Page 105 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

WHAT TO SEE

COLLECTING METEORITES

If you think about it, meteorites are the only
substantial things not originating from Earth that
you can collect. For as little as £5 a gram you
can get your hands on something that may
have originated far out in space in the
asteroid belt. Of course, for this amount
of money, your meteorites will be small,
and getting hold of a fragment of a
meteorite from Mars or the Moon will
be much more expensive – we’re talking
hundreds of pounds a gram. There are
plenty of sites on the internet where you
can buy meteorites: try starting a search at
www.spacerocksuk.com or www.aerolite.org.

Discovered in Namibia in 1838, a fragment
of the Gibeon meteorite costs £2 a gram

iron. From this, you would think that most of the ROCKS THAT FELL FROM SPACE
20,000 or so meteorites found so far on Earth are
stony. In fact, because stony meteorites crumble THE CARANCAS
away more easily in the atmosphere and look METEORITE
remarkably like ordinary stones, the majority of Peru, 15 September 2007
After streaking through the sky
collected meteorites are stony-iron and iron types;
just before midday, the fl aming
their markings and colour make them stand out
rock hit Earth with a massive
from their surroundings. explosion that broke windows
There are places in the world where any over a kilometre away. The
meteorites, regardless of type, will instantly be resulting crater was about 13m
identifi ed – areas such as the Sahara and Atacama across and 4.5m deep. Locals
who fl ocked to the impact site
deserts and the Antarctic snowfi elds. Several rocks
saw boiling water in the crater
from Mars and the Moon have been found in
and gases billowing out. Later,
Antarctica, which goes to show that meteorite- many of them fell sick. Studies
delivering collisions can happen anywhere in the revealed it was due to inhaling
Solar System and not just in the asteroid belt. the gases from the crater. It
turned out not to be a space
DEEP IMPACT virus, but a sulphur compound
in the rock that was released The 13m x 4.5m impact crater near the
Of course, Earth has encountered things
by the impact. village of Carancas in Peru
much larger than small rocks over its lifetime
– meteorites that are never found, but which have THE BUZZARD
certainly left their mark. Big rocks, measuring tens COULEE METEORITE
of metres across and weighing more than 1,000 Canada, 20 November 2008
tonnes, aren’t slowed down or burnt up in the Thousands saw this rock,
atmosphere, unlike their much smaller cousins. As estimated to weigh 10 tonnes,
as it fl amed through the sky. It
a result, these falling rocks end up smashing into
was certainly disintegrating as,
Earth’s surface with colossal force; the average to date, no impact crater has SINCLAIR STAMMERS/SCIENCE PHOTO LIBRARY, PAPHOTOS, GARY SEMMENS/UNIVERSITY OF CALGARY, MARK FORD
speed of a body entering our atmosphere is about been found, although many
20km/s (45,000mph). meteorites from the broken-up
The Chicxulub Crater in Mexico is the site of parent were spread over a
a 180km (112 mile) wide crater created when an large area. Space-rock hunters
converged on the expected
object about 10km (6 miles) in diameter hit Earth
area and it wasn’t long before
roughly 65 million years ago, maybe contributing
meteorites were located. Large
to the demise of the dinosaurs. An easier to view, chunks have already been
smaller example is the famous Barringer Crater found, one weighing 13kg.
near Flagstaff in Arizona, which is over 1km across Current estimates are that there
and 170m deep. It was made about 50,000 years are possibly tens of thousands
of meteorites from this event This 13kg rock is the largest piece of the
ago by an object 50m in diameter. When will the
waiting to be discovered. Buzzard Coulee meteorite found so far
next big one hit? Only time will tell.
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