There is a chance that an asteroid will hit Earth. There are tens of thousands of asteroids classified as Near-Earth Asteroids. As better survey telescopes come online, the number of new detections will increase.
NASA has developed a new system to classify asteroids.
There are different classifications for objects that come close to Earth.
A Near-Earth object has a perihelion of less than 1.3AU. A Near-Earth Asteroid or a Near-Earth Comet can be a NEO. If a NEO is larger than 140 meters in diameter, it is a Potentially Hazardous object. Most PHOs are asteroids.
We know of over one hundred Near-Earth comets. NASA needed a better way to assess the impact probabilities for all those objects. They have developed a next-generation algorithm.
asteroids and comets aren't chaotic and unpredictable. In the distant past, planets migrated and asteroids were thrown around as a result. But now, they follow a predictable path. The situation is manageable even though there are tens of thousands of them.
asteroids are no exception to the chaos and unpredictability of nature. There are small uncertainties in asteroids. There is no room for carelessness when you only have one home.
The Center for Near-Earth Object Studies (CNEOS) at JPL in California is maintained by NASA. The Planetary Defense Coordination Office is integrated with it. The Center for Near-Earth Object Studies (CNEOS) makes their results available on their website.
The data scientists use to compute a NEO's orbit is not perfect. Different telescopes can come up with different positions for asteroids. The differences can result in different computed orbits. The CNEOS uses a program called Sentry to analyze a range of possible asteroids. Then it calculates the probabilities for an impact with the Earth's surface reaching 100 years into the future.
The original Sentry was very powerful.
The first version of the system was in use for almost two decades, according to the man who led the development of the second version. It was based on some very smart mathematics, and it was possible to get the impact probability for a newly discovered asteroid over the next 100 years.
Sentry is a powerful system, but it has drawbacks. The power of its computing was based on the influence of the inner Solar System. An asteroid's orbit is shaped by more than gravity. The Yarkovsky effect makes some asteroids special cases.
Ivan Osipovich Yarkovsky is a Polish-Russian engineer. Yarkovsky found that small rotating objects in space would experience daily heating and that heating could cause small changes in the object's trajectory. The Yarkovsky effect is not consequential on short time scales. It can add up over time. The Yarkovsky effect was not taken into account by the original Sentry.
The Yarkovsky effect is explained in this illustration. The Yarkovsky effect can change the direction of smaller NEOs. The image is from English Wikipedia, CC BY-SA 3.0.
NASA has implemented a successor to Sentry. The limitation that its predecessor had won't be a problem for Sentry- II.
Davide Farnocchia, a navigation engineer at JPL, said that the Yarkovsky effect was a limitation. We had to do complex and time-Consuming manual analyses when we came across special cases. We don't have to do that anymore.
The original Sentry was unable to accurately predict the impact probabilities for asteroids that went through close encounters with Earth. It is difficult to calculate an NEA's altered path into the future after such an encounter. Post- Earth trajectory can be altered dramatically by a close encounter with Earth, and those calculations had to be done manually.
But Sentry- II is able to handle that problem. As we detect more and more NEAs, the number of special cases will grow.
Roa Vicens said that the special cases were a tiny fraction of the NEAs that they would calculate impact probabilities for. We need to be prepared because we are going to discover many more of these special cases when the Vera C. Rubin Observatory goes online.
The Vera C. Rubin Observatory will be able to detect NEAs. Each area of the sky will be imaged 1000 times. It will do so with a powerful camera. The Rubin will take pictures of the sky every two nights.
The space telescope is scheduled for launch in the year of 2026. Most of the ones that are visible in optical light have already been found. The Sun gets warmed as a NEO approaches. The energy will be watched by the NEO Surveyor.
The cumulative number of known Near-Earth Asteroids is shown in the chart. It shows totals for NEAs of all sizes, those larger than 140m in diameter and those larger than 1 km in diameter. The rise in detections in the last two decades is likely to continue as the Vera C. Rubin facilities start operating. The image is Credit: CNEOS.
NASA needed a new way to calculate NEA detections because the NEO Surveyor and Vera C. Rubin Observatory could lead to a lot of detections.
asteroids are similar to electrons. We can't tell you where an electron is because we don't know its position and velocity. We don't know the probabilities of an electron being in one position.
NEA detection is similar. More than one telescope observes a new NEA. The Minor Planet Center gets the observed position from each one. The data is taken and the asteroid's most likely path is calculated. The most likely range is somewhere inside, and the true orbit is there.
This is where the power of Sentry-II becomes evident.
Some assumptions were used to compute an asteroid's orbit. The uncertainty region has points that represent a slightly different location of the asteroid. It would project into the future and watch as asteroids passed by the Sun. If any came near the Earth, it would look more closely to see if any of the points would impact the Earth. The probability of an impact would be calculated if they did. Over time, uncertainties grow.
The animation shows how the uncertainties in a near-Earth asteroid can evolve with time. The possibility of future impacts is more difficult to assess after a close encounter with Earth.
It is handled differently by Sentry-II.
It takes thousands of points within the uncertainty region without knowing how the uncertainty region will evolve over time. Then, the program asks itself, what are the possible paths that could hit Earth?
The main difference is that Sentry- II can zero in on low-probability impact scenarios that its predecessor may miss.
A press release likens it to finding a needle in a haystack. The haystack is larger if the region of uncertainty for an asteroid is larger. Each needle is a possibility of hitting something.
The original Sentry would look through a haystack for possible impact scenarios. This was the best way to find needles and impact scenarios, according to the artificial intelligence.
But Sentry-ii does something different. It doesn't make any assumptions about the impacts through the haystack. Instead, it uses thousands of magnets, which are thrown randomly throughout the haystack. The magnets are attracted to the impact scenarios.
Steve Chesley is a senior research scientist at JPL and he said that the advancement in finding tiny impact probabilities for a huge range of scenarios is a fantastic advancement. He was involved in the development of Sentry. It pays to find the smallest impact risk hidden in the data when the consequences of a future asteroid impact are so large.
Artificial intelligence, machine learning, and super- computers are playing an increasingly important role in our modern age. The Vera C. Rubin Observatory will generate a lot of data. Machine learning and artificial intelligence are needed to make sense of it all.
It could be that artificial intelligence saves us from an asteroid impact.
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