Asteroids approach our planet almost daily. Collision is unlikely

New York City flattened in a fictional asteroid impact scenario in 2019. Minor Planet Center publishes all close approaches.

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This view of asteroid Bennu ejecting particles from its surface on Jan. 6, 2019, was created by combining two images taken by the NavCam 1 imager aboard NASA's OSIRIS-REx spacecraft. (Source: NASA/Goddard/University of Arizona/Lockheed Martin)

A glossary of words is also published online.

After months of observation, astronomers have confirmed that an asteroid will hit the Earth in late April 2027. The object with 185 metres in diameter, detected in 2019, goes under the name ‘2019 PDC’. It is going to impact along a narrow band stretching from Hawaii to Africa.

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Provided your blood pressure has just ramped up, it is now fair to say no Armageddon will occur, nor Bruce Willis be called in to save humanity. The ‘2019 PDC’ was part of a fictional scenario during the 2019 IAA Planetary Defense Conference (PDC), also attended by Slovak astronomer Peter Vereš.

Even though the probability of an asteroid colliding with Earth is 100 percent, Vereš noted “the probability that it will happen today is extremely small”.

The Slovak astronomer, who works for the Minor Planet Center (MPC) at the Harvard-Smithsonian Center for Astrophysics that identifies, computes the orbits of, and catalogues asteroids and comets, has himself co-discovered thousands of asteroids. Experts have discovered 958,282 asteroids, known also as minor planets, to date.

“I remember the object discovered in 1999, which later received my name [(75009) Petervereš = 1999 UC],” he said.

Some asteroids are named after Slovak towns, including Prešov and Lučenec, or have other ties to Slovakia. One of those is called (1807) Slovakia, discovered at the Skalnaté pleso observatory in the early seventies.

Potentially hazardous asteroids

Most of the irregular-shaped asteroids of different sizes and composition, created 4.6 billion years ago alongside our solar system, exist in the main asteroid belt between Mars and Jupiter, orbiting the Sun. Their total mass and numbers are only estimated since telescopes can hardly discover asteroids smaller than 1km in the main belt and beyond.

“There are about a million objects larger than 1km in the main belt, which we have mapped, but just under a thousand asteroids of this size are close to Earth,” Vereš said.

If asteroids close to Earth, called Near-Earth Objects (NEOs), and of this size impacted our planet, it would cause a cataclysm at a continent or even global level. A close approach by large asteroids is, however, very rare. Lately, a large, 2-kilometre-wide asteroid 1998 OR2 flew past the Earth on April 28 of this year, the National Aeronautics and Space Administration (NASA) informed.

Discovery is the best defence

Nonetheless, NEOs larger than 140m may expose a large continental area to danger as well; a small asteroid of about 50 metres in diameter caused the 1908 Tunguska event uprooting and damaging millions of trees in Russia. Scientists, therefore, try to identify all asteroids of 140m and larger, also considering moving the lower limit to 100m.

“The US Congress set a goal of finding 90 percent of these objects by 2018,” Vereš noted. It is estimated there are 30,000 asteroids, ranging in size from 140m to 1km, close to Earth - only 30 percent have been discovered.

Being able to discover asteroids today, the Slovak astronomer continued: “We are trying to complete their population above a given size because it is our best and cheapest defence against them”.

Even if NEOs do not ‘live’ long – a million or a few million years – for their orbits to destabilise after they get close to the Sun or the planets, they are replenished with new ones from the main belt. When a very small NEO hits Earth’s atmosphere, people can observe it in the sky as a streak of bright light, called a meteor. In 2010, pieces of a small meteoroid originally of estimated size of one metre and a mass of 3.5t, landed near Košice.

Telescopes ‘harvesting’ the sky

Three years later, a 20-metre and 12 thousand-ton asteroid entered the Earth’s atmosphere. As it came from the direction of the Sun, astronomers could not detect it with ground-based telescopes. The meteor then exploded in the air over Chelyabinsk Oblast in Russia, generating a large shock wave and harming 1,500 people.

There are several NASA-funded survey telescopes, such as the ATLAS and Pan-STARRS systems in Hawaii, Zwicky Transient Facility in California, and the Catalina Sky Survey (CSS) in Arizona, and NEOWISE in space that hunt and track potentially dangerous NEOs.
“My task was to compute whether the Pan-STARRS can detect an asteroid that can hit the Earth,” Vereš recalled his first experience with this telescope from 2008 when visiting the Hawaii’s Institute for Astronomy as a researcher for several months.

In 2011, he returned to work before moving over to California four years later where he took up a job at the Jet Propulsion Laboratory, which carries out robotic space missions to study objects in the solar system. Vereš was to find out if the Chile-based Large Synoptic Survey Telescope [now the Vera C. Rubin Observatory], expected to be completed in 2022, would discover as many NEOs as claimed in 2015 when its construction began.

“In 10 years, it will not catalogue 90 percent of NEOs bigger than 140m as originally expected,” Vereš claimed, who is now working on the development of new software for Harvard University’s MPC.

The simulated asteroid hits NYC

Going back to last year’s PDC conference and its simulation, the question arises if eight years is enough to prevent an asteroid impact.

“It depends on the given object. If it is observable for a year or two, it could be enough,” Vereš said. “Nonetheless, the objects are unobservable most of the time.”

Scientists at the conference would have an opportunity to study the ‘2019 PDC’ simulated object for several months in 2020-22, then for some time in 2024 and a year after.

“When we detect an asteroid for the first time, we do not know its orbit. We need days, weeks, months of observations to say whether it will, in fact, hit the Earth,” the Slovak astronomer said.

In the simulated scenario, astronomers decided to send a probe to the ‘2019 PDC’ to analyse it. At the same time, they decided to send other spacecrafts in 2023 to hard-impact them into the asteroid and thus change its momentum, instead of choosing a nuclear explosion hundreds of metres away from it.

Getting a probe to any asteroid always takes months or years and the timing is also important as asteroids orbit.

“A probe flies relatively fast and if it hits an asteroid head-on, the probe will steal a tiny momentum of the asteroid,” the astronomer said.

The asteroid’s momentum change may be small, but it is enough, Vereš continued, to change its orbit over the years and avoid a collision. The whole process takes years, not days, and is not so easy as deploying a bomb on the asteroid to avoid the impact as seen in the film Armageddon.

The simulation further unveiled that the probe, which had analysed the ‘2019 PDC’, was destroyed by debris after one of the three spacecrafts caused disintegration of the asteroid in the year 2024. The asteroid thus became unobservable, but the data suggested a 65-metre fragment was still to explode in the atmosphere somewhere between Chicago and the Atlantic Ocean. The only solution left of a nuclear weapon would not be ready in time.

“A few months before impact, it was clear that the asteroid would hit somewhere over New York City shortly after midnight on April 29, 2027,” Vereš said.

The fictional cataclysm concluded the fragment would hit Central Park and the population would have to be resettled months before the collision, with economic damage being massive.

“The result of the hypothetical scenario and today’s technological possibilities showed humanity is not prepared for similar threats that we will one day have to face,” Vereš claimed. He added most participants in the conference were American, which corresponds with the fact that the USA invests the most in planetary defence.

Two different astronomy worlds

Even when asteroids might be seen as a threat, people could mine rare metals on them in future, Vereš noted, since asteroids contain higher abundances of them than Earth’s crust.

“The Subject of astronomy is as wide as the whole universe,” the Slovak astronomer said.

Vereš started off his career at AGO Modra observatory, belonging to Comenius University near Bratislava, where he “was wide awake all night and slept during the day”.

“At present, Modra is not competitive in asteroid discovery anymore and they focus on other science topics,” he also noted.

A total of 142 numbered asteroids were discovered at Modra in the past, the last of which was detected in 2009. The observatory currently measures asteroid light curves and monitors meteors in cooperation with other observatories around the world today. It also monitors space debris – defunct man-made objects orbiting around Earth – such as dysfunctional satellites and launch vehicles.

Whereas at the Modra observatory Vereš had to be physically present to open its dome and then observe the sky, he is now aware of what astronomy’s future feels like after years spent in the USA.

“I did not have to travel to an observatory at the top of a Hawaiian volcano,” he recalled. “I scheduled my targets and the observatory staff on a neighbouring island then provided the data.”

He would study the data at the Institute for Astronomy in Honolulu and worked on software development. Vereš, who has loved all sorts of discoveries since a young age, perhaps achieved all the goals in his career but the one thing he misses is university teaching, which he used to do in Slovakia.

The young astronomer would like to return home provided science gets a boost one day, adding that: “Astronomy and space are a natural magnet to attract people to science, technology and critical thinking”.

The Spectator College is a programme designed to support the study and teaching of English in Slovakia, as well as to inspire interest in important public issues among young people.

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