The Center for Near Earth Object Studies (CNEOS) at JPL calculated the orbits of 2,200 potentially hazardous objects. The asteroid Didymos is the target of the DART mission. Credit: Caltech.
Over the course of time, nearly 28,000 near-Earth asteroids have been found by survey telescopes, adding new discoveries at a rate of about 3000 per year. A rapid increase in discoveries is expected as larger and more advanced telescopes intensify the search. NASA has developed a new impact monitoring tool to better evaluate NEA impact probabilities.
Popular culture often depicts asteroids as chaotic objects that zoom around our solar system, changing course without warning and threatening our planet. This isn't the reality. The laws of physics allow asteroids to follow known paths around the Sun.
Sometimes, those paths can come very close to Earth's future position and, because of small uncertainties in the asteroids' positions, a future Earth impact cannot be completely ruled out. Astronomers use impact monitoring software to calculate the impact risk.
Every known NEA is calculated by the Center for Near Earth Object Studies to improve impact hazard assessments in support of NASA's Planetary Defense Coordination Office. The impact risk posed by NEAs has been monitored.
"The first version of Sentry was a very capable system that was in operation for almost 20 years, and it was led by a navigation engineer who recently moved to SpaceX," said Javier Roa Vicens, who led the development of Sentry-II while working at JPL as a navigation engineer 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.
NASA has a tool that can quickly calculate impact probabilities for all known NEAs, including some special cases not captured by the original Sentry. The objects of most risk are reported in the Sentry Table.
The researchers have made the impact monitoring system more robust by calculating impact probabilities in this new way.
The video explains how asteroid Bennu was determined by considering both gravity and non-gravity forces, helping scientists understand how the asteroid will change over time. The NASA's Goddard Space Flight Center.
There are special cases.
The Sun's pull on the planets will affect the path of an asteroid's journey through the solar system. The model was used to predict where the asteroid will be in the future. The thermal forces caused by the Sun's heat are the most significant.
The sun shines on the object's dayside. The asteroid's shaded nightside will be the location of the heated surface. As the temperature cools, the energy is released, generating a small thrust on the asteroid. The Yarkovsky effect has little effect on the asteroid's motion over short periods, but can change its path over decades and centuries.
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.
It was not always possible to accurately predict the impact probability of asteroids that go very close to Earth. The motion of these NEAs is affected by our planet's gravity, and can grow dramatically. The old Sentry's calculations could fail in those cases. That limitation is not present in Sentry- II.
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 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. Credit: Caltech.
There are needles and a haystack.
When telescopes track a new NEA, they measure the asteroid's observed positions in the sky and report them to the Minor Planet Center. The data is used to determine the asteroid's most likely path around the Sun. There are slight uncertainties in the asteroid's observed position, so its "most likely orbit" might not be its true one. There is a cloud of possibilities surrounding the most likely orbit.
The original Sentry would make assumptions about how the uncertainty region may evolve to assess whether an impact is possible. It would pick a set of points along a line. Each point showed a different location of the asteroid.
If there were any "virtual asteroids" that came near Earth in the future, Sentry would wind the clock forward and watch them. If that were the case, then further calculations would have to be done to see if any intermediate points would impact Earth.
There is a different philosophy in Sentry-II. The uncertainty region is not limited by any assumptions and the new algorithm selects random points throughout the uncertainty region. What are the possible paths within the region of uncertainty that could hit Earth?
The calculations aren't shaped by assumptions about which parts of the uncertainty region might have an impact. This allows Sentry-II to zero in on low probability impact scenarios that may have been missed.
The process of searching for needles in a haystack is similar to looking for a needle in a haystack. The bigger the haystack, the more uncertain an asteroid's position is. Sentry would randomly look for needles in the haystack, looking for a single line stretching through the haystack. The assumption was that following this line was the best way to look for needles. The haystack is thrown with thousands of tiny magnets randomly all over it, which quickly 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609-
"Sentry-II is a fantastic advancement in finding tiny impact probabilities for a huge range of scenarios," said Steve Chesley, senior research scientist at JPL, who led the development of Sentry and collaborated on Sentry-II. It pays to find the smallest impact risk hidden in the data when the consequences of a future asteroid impact are so large.
A study about Sentry- II was published in the journal.
A novel approach to asteroid impact monitoring was written by Roa and his colleagues. There is a book titled "10847/1538-3881/ac193f".
There is more information about asteroids at cneos.jpl.nasa.gov.
The journal has information about astronomy.
NASA's next-generation asteroid impact monitoring system goes online on December 7, 2021.
The document is copyrighted. Any fair dealing for the purpose of private study or research cannot be reproduced without written permission. The content is not intended to be used for anything other than information purposes.
