they caught a chance alignment with one of three possible objects: an icy body beyond the edge of the Kuiper belt, a planet a couple of times as wide as Earth and around 45 billion kilometers away or a brown dwarf 3 trillion kilometers away — 20,000 times as far from the sun as Earth.
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In both cases, the teams report only two observations, which means it’s premature to assume that either detection is one moving object. “Anything could create two random detections, and you can always fit a straight line through any two points,” says Scott Sheppard, a planetary scientist at the Carnegie Institution for Science in Washington, D.C. Researchers typically wait until they’ve seen something three times before reporting a new member of the solar system. “If they actually had three detections that all fit the same movement pattern,” Sheppard says, “then I would think it was interesting.”
A large hidden member of the solar system is not a crazy idea. The solar system is still largely unexplored and there are plenty of places to hide a distant rocky planet. Odd patterns seen in the orbits of icy bodies past the Kuiper belt hint at such a world orbiting several hundred times as far from the sun as Earth (SN: 11/29/14, p. 18), but researchers have yet to find anything definitive.
By posting the findings online, “we were soliciting feedback to avoid publishing something obviously wrong,” Vlemmings says. They’ve already learned that the mystery object by W Aql would have shown up in data from the WISE mission, a space-based telescope that mapped the infrared glow of the entire sky in 2010 and 2011. Data from that mission have previously ruled out a planet the size of Saturn within about 4.2 trillion kilometers of the sun and a planet the size of Jupiter nearly three times as far away.
Still, Vlemmings says that he and his colleagues will sift through more-recent ALMA data to see if the object shows up a third time. A ninth planet or dim star looping around the sun would be an extraordinary discovery, but it’s going to require some extraordinary evidence first.