Hubble Space Telescope Observations of Active Asteroid 324P/La Sagra

Status Report From: e-Print archive
Posted: Tuesday, July 5, 2016

David Jewitt, Jessica Agarwal, Harold Weaver, Max Mutchler, Jing Li, Stephen Larson
(Submitted on 28 Jun 2016)

Hubble Space Telescope observations of active asteroid 324P/La Sagra near perihelion show continued mass loss consistent with the sublimation of near-surface ice. Isophotes of the coma measured from a vantage point below the orbital plane are best matched by steady emission of particles having a nominal size a∼ 100 μm. The inferred rate of mass loss, dMd/dt∼0.2 kg s−1, can be supplied by sublimation of water ice in thermal equilibrium with sunlight from an area as small as 930 m2, corresponding to about 0.2\% of the nucleus surface. Observations taken from a vantage point only 0.6\degr~from the orbital plane of 324P set a limit to the velocity of ejection of dust in the direction perpendicular to the plane, V⊥< 1 m s−1. Short-term photometric variations of the near-nucleus region, if related to rotation of the underlying nucleus, rule out periods ≤ 3.8 hr and suggest that rotation probably does not play a central role in driving the observed mass loss. We estimate that, in the previous orbit, 324P lost about 4×107 kg in dust particles, corresponding to 6×10−5 of the mass of a 550 m spherical nucleus of assumed density ρ = 1000 kg m−3. If continued, mass loss at this rate would limit the lifetime of 324P to ∼1.6×104 orbits (about 105 yr). To survive for the 100 Myr to 400 Myr timescales corresponding, respectively, to dynamical and collisional stability requires a duty cycle 2×10−4≤fd≤8×10−4. Unless its time in orbit is over-estimated by many orders of magnitude, 324P is revealed as a briefly-active member of a vast population of otherwise dormant ice-containing asteroids.

Comments: 31 pages, 6 figures, 4 tables, Accepted by The Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1606.08522 [astro-ph.EP] (or arXiv:1606.08522v1 [astro-ph.EP] for this version)
Submission history
From: Jing Li
[v1] Tue, 28 Jun 2016 00:33:27 GMT (1861kb,D)

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