How humanity survived the approach of another star

Popular scary movies often depict a situation where another star is approaching the Sun and something terrible happens at that moment: a hail of comets, an alien invasion, or some kind of gravitational anomaly. However, humanity has already experienced such a situation before. We are talking about the Scholz Star, which passed through the Oort Cloud some 70-80 thousand years ago.

An amazing discovery

Space disaster movies often begin with a scientist seeing a speck in the sky and, after complicated calculations, concluding that something is flying towards us. It is this speck that becomes the source of all misfortune in the plot.

In 2013, a very similar story happened to the German astronomer Ralf-Dieter Scholz. He was working on images taken by the WISE space telescope. This orbiting observatory is known for its high-precision infrared survey of the entire sky and the discovery of many objects near us that we had not previously noticed, including the Luhman 16 system, the third most distant from us.

However, most of these red and brown dwarfs have one thing in common: their own motion. During the year, they move significantly against the background of more distant stars. This is because, in fact, all the bodies in the Milky Way orbit its center at different speeds, and those we see nearby have been around for a fairly short period of time compared to the age of our star system.

Ральф-Дітер Шольц
Ralf-Dieter Scholz. Source:

However, Scholz found something truly unusual. The red dwarf WISE 0720-0846, which is only 20 light-years away, had virtually no motion of its own. This could mean one of two things: it is either moving away from us along a straight trajectory or moving exactly toward us. In the second case, this would mean that in the future it could pass very close to us, or even collide with the Sun.

However, a quick analysis of the dwarf’s Doppler shift showed that it was moving away from us, meaning that a catastrophe would not occur in the future. Thus, the first assumption was correct: this small red star passed very close to us sometime in the not too distant past.

Meeting a red dwarf

In 2015, astronomers completed the calculations and announced that the red dwarf, which was named the Scholz star in honor of the discoverer, passed at a distance of only 52 thousand AU from the solar system about 70 thousand years ago. The Earth was dominated by the Paleolithic period, and the tiny dwarf, even at the maximum approach for terrestrial observers, hardly had a brilliance above 10th magnitude. That is, it was definitely impossible to see it with the naked eye.

Рух Зорі Шольца крізь Хмару Оорта

Movement of Scholz’s Star through the Oort Cloud. Source:

However, this visit could have left other evidence. The tiny star would not have been able to change the orbits of the planets with its gravity, but the distance of 0.82 light-years at which it was believed to have passed by our system is already the Oort Cloud, which is a region of space filled with numerous cometary nuclei. Theoretically, this passage could have directed some of them toward the Sun, where they would have a chance to collide with the Earth.

However, no traces of this have been found. But some astronomers have suggested that the comets affected by Scholz’s star have moved to such long-period orbits that we will see them in a couple of million years. Later, there were versions that the impact of the brown dwarf’s passage on the Oort Cloud was underestimated, but they were all crossed out by a new publication that appeared in 2019. In it, the authors further clarified the parameters of the Scholz star’s motion and found that the passage occurred about 80 thousand years ago at a distance of 68 thousand AU, which is much more than one light year, and the Oort Cloud should have been barely touched by this star.

What does the Scholz star look like?

According to the updated data, Scholz’s star is now located 22 light-years away in the constellation of the Unicorn. In fact, it is a system consisting of at least two bodies. The main one is a red dwarf of the M9 class, whose mass is 99 times that of Jupiter, i.e., about 10% of the solar mass.

Зоря Шольца та її компаньон
The Scholz star and its companion. Source:

Its companion is a brown dwarf, its mass is 66 times that of Jupiter, and its surface temperature is 1250 K. This indicates that it has already cooled down, which means that the system is quite old – its age is several billion years. Its components orbit a common center of mass with a period of 8 years.

No other celestial bodies have been detected near the Scholz star. It may have planets, but we do not see any signs of their presence.

Is this event unique?

In fact, there is nothing unique about such a close passage of a star next to the Sun. According to astronomers, the approach of another luminary at a distance of up to a light year occurs on average once every 100 thousand years. This may seem like a huge period of time, but since the genus Homo originated in Africa, such approaches must have occurred dozens of times. And no evidence has been found that they had any effect on the orbits of the planets or the frequency of meteorite impacts.

Сучасне положення Глізе 710 на небі
The current position of Gliese 710 in the sky. Source: Wikipedia

Moreover, much closer convergences should occur every millions and tens of millions of years. For example, in about 1.3 million years in the future, the star Gliese 710 should pass at a distance of only 10,520 AU (1.6 trillion km) from the Sun. It is currently 62 light-years away. This luminary is much bigger than the Scholz star – its mass reaches 57% of the Sun’s. During its passage, it may become the brightest star in the sky. However, this flyby will not have a significant impact on planetary orbits. How it will affect the Oort cloud is currently unknown, but, as mentioned, there is no evidence that such phenomena have caused anything terrible in the past.

Interstellar flight during convergence

Another interesting question concerns whether such convergences can be used for interstellar travel. It all depends on how close the other luminary will come to us and how much the spacecraft can accelerate.

For example, if the imaginary aliens at the Scholz star 80 thousand years ago had technologies comparable to ours today, they could have achieved a flight speed of about 20 km/s (this is roughly the same as the Voyager and New Horizons spacecraft). Then they would have traveled to Earth in 16 thousand years, so it would still be a difficult task.

Міжзоряний переліт може виявитися простою справою при зближенні
Interstellar flight may turn out to be a simple matter during the convergence. Source:

But if their technology were much more advanced than ours, and alien spacecraft could travel at least one percent of light speed, such a trip would take only 108 years, allowing automatic or manned ships to make a round trip.

And if we reached 10% of the speed of light, such a flight would take less than 11 years, which would allow them to systematically study our planet for a long time. Although, again, there is no serious evidence that anyone has ever visited us.

In the future, when Gliese 710 comes closer to us, the conditions for visiting it will be much better for us. Of course, traveling to it with modern technology will still take thousands of years. However, if we learn to fly at least a hundred times faster, it will be enough to make the round trip in just a few decades. However, according to the latest data, this star has no planets that might be of interest to us.