Tag: near earth asteroids

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ATLAS Asteroid Hunting Network Now Fully Operational

ATLAS, a vital sentinel in the search for near Earth asteroids is now fully operational.


From right to left: an artist’s conception of NEO Surveyor (Credit: NASA). DART at Didymos (Credit: NASA/Johns Hopkins). ATLAS-El Sauce observatory in Chile (Credit: University of Hawai’i). ATLAS-Sutherland observatory in South Africa (Credit: Willie Koorts (SAAO).

It’s one of the most vital endeavors in modern astronomy. NASA recently announced that the Asteroid Terrestrial-impact Last Alert System (ATLAS) now is, with the addition of two separate southern hemisphere sites—complete. Operated by the University of Hawai’i Institute for Astronomy on behalf of the agency’s Planetary Defense Coordination Office (PDCO) the addition of two new sites, one in Chile and another in South Africa, now includes four telescopes overall, in addition to the two northern hemisphere telescopes based and Maunaloa and Haleakala in Hawai’i, now affords all-sky coverage of both hemispheres of the sky every night, looking for near Earth asteroids.

“An important part of planetary defense is finding asteroids before they find us, so if necessary, we can get them before they get us,” says Kelly Fast (NASA/PDCO) in a recent press release. “With the addition of these two telescopes, ATLAS is now capable of searching the entire sky every 24 hours, making it an important asset for NASA’s continous effort to find, track and monitor NEOs.”

The first two telescopes were developed under a 2013 grant from NASA’s Near-Earth Objects Objects Observations Program, and came online in 2017. The two new telescopes are located at the El Sauce Observatory in the Rio Hurtado Valley in Chile, and the Sutherland Observatory in South Africa, respectively. Each site features a 0.5 meter telescope, capable of scanning a 5-degree wide swath of the sky 100 times the size of the Full Moon. Since 2017, ATLAS has discovered over 700 near-Earth Asteroids (NEAs) and 66 comets and counting, many of which later put on a fine celestial show.

The system has already demonstrated the viability of the “Last Alert” part of its name: two small asteroids –2018 LA and 2019 MO—were detected just hours before impact. The ATLAS-Sutherland observatory has already made its very first solo detection: asteroid 2022 BK, a 100-meter asteroid that passed 5.6 million miles from the Earth on January 28th, 2022.

Tracking near-Earth asteroids is especially tricky for large professional telescopes, as they’re relatively fast movers against the starry background. With a wide field of view and an agile response time, the ATLAS system excels in nabbing new objects that come within the sphere of the Earth-Moon system, about a quarter of a million miles distant.

Worldwide coverage is critical: until ATLAS came online, we were often only hearing about close asteroid passes near Earth after they occurred. Chelyabinsk was also a wake-up call, as a 20-metre asteroid exploded over the Russian city of 1.1 million the morning after Valentine’s Day 2013. This particular space rock snuck in at Earth undetected from a sunward direction.

Another mission may soon take this vigilance against low-flying rocks into space. NASA’s Near-Earth Object Surveyor mission (NEO Surveyor) recently received the green-light to move ahead into Preliminary Design/Key Decision Point-B. This mission would launch in 2026, and use a 50-centimeter mirror to hunt for NEOs in the infrared from its Sun-Earth Lagrange Point 1 (L1) vantage point.

But we’re not waiting for the hazardous asteroids to come to us. NASA’s DART (Double Asteroid Re-Direction Test) launched in November 2021 headed to impact asteroid 65803 Didymos’ moon Dimorphos in late September/early October of this year. OSIRIS-Rex is bringing samples back from 101955 Bennu on September 24th, 2023, an asteroid that could, centuries from now, possibly hit the Earth. And launching along with nine other smallsat missions on SLS Artemis-1 this April is NEA Scout, a small solar sail mission aiming to intercept the 15-metre asteroid 2020 GE in 2024.

We can never know too much about hazardous asteroids and our local solar neighborhood. Expect to see a lot more comets named ‘ATLAS’ very soon.

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Next Generation Sentry II System to Assess Risk From Possible Hazardous Asteroids

NASA’s new Sentry II system will refine long term collision predictions for Near Earth Asteroids.


The convoluted future path of asteroid Didymos through the inner solar system. Credit: NASA/JPL

NASA has a powerful new tool in its arsenal for defending the Earth from hazardous asteroids. Since 2002, the space agency has used the Sentry system to predict the future path of near Earth asteroids (NEAs), and assess their risk for a potential future impact with the Earth. This system, however, has its limitations. As the number of known NEAs nears 28,000 and grows by 3,000 new asteroids per year, a new system is needed to keep up with demand.

The new system named Sentry II will meet this need. Sentry II just went online in December 2021, and will use an enhanced algorithm to look at all of the factors impacting an asteroid’s future trajectory. Astronomers expect to see better, more accurate projections further into the future, using the Sentry II system.

Sentry’s Original Limitations

NASA’s Center for Near Earth Object Studies (CNEOS) based out of the Jet Propulsion Laboratory in Pasadena, California works together with the agency’s Planetary Defense Coordination Office (PDCO) to assess impact probabilities over the next century. The system could run the predictions in under an hour, a vital resource especially in terms of seeing small asteroids inbound, which are often discovered with little advance warning. A good example was the Chelyabinsk impactor which struck Russia the day after Valentine’s Day in 2013. The Chelyabinsk rock came at Earth from a sunward direction, and was undetected prior to impact.

However, the original Sentry system had its drawbacks. Asteroid path predictions are limited by the number of observations made: the more observations, the better we know its future path. Not only does this path become more indefinite over time, but small tugs by other planets in the solar system perturb an asteroid’s path. Sentry accounted for this, but it didn’t factor in the complex effect of thermal heating from the Sun via what’s known as the Yarkovsky effect, which slowly nudges an asteroid over time. Small changes add up, and Sentry II will take these into account.

“The fact that Sentry couldn’t automatically handle the Yarkovsky effect was a limitation,” says Davide Farnocchia (NASA-JPL) in a recent press release. “Every time we came across a special case—like asteroids Apophis, Bennu or 1950 DA—we had to do complex and time-consuming manual analyses. With Sentry II, we don’t have to do that anymore.”

The previous method would often break down—especially in the case of close Earth flybys—requiring manual analysis of the future trajectory of the asteroid. Sentry II eliminates this with a different mathematical approach, allowing it to focus in on low probability impact zones (known as keyholes). These are regions which would made a future impact more likely, were an asteroid to pass through these narrow zones.

Sentry II is vital, as new all-sky surveys such as the Vera C. Rubin telescope come online over the next few years. Expect to see a flood of new discoveries of ever smaller asteroids, necessitating the need for a more powerful prediction model such as Sentry II.

101955 Bennu and 99942 Apophis are good case studies in narrowing down the uncertainty of a future impact. Discovered in 2004, 450 meter Apophis generated a brief amount of excitement when it looked like there was a small chance of impact with Earth on April 13 (yes, Friday the 13th) 2029. Better observations and predictions soon ruled this out, though there was still a small chance of an impact later this century in 2068, though that was also ruled out earlier this year.

Thanks to the OSIRIS-Rex mission, we now know the orbit and characteristics of Bennu better than any other asteroid in the solar system. This 530-metre space rock has a small (1-in-2,700) chance of impacting the Earth on September 24th 2182, if it happens to pass through a gravitational keyhole in 2135.

But NASA isn’t just passively hunting for asteroids. On November 24th, the agency launched the Double Asteroid Redirection Test (DART) mission headed towards double asteroid Didymos, where it will impact the asteroid’s tiny moon Dimorphos in late September-early October 2022. This exercise, coupled with the Sentry II system may prove useful, if we ever did need to move a potentially hazardous asteroid out of harm’s way.