Space agency ups risk of asteroid-Earth collision


Assessment pushes new rock up the danger list, but possibility remains very remote. Andrew Masterson reports.


A close-up of Bennu's North Pole region, captured by Osiris Rex in December, 2019.

A close-up of Bennu's North Pole region, captured by Osiris Rex in December, 2018.

NASA/Goddard/University of Arizona

The European Space Agency’s Near Earth Object Coordination Centre – the world’s primary watchdog for lumps of rock orbiting close to the planet – has upped the risk level for one of the 19,563 asteroids and 107 comets listed as passing through the Earth’s neighbourhood.

According to the agency, recent observations of an asteroid discovered last year and dubbed, thus, XB 2018, have prompted a recalculation of its likelihood of impacting the planet.

It is now considered the fifth most dangerous Near Earth Object (NEO) in the sky – but still represents very little cause for concern.

XB 2018 is now estimated to have “a probability of about 1 in 7000 to collide with Earth in year 2092”, the ESA reports in its latest bulletin.

Its risk rating may change again – up or down.

The object’s current orbital position makes it challenging to observe, but astronomers are confident it will become visible again later in the year.

No such delays are likely for one of the most recently discovered NEOs, named 2019 AQ3.

First detected in January by astronomers at the Zwicky Transient Facility at Mount Palomar in California, US, the kilometre-sized bolide has been confirmed as having the shortest orbital period of all known asteroids.

It completes its journey, which loops around the sun, approaching Mercury’s orbital path at one end and just passing that of Venus in the other, in just 165 days.

2019 AQ3 is not considered ever likely to smack into Earth, but the ESA’s official Risk List contains 816 objects that have a non-zero probability of doing so at some point in the future. They range from rocks with a diameter of just nine metres, to comparative monsters two kilometres in girth.

One of the latter is 101955 Bennu, an asteroid in the Apollo group first identified in 1999.

Bennu is currently the subject of intense scrutiny by NASA’s Osiris-Rex spacecraft, which is currently in a tight orbit around the object ahead of briefly touching down, collecting some surface material and returning it to Earth.

The asteroid has the second highest danger rating on the Palermo Technical Impact Hazard Scale – a risk assessment tool used by astronomers to calculate the hazards posed by NEOS. Bennu is considered to have a one-in-2700 chance of hitting Earth between 2175 and 2199.

Overall, the number of NEOs – the vast majority of them representing no danger – continues to grow. The ESA added 271 new candidates to its list in the first month of 2019.

  1. http://neo.ssa.esa.int/risk-page
  2. https://www.asteroidmission.org/orbital-a-phase/
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