The solar system is a dangerous place.
One hazard is impacts from rocky debris
traveling tens of thousands of miles an hour.
Large fragments can tear a spacecraft apart, but even the smallest
pieces gradually take their toll, eroding spacecraft surfaces
and components. Dust-sized particles shed
from comets and asteroids and smaller than a single grain of sand,
traverse the solar system at speeds reaching 40,000 miles an hour.
Our best knowledge of these tiniest meteoroids
comes from measurements made near Earth.
Now, a clever new technique using the LISA Pathfinder spacecraft is measuring
this population of particles at nearly a million miles away.
Launched in 2015, LISA Pathfinder is a
technology demonstrator for the space-based detection of gravitational waves
led by the European Space Agency and with participation
by NASA. The full observatory would work by tracking
reference objects called proof masses that move under the
influence of gravity, which means the spacecraft must reduce all
other forces to an astonishing degree. Tests show
LISA Pathfinder is the most precise tool for measuring accelerations
ever flown, reducing non-gravitational forces to levels
required to detect passing gravitational waves.
Because LISA Pathfinder is extremely sensitive to its environment,
it's also sensitive to those tiny nudges from micrometeoroids.
These impacts would be reflected in motions of the proof masses,
how the spacecraft thrusters fired to counteract the impact, and other data.
Using software originally written to sift out the the faint signatures of
gravitational waves in ground-based detectors, the science team found
several impacts. When it is struck, the impact
both pushes and twists the spacecraft. Onboard sensors
detect this change and fire the Pathfinder's ultra-precise thrusters to
compensate. At full power, each of these only generates about as much
force as the weight of a mosquito. Knowing what it took to restore
the spacecraft's orientation gives scientists information
on the original direction of the particle, its momentum, and where it struck the
spacecraft. LISA Pathfinder is located at Earth-sun L1,
a gravitational balance point about million miles from Earth's
sunward side. This is essentially unexplored territory for
understanding the solar system's dust distribution. By comparing
how often Pathfinder is hit, and the particles' origins,
scientists can refine their models of solar system composition and formation.
By improving our understanding of the solar system's
dust environment, LISA Pathfinder will also help pave the way
for future giant telescopes whose large optics could be degraded
by these impacts. It's an intriguing side benefit from testing spacecraft
technology that will one day be used to observe merging black holes
billions of light years away.
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