[meteorite-list] Gravity Wave Mission to Help Study Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 10 Apr 2009 14:42:54 -0700 (PDT)
Message-ID: <200904102142.OAA06379_at_zagami.jpl.nasa.gov>

http://www.astronomynow.com/090407Gravitywavemissiontohelpstudyasteroids.html

Gravity wave mission to help study asteroids
BY DR EMILY BALDWIN
ASTRONOMY NOW
07 April, 2009

LISA, NASA and ESA's Laser interferometer Space Antenna, which will
attempt to detect gravitational waves, will also turn its "noise" into
useful information about near-Earth asteroids.

Gravity waves are associated with the warping of the space-time
continuum, believed to be caused by supernovae events or colliding black
holes sending ripples through the Universe. These ripples are what LISA
is hoping to detect. The mission will comprise three satellites
connected by laser beams, and if a gravitational wave passes them by,
their separation should change by a distance less than the width of an
atom.

Planetary scientists also realised that they too could exploit LISA,
since asteroids would also make the spacecraft wobble, leaving a
distinct signature in the data being collected. Pasquale Tricarico of
the Planetary Science Institute in Tucson, Arizona, developed this idea
to predict the number of asteroid encounters LISA can expect and how
those encounters can be used to determine the mass of passing asteroids.

The three LISA spacecraft will be placed in orbits that form a
triangular formation separated by 5 million km. Ripples in the fabric of
space and time will cause LISA to wobble. Passing asteroids will also
cause the spacecraft to wobble, providing useful insight into the
properties of NEAs. Image: NASA.

Mass may seem like an obvious vital statistic to know about a planetary
body, but Tricarico reveals that only the mass of asteroids that have
been visited by spacecraft or the mass of a few binary asteroids
observed from Earth are known. "We always wonder about the porosity, the
density, and this will give us measurements from additional asteroids,"
he says. Because LISA will look at known Near-Earth Asteroids (NEAs),
data on their trajectories will already be well-defined. "So from the
signal, we can indirectly measure the asteroid's mass because that's the
only uncertainty in the equation," he adds. Tricarico also points out
that if a known asteroid passes one of the satellites and doesn't leave
a signature then an upper limit can be placed on the mass of that asteroid.

The mission could also provide information on the distribution of sizes
of the NEA population. "We don't have good constraints on the size
distribution for small asteroids because they have to come very close to
Earth for us to observe them using ground-based telescopes," says
Tricarico, who predicts that LISA will "feel" one or two known
near-Earth asteroids a year, and a total of around ten during the
expected mission lifetime. But if LISA starts detecting five asteroids a
year instead of two or three, this could modify theories concerning the
distribution of sizes in the NEA population.

There will be a while to wait before any results are seen, however, for
LISA will be launched no earlier than 2018. Tricarico's paper describing
the way in which LISA can be exploited for studying asteroids will be
published in the Classical and Quantum Gravity journal. His research was
supported by NASA's Applied Information Research Program.
Received on Fri 10 Apr 2009 05:42:54 PM PDT