Can we measure dark matter in our solar system?

See bigger. | Artist’s concept of the furthest outgoing spacecraft from Earth, Traveler 1, launched in the late 1970s. The circles represent the orbits of the main outer planets of our solar system: Jupiter, Saturn, Uranus and Neptune. Voyager 1 is now more than 14 billion miles (23 billion km; about 150 Earth-Sun Units or AU) from Earth. To detect dark matter in our solar system, scientists say, a spacecraft could be less distant than Voyager 1 currently is. Picture via Nasa/ ESA/ G. Bacon.

Dark matter is invading our solar system

Black matter does not interact with ordinary matter. It is invisible to light and other forms of electromagnetic radiation. Modern instruments therefore cannot “see” it. But dark matter has mass. And that means it has a gravitational pull. Through studies of its attraction, astronomers have gathered overwhelming indirect evidence to suggest that dark matter permeates our universe. And so our solar system – our family of planets orbiting the sun – must also contain dark matter. On February 1, 2022, NASA reported on a new study that calculates the attraction of dark matter to objects in our solar system, for example, spacecraft and distant comets. Then, the study proposes an experiment to detect dark matter within our solar system.

The 2022 lunar calendars are here. Order yours before they’re gone!

The study is called Leaving the solar system: dark matter makes the difference. the Peer-reviewed newspaper Royal Astronomical Society Monthly Notices published it.

The lead author of the study is a mathematician and astrophysicist Edward Belbruno from Princeton University and Yeshiva University. He calculated what he called the galactic forcethat is, the overall gravitational pull of normal matter combined with dark matter, of the entire Milky Way galaxy.

The solar system is half dark matter and half normal matter.

He discovered that in our solar system, about 45% of this force comes from dark matter and 55% comes from normal matter, called baryonic matter. This suggests a roughly 50/50 split between the mass of dark matter and normal matter in our sun’s family.

So half of the solar system could be dark matter! Still, Belbruno said he was surprised that the percentage of dark matter in our solar system isn’t higher:

I was a bit surprised by the relatively small contribution of galactic force due to dark matter felt in our solar system compared to the force due to normal matter. This is because most dark matter is found in the outer parts of our galaxy, far from our solar system.

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Pie chart showing dark matter, ordinary matter and dark energy.
You see slightly varying estimates for the percentage of dark matter in our universe. But, according to modern theorists, there is far more dark matter than ordinary matter in the universe. Picture via NASA/ WMAP.

The Galactic Force and Our Outgoing Spaceship

NASA explained that Belbruno and the study’s co-author james green from NASA went on to predict that the gravity of dark matter interacts “very slightly” with all spacecraft that NASA has sent on paths outside our solar system:

This could include, for example, retirees Pioneer 10 and 11 probes launched in 1972 and 1973, respectively; the Voyager 1 and 2 probes that have been exploring for more than 40 years and have entered interstellar space; and the New Horizons spacecraft that flew over Pluto and Arrokoth in the Kuiper Belt.

It’s a very small effect. After traveling billions of miles, the trajectory of a spacecraft like Pioneer 10 would deviate only about 1.5 meters due to the influence of dark matter, NASA explained. Yet… the space is vast. And our outgoing spacecraft will eventually travel billions of miles.

The attraction of dark matter beyond Pluto

Belbruno and Green calculated that Earth craft would feel the pull of dark matter about 30,000 astronomical units (AU) from the sun. That’s 30,000 times the Earth-Sun distance. It’s way beyond Pluto, but still inside the Oort cloud, which extends out to 100,000 astronomical units. So that would have big implications. NASA explained:

This means that the gravity of dark matter could have played a role in the trajectory of objects like ‘Oumuamua, the comet or the cigar-shaped asteroid that came from another star system and passed through the inner solar system. in 2017. Its unusually fast speed could be explained by the gravity of dark matter pushing it along for millions of years, the authors say.

If there’s a giant planet in the far reaches of the solar system — a hypothetical object called Planet 9 or Planet X that scientists have been searching for in recent years — dark matter would also influence its orbit. If this planet exists, dark matter might even push it away from the area where scientists are currently looking for it, write Green and Belbruno. Dark matter may also have caused some of the Oort Cloud’s comets to escape the Sun’s orbit altogether.

Could we measure the attraction of dark matter in our solar system?

These scientists believe that – to measure the effects of dark matter in our solar system – a future spacecraft would not necessarily have to travel 30,000 AU. But he would have to carry the right equipment. At a distance of 100 AU, they said, a future spacecraft could help astronomers measure the influence of dark matter in the following ways:

Specifically, a spacecraft equipped with radioisotope power, a technology that allowed Pioneer 10 and 11, the Voyagers and New Horizon to fly very far from the sun, may be able to make this measurement. Such a spaceship could carry a reflective ball and drop it an appropriate distance. The bullet would only feel galactic forces [combined gravitational force from both dark and ordinary matter]. During this time, the spacecraft would experience a thermal strength of the decaying radioactive element in its power system, in addition to galactic forces.

By subtracting the thermal force, the researchers could then examine how the galactic force relates to deviations from the respective trajectories of the bullet and the spacecraft. These deviations would be measured with a laser when the two objects fly parallel to each other.

Interstellar probe mission

A proposed NASA mission called Interstellar probe might be able to do that. This 50-year one-way mission into the depths of space is currently being studied by the Johns Hopkins Applied Physics Laboratory. Its goal is to travel about 500 AU from the sun – 500 times the Earth-Sun distance – to explore the space between the stars. Can we equip this mission with a “reflecting ball”, as described above? I vote yes!

Learn more from NASA about measuring dark matter in our solar system

5 spaceships leaving the solar system.
See bigger. | These 5 man-made spaceships are currently leaving the solar system. Picture via Nasa.

Conclusion: Science is about measuring things. And, according to modern astronomers, dark matter permeates our solar system. Can we find a way to measure it? Two scientists say yes and propose a mechanism.

Source: Leaving the solar system, dark matter makes the difference

Via NASA

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