In August 2020, the asteroid “HQ 2020“In case no one had discovered it before, it set the last record of a non-colliding asteroid flying past the earth in the history of observing, and it was only 2,950 kilometers away when it was closest to the earth. Few months later, in November “2020VT4“Renew this record again, the closest time is only 370 kilometers. The former is approximately the size of a recreational vehicle, and the diameter of the latter is approximatelyAbout 5-11 meters。
Although this year half October, the DART project (Double Asteroid Redirection Test, double asteroid redirection test, NASA’s z-launch probe hits one of the double asteroids to test if it can deviate from its orbit) has announced that it has obtained better than expected results, which is very exciting for planetary defense Excited that the system is improving, but before defending, how do you “find” that an asteroid is approaching? NASA announced on the 22ndride NEO surveyor projectit will comprehensively examine menacing asteroids and comets around the earth and is expected to launch in 2028.
NEO Surveyor (Near-Earth Object Surveyor, Near-Earth Object Surveyor) operates mainly in two infrared bands, with a primary mirror of about 50 cm. The goal is to find 90% of asteroids larger than 140 meters within 10 years of launch, and include them in the management and near-Earth objects. A celestial body larger than this size, if it strikes the Earth, will cause significant damage in the area of fall and is a potential threat to the Earth.
NEO Surveyor can be regarded as an extension of the “NEOWISE” space telescope, which has been observing asteroids and comets since 2013. NEOWISE, formerly known as “WISE (Wide-field Infrared Survey Explorer, Wide-field Infrared Survey Explorer)”, was launched in 2009 and transitioned to near-Earth observations after the end of the original 10-month main sky survey mission, and once it went into hibernation. The operation was restarted in 2013 and both the satellite and the project were renamed NEOWISE, with asteroids and comets as the main surveying and mapping targets. NEOWISE’s current mission is extended through 2023.
The reason why asteroids or near-Earth objects like 2020 QG and 2020 VT4 are difficult to observe in advance is that in addition to their small size, the problem is that as they approach earth, they are approaching from the “same direction” as the Sun. In general, if you want to find an asteroid, you need to see sunlight reflected off the asteroid through a telescope to observe it, so most objects discovered are near-Earth objects approaching from the “opposite direction” of the sun.
When the approaching asteroid is between the Earth and the sun, it is nearly impossible to find the glow of an asteroid only 1.5 meters in diameter amid the glare of sunlight 109 times the diameter of the Earth. As for 2020 HQ, its existence was not known until it passed the earth for 6 hours.
Unlike NEOWISE, which operates in a sun-synchronous orbit around the Earth, NEO Surveyor is expected to fly 1.6 million kilometers (1 million miles) to the Lagrangian point L1. The satellites are arrayed at the Lagrangian points, which can maintain gravitational balance and keep the relative positions of the satellites, the earth and the sun unchanged. According to NASA, NEO Surveyor’s initial 5-year mission is expected to take place at the Lagrangian point L1.
Also, since the asteroid will be heated by the sun during the approach, infrared wavelengths may be transmitted instead of visible light observations. Infrared wavelengths are on the surface and will be absorbed by the Earth’s atmosphere, making it difficult to observe. The results of NEOWISE’s detection and observation of near-Earth objects show that infrared telescopes are excellent in confirming near-Earth objects. NEO Surveyor is built on top of NEOWISE, the first purpose-built space telescope and space mission for the detection of near-Earth objects.
In addition to its implications for planetary defense, NASA says NEO Surveyor will help find”Earth Trojan asteroid(Earth’s Trojan asteroid).” These asteroids share orbits with larger planets, and Neptune, Mars, and Jupiter share orbits with Trojan asteroids. While these asteroids pose no threat to impact earth, they are also easily obstructed by sunlight because they are always in front of or behind the earth by a small distance in orbit.
Finally, while not relevant to the primary planetary defense mission, NEO’s observations also help to understand the composition, shape, rotation and orbit of celestial objects. Just like the information on the evolution of the solar system obtained from Japan’s detection of the asteroid “Ryugu”, asteroids and comets are the living fossils of the solar system. Analyzing information from asteroids and comets can help us better understand the evolution of near-Earth objects and the solar system.
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