Rotational Mass Shedding from Asteroid (6478) Gault. (arXiv:2103.05601v2 [astro-ph.EP] UPDATED)

Rotational Mass Shedding from Asteroid (6478) Gault. (arXiv:2103.05601v2 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Luu_J/0/1/0/all/0/1">J. X. Luu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jewitt_D/0/1/0/all/0/1">D. C. Jewitt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mutchler_M/0/1/0/all/0/1">M. Mutchler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Agarwal_J/0/1/0/all/0/1">J. Agarwal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kim_Y/0/1/0/all/0/1">Y. Kim</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_J/0/1/0/all/0/1">J. Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weaver_H/0/1/0/all/0/1">H. Weaver</a>

The $sim$4 km diameter main belt asteroid 6478 Gault has ejected dust
intermittently since at least 2013. The character of the emission, including
its episodic nature and the low speed of the ejected particles ($V sim $ 0.15
m s$^{-1}$), is most consistent with mass loss from a body rotating near
rotational breakup. Owing to dust contamination of the nucleus signal, this
conclusion has not yet been confirmed. To test this idea, we have obtained new
images of Gault in August 2020, in the absence of dust. Our photometry shows a
lightcurve having a very small amplitude (maximum $sim 0.05$ mag) and a
periodicity of $ 2.55 pm 0.10$ hours. The new observations are consistent with
a model in which Gault is rotating near breakup, with centrifugal forces
responsible for its episodic mass loss. Approximated as a strengthless (fluid)
spherical body, the implied density is $rho$ = 1700 kg m$^{-3}$. We use the
Froude number $Fr$, defined here as the ratio between centrifugal force and
gravitational force, as a way to investigate mass loss regimes in fast spinning
asteroids and find that mass shedding starts at $Fr sim 0.5$.

The $sim$4 km diameter main belt asteroid 6478 Gault has ejected dust
intermittently since at least 2013. The character of the emission, including
its episodic nature and the low speed of the ejected particles ($V sim $ 0.15
m s$^{-1}$), is most consistent with mass loss from a body rotating near
rotational breakup. Owing to dust contamination of the nucleus signal, this
conclusion has not yet been confirmed. To test this idea, we have obtained new
images of Gault in August 2020, in the absence of dust. Our photometry shows a
lightcurve having a very small amplitude (maximum $sim 0.05$ mag) and a
periodicity of $ 2.55 pm 0.10$ hours. The new observations are consistent with
a model in which Gault is rotating near breakup, with centrifugal forces
responsible for its episodic mass loss. Approximated as a strengthless (fluid)
spherical body, the implied density is $rho$ = 1700 kg m$^{-3}$. We use the
Froude number $Fr$, defined here as the ratio between centrifugal force and
gravitational force, as a way to investigate mass loss regimes in fast spinning
asteroids and find that mass shedding starts at $Fr sim 0.5$.

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