The never-ending story of Apophis - part two

Why was he given the name Apophis, and what damage could be caused if he were able to fall to earth. Part two in the series by Dr. Noah Brosh, Galileo 96

Once 2004 MN4 had been accurately orbited, it was given its fixed name, recognized by the astronomical community. Because of the (relatively) high chance of harming the Earth, a meaningful name from ancient Egyptian mythology was chosen: the name of the god Apep, or Apophys in the Greek pronunciation accepted today, the god responsible for destruction and doom.

The god Apophis has nowadays become a character in science fiction films. In the TV series "Stargate" he is the evil leader, who tries to take over the humans. As in Egyptian mythology, Apophis is the sworn enemy of the sun god, Ra (Ra). He also sometimes appears in the form of a snake ("the snake that swallowed the sun" during a total solar eclipse).

And indeed, the picture did not look encouraging: any possible impact of Apophis on the Earth would have caused great destruction, as seen in the figure below. Since the Earth is mostly covered in water, there was a high probability that the impact would occur in the ocean. This would have caused huge tsunami waves, which would have washed the shores of the affected ocean and caused much more destruction than the earthquake in Southeast Asia at the end of 2004.

This is the place to compliment the astronomical community that studies the near-Earth objects for its measured behavior in the first days, when the possibility of a future impact on the Earth became clear. As mentioned, on December 18, 2004, the observations of Tholan and his friends were combined with those made from Australia, and it became clear that 2004 MN4 will pass very close to Earth in 2029. On December 23, the system of the University of Pisa calculated, based on new observations, that the launch distance on April 13, 2029 will be 780,000 km, twice the distance to the moon. Nevertheless, a small chance of actual harm could not be ruled out. Since it was a body whose diameter was estimated to be about 400 meters, and since its speed relative to the Earth at that time is supposed to be about 11 km per second, a possible impact would have caused a real disaster - the energy that would have been released would have been a hundred times greater than that of the body that created the "meteor crater" ” in Arizona.

Since on December 23 Pisa estimated the chances of impact at 1:170, the researchers raised the risk level according to the Torino scale to 2, the highest level reached by a near-Earth asteroid since this risk scale began to be used. This was published on the Internet among the experts, to draw their attention to the threatening body. The next day, new observations were added to the database. For the most part, the trajectory correction calculated based on new observations shows that the risk of impact is smaller than originally thought. However, this time, the new data actually increased the chances of being hit in 2029 to 1:60. This situation requires an additional increase of the Torino level for the event, to a value of 4.

According to the decision of the International Astronomical Union, this situation requires the astronomers to inform the political parties if the predicted collision is going to happen in less than ten years. The expected time of collision was, of course, greater than ten years; Nevertheless, the author of the article decided to bring the findings to the attention of the Director General of the Israel Space Agency (ISA), Dr. Zvi Kaplan. SLA, in the Ministry of Science and Technology, is a governmental civilian body in charge of space activities, and we are the entity that finances the activities of the National Knowledge Center for Small Bodies. The center operates at Tel Aviv University and operates a dedicated telescope at the Wise Observatory in Mitzpe Ramon, for the discovery and tracking of near-Earth bodies. The author of this article manages the Knowledge Center, which is an advisory body to the Israeli government on NEOs. On the author's advice, Dr. Kaplan decided not to pass the information on to the government at this stage, due to the long time until the possible injury and due to the assessment that the likelihood of the collision will decrease in the follow-up. It was decided to wait a few days to monitor the level of the threat, while making as many measurements as possible from Mitzpe Ramon.

On that day, December 24, the journalist Rob Britt (Britt), a writer on the website space.com, discovered the information (which was not confidential, but was accessible on the Internet) and published it. He also noticed that the odds of 4MN 2004 hitting the Earth had increased and stood at 1:45 at that time. Britt even pointed out that there is a reasonable chance that new observations will cause another change in the estimated route, which will show that the danger is actually smaller. On December 27th, with the accumulation of new observations, the odds of the impact increased again, reaching 1:37!

On December 26, the deadly earthquake occurred in Southeast Asia, and with it the tsunami wave that washed over many beaches and caused hundreds of thousands of victims. Journalistic attention was focused on the present and immediate disaster, and the press did not pay attention to 2004 MN4, which seemed like a danger to future generations. The astronomers, however, continued to observe and report the location of the new body, and also searched databases for past observations where the body might appear. On December 27, these searches yielded results: astronomers Jeffrey Larsen and Anne Descour of the American Spacewatch project, whose mission is to discover near-Earth asteroids, found in their databases images of 2004 MN4 taken three months before the discovery of Tolan and his colleagues. This finding enabled a significant improvement of the trajectory calculation, to such an extent that Don Yeomans from the center at JPL was able to announce that the chances of impact in 2029 had dropped to zero, and that during this passage the sky gram would pass at a distance of 60,000 km from the Earth. The size of the calculated orbit around the sun has since changed following additional measurements, both by optical means and by radar, when the asteroid passed close to the Earth, and the minimum distance from the Earth is currently 36,350 km.

The astronomical community acted in this case exactly according to the rules it set for itself, and the astronomers did not issue dramatic press releases. Such messages can sow fear and mass panic. The wait paid off, and it was possible to release a "reassurance siren" after Youmans' announcement.

Continue in the third and last part

Box: Apophis - current information

To estimate the expected damage from the impact of a near-Earth asteroid on the Earth, it is important to know some details about the possible impacting body. The most important detail is if an injury will indeed occur, but the relative speed between the body and the ground at the time of the encounter is also important. Also, you need to know what is the mass of the asteroid, what is its internal texture and what is its shape. Measuring the mass is only possible if it is possible to get close to the asteroid in a spacecraft that can be tracked with precision, or if the asteroid happens to have a close companion. From slight deviations in the orbit of a spacecraft passing close to an asteroid, due to its gravity, its mass can be estimated. If it is not possible to pass close to the asteroid, and it is not a member of a double system of two asteroids, another way is to calculate its external size by measurements from the Earth, assume a certain value regarding its density, and thus estimate the mass to a fairly good approximation.

As for Apophis, the current mass measurements are based on physical size and an assumption about its density. It seems that this is a body whose long axis is about 320 meters long, so its mass is probably about 46 million tons (4.6×1010 kg). At this point there is no information about its exact shape or its internal texture. In any possible impact, the relative speed between Apophis and Eretz will be about 12.6 km per second. In terms of the classification of near-Earth asteroids, Apophis belongs to the "Aten" body family (Aten, named after the asteroid that is the prototype for the family). These asteroids orbit the Sun in elliptical orbits, where most of the time the asteroid is inward from the Earth's orbit. The orbits of the Earth and the asteroid intersect twice: when the asteroid moves away from the Sun and when it approaches it again. Since Aten bodies are mostly inland from the Earth relative to the Sun, they are usually visible from the Earth near the Sun, near its sunset or before its sunrise, and only rarely can they be seen far from the Sun, near midnight. Because of this, the duration of time that can be observed when darkness prevails is short.

Here is the place to emphasize that the type of near-Earth asteroids "Aten" is also characterized by the average distance of the asteroid from the Sun; This is a smaller distance than the Earth's average distance from the Sun (the "astronomical unit"), although the elliptical orbit sometimes causes the asteroid to move further from the Sun than the Earth. Following the passage near the Earth in 2029, and the change in the orbit of Apophis that will occur at that time, the average distance from the Sun will increase.