Get Technology: Be in the know. Upgrade your future by Gerald Lynch

Author:Gerald Lynch
Language: eng
Format: epub
Publisher: MBI
Published: 2018-05-27T04:00:00+00:00

ASTEROID DEFENCES

Ever wished upon a shooting star? Then you’ve probably spotted a small meteoroid enter Earth’s atmosphere before burning up and disintegrating ahead of impact. Breaking Earth’s atmosphere is usually more structurally stressful than small objects from space can withstand. But what about larger, tougher meteorites and asteroids?

It’s now largely agreed that the age of the dinosaurs was brought to an end 66 million years ago as a result of the impact of the Chicxulub asteroid. Releasing 10 billion times the energy of the 1945 Hiroshima nuclear bomb, it left a 110-mile-(180-km)-wide crater, triggering earthquakes, tsunamis and firestorms, throwing as much as 70 billion tonnes of debris into the sky and plunging the world into a two-year impact winter that blocked out the Sun. While the Earth has avoided any such similarly apocalyptic event since, the threat of impact from space objects and comets still stands. As recently as 2013, a meteorite roughly 19m in diameter struck Chelyabinsk in Russia, managing to avoid detection before impacting with the force of 450,000 tons of TNT detonating – and miraculously with no loss of life.

So, what’s being done to protect us from intergalactic Armageddon?

A number of observation systems are in place to offer advanced warning of the potential dangers of near-Earth objects (NEOs), with NASA’s Planetary Defense Co-ordination Office leading efforts to identify hazardous bodies. An array of worldwide ground-based telescopes help spot the NEOs of note, along with the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission – which uses a repurposed spacecraft previously tasked with making infrared scans of space to identify and classify NEOs, building a picture of their diameters and albedos (the amount of light an object reflects), and assessing their trajectories and threat level.

Identifying a NEO and its potential threat to Earth is a multi-stage process, and one that is more accurately carried out over longer stretches of time. Once a telescope finds an anomaly (usually spotted by tracking small objects moving across known, relatively stationary stars), photometric studies look at variations in brightness in the NEO over a period of time, establishing a light curve in relation to the Sun. As NEOs tend to be irregularly shaped, they will reflect light with different intensities as they travel and rotate. Once this light curve pattern starts repeating, the ‘day’ of the object can be identified and the amplitude of its light curve recorded, helping to define the NEO’s size and shape.

To establish an orbit, multiple observations must be made, keeping in mind the gravitational pull of larger objects and planets in the solar system, and the fact that the distance from the Sun can have a bearing on speed too. As a result, it can be weeks before an orbit is confidently plotted.

A so-called ‘close approach’ occurs when a NEO moves within the orbit of Earth’s Moon, and it’s these close calls that highlight the need for planetary defence systems.

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