Mars Could Be the Key to Finally Spotting Dark Matter
One theory surrounding dark matter is that it isn’t an exotic particle at all, but instead a collection of primordial black holes formed during the Big Bang that’ve been zipping around the cosmos ever since.
Now, a new study posits that scientists could potentially detect one of these hypothetical intergalactic travelers as it zoomed through the inner Solar System by measuring a “wobble” in Mars’ orbit.
Unfortunately, a primordial black hole would likely perform a flyby like that only once every decade, and sorting through the data to detect the influence of this passing microscopic black hole would be a herculean task.
Less than 20 percent of the matter in the known universe is the kind of stuff that we can see and interact with. The rest is made up of the perennial mystery of physics—the yet-to-be-detected dark matter. While many physicists theorized that dark matter is some form of exotic particle (like an axion, for example) other ideas look back to the Big Bang to explain dark matter’s origin story.
According to one theory, it was in the first moments of... well... everything that the universe formed microscopic black holes known as primordial black holes (PBHs). Instead of forming from collapsed stars like your typical, run-of-the-mill black hole, these structures would’ve formed from a collapse of gas and then spread throughout the cosmos as the universe expanded and cooled. If this is the case, a team of scientists from MIT and University of California, Santa Cruz (UCSC) argue that you should be able to detect near-flying PBHs by measuring the orbit of Mars. A study detailing this technique was published this week in the journal Physical Review D.
“Given decades of precision telemetry, scientists know the distance between Earth and Mars to an accuracy of about 10 centimeters,” MIT’s David Kaiser, a co-author of the study, said in a press statement. “We’re taking advantage of this highly instrumented region of space to try and look for a small effect. If we see it, that would count as a real reason to keep pursuing this delightful idea that all of dark matter consists of black holes that were spawned in less than a second after the Big Bang.”
The idea came from an innocent question: What would happen if a PBH passed through a human? If they exist (PBHs are still very much hypothetical objects), scientists estimate that these black holes could be as small as an atom, but as heavy as the largest asteroids. The team estimated that the force of these objects colliding with a person could push someone roughly 20 feet in about a second. While the odds of such a collision are unfathomably small, an interaction with a planetary system—or even the inner Solar System—could be a much bigger (and therefore much more likely) target.
The team crunched some numbers, and theorized that PBHs would likely pass through the inner Solar System at some point once a decade or so. Using detailed models of the Solar System, the researchers then analyzed whether an asteroid-mass black hole could have a detectable effect on Earth or the Moon. It turns out that noticing such an impact on our planet or its satellite would be too uncertain—but Mars, on the other hand, showed promise. If a primordial black hole passed within a few hundred million miles of the Red Planet, then a few years later, the planet’s orbit would have shifted by the small (but technically detectable) distance of about a meter.
Of course, even this planetary detection method comes with a few shortcomings.
“We need as much clarity as we can of the expected backgrounds, such as the typical speeds and distributions of boring space rocks, versus these primordial black holes,” Kaiser said in a press statement. “Luckily for us, astronomers have been tracking ordinary space rocks for decades as they have flown through our Solar System, so we could calculate typical properties of their trajectories and begin to compare them with the very different types of paths and speeds that primordial black holes should follow.”
This method would rely on quite a bit of luck, as a passing PBH would need to travel through a particular path, and hunting for that signal in real data could be a pretty daunting task.
For now, the team is calibrating their models to simulate more and more objects in order to test close encounter scenarios with more precision. Once that process is complete, they’ll be ready if (or when) a primordial remnant of the Big Bang decides to drop by our Solar System for a quick visit.
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