Undetected-planet idea back in focus
FAYETTEVILLE — Finding an undiscovered planet in the solar system isn’t easy, said astrophysicist Daniel Whitmire.
In the vastness of sky, “the problem is, you don’t know where to look,” said Whitmire.
His research in the 1980s while working at the University of Louisiana at Lafayette described the possibility of an undiscovered world orbiting the sun.
Such a planet would be more than just an important astronomical discovery, according to an idea put forward by Whitmire and colleague John Matese. Their work described a planet where the orbit around the sun took much longer to complete than Earth’s or any known planet, and whose path varied in a predictable way so that every several millions of years it dislodged clusters of distant comets.
Shaken loose by the hidden planet’s gravity as it approached, the comets would then break away in all directions — including toward Earth.
“In hindsight, the odds were not too good in finding it,” said the soft-spoken Whitmire, 74 and now a math instructor at the University of Arkansas, Fayetteville. “Now, today, the odds are much better.”
Decades after Whitmire’s ideas gained popular attention and were part of a Time magazine cover story, other astrophysicists have independently declared new ideas about undiscovered planets at the fringes of the solar system. Volunteers and scientists alike are seeking to directly observe what for now remains unproven.
But unlike their work, Whitmire ties together the possibility of an unseen planet and the idea of catastrophe on Earth.
He reasons that some comets shaken loose would strike Earth and cause global harm.
His theoretical research is based “on the need to find an astronomical explanation for periodic mass extinctions,”
Whitmire said, with the next comet shower event predicted in his hypothesis about 16 million years away. “You can relax,” he said. Some scientists told the Arkansas Democrat-Gazette they doubt details of extinction that led Whitmire to develop his hypothesis, and Whitmire acknowledged disagreement among paleontologists.
When it comes to the new work by astrophysicists on possible planets, however, nothing rules out what he proposed decades ago, he said.
In academic journal Nature, Whitmire and Matese laid out an idea for a “Planet X” that interacts gravitationally every 26 million years with objects in what is known as the Kuiper belt, a region beyond Neptune. Whitmire said the best estimate now is that this happens every 27 million years.
The Planet X hypothesis states that it rotates around the sun about every 1,000 years. But as it moves, its orbit “reorients itself very slowly, over millions of years,” Whitmire said.
Twice during what’s known as a precession, a period that Whitmire described as lasting 54 million years, it causes comets in the Kuiper belt to become dislodged from their typical orbital patterns in space.
“It plows into, gravitationally speaking, some comets and scatters them all over the place,” Whitmire said.
Planet X likely would be “around one Earth mass,” though it could be up to five times as big, he said.
Last year, academic journal Monthly Notices of the Royal Astronomical Society published an update from Whitmire in light of new work done by other astrophysicists.
At the time he and Matese first published their ideas, “there was a lot of skepticism” about the existence of another planet in the solar system, Whitmire said.
“That’s been gradually changing over the years,” he said.
California Institute of Technology researchers last year described evidence pointing to what they refer to as Planet Nine, roughly 10 times the mass of Earth. Konstantin Batygin and Mike Brown announced their findings about a distant planet, with Brown telling The New York Times, “we are pretty sure there’s one out there.”
Whitmire called the researchers’ Planet Nine work “truly mainstream.”
“You’ve got every astronomer in the world looking for it,” said Whitmire.
The University of Arizona last month announced that researchers also posit the existence of an unseen planet, perhaps less massive than Earth.
Whitmire said he moved to Northwest Arkansas for family reasons, and his interest in space goes back to his boyhood in Georgia. He became enthralled by an aunt’s encyclopedia and its information about the planets, he said.
“My parents were not highly educated. They didn’t go to college,” Whitmire said. At every visit to his aunt’s, “Boy, I’d go in there and dig that out, read everything” Whitmire said.
Scientists describe the solar system differently, compared with decades past. Eight planets have been observed, with Neptune the farthest away. Scientists once included Pluto as a ninth planet before taking note of how small it is.
Whitmire said he also collaborated on another research paper in the 1980s that proposed a larger planet sometimes described as “Nemesis.”
“The Nemesis model is not 100 percent rejected yet,” Whitmire said.
But data relating to the possibility of periodic mass extinctions have not supported the details of such a “Nemesis” planet, Whitmire said.
He referred to the work of University of Kansas physics and astronomy professor Adrian Melott.
Melott said he’s found “strong evidence” that, going back about 500 million years, “there is a pattern of recurring [extinction] events every 27 million years.”
“Whitmire’s explanation is the only one that does not have a serious problem,” said Melott, who has collaborated with Richard Bambach, a paleobiology research associate at the National Museum of Natural History.
Paleontologists describe mass extinctions as the dying off of species within a relatively short period of time. Some disagreed about the details of such global events.
Gerta Keller, a Princeton geosciences professor, in an email said that “by the late 1980s this periodicity idea was thoroughly discredited.”
Others spoke less harshly, but said it’s far from settled.
“I think the big problem is, it depends on how you define the term ‘mass extinction,’” said David Jablonski, a professor in the geophysical sciences department at the University of Chicago.
In paleontology, “everyone agrees that there were f ive really major ones,” Jablonski said.
Those events were not spaced out in identical time intervals, he said, but analyses take into account “a whole family of smaller pulses,” he said. Methods of dating geological evidence improve, leading to better — but shifting — information, he said.
“It’s a very difficult, subtle problem,” Jablonski said, calling it “not obvious” that mass extinctions took place at regular intervals.
Jonathan Payne, a Stanford professor of geological sciences, said there is “at least some evidence for cyclicity in extinctions.”
Scientists have found evidence of an impact event coinciding with a mass extinction taking place at the end of what’s known as the Cretaceous Period, he said.
For other mass extinctions, however, “the best evidence right now is not pointing towards an impact event” as their cause, Payne said.
Astrophysicists looking at the solar system described both indirect data suggesting another planet and efforts aimed at direct observation.
This February, NASA called for volunteers to help look through images captured by the agency’s Widefield Infrared Survey Explorer mission.
Marc Kuchner, a NASA astrophysicist, is principal investigator for the Backyard Worlds: Planet 9 project.
Over the past 10 years or so, “just like cameras on your cellphone have been getting bigger, cameras in telescopes have also been getting bigger, and it’s opened up new areas of science that people haven’t been able to consider before,” Kuchner said.
The University of Arizona researchers announced last month a possible planet affecting objects in the Kuiper belt.
“There’s a long history of trying to go look at objects in the solar system and see if there are unexplained gravitational effects on those objects that could be associated with something we haven’t discovered yet,” said Kat Volk, a University of Arizona postdoctoral researcher, explaining her work with Renu Malhotra, a University of Arizona planetary sciences professor.
After observing an unexplained tilt to objects in the Kuiper belt, “we think an unseen planet is the most likely explanation,” Volk said.
She said that it can be difficult to observe an object if it lies in a portion of the sky that falls within what’s called the galactic plane, which is where the Milky Way in a dark night sky can be seen.
The solar system lies in the Milky Way galaxy, and Volk said it can be very difficult to “pick out these fainter moving objects” in a crowded, starry background.
Motion of objects in the solar system is detected by comparing images taken at different time intervals, requiring patience to detect a faraway object that appears to move more slowly against its background, Volk said.
She also said that “a very big area of sky” remains that has yet to be surveyed thoroughly.
The NASA Backyard Worlds project would not uncover a planet smaller than Neptune, Kuchner said. Neptune has about 17 times as much mass as Earth, according to NASA.
Discovery of a new planet in the solar system “would end up in textbooks,” said Kuchner. “It would end up in every children’s book on the solar system.”
Another NASA project, the Large Synoptic Survey Telescope, or LSST, is under construction in Chile. It is expected to begin operations in 2022, Ivy Kupec, a NASA public affairs specialist, said in an email.
“LSST should be sensitive to, I think all of these different potential planets,” Kuchner said. “If LSST doesn’t find it, then it probably doesn’t exist,” Kuchner said. Volk said she thinks “we’ll get an answer within the next decade.”
Whitmire holds on to the idea that the planet he hypothesized about more than 30 years ago could be observed directly. Many speculative theories get shot down quickly by other scientists, he said, with Planet X still remaining a possibility.
“Planet Nine is still not a done deal at all, and ours is also not a done deal,” said Whitmire. “It’s just that ours has been around for all this time.”