Here is a link to a two-minute podcast by Dr Al Grauer from the Spreaker ‘Travelers in the Night‘ channel about how some asteroids can have a comet-like tail, and are also responsible for some meteor showers (the asteroid 3200 Phaethon, which passes very close to the sun, is associated with the Geminid meteor shower; this December 2017 Phaethon will pass ‘just’ six million miles from the Earth).
In order to better understand the links between comets and ‘active asteroids’ we will need more information about their composition from future missions.
Unfortunately, a nearly-full moon will hamper observations of the Perseid meteor shower this year (close to 12th August) and the weather in north-west Europe is also not ideal. If you don’t see any Perseids this year, then you may wish to take a look at the International Meteor Organization’s calendar which lists all expected meteor shows for 2017 with comments as to the likely viewing conditions.
Meteor shows are in general due to dust particles shed by comets as they approached the sun on previous orbits. The Perseids are associated with comet Swift-Tuttle, a 27 km large body which last passed near Earth in 1992 and is not expected again until 2126. We see ‘shooting stars’ because the dust particles are traveling at about 60 km/s relative to the Earth, and this is fast enough that air friction heats the tiny dust particles to white heat in the upper atmosphere, about 90 km above us.
Space.com has posted a video showing early Perseids from this years shower, photographed by a NASA all-sky camera.
This video released by ESA shows scans made by the MIDAS instrument (an atomic force microscope) on the Rosetta spacecraft of dust grains lost from the comet 67P/Churyumov-Gerasimenko. An atomic force microscope uses a very fine needle to scan the three-dimensional shape of tiny particles with nanometre resolution, and MIDAS is the first ever such instrument launched into space.. The full description of the results can be seen in this technical publication from September 2016, and a less-technical summary here. The dust particles were collected by the Rosetta spacecraft over the winter of 2014/2015. A key result of the scans is that the dust ‘particles’ are themselves aggregates of smaller particles , and that both conpact and ‘fluffy’ grains exist. Knowing this structure may help us to understand why the dust on the surface of the comet is so loosly bound. The properties of the particles are generally similar to those of interplanetary dust particles (IDPs) that have been collected and studied on Earth.