Riskiest Asteroid Known to Humankind in the Last Year Will Not Strike Earth for at Least 100 Years
By EUROPEAN SPACE AGENCY (ESA)
With Asteroid Day Live 2022 on June 30, we can safely
say that the riskiest asteroid known to humankind in the last year will not
impact the Earth – at least not for the next century.
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| Asteroid 2021 QM1, once thought to have a chance of impacting Earth in 2052, was spotted passing through a region of the sky with the Milky Way just behind it. The small, faint, receding asteroid had to be found against a backdrop of thousands of stars, with red crosses indicating the path of the object. Credit: ESO/O. Hainaut |
Impact 2052
2021 QM1 was first discovered on August 28, 2021, by the
Mount Lemmon Observatory, located north of Tucson, Arizona. At the beginning,
nothing stood out as unusual about the discovery – about a dozen new near-Earth
asteroids are identified every dark night. Routine follow-up observations were
subsequently acquired from telescopes around the globe, but these began to tell
a more worrying story.
“These early observations gave us more information about the
asteroid’s path, which we then projected into the future,” said Richard Moissl,
ESA’s Head of Planetary Defense.
“We could see its future paths around the Sun, and in 2052
it could come dangerously close to Earth. The more the asteroid was observed,
the greater that risk became.”
It’s important to note that orbit calculations based on only
a few nights of observations are subject to some uncertainty, which is why
asteroids often get added to ESA’s risk list soon after they are discovered and
are then subsequently removed once more data is gathered, uncertainties shrink,
and the asteroid is proven safe. On this occasion, that was not possible.
Unfortunate cosmic alignment
Just as the risk appeared to be increasing, an (im)perfect
cosmic alignment occurred: the asteroid’s path brought it closer to the Sun as
seen from Earth, and for months it became impossible to see due to our host
star’s brilliant glare.
“We just had to wait,” explained Marco Micheli, Astronomer at ESA’s Near-Earth Object Coordination Center (NEOCC).
“But to cap things off, we knew that 2021 QM1 was also
moving away from Earth in its current orbit – meaning by the time it passed out
of the Sun’s glare, it could be too faint to detect.”
While they waited, they prepared.
Priority access to one of Earth’s
most powerful telescopes
The European Southern Observatory’s Very Large Telescope (VLT) was primed and ready. As soon as the 50-meter asteroid edged out from the sunlight – and if and when weather conditions allowed – ESO’s VLT would focus its 8 m mirror on the disappearing rock.
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| The position of each asteroid at 12:00 CEST on June 13, 2022, is plotted. Each asteroid is a segment representing its motion over 10 days. Inner bodies move faster around the Sun (yellow circle at the center). Blue represents the inner part of the Solar System, where the Near Earth Asteroids, Mars crossers, and terrestrial planets are. The Main Belt, between Mars and Jupiter, is green. The two orange ‘clouds’ correspond to the Trojan asteroids of Jupiter. Credit: © ESA/Gaia/DPAC; CC BY-SA 3.0 IGO, Acknowledgments: P. Tanga (Observatoire de la Côte d’Azur) |
“We had a brief window in which to spot our risky asteroid,”
explained Olivier Hainaut, Astronomer at ESO.
“To make matters worse, it was passing through a region of
the sky with the Milky Way just behind. Our small,
faint, receding asteroid would have to be found against a backdrop of thousands
of stars. These would turn out to be some of the trickiest asteroid observations
we have ever made”.
Faintest asteroid ever observed
Over the night of May 24, ESO’s VLT took a series of new
images. The data arrived and Olivier and Marco began to process them, stacking
subsequent observations on top of each other and removing the background stars:
it took some time.
The result? A positive detection of the faintest asteroid ever observed. With a magnitude of 27 on the scale used by astronomers to describe the brightness of objects in the sky, 2021 QM1 was 250 million times fainter than the faintest stars visible to the naked eye from a dark spot. (In this astronomical scale of visible magnitudes, the brighter an object appears the lower the value of its magnitude, while the brightest objects reach negative values, e.g. the Sun is magnitude -27).
Olivier was certain this small blur was in fact an asteroid,
and Marco was certain that given its location, it was our asteroid.
Safe at last?
With these new observations, our risky asteroid’s path was refined, ruling out an impact in 2052, and 2021 QM1 was removed from ESA’s risk list. Another 1,377 remain.
More than one million asteroids have been discovered in the Solar System, almost 30 000 of which pass near Earth, with many more expected to be out there. ESA’s Planetary Defence Office, NEOCC and astronomers around the globe are looking up to keep us safe, working together to ensure we know well in advance if an asteroid is discovered on a collision course.
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| Fallen trees at Tunguska, Imperial Russia, seen in 1929, 15 km from epicenter of the aerial blast site, caused by the explosion of a meteor in 1908. Credit: Photo N. A. Setrukov, 1928 |
Asteroid Day is the United Nations-sanctioned day of public awareness of the risks of asteroid impacts, held annually on June 30. This year sees its return to Luxembourg for an in-person event following two years of living entirely in the virtual realm. Asteroid experts from ESA, from across Europe and worldwide will converge on the city to take part in a packed four-hour live program of panels and one-on-one interviews.
What was it like to track this asteroid? Get the full story in ESA’s fascinating behind-the-scenes look at how European experts handle asteroid risks in the official countdown to Asteroid Day live on June 30, airing at 10:25 CEST on AsteroidDay.org and via ESA WebTV.
