For decades, the four known forces of nature, gravity, electromagnetism, and the strong and weak nuclear forces, have accounted for every interaction physicists can measure in a laboratory or a spacecraft trajectory. But a study by Slava G. Turyshev, a physicist at NASA’s Jet Propulsion Laboratory, argues that a long-range interaction beyond those four, sometimes called a “fifth force,” could be operating inside our own solar system while slipping past every test designed to catch it.
Turyshev has not found such a force. What he has done, in a paper posted on arXiv with a Physical Review D reference, is map out exactly how precise future experiments would need to be to detect one, and why current instruments may be falling short. The arXiv listing carries a journal reference to Physical Review D, indicating the paper has been accepted or is in press, though readers should verify the final publication status through the journal itself. The work arrives as fresh tracking data from NASA’s OSIRIS-REx asteroid mission is already narrowing the window where a hidden force could exist.
The “Great Disconnect”
At the heart of Turyshev’s argument is a puzzle he calls the “Great Disconnect.” Observations at cosmological scales, galaxy rotation curves, the accelerating expansion of the universe, point to something beyond ordinary matter and Einstein’s general relativity. Physicists label those unknowns dark matter and dark energy, placeholder names for phenomena that together appear to account for roughly 95 percent of the universe’s total energy content. Some theoretical models predict that dark energy, in particular, could manifest as a new long-range force, a fifth fundamental interaction layered on top of gravity.
Yet every precision test conducted inside the solar system has come back clean. Spacecraft tracking, lunar laser ranging, and planetary ephemeris calculations all confirm general relativity to extraordinary accuracy. “If a fifth force exists, it is not showing up where instruments are sharpest,” as Turyshev frames the problem in his paper, describing the tension as a fundamental challenge for experimental gravitational physics.
Turyshev’s explanation draws on a class of theoretical proposals known as screening mechanisms. The two he highlights, the chameleon effect and the Vainshtein mechanism, work like a kind of gravitational camouflage. In dense environments such as the inner solar system, where massive bodies like the Sun and Earth dominate the gravitational landscape, these mechanisms would suppress a fifth force to levels too faint for current detectors. Only at vast cosmological distances, where matter is sparse, would the force emerge at full strength.
A roadmap, not a discovery
The paper is best understood as an experimental blueprint. Turyshev forecasts specific sensitivity thresholds for a quantity called the parameterized post-Newtonian (PPN) gamma parameter, which measures how much space-time curvature a mass produces. In plain terms, gamma is a dial: general relativity predicts it should read exactly 1. A screened fifth force would nudge it off that mark by a tiny amount, potentially detectable through Shapiro delay measurements, which track how much a planet’s or spacecraft’s radio signal slows as it passes through the Sun’s gravitational field.
The study builds on a longer research program. Turyshev and collaborators have previously published overviews of solar system techniques for testing gravity, including spacecraft tracking, laser ranging, and equivalence-principle experiments. The new paper updates those targets with specific predictions tied to dark energy and dark matter searches, arguing that the solar system’s wealth of precisely tracked objects makes it a uniquely controlled environment for the hunt. As Turyshev writes, the solar system functions as a “precision laboratory” whose navigated spacecraft and tracked small bodies offer measurement baselines unavailable anywhere else in observational science.
NASA’s institutional interest lends the program credibility without confirming its conclusions. JPL has publicly described its role in testing gravity and probing dark energy, framing the work as constraining departures from general relativity. The agency’s NASA Innovative Advanced Concepts (NIAC) program has funded a concept study called the Gravity Observation and Dark Energy Detection Explorer in the Solar System, envisioned as a dedicated space-based gravity laboratory. As of spring 2026, that concept remains a study, with no approved mission, timeline, or budget for hardware. The gap between a NIAC study and a launched spacecraft is wide, but the funding signals that the scientific community considers the question worth serious investment.
What asteroid Bennu already revealed
While Turyshev’s paper charts the path forward, a separate team has already put one stretch of that path to the test. A peer-reviewed analysis published in Communications Physics used precision orbit tracking of asteroid Bennu, collected during NASA’s OSIRIS-REx sample-return mission, to search for Yukawa-type fifth forces and ultralight dark matter mediators.
OSIRIS-REx spent more than two years orbiting Bennu, mapping its surface and measuring its trajectory with a level of detail rarely achieved for a small body. The mission’s navigation team reported ranging precision on the order of meters over interplanetary distances, placing Bennu’s orbit determination among the most accurate ever achieved for an asteroid. The research team modeled that trajectory against predictions from general relativity and looked for any residual tug that could not be explained by known physics. The result was a set of exclusion limits: across a wide range of hypothetical mediator masses, the data ruled out fifth-force couplings above certain strengths. Some theoretical models were eliminated outright; others survived within a narrower band of allowed parameters.
These are null results, and in fundamental physics, null results carry real weight. They do not prove a fifth force exists, but they sharpen the boundaries of where it could hide. The parameter space that Bennu’s data left open is precisely the territory Turyshev’s proposed Shapiro delay and PPN gamma experiments aim to probe next.
Where the shrinking parameter space leaves the search
A confirmed detection would rank among the most consequential findings in modern physics. It would mean the Standard Model of particle physics and general relativity are both incomplete in a measurable, local way, not just at the extreme scales of black holes or the early universe. Depending on the force’s properties, it could reshape understanding of dark energy, offer a laboratory handle on dark matter, or point toward entirely new particles acting as force carriers.
But confirmation is not close. The current state of play is a tightening net of constraints: cosmological observations that demand something new, solar system tests that keep returning results consistent with Einstein, and a shrinking but still real gap between the two. Screening mechanisms offer a plausible reason for that gap, but they remain unverified theoretical constructs. Competing frameworks, including modified Newtonian dynamics (MOND) and various emergent-gravity proposals, offer alternative explanations for the same cosmological anomalies without invoking a new force at all.
Turyshev’s contribution is to insist that the question is answerable with technology either in hand or within reach. Dedicated ranging missions, improved Shapiro delay measurements, and continued asteroid-tracking campaigns could, over the next decade, either detect a screened fifth force or push its allowed parameter space to the vanishing point. As he argues in the paper, the tools already exist to turn the “Great Disconnect” from an abstract puzzle into a testable proposition, and the solar system’s precisely tracked orbits are the proving ground where that test will play out.
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*This article was researched with the help of AI, with human editors creating the final content.
