Chapter 7
The Loss of Comets
Estimates of the mass loss rates caused by sublimation from comets, combined with
their sizes and densities, suggest that a typical short period comet can maintain
activity for around 1000 revolutions in the inner Solar System before the material is
exhausted. As noted above, the timescale for 67P against complete erosion of the
nucleus in the current orbit is ~6000 years, for example. This timescale can be
increased by airfall deposition of more inert material leading to a slow choking of the
activity reducing the mass loss rate. This concept is often assumed to explain the
existence of inactive or very weakly active objects in comet-like orbits. Asteroid
(3552) Don Quixote (1983 SA), for example, is in an orbit that strongly resembles
that of a short-period comet (Bottke et al. 2002) and has the reddened spectrum of a
D-type asteroid which is also often taken as an indicator of having a comet-like
composition. Mommert et al. (2014) used data from the Spitzer infrared telescope
acquired in 2009 to show that the object was emitting dust at a rate of ~1.9 kg s
À1
(see also Mommert et al. 2020). Emission from gaseous CO 2 was also detected.
Visiting objects like (3552) Don Quixote with a spacecraft could provide additional about this hypothesis and indeed, in the past, Don Quixote has been proposed
as a target for future space missions. High resolution mapping of the surface could
provide an estimate of the length of time that the object has been in this near-inert
state. One approach would be to use crater statistics. Teanby (2015) estimated impact
rates onto the surface of Mars based partially on HiRISE observations of recent
impacts (Daubar et al. 2013). These results are shown in Fig. 7.1 after being adapted
to show the area of the surface influenced by impacts over a 1000 year period as a
function of the impact size for which the crater diameter is assumed to be a proxy.
The turnover at small crater diameters probably arises from the effect of the Martian
atmosphere and extrapolation of the more linear part of the curve at larger crater
diameters to smaller crater diameters is likely to be more realistic. The integral of this
curve gives a value of 6.2% kyear
À1 which suggests that saturation would occur in
around 20,000 years if a Martian impact distribution can be used for this type of
estimate.
© Springer Nature Switzerland AG 2020
N. Thomas, An Introduction to Comets, Astronomy and Astrophysics Library,
https://doi.org/10.1007/978-3-030-50574-5_7
433
The Loss of Comets
Estimates of the mass loss rates caused by sublimation from comets, combined with
their sizes and densities, suggest that a typical short period comet can maintain
activity for around 1000 revolutions in the inner Solar System before the material is
exhausted. As noted above, the timescale for 67P against complete erosion of the
nucleus in the current orbit is ~6000 years, for example. This timescale can be
increased by airfall deposition of more inert material leading to a slow choking of the
activity reducing the mass loss rate. This concept is often assumed to explain the
existence of inactive or very weakly active objects in comet-like orbits. Asteroid
(3552) Don Quixote (1983 SA), for example, is in an orbit that strongly resembles
that of a short-period comet (Bottke et al. 2002) and has the reddened spectrum of a
D-type asteroid which is also often taken as an indicator of having a comet-like
composition. Mommert et al. (2014) used data from the Spitzer infrared telescope
acquired in 2009 to show that the object was emitting dust at a rate of ~1.9 kg s
À1
(see also Mommert et al. 2020). Emission from gaseous CO 2 was also detected.
Visiting objects like (3552) Don Quixote with a spacecraft could provide additional about this hypothesis and indeed, in the past, Don Quixote has been proposed
as a target for future space missions. High resolution mapping of the surface could
provide an estimate of the length of time that the object has been in this near-inert
state. One approach would be to use crater statistics. Teanby (2015) estimated impact
rates onto the surface of Mars based partially on HiRISE observations of recent
impacts (Daubar et al. 2013). These results are shown in Fig. 7.1 after being adapted
to show the area of the surface influenced by impacts over a 1000 year period as a
function of the impact size for which the crater diameter is assumed to be a proxy.
The turnover at small crater diameters probably arises from the effect of the Martian
atmosphere and extrapolation of the more linear part of the curve at larger crater
diameters to smaller crater diameters is likely to be more realistic. The integral of this
curve gives a value of 6.2% kyear
À1 which suggests that saturation would occur in
around 20,000 years if a Martian impact distribution can be used for this type of
estimate.
© Springer Nature Switzerland AG 2020
N. Thomas, An Introduction to Comets, Astronomy and Astrophysics Library,
https://doi.org/10.1007/978-3-030-50574-5_7
433