On April 12, the world celebrates the International Day of Human Space Flight. Humanity has been exploring space for 60 years, step by step, but it still has many surprises, one of which is asteroids. Predicting their appearance in near-Earth space is an extremely difficult task, and scientists in TSU’s Department of Celestial Mechanics and Astrometry of the Research Institute of Applied Mathematics and Mechanics are engaged in solving it. Tatyana Galushina, a leading researcher and head of the Laboratory of Computer Modeling and Machine Analysis of Astronomical Data, spoke about how to predict the fall of an asteroid to the Earth, what factors affect its movement, and whether humanity can protect itself from a space guest.
- Tatyana Yurievna, what asteroids are considered potentially dangerous for our planet?
- Speaking about asteroids approaching the Earth, we often omit the word "potentially" and do not attach meaning to it. This is very important. Two factors matter when assessing a potential threat: the size of a celestial body and the distance, moreover, not even between objects (an asteroid and the Earth), but between orbits. If we talk about size, then it is difficult to estimate it, because when we observe an asteroid, we just see a dot. We can only estimate asteroids by their brightness. Potentially dangerous are those whose absolute magnitude is not weaker than the 22nd magnitude.
I'll try to explain what it means. There is a concept of albedo that means reflectivity.
Imagine a piece of ice or coal. Depending on what the object consists of, it can have different sizes at the same brightness. If we take the average albedo for asteroids, then the 22nd magnitude is about 140 meters. If the asteroid is larger, it is considered potentially hazardous. And if the distance between its orbit and the Earth's orbit is less than 7.5 million kilometers, then the asteroid can be attributed to this category. At such a distance, the celestial body and the Earth can meet. But this may not happen.
Because the position in orbit is the most poorly determined coordinate, at some point a meeting with the Earth can occur, so these asteroids are classified as potentially dangerous. They receive special attention because in the future they can pose a real threat.
- How many asteroids are currently classified as potentially dangerous?
- Their number is constantly changing, as new ones are regularly detected. One of the most complete databases about them is on the NASA website. The number of discovered asteroids, approaching the Earth, already exceeds 25,000, and 2,172 are recognized as potentially dangerous. Of these, 158 have a diameter of more than one kilometer.
- Is it possible that the asteroid will approach the critical distance to the Earth while remaining unnoticed?
- The question is, what do we know about asteroids in general? At the moment, we know almost all asteroids larger than one kilometer. Now they are rarely detected.
The smaller the object, the more difficult it is to track. So, if we give an example of an asteroid about 15 meters in size, then we know a small part of such objects. There are many times more of them than we know. The smaller the object, the more likely it is to fall to Earth unnoticed. It is of great importance when and from which side the asteroid came. For example, the Chelyabinsk meteorite fell in the morning, while it was coming from the direction of the sun, so no one saw it. The probability that the asteroid will approach unnoticed and fall is very high. They fall constantly. The question is where and what size.
- Do you mean it will fall on a settlement, or on a region without human life?
- Of course, we are more and more mastering the territory of the Earth. Most of it is covered by oceans, and asteroids fall there too. If this is an object of small size, then this does not entail any consequences for humans, but if the asteroid is large and falls close to the coast, it can cause a tsunami. If we take, for example, 1908, when the Tunguska catastrophe occurred, then it was in a sparsely populated area. If this happened anywhere in Europe, there would be many victims.
In 1947, the Sikhote-Alin meteorite fell in the Ussuri taiga. It shattered in the atmosphere and fell like an iron rain over an area of 35 sq km. This happened in a sparsely populated area, one might say, luckily. Parts of the meteorite are stored in many places, even in our planetarium. In this century, the Chelyabinsk meteorite fell close to the city. So the more we master the planet, the more likely it is that a celestial body will fall on a settlement. Moreover, at the moment there are only three asteroid falls that could be predicted. Therefore, more often than not, something falls unexpectedly.
- What kind of falls did scientists manage to predict?
- In October 2008, an asteroid with a diameter of about three meters was discovered the day before the fall. On the trajectory, it was supposed to fall in the Sudanese desert, which is what happened. An expedition was organized, and pieces of the meteorite were found.
Another object was discovered on January 1, 2014, and on January 2, it collided with our planet. Presumably, the asteroid could have fallen in Africa, but we were lucky because it fell into the ocean.
The third case was in early June 2018. The small asteroid 2018 LA was discovered hours before it burned up in Earth's atmosphere and exploded in the skies over Africa.