# Uninvited guests or distant friends? This asteroid has yet to be identified.

Recently, it was reported that an asteroid with a diameter of about 128 meters has a 2.6% chance of crashing into Earth on May 6, 2022. News of the visit three years later was quickly posted on Twitter. However, a number of experts in an interview recently said that the news is a bit “oolong”.

The asteroid is only 13 meters in diameter, about 2,800 tons of mass, the probability of impact on the Earth is only 0.026%, the impact of the energy generated by about 230,000 tons of TNT explosion energy, the threat to the Earth – “Turin index” of 0. Experts say this means the asteroid poses little threat to Earth.

But experts say the current observations come from just over a day, and whether the asteroid will “get ahead” of Earth, taking into account its orbit, diameter size, planetary texture and other parameters.

One day’s observation is not enough

“Asteroids that pose a potential threat to Earth are generally less than 0.05 astronomical units, about 7.5 million kilometers, or 20 times the Earth’s moon distance. In addition, asteroids with a diameter of more than 140 meters can cause ‘serious damage’ to Earth. Asteroids more than a kilometer in diameter would cause a global catastrophe for The Earth, with an impact power equivalent to 100 billion tons of TNT. Zhao Haibin, a researcher at the Zijinshan Observatory of the Chinese Academy of Sciences and chief scientist of the Near-Earth Object Telescope Group, said.

For the earth, the arrival of any uninvited visitor, can not be taken lightly. What does the 0.026% probability of impact in the asteroid 2009 JF1 information released by NASA’s Near-Earth Object Research Center mean?

Zhao Haibin introduced that the probability of impact is related to orbital accuracy, and orbital parameters include half-length diameter, orbital eccentricity, orbital inclination, near-day point angle and other constants.

Asteroids and Earth have their own orbits, and when the two orbits intersect, it is possible to stage an “air crash”. However, the parameters of orbit operation, subject to the influence of observation data, will have accuracy errors. “Observations of the 2009 JF1 are only over one day, and the orbitof the celestial body is constantly changing, and the confidence level is far from sufficient in terms of current observations. Zhao Haibin said.

For example, the “Apofis” asteroid, discovered in June 2004, was initially estimated to have a 2.7 per cent chance of hitting the Earth. Since then, after long observations, the probability of the asteroid hitting Earth in April has become less than one in 100,000.

Turin Index Indicates Threat Level

In data released by NASA’s Center for Near-Earth Object Research, the “Turin Index” of asteroid 2009 JF1 is 0. Zhao Haibin introduced that the threat of asteroids to the Earth, with the “Turin index” to express more intuitive. It consists of a total of 11 levels of 0-10, the larger the number, the higher the impact risk level. Zhao Haibin explained, “0 indicates that there is no great danger, but the object needs to attract observational attention,10 indicates that the asteroid is sure to hit the Earth, and it is causing a global catastrophe impact.” “

Whether an asteroid will cause damage to the Earth also depends on its diameter, Zhao said, and asteroids with a diameter of less than 10 meters are largely ablated as they pass through the atmosphere;

“The determination of asteroid size is currently based on brightness, which may have a large margin of error because it depends on the albedo of the asteroid’s surface. Zhao Haibin said.

How do scientists monitor asteroids? Zhao Haibin said that the current international use of satellite observation seduces data collection, if there is more accurate means of radar and other observations, the data may be more accurate, but the limitation of radar observation is that the range of observation is not too far.

At present, the Near-Earth Object Telescope of the Zijinshan Observatory of the Chinese Academy of Sciences is also responsible for the search and observation of asteroids, and routinely monitors information on the size, probability of impact and relative velocity of NEO objects. “In addition to a large number of ground-based telescopes, the United States and Europe and other countries have space telescopes to search and monitor near-Earth asteroids. Zhao Haibin said.

Kang Guohua, a professor at nanjing University of Aeronautics and Astronautics, said that in the past, scientists have also used optical telescopes to carry out international collaborative observations, and with the development of artificial intelligence technology, the academic community has begun to try to use deep learning and other technologies to identify new objects, “at present, all asteroids that may hit the Earth have cataloguing, but their probability of impact is very low.” “

How will future asteroids be protected against a large reverity of impact threats to Earth? Over the years, scientists from many countries have been studying ways to defend against asteroid impacts on Earth. For example, on 4 July 2005, the impact module launched by NASA’s Deep Impact successfully hit Comet Temple-1 to study the composition of the comet’s nucleus while indirectly attempting to defend itself against an asteroid impact. In the future, the international “DART program” will also be promoted, trying to hit an asteroid with a space “dart” to change its orbit.