The blast from a supernova should be enough to clear almost all the dust from the solar system, and this may have last happened 3 million years ago. But like the dust on furniture, these fine particles will gradually be replenished.
Dust we see drifting through space consists of small grains, resulting from events such as asteroid collisions. The grains are typically less than a millimetre in size, going down to just nanometres across. About 70 per cent of the solar system鈥檚 dust is concentrated in the Kuiper belt, a region of icy asteroids and comets beyond Neptune, where there are an estimated tiny grains.
at Boston University and his colleagues have modelled what would happen to the dust in the Kuiper belt if a star exploded within 160 light years of Earth, or if our solar system passed through a dense star-forming interstellar cloud of material.
Advertisement
One of these events is thought to have occurred about 3 million years ago based on increases in levels of a radioactive isotope of iron 鈥� iron-60 鈥� seen in ice on Earth dating to that period. The isotopes would have been delivered when the blast also removed the sun鈥檚 heliosphere, which protects planets in our solar system from the galaxy鈥檚 radiation.
Miller and his colleagues have found that either event would sweep all dust smaller than a millimetre from the Kuiper belt. 鈥淚t鈥檚 like turning on a giant fan,鈥� says Miller. 鈥淭here鈥檚 a lot of hydrogen atoms hitting these dust grains and changing their orbits鈥�, with the dust either being pushed into the sun or ejected from the solar system entirely.
at Cardiff University, UK, says the wind produced by a supernova can travel at 鈥渁 few thousand to 10,000 kilometres per second鈥�, which could have 鈥渆nough kinetic energy to blow off material in the solar system鈥�.
It would have taken tens of thousands of years for the solar system to pass through the supernova鈥檚 blast wave, but up to a million years to traverse an interstellar cloud.
The former鈥檚 low density, 鈥渋n the ballpark of 0.01 atoms per cubic centimetre鈥�, says Miller, would mean it would have been halted at about Saturn鈥檚 orbit by the solar wind of charged particles heading outwards from the sun. An interstellar cloud 鈥� being much denser, at 1000 atoms per cubic centimetre, but much slower, at about 20 kilometres per second 鈥� could have reached the orbit of Mercury, reducing the amount of interplanetary dust near Earth, although 鈥渨e don鈥檛 have a lot of dust near Earth鈥� compared with in the Kuiper belt, says Miller.
Some of the dust in the Kuiper belt could also have been moved into reservoirs in a different orbit out of the flat plane of the solar system. 鈥淭hat would mean it鈥檚 not interacting with the planets as much,鈥� says Miller. This could explain why NASA鈥檚 New Horizons spacecraft, currently travelling through the Kuiper belt region, has recently detected an increase in dust, as it is possibly moving through such an area.
The researchers calculate that it should take about 11 million years for dust in our solar system to return to an equilibrium state, where it is being produced as fast as it is falling into the sun or being ejected by more usual processes. If a dust-sweeping event happened 3 million years ago, that 鈥渕eans we鈥檙e still in the building-up phase鈥�, says Miller.
arXiv
