Tuesday, August 7, 2012


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.

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.

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