Last Friday (4) a piece of rocket propellant, with an estimated mass of three tons, collided with the Moon and created a new crater on Earth’s natural satellite.
A terrestrial object colliding with the Moon is not unheard of — although this is the first time it has happened unintentionally.
Many questions remain in the air after the collision. No one knows with absolute certainty who is responsible for the rest of the rocket, nor the exact place where the crash took place.
There are, however, the main suspects. According to experts, the rocket is very likely to be part of China’s Chang’e 5-T1 mission, part of the Asian country’s lunar exploration program. China, however, denies it.
And, according to Scientific American, the collision happened near the Hetzprung crater, which is 540 kilometers in diameter and is on the far side of the Moon (so it was not possible to follow the collision with telescopes).
The event, while not immediately impacting life on Earth or space exploration, raises a number of questions about space junk, the difficulties of identifying objects far from low Earth orbit and our relationship to the Moon.
A new crater on the Moon
Although this is a nearly three-ton body that traveled for seven years at a speed of 9,300 km/h, the impact is unlikely to change much in lunar geography.
“In terms of impact, three tons is almost nothing. To give you an idea, in 2013 Russia was hit by Chelyabinsk, a meteorite weighing 9 thousand tons. [3 mil vezes mais]”, recalls Gustavo Rojas, astrophysicist at the Interactive Center for Astronomy and Innovation in Education (in Portugal) and professor at the Federal University of São Carlos (UFSCar) to CNN.
“Of course, since the Moon has no atmosphere, the impact happens directly on the ground. But that should produce a crater ten to twenty meters in diameter. Even so, it will take some work to find her”, comments Rojas.
The animation below, produced with the Systems Tool Kit (STK) and Orbital Determination Tool Kit (ODTK) software, normally used to produce complex missile simulations, shows how the possible impact on the Moon was:
Although the crater is on the far side of the Moon and is small, it will not be impossible to find it.
“We have a very accurate mapping of the Moon and its craters. Using artificial intelligence it is possible to compare the changes and notice the changes. In the near future, we will be able to identify the crater”, explains Erika Rossetto, director of the Space Data Association (a global organization that monitors satellites) and a master’s degree in astronomy from UFRJ to the CNN.
Finding out where the crater is is not just a matter of scientific curiosity. “For future lunar missions, you need to know if there are any objects in the region that could interfere with a manned landing, for example”, explains Erika.
In addition, by observing the crater we will be able to discover some new aspect of the Moon. This is precisely why, in 2009, NASA purposely launched a piece of rocket on the Moon. At the time, the space agency was looking for chunks of frozen water.
“It is possible that the analysis of the new crater will help us to identify some mineral or lunar remnant that was not identifiable until then”, says Erika.
Finding the crater will, above all, help solve the biggest mystery to date: who is responsible for the piece of rocket that crashed into the Moon.
“There are ways to tell if a crater is recent by its color. And by identifying it, it is possible to assess the energy of the impact. Knowing the energy and velocity, you can more accurately calculate the mass and, consequently, know more about the origin of the object”, says Rojas.
But why is it so difficult to know where the rocket piece came from?
Who’s the owner?
The chunk of rocket was discovered in January, almost by chance, by astronomer Bill Gray, who is in charge of Project Pluto, a series of programs that monitor meteorites close to the Sun.
“Objects far from low orbit are not tracked by companies or large companies. And that’s where the community of independent astronomers helps us find these transient objects in the sky,” explains Karolina Garcia, a doctoral student in astronomy at the University of Florida to CNN.
Initial calculations by Gray suggested the chunk of rocket was part of Elon Musk’s SpaceX Falcon 9, launched in February 2015.
However, after further observations and further calculations, researchers at the University of Arizona came to the conclusion that it was a stage of the Long March rocket, which took off in 2014 for China’s Chang’e 5-T1 lunar mission.
Beijing, in turn, denied and said that the space equipment would have already fallen to Earth and combusted.
According to Erika, there are indeed records that the Chinese mission returned to the Earth’s atmosphere, but that does not completely rule out the possibility that the garbage was part of the Chinese mission.
“We don’t monitor very often what is far from low Earth orbit. So it’s possible that the system hasn’t been updated with fragments that haven’t re-entered,” says Erika.
But how is it possible for us to identify galaxies and stars light-years away and not accurately recognize a piece of rocket next to the Moon?
“When you look at a distant object, like a star, you identify the light profile of that object”, explains Erika. “If you take a rough image of a galaxy, you will only see a black background with little white dots. You have to analyze the light spectra and put the puzzle together to recognize those stars,” she says.
In the case of the rocket, although it is “close”, it is much smaller than a star. “It’s actually admirable that they were able to identify this piece of rocket. It is a small object to be recognized at such a distance”, says Rojas.
But there are other obstacles. “It is an artificial object and therefore does not emit light. In addition, several rockets are composed of the same material. It is difficult to decompose the thermal or spectral characteristics and be sure what their origin is”, says Erika.
However, as the astronomer explains, “from the moment you identify the object, it is possible to make systematic observations and calculate its route. From there, he can do the opposite way and see the path he took”. That’s how scientists came to the conclusion that the object is leftover from the Chinese mission.
The glow reflected by the painting also helped to reach the conclusions. “By observing the variation in brightness, through something astronomers call a light curve, you get information about how long the object takes to make a movement, its size and paint. As the Chinese rocket and the SpaceX rocket have different paintings, the reflectivity helped to conclude that it is the Chinese one”, explains Rojas,
But we won’t know more until astronomers find the crater and more accurately estimate the object’s mass.
The risks of space junk
Fortunately, before hitting the Moon, the rocket shard did not cause any accidents. But it could—though the odds are remote.
“There is a concern, at this moment when we are talking about interplanetary travel, that an event like this could impact even space telescopes, such as James Webb, which has just entered orbit”, says Erika. “While the odds of colliding with another object are low, the consequences would be catastrophic,” she adds.
Right now, there is still concern that such an object could eventually disrupt a moon landing — hence the importance of finding the crater.
There was still the fear of such an object colliding with an object already left on the Moon. “There is attention to preserve the jeeps, the lunar base modules and other remnants of our travels that are still there. These sites are World Heritage Sites,” says Rojas. “That said, the chances of an object falling right where there is a site are very small,” he says.
The chances of a collision within space or even on the Moon are extremely remote, but they could grow as we launch more objects into space. And, therefore, they demand attention and debate.
There’s a slightly more immediate concern: space junk in low-Earth orbit—one that is up to 2,000 km away from sea level.
In November 2021, the International Space Station, for example, needed to initiate a security protocol to dodge a cloud of debris generated by debris from an anti-satellite test conducted by Russia.
The growth of space junk could lead to the so-called Kessler syndrome, theorized in 1978 by the then NASA scientist Donald J. Kessler.
In this hypothesis, the space debris present in low Earth orbit — up to 2,000 kilometers from the planet’s surface — would be such that collisions between debris would generate a ripple effect.
As a result, entire layers of low earth orbit would become unusable, which is a problem, since that’s where the satellites used for communication, GPS, Earth monitoring, among other functions are.
Today, NASA estimates that there are about 100 million pieces of space junk more than a millimeter in diameter at different heights in Earth’s orbit.
Although the number seems high, the Kessler syndrome hypothesis is quite a long way off — and efforts are being made to prevent it from getting to that point. “I joke that we call space ‘space’ precisely because there’s a lot of space there,” says Rojas.
“Today we are very careful with the monitoring and control of space debris. There are several security measures to prevent the problem from growing, there are initiatives going into operation to remove this waste”, says Erika.
According to astronomers consulted by the CNN, however, is a debate that needs to grow — especially as more and more satellites are launched. “The more objects we put into orbit, the more likely a collision will happen. And that can have a terrible impact on our society, because we are so dependent on satellites,” says Rojas.
Starlink, owned by South African Elon Musk, alone, has already received authorization from the US government to place 42,000 satellites in orbit in the coming years, of which almost 2,000 have already been launched.
The company says that, after it stops working, the equipment should take between one and five years to disintegrate in the Earth’s atmosphere without further complications and without causing harm to the population.
“I think it is essential to invest in this way of removing objects in a controlled way or taking them to an orbit that will not interfere with operations. But there is still a lot to be done and we have to keep investing in it until we find a balance between risks and benefits”, says Erika.
There is also an impact on observations.
“Until ten years ago you looked at the sky and saw no passing objects. I saw a “shooting star”, at most. The other day I was on an observation night and within a minute I could see at least three objects cutting across the sky. That’s when I realized how this will really get in the way of observations”, says Karolina.
“When we look at the sky, we have to make some corrections for cosmic rays, some stars that can blur our focus, etc. Now, the more satellites and objects that appear, the more we’re going to have to do this kind of correction. Until at some point I don’t even know if it will be possible anymore”, explains Karolina.
But do not worry. The chances of space junk falling on someone today are extremely low according to the ESA, the chance of a person being struck by lightning is 60,000 times greater than the chance of being surprised with a rocket fragment falling on their head. Only one such case has ever been recorded, in 1997, with American Lottie Williams, who was not injured.
* With information from Giuliana Viggiano
Source: CNN Brasil
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