Planet Care

23: Detecting and combating asteroids


Asteroid collisions can destroy or seriously damage the Planet.


Programs to detect asteroids on hazardous orbits.

These programs were started after there was much public discussion of the fact that the Hollywood film industry had just spent much more money on making two fictional films about asteroids that were heading for Earth than had ever been spent on attempting to detect such asteroids in time to do anything about them.

One key scientist who has made great progress in killer asteroid warning systems is John Tonry. Tonry studied mathematics at Princeton University until 1975 and received his PhD in physics from Harvard University in 1980.

In 1986 he became a professor at MIT, a year later, he moved to the Department of Astronomy at the University of Hawaii. There, between 1993 and 1995, with Kenneth Chambers and Nicholas Kaiser, Tonry discovered two asteroids.

Between 2002 and 2010 Tonry developed the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). This was an AFRL (Air Force Research Laboratory) funded effort to build a telescope and imager to carry out wide-field (3 deg), deep imagery of the whole sky.

What was different about Pan-STARRS was that they were doing this every night and covering the whole sky many times to try to detect any asteroid whose orbit makes it a potential danger to Earth.

The work does not itself reduce the risk of an asteroid strike but might make it possible to take action to divert the asteroid or evacuate the impact area.

Even more efficient is ATLAS (Asteroid Terrestrial-impact Last Alert System), developed at the University of Hawaii with US$ 5 million funding from NASA.

Its first telescope at Haleakala observatory (ATLAS-HKO) became fully operational at the end of 2015, and the second one 100 mi. (160 km) away at Mauna Loa observatory (ATLAS-MLO) in March 2017.

In the photo above, Frank Melsheimer of DFM Engineering stands beside the ATLAS telescope.

Replacement of the initially substandard Schmidt corrector plates of both telescopes in June 2017, brought their image quality closer to its nominal 2 pixels (3.8 in./9.7 cm) width and consequently improved their sensitivity by one magnitude.

NASA then confirmed that it will provide US$3.8 million over the next 4 years to support the construction and operation of two asteroid-hunting observatories south of the Equator. Researchers plan to build one facility in South Africa, but are still deciding on a location for the second outpost.

ATLAS comprises four 200 in. (500 cm) telescopes that can only see things 10x brighter than Pan-STARRS can, so it is only able to work to a third or a half of the distance of Pan-STARRS.

What is different is that ATLAS patrols the entire, visible sky twice a night, whereas Pan-STARRS is much slower. Pan-STARRS is narrow and deep; ATLAS is wide and shallow.

The motivation for ATLAS is to provide warning of an asteroid on its final, impact trajectory: maybe a week’s warning for a 2 Mton explosion and three weeks’ warning for a 100 Mton explosion.

Recently ATLAS found a 10 Mton asteroid ( K17Q60) that missed us by 10 Earth radii, and another (A103wzq) still on the MPC confirmation page whose MOID (minimum orbital intersection distance) could be less than an Earth radius (it might hit us).

The Last Alert part of the system name acknowledges that ATLAS will find smaller asteroids years too late for potential deflection but would provide the days or weeks of warning needed to evacuate and otherwise prepare a target area.

This gives enough time to evacuate the area of people, take measures to protect buildings and other infrastructure, and be alert to a tsunami danger generated by ocean impacts.

Tonry explained that if ATLAS had been up and running, astronomers might very well have seen the Chelyabinsk meteor that hit Russia in 2013 and could have provided one to two days’ warning, so enabling most of the injuries it caused to be avoided, because news broadcasts could have warned people to keep away from windows.

Most of the people injured were looking at the meteor’s dust trail through windows that shattered on the arrival a couple of minutes later of the shock wave caused by passage of the meteor through the air.

In August 2018, ATLAS obtained US$ 3.8 million of additional NASA funding to install two telescopes in the Southern hemisphere, one of which will be hosted by the South African Astronomical Observatory, while the other most likely installed in Chile.

This geographical expansion of ATLAS will provide visibility of the far Southern sky, more continuous coverage, better resilience to bad weather, and additional information on the asteroid orbit from the parallax effect. The full ATLAS concept consists of eight telescopes, spread over the globe for full-sky and 24h/24h coverage.

So far ATLAS has discovered 33 potentially hazardous asteroids and 304 near-Earth asteroids. For his work on asteroid surveillance, in 2016, asteroid 40919 was named after John Tonry and in 2018 he was elected to the National Academy of Sciences.

Another machine involves the seven-year Double Asteroid Redirection Test (DART)’s kinetic impactor. U.S. agencies, principally the Air Force, and the European Space Agency will each design and build three NEO (Near Earth Orbiting) shield kinetic impactor spacecraft, for a total of six. Each will be propelled by Fregat, the upper stage of the Soyuz launcher. The hope is that at least two of them will hit the asteroid with enough force to slightly deflect it. The effort costs billions of dollars, but this is a crash program, with the highest international priority.

In 2022, DART is scheduled to reach an asteroid renamed Dimorphos (ex binary pair DidymosB) which means ‘two forms,’ so reflecting the status of this object as the first celestial body to have the ‘form’ of its orbit significantly changed by humanity, in this case, by the DART impact.

The European Space Agency (ESA) compares the size of Dimorphos with the Great Pyramid of Egypt. DART’s exploits will be witnessed by a small CubeSat companion from the Italian Space Agency.

Two years later, ESA will launch its own Hera spacecraft to visit Didymos and examine the results of the DART mission.
Nonetheless, in March 2019, scientists reported that asteroids may be much more difficult to destroy than thought earlier. In addition, an asteroid may reassemble itself due to gravity after being disrupted.

A team of researchers at Leiden University in the Netherlands have developed a neural network called “Hazardous Object Identifier” that they say can predict if an asteroid is on a collision course with Earth. Using a supercomputer, the researchers fast-forwarded through a simulation of 10,000 years of orbital movements of the Solar System’s planets.

The team then reversed the simulation, simulating future Earth-impacting asteroids by flinging them away from Earth and tracking their exact locations and orbits.

Their new AI identified 11 asteroids that were not previously classified by NASA as hazardous, and which were larger than 100 meters in diameter. They also focused on space rocks that could come within 4.7 million miles of Earth.

The team is now working on making its neural network even more accurate.

John Tonry “Description of ATLAS” Publications of the Astronomical Society of the Pacific volume 123, pages 58-73, 2011;
Traci Watson,“Project that spots city-killing asteroids expands to Southern Hemisphere” nature, 14 August 2018;
John D. Hefele, Francesco Bortolussi and Simon Zwart, “Identifying Earth-impacting asteroids using an artificial neural network,” Astronomy & Astrophysics, Volume 634, February 2020.

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