According to NASA’s ‘Close Approach Data’ for near-Earth objects, or NEOs, an asteroid with an estimated diameter of 13 to 20 meters (43 to 95 feet) is fast approaching Earth at an astounding speed of 20,000 miles per hour.
Researchers tracking the space rock at the Jet Propulsion Laboratory (JPL) in Pasadena, California, expect the NASA-classified “small body” asteroid, nicknamed 2018 XE4, to fly past our planet at a distance of 1.2 million miles at 8:37 p.m. GMT (3:37 pm Eastern Time) on Boxing Day (December 26).
Although it’s going to miss us by a margin that’s 5.34 times the distance between Earth and Moon, it’s still too close for comfort in space terms.
Smaller asteroids that have struck Earth in the past have caused extensive destruction and mayhem; so, one can imagine the kind of damage an asteroid the size of 2018 XE4 traveling at more than 26 times the speed of sound would cause if it were to hit us.
The 2013 meteor that injured at least 1,500 people in Russia is a case in point.
The 66-foot-wide supersonic meteor smashed into the atmosphere above the city of Chelyabinsk in the Ural Mountains, sending shockwaves so powerful that 1,200 people were injured and more than 7,000 buildings in six cities were damaged.
The flash from the streaking meteor was brighter than the Sun and was seen as far away as Kazakhstan, 80 miles south, and Nizhny Tagil, nearly 300 miles to the north.
Nasa says: “As they orbit the Sun, Near-Earth Objects can occasionally approach close to Earth.
“As the primitive, leftover building blocks of the solar system formation process, comets and asteroids offer clues to the chemical mixture from which the planets formed some 4.6 billion years ago.
‘If we wish to know the composition of the primordial mixture from which the planets formed, then we must determine the chemical constituents of the leftover debris from this formation process – the comets and asteroids.”
For any Solar System body to qualify as a near-Earth object, its closest approach to the Sun has to be less than 1.3 astronomical units (AU), the equivalent of nearly 121 million miles.
With some 20,000 near-Earth asteroids and comets orbiting the Sun, NASA and other space agencies have been constantly tracking NEOs since the 1990s in a collective initiative called ‘Spaceguard.’
The biggest threat to Earth, however, is from a 500-meter-wide asteroid called Bennu, which has a 1-in-2,700 chance of smashing into Earth sometime between 2175 and 2196, say scientists.
The potentially hazardous object (PHO), “listed on the Sentry Risk Table with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale,” is currently 54 million miles from Earth.
The Sun-orbiting asteroid has been in NASA’s crosshairs ever since its discovery by the Lincoln Near-Earth Asteroid Research (LINEAR) project in 1999.
So focussed has the space agency been on Bennu that in 2016 it sent its ORISIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) spacecraft to the asteroid on a sample-return mission.
After traveling through space for more than two years, the spacecraft finally reached the proximity of Bennu earlier this month.
Spectroscopic surveys of its surface revealed the presence of hydrated minerals, signifying that the space rock had interacted with liquid water at some point in its past.
Although NORISIS-REx’s onboard spectrometers didn’t detect water per se, they did find hydrogen and oxygen bonds called hydroxyls trapped in clay-bearing material all over Bennu’s rock-strewn topography.
Speaking at a press conference at the American Geophysical Union (AGU) meeting in Washington DC, on Dec 10, Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center, said the discovery was “evidence of liquid water in Bennu’s past.”
“The presence of hydrated minerals across the asteroid confirms that Bennu, a remnant from early in the formation of the solar system, is an excellent specimen for the OSIRIS-REx mission to study the composition of primitive volatiles and organics,” Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center said in an agency press release.
Over the coming months, the NASA spaceship, which is on an asteroid probe and sample-return mission to Bennu, will make increasingly closer passes of the asteroid, entering orbit on New Year’s Eve.
It will then begin mapping the asteroid to identify the best possible sample site before making a slow descent to the surface to collect samples using its robotic arm.
OSIRIS-REx is capable of making as many as three attempts at collecting the samples, after which it will have to begin its return journey, with its precious cargo of Bennu samples safely tucked away inside a Sample-Return Capsule (SRC).
The SRC is expected to re-enter Earth’s atmosphere and land at the US Air Force’s Utah Test and Training Range on Sep 24, 2023.
“When samples of this material are returned by the mission to Earth in 2023, scientists will receive a treasure trove of new information about the history and evolution of our solar system,” Simon said in the press release.
“We targeted Bennu precisely because we thought it had water-bearing minerals and — by analogy with the carbonaceous chondrite meteorites that we’ve been studying — organic material,” Space.com quoted Lauretta as saying.
“That still remains to be seen — we have not detected the organics — but it definitely looks like we’ve gone to the right place,” she added.
If NASA can land a spacecraft on an asteroid 54 million miles away and bring back samples from there, it can pretty much nuke Bennu to smithereens should the need arise.
So, rest easy in the knowledge that the likes of NASA and other space agencies of the world are keeping a watchful eye on the Bennus of space.