00:00You stand next to a huge window of the ground at the ceiling of this wandering space ship that you have called your home for a dozen years, with a few hundred other people.
00:12You observe a fascinating object approaching your ship, asking you if it will end this journey and your life.
00:19It looks like an asteroid but acts like a comet.
00:22Moving as if something was pushing it, could it be an engine created by another space civilization?
00:28Are you doomed or about to come into contact with another kind of intelligence?
00:33Now, let's leave this post-apocalyptic fantasy aside and take a closer look at these space invaders called dark comets.
00:41The most intriguing question is obviously, what made them move?
00:45Most likely, it is gas or material escaping from the surface of these space objects.
00:50Interesting fact, until recently, no one was even sure of their existence.
00:55The first dark asteroid was discovered only a few years ago, and since then, researchers have identified 14, including 7 new discoveries very recently.
01:05The history of dark comets began in 2016, when scientists noticed something strange about an asteroid called 2003RM.
01:17Its orbit was not quite what they expected, it had slightly deviated, and no one could explain this change by the typical behavior of an asteroid,
01:26when they receive small pushes caused by the unequal heating of an asteroid by sunlight.
01:32Instead, the movement suggested that 2003RM could have released material, which is often done by comets.
01:40But there was a hitch, the object did not look like a comet.
01:44There was no tail, no visible gas cloud, it was just a small point of light, like an ordinary asteroid.
01:51At first, scientists thought that 2003RM was just an isolated enigma.
01:56But in 2017, a telescope spotted another strange object, the one from outside our solar system.
02:03It was Oumuamua.
02:05It also looked like an asteroid, but had a trajectory that changed as if gas escaped from it.
02:11The similarities between Oumuamua and 2003RM led researchers to think that there could be more such strange objects in the universe.
02:20In 2023, 7 others had been discovered in our solar system.
02:24These discoveries were enough to give this new type of object the name of dark comet.
02:29Now, scientists have enough data to start noticing patterns, and learn more about their characteristics.
02:37Thus, they identified two main groups of dark comets.
02:41The first group, called external dark comets, is larger, with sizes ranging from hundreds of feet and even more.
02:49They follow long and elliptical orbits, similar to those of traditional comets that come from regions close to Jupiter.
02:56The second group, the internal dark comets, is smaller, usually about ten feet in diameter.
03:03These comets move on almost circular orbits, and remain closer to the Sun, near planets such as Earth, Venus and Mars.
03:12The main question today is, where do dark comets come from?
03:16Can they be the remains of larger bodies that have disintegrated?
03:20These celestial bodies could help us understand the history of the solar system.
03:25And if they had brought the ingredients of life to primitive Earth,
03:29once we have studied dark comets in more depth,
03:33we could determine whether they contain materials such as ice or organic compounds.
03:39Indeed, some researchers are certain that dark comets can contain or could contain ice,
03:45and played an important role in the water supply on Earth.
03:48According to some studies, some asteroids in the asteroid belt,
03:52a region between Mars and Jupiter filled with rocky debris,
03:55could have ice under their surface.
03:58And this ice from the asteroid belt could have traveled to space near Earth.
04:04In other words, it could be a way for water to reach our planet.
04:09So far, no one has claimed that dark comets have definitely brought water to Earth.
04:14But it could be another mechanism for moving ice from one part of the solar system to another.
04:21The study also suggests a connection between dark comets
04:24and a group known as the Jupiter family of comets.
04:28These are comets whose orbits are strongly influenced by Jupiter's gravity,
04:33often attracting them to the Sun.
04:35This connection makes it even more difficult to understand the origin of dark comets and their behavior.
04:41Now, let's take a closer look at the differences between asteroids and comets.
04:46Traditional asteroids are rocky bodies that orbit relatively close to the Sun,
04:51usually inside the ice line.
04:54This region is so close to the Sun that any ice present on the surface of an asteroid
04:59would transform directly from a solid state to a gaseous state,
05:03leaving behind only rock.
05:06Comets, on the other hand, are icy bodies that form further from the Sun.
05:10When they approach the inner solar system,
05:13their ice also begins to go from a solid state to a gaseous state,
05:17creating a visible cloud, called a hair, or a tail, while releasing dust and gas.
05:23Dark comets muddle these definitions.
05:27They appear as rocky objects similar to asteroids without a coma or tail,
05:32but they present a typical behavior of comets,
05:35namely small non-gravitational accelerations.
05:39These accelerations occur when the ice turns into gas,
05:43giving the object a slight impulse.
05:46After analyzing 7 known dark comets,
05:48astronomers estimated that between 0.5% and 60% of all geocruisers
05:54could belong to this mysterious category.
05:57And since dark comets probably come from the asteroid belt,
06:01it is likely that ice exists even in the regions of the belt
06:04previously considered too hot.
06:07Now, objects close to Earth, such as dark comets,
06:10do not remain eternally in the same orbit.
06:13The environment close to Earth is unstable,
06:16and objects generally remain there for about 10 million years.
06:19Since the solar system is over 4.5 billion years old,
06:23this means that new objects close to Earth
06:26must constantly replace those that are lost.
06:29Astronomers have used computer models to simulate the movement of objects
06:33under the influence of non-gravitational accelerations.
06:36They traced the trajectories of these objects over a period of 100,000 years,
06:41and discovered that many of them were in the same regions
06:44where we find dark comets today.
06:47Now, you remember this space rock 2003 RM,
06:51which was the first to be called a dark comet.
06:55Well, it provided a particularly interesting clue.
06:59Its elliptical orbit brings it closer to Earth,
07:01then takes it near Jupiter, before returning to Earth.
07:05This trajectory corresponds to what scientists would expect
07:08from a comet of the Jupiter family,
07:11an object that has probably been deflected towards the interior of its original orbit.
07:16However, most of the other dark comets studied
07:20seem to come from the interior regions of the asteroid belt,
07:23closer to Mars.
07:25Dark comets are often small and spin fast.
07:29Astronomers often describe them as dirty ice cubes.
07:32All this because these objects are a mixture of rock and ice,
07:36and when they cross the ice line, their ice begins to turn into gas.
07:41This process not only causes these small non-gravitational accelerations,
07:45but also increases their rotational speed.
07:48And the faster these objects spin,
07:50the easier they can disintegrate into smaller fragments.
07:54The pieces that detach also contain ice.
07:57And as they spin faster and faster,
08:00they break into even smaller pieces.
08:03This process continues until there are only very small objects left,
08:07spinning rapidly.
08:09This cycle of fragmentation helps explain
08:11why dark comets are often so tiny.
08:14But it could also mean that there are more of them than we currently know.
08:19Research on dark comets offers new perspectives
08:22on the distribution of ice in the solar system
08:25and its potential routes to the environment near Earth.
08:29It also raises intriguing questions.
08:31For example, how much ice remains hidden in the asteroid belt?
08:36Or, have dark comets been able to play a role
08:39in the delivery of water or organic matter to Earth?
08:43One of the most important points is that dark comets
08:46could represent a significant part of geocruiser objects.
08:50If this is true, it could mean that our understanding
08:53of the population of geocruiser objects
08:56and their potential risks for our planet is far from complete.
09:00Processes shaping dark comets,
09:03from sublimation to fragmentation,
09:06could be a major factor in the evolution of ice cores
09:09through the solar system.
09:11Fortunately, nowadays, scientists have the opportunity
09:15to combine advanced modelling with observations,
09:19which could possibly enlighten this class of very unobtrusive objects
09:23and provide clues about the history of water and life on Earth.
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