Dark matter constitutes 84 percent of the matter in the universe and unlike normal matter, dark matter neither emits nor absorbs electromagnetic radiation and its existence can only be observed from its gravitational effects. A class of exotic bodies known as compact ultra dense objects (CUDOs) can serve as a potential candidate for dark matter. CUDOs are incredibly dense gravitationally bound objects with typical densities several orders of magnitude greater than nuclear density. At the upper mass limits, a CUDO with the mass of planet Mars is expected to measure just 20 cm across. However, a typical CUDO is likely to be a lot less massive.
Rocky bodies in the Solar System such as
the Earth, Mercury, Venus, Mars, the Moon and the large asteroid Vesta can be
used to detect the presence of CUDOs since the impact signature of a CUDO with
a rocky body is likely to persist over geological timescales. The very high
surface gravity of a CUDO keeps its stable and intact during an impact event. A
CUDO entering the Solar System is likely to be moving at 30 to 50 km/s. As
such, an impacting CUDO travelling through the Earth’s mantle will be going
supersonic since the speed of sound in the mantle is only around 8 km/s.
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Image: South Pole of Vesta (Credit:
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
During its passage through the Earth,
the strong gravitational pull from the CUDO is expected to entrain a fair
amount of terrestrial material along its trajectory. This is expected to slow
the CUDO as it transfers some of its kinetic energy to the entrained material.
Although the loss of kinetic energy is likely to be small enough such that the
CUDO will pass completely through the Earth, the loss may still be sufficient
to cause the CUDO and its entrained material to be captured into an orbit
around the Sun. The supersonic shock wave generated by the passage of the CUDO
through the Earth should disrupt surface geology over a wide area as the shock
wave reaches and interacts with the Earth’s crust.
Siderophile elements are “iron-loving” transition
metals which dissolve readily in iron and they are very rare in the Earth’s
crust since most of them are concentrated within the Earth’s iron core. The
ability for a CUDO to pull material in the direction of its passage creates a
transport mechanism which allows material to be dragged up from the Earth’s
interior. As a result, deposits of siderophile elements such as gold and
platinum in the Earth’s crust could be created by the dragging up of core
material from the passage of CUDOs through the Earth. Furthermore, the exit of
a CUDO after its passage through the Earth can deliver a large amount of
material into the Earth’s upper atmosphere as the CUDO sheds some of its
entrained material. The effects from such an event can be catastrophic for life
on Earth. Interestingly, a CUDO exiting the Earth from an ocean can entrain a
mantle of water which allows it to disguise itself as a comet.
Isolated instances of volcanism on the
Earth’s crust can be produced from the exit of a CUDO as its trajectory through
the Earth pulls up material and creates a mantle plume beneath the crust. One
possible example is the hot spot responsible for the Hawaiian Islands in the
middle of the Pacific Ocean, far from any plate boundary. Additionally, solid
bodies such as Mercury, Mars, the Moon and Vesta are generally considered to be
volcanically inactive. As a result, geological features indicated of recent volcanic
activities on these bodies could be attributed to the passage of CUDOs through
them.
A CUDO that happens to be captured into
an orbit around the Sun after impacting and exiting a planet can disguise
itself as either a comet or an asteroid, depending on the type of material it
entrains. Such an object can give itself away as it is expected to have a
higher apparent density. In the unlikely but nevertheless interesting
possibility of a CUDO being gravitationally captured by its target rocky planet,
multiple entries and exits can be produced as the CUDO sheds its kinetic energy
through the bulk of the planet. An event like this can create surface geological
features that are indicative of an odd number of nearly coincidental impacts.
References:
1. Johann Rafelski, et al. (2012),
“Solar System Signatures of Impacts by Compact Ultra Dense Objects”,
arXiv:1104.4572v2 [astro-ph.EP]
2. Lance Labun, et al., “Properties of
Gravitationally Bound Dark Compact Ultra Dense Objects”, Physics Letters B 709
(2012) 123–127