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The solar system is a dangerous place.

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One hazard is impacts from rocky debris

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traveling tens of thousands of miles an hour.

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Large fragments can tear a spacecraft apart, but even the smallest

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pieces gradually take their toll, eroding spacecraft surfaces

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and components. Dust-sized particles shed 

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from comets and asteroids and smaller than a single grain of sand,

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traverse the solar system at speeds reaching 40,000 miles an hour.

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Our best knowledge of these tiniest meteoroids

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comes from measurements made near Earth.

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Now, a clever new technique using the LISA Pathfinder spacecraft is measuring

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this population of particles at nearly a million miles away.

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Launched in 2015, LISA Pathfinder is a 

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technology demonstrator for the space-based detection of gravitational waves

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led by the European Space Agency and with participation

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by NASA. The full observatory would work by tracking

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reference objects called proof masses that move under the 

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influence of gravity, which means the spacecraft must reduce all

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other forces to an astonishing degree. Tests show

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LISA Pathfinder is the most precise tool for measuring accelerations

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ever flown, reducing non-gravitational forces to levels

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required to detect passing gravitational waves.

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Because LISA Pathfinder is extremely sensitive to its environment,

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it's also sensitive to those tiny nudges from micrometeoroids.

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These impacts would be reflected in motions of the proof masses,

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how the spacecraft thrusters fired to counteract the impact, and other data.

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Using software originally written to sift out the the faint signatures of

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gravitational waves in ground-based detectors, the science team found

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several impacts. When it is struck, the impact

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both pushes and twists the spacecraft. Onboard sensors

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detect this change and fire the Pathfinder's ultra-precise thrusters to

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compensate. At full power, each of these only generates about as much

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force as the weight of a mosquito. Knowing what it took to restore

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the spacecraft's orientation gives scientists information

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on the original direction of the particle, its momentum, and where it struck the

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spacecraft. LISA Pathfinder is located at Earth-sun L1,

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a gravitational balance point about million miles from Earth's

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sunward side. This is essentially unexplored territory for 

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understanding the solar system's dust distribution. By comparing

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how often Pathfinder is hit, and the particles' origins, 

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scientists can refine their models of solar system composition and formation.

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By improving our understanding of the solar system's

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dust environment, LISA Pathfinder will also help pave the way

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for future giant telescopes whose large optics could be degraded

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by these impacts. It's an intriguing side benefit from testing spacecraft

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technology that will one day be used to observe merging black holes

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billions of light years away.

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[Music]

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[Beeping]

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[Beeping]

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[Beeping]