Is Earth Weighed Down By Dark Matter?

GPS satellite measurements hint Earth may be more massive than expected.

There may be a giant ring of dark matter invisibly encircling the Earth, increasing its mass and pulling much harder on orbiting satellites than anything invisible should pull, according to preliminary research from a scientist specializing the physics of GPS signaling and satellite engineering.

The dark-matter belt around the Earth could represent the beginning of a radically new understanding of how dark matter works and how it affects the human universe, or it could be something perfectly valid but less exciting despite having been written up by New Scientist and spreading to the rest of the geek universe on the basis of a single oral presentation of preliminary research at a meeting of the American Geophysical Union in December.

The presentation came from telecom- and GPS satellite expert Ben Harris, an assistant professor of mechanical and aerospace engineering at the University of Texas- Arlington, who based his conclusion on nine months’ worth of data that could indicate Earth’s gravity was pulling harder on its ring of geostationary GPS satellites than the accepted mass of the Earth would normally allow.

Since planets can’t gain weight over the holidays, Harris’ conclusion was that something else was adding to the mass and gravitational power of Earth – something that would have to be pretty massive but almost completely undetectable, which would sound crazy if predominant theories about the composition of the universe didn’t assume 80 percent of it was made up of invisible dark matter.

Harris calculated that the increase in gravity could have come from dark matter, but would have had to be an unexpectedly thick collection of it – one ringing the earth in a band 120 miles thick and 45,000 miles wide.

Harris, an expert in Global Positioning Systems, GPS networks, spacecraft systems engineering and founder of the open-source GPS software project GPS ToolKit, wasn’t looking for dark matter specifically, but was trying to explain observations that suggested the Juno space probe NASA launched in August seemed to be going faster than it should have while taking a loop around the Earth to pick up a little speed for its trip to Jupiter.

The probe’s unexpected extra bit of speed, other researchers suggested, could have been caused by something different about Earth’s gravity, though what that could have been wasn’t clear.

One possibility was that the 1964 calculation by the venerable International Astronomical Union underestimated the Earth’s mass –and therefore its gravitational pull – causing NASA scientists to underestimate the speed the Juno probe would build up running “downhill” into Earth’s gravity well during its final fly-by.

In an analysis published in 2009, Institute for Advanced Study researcher Stephen Adler suggested the reason for the anomaly could have been that the density of dark matter within the Solar System – and around the Earth in particular – could be much higher than astrophysicists had assumed.

Dark matter – invisible and so-far almost undetectable – was invented to try to explain why the universe does seem to be expanding from a single point as Big Bang theory predicts, but not nearly as fast as it should.

Galaxies, stars and other matter should only crawl away from each other at current speeds if there were a lot more gravity holding them back than there would be if the matter we could see were all the matter in the universe. Making the math work – getting it to agree with what the universe had already decided to do – meant bumping up the guesstimated weight of the universe by 80 percent, with nothing to explain what all that mass actually was. Dark matter is widely accepted as real among physicists, but is still more a “mystery filler” substance than an actual, explainable phenomenon.

Unlike most research about dark matter, Adler’s 2008 analysis tried to pin blame for a specific micro-event on a massive, invisible force whose invisibility shows our inability to see the answer to a question we can’t quite understand, or could be a fantasy created to make the math work until someone can put a finger on a more obvious and simple mistake.

One anomalous speed reading during a single flyby isn’t much to hang a major proof on, however.

A dense ring of closely watched, constantly managed spacecraft in a sphere covering almost every inch of the Earth make a decent set of measurement tools. Unlike wide-orbiting, long-distance probes, GPS satellites fly in tight, precisely ordered and measured orbits that are constantly measured and adjusted by ground crews to keep each in exactly the right place to let GPS systems on the ground get consistent calculations of their own locations.

Harris took nine months of data from the U.S. network of GPS satellites, the Russian GLONASS GPS network and European Galileo satellites and started looking for differences between what the Earth’s pull actually was compared to what it was supposed to be.

“The nice thing about GPS satellites is that we know their orbits really, really well,” he told New Scientist. which posted a story Jan. 2 about his talk in mid-December.

Harris, who made an oral presentation of his findings but had no paper showing the data and calculations for other scientists to vet, and admitted his calculations were preliminary and presentation incomplete.

He hadn’t calculated the effect of relativity on the orbits of the satellites for example, he warned New Scientist. He also hadn’t yet accounted for the gravitational pull of the sun and moon or other possible influences.

Other data presented at the same meeting suggested the Juno probe was not, in fact, speeding when it passed by the Earth which, if true, would have made Harris’ conclusion more tentative.

Harris concluded that the mass of Earth is between .005 percent and .008 percent higher than the figure that had been accepted almost universally since the IAU calculated it 50 years ago.

It’s not like discovering an invisible new moon, but is still a pretty significant mistake, if that’s what it was.

Not everyone agrees the mistake is in the IAU’s figures, or even that Harris has presented enough information to know anything new about either dark matter or the Earth.

Making elaborate claims in oral presentations, without nailing down all the variables that could keep a set of results from being twisted into something more interesting than the truth is a red flag for any scientific presentation, let alone one making audacious claims about the way dark matter behaves or weight of the Earth, according to an exasperated counterargument from Matthew R. Francis, who earned a Ph.D. in physics and astronomy from Rutgers in 2005, held visiting and assistant professorships at several Northeastern universities and whose science writing has appeared in Ars Technica, The New Yorker, Nautilus, BBC Future and others including his own science blog at Galileo’s Pendulum.

Dark matter might clump up around Earth as Harris suggested, but only if its particles pull more strongly on each other than most physicists expect. If they do, and if it has gathered in unlikely density around the Earth, it could have a measurable gravitational effect, but even the mass of the sun hasn’t attracted dense, powerful clumps of dark matter, at least not that anyone has discovered, Francis wrote.

Prevailing theories about dark matter paint is as being much more evenly distributed throughout the galaxy, at densities equivalent to about 600 electrons within the area of a cube a centimeter on each side. In human terms that’s something lower than undetectable, not something likely to create more pull on a satellite than anyone had previously found or failed to explain more simply.

Dark matter is not space dirt; it hardly interacts with “normal” matter at all.

Particles of dark matter, like Higgs Bosons, neutrinos and other particles that are difficult for humans even to detect, pass straight through each of us all the time, though “whether you find that creepy or not depends on your mindset” and how many are doing it at an one time depends on what dark matter will actually turn out to be.

“To dark matter, you’re basically transparent,” Francis wrote.

Francis’ Jan. 2 blog entry carries the tag “debunkery,” but he doesn’t say Harris’ conclusions are wrong, criticize his research methods or even accuse Harris of anything unsavory.

He does complain that Harris presented his conclusions and got publicity from New Scientist for them without having passed through the gauntlet of skepticism and peer review designed to filter most of the mistakes out of new research before it’s published, with its data and methodology exposed so the rest of its faults can be pummeled away.

Conferences like the one at which Harris spoke are “good opportunities to present ideas that might or might not be publishable in journals,” Francis wrote.

“Not publishable” can mean good science that has not yet been sufficiently vetted but ultimately will be, and complete quackery, though Francis doesn’t even address which Harris’ work might be.

The problem isn’t the quality of the work, or its conclusions. The problem is that it was presented in too informal a way for other scientists to judge its quality, given more exposure by the New Scientist writeup and went proto-viral through the geekosphere as it was picked up writers and editors [ahem] who recognized the potential impact of Harris’ results without looking hard enough at the data supporting his conclusions.

“I’ve seen (and even given) talks based on preliminary research that aren’t ready yet, and I suspect this talk fell into that category,” Francis wrote. “When Harris has taken general relativity and the effects of the Sun and Moon into account and if he still sees this phenomenon, then we might have something to talk about.”

Francis added a sentence concluding that dark matter does not play a role in the motion of GPS satellites, but I left that out in deference to his concern about accuracy. Even if every word Harris said was wrong, it would only mean we have no idea whether dark matter can affect satellites, any more than we would know whether it likes to clump, gather in halos around tiny gravity wells or whether it resents being called dark and mysterious just because one planet’s biological infection can’t see well enough to detect 80 percent of the universe.

Better to just skip that discussion altogether.


Image: NASA