Ever since the first asteroid was discovered in 1801, astronomers have looked to find other similar objects in our Solar System. Many of these minor planets can be found in a belt between Mars and Jupiter. However, often many asteroids are lone wanderers, roaming beyond the limits of the Asteroid Belt and they often find themselves drifting into the inner Solar System skimming past the Earth and often a little too close for comfort.

Asteroids lurking around the Earth? An artist impression of an asteroid belt around a nearby star HD69830. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

Asteroids lurking around the Earth? An artist impression of an asteroid belt around a nearby star HD69830. (Image credit: NASA/JPL-Caltech/T. Pyle (SSC)


One asteroid with a suitably menacing name and an equally threatening demeanor is the asteroid 99942, Apophis, discovered in 2004.  Named after the ancient Egyptian god  of darkness and chaos, this asteroid  sought fame as it had promised to live up to its name and plunge the Earth into turmoil as its orbit brought it straight in line with a head-on collision with the Earth in 2036. Before the Aerosmith Armageddon track starts playing in your head, relax the risk of this happening has now been downgraded significantly!

Goldstone radar dish helped earth determine the future of Apophis. (Image credit: NASA)

Goldstone radar dish helped Earth determine the future of Apophis. (Image credit: NASA)


In 2004 when this asteroid was first discovered there was an estimated 2.7% chance that it would collide with the Earth.  Doomsday’s date was originally predicted for Friday 13th April 2029. Apophis was estimated to be 250m wide so the potential destruction caused by an impact would have been catastrophic. However, the original calculations suggested that although the asteroid would come within 19 000 miles of the Earth in 2029,  interference with the Earth’s gravity during that fly-by would in fact alter the orbital path just enough so that a collision was actually more likely seven years later. Depending on precisely how the asteroid moved in 2029 would determine its future, and more to the point the Earth’s future. The new postponed doomsday date was April 13th 2036.

Apophis temperature model from January 2013. Although a spherical model, measurements suggest that the asteroid is more elongated.
(Image credit: ESA/Herschel/MACH-11/T.Müller MPE (Germany)


Observations of Apophis after its discovery were difficult because of its location relative to the Sun. Enough detail wasn’t available to accurately predict how this asteroid was moving.  Not only would the Earth’s gravity have an effect but astronomers also feared the Sun’s efforts too, in the obscure yet threatening phenomenon called the Yarkovsky effect. This when daily heating caused by the Sun on a rotating object, like an asteroid,  causes it to move by a tiny but steady amount over time.  Like a tiny fall of snow triggering an avalanche, the fall of  sunshine on Apophis could push it our way! Optical telescopes were unable to get a good view until 2011 and more accurate radar measurements were not available until this year. Until then, the tentative wait meant that people of Earth were faced with the 1-45,000 chance of extinction or widespread destruction. If Apophis hit the Earth it would have been the same impact as 20 000 Hiroshima bombs! Thankfully the radar data available from the NASA sponsored Goldstone Solar System Radar has ruled out the chance of impact in 2036. The risk now stands at just 1 in 250,000.

On 9January 2013, Apophis passed the Earth by 9 million miles.  Tracking by the Goldstone radar dish allowed trajectory paths to be calculated for Apophis for the next decades. In 2036 Apophis should pass us at 14 million miles above the Earth. Although the risk for 2029 and 2036 have been ruled out, forward mapping of this asteroid’s movements brings this beast back in line with Earth in 2068. Hopefully more detailed observations in the future will also rule out this collision!

3 colour photo taken by Herschel of Apophis in January 2013. Credit: ESA/Herschel/PACS/MACH-11/MPE/B.Altieri (ESAC) and C. Kiss (Konkoly Observatory)

3 colour photo taken by Herschel of Apophis in January 2013.
(Image credit: ESA/Herschel/PACS/MACH-11/MPE/B.Altieri (ESAC) and C. Kiss (Konkoly Observatory)


This recent close fly-by has not only allowed astronomers to produce a more accurate trajectory for this asteroid but we now also know more about the characteristics of this giant piece of debris. ESA’s Herschel space observatory also got the opportunity to observe this asteroid on its fly-by in January for around two hours.  Herschel was until 29 April 2013 the largest space-based infrared telescope and it was typically looking for clues to the evolution of the Universe. Herschel was able to determine a temperature model for Apophis using infrared imaging. Herschel has also provided a more detailed estimate of size. Apophis is now 20% bigger than first thought at around 325m wide.  This is only the second time that Herschel has viewed a near-earth object, but hopefully this evidence produced will only enhance and help in the knowledge of these uninvited visitors.

image of Herschel_telescope

Herschel space observatory, usually more likely to be looking into deep space, has for only the second time turned towards a Near-Earth object. (Image credit: ESA and SPIRE & PACS consortia, Ph. André (CEA Saclay) for Gould’s Belt Key Programme Consortia)

So the risks of Apophis aren’t worth lying awake at night over, but we do know that a massive asteroid has struck the Earth before,  around 65 million years ago one caused a mass extinction. This isn’t an impossibility or something that Hollywood has invented. Hopefully what Apophis has shown us is that we as a united humankind need to be thinking of ways to protect the longevity of our planet, and there are plans and international organisations in place. Whether sending a craft to intentionally crash into the asteroid and knock it out of orbit or to carefully send a spacecraft to orbit the asteroid and gently pull it out of orbit, these are the main plans of attack. Roscosmos the Russian space agency are even suggesting sending a tracking beacon up to Apophis as a way of monitoring and as an instrument of planetary defence.

So Apophis is not quite going to bring the doom and destruction that was initially predicted so don’t lose any sleep over it. However, the risk of an asteroid hitting the Earth still exists and the Earth needs to be prepared.  Apophis may just be the warning light on the dashboard, while we still have the time, skill and knowledge we need to develop and fine-tune these defence methods to give us a better chance of survival than the defenceless dinosaurs.

(Article by Martina Redpath, Education Support Officer)


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