There are only a few celestial bodies known to pose a serious threat to Earth, and the giant asteroid Apophis is one of them.
Artist's depiction of near-Earth objects. Image: NASA/JPL California Institute of Technology
There are only a few celestial bodies known to pose a serious threat to Earth, and the giant asteroid Apophis is one of them. Based on further observations, the researchers are reassessing the likelihood that it will hit Earth 48 years from now.
Earlier this year, astronomers observed the Subaru Telescope in Hawaii to better understand how the Yakovsky effect affected Apophis (asteroid 99942). The Yakovsky effect is like a built-in asteroid propulsion system. In this system, the leaked trace amount of thermal radiation can alter the momentum of an object in space, causing it to drift slightly from the path chosen by gravity.
"Apophis could pose a threat even without considering the drift caused by the Yakovsky effect, just not in 2068," Dave Tholen, a researcher at the Institute for Astronomy at the University of Hawaii 'i and one of the study's co-authors, explained in an email. The collision of 2068 will still be staged, and the possibility is small, but not zero. ”
The asteroid Apophis (circle) appeared when it was discovered in 2004. Image: UH/IA
Together with Davide Farnocchia of NASA's Jet Propulsion Laboratory, Tholen analyzed a large body of new data and argued that the acceleration generated by the Yarkovsky effect was holding the Apophis crisis under control within 2068. Their findings were published at the 2020 virtual meeting of the American Astronomical Society's Planetary Sciences Division.
Apophis is currently ranked third on NASA's Sentinel Risk Table. According to the Palermo Impact Hazard Index estimates, the probability of Apophis hitting earth on April 12, 2068 is 1 in 150,000 (mark it on the calendar). Or if you like to express it as a percentage, there is a 0.00067% chance of hitting the Earth. Toruhn said that according to neodyS (Near Earth Objects Dynamic Site) collision monitoring service, that probability is actually close to one in 530,000, which takes into account the nominal Yarkovsky drift rate.
The new analysis will correct Apophis' threat risk, but even so, Toruń said it still needs to be "carefully calculated" because there are other variables to consider. And in fact, as astronomers better grasp the asteroid's itinerary, we should see the probabilities change over time.
A collision with Earth – although it may seem unlikely – would be very bad. Composed of nickel and iron, Apophis is more than 1,000 feet (300 meters) wide. If you like the image statement, then it is wider than three football fields. Hitting the surface will release energy equivalent to 1151 megatons of TNT. Such catastrophic events occur on Earth about once every 80,000 years.
So it makes sense that scientists are paying close attention to Apophis to improve predictions. When the near-Earth asteroid was discovered in 2004, astronomers thought it had a frightening 2.7 percent chance of Earth hitting Earth in 2029. Later astronomers ruled out this possibility, as well as a possible impact in 2036. As for the 2068 attack, at least for now, this possibility cannot be ruled out, because the Jakowski effect is affecting Apophis.
The asteroid absorbs a lot of energy due to its exposure to solar rays. Eventually, however, this heat is re-emitted into space rather than passing directly through the asteroid. This gives the star extra acceleration so that its trajectory can be changed.
"The light radiated by the celestial body gives the celestial body a tiny thrust. The hotter side of the asteroid has slightly more thrust on the colder side, because the hotter side emits more light (invisible infrared bands), so in general the object is subject to a non-gravitational effect. Toruń, co-discoverer of Apophis, explains, "It's a very small force that's not obvious to larger objects, but the smaller the object, the easier it is to detect this effect." ”
Toruń and his colleagues have been tracking Apophis' location for the past 16 years, and they now notice that it deviates slightly from its original orbit, which was completely constrained by gravity.
"Observations using the Subaru telescope in January and March of this year were crucial to the success of this work, as it allowed us to determine the asteroid's position with twice the volume of the asteroid itself." "Apophis is about 300 meters in diameter, and the location we measured is about 700 meters wide, although we are about 70 million kilometers away from the object," he said. ”
His team's calculations show that the semi-major axis of Apophis orbit (half of the elliptical major axis) is currently shrinking at a rate of about 170 meters per year, a result of the Yakovsky effect, not gravity. He said that when Apophis skims over the Earth in 2029, its semi-major axis will increase significantly due to earth's gravity.
More observations should improve judgments, including a better description of how the Yarkovsky effect affects the Apophis drift rate. It's fairly safe to say that by 2068, astronomers will know if an impact is inevitable.
Author: George Dvorsky
FY: Wednesday
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