Asteroids and comets are both remnants of the early formation of the solar system 4.5 billion years ago. As of August 2011, there were less than 4,500 known comets in the solar system, compared to over 550,000 known asteroids (although there are thought to be many millions more).

Asteroids are composed of rocky material and metals, while comets are made of ice. As a result, asteroids formed nearer the Sun than comets, because ice could not remain solid at a close distance. Comets that formed further out and later approached the Sun lose material with each orbit because the ice melts, forming a tail behind the body. Asteroids, on the other hand, do not lose material, and thus do not have a tail. Comets are often found in large elongated orbits extending outwards up to 50,000 times the distance from the Earth to the Sun. By comparison, Neptune – the furthest planet of the solar system – is just 30 times further from the Sun than the Earth.

Concurrently, asteroids are usually found following a circular orbit around the Sun and they tend to group together in belts, such as the asteroid belt found between Jupiter and Mars, which was formed when the gravitational pull of Jupiter prevented the asteroids from forming into another planet.

Asked by: Jenna Kelly

Ice is transparent but not totally clear if it contains air bubbles or imperfections. Snowflakes are made of tiny ice crystals that join together in the air. They are not made of perfect blocks of ice, but have much more interesting shapes. Light ends up scattering in many directions as it meets the borders of those crystals and the air locked inside, making it look white. Even when they land there is a lot of air trapped, and that’s why fresh snow feels very soft when you walk over it.

José Monteiro

Capturing an iceberg collapsing or calving is a rare sight, and this couple filming off Labrador, Canada, picked up their camcorder just in time to catch the dramatic event. The pair and their dog are clearly excited about what they’ve just witnessed, but are soon chased away by a rush of smashed up ice that starts floating towards them. For an in-depth look at how icebergs are formed check out issue five of How It Works, which goes on sale on 25 February. By the way, when you watch this video just try not to imagine Kermit the Frog is behind the camera. You’ll see what we mean.

Image courtesy of NASA

The Moderate-Resolution Imaging Spectroradiometer (or MODIS) on board NASA’s Terra satellite captured this incredibly chilling image of Great Britain on 7 January as most areas experienced freezing temperatures of -10C on the coldest night of the winter so far. Isolated areas were even subjected to lows of -22C in the Scottish Highlands.

Snowfall followed by freezing temperatures left areas dangerously icy, resulting in widespread chaos on the roads. Schools across the nation were closed and many businesses sent staff home. The emergency services, including roadside assistance, were inundated with incidents.

One possible reason for the severely cold conditions across the Northern Hemisphere this last month is an extreme negative phase of Arctic Oscillation (AO). AO refers to a state of seesawing atmospheric pressure over the Arctic. The negative phase of AO causes high pressure over the polar region and low pressure at mid-latitudes.

MODIS images the entire Earth every one to two days. The grey areas against the white land surface on the map are actually the cities of Manchester, Birmingham and London.